Patent Application
20140352913
The subject matter disclosed herein relates to refrigeration units and, in particular, to refrigeration units in an aircraft.
Typical commercial aircraft include one or more cooling systems configured to provide temperature control to various regions of the aircraft. The aircraft cooling system(s) can include one or more vapor cycle refrigeration units. This type of refrigeration unit, in addition to other components, generally includes an evaporator in which a refrigerant absorbs heat from a fluid flow, e.g., air, in order to cool the flow. The cooled flow can be used to regulate the temperature of a designated area of the aircraft. The industry would appreciate increases to the lifespan and efficiency of refrigeration units.
According to one embodiment, a refrigeration unit for an aircraft is disclosed. The refrigeration unit includes an evaporator receptive of an airflow and a refrigerant and operatively arranged to transfer heat from the airflow to the refrigerant in order to evaporate at least some of the refrigerant and cool the airflow as the airflow travels from an inlet at an inlet side of the evaporator to an outlet at an outlet side of the evaporator and the refrigerant travels from an input of the evaporator to an output of the evaporator, the outlet being in fluid communication with a compartment of the aircraft; a heater positioned at the inlet side of the evaporator that heats the airflow before the airflow passes through the outlet of the evaporator; a compressor that receives the refrigerant from the output of the evaporator and pressurizes the refrigerant; and a condenser that receives the refrigerant from the compressor and condenses the refrigerant to liquid phase.
According to another embodiment, a method of regulating a temperature of a compartment of an aircraft is disclosed. The method includes directing an airflow through an evaporator of a refrigeration unit; directing a refrigerant through the evaporator; heating the airflow with a heater positioned at the inlet side of the evaporator; transferring heat from the airflow to the refrigerant in order to evaporate at least some of the refrigerant and cool the airflow as the airflow travels from an inlet at an inlet side of the evaporator to an outlet at an outlet side of the evaporator and the refrigerant travels from an input of the evaporator to an output of the evaporator; directing the airflow into the compartment of the aircraft for regulating a temperature of the compartment; directing the refrigerant from the output of the evaporator to a compressor and compressing the refrigerant with the compressor; directing the refrigerant from the compressor to a condenser and condensing at least some of the refrigerant; and directing the refrigerant from the condenser to the input of the evaporator.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
As discussed above, there are existing refrigeration units that work suitably for their intended purposes. One possible obstacle faced by some of these refrigeration units, however, is the formation of ice within the evaporator, particularly when the cooled flow contains a relatively high moisture content that condenses and freezes on fins or other surfaces of the evaporator. For example, the fluid flow may be a flow of air recycled from a passenger cabin of the aircraft that is relatively moisture-rich due to normal respiratory functions of passengers in the cabin. The formation of ice may lead to problems in the operation of the refrigeration unit, including inefficient operation and shortened life.
One or more of the embodiments disclosed herein may solve one or more of the above noted or other issues. Embodiments that are described in greater detail below may improve the efficiency and lifespan of an aircraft refrigeration unit by balancing heat loading within the refrigeration unit. More particularly, the embodiments disclosed herein may quickly and efficiently eliminate and/or avoid the formation of ice within heat exchangers, namely evaporators, of the refrigeration units. Formation of ice within evaporators of current refrigeration units can lead to inefficiency or failure of the refrigeration unit or components thereof, and action is typically taken upon detection of ice or conditions that indicate that ice may be present. De-icing activities typically include operating the compressor(s) of the system at low speeds, and/or shutting off the compressor(s) completely, particularly if the ice persists even after first reducing the operating speed of the compressor(s). The life of typical compressors is limited by the number of pressure cycles the compressors must undergo. Operating the compressors at constant speeds helps to reduce pressure cycling, thereby enhancing the lifespan of the compressors, while changing speeds and turning the compressor off-and-on may cause the compressors to experience potentially damaging pressure cycles. Another issue that may be faced by known refrigeration units is that more than one compressor is typically used by each refrigeration unit, and one of the compressors generally outperforms the other(s) when run at restricted speeds. This results in the outperforming compressor “robbing” needed oil (e.g., carried with the refrigerant being compressed) from the other compressor(s), further reducing the life and effectiveness of the units.
In one embodiment, the system 106 includes a refrigeration unit 108, illustrated in more detail in
In one embodiment, the control unit 110 is a computerized device that includes any combination of a processor, logic unit, memory, etc., as needed to interpret inputted or received signals, e.g., user inputted or measured by a sensor in signal communication with the control unit 110. By signal communication it is meant that data, information, or instructions can be conveyed via electrical current or other electronic signals between the components. The signals can be used by the unit 110 to control the operation of valves, motors, and other components of the system 106 in response to inputted or received signals. In this way, the control unit 110 can automatically control the system 106 to maintain user inputted or preprogrammed conditions, e.g., temperatures, within corresponding areas of the aircraft 100, e.g., the cargo compartment 104.
In the illustrated embodiment, the refrigeration unit 108 includes a refrigeration loop or cycle 112 comprising lines, pipes, tubing, or conduits suitable for carrying a fluid refrigerant. The refrigerant can be any suitable refrigerant known in the art, and in one embodiment takes the form of R-134a. The refrigerant is used to exchange heat with a fluid in order to regulate the temperature of an area of the aircraft 100, such as the cargo compartment 104. More particularly, the refrigerant is arranged to absorb heat from an airflow 114 when both are directed through a heat exchanger in the form of an evaporator 116. The absorbed heat may be used to evaporate at least some of the refrigerant. The absorbed heat cools the airflow 114 and promotes evaporation of the refrigerant. The evaporator 116 includes an inlet 118 at an inlet side 120 and an outlet 122 at an outlet side 124 for the airflow 114 and an input 123 and an output 125 for the refrigerant to pass through the evaporator 116 while being directed through the cycle 112. As noted above, due to heat exchange within the evaporator 116, the refrigerant is at least partially converted to its gaseous phase when passing from the input 123 to the output 125. In one embodiment, the inlet 118 is in fluid communication with the cabin 102, i.e., the airflow 114 is, or includes, recycled cabin air, and the outlet 122 is in fluid communication with the cargo compartment 104 for enabling the temperature of the cargo compartment 104 to be regulated by cooling the air 114.
In addition to the evaporator 116, the unit 108 generally includes one or more compressors 126 which pressurize and heat the refrigerant, and pump the refrigerant to a condenser 128. The condenser 128 rejects heat from the compressed refrigerant to convert the refrigerant back into liquid phase. Cooling of the refrigerant in the condenser 128 can be accomplished by a coolant flow 130 as shown in
Moisture within the airflow 114, e.g., introduced due to the breathing of passengers within the cabin 102, may condense and freeze within the evaporator 116 under some circumstances. In one embodiment, ice is detected by monitoring delta temperature and/or delta pressure between the inlet and outlet sides 120 and 124 of the evaporator 116, e.g., via sensors 136a and 136b, respectively. In one embodiment ice is detected by monitoring the refrigerant in the cycle 112, e.g., via sensors 136c and/or 136d located at the inlet and outlet sides of the compressor 118, respectively. For example, it could be detected by the sensor 136c that the refrigerant is not fully converting to gaseous phase, thereby indicating inefficiency within the evaporator due to the formation of ice. The sensors 136a, 136b, 136c, and 136d (collectively “the sensors 136”) may also or alternatively be arranged to detect other parameters of the air 114 and/or the refrigerant of the cycle 112.
Some embodiments herein may take advantage of the discovery that heating the already relatively hot air at the inlet side 120 of the evaporator can promote a longer lifespan, particularly with respect to the compressors 126, and increased overall efficiency of the unit 108. That is, for example, the refrigeration unit 108 includes a heater 138 positioned at the inlet side 120 for heating the airflow 114 before or as it enters the evaporator 116 and/or transfers heat with the refrigerant in the cycle 112. By positioned at the inlet side 120, it is meant that the heater 138 is upstream of the evaporator 116 with respect to the direction of the airflow 114. In this way, instead of shutting down the unit 108, or reducing the operating speed of the compressors 126, as would be performed to de-ice previous refrigeration units, the heater 138 can instead be controlled for balancing the heat load in the refrigerant of the cycle 112 as well as in the airflow 114 downstream of the evaporator 116. In one embodiment, the heater 138 is an electric resistance heater. Electric heaters make heat nearly instantaneously available for use. In one embodiment, the heater 138 operates in the range of about 1 kW to 5 kW, although other ranges may be utilized.
The heater 138 can be arranged to turn on and/or off at preset or predetermined intervals, on demand, or automatically in response to detected conditions or parameters. In one embodiment, the heater 138 is in signal communication with the control unit 110, and the control unit 110 controls operation of the heater 138, e.g., when the heater 138 is turned on and off and for how long, the power delivered to the heater 138, etc. In a further embodiment, the control unit 110 is in signal communication with one or more sensors, e.g., any combination of the sensors 136, and the measurements made by the sensors 136 are used by the control unit 110 to determine when to turn the heater 138 on and off. For example, in one embodiment, the sensors 136a and 136b are used to detect the temperature of the air 114 and the heater 138 is automatically turned on when the temperature at the outlet side 124 of the evaporator 116 reaches or approaches the freezing point of water. In a further embodiment, the control unit 110 also takes into account the altitude of the aircraft 100 and compares the measured temperature to the freezing temperature of water at the current altitude of the aircraft. For example, in one embodiment, the threshold temperature at which the heater 138 is turned on, e.g., as measured by the sensor 136a, is about 35° F. (2° C.) at sea level and about 25° F. (−4° C.) at about 25,000 feet (7,620 m). In general, the heater 138 can be arranged to turn on any time the control unit identifies the formation of ice or conditions that indicate the possible or likely formation of ice.
The heater 138 can also be triggered in order to control the temperature of the airflow 114 downstream of the evaporator 116. For example, sensors could be positioned within the cargo compartment 104 and/or along the outlet 132 and the heater 138 triggered in order to more accurately regulate the temperature of the cargo compartment 104, e.g., in case the refrigeration unit 104 has overly cooled the area 104, it is desired to heat the area 104, or a new temperature for the area 104 becomes desired. Additionally, the heater 138 could be turned on in order to balance the heat load in the cycle 112 by maintaining the refrigerant at a desired or consistent temperature as the refrigerant exits the evaporator 114. In this way, relevant properties of the refrigerant can be affected by the heater 138 to enable the compressors 126 to more effectively or efficiently operate, e.g., to run at a constant speed. For example, the heater 138 can be arranged to heat the refrigerant or more completely evaporate the refrigerant into gaseous phase, e.g., in response to parameters or conditions detected by the sensor 136c, such that the refrigerant is optimized for the compressors 126. Of course, other threshold temperatures and/or threshold values for other parameters or properties than those stated could be used in other embodiments.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
