Field of Invention
The present invention relates to an evaporator of an automotive air-conditioning
system, and more particularly to evaporators of a stack type composed of a
multiplicity of laminated heat exchanger elements having tank at one side and
communicated together by U-shaped flow passages.
Background of the Invention
A conventional single tank stacked heat exchanger, shown in Fig. 1 of JP 7-
39895, has an inlet pipe 26 and outlet pipe 27 connected to the front of an
evaporator body as viewed from the direction of flow of air to be cooled. This
type of evaporator is used as a cooling unit in an air-conditioning system of a
vehicle.
An evaporator (1) of this type used in auto air-conditioning refrigeration cycle
includes a heat exchanging elements through which refrigerant passes and fins
disposed perpendicular to the longitudinal direction of the heat exchanging
element, so that heat exchanging is performed between the air going to the
passenger compartment and the refrigerant passing through the heat exchanging
element via fin. Conventional single tank stack type evaporator designs are
having multi-passes 25a, 25b, 25c & 25d, in which the airflow through the tube
elements carrying the initial pass of refrigerant is cooled to a greater extent than
the air passing farther downstream of the refrigerant flow. This provides the
temperature spread of air leaving the evaporator (1) and reduces the cooling
capacity of the evaporator. The cooling performance improvement due to an
increase of the number of said passes results in higher refrigerant pressure drop.
The dryness of the refrigerant at the evaporator exit influences the cooling
efficiency of evaporator. The prior art evaporator shown in Fig.1 has the
refrigerant inlet 26 at the upstream airside A1 (air inlet). The refiigerant (vaporliquid
phase refrigerant) enters from a refrigerant inlet pipe 26 to the tank 21 at
the upstream airside AI, which has a smaller dryness and a smaller specific
volume. As the refrigerant flows through refrigerant passage 25a, due to heat
exchange with air, some refrigerant vaporizes or the dryness of refrigerant
increases before entering into downstream side of refrigerant passage 25b. The
dryness fraction increases further when it flows through refrigerant passage 25c
and refrigerant passage 25d and diminishes the heat exchange between the
ambient air and refrigerant passing through the heat exchanging elements in that
region. The vaporized refrigerant flows out through a refrigerant outlet 27
installed on to the tank 24 at the upstream air side AI. This type of refrigerant
flow pass arrangement gives a higher temperature spread across the evaporator
downstream face and reduces the cooling performance of the evaporator.
Summary of the Invention
An object of the present invention is to provide a single-tank stack-type
evaporator which is capable of overcoming the above mentioned difficulties in
the prior art by providing a different refrigerant flow pass structure.
Another object of the present invention is to reduce the number of different
types of tube elements used in the manufacturing of evaporator.
To achieve said objectives this invention provides a multi-pass plate-fin
evaporator comprising:
- pairs of rectangular adjacent plates (104 or 105) joined together along
with the periphery of the plates to form juxtaposed flat tubes 103 to
increase heat transfer coefficient and allow fluid mixing,
- said flat tubes has U-shaped fluid channel 207 at one end and cup-shaped
tank 202A, 202B at the other end,
- fins 106 are placed in between said flat tubes 103 to form the evaporator
core 100,
- the refrigerant inlet 10 1 to the evaporator core 100 is provided at the airdownstream
side A0 and refrigerant outlet 102 is provided at the airupstream
side A1 as viewed from the direction of the flow of the air to
be cooled,
- the refrigerant from tank 52, 54 at an air-upstream side A1 is connected
with the tank 5 1, 53 at the air-downstream side A0 through U-shaped
fluid channel 207 of the flat tubes in each refrigerant passage,
- a bypass chamber 152 is provided in between the tanks of the evaporator
core transferring the refrigerant from upstream tank 52 to downstream
tank 53 and makes the evaporator 100 multi-pass to improve the air
exit temperature distribution and cooling capacity.
The flat tube 103 has dimples 205, 206 in the refrigerant flow path to increase
heat transfer coefficient and allow fluid mixing.
The said flat tube 103 has U-shaped fluid channel 207 at one end and cup-
@ shaped tank 202A, 202B at the other end, such stacks of flat tubes forms the
core of the evaporator 100.
A refrigerant inlet 101 to the evaporator is provided at air-downstream side A0
and refrigerant outlet 102 is provided at the air-upstream side A1 as viewed from
the direction of the air flow to be cooled.
The direction of flow of refrigerant is from tank at an air-upstream side (AI) to
the tank at an air-downstream side (AO) through U-shaped fluid channel (207)
of the flat tube (103) in each refrigerant passage to achieve better refrigeration
capacity..
The invention will now be described with reference to the accompanying
drawings
Figure 1 is a conventional perspective view of the evaporator for explaining the
flow direction of a refrigerant according to the Japanese patent no. 7-39895
(prior art) and has been described under the heading background.
Figure 2 and 3 are a front elevational view and a top plan view, respectively, of
a multi -layered heat exchanger (evaporator) constructed in accordance with the
present invention.
Figure 4 is a horizontal cross-section view according to the line X-X of Figure
2, wherein refrigerant path along with the bypass chamber is shown.
Figures 5 and 6 are front elevation of pressed plates (104, 105) for use in the
multi-layered heat exchanger (evaporator) of Figure 2.
Figure 7 is a perspective view of a pair of pressed plates (104) to make flat tube
away from bypass chamber.
Figure 8 is a perspective view of a pair of pressed plates (104, 105) to make flat
tube close to bypass chamber.
Figure 9 shows the attachment of the pressed plates (109) and pair of pockets
(1 53) to form a bypass chamber.
Figure 10 is a perspective view illustrating the flow of a refrigerant through the
multi-layered heat exchanger (evaporator) of Figure 2.
Detailed Description:
Figure 1 has been explained under the heading 'Background'.
In Figures 2 and 3, the evaporator 100, which is intended for use in an airconditioner
of the interior compartment of a motor vehicle, comprises a first
group of heat exchanging flat tubes 1 11, a second group of heat exchanging flat
tubes 1 12, and a plurality of heat radiation fins 106 interposed between every
adjacent flat tubes 1 1 1 and 1 12. Each of the flat tubes 103 in said group of flat
tubes 1 1 1, 1 12 are formed by brazing a pair of pressed plates 104, 105 or only
pair of plates 104. There are two plates 105 connectable to the bypass chamber
152. The bypass chamber is formed by brazing a pair of pockets 153. The
liquid-gaseous refrigerant is fed into the evaporator 100 through the inlet 101,
and the gaseous refrigerant is discharged from evaporator 100 through the outlet
102. At one end of the evaporator 100, there is provided a bypass chamber 152.
Two end plates 107 are respectively situated on both side ends of the evaporator
to reinforce the structure of the evaporator 100 while brazing.
Figure 4 is a sectional, plan-view of the evaporator 100, along the line X-X as
indicated in Figure 2. The refrigerant transfers from tank 52 at air-upstream side
A1 to tank 53 at air-downstream side A0 via bypass chamber 152.
The pressed plates 104, 105 have been shown in Figure 5 and Figure 6
respectively to form each of the first group of flat tubes 11 1, and second group
of flat tubes 1 12. The plates 104, 105 are formed by pressing thin aluminum
alloy sheet having a high thermal conductivity. The pair of pressed plates are
joined together by brazing to form flat tubes 103. Each pressed plate 104 have a
pair of cup portions 202A, 202B on its upper end portion and two slots 203A,
203B are respectively formed in the cup portions 202A, 202B respectively.
Each pressed plate 105 has a slot 203A on its upper end portion. A plurality of
small circular protrusions 205 are projected along the plate length and a
plurality of elongated protrusions 206 are formed on the U-turn portion 207.
When plates 104 are stacked side by side, the pockets 202A and 202B
communicate in a row through the slots 203 and forms tanks 5 1, 52, 53 and 54
(Figure 4). A rectangular flange 201 and a partition rib 204 for dividing a space
surrounded by the flange 201 into U-shaped portion 207.
As shown in Figure 7, the two identical pressed metal plates 104 are coupled in
a so-called face-to-face connecting manner to define therebetween a
hermetically sealed U-shaped flow passage 207 to make the flat tube 103 away
from bypass chamber 1 52.
As shown in Figure 8, the two different metal plates 104 and 105 are coupled in
a so-called face-to-face connecting manner to define therebetween a
hermetically sealed U-shaped flow passage 207 to make the flat tube 103 close
@ to the bypass chamber 152.
Figure 9 represents the pockets 153 are coupled with the pressed plates 105,
which forms bypass chamber 152 to transfer refrigerant from upstream tank 52
to downstream tank 53 with respect to airflow (See Fig. 4).
Figure 10 shows the flow of a refrigerant in the evaporator of Figure 2, the
refrigerant (vapor-liquid phase refrigerant) enters into the left section of the tank
5 1 through the refrigerant inlet 101 at the air-downstream side AO, flows
downward in the part of tubes 55a to the U turn and hrther flows to the tank 52
at the air-upstream side AI. A bypass chamber 152 provided at the tank, which
transfers the refrigerant from the tank 52 at the air-upstream side A1 to the tank
53 at the air-downstream side A0 and makes evaporator 100 multi-passes as
shown in Figure 10. The refrigerant from tank 53 flows downward in the part of
tubes 55c to the U turn and hrther flows to the tank 54 at the air-upstream side
A1 and finally flows out of the evaporator through the refrigerant outlet 102.
This has improved the air exit temperature distribution and cooling capacity
compared to prior art single-tank stack-type evaporator described in the
Japanese patent.

Claims:
@ 1. A multi-pass plate-fin evaporator comprising:
- pairs of adjacent rectangular plates (1 04, 105) joined together along with
the periphery of the plates to form juxtaposed flat tubes (103) to
increase heat transfer coefficient and allow fluid mixing,
- said flat tubes has U-shaped fluid channel (207) at one end and cupshaped
tank (202A, 202B) at other end,
- fins (106) are placed in between said flat tubes (103) to form evaporator
core (loo),
- refrigerant inlet (101) to the evaporator core (100) is provided at airdownstream
side (AO) and refrigerant outlet (102) is provided at airupstream
side (AI) as viewed from the direction of flow of air to be
cooled,
- the refrigerant from tank (52, 54) at the air-upstream side (AI) is
connected with the tank (51, 53) at the air-downstream side (AO)
through U-shaped fluid channel (207) of the flat tubes in each
refrigerant passage,
- a bypass chamber (152) is provided in between the tanks of the
evaporator core transferring the refrigerant from upstream tank (52) to
downstream tank (53) and makes the evaporator (100) multi-pass to
improve the air exit temperature distribution and cooling capacity.
2. A multi-pass plate-fin evaporator as claimed in claim 1, wherein the flat tube
(103) has dimples (205, 206) in the refrigerant flow path to increase heat
transfer coefficient and allow fluid mixing.
3. A multi-pass plate-fin evaporator as claimed in claim 1, wherein said flat tube
(103) has U-shaped fluid channel (207) at one end and cup-shaped tank (202A,
202B) at the other end, such stacks of the flat tubes forms the core of the
evaporator (1 00).
4. A multi-pass plate-fin evaporator as claimed in claim 1, wherein a refrigerant
inlet (101) to the evaporator is provided at air-downstream side (AO) and
refrigerant outlet (102) is provided at the air-upstream side (AI) as viewed from
the direction of the air flow to be cooled.
5. A multi-pass plate-fin evaporator as claimed in claim 1, wherein direction of
flow of refiigerant is from tank at an air-upstream side (AI) to the tank at an airdownstream
side (AO) through U-shaped fluid channel (207) of the flat tube
(1 03) in each refrigerant passage to achieve better refrigeration capacity.
6. A multi-pass plate-fin evaporator substantially as herein described with
reference to and as illustrated in the accompanying drawings.