Variable flow section Condenser
1. Field of invention
The present invention relates to a refrigerant condenser with multiple passes for air conditioning system. A refrigerant condenser of this type is known as multi flow (MF) type condenser and can have an integrated receiver dryer and is referred as MF Condenser with Integrated receiver dryer (IRD).
2. Prior art
The available heat exchangers presently available in the market for the air conditioning systems and particularly for the vehicular air conditioning modules are symmetrical structures of tubes which act as carriers of liquid refrigerant and the embedded fins to maximize the heat transfer area having all the tubes of the same cross section area.
3. Disadvantages of the prior art
The inbuilt disadvantage of this type of construction is that equal flow area is given for all the stages of heat transfer. This is good from heat exchanging point of view only when the refrigerant or any other fluid in side the tubes or outside remains only in one state. But in the case of heat exchange when the fluid exists in the different phases the obvious limitations with the prior art designed heat exchangers are:-
A. Less heat transfer area in the zone which requires a larger heat transfer area
inherently due to its phase of existence.
B. More heat transfer area is provided for the zones which require a lesser heat transfer
area inherently due to its phase of existence.
C. More contact area and thus higher pressure drops in the zone where the same heat
transfer can be possible in a lesser contact area.
4. Objective of present invention
The objectives of the disclosed invention are:-
• To increase the efficiency of the multi phase heat exchangers in view of the observation that phase of the refrigerant may impact the efficiency of the heat exchanger because different phases of refrigerant typically possess different heat transfer properties.
• To enhance the heat transfer from the said heat exchanger as the vapor phase
refrigerant may pass through the flow channels at a higher velocity than liquid
phase refrigerant, resulting in less heat transfer occurring for the tubes containing
the vapor phase refrigerant.
• To optimize the contact area in view of the observation that in condenser, the vapor refrigerant may need to give off both latent and sensible heat to become a liquid refrigerant while the liquid refrigerant may need to give off only sensible heat to undergo sub cooling.
• To reduce the pressure drop by taking advantage of the fact that refrigerant phase may affect the pressure drop that occurs within the flow channels. It is desirable to minimize the pressure drop by using an increased flow area, thereby improving system efficiency.
5. Summary of invention
An integrated receiver drier condenser assembly (Fig. 1) with varying cross sectional area tubes (Fig. 2) with varying tube heights says 1.2 mm, 1.4 mm & 1.7mm for the various passes respectively.
High temperature, high pressure refrigerant enters from orifice/connector and passes through condensation area. The entire process of condensation can be divided into three main parts:-
(A) De superheating zone
(B) Condensation zone
(C) Sub cooling zone
These zones are described in the literature and theory of condensation as below:-
During condensation heat gets released from the Refrigerant gas because of higher heat content and enthalpy and the gaseous refrigerant loses its heat content and temperature till it comes to the temperature at which the phase change is initiated. This phase of heat release from gaseous refrigerant up to the point at which the gaseous refrigerant is cooled down to
the boiling point and hence the initiation of phase change starts at this point is known as de superheating zone.
After the completion of de superheating, the next stage is of condensation where the gaseous refrigerant starts changing into the liquid refrigerant at the same temperature. In this region the temperature remains constant and the heat transfer is due to only phase change. This phase constitutes the main part of the heat releasing process and the rate of heat rejection remains constant due to a constant temperature. This ensures a constant good heat transfer. This phase is known as the condensation phase.
After the condensation phase, refrigerant is in the liquid state but its temperature is still significantly high to ensure that heat transfer continues. This phase of sensible heat rejection involves a drop in the temperature of the refrigerant and continues to be in a liquid state. This third and final phase of the heat transfer process taking place in the condenser is called as sub cooling zone.
This phase is important from the point of view that it ensures that refrigerant in the gaseous phase does not go forward and the complete conversion of gas to liquid refrigerant is ensured.
The bigger sub cool area will reduce the capacity of the condenser and the condenser with maximum condensation zone gives a high heat transfer.
The invention disclosed herewith describes an integrated receiver drier condenser assembly as described in figure 4 and which uses the tubes as described in figure 3 focusing on the points enumerated below:-
1. Flow paths of the first multi channel tube should be smaller than the flow paths of the second multi channel tube,
2. Flow paths of the first multi channel tube should be of different cross-sectional shape than the flow paths of the second multi channel tube,
3. First multi channel tube should have more flow paths man the second multi channel
tube.
In accomplishing the foregoing objects of inventions, Tubes of different sizes for
refrigerant path/Fin block, header plates are arranged on both sides.
Header plates have partition /Separator to create multi pass flow.
Hence tube /Fin block at 1st condensation region has different refrigeration path than 2nd
condensation region and so on.
Refrigerant after entering into header plate from inlet connector passes to 1st condensation
region. It moves to the 2nd condensation region due to partition provided inside header plate.
Cross section area of Tubes at 2nd condensation region is greater than 1st condensation
region.
Further objects, features and advantages of the invention will become apparent from the
detailed description of preferred embodiments that follows, when considered together with
the accompanying figures of drawings.

We claim
The invention of the disclosed variable flow section condenser has the following features and advantages
1. The disclosed heat exchanging device constitutes of dissimilar tubes where the tubes are of multi channel micro voids type and the dissimilarity in the tubes is purposely embedded in the design to optimize the performance by giving the requisite flow area for a particular phase depending on the thermal characteristics of the said phase.
2. The gaseous Flow paths in the heat exchanger which is in the first zone (de superheating zone as described in the related literature) are kept smaller than the flow paths of the second & third phase
3. The purposeful advantage of the different tube heights for different working zones in the condenser as described in the claim B above is that the pressure drop decreases due to higher flow cross section per tube for gas-liquid phase flow thro' the tube and lower contact surface area.
4. The pressure drop decrement will have a direct impact on the system overall power consumption and hence a higher coefficient of performance.
5. Resulting flow rates (and flow velocities) and consequent thermal transfer rates due to the changed internal surface area of the tube is thus enhanced because different flow rates and velocities are preferred for vapor phase flow, liquid phase flow or mixed phase flow.
6. Small diameter flow channels for de superheat zone as described in current disclosure increases die surface area for heat transfer and thus increasing the heat transfer
7. Larger diameter flow channels for sub cooled zone as described in current disclosure increases the flow cross section and thus decreasing the pressure drop.
8. Another objective and claim of the disclosed heat exchanger embodiment also helps in designing a condenser with a lesser weight and hence a reduced cost with optimized performance, as bigger size tubes at condensing / sub cool areas reduces no. of tubes per pass required.