Patent Application
20150233637
The present invention relates generally to heating and drying technologies and, in particular, to heating and drying assisted with ultrasound.
It is well known that the majority of energy intensive processes are driven by the rates of the heat and mass transfer. Specific details of a particular application, such as the chemistry of a substrate to be dried (e.g., a factor in label printing, sheet-fed and continuous printing, converting, packaging, mass mailing), the temperature of a material being applied, the needed residence time for a coating to dry, and water or solvent evaporation rates, are necessary for a drying and heating process to work properly. These factors dictate the size of the drying equipment.
It is also well known that the main thing that prevents an increase in heating and drying rates is the boundary layer that is formed around the subject or material to be heated or dried. In modern heating and drying practice there are several methods to disrupt the boundary layer. The most common method is to add hot convection air to other heating methods, such as, for example, radiant heating.
With convective heat, high-velocity impinging jets of hot air are directed onto the material and, consequently, onto the boundary layer to agitate the boundary layer. Similarly, impinging hot-air jets are used in infrared-light heating. Applying a convective airflow or infrared light typically increases the heat transfer rate by about 10-25%. Thus, these approaches have provided some improvement in heat-transfer rates, but further improvements are needed.
There are also known efforts of using pulse combustion to establish pulsating heat jets and apply them onto a material in order to reduce the boundary layer. With pulse combustion jets, flame generates sound in the audible frequency range. The use of pulse combustion jets typically increases the heat transfer rate by about 200-500% (when making a comparison with the same steady-state velocities, Reynolds numbers, and temperatures). Thus, this approach has provided significant improvement in heat-transfer rates, but the pulse combustion equipment is large/space-consuming and costly to purchase and operate. Additionally, a variety of industries require more compact equipment, and combustion gases sometimes are not allowed in the process due to its chemical nature (food, paints, coatings, printing, concerns of explosives, building codes, needs for additional natural gas lines, its maintenance, etc.).
Accordingly, it can be seen that a need exists for improved drying technologies that produce significantly increased heat-transfer rates but that are cost-efficient to make and use and preferably have a smaller footprint and require less material. It is to the provision of solutions meeting this and other needs that the present invention is primarily directed.
Generally described, the present invention provides a drying apparatus including a delivery air enclosure, through which forced air is directed toward the material, and at least one ultrasonic transducer. The ultrasonic transducer is arranged and operated to generate acoustic oscillations that effectively break down the boundary layer to increase the heat transfer rate. In particular, the acoustic outlet of the ultrasonic transducer is positioned a spaced distance from the material such that the acoustic oscillations are in the range of about 120 dB to about 190 dB at the interface surface of the material. Preferably, the acoustic oscillations are in the range of about 160 dB to about 185 dB at the interface surface of the material.
In another aspect of the invention, the ultrasonic transducers are positioned a spaced distance from the material to be dried of about (λ)(n/4), where λ is the wavelength of the ultrasonic oscillations and “n” is plus or minus 0.5 of an odd integer (0.5 to 1.5, 2.5 to 3.5, 4.5 to 5.5, etc.). Preferably, the ultrasonic transducers are positioned relative to the material to be dried the spaced distance of about (λ)(n/4), where “n” is an odd integer (1, 3, 5, 7, etc.). In this way, the amplitude of the acoustic oscillations is at about maximum at the interface surface of the material to more effectively agitate the boundary layer.
In a first example embodiment of the invention, the apparatus includes a return air enclosure for drawing moist air away from the material, with the delivery enclosure positioned within the delivery enclosure so that the warm moist return air in the return enclosure helps reduce heat loss by the air in the delivery enclosure. The ultrasonic transducer is of a pneumatic type that is positioned within an air outlet of the delivery enclosure so that all or at least a portion of the forced air is directed through the pneumatic ultrasonic transducer.
In a second example embodiment of the invention, the apparatus is included in a printing system that additionally includes other components known to those skilled in the art. In this embodiment, the apparatus includes two delivery enclosures, one return enclosure, and two ultrasonic transducers. In addition to the apparatus, the printing system includes an air-mover (e.g., a fan, blower, or compressor) and a heater that cooperate to deliver heated steady-state air to the apparatus.
In a third example embodiment of the invention, the apparatus is included in a printing system that additionally includes other components known to those skilled in the art. In this embodiment, the apparatus includes five delivery enclosures each having at least one ultrasonic transducer. In addition to the apparatus, the printing system includes an air-mover and control valving that can be controlled to operate all or only selected ones of the ultrasonic transducer for localizing the drying, depending on the particular job at hand.
In fourth and fifth example embodiments of the invention, the apparatus each include a return enclosure with a plurality of return air inlets and three delivery enclosures within the return enclosure. In these embodiments, one delivery enclosure is dedicated for delivering steady-state air and the other two have ultrasonic transducers for delivering the acoustic oscillations to the material. In the fourth example embodiment, the two acoustic delivery enclosures are positioned immediately before and after (relative to the moving material) the dedicated air delivery enclosure. And in the fifth example embodiment, the two acoustic delivery enclosures are positioned at the front and rear ends (relative to the moving material) of the return enclosure, that is, at the very beginning and end of the drying zone.
In a sixth example embodiment of the invention, the apparatus includes a return enclosure, a delivery enclosure, and an ultrasonic transducer. However, the delivery enclosure is not positioned within the return enclosure; instead, these enclosures are arranged in a side-by-side configuration. In addition, an electric heater is mounted to the delivery enclosure for applying heat directly to the material.
In a seventh example embodiment of the invention, the apparatus includes a delivery enclosure, an ultrasonic transducer, and a heater. The heater may be bi-directional for heating the air inside the delivery enclosure (convective heat) and directly heating the material (radiant heat).
In eighth, ninth, and tenth example embodiments of the invention, the apparatus include a delivery enclosure with a plurality of air outlets and a plurality of electric ultrasonic transducers. In the eighth example embodiment, the air outlets and electric ultrasonic transducers are positioned in an alternating, repeating arrangement. The ninth example embodiment includes an electric heater within the delivery enclosure. And the tenth example embodiment includes waveguides housing the ultrasonic transducers for focusing/enhancing and directing the acoustic oscillations toward the material.
In an eleventh example embodiment of the invention, the apparatus includes a delivery enclosure with a plurality of air outlets and a plurality of electric ultrasonic transducers. In addition, the apparatus includes infrared-light-emitting heaters.
In a twelfth example embodiment of the invention, the apparatus is a stand-alone device including a delivery enclosure with a plurality of air outlets and housing a plurality of electric ultrasonic transducers, a plurality of infrared-light-emitting heaters, and an air mover.
In a thirteenth example embodiment of the invention, the apparatus includes a delivery enclosure with a plurality of air outlets, a plurality of electric ultrasonic transducers, and a plurality of infrared-light-emitting heaters. In this embodiment, steady-state air is not forced by an air mover through the delivery enclosure, but instead the infrared heater by itself generates the heat and the airflow.
In a fourteenth example embodiment of the invention, the apparatus includes a plurality of ultrasonic transducers mounted on a panel, with no steady-state air forced by an air mover through an enclosure. Instead, the apparatus includes at least one ultraviolet (UV) heater for generating the heat and the airflow.
In fifteenth and sixteenth example embodiments of the invention, the apparatus each include a delivery enclosure with an air outlet for delivering forced air to the material, and at least one ultrasonic transducer for delivering acoustic oscillations to the material. The ultrasonic transducers are mounted within the delivery enclosure to set up a field of acoustic oscillations through which the forced air passes before reaching the material to be dried, and they are not oriented to direct the acoustic oscillations toward the air outlet. In the fifteenth example embodiment, three rows of ultrasonic transducers are mounted to an inner wall of the delivery enclosure to set up a field of acoustic oscillations throughout the delivery enclosure. And in the sixteenth example embodiment, the ultrasonic transducer is mounted immediately adjacent the air outlet. In addition, wing elements can be mounted to the electric ultrasonic transducers to enhance the acoustic oscillations for more effective disruption of the boundary layer.
In addition, the present invention provides a method of calibrating drying apparatus such as those described above. The method includes the steps of calculating the spaced distance using the formula (λ)(n/4); positioning the ultrasonic transducer outlet and the material at the spaced distance from each other; positioning a sound input device immediately adjacent the interface surface of the material; connecting the sound input device to a signal conditioner; measuring the pressure of the acoustic oscillations at the interface surface of the material using the sound input device and the signal conditioner; converting the measured pressure to decibels; and repositioning the ultrasonic transducer relative to the material and repeating the measuring and converting steps until the decibel level at the interface surface of the material is in the range of about 120 dB to about 190 dB, or more preferably in the range of about 160 dB to about 185 dB. In the formula (λ)(n/4), “λ” is the wavelength of the ultrasonic oscillations and “n” is in the range of plus or minus 0.5 of an odd integer so that the acoustic oscillations at the interface surface of the material are within about a 90-degree range centered at about maximum amplitude. Preferably, “n” is an odd integer so that the acoustic oscillations at the interface surface of the material are at about maximum amplitude.
The specific techniques and structures employed by the invention to improve over the drawbacks of the prior devices and accomplish the advantages described herein will become apparent from the following detailed description of the example embodiments of the invention and the appended drawings and claims.
The present invention provides drying systems and methods that include the use of ultrasound to more effectively break down the boundary layer and thereby increase the heat and/or mass transfer rate. Example embodiments of the invention are described herein in general configurations for illustration purposes. The invention also provides specific configurations for use in specific applications such as but not limited to printing, residential and commercial cooking appliances, food processing equipment, textiles, carpets, converting industries, fabric dyeing, and so on. In particular, the invention can be configured for flexographic and gravure printing of wallpaper, gift-wrap paper, corrugated containers, folding cartons, paper sacks, plastic bags, milk and beverage cartons, candy and food wrappers, disposable cups, labels, adhesive tapes, envelopes, newspapers, magazines, greeting cards, and advertising pieces. The invention can be adapted for these and many other batch and continuous heating and drying processes.
Referring now to the drawing figures,
The material 20 to be dried can be any of a wide range of materials, depending on the application. For example, in printing applications the material to be dried is ink on paper, cardboard, plastic, fabric, etc., and for food processing equipment the material is food. Thus, the material 20 can be any substance or object for which heating and drying is desired.
In the depicted embodiment, the material 20 is conveyed beneath the apparatus 10 by a conventional conveyor system 34. In alternative embodiments, the material 20 is conveyed into operational engagement with the apparatus 10 by another device and/or the apparatus is moved relative to the material.
A steady-state forced airflow 21 is delivered to the delivery enclosure 12 under positive pressure by an air-moving device 50 that is connected to the air inlet 26 by an air conduit 52 (see
In typical commercial embodiments, the steady-state inlet airflow 21 is pre-heated by a heat source 54 that is positioned near the apparatus 10 and connected to the delivery enclosure inlet 26 (see
The delivery enclosure 12, the return enclosure 14, and the ultrasonic transducer 16 of the depicted embodiment are arranged for enhanced thermal insulation of the heated delivery airflow 21. In particular, the delivery enclosure 12 is positioned inside the return enclosure 14 so that the warm moist return air 24 in the return enclosure helps reduce heat loss by the heated air 21 in the delivery enclosure. The ultrasonic transducer 16 is positioned in the delivery enclosure air outlet 28 and extends through the return enclosure 14. In alternative embodiments in which the heater is positioned within the delivery enclosure, only the portion of the delivery enclosure carrying heated air is positioned within the return enclosure. In other alternative embodiments, the delivery enclosure and the return enclosure are positioned in a side-by-side arrangement with the delivery enclosure positioned ahead of the return enclosure relative to the moving material. And in yet other alternative embodiments, the apparatus includes a plurality of the delivery enclosures, return enclosures, and ultrasonic transducers arranged concentrically, side-by-side, or otherwise.
The ultrasonic transducer 16 of the depicted embodiment is an elongated pneumatic ultrasonic transducer, the air outlet 28 of the delivery enclosure 14 is slot-shaped, and the transducer is positioned in the air outlet so that all of the steady-state airflow 21 is forced through the transducer. In this way, the heated airflow 22 and the acoustic oscillations 18 are delivered together onto the material 20. In alternate embodiments, the size and shape of the ultrasonic transducer 16 and the delivery enclosure air outlet 28 are selected so that some of the heated airflow 21 is not routed through the ultrasonic transducer but instead is routed around it and through the same or another air outlet. In other alternative embodiments, the apparatus 10 includes a plurality of the pneumatic ultrasonic transducers 16 (elongated or not) and the delivery enclosure 14 includes a plurality of the air outlets 28 (slot-shaped or not) for the transducers.
The ultrasonic transducer 16 depicted in
In alternative embodiments, the ultrasonic transducer 16 has more or fewer grooves, deeper or shallower grooves, different shaped grooves, a greater spacing between the grooves on the same wall, and/or a greater spacing between the walls. In other alternative embodiments, the ultrasonic transducer 16 has a U-shaped air passage that induces the acoustic oscillations. And in still other alternative embodiments, the ultrasonic transducer 16 is provided by another design of pneumatic transducer and/or by an electric-operated ultrasonic transducer.
The ultrasonic transducer 16 is operable to produce fixed frequency ultrasonic acoustic oscillations in the sound pressure range of about 120 dB to about 190 dB at the interface surface of the material 20 being treated. Preferably, the ultrasonic transducer 16 is designed for producing acoustic oscillations in the sound pressure range of about 130 dB to about 185 dB at the interface surface of the material 20 being treated, more preferably about 160 dB to about 185 dB, and most preferably about 170 dB to about 180 dB. These are the decibel levels at the interface surface of the material 20, not necessarily the output decibel level range of the ultrasonic transducer 16. In typical commercial embodiments, the ultrasonic transducer 16 is selected to generate up to about 170 to about 190 dBs, though higher or lower dB transducers could be used. Ultrasonic transducers that are operable to produce these decibel levels are not known to be commercially available and are not known to be used in commercially available heating and drying equipment.
Sound (ultrasound is part of it) dissipates with the second power to the distance, so the closer the ultrasonic transducer is positioned to the material, the lower in the dB range the dB level generated by the transducer can be. Many applications, by the nature of the process, require a transducer-to-material distance of from about 10 mm to about 100 mm. The longer the distance, the higher the dB level that must be generated by the ultrasonic transducer in order to obtain the needed dB level at the interface surface of the material. In addition, dB levels above the high end of the dB range could be used in some applications, but generally the larger transducers that would be needed are not as cost-effective and the sound level would be so high that humans could not safely or at least comfortably be present in the work area.
As shown in
In order for the ultrasonic transducer 16 to be spaced from the material 20 in this way, the apparatus 10 can be provided with a register surface fixing the distance D. For example, the register surface can be provided by a flat sheet and the material 20 can be conveyed across it on a conveyor belt driven by drive rollers before and after the sheet. Or the register surface can be provided by one or more rollers that support the material directly, by a conveyor belt supporting the material 20, or by another surface know to those skilled in the art. In any event, the register surface is spaced the distance D from the ultrasonic transducer 16 (or positioned slightly more than the distance D from the ultrasonic transducer to account for the thickness of the material 20 and the conveyor belt). Embodiments without a register surface are typically used when the material is web-based, otherwise self-supporting, or tensioned by conventional tensioning mechanisms.
In addition, the apparatus can be provided with an adjustment mechanism for adjusting the distance between the ultrasonic transducer 16 and the material 20. The adjustment mechanism may be provided by conventional devices such rack and pinion gearing, screw gearing or the like. The adjustment mechanism may be designed to move the air-delivery enclosure 12, air-return enclosure 14, and ultrasonic transducer 16 assembly closer to the material, to move the material closer to the ultrasonic transducer, or both.
In order to consistently produce the precise decibel levels at the interface surface of the material 20, a method of manufacturing and/or installing the apparatus 10 is provided. The method includes calibrating the apparatus 10 for the desired decibel levels. First, the distance D is calculated based on the frequency of the selected ultrasonic transducer 16. For example, an ultrasonic transducer 16 with an operating frequency of 33,000 Hz has a wavelength of about 0.33 inches at a fixed temperature, so acceptable distances D include (0.33)(3/4) equals 0.25 inches and (0.33)(5/4) equals 0.41 inches, based on the formula D equals (λ)(n/4). Similarly, an ultrasonic transducer 16 with an operating frequency of 33 kHz has a wavelength of about 0.41 inches, so acceptable distances D include (0.41)(3/4) equals 0.31 inches and (0.41)(5/4) equals 0.51 inches.
Then the ultrasonic transducer 16 is positioned at the calculated distance D from the material 20 (or from the conveyor belt that will carry the material, or from the register surface). Next, a sound input device (e.g., a microphone) is placed at the material 20 (or at the conveyor belt that will carry the material, or at the register surface, or at the distance D from the ultrasonic transducer 16). The sound input device is connected to a signal conditioner. The sound input device and the signal conditioner are used to measure the air pressure wave (i.e., the acoustic oscillations 18) in psig and convert that to decibels (dB). For example, at a temperature of 120° F. and a flow rate of 35 ft/sec, a sound wave measured at 5 psig converts to 185 dB. Suitable microphones and signal conditioners are commercially available from Endevco Corporation (San Juan Capistrano, Calif.) and from Bruel & Kjer (Switzerland).
Once this baseline decibel level has been determined, the apparatus 10 can be adjusted for maximum effectiveness. For example, the adjustment mechanism can be adjusted to alter the preset distance D to see if the decibel level increases or decreases at the altered distance. If it decreases, then the preset distance D was accurate to produce the maximum amplitude A, and this distance is used. But if it increases, then the altered distance D is used as the new baseline and the distance is adjusted again. This fine-tuning process is repeated until the maximum amplitude A within the design ranged is found.
In addition, because the depicted embodiment includes a pneumatic-type ultrasonic transducer 16, it is operable to produce the desired decibel levels by adjusting the flow-rate of the steady-state inlet airflow 21. So if the baseline decibel level is not in the desired range, then the inlet airflow 21 rate can be adjusted (e.g., by increasing the speed of the fan or blower) until the decibel level is in the desired range. Exactly the same procedure can be applied to electrically powered ultrasonic transducers. Similar adjustments can be made with a signal amplifier, when electrically based ultrasonic transducers are used.
Table 1 shows test data demonstrating the resulting increased effectiveness of the apparatus 10. The test data in Table 1 was generated using the apparatus 10 of
The “Distance” is the distance D between the ultrasonic transducer 16 and the material 20, in inches. The “Δ Pressure” is the differential pressure drop in the air supply line in both experiments, measured in inches of water column, representing that the same amount of air was delivered through the acoustic dryer and non-acoustic dryer at the same temperature. The differential pressure of air corresponds to the amount of air supplied from the regenerative blower, it was the same in both cases, so the only difference between two series of experiments was ultrasound. Measurement of differential pressure in the air supply line is the most accurate and inexpensive method of measuring the quantity of air delivered by the blower. The “Temp.” is the temperature of the inlet steady-state air 21. The “Speed” is the speed of the conveyer (i.e., the speed of the material 20 passing under the ultrasonic transducer 16). The “Water Removal” is the amount of water removed by the apparatus 10, first when operated at an airflow rate so that the ultrasonic transducer 16 produces acoustic oscillations 18 at the interface surface of the material 20 of 169 dB and then of 175 dB. As can be seen, a noted improvement is provided by operating the apparatus 10 so that it produces 175 dB acoustic oscillations at the interface surface of the material 20 instead of 169 dB.
Furthermore, an electric heater 554 is embedded in or mounted to the delivery enclosure 512 for applying heat directly to the material instead of (or in addition to) pre-heating the air to be delivered to the material. So the function of the air forced through the ultrasonic transducer 516 is only being a carrier for the ultrasound. The electric heater 554 can be mounted to the outside bottom surface of the delivery enclosure 512 or it can be mounted within the enclosure to the inside bottom surface (provided that the bottom wall of the enclosure has a sufficiently high thermal conductivity). The heater 554 can be of a conventional electric type or another type known to those skilled in the art.
In addition, the heater 654 of this embodiment includes an inner heater element 654a and an outer heater element 654b mounted to the inside and outside surfaces of the bottom wall of the delivery enclosure 612 (see
In this embodiment, however, the ultrasonic transducers 716 are provided by electric-operated ultrasonic transducers. Such ultrasonic transducers are commercially available (with customizations for the desired decibel levels described herein) for example from Dukane Corporation (St. Charles, Ill.). The electric ultrasonic transducers 716 can be mounted to the exterior surface of the bottom wall 711 of the delivery enclosure 712 or positioned within openings in the bottom wall.
In addition, the ultrasonic transducers 716 and the air outlets 728 are arranged in an array on the delivery enclosure 712, preferably in a repeating alternating arrangement and also preferably in a staggered arrangement with a shift to avoid dead spots (e.g., with a 30-degree shift). The ultrasonic transducers 716 and the air outlets 728 may be circular, though they can be provided in other shapes such as rectangular, oval, or other regular or irregular shapes. In addition, the ultrasonic transducers 716 may have a diameter of about 2 inches, and the air outlets 728 may have a diameter of about 0.4 to 0.8 inches, though these can be provided in other larger or smaller sizes. Furthermore, the ultrasonic transducers 716 may be spaced apart at about 1 to 50 diameters, though larger or smaller spacings can be used. The number of ultrasonic transducers 716 and air outlets 728 are selected to provide the drying desired for a given application, and in typical commercial embodiments are provided in about equal numbers anywhere in the range of about 1 to about 100, depending on the physical properties of an individual transducer, that is, its physical size, the area of coverage, etc.
Having described numerous embodiments of the invention, it should be noted that the individual elements of the various embodiments described herein can be combined into other arrangements that form additional embodiments not expressly described herein. For example, such additional embodiments include modular versions of the various embodiments that can be combined in different arrangements depending on the particular application. As additional examples, the apparatus of
It is to be understood that this invention is not limited to the specific devices, methods, conditions, or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only. Thus, the terminology is intended to be broadly construed and is not intended to be limiting of the claimed invention. For example, as used in the specification including the appended claims, the singular forms “a,” “an,” and “the” include the plural, the term “or” means “and/or,” and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. In addition, any methods described herein are not intended to be limited to the sequence of steps described but can be carried out in other sequences, unless expressly stated otherwise herein.
While the invention has been shown and described in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention as defined by the following claims.
This application is a continuation of U.S. application Ser. No. 12/367,803, filed Feb. 9, 2009, which is hereby specifically incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12367803 | Feb 2009 | US |
| Child | 14698104 | US |
