ICE REMOVAL FROM HVACR SURFACES

Abstract

A vapor compression heat transfer system includes an evaporator assembly, an ice-prone surface, and an ultrasonic energy source. The ultrasonic energy source when energized vibrating the ice-prone surface at a frequency of from 30 kHz to 60 kHz. The ultrasonic energy source can be a piezoelectric transducer. The piezoelectric transducer can be operated in an ice sensing mode and a deicing mode and can also verify the removal of ice. A method of conducting one of heating, ventilation, air conditioning and refrigeration (HVACR) is also disclosed.

Description

FIELD OF THE INVENTION

The present invention relates generally to heating, ventilation, air conditioning and refrigeration (HVACR) systems, and more particularly to systems and methods for deicing and preventing ice formation on HVACR system components.

BACKGROUND OF THE INVENTION

Residential and commercial buildings account for 39% of energy use and consume approximately 74% of electricity generated while being responsible for 35% of carbon emissions. Heating, ventilation, air conditioning, and refrigeration equipment (HVACR) are the major electrical appliances with significant energy footprint in buildings, accounting for ˜6.6 Quads of primary energy consumption, resulting in 245 Mt of CO₂.

The primary cooling and refrigeration component in the refrigerator comprises an evaporator where the liquid refrigerant vaporizes while cooling the entrained air around it and producing the desired thermal environment for air conditioning, food storage and dispensing. Additionally, the evaporator in refrigerators and air conditioners operates at a temperature below the dew point leading to condensation of the moisture present in the air. As a result, the cold metal surface of the evaporator heat exchanger and some components that surround it eventually accumulate ice crystals as a thick layer impeding the heat transfer as well as air flow rate, reducing the energy efficiency of the equipment. Thus, to maintain system performance and attain the desired cold temperatures, evaporators require periodic heating to melt and remove the frost and ice formation.

Currently, most thermal sources used in HVACR to remove frost and ice include a joule/resistive heater or hot gas flush to supply radiant heat as well as provide conductive heat transfer to melt the ice and frost layer. The high specific heat capacity and good insulation properties of accumulated frost and ice require a considerable amount of energy to melt. For instance, in refrigeration equipment, a heater consumes significant power in the range of 300-800 W to generate high temperatures. During this melting cycle the compressor is switched off making it difficult to maintain the cooling and freezing compartment temperatures. The excessive power consumption of these heaters deteriorates cooling and refrigeration energy efficiency and the condition of the food in the case of freezers, and human comfort in the case of air conditioning equipment. Additionally, the run time of the compressor is extended to cool down the thermal mass of the evaporator heat exchanger after each defrost cycle, further leading to a decline in the energy efficiency.

Commercial class refrigeration systems utilize a variety of techniques to deice, including off-cycle defrost, electric defrost, and hot gas defrost. The most basic defrost method is the off-cycle defrost, in which the refrigerant flow to the evaporator is interrupted. The evaporator fans then blow air across the frosted evaporator, thereby melting the accumulated frost. Since this method relies on the circulation of relatively warm air over the evaporator to melt the frost, this technique is limited to only medium temperature applications. Electric defrost methods make use of electrical heating elements which are mounted adjacent to the evaporator coil or integrated into the evaporator coil, similar to the residential refrigerators. In the hot gas defrost method, the liquid refrigerant flow to the evaporator is first interrupted via a solenoid valve and the evaporator fans are turned off. Then, the hot gas defrost solenoid opens, which allows high pressure, high temperature refrigerant gas from the compressor discharge to flow into the evaporator. As the hot refrigerant gas flows through the evaporator, it condenses, thus releasing its latent heat, warming up the evaporator and melting the frost.

Typical defrost cycle operating strategies in commercial refrigeration include time-temperature control, time-pressure control, airflow measurement, optical sensor control amongst many other techniques. The control strategy is dictated by the first cost requirements, food quality control, and operating cost expectations. It is estimated that the total energy burden of a food storage case deicing process is ˜150-270 kWh per year per foot of refrigerator length.

Ice is an important commodity both as a direct use product and as a nuisance in day-to-day heating, ventilation, cooling, and refrigeration (HVACR) related equipment. It is utilized as an energy storage medium at industrial scale, in the food service industry, in domestic household refrigeration, and in supermarkets. Additionally, demand deicing in cold display cases, food storage facilities, evaporator heat exchangers of heat pumps consume significant amount of parasitic energy in maintaining the equipment by shedding the ice. Ice making as well as deicing are energy intensive processes. For instance, ˜8-15 kWh of electrical energy is consumed in making 100 lb. of ice and it could be as high as 45 kWh if one considers the source-to-site losses. About 30% of this energy is exclusively consumed during the dispensing or deicing process which involves mold heating for dislodging the ice followed by re-cooling of the thermal mass to attain the desired temperature for the next cycle. Given the amount of energy being consumed in such processes, there is need to develop an energy efficient method to help dispense the ice in an energy efficient manner.

According to the US Department of Energy, an estimated 2.7 Quads of primary energy per year is used by refrigeration equipment, 0.87 Quads of which is accounted for by ice making machines. Another independent study suggested that the entire inventory of ice machines used in the United States in 2012 was almost 3 million units. Residential refrigerators are the largest domestic use of electricity in the United States and most developed countries, and thus have become a target for efficiency improvements. The energy footprint of automatic ice makers in domestic refrigerators was studied, and the range of energy consumption varied between 0.12 to 0.3 kWh per pound of ice, accounting for approximately 12%-20% of total energy consumed by refrigerators. The scale of energy consumption in ice-related processes presents a significant potential for energy efficiency improvement and carbon footprint reduction.

Ice also has significance as a direct use product. It is used as an energy storage medium at the industrial scale in the food service, hospitality, and medical industries, in domestic household refrigeration, cold-chain (e.g. certain vaccines), and supermarkets. Depending on the application, primary shapes of the manufactured ice include cube, crescent, cylindrical, sphere, flake, tube, rectangular block, and clear cube. Residential ice makers include domestic refrigerators and stand-alone tabletop portable ice makers, with daily capacities in the range of 3 to 25 lb. Conversely, commercial ice maker daily capacities vary from 35 to 500 lb for medium-scale applications in the food service and hospitality industries, and the daily industrial-scale production varies from 10,000 to 40,000 lb, mostly for applications in shipping, food, and medical industries.

The freezing process of water has been extensively investigated. Ice making involves a complete refrigeration cycle with four key components: the evaporator, condenser, compressor, and throttle valve. The compressor compresses low-pressure refrigerant vapor to high-pressure vapor, which is condensed (in the condensing heat exchanger) into high-pressure liquid and drained through the throttle valve to generate low-pressure liquid. The evaporator eventually exchanges heat from the thermal mass to be cooled, in this case water. Primary ice-harvesting mechanisms include exposure of the ice mold, the evaporator heat exchanger, to a heating element or hot refrigerant, as explained above.

Ice making and deicing is an energy-intensive process. The power consumption of ice makers ranges from 0.2 to 50 KW, depending on the scale of the machine. The energy footprint could be as high as 15 kWh per 100 lb of ice, and higher if the primary energy source-to-site inefficiency is considered. Almost 30% of this energy is estimated to be exclusively consumed during the dispensing or deicing process, at approximately 4 to 9 kWh per 100 lb of ice at the site.

Given the amount of energy being consumed in such processes, there is a need to develop an energy efficient solution to separate the frost and ice from HVACR surfaces.

SUMMARY OF THE INVENTION

A vapor compression heat transfer system includes an evaporator assembly and an ice-prone surface, and an ultrasonic energy source, the ultrasonic energy source when energized vibrating the ice-prone surface at a frequency of from 30 kHz to 60 KHz. The vapor compression system can comprise at least one selected from the group consisting of an ice maker, heat pump, air conditioner, a refrigerator, and a freezer.

The ultrasonic energy source can include a transducer. The transducer can be a piezoelectric transducer. At least two piezoelectric transducers can be connected to the ice-prone surface, and each transducer is spaced from 12 in. to 18 in. from an adjacent transducer.

The evaporator assembly can include an evaporator tube having an ice-prone surface, and the ultrasonic energy source vibrates the ice-prone surface and the evaporator tube. The evaporator assembly can include an evaporator fin thermally and mechanically coupled with the outer surface of the evaporator tube. At least one of the evaporator tube and the evaporator fin comprise an ice-prone surface, such that vibration of one of the evaporator tube and the evaporator fin by the ultrasonic energy source will vibrate the ice-prone surface. The evaporator tube and/or the evaporator fin can be made from at least one selected from the group consisting of Cu, Al, Fe, and alloys thereof. Other materials are possible.

A layer of icephobic material can be coated on the ice-prone surface. The icephobic material will reduce ice formation on the ice-prone surface during operation of the evaporator and reduce adhesion of the formed ice to the ice-prone surface. The icephobic material can comprise polymeric low interfacial toughness (LIT) materials. The LIT material can be at least one selected from the group consisting of polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE). Other materials are possible.

The evaporator assembly can include supporting structure for the evaporator. The ultrasonic energy device can be mechanically connected to the supporting structure such that the ultrasonic energy source will vibrate the supporting structure and the vibration will be transmitted through the supporting structure to the evaporator and the ice-prone surface.

The vapor compression heat transfer system can further comprise controller circuitry communicatively coupled with the ultrasonic energy source and configured to instruct the ultrasonic energy source to vibrate the ice-prone surface to cause removal of ice from the ice-prone surface. The vapor compression heat transfer system can also include an ice detector for detecting the presence of ice on the ice-prone surface, the ice detector being connected to the controller circuitry to operate the ultrasonic energy source when a threshold amount of ice is detected by the ice detector on the ice-prone surface. The ice detector can include at least one selected from the group consisting of resistive sensor, photoelectric sensors, fiber optic sensors, and capacitive sensors.

The ice detector can include an impedance analyzer. The impedance analyzer measures the impedance of the ice-prone surface and produces an impedance signal relating to the impedance of the ice-prone surface to the controller circuitry. The controller circuitry determines from the impedance signal the resonant frequency of the ice-prone surface and compares the resonant frequency to a set point resonant frequency for the ice-prone surface to determine the presence of ice on the ice-prone surface. The ultrasonic energy source can be operable as an ice detector in an ice-detecting mode, in conjunction with the controller. The ultrasonic energy source can be operable in the ice-detecting mode over a range of 0.05 W/in²-0.1 W/in², and in an ice-removal mode over a range of 0.5 W/in²-1.5 W/in². The controller circuitry can also comprise a function generator configured to energize the ultrasonic energy device according to predetermined functions.

A low temperature chamber has walls and a ceiling comprising an ice-prone surface. The chamber includes one or more ultrasonic energy sources disposed on one or more of the walls or the ceiling. The ultrasonic energy source when energized vibrates the ice-prone surface at a frequency of from 30 KHz to 60 KHz. The chamber can be at least one selected from the group consisting of cold storage, walk-in freezer, reach-in display case, frozen fry dispenser, walk-in cooler, and refrigerated transportation container. An evaporator can be attached to the low temperature chamber.

The low temperature chamber can further include a layer of icephobic material coated on the ice-prone surface. The icephobic material will reduce ice formation on the ice-prone surface while the temperature in the chamber is below the dew point temperature and reduce adhesion of formed ice to the ice-prone surface. The icephobic material can include a low interfacial toughness (LIT) material. The LIT material can be at least one selected from the group consisting of polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE).

A method of conducting one of heating, ventilation, air conditioning and refrigeration (HVACR), wherein the HVACR system comprises an evaporator assembly and an ice-prone surface, includes the steps of providing an ultrasonic energy source, and operating the ultrasonic energy source to vibrate the ice-prone surface at a frequency of from 30 KHz to 60 KHz. The method can further include the step of using an ice detector to determine whether ice formed on the ice-prone surface has exceeded a predetermined upper threshold, and selectively instruct the ultrasonic energy source to vibrate the ice-prone surface in response to the determination. The ice detector can be used to determine whether the formed ice has fallen below a predetermined lower threshold, and selectively turn off the ultrasonic energy source to cease vibration of the ice-prone surface in response to the determination.

The method can further include the step of instructing the ultrasonic energy source to vibrate the ice-prone surface in accordance with a predetermined schedule. The HVACR system can include at least one selected from the group consisting of an ice maker, heat pump, air conditioner, a refrigerator, and a freezer. The power per unit area produced by the ultrasonic energy source can be from 0.5 W/in² to 1.5 W/in².

An evaporator assembly for a heating, ventilation, air conditioning and refrigeration (HVACR) apparatus includes an evaporator and an ice-prone surface, and an ultrasonic energy source. The ultrasonic energy source when energized vibrates the evaporator at a frequency of from 30 kHz to 60 KHz.

BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in the drawings embodiments that are presently preferred it being understood that the invention is not limited to the arrangements and instrumentalities shown, wherein:

FIG. 1 is a schematic diagram of a generalized HVACR cycle.

FIG. 2 is a schematic depiction of a plate simulation for ice removal.

FIG. 3 is a plot of normalized maximum displacement vs. position (mm).

FIG. 4 is a schematic depiction of a finger mold simulation for ice removal.

FIG. 5 is a schematic depiction of an ice tray simulation for ice removal.

FIG. 6 is a schematic depiction of a fin and tube simulation for ice removal.

FIG. 7 is a schematic depiction of a plate and transducer for an ice removal test.

FIG. 8 is a schematic depiction of the plate and transducer if FIG. 7 with a single ice cube on the plate for an ice removal test.

FIG. 9 is a schematic depiction of the plate and transducer of FIG. 7 with two ice cubes on the plate for an ice removal test.

FIG. 10 is a schematic depiction of the plate and transducer of FIG. 7 with a three ice cubes on the plate for an ice removal test.

FIG. 11 is a schematic depiction of the plate and transducer of FIG. 7 with five ice cubes on the plate for an ice removal test.

FIG. 12 is a schematic depiction of the transducer action to remove ice from the plate of FIG. 11.

FIG. 13 is a schematic depiction of the plate of FIG. 12 after deicing.

FIG. 14 is a plot of power (Watts) vs. time (seconds)

FIG. 15 is a plot of power (Watts) vs. time (seconds).

FIG. 16 is a plot of energy and time savings (vs baseline) for total energy and total time with a coating, ultrasonic vibration, and combined coating and ultrasonic vibration.

FIG. 17 is a plot of amplitude vs. frequency (kHz).

FIG. 18 is a plot of impedance (ohms) vs. frequency (Hz).

FIG. 19 is a schematic depiction of an ice sensing system.

FIG. 20 is a schematic plan elevation, partially in phantom, of a refrigerated container in a first mode of operation.

FIG. 21 is the schematic plan elevation of FIG. 20 in a second mode of operation.

FIG. 22 is the schematic plan elevation of FIG. 20 in a third mode of operation.

FIG. 23 is the schematic plan elevation of FIG. 20 in a fourth mode of operation.

FIG. 24 is the schematic plan elevation of FIG. 20 in a fifth mode of operation.

FIG. 25 is a perspective view of an evaporator coil assembly according to the invention.

FIG. 26 is a perspective view of a walk-in freezer according to the invention.

FIG. 27 is a perspective view of a refrigerated container according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

A vapor compression heat transfer system for HVACR includes an evaporator assembly and an ice-prone surface, and an ultrasonic energy source. The ultrasonic energy source when energized vibrates the ice-prone surface at a frequency of from 30 kHz to 60 KHz.

The vapor compression heat transfer system can be any of several types of such devices. The vapor compression system can be, but is not limited to, an ice maker, heat pump, air conditioner, a refrigerator, or a freezer. Other vapor compression heat transfer devices are possible.

The ultrasonic energy source can be a transducer or other electronic device that is capable of inducing vibration in the ice-prone surface. The transducer can be a piezoelectric transducer. Any number of ultrasonic energy devices can be used. The ultrasonic energy devices can be distributed around the ice-prone surfaces to effectively remove ice wherever it forms. For example, at least two piezoelectric transducers can be connected to the ice-prone surface, and each transducer can spaced from 12 in. to 18 in. from an adjacent transducer. The distance between the transducers will depend on a number of factors, for example the energy of the transducers, the material and thickness of the wall making up the ice-prone surface, the expected level of ice formation, and other factors.

The evaporator assembly can take a number of different forms. The evaporator assembly can include an evaporator tube having an ice-prone surface. The ultrasonic energy source can be positioned to vibrate the ice-prone surface and the evaporator tube. The evaporator assembly can comprise one or more supporting brackets or structure, and possibly also a protective housing. The ultrasonic energy devices can be configured to also vibrate such structures where the vibration of such will also vibrate the ice-prone surface.

The evaporator assembly can comprise an evaporator fin thermally and mechanically coupled with the outer surface of the evaporator tube. At least one of the evaporator tubes and the evaporator fin can have an ice-prone surface, and vibration of one of the evaporator tubes and the evaporator fin by the ultrasonic energy source will vibrate the ice-prone surface to de-ice these surfaces. The evaporator tube and/or the evaporator fin can be constructed of any suitable material. The evaporator tube and evaporator fin can comprise at least one selected from the group consisting of Cu, Al, Fe, and alloys thereof.

The vapor compression heat transfer system of the invention can further include a layer of icephobic material coated on the ice-prone surface. The icephobic material will reduce ice formation on the ice-prone surface during the operation of the evaporator, and reduce the adhesion of the formed ice to the ice-prone surface. The icephobic material can be any of several possible materials. Examples of anti-icing and icephobic coating materials include polysiloxanes such as polydimethylsiloxane (PDMS), slippery liquid-infused porous surfaces (SLIPS), silicones, polytetrafluoroethylene, elastomers, polystyrene, polyisobutylene, perfluoropolyethers, fluorinated polyurethane polyol, superhydrophobic coatings such as fluorinated silanes and fluoropolymers, and chemical-based nanocomposite protective layers. Other icephobic materials are possible.

The icephobic material can comprise polymeric low interfacial toughness (LIT) material. Low Interfacial Toughness (LIT) materials are suitable for large surface areas, as they encourage cracks to form between the ice and the surface. Unlike breaking an ice sheet's surface adhesion, which requires tearing the entire sheet free, a crack only breaks the surface free along its leading edge. Once that crack has formed, it can quickly spread across the entire iced surface, regardless of its size. The combination of LIT materials with ultrasonic energy sources targets the interfacial layer between the substrate/surface and ice sheet using ultrasonic vibration, and can reduce the energy demands required to remove the ice. The combination of these two methodologies avoids thermal mass heating and re-cooling, decreasing the process time and energy intensity.

The ice-prone surface can be connected to supporting structures, such as but not limited to supporting plates, braces and brackets. The ultrasonic energy devices can be mechanically connected to such supporting structures such that the ultrasonic energy source will vibrate the supporting structure and the vibration will be transmitted through the supporting structure to the ice-prone surface.

The vapor compression heat transfer system can further include controller circuitry communicatively coupled with the ultrasonic energy source and configured to instruct the ultrasonic energy source to vibrate the ice-prone surface to cause removal of ice from the ice-prone surface. The vapor compression heat transfer system can include an ice detector for detecting the presence of ice on the ice-prone surface. The ice detector can be connected to the controller circuitry to operate the ultrasonic energy source when a threshold amount of ice is detected by the ice detector on the ice-prone surface. The ice detector can be any of several technologies, including but not limited to resistive sensors, photoelectric sensors, fiber optic sensors, and capacitive sensors.

The ice detector can be an impedance analyzer. The impedance analyzer measures the impedance of the ice-prone surface and produces an impedance signal relating to the impedance of the ice-prone surface to the controller circuitry. The controller circuitry determines from the impedance signal the resonant frequency of the ice-prone surface and compares the resonant frequency to a set point resonant frequency for the ice-prone surface to determine the presence of ice on the ice-prone surface. The resonant frequency of the surface when no ice is present will serve as set point or reference to which future readings will be compared. When the resonant frequency changes it will provide a signal that ice is present (or remains after an ice-removal step) and ice removal must be performed or repeated.

In the sensing mode, the ultrasonic generator will provide low power to excite the ultrasonic transducer. Meanwhile, the impedance analyzer will measure the impedance of the ultrasonic transducer-wall-ice system at different frequencies (e.g., 20 kHz to 80 kHz). The resonance frequency f is the frequency at which the impedance has the lowest value in the frequency range. Once the ice is formed on the wall near the transducer, the measured resonance frequency will be a different value as f+Δf. Therefore, if a different resonance frequency is detected, this provides a signal that ice has formed near the transducer. The high-power ultrasound will be activated from the ultrasonic generator. Ice on the wall will be removed with the high-power ultrasound. The sensing procedure will be repeated to check if the resonance frequency is back to its original value. If yes, it indicates all the ice has been removed.

The ultrasonic energy source can in some devices be operable as an ice detector in an ice-detecting mode, in conjunction with the controller. It is also possible to utilize a dedicated ice detector that is separate from the ultrasonic energy source. The ultrasonic energy source is operable in the ice-detecting mode over a range of 0.05 W/in²-0.1 W/in², and in an ice-removal mode over a range of 0.5 W/in²-1.5 W/in². The controller circuitry can include a function generator configured to energize the ultrasonic energy device according to predetermined functions.

A low-temperature chamber utilizing the invention can having walls and a ceiling comprising an ice-prone surface. The chamber can have one or more ultrasonic energy sources disposed on one or more of the walls or the ceiling. The ultrasonic energy source when energized vibrates the ice-prone surface at a frequency of from 30 kHz to 60 KHz. The chamber is at least one selected from the group consisting of cold storage, walk-in freezer, reach-in display case, frozen fry dispenser, walk-in cooler, and refrigerated transportation container. The invention can be utilized with other devices which have ice-prone surfaces.

The low temperature chamber can include an evaporator attached to the low temperature chamber. The low temperature chamber can further include a layer of icephobic material coated on the ice-prone surface. The icephobic material will reduce ice formation on the ice-prone surface while the temperature in the chamber is below the dew point temperature and reduce adhesion of formed ice to the ice-prone surface.

A method of conducting one of heating, ventilation, air conditioning and refrigeration (HVACR), wherein the HVACR system comprises an evaporator assembly and an ice-prone surface, includes the steps of providing an ultrasonic energy source, and operating the ultrasonic energy source to vibrate the ice-prone surface at a frequency of from 30 kHz to 60 KHz. The method can further include the step of using an ice detector to determine whether ice formed on the ice-prone surface has exceeded a predetermined upper threshold, and to selectively instruct the ultrasonic energy source to vibrate the ice-prone surface in response to the determination. The ice detector can be used to determine whether the formed ice has fallen below a predetermined lower threshold, and selectively turn off the ultrasonic energy source to cease vibration of the ice-prone surface in response to the determination.

The method can further include a step of instructing the ultrasonic energy source to vibrate the ice-prone surface in accordance with a predetermined schedule. The power per unit area produced by the ultrasonic energy source can be from 0.5 W/in² to 1.5 W/in².

An evaporator assembly according to the invention can be provided for a heating, ventilation, air conditioning and refrigeration (HVACR) apparatus. The evaporator assembly can include an evaporator and an ice-prone surface, and an ultrasonic energy source. The ultrasonic energy source when energized vibrates the evaporator at a frequency of from 30 kHz to 60 KHz.

A typical HVACR cycle 10 is shown in FIG. 1. The system 10 is a type of vapor compression heat transfer system in which an evaporator 14 receives a low temperature working fluid or refrigerant, and in the evaporator 14 the working fluid absorbs heat from something that is to be cooled. The heated working fluid then passes to a compressor 18, where it is becomes a high temperature compressed gas. The hot compressed gas is then transmitted to the condenser 22, where the high temperature high-pressure compressed gas is condensed to a liquid, giving off heat in the process. The condensed working liquid then passes through an expansion valve 26, where the pressure is reduced, and the working liquid is cooled. The low-pressure, low temperature working liquid is then passed back to the evaporator 14, where it absorbs heat as it changes state to a gas.

The evaporator 14 is the location where a significant amount of heat is absorbed, in an HVACR system usually from air or a surface in contact with air. Such a surface is prone to the formation of ice as water is condensed from the air and frozen. Air surrounding the evaporator 14 is often close to the dew point, and ice typically forms either at the evaporator or at a surface that is to be cooled that is thermally in contact with the evaporator 14. The invention is not limited to such an HVACR system, but instead is applicable to any vapor compression heat exchange system where there is a likelihood of ice formation on such an ice-prone surface.

The working fluid passes through an evaporator chamber 34, which can be tubes, absorbing heat in the process. An item to be cooled that is in thermal contact with the evaporator chamber 34 will transfer heat to the evaporator 14. This can be a source gas such as, in the case of HVAC, air flowing over the evaporator, or fins or other heat transfer structure thermally connected to the evaporator 14. Also, coils 36 can be in thermal contact with the evaporator 34 and can transmit a cooling source fluid to be cooled by heat exchange with the working fluid. In some HVACR systems, this cooled fluid is circulated to the structure that is to be cooled, for example, the surface 40 of a walk-in refrigerator or freezer. The evaporator 14 can include a surrounding supporting framework or housing 38.

One or more ultrasonic energy sources 50 can be mechanically connected to the evaporator 14 such that the ultrasonic energy source when operated will cause the evaporator 14 or an ice-prone surface cooled by the evaporator 14 to vibrate at a frequency of from 30 kHz to 60 kHz. An ultrasonic energy source 54 can be mechanically connected to the supporting framework or housing 38 to cause vibration of the framework or housing 38. Still another ultrasonic energy device 56 could be connected to the ice-prone surface 40.

The condenser 22 can comprise a condensing chamber 44 and can have a supporting framework or housing 48. A coil 43 can be in thermal contact with the condenser to transport a fluid which carries heat away from the condenser 22. The condenser 22 will not normally require deicing but can in some cases also have ultrasonic energy source 60 connected to the condensing chamber 44 or ultrasonic energy source 64 connected to the supporting framework or housing 48 to remove dirt and other foul deposits from the condenser using an ultrasonic transducer.

Different ice-making structures were simulated under ultrasonic excitation for ultrasonic deicing purposes. The first type of structure simulated is a plate. A plate can be used to simulate a wide variety of ice-prone surfaces that are found in HVACR equipment. The second type is a finger-type ice mold tube structure, and the third is a rectangular ice mold. These three structures are commonly used in commercial ice makers. The fourth is a tube-and-fin structure, which is representative structure for evaporative heat exchange structures in HVACR equipment.

FIG. 2 shows a plate structure 80 comprising a simulated copper plate 84 with a thickness of 2 mm that was used to simulate the response under ultrasonic excitation in Abaqus (Dassault Systemes, USA). A simulated ultrasonic energy device 88 is mechanically connected to vibration source area 90 of the plate 84 and vibration throughout the plate 84 was calculated by the simulation. The detailed mechanical parameters for the copper material are listed in Table 1. The plate 84 had a dimension of 150 mm×150 mm, and the ultrasonic excitation was applied at the center of the plate in the area 90 with a radius of 25 mm. The Abaqus model was used and the plate was simulated with a shell in Abaqus. As the boundary condition, the four corners were fixed with zero displacement in the x, y, and z directions. The z-direction is perpendicular to the plate plane. A simulated pressure loading was applied at the center circular area with a sinusoidal function of 40 kHz and a maximum amplitude of 1 MPa.

TABLE 1
Mechanical parameters for the copper used in Abaqus simulation.
	Parameters	Value
	Elastic modulus	130	GPa
	Poisson's ratio	0.34
	Density	8.94 103	kg/m3

The displacement field map of the copper plate under the ultrasonic excitation at a frequency of 40 kHz showed that the maximum displacement in the z-direction was 4.801 mm, located at the center of the excitation area. The displacements were picked up at multiple points from the center to the edge of the plate (nodal points on the horizontal line in the figure). FIG. 3 shows the relative maximum displacement from the center to the edge normalized by the displacement at the center (at 0 mm), and plots the displacements at different locations versus the corresponding locations. FIG. 3 shows that the center of the excitation area in FIG. 2 is at 0 mm, while the right edge point in is at 75 mm. All the displacements were normalized by the displacement at the center position.

At the position of 25 mm, where the boundary of the excitation area is located, the displacement is still 91% of the maximum displacement. At 50 mm, two times the excitation radius, the displacement is 72% of the maximum displacement. Even at the edge of the plate (75 mm), the displacement was still at 55%. This indicates that ultrasonic excitation can generate an effective vibration area of three times the area radius with a displacement of no less than 55% of the maximum displacement. Therefore, the ultrasonic actuator can be used for deicing at a large area on a plate structure.

The second type of common ice mold is a finger tube structure, widely used in small-size ice makers for making hollow cubes with finger-like dimensions. FIG. 4 shows one of the finger molds 100 as would be used in a small commercial ice maker. In the Abaqus simulation, only one of the finger segments 104 connected to a cooling fluid manifold 110 was modeled and analyzed under ultrasonic excitation as by an ultrasonic energy source 120. The horizontal rectangular tube manifold 110 has a length of 35 mm with a section dimension of 10.5 mm×14 mm. The vertical circular finger mold tube 104 is under the horizontal tube 110 with a diameter of 10 mm and a height of 33.5 mm. Both the horizontal tube 110 and the vertical finger tube 104 have a thickness of 0.5 mm.

Two loading modes corresponding to the two ultrasonic excitation modes from ultrasonic energy sources were analyzed. The loading is applied on the top surface of the segments. The first one is vertical loading induced by a thickness model ultrasonic actuator 120, and the other one is horizontal loading induced by a shear mode ultrasonic actuator 124. The ice cube will be generated around the finger tube 104. The ice cube can be removed if the ultrasonic excitation can create a large enough displacement on the finger tube surface in the Y-direction. Therefore, the displacement from a sensing point at the middle height of the finger tube 104 was used to compare the performance of the two loading modes. The displacement field for the segment indicated that, for vertical loading, the maximum displacement in the Y-direction for the sensing point is 7.3×10⁻³. The maximum displacement for the horizontal loading is only 1.6×10⁻³. Therefore, the vertical loading excited by the thickness mode ultrasonic actuator 120 will be more efficient for the deicing performance on the finger mold 104. Here, the maximum displacement on the simulated segment was two orders smaller than the displacement on the plate structure. A higher power may be needed for deicing on the finger mold 100 than for the plate structure 80.

A rectangular mold such as is commonly used ice mold for making ice cubes is shown in FIG. 5. The rectangular mold 140 has a top 142, bottom 144 and dividers 150 substantially perpendicular to the top 142 and bottom 144. The mold 140 has a copper body with a thickness of 0.91 mm and a nickel coating. The ultrasonic excitation can only be applied on the top and side surfaces, while the back surface is inaccessible. Only one row of the rectangular mold was investigated in the simulation. Two scenarios were simulated with the ultrasonic excitation applied only on the top surfaces as by ultrasonic energy sources 160 and on both top and side surfaces as with ultrasonic energy source 164. The loading on each surface area was 1 MPa, the same as in previous studies.

The simulation results indicated that with top surface loading and side surface loading, the displacement of the rectangular mold 140 shows a more significant displacement than the one with only top surface loading. Larger displacements were observed, especially for the vertical separators 150. The bottom plates of the mold also show more significant displacement with extra side surface excitation. Large displacements in these positions could contribute to a better performance in breaking the boundary between the ice and mold surfaces. Since the rectangular mold has limited surface area for applying the ultrasonic excitation, multiple ultrasonic actuators with different excitation locations could be used to improve deicing performance.

The tube-and-fin structure 180 shown in FIG. 6 is a typical type of structure for an evaporator heater exchanger. This tube-and-fin structure 180 includes two thick aluminum plates 186 on the sides to support the tubes 184 and fins 188. The copper tubes 184 cross the plates 186 and the thin aluminum fins 188. An ultrasonic energy source 190 can be connected to the tube 184. An ultrasonic energy source 194 can be connected to the steel plates 186. Ultrasonic deicing is used to apply ultrasonic excitation on the two side plates 186 or the copper tubes 184. Then, the vibration will propagate through the copper tubes 184 to the fins 188, removing the ice on the tubes 184, fins 188, and steel plates 186. A simplified Abaqus model was built. The tube had a length of 50 mm, a diameter of 10 mm, and a thickness of 2 mm. The side plate and fins have the same dimension of 40 mm×40 mm. The plate has a thickness of 2 mm, while the fins are much thinner, with a thickness of 0.3 mm.

The material properties of the tube-and-fin structure are summarized in Table 2. Two loading scenarios were studied with different loading locations. First, the ultrasonic excitation was applied on the side aluminum plate by the ultrasonic energy source 194 with a pressure of 1 MPa. For the second scenario, the excitation was applied on the end tube surface by the ultrasonic energy source 190 as a shear traction of 1 MPa. The simulation results for the two excitation scenarios indicated that the ultrasonic vibration can propagate to all the components, including the fins 186, tube 184, and side plates 186. This indicated that the ultrasonic excitation on one end of the structure may be able to remove the ice on the far end. Additionally, the whole structure under the excitation on the side plate 186 demonstrated much higher displacement than loading on the end tube 184. One reason is that the plate 186 has a large loading area while the end tube 184 has a limited area for the excitation. In a real application, mounting the ultrasonic actuators on the side plates might be more practical and efficient for deicing.

TABLE 2
Mechanical parameters for the materials
of the tube-and-fin structure.
	Material		Copper	Aluminum
	Elastic modulus	130	GPa	69	GPa
	Poisson's ratio	0.34	0.334
	Density	8.94 × 103	kg/m3	2.7 × 103	kg/m3

There is shown in FIGS. 7-13 a schematic diagram depicting an experiment that was performed in which the ultrasonic energy sources were used to determine the presence of ice. A plate 200 having a surface 204 was fitted with a transducer 210 having a signal line 214 (FIG. 7) and was initially provided with a sensing power of 1 W. The resonance frequency and maximum current were determined for a single ice cube 220 A on the plate 204 (FIG. 8), two ice cubes 220 A-B (FIG. 9), three ice cubes 220 A-C (FIG. 10), and five ice cubes 220 A-E (FIG. 11). The resonance frequency and maximum current were then measured at a power of 25 W sufficient to dislodge the ice cubes 220 A-E (FIG. 12) from their original positions 230 A-E on the plate 204 (FIG. 13). The excitation power, resonance frequency and maximum current are shown in Table 3:

	TABLE 3
	0 cubes	1 cube	2 cubes	3 cubes	5 cubes	Dislodge
Excitation	1 W	1 W	1 W	1 W	1 W	25 W
Resonance	38.3	38.28	38.52	38.4	39.25	38.27
frequency
(kHz)
Max. current	118	N/A	79.8	83	73	87.5
(mA)

The tests were repeated, and the results are shown in Table 4:

	TABLE 4
	0 cubes	1 cube	2 cubes	3 cubes	5 cubes	Dislodge
Excitation	1 W	1 W	1 W	1 W	21 W	1 W
Resonance	38.09	39.56	39.28	39.25	N/A	38.11
frequency
(kHz)
Max. current	89.9	43.6	45.2	45.4	N/A	87.5
(mA)

These results show that the transducer can be used to determine the presence of ice. After the ice is dislodged from the plate surface 204, the resonance frequency returns to near the value obtained for 0 cubes. The transducer 210 can thereby be used to sense the presence of ice, the power can be increased to remove the ice, and then the power can be decreased to sense if the removal has been successfully completed. If ice remains, the transducer can be powered up again to remove remaining ice until no more ice is sensed. During sensing mode, the ultrasonic generator emits low-power signals to stimulate the transducer. The impedance analyzer concurrently measures the impedance of the transducer-wall-ice system across a frequency sweep (e.g., 20 kHz to 80 kHz). Resonance frequency signifies the point of minimum impedance. Ice formation near the transducer alters the measured resonance frequency. This shift triggers the activation of high-power ultrasound from the generator to remove the ice. Subsequently, the system repeats the sensing process to verify successful removal by confirming the resonance frequency returns to its original value.

A commercial ice maker was evaluated for its energy consumption and cycle time for making ice. A power meter was utilized to collect the power consumption of the machine, as a function of time. Similarly, the same system was upgraded with an icephobic coating and also installed with an ultrasonic transducer. FIGS. 14 and 15 display the power consumption as a function of time during the harvesting portion of both ice makers without (FIG. 14) and with (FIG. 15) an ultrasonic energy source and an icephobic coating. Integrating the area under the power versus time curve was repeated for both harvesting time period and the entire ice making cycle. The harvesting stage involves heating the evaporator to dislodge the ice from the evaporator ice mold. The total cycle represents bringing the evaporator ice mold to the freezing temperature, holding the temperature for forming the ice, followed by heating the mold to remove the ice. The cycle repeats for the next batch of ice.

Due to shortened harvesting cycle of the system with an ultrasonic energy source and an icephobic coating, the total energy consumption and cycle time was reduced. FIG. 16 shows the energy and time savings (compared to the baseline ice maker system) associated with utilizing an icephobic coating or ultrasonic energy source or both upgrades. FIG. 16 shows that the total % energy savings and % time savings compared to the baseline system was significant. This is due to the limited heating during the harvesting cycle with coating and ultrasonic enhancement, whereby the energy needed for the follow-on cycle is lower due to lower starting temperature of the upgraded system compared to the baseline system.

High-power ultrasound frequencies are typically in the range of 20 kHz to 100 kHz for several reasons. Such frequencies provide improved propagation distance and wave attenuation. Since most ice-related structures are plates (mm thick), lower-frequency ultrasonic waves can propagate farther distances than can the higher-frequency (>100 kHz) ultrasonic waves. Therefore, the use of lower-frequency ultrasound waves can cover a larger area than higher-frequency ultrasound waves. Higher-frequency ultrasound waves will attenuate faster in the propagation than lower-frequency ultrasound waves.

Lower-frequency ultrasound also provides energy efficiency. The ultrasonic actuator is a device to convert electrical energy into mechanical energy. In the frequency range of <100 kHz, it has a higher efficiency for energy conversion, which is crucial for generating high-intensity ultrasound needed for deicing.

Lower-frequency ultrasound allows for improved ultrasonic actuator design. An ultrasound actuator (PZT disk or Langevin transducer) designed to operate in this frequency range can be built at a reasonable size and cost while still achieving the necessary power levels for many applications. The actuator for higher frequencies is smaller and thinner, which makes it difficult to provide enough energy since higher excitation voltages can compromise the mechanical integrity.

Lower-frequency ultrasound avoids the human hearing range. Frequencies in the range of 20 kHz to 100 kHz are generally outside of the human hearing range (20 Hz to 20 kHz). This is important for applications where the ultrasound needs to be powerful but imperceptible to humans. The frequency of the ultrasound can be 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100 kHz, and can be within a range of any high value and low value selected from these values. A range of 30-60 kHz can be sued.

The specific frequency that is used depends on the ultrasonic actuator used and the structure it is attached to. The most efficient working frequency can be determined using a laser Doppler vibrometer by sweeping the excitation frequency in a frequency range and measuring the responses at different frequencies. In FIG. 17, the frequency response is plotted for an ultrasonic actuator installed on an ice tray when sweeping the frequency from 25 kHz to 120 KHz. Peaks exist at 42.4 kHz, 48.8 kHz, and 54.4 kHz. The peak at 25 kHz can be ignored due to side effects. The optimal frequency taken from this plot would be 42.4 kHz or 54.4 KHz.

The normalized power per unit area for defrost/deicing process is from 0.5 W/in² to 1.5 W/in². One or more actuators can be provided. A suitable distance between each actuator was found to be 12″ to 18″. Other distances are possible.

The invention provides for both the sensing of frost formation and defrosting with ultrasonic vibration, which can be followed by frost removal verification. An alternative method to find the optimal frequency is using an impedance analyzer. FIG. 18 shows the impedance curve for a PZT actuator installed on an ice-covered plate. The lowest impedance point identifies the resonance frequency (32 kHz in the figure) of the system (actuator and structure), which is the optimal working frequency.

The above phenomenon can be exploited to perform two different functions with the same actuator, a sensing mode and a deicing mode. The sensing mode of the same ultrasonic actuator could be achieved to sense the existence of frost/ice and verify the performance of deicing. Once the ice forms on the structure (e.g., plate), the weight and stiffness of the whole system increases. These changes will change the resonance frequency of the actuator (e.g., shift to 33 kHz). This frequency shift can be found (by the controller/system electronics) by repeating the impedance analyzing procedure. Once the high-power ultrasound (e.g., 50 W) is fired and the ice is removed, the impedance analyzing procedure can be repeated to check if the resonance frequency goes back to its original value (32 kHz). If the frequency is back to 32 kHz, it indicates all the ice is removed, and the system is back to its original status.

Such a system for sensing, deicing, and then verifying deicing is shown in FIG. 19. The system 300 includes a plate or wall 310 with an ultrasonic transducer 320 on a side of the wall opposite the side that is prone to formation of ice 330. The transducer 320 is connected by a signal line 340 to an impedance analyzer 350. The impedance analyzer 350 is connected by a line 360 to an ultrasonic generator 370 which powers the ultrasonic transducer 320. Connecting an ultrasonic generator, impedance analyzer, and ultrasonic transducer involves two key steps: electrical and physical. Electrically, the generator's output typically connects to the transducer while the analyzer will sense the input signal to the transducer and the feedback from the transducer. Physically, the transducer itself needs to be mounted on the structure of interest, often with a coupling material to ensure good acoustic transmission. The generator's ground and the analyzer's ground should also be connected to a common reference point. Following these steps allows the system to send and receive ultrasonic signals through the transducer for impedance analysis.

The invention can be used in a variety of applications. A cold storage container 400 is shown in FIG. 20. Typically, the defrost heating cycle thaws the ice and as a result the stored food temperature increases, which can result in the loss of product and a decrease in product quality. This happens due to the high temperature and high humidity created by heating elements resulting in stored food temperature exceeding the threshold temperature (41° F.) and spoiling the food (e.g., bacterial activity). The storage container 400 includes a floor 404 and a first side wall 410. The first side wall 410 has a suitable ultrasonic energy device such as PZT 411 which communicates by a connecting line 412 to a processor 430. A second side wall 414 has a PZT 415 which communicates through line 416 with processor 430. A rear wall 418 has a PZT 419 which communicates through line 424 with processor 430. A top wall 422 has a PZT 423 which communicates through line 424 with the processor 430.

The processor 430 can be used to control the PZTs between a sensing mode, a deicing mode, and another sensing mode to determine if all ice has been removed. For example, in FIG. 21 an ice patch 450 has formed on the top wall 422. The ice patch is sensed by PZT 423 in sensing mode. The remaining PZTs do not sense any ice. The processor 430 then energizes the PZT 423 to a deicing power to vibrate in deicing mode causing the ice 450 to dislodge and fall as shown by arrows 452 to form a pile of dislodged ice 454 which can be easily removed from the floor 404. The remaining PZTs 411, 415, and 419 remain in sensing mode because no ice was detected by these PZTs.

FIGS. 23-24 show a different situation where ice 460 has formed on the rear wall 418. The ice 460 is sensed by the PZT 419, which communicates to the processor 430 through the line 420. The remaining PZTs 411, 415 and 423 do not sense any ice. The processor 430 causes the PZT 419 to enter deicing mode at a higher power than the sensing power, which causes the ice 460 to dislodge from the wall 418 and fall as indicated by arrows 462 to form a pile of ice 464 on the floor 404.

The invention allows only the PZT that is adjacent to ice to be energized into ice removal mode. All other PZTs can remain in sensing mode. There is a significant energy savings because only the PZT that is adjacent to ice is energized to a power suitable for deicing. Further, because the PZT that is energized for ice removal can be returned to sensing mode to determine if all ice has been successfully removed, an excessive use of energy to assure the removal of all ice is not necessary. The energy usage is confined to that necessary to remove the ice, and little or no more energy is wasted.

FIG. 25 shoes the invention as incorporated directly on an evaporator assembly 500. The evaporator assembly 500 can include coils 510, cooling fins 520, and one or more supporting brackets such as top bracket 530 and side bracket 540. Ice sensing and deicing can be performed by one or more PZTs such as PZT 550 on the side bracket 540, PZT 560 on the top bracket 530, and PZT 570 which can be affixed to one or more of the coils 510. Some PZTs could also be positioned elsewhere, for example, connected to the coils 520.

FIG. 26 depicts a walk-in freezer 600. The walk-in freezer 600 has a floor 604, a front wall 610 and door 615, first side PZT 620 connected to first side wall 625, top PZT 630 connected to top wall 635, and second side PZT connected to second side wall 645. The PZTs can be used in both ice sensing and ice removal modes.

FIG. 27 depicts a refrigerated container 700. The refrigerated container 700 has a floor 710, first side wall 720 with first side PZT 725, second side wall 730 with second side 735, top 740 with top PZT 745, and doors 750. More or fewer PZTs can be provided, depending on the expected ice formation patterns in the container 700.

The invention as shown in the drawings and described in detail herein disclose arrangements of elements of particular construction and configuration for illustrating preferred embodiments of structure and method of operation of the present invention. It is to be understood however, that elements of different construction and configuration and other arrangements thereof, other than those illustrated and described may be employed in accordance with the spirit of the invention, and such changes, alternations and modifications as would occur to those skilled in the art are considered to be within the scope of this invention as broadly defined in the appended claims. In addition, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

Claims

1. A vapor compression heat transfer system, comprising an evaporator assembly and an ice-prone surface, and an ultrasonic energy source, the ultrasonic energy source when energized vibrating the ice-prone surface at a frequency of from 30 kHz to 60 KHz.

2. The vapor compression heat transfer system of claim 1, wherein the vapor compression system comprises at least one selected from the group consisting of an ice maker, heat pump, air conditioner, a refrigerator, and a freezer.

3. The vapor compression heat transfer system of claim 1, wherein the ultrasonic energy source comprises a transducer.

4. The vapor compression heat transfer system of claim 3, wherein the transducer is a piezoelectric transducer.

5. The vapor compression and heat transfer system of claim 4, wherein at least two piezoelectric transducers are connected to the ice-prone surface, and each transducer is spaced from 12 in. to 18 in. from an adjacent transducer.

6. The vapor compression heat transfer system of claim 1, wherein the evaporator assembly comprises an evaporator tube having an ice-prone surface, and the ultrasonic energy source vibrates the ice-prone surface and the evaporator tube.

7. The vapor compression heat transfer system of claim 6, wherein the evaporator assembly comprises an evaporator fin thermally and mechanically coupled with the outer surface of the evaporator tube, at least one of the evaporator tube and the evaporator fin comprising an ice-prone surface, such that vibration of one of the evaporator tube and the evaporator fin by the ultrasonic energy source will vibrate the ice-prone surface.

8. The vapor compression heat transfer system of claim 7, wherein the evaporator tube and/or the evaporator fin comprises at least one selected from the group consisting of Cu, Al, Fe, and alloys thereof.

9. The vapor compression heat transfer system of claim 1, further comprising a layer of icephobic material coated on the ice-prone surface, wherein the icephobic material will reduce ice formation on the ice-prone surface during operation of the evaporator and reduce adhesion of the formed ice to the ice-prone surface.

10. The vapor compression heat transfer system of claim 9, wherein the icephobic material comprises polymeric low interfacial toughness (LIT) material.

11. The vapor compression heat transfer system of claim 10, wherein the LIT material is at least one selected from the group consisting of polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE).

12. The vapor compression system of claim 1, wherein the evaporator assembly comprises supporting structure for the evaporator, and the ultrasonic energy device is mechanically connected to the supporting structure such that the ultrasonic energy source will vibrate the supporting structure and the vibration will be transmitted through the supporting structure to the evaporator and the ice-prone surface.

13. The vapor compression heat transfer system of claim 1, further comprising controller circuitry communicatively coupled with the ultrasonic energy source and configured to instruct the ultrasonic energy source to vibrate the ice-prone surface to cause removal of ice from the ice-prone surface.

14. The vapor compression heat transfer system of claim 13, further comprising an ice detector for detecting the presence of ice on the ice-prone surface, the ice detector being connected to the controller circuitry to operate the ultrasonic energy source when a threshold amount of ice is detected by the ice detector on the ice-prone surface.

15. The vapor compression heat transfer system of claim 14, wherein the ice detector comprises at least one selected from the group consisting of resistive sensor, photoelectric sensors, fiber optic sensors, and capacitive sensors.

16. The vapor compression heat transfer system of claim 15, wherein the ice detector comprises an impedance analyzer, the impedance analyzer measuring the impedance of the ice-prone surface and producing an impedance signal relating to the impedance of the ice-prone surface to the controller circuitry, the controller circuitry determining from the impedance signal the resonant frequency of the ice-prone surface and comparing the resonant frequency to a set point resonant frequency for the ice-prone surface to determine the presence of ice on the ice-prone surface.

17. The vapor compression heat transfer system of claim 14, wherein the ultrasonic energy source is operable as an ice detector in an ice-detecting mode, in conjunction with the controller.

18. The vapor compression heat transfer system of claim 17, wherein the ultrasonic energy source is operable in the ice-detecting mode over a range of 0.05 W/in2-0.1 W/in2, and in an ice-removal mode over a range of 0.5 W/in2-1.5 W/in2.

19. The vapor compression heat transfer system of claim 14, wherein the controller circuitry comprises a function generator configured to energize the ultrasonic energy device according to predetermined functions.

20. A low temperature chamber having walls and a ceiling comprising an ice-prone surface, the chamber comprising one or more ultrasonic energy sources disposed on one or more of the walls or the ceiling, the ultrasonic energy source when energized vibrating the ice-prone surface at a frequency of from 30 kHz to 60 KHz.

21. The low temperature chamber of claim 20, wherein the chamber is at least one selected from the group consisting of cold storage, walk-in freezer, reach-in display case, frozen fry dispenser, walk-in cooler, and refrigerated transportation container.

22. The low temperature chamber of claim 20, further comprising an evaporator attached to the low temperature chamber.

23. The low temperature chamber of claim 20, further comprising a layer of icephobic material coated on the ice-prone surface, wherein the icephobic material will reduce ice formation on the ice-prone surface while the temperature in the chamber is below the dew point temperature and reduce adhesion of formed ice to the ice-prone surface.

24. The low temperature chamber of claim 23, wherein the icephobic material comprises a low interfacial toughness (LIT) material, wherein the LIT material is at least one selected from the group consisting of polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE).

25. A method of conducting one of heating, ventilation, air conditioning and refrigeration (HVACR), wherein the HVACR system comprises an evaporator assembly and an ice-prone surface, the method comprising the steps of: providing an ultrasonic energy source; and,operating the ultrasonic energy source to vibrate the ice-prone surface at a frequency of from 30 KHz to 60 KHz.

26. The method of claim 25, further comprising the step of using an ice detector to determine whether ice formed on the ice-prone surface has exceeded a predetermined upper threshold, and selectively instruct the ultrasonic energy source to vibrate the ice-prone surface in response to the determination; and, using the ice detector to determine whether the formed ice has fallen below a predetermined lower threshold, and selectively turn off the ultrasonic energy source to cease vibration of the ice-prone surface in response to the determination.

27. The method of claim 25, further comprising the step of instructing the ultrasonic energy source to vibrate the ice-prone surface in accordance with a predetermined schedule.

28. The method of claim 25 wherein the HVACR system comprises at least one selected from the group consisting of an ice maker, heat pump, air conditioner, a refrigerator, and a freezer.

29. The method of claim 25, wherein the power per unit area produced by the ultrasonic energy source is from 0.5 W/in2 to 1.5 W/in2.

30. An evaporator assembly for a heating, ventilation, air conditioning and refrigeration (HVACR) apparatus, the evaporator assembly comprising an evaporator and an ice-prone surface, and an ultrasonic energy source, the ultrasonic energy source when energized vibrating the evaporator at a frequency of from 30 KHz to 60 KHz.