Casing for a heat exchanger in an air-conditioner, in particular for a vehicle cabin

In an air-conditioner or heater for a motor vehicle cabin, the casing (10) housing the heat exchanger (12) proper essentially comprises an air inlet duct (26) leading to the upstream face (22) of the heat exchanger and an air outlet duct (28) leading away from the downstream face (24) of the heat exchanger. A baffle wall (38) extends adjacent to the downstream face (24) to hinder the flow of air through portions of the heat exchanger where it would otherwise flow fastest. This increases the overall efficiency of the heat exchanger.

The invention relates to a casing for a heat exchanger in an 
air-conditioner, in particular for heating and/or cooling the cabin of a 
motor vehicle. 
BACKGROUND OF THE INVENTION 
In known manner such a casing includes a housing for receiving the heat 
exchanger while leaving the two large faces of its core of heat exchange 
tubes free for the passage of air. The casing further includes an air 
inlet duct leading to the upstream large face and an air outlet duct 
leading away from the downstream large face, together with items such as 
flaps or the like for controlling the temperature of the air admitted to 
the cabin by controlling the air flow through the heat exchanger and also 
for directing the air to various different outlets in the vehicle cabin. 
The size of the casing, and the shape it has to adopt to fit into the 
vehicle and connect to sources of heating and/or cooling liquid depends on 
the space available in the engine compartment and on the locations of 
various inlet and outlet fittings. 
As a result, the air inlet and outlet ducts are often directed towards the 
corresonding large faces of the heat exchanger at oblique angles which 
results in a highly non-uniform distribution of air flow through the heat 
exchanger core. As a general rule the air flows much faster through one 
end of the core than it does through the other end. Thus, for a given 
overall flow rate, the heat exchange efficiency of the heat exchanger is 
generally reduced. This loss of capacity is defined in practice in terms 
of a matching coefficient for the heat exchanger in the casing, where the 
matching coefficient is the ratio of the heat exchanged on a test bench 
(ie. under conditions of uniform air flow) to the heat exchanged by the 
same heat exchanger when mounted in the casing. The matching coefficient 
is generally about 0.9 which is equivalent to a loss in exchanger 
efficiency of 10% due to its being mounted in the casing. 
Preferred embodiments of the invention improve the matching coefficient of 
a given heat exchanger/casing combination by about 5%, without altering 
the nominal characteristics of the heat exchanger nor the relative 
orientations of the inlet and outlet ducts relative to the large faces of 
the heat exchanger. 
SUMMARY OF THE INVENTION 
The present invention provides a casing for a heat exchanger in an air 
conditioner, in particular for the cabin of a motor vehicle, the casing 
comprising a housing for receiving the heat exchanger, an air inlet duct, 
and an air outlet duct, each of said ducts leading to a respective one of 
the large faces of the heat exchanger core, with the air arriving at the 
upstream face of the core being so guided as to pass through the core at 
speeds which vary from one part of the core to another, the improvement 
wherein a baffle wall means is included adjacent the downstream face of 
the heat exchanger core over a portion of the core through which the air 
flow speed is highest. 
In a surprising manner, placing a baffle or wall opposite to the portion of 
the downstream face through which the air speed was greatest, and thus 
creating a loss of head in this region, has the effect of making the air 
flow through the heat exchanger core more uniform, of reducing the overall 
head loss through the device, and simultaneously increasing the heat 
exchanging power of the exchanger as well as increasing the total quantity 
of air passing through it. 
The baffle may extend from that end of the downstream face where the air 
flow was highest. It may extend over the entire length of said end or over 
only a portion thereof, and its width may be between 10% and 20% of the 
corresponding dimension of the heat exchanger core in the same direction. 
The distance between the baffle and the downstream face is preferably less 
than half the width of the baffle. 
The invention thus enables the matching coefficient to be increased by 
about 5% and at the same time increases the air flow through the heat 
exchanger by about 10%. 
Director blades may be installed upstream from the upstream face of the 
heat exchanger core to direct the incoming air towards the portions of the 
core through which the air would otherwise flow more slowly. This feature, 
when used in combination with the said baffle, further increases the 
matching coefficient without reducing the air flow through the heat 
exchanger.

MORE DETAILED DESCRIPTION 
In FIG. 1, 10 designates a casing which forms a part of an air-conditioner 
for a motor vehicle cabin. It includes a housing for receiving a heat 
exchanger 12 constituting, for example, a heater radiator of a type which 
is conventional in the motor industry, comprising a bundle or core of 
parallel rectilinear tube 14 (extending perpendicularly to the plane of 
FIG. 1) which are fitted with plane parallel fins 16 extending 
perpendicularly to the direction of the tubes 14. Water boxes or headers 
are provided at each end of the core and include means for connecting the 
heat exchanger to a circuit for a heating liquid to cause the liquid to 
pass through the tubes 14. 
The housing for the heat exchanger 12 in the casing 10 comprises two 
parallel walls 18 and 20 which are perpendicular to the fins 16, together 
with at least an optional further wall parallel to the plane of the figure 
and extending between the walls 18 and 20. The two large faces 22 and 24 
of the heat exchanger core are free when the heat exchanger 12 is in place 
in its housing in the casing 10, and the casing 10 provides an air inlet 
duct 26 and an air outlet duct 28 each of which leads to a respective one 
of the large faces 22 and 24 of the heat exchanger core. A flap 30 is 
mounted inside the casing 10 to pivot about an axis 32 at one end of the 
wall 20 of the housing. It is free to pivot between two extreme positions, 
one of which is shown in FIG. 1 in solid lines (the maximum heat position) 
and the other of which is shown in dash-dotted lines (the minimum heat 
position). 
The temperature of the air admitted to the vehicle cabin is adjusted by 
moving the flap between these two extreme positions. 
The inlet duct 26 is connected to the outlet of a blower fan or other means 
for blowing air (or may constitute a part of said blower outlet) and is at 
an oblique angle relative to the upstream face 22 of the heat exchanger 
core, so that the air arriving via the duct 26 (when the flap 30 is wide 
open as shown in solid lines) is unevenly distributed over the upstream 
face 22 of the core. This causes the air to pass through the core with a 
highly irregular distribution and speed pattern with maximum speeds 
through the core being located close to the wall 20 and minimum speeds 
being located close to the other end of the core close to the wall 18. 
This uneven flow distribution becomes even more uneven when the duct 26 
makes an acute angle with portion 39 of the wall 18 to constitute a shelf 
34 extending in front of the upstream face 22 of the heat exchanger core 
to serve as a stop for the flap 30 when it is in the heater cut-off 
position. Providing such a shelf 34 enables a shorter flap 30 to be used, 
which helps to avoid the problems of rigidity and vibration sensitivity 
which are associated with long flaps. 
When the air temperature is adjusted by means of a cook for adjusting the 
flow of heating or cooling fluid through the heat exchanger, the flap 30 
is not fitted and it is replaced by a fixed wall which occupies the 
position drawn in solid lines. In such a case, a shelf 34 is pointless. 
The outlet duct 28 into which the air arrives after passing through the 
downstream face 24 of the heat exchanger is similarly at an oblique angle 
relative to the downstream face and follows a bend to reach one or more 
air outlet orifices 36 having flaps (not shown) just upstream therefrom 
for directing the air flow into the vehicle cabin via a selection of 
openings. 
This particular disposition of the ducts 26 and 28, and of the heat 
exchanger 12 in the casing 10 is found very often in practice because of 
various constraints to do with the availability of space, connections to 
fluid supplies, etc. It causes the air to flow very fast through the 
portion of the heat exchanger core which is close to the wall 20, and very 
slowly through the other end of the core. The fast moving air is heated 
relatively little as it passes through the heat exchanger core, while the 
slow moving air is heated much more. 
In practice this results in a reduction of the heater's heating power in 
comparison with its heating power as measured with the heat exchanger on a 
test bench where the air is passed through the heat exchanger in a regular 
and uniform manner. 
In a surprising manner, the invention increases air flow through the heat 
exchanger core and increases the heat transferred thereto by providing a 
baffle wall 38 which runs along the downstream face 24 of the heat 
exchanger. The baffle wall 38 extends over all or a part only of the 
length of the core in the region where the air flow rate through the core 
is highest, i.e. in the case shown, starting from the end of the core 
which is sealed to the wall 20. 
It has been observed that satisfactory results are obtained with a baffle 
wall 38 extending over the full length of the core and having a width of 
between 10% and 20% of the corresponding size of the downstream face 24 of 
the core, ie. 10% to 20% of the length of the fins 16. The baffle wall 38 
is preferably 15% of said length. 
It is also preferable for the baffle wall 38 not to be too far away from 
the downstream face 24 of the core. It should extend parallel to this face 
at a distance which is less than half the width of the baffle wall. 
The baffle wall 38 may be an integral part of the wall 20 of the casing 10, 
in which it constitutes a flange or rim thereon, or alternatively it may 
be added on and fixed inside the casing 10 by any suitable means. 
In operation, the baffle wall 38 causes loss of head on the downstream face 
24 of the core over that portion of the core through which the air speed 
is at a maximum. This has the effect of reducing the air speed in this 
portion of the core, thereby increasing the temperature of the air as it 
leaves the heat exchanger, and also increases the speed of the air flow 
through the rest of the heat exchanger, and thus increases the flow 
through the core close to the wall 18. 
As a result, there is an overall increase in the matching coefficient for 
the heat exchanger in the casing of about 5% and an increase in total air 
flow through the heat exchanger 12 of about 10%, other things being equal. 
To get a clearer idea, when the matching coefficient of the heat exchanger 
12 in the casing 10 is 0.91, and when the air flow through the heat 
exchanger core is 100 mass units per unit time for a casing 10 that does 
not include a baffle wall 38, the matching coefficient rises to 0.96 and 
the flow rate rises to 108 units when a baffle 38 is fitted over the 
entire length of the core and extends over a width of about 20 mm. These 
figures are given for constant pressure upstream from the duct 26. 
The matching coefficient can be further improved if director blades 40 are 
provided in front of the upstream face 22 of the heat exchanger to deflect 
the air towards the portion of the heat exchanger which is nearer to the 
wall 18. In the above numerical example, the combination of the baffle 38 
and the blades 40 causes the matching coefficient to rise to 0.97, whereas 
fitting the blades 40 without a baffle 38 only rises the matching 
coefficient to 0.95 and reduces the air flow to 98 mass units per unit 
time. 
Reference is now made to FIG. 2, which shows a variant embodiment of the 
invention which differs from the FIG. 1 embodiment in that the tubes 14 of 
the heat exchanger core are now parallel to the plane of the figure while 
the fins 16 are perpendicular to this plane. The baffle wall 42 
corresponding to the baffle wall 38 extends parallel to the downstream 
face 24 of the heat exchanger core in the region where the air speed 
through the core would otherwise be greatest. 
The headers or water boxes 44 and 46 mounted at the ends of the heat 
exchanger core can be seen in FIG. 2. 
In variants of the invention, the head-loss creating means may be a wall or 
baffle mounted on the heat exchanger. The baffle may be on the header, as 
suggested in FIG. 3, in the form of a rib, or an integral part of the 
header. The baffle may also be snap fitted, or glued to the core as 
suggested at 50 in FIG. 4. 
In another variant, the baffle may be defined by locally deforming the 
core, eg. by folding, crushing or pressing together the edges of the heat 
exchanger fins as suggested at 52 in FIG. 5.