Patent Application
20100018246
The invention relates to an internal heat exchanger assembly for an automotive air conditioning system; more particularly, to an internal heat exchanger assembly having an internal helical coil, in which the internal helical coil is maintained in a predetermined position by an internal baffle having radially extending fingers defining a double helix.
A typical automotive air conditioning system includes a compressor, a condenser, an expansion device, and an evaporator. Hydraulically connecting the aforementioned components in series are refrigerant tubes that are capable of conveying high and low pressure refrigerant flows. A two phase refrigerant used in a modern automotive air conditioning system is an environmentally friendly refrigerant known as R-134a and low Global Warming Potential (GWP) refrigerants such as HFO-1234yf.
The compressor is commonly referred to as the heart of the air conditioning system in which it is responsible for compressing and transferring the refrigerant throughout the system. The compressor includes a suction side and a discharge side. The suction side is referred to as the low pressure side and the discharge side is referred to as the high pressure side.
The evaporator is disposed in the passenger cabin of the automobile and the condenser is disposed in the front portion of the engine compartment or more precisely, in front of the radiator. Within the evaporator, cold low pressure liquid refrigerant boils by absorbing heat from the passenger compartment. The low pressure vapor refrigerant exiting from the evaporator is drawn and compressed by the compressor into a high temperature vapor refrigerant. The compressed high temperature vapor refrigerant is then discharged by the compressor to the condenser. As the high pressure vapor refrigerant passes through the condenser, the refrigerant is condensed to a high pressure lower temperature liquid refrigerant as it releases the heat it absorbed from the passenger cabin to the ambient air outside of the passenger cabin. Exiting the condenser, the high pressure liquid refrigerant passes through an expansion device that regulates the flow of the high pressure liquid refrigerant to the evaporator to repeat the process of heat transfer from the cabin to the outside ambient air.
The temperature of the returning low pressure vapor refrigerant to the compressor from the evaporator is typically 40° F. to 100° F. lower than the high pressure liquid refrigerant exiting the condenser. An internal heat exchanger, such as a double pipe counter-flow heat exchanger, is known to be used to take advantage of the temperature differential between the low pressure low temperature vapor refrigerant and the high pressure high temperature liquid refrigerant to improve the overall cooling capacity of the air conditioning system. The double pipe heat exchanger includes an outer pipe and an inner pipe co-axially located within the outer pipe. The diameter of the inner pipe is smaller than the diameter of the outer pipe, thereby defining an annular gap between the inner pipe and outer pipe for refrigerant flow. The relatively cooler low pressure vapor refrigerant exiting the evaporator is passed through the annular gap and the relatively hotter liquid refrigerant exiting the condenser is passed through the inner pipe. Heat is transferred from the high pressure liquid refrigerant exiting the condenser to the cooler low pressure vapor refrigerant returning to the compressor in the internal heat exchanger. By decreasing the temperature of the high pressure liquid refrigerant prior to its flowing through the expansion device, the expansion device may be set at a lower temperature; therefore the temperature of the refrigerant entering the evaporator is at a lower temperature. A SAE International Publication No. 2007-01-1523 has shown that an internal heat exchanger such as the one described above can increase the amount of internal heat exchange from 390 W to 550 W; thereby improving the cooling performance of the air conditioning system.
The internal heat exchanger describe above has its disadvantages. The installation of such a heat exchanger into an engine compartment is difficult due to the limited amount of space within an engine compartment. Furthermore, such a double pipe heat exchanger is also known for low heat transfer efficiency and high pressure drop. It is therefore desirable to have an internal heat exchanger that is compact, but with a high heat transfer effectiveness and low pressure drop. It is further desirable to have a compact internal heat exchanger that is robust during normal operating conditions. It is still further desirable to have a compact internal heat exchanger that is cost effective to manufacture.
The present invention relates to an internal heat exchanger assembly for an air conditioning system. The internal heat exchanger includes a housing having a first end, a second end axially opposed to the first end, and an interior surface therebetween defining a substantially cylindrical cavity. A helical coiled tube is disposed about the axis within the cylindrical cavity. The helical coiled tube includes first and second tube ends extending in opposing directions substantially parallel to the axis beyond the first and second ends of the housing. The helical coiled tube further includes a plurality of adjacent coils having a predetermined coil pitch.
Coaxially disposed within the substantially cylindrical cavity is an elongated twisted strip extending from the first end to the second end. The elongated strip includes opposed edges defining, when twisted from its initial flat state, a double helix. A plurality of spaced fingers extends radially from the edges. The fingers are sized to fit closely between the coils, thereby inhibiting lateral movement of coils.
Sealing the ends of the substantially cylindrical cavity is a first end cap and a second end cap. Each end cap includes a first port in hydraulic communication with the cylindrical cavity and a tube coupling adapted to support a tube end.
The helical coiled tube includes a basic tube outer diameter (Dtube) and a helical coil outer diameter (Dcoil). Helical coil outer diameter (Dcoil) is sized to fit substantially within the diameter of the substantially cylindrical cavity (Dcavity) with an annular gap between the outer coil diameter (Dcoil) and cavity diameter (Dcavity). The annular gap is sized to provide a substantially unobstructed pathway for refrigerant flow through the cylindrical cavity; thereby, improving the overall heat transfer in several ways and decreasing the pressure drop significantly. The extending fingers of the elongated twisted strip maintain the annular gap of the helical coiled tube within the cylindrical cavity.
The invention provides an internal heat exchanger that is compact, with a high heat transfer effectiveness and low pressure drop. The invention further provides a compact internal heat exchanger that is robust during normal operating conditions and cost effective to manufacture. The decrease in pressure drop of the refrigerant in the internal heat exchanger increases cooling capacity of the overall air conditioning system.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of an embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.
This invention will be further described with reference to the accompanying drawings in which:
In accordance with a preferred embodiment of this invention, referring to
Shown in
Internal heat exchanger assembly 100 is disposed in the air conditioning system 10 between discharge side of evaporator 18 and discharge side of condenser 14 prior to expansion device 16. The flow of low pressure vapor refrigerant from evaporator 18 is counter-current to the flow of high pressure liquid refrigerant from condenser 14 through internal heat exchanger assembly 100. An alternative embodiment (not shown) is that the flow of low pressure vapor refrigerant is co-current with the flow of high pressure vapor refrigerant. The relatively lower temperature low pressure vapor refrigerant exiting the evaporator 18 is used to pre-cool the relatively higher temperature high pressure liquid refrigerant exiting the condenser 14 prior to expansion device 16. The temperature of the returning low pressure vapor refrigerant to compressor 14 from evaporator 18 is typically 40° F. to 100° F. lower than the high pressure liquid refrigerant exiting condenser 14.
Shown in
Housing 102 includes exterior surface 104, first end 134 and axially opposed second end 136 and central axis A. Interior surface 106 defines a substantially cylindrical cavity 130 disposed about Axis A. Best shown in
Referring to
Referring back to
Referring back to
Each baffle edge 148, 150 includes a plurality of fingers 152 extending perpendicularly from its respective baffle edge 148, 150 and radially away from Axis A, taking on the same double helix as the twisted edges 148 and 150. Each finger 152 includes a distal end 151 and a center portion 154 bounded by a first side 156 and an opposite second side 158. First side 156 of finger 152 faces the second side 158 of its immediate adjacent finger 152 to define slot 160 therebetween. The length of each finger 152 is sufficient for distal end 151 to abut interior surface 106 of housing 102 to co-axially align and support twisted elongated baffle 146 along Axis A. Each slot 160 is adapted to accept a portion of a coil 109, in which the sides 156, 158 of adjacent fingers cooperate with a portion of edge 148, 150 located between fingers 152 to secure helical coiled tube 108 in a predetermined position within cylindrical cavity 130 and maintain annular gap distance (GAPdistance) between distal ends 140, 142 of coils 109 and interior surface 106 of the housing. Radially extending fingers 152 allow internal heat exchanger 100 to be bent into an arch or semi-circular shape (not shown) for packaging requirements without damaging or dislocating helical coiled tube 108 from its predetermined position.
Elongated ribs (not shown) may be formed onto a portion of the interior surface 106 of internal heat exchanger assembly 100. The elongated ribs may extend substantially parallel to the A-axis or spiraled about the A-axis. Each rib includes a distal surface spaced apart from interior surface 106, in which the distal surface abuts helical coiled tube 108. The elongated ribs assist in securing helical coiled tube 108 in the predetermined position to maintain the desired annular gap distance (GAPdistance).
Sealing first and second ends of cylindrical cavity 130 are first and second end caps 114, 116, respectively. Each of first and second end caps 114, 116 includes a port 118, 120 in hydraulic communication with cylindrical cavity 130, and a tube coupling 124, 126. Each of tube coupling 124, 126 is adapted to support respective tube ends 110, 112 of helical coiled tube 108. An alternative embodiment, not shown, is that one of end caps 114, 116 is formed integrally with corresponding tube end 110, 112.
The relatively cooler low pressure gas refrigerant from evaporator 18 is introduced into cylindrical cavity 130 through one of ports 118, 120. The relatively hotter high pressure liquid refrigerant discharge from condenser 14 is introduced into helical coiled tube 108 via one of tube ends 110, 112. Heat is transferred from the high pressure liquid refrigerant in helical coiled tube 108 to the low pressure vapor refrigerant in cylindrical cavity 130 via conduction by counter-current or con-current refrigerant flow.
Best shown in
Internal heat exchanger assembly 100 may be manufactured by any method known to those skilled in the art. Housing 102 and one of end caps 114, 116 may be molded or fabricated as one integral unit. The other remaining end cap 114, 116 may be manufactured as a separate piece. Helical coil tube 108 may be attached to elongated baffle 146 by continually twisting successive adjacent coils 109 onto radially extending fingers 152 of elongated baffle 146 until helical coil tube 108 is completely assembled onto elongated baffle 146. The assembly of elongated baffle 146 and helical coil tube 108 is then joined by brazing or other known means before the assembly is inserted into cylindrical cavity 130. Once the assembly is inserted and properly located within the cylindrical cavity 130, the other remaining end cap 114, 116 is fitted onto the respective end 134, 136 to seal cylindrical cavity 130. If the components of internal heat exchanger assembly 100 are amenable to brazing, the individual components may be assembled as a whole and brazed to from one integrated unit.
Those skilled in the art would recognize that the rate of heat transfer effectiveness of heat from a fluid within a tube to the ambient fluid outside of the tube is directly proportional to the velocity of the ambient fluid flow over the surface of the tube; the greater the velocity, the greater the heat transfer effectiveness. An example would be a fan inducing an air stream over the tubes of a radiator of an automobile to increase the heat transfer effectiveness of the radiator. Internal heat exchanger assembly 100 described herein above provides increased heat transfer effectiveness with decreased velocity of refrigerant over the surface area of the helical coil. Decreased refrigerant velocity results in the decrease of pressure drop through internal heat exchanger 100, thereby increasing the cooling capacity of the overall air conditioning system, which will be discussed in detail below.
Presented in
As shown in FIGS. 5(B)-(D), the change in tube outer diameter (Dtube), the annular gap distance (GAPdistance), and coil pitch (Coilpitch) also affect heat transfer effectiveness, but have minimal effect on refrigerant velocity. For improved heat transfer effectiveness and decreased pressure drop across internal heat exchanger 100 for an automotive air conditioning system, the cavity Diameter (Dcavity) ranges between 25 to 45 mm, preferably 32 mm to 38 mm; the basic tube diameter (Dtube) ranges between 6 mm to 10 mm, preferably 7 mm to 9 mm; the coil pitch (Coilpitch) ranges between 2 mm to 8 mm, preferably 4 mm to 6 mm; and the annular gap distance (GAPdistance) ranges between 0.5 to 3 mm, preferably 1 mm to 2 mm.
As shown in
An advantage of the internal heat exchanger disclosed herein is that it provides maximum heat transfer effectiveness within the internal heat exchanger and increased heat transfer capacity of the air conditioning system. Another advantage is that internal twisted baffle's radially extending fingers maintain the lateral and radial positions of the internal helical coiled tube within the housing, thereby ensuring maximum performance and minimizing vibrations during normal operating conditions. Still another advantage is that the contact of the distal ends of the radial fingers with the inner surface of the cylindrical inner surface increases the structural rigidity of the internal heat exchanger. Yet another advantage is that the internal heat exchanger is manufactured of standard materials that are easily assembled and brazed, or interference fitted together. Another advantage is that the internal twisted baffle's radially extending fingers allow the internal heat exchanger 100 to be bent into an arch shape without damaging or dislocating the helical coiled tube from its predetermined position.
While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.
| Number | Date | Country | |
|---|---|---|---|
| 61135825 | Jul 2008 | US |
