Liquid-Gas separator in Condenser for performance enhancement
1. Field of invention
This invention relates to the design method and system of a
micro channel and multi flow with or without integrated receiver drier condensers for air conditioning applications in general and specifically suited for the vehicular applications.
2. Prior art
Refrigeration systems utilize the thermal cycle to condition a secondary
fluid which in turn extracts heat from the primary refrigerant such as air which is further delivered to a climate controlled space. In a basic refrigerant system, the refrigerant is compressed in a compressor, and flows downstream to a heat exchanger (a condenser for sub critical applications and a gas cooler for transcritical applications), where heat is typically rejected from the refrigerant to ambient environment during heat transfer interaction with this ambient environment. Then refrigerant flows through an expansion device, where it is expanded isenthalpically to a lower pressure and temperature, and to an evaporator, where during heat transfer interaction with another secondary fluid (e.g., indoor air), the refrigerant is evaporated and typically superheated, while cooling and often dehumidifying this secondary fluid. Automotive refrigeration systems of the type having a thermostatic expansion valve may benefit from having a receiver fitted into the system between as it provides a space for storing refrigerant volume which is sufficient to accommodate for variations in system operating conditions and loss of refrigerant due to diffusion and small leaks.
In recent years, much interest and design effort has been focused on the efficient operation of the heat exchangers (e.g., condensers, gas coolers and evaporators) in the refrigerant systems. Recent advancement in the heat exchanger technology is the development and application of parallel flow, or so-called micro channel or mini channel, heat exchangers, as the condensers and evaporators. These heat exchangers are provided with a plurality of parallel heat transfer tubes among which refrigerant is distributed and flown in a parallel manner. The heat transfer tubes are orientated generally substantially perpendicular to a refrigerant flow direction in the inlet and outlet manifolds that are in flow communication with the heat transfer tubes. The primary reasons for the employment of the parallel flow heat exchangers, which usually have aluminum furnace-brazed construction, are related to their superior performance, high degree of compactness, structural rigidity and enhanced resistance to corrosion. In many cases, these heat exchangers are designed for a multi-pass configuration, typically with a plurality

of parallel heat transfer tubes within each refrigerant pass, in order to obtain a superior performance by balancing and optimizing heat transfer and pressure drop characteristics. In such designs, the refrigerant that enters an inlet manifold (or so called inlet header) travels through a first multi-tube pass across a width of the heat exchanger to an opposed, typically intermediate, manifold. The refrigerant collected in a first intermediate manifold reverses its direction, is distributed among the heat transfer tubes in the second pass and flows to a second intermediate manifold. This flow pattern can be repeated for a number of times, to achieve optimum heat exchanger performance, until the refrigerant reaches an outlet manifold (or so-called outlet header). Obviously, in a single pass configuration, the refrigerant travels only once across the heat exchanger core from the inlet manifold to the outlet manifold. Typically, the individual manifolds are of a cylindrical shape (although other shapes are also known in the art) and are represented by different chambers separated by partitions within the same manifold construction assembly. Corrugated and typically louvered fins are placed between the heat transfer tubes for outside heat transfer enhancement and construction rigidity. These fins are typically attached to the heat transfer tubes during a furnace braze operation. Furthermore, each heat transfer tube preferably contains a plurality of relatively small parallel channels for in-tube heat transfer augmentation and structural rigidity. The heat exchanger core includes an header plate connecting along the axis to the receiver dryer to direct the refrigerant through the core, with the tubes spaced along the header and having ends received there in to direct refrigerant to and from the header and at least separator in the header to separate the header into a first condensation portion that receives refrigerant from 1st set of tubes and a second condensation portion that directs the refrigerant to 2nd set of tubes and so on as per condenser design. The receiver housing is mounted to the core with one end connecting to the header plate and other end to the outlet of refrigerant. Integration of a multi-pass condenser with receiver dryer is used in the air conditioning system of motor vehicles because such integration can provide a compact construction and can minimize numbers of joints. In this type of integration receiver dryer is located down stream of all passes of the condenser. While known integrated condenser/receivers may perform well for their desired applications, there is always room for improvement.
3. Disadvantages of the prior art
The limitations and easily visible disadvantages of the prior art are:-
(A) It can not be ensured that only liquid will pass from condenser to the evaporator through TXV valve. There always remains a possibility of gaseous refrigerant leaking into the evaporator and thus hampering the overall performance.
(B) In the prior art, the openings to receive the multi channel tubes are formed in a manifold
wall by punching the wall inwardly. The heat transfer tubes are inserted into these
openings, but do not extend much further into the manifold past the ends of the punched
material, since it would create additional impedance for the refrigerant flow within the
manifold
(C) Automotive refrigeration systems operating with a receiver and a proper refrigerant
charge level such as to maintain the gas/liquid interface within the volume enclosed by
such receiver under applicable operating conditions may achieve a higher performance
levels with the given system components by employing a separate sub cooler arranged
between the receiver and the thermostatic expansion valve. However, known systems
employing sub coolers have the disadvantages of added cost, complexity, and a greater
possibility of refrigerant leaks
(D) Since the heat transfer tube edges are located at approximately the same positions as
the ends of the punched material of the manifold openings, brazing material has a high
potential of flowing into some of the channels during the brazing process and blocking
these channels. This is, of course, undesirable and should be avoided, since at least
partially blocked heat transfer tubes are not utilized to their full heat transfer potential.
(E) To achieve satisfactory results condenser receiver must be arranged downstream of the
point at which condensation of the refrigerant occurs, have an internal configuration
including sufficient volume and/or internal centrifuge or baffling to permit separation of the
gaseous and liquid phases of the refrigerant, have a liquid outlet arranged to
communicate with liquid below the gas/liquid interface, and the refrigeration system be
charged with a quantity of refrigerant such that the gas/liquid interface occurs within the
volume enclosed by such receiver under applicable operating conditions. Thus, receiver
design itself poses challenging and often unpredictable parameters which are very hard
to monitor and may result in system performance deterioration.
(F) Interface would normally not be horizontal or wholly continuous under driving conditions,
due to vertical and horizontal acceleration forces to which condenser would be
continuously exposed. Hence, the sub cooling change is imminent and this can hamper
the performance.
(G) The heat transfer tubes are inserted into tank header openings, but do not extend much further into the manifold past the ends of the punched material, since it would create additional impedance for the refrigerant flow within the manifold, promote refrigerant maldistribution and degrade heat exchanger performance
(H) Since the heat transfer tube edges are located at approximately the same positions as the ends of the punched material of the manifold openings, brazing material has a high potential of flowing into some of the channels during the brazing process and blocking these channels and so an additional hydraulic resistance on the refrigerant side is offered and promote refrigerant maldistribution conditions. All these factors negatively impact heat exchanger performance.
(I) For a receiver to be effective, it must be arranged downstream of the point at which condensation of the refrigerant occurs, have an internal configuration including sufficient volume and/or internal centrifuge or baffling to permit separation of the gaseous and liquid phases of the refrigerant, have a liquid outlet arranged to communicate with liquid below the gas/liquid interface, and the refrigeration system be charged with a quantity of refrigerant such that the gas/liquid interface occurs within the volume enclosed by such receiver under applicable operating conditions.
(J) Where an automotive refrigeration system is provided with a receiver and the refrigerant charge level of the system does not overfill the receiver under applicable operating conditions, a conventional condenser provides essentially zero refrigerants sub cooling. Thus there exists an opportunity for improving the condenser in this aspect.
In the event that overfilling of the receiver occurs, a conventional condenser may provide a level of sub cooling that varies directly with the amount of refrigerant overfill and system operating conditions, but it is desirable to substantially avoid such sub cooling in that it decreases the volume within the condenser available for condensing of refrigerant resulting in higher condenser pressures and lower system performance. Thus, there is a need to design a condenser where sub cooling should happen without decreasing the heat transfer area and thus increasing the high side pressure.
4. Objective of present invention
The present invention is directed towards a condenser particularly adapted for use in an automotive refrigeration system of the type having a thermostatic expansion valve. The preferred embodiment of automotive condenser design as per the teaching disclosed in the present invention where in a tubular element is inserted into the outlet tank header so that the refrigerant from tube outlet has to pass through with at least one horizontally extending member and thus as a result placing the lower volume in flow communication with the outlet and thus goes to complete the refrigeration cycle while the upper volume of refrigerant gas gets trapped and ultimately looses it's enthalpy with time to condense and thus ensuring that only liquid refrigerant is passed through the cycle and thus ensuring the performance enhancement.
5. BRIEF DESCRIPTION OF THE DRAWINGS
The nature and mode of operation of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein:
FIG. 1 is a diagrammatic view of a conventional automotive refrigeration system;
FIG. 2 is a view of a refrigeration cycle using the sub cool device separately
FIG. 3 is a diagrammatic view of a conventional automotive refrigeration system tank header design
FIG. 4 is a view of tank design embodiment of the present invention
6. Summary of invention
Reference is first made to FIG. 1, wherein a conventional automotive refrigeration system is displayed and illustrated which comprise of a serially connected condenser 1; receiver 2; thermostatic expansion valve 3; evaporator 4; and compressor 5. Compressor 5 serves to circulate refrigerant through the system, whereby high pressure gaseous refrigerant is supplied by the compressor to condenser 1 via conduit; the condenser dissipates heat from the gaseous refrigerant and supplies receiver 2 with liquid or liquid/cool gaseous refrigerant via a conduit; the receiver defines a liquid/gas interface and supplies valve 3 with liquid refrigerant via a conduit, the valve reduces pressure of the liquid refrigerant and supplies a liquid/gas mixture at a lower pressure and lower temperature to evaporator 4 via a conduit; and the evaporator absorbs
heat from a space/fluid to be cooled and supplies low temperature/pressure gaseous refrigerant to the compressor via a conduit. In a typical system, receiver 2 may include a removable cartridge having a suitable filter and a desiccant for removing water from the refrigerant, and is provided with an internal configuration, e.g. volume and/or suitable liquid/gas separating device, such as a centrifugal or baffled separator, to ensure separation of liquid and gas phases of the refrigerant in order to provide a well defined liquid/gas interface. Receiver also normally serves to prevent the backup of liquid refrigerant into condenser which when of standard design would have its operation adversely affected, and to provide a reservoir of liquid refrigerant sufficient to accommodate for loss of refrigerant due to diffusion or small leaks.
FIG. 2 illustrates a typical air conditioning cycle using sub cooler sub systems which ensure complete condensation and thereof sub cooling in condenser but they are quite expensive and complex devices requiring regular frequent maintenance either due to charge leakage or due to any other operational problem.
Figure 3 shows the conventional tank header design wherein the last pass (sub cool pass in case of integral receiver drier condenser) is meant for sub cool. The refrigerant from the last tubes (sub cool) get accumulated in the outlet tank header from where it goes to expansion device after passing through the receiver. But in some cases it may happen that the some gaseous portion of the refrigerant also gets escaped into the receiver from where it being lighter goes to the evaporating section through the expansion valve and thus decreasing the desired output and de graded performance.
Some designers and those expert in the art may know the commonly used strategy to crack this problem by increasing the internal cross-sectional area of outlet header so that it is sufficiently large to permit refrigerant gas to substantially separate from liquid refrigerant produced from refrigerant gas passing through last pass tubes whereby to define an upper volume containing mostly gas and a lower volume containing mostly liquid, which are divided by an interface. But the problem may still hound as Interface would normally not be horizontal or wholly continuous under driving conditions, due to vertical and horizontal acceleration forces to which condenser would be continuously exposed.
It is sufficient for the practice of the present invention that chamber of outlet header be internally sized to ensure that the velocity of fluid passing there through is reduced to a point at which the gas phase can separate from the liquid phase under the influence of gravity and not be swept along with the liquid phase exiting through outlet whereby to achieve and maintain substantial separation between the gas and liquid phases of the refrigerant within the second header during normal use conditions and that outlet be connected into a lowermost region of volume. Flow of refrigerant through tubes below interface is not adversely affected by this design concept.
Figure 4 shows the preferred embodiment as per the teaching disclosed in the present invention where in a tubular element is inserted into the outlet tank header so that the refrigerant from tube outlet has to pass through with at least one horizontally extending member and thus as a result placing the lower volume in flow communication with the outlet and thus goes to complete the refrigeration cycle while the upper volume of refrigerant gas gets trapped and ultimately looses it's enthalpy with time to condense and thus ensuring that only liquid refrigerant is passed through the cycle and thus ensuring the performance enhancement.
Additionally, if the internal cross-sectional area of outlet header is made sufficiently large to permit refrigerant gas to substantially separate from liquid refrigerant produced from refrigerant gas passing through last pass tubes whereby to define an upper volume containing mostly gas and a lower volume containing mostly liquid, which are divided by an interface, then also Interface would normally not be horizontal or wholly continuous under driving conditions, due to vertical and horizontal acceleration forces to which condenser would be continuously exposed. It is sufficient for the practice of the present invention that chamber of outlet header be internally sized to ensure that the velocity of fluid passing there through is reduced to a point at which the gas phase can separate from the liquid phase under the influence of gravity and not be swept along with the liquid phase exiting through outlet whereby to achieve and maintain substantial separation between the gas and liquid phases of the refrigerant within the second header during normal use conditions, and that outlet be connected into a lowermost region of volume. It is critical to the practice of the present invention that the refrigerant charge to the system be selected such that during normal operating conditions for which the system is designed, lower volume consisting mostly of liquid refrigerant be constantly maintained within outlet header.
If the teachings of the present invention are practiced alone, then also we can achieve a certain amount of sub cooling without the use of any extra sub cooling device. But if the embodiment as described in the present work is practiced along with a larger outlet header area of cross section we can achieve a good sub cooling without utilizing the condenser frontal area and thus result in a more compact heat exchanger design.
It is preferable to arrange all of tubes in parallel in order to maximize the available vertical dimension of the applicable receiver volume within outlet header. The design of tubes may be conventional, but in any event is not limiting on the practice of the present invention.

7. We claim
1. A multiflow condenser intended for vehicular air conditioning applications comprising of a
first and second generally vertically upstanding headers; a plurality of generally
horizontally disposed condenser tubes, said tubes having inlet ends connected into said
first header and outlet ends connected into said second header and forming parallel
refrigerant gas conducting flow paths connecting said first and second headers; a
refrigerant gas inlet communicating with said inlet ends and a refrigerant liquid outlet
communicating with a lower portion of said second header and a tube inserted into the
second header which will provide a horizontal surface for the refrigerant flow and thus will
ensure that only the liquid part of the refrigerant passes to the evaporator.
2. A multiflow condenser intended for vehicular air conditioning applications comprising of a
first and second generally vertically upstanding headers; a plurality of generally
horizontally disposed condenser tubes, said tubes having inlet ends connected into said
first header and outlet ends connected into said second header and forming parallel
refrigerant gas conducting flow paths connecting said first and second headers; a
refrigerant gas inlet communicating with said inlet ends and a refrigerant liquid outlet
communicating with a lower portion of said second header and a tube inserted into the
second header which will provide a horizontal surface for the refrigerant flow and thus will
ensure a certain amount of refrigerant sub cooling irrespective of the volume of receiver
drier and operational conditions.
3. A condenser according to claim 1, wherein said refrigerant liquid outlet communicates
with said lower volume via at least one tube insert which provides a minimal horizontal
surface sufficient to stop any gaseous refrigerant going further.
4. The possibility of removal of IRD bottle is also there if the design as per this invention is
coupled with the practice of increasing the cross sectional area of the outlet header or
even without increasing the same as some sub cooling will always be ensured.
5. A condenser according to claim 3, wherein said outlet header is divided by a said tube
insert which further defines a relatively upper chamber bounding said upper and lower
volumes and a lower chamber connected to said lower chamber of said first header by a
second sub cooling tube, and said refrigerant liquid outlet communicates with said chamber of said outlet header.
6. The design as enclosed in the present invention will ensure that increased impedance will
be pre known and thus it could be considered at a design stage itself.
7. A refrigeration condenser comprising in combination: first and second generally vertically
upstanding headers defining first and second chambers, respectively, at least one of said
headers defining an additional lower chamber an inlet for supplying refrigerant gas to said
first chamber of said first header, said second chamber having liquid outlet means, and
said additional lower chamber having a refrigerant liquid outlet; a plurality of condenser
tubes, at least certain of which have inlet ends connected into said first chamber and
outlet ends connected into said second chamber and forming parallel refrigerant gas
conducting flow paths connecting said first and second chambers, said liquid outlet
means being disposed below a lowermost of said flow paths, said second chamber of
said second header being dimensioned of sufficiently large internal cross-sectional area
such that when charged with sufficient refrigerant to maintain a liquid to gas interface
above said liquid outlet means refrigerant gas is permitted to substantially separate from
refrigerant liquid produced from said refrigerant gas passing through said tubes to
produce an upper volume of refrigerant gas and a sufficient lower volume of refrigerant
liquid within said second chamber and the velocity of refrigerant liquid flowing towards
said liquid outlet means is not sufficient to sweep refrigerant gas entering said lower
volume from the lowermost of said flow paths, flowing under the influence of gravity from
the lower volume to the upper volume, through said liquid outlet means; and a sub
cooling tube connecting said liquid outlet means in flow communication with said
additional lower chamber.
8. The improvement according to claim wherein said tube insert means communicates with
said lower volume via at least one sub cooling tube extending essentially parallel to said
tubes.
9. The improvement according to claim 8, wherein at least one sub cooling tube is disposed
essentially parallel to said tubes, said first header is divided to define relatively upper and
lower chambers, said upper chamber communicates with said inlet ends, said tube insert
communicates with said lower volume and said lower chamber, and said outlet means
communicates with said lower volume via said lower chamber and said one tube insert.
10. The present work may be used to explore the possibility of receiver bottle deletion which
can fetch us saving in cost and light weight receiver drier bottle.
11. This application relates to a parallel flow heat exchanger, wherein parallel tubes are
configured and mounted in a manifold in a manner that minimizes brazing material
blocking channels in the tubes.