Abstract:
A refrigeration unit and a method of regulating a temperature of a compartment of an aircraft is described. 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 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. The outlet is in fluid communication with a compartment of the aircraft. A heater is positioned at the inlet side of the evaporator and heats the airflow before the airflow passes through the outlet of the evaporator. A compressor receives the refrigerant from the output of the evaporator and pressurizes the refrigerant. A condenser receives the refrigerant from the compressor and condenses the refrigerant to liquid phase.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to refrigeration units and, in particular, to refrigeration units in an aircraft. 
         [0002]    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. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    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. 
         [0004]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    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: 
           [0006]      FIG. 1  is a block diagram schematically illustrating an aircraft having a refrigeration unit; and 
           [0007]      FIG. 2  is a block diagram illustrating the refrigeration unit of  FIG. 1  according to one embodiment disclosed herein. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]    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. 
         [0009]    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. 
         [0010]      FIG. 1  schematically illustrates an aircraft  100  having a passenger compartment or cabin  102  and a cargo compartment  104 . A thermal management system  106  is depicted schematically, and can be arranged to interface with the cabin  102 , cargo compartment  104 , ambient outside air, other thermal management or environmental control systems, etc., in order to assist in the regulation of the climate, e.g., temperature and pressure, within the aircraft  100 . 
         [0011]    In one embodiment, the system  106  includes a refrigeration unit  108 , illustrated in more detail in  FIG. 2 , and a control unit  110  for controlling operation of the system  106  and the refrigeration unit  108 . As will be better appreciated in view of the following discussion, the refrigeration unit  108  is arranged to control the temperature of a flow of fluid, namely, air, within the aircraft  100 . In one embodiment, the refrigeration unit  108  takes in a flow of air recycled from the cabin  102 , cools the flow of air as it travels through a heat exchanger of the refrigeration unit  108 , and utilizes the cooled flow of air to control the temperature of the cargo compartment  104 . In one embodiment, the cargo compartment  104  is arranged to hold live animals, perishable goods, or other contents that benefit from a temperature controlled environment. The air recycled from the cabin  102  may be mixed with air from other sources, or otherwise pre-processed or conditioned before being delivered to the refrigeration unit  108 . 
         [0012]    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 . 
         [0013]    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 . 
         [0014]    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  FIG. 2 . In one embodiment, the coolant flow  130  is part of another refrigeration unit, temperature management system, or environmental control system utilized by the aircraft  100 , e.g., for maintaining the temperature of another area of the aircraft  100 . The refrigerant from the condenser  128  is transferred via the cycle  112  to an expansion tank  132 , where relatively cooled liquid refrigerant can be delivered to the evaporator  116  via a metering device or valve  134  and flash steam is recycled back to the compressors  126 . The control unit  110  can be used to control operation of the compressors  126  (e.g., speed of a motor driving the compressor  118 ), the valve  134  (e.g., flow rate of refrigerant through the valve  134  to the evaporator  116 , and thus, cooling capability for the airflow  114 ), etc. Additional or alternate valves, e.g., valves  131 , devices, e.g., one or more motors  133  for the compressors  126 , or other components, e.g., a filter/dryer  135 , can be connected along the cycle  112  or with the unit  108  as desired for facilitating or affecting the operation of the unit  108 . One of ordinary skill in the art will recognize similarity between various components of the unit  108  and those of other vapor cycle refrigeration units known generally in the art, so further description of the general arrangement of these components is not necessary. 
         [0015]    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  136   a  and  136   b , respectively. In one embodiment ice is detected by monitoring the refrigerant in the cycle  112 , e.g., via sensors  136   c  and/or  136   d  located at the inlet and outlet sides of the compressor  118 , respectively. For example, it could be detected by the sensor  136   c  that the refrigerant is not fully converting to gaseous phase, thereby indicating inefficiency within the evaporator due to the formation of ice. The sensors  136   a ,  136   b ,  136   c , and  136   d  (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 . 
         [0016]    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. 
         [0017]    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  136   a  and  136   b  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  136   a , 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. 
         [0018]    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  136   c , 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. 
         [0019]    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.