Motor vehicle passenger compartment heater

A motor vehicle passenger compartment heater having a greater number of tubes in the inlet pass than in the outlet pass of the core.

TECHNICAL FIELD 
This invention relates to motor vehicle passenger compartment heaters, and 
more particularly to those of tube and manifold construction wherein a 
first group of the tubes (inlet tubes) conveys engine coolant from an 
inlet side of one manifold to the other manifold and a second group of 
tubes (outlet tubes) conveys the fluid from the latter manifold back to an 
outlet side of the first mentioned manifold. 
BACKGROUND OF THE INVENTION 
In motor vehicle passenger compartment heaters of the above type, the 
current state of the art is to have an equal or nearly equal number of 
tubes in each group or pass. By doing this, the coolant velocity in all 
the tubes is nearly identical for what was believed to be best heat 
transfer performance. However, there can be debris in the coolant system 
and if this debris lodges in the tube inlets, the entrance velocity into 
these tubes increases making the heater core more susceptible to erosion. 
SUMMARY OF THE INVENTION 
In studying the above problem, it was discovered that while some of the 
inlet tubes may have been plugged up to 75% or more of their total 
entrance ("plugged" meaning partial to total blockage), the entrances to 
the outlet tubes were virtually clean in the same cores with the result 
that the affected inlet tubes suffered from erosion because of increased 
velocity therein while the outlet tubes did not. Recognizing this, the 
present invention conceived of manifolding the heater core with the 
minimum number of outlet tubes required to establish an acceptable 
velocity therein from the erosion standpoint and with a significantly 
greater number of inlet tubes than outlet tubes so that in this way the 
core would be less prone to erosion by inlet tube plugging yet not suffer 
significant heat transfer performance. Thus the present invention provides 
for a calculated allowance of inlet tube plugging without increased 
erosion by initially establishing the inlet tube velocities at a much 
lower level than normal by simply adding sacrificial inlet tubes to 
compensate for the increase in flow through the total inlet tube flow area 
as plugging does occur. 
It is thus an object of the present invention to provide a new and improved 
motor vehicle passenger compartment heater having improved erosion 
resistance without significant loss in heat transfer performance. 
Another object is to provide in a motor vehicle passenger compartment 
heater a greater number of tubes in the inlet pass than in the outlet pass 
so that correspondingly the fluid velocity in the individual tubes in the 
inlet pass is initially significantly less than in the outlet pass and 
thereby less prone to erosion with increased velocities that result from 
inlet tube plugging. 
Another object is to provide in a motor vehicle passenger compartment 
heater of tube and manifold construction, an inlet pass having additional 
sacrificial tubes to decrease the initial fluid flow velocity in the 
individual tubes of the inlet pass and thereby render the core less 
susceptible to erosion by inlet tube plugging.

DETAILED DESCRIPTION OF INVENTION 
Referring to FIG. 1, there is shown an automotive passenger compartment 
heater comprising an inlet/outlet manifold 10, a return manifold 12, a 
plurality of flat sided identical tubes 14 connected at their opposite 
ends to the respective manifolds, and a plurality of corrugated fins or 
air centers 16 individually sandwiched between adjacent tubes. The 
manifolds 10 and 12 are of tank type construction comprising a header 
plate 18 and 20 to which the tubes are directly joined, and a concave 
shell 22 and 24 which cooperates with the respective header plate to form 
the manifold or tank. The inlet/outlet manifold 10 is divided internally 
by a partition 26 into an inlet chamber 27 and an outlet chamber 28 which 
are respectively open to selected groups 29 and 30 of the tubes. The inlet 
chamber 27 is also open to an inlet fitting 31 that is attached in an 
opening in the shell 22 and connected to receive coolant from an engine 
coolant system (not shown). Similarly, the outlet chamber 28 is open to an 
outlet fitting 32 that is joined to the shell 22 but on the opposite side 
of the partition 26 and connected to return the coolant to the engine 
coolant system. In addition, there are provided reinforcement side members 
34 and 36 on opposite sides of the sandwiched tubes and fins which extend 
to the respective manifolds and together with the manifolds and the other 
core parts are all brazed together in their properly assembled position as 
shown. In the resulting integral structure, the tube group 29 forms an 
inlet pass that conveys engine coolant from the inlet chamber 27 to the 
return manifold 12 while the other tube group 30 forms an outlet pass that 
conveys the coolant from the return manifold to the outlet chamber 28 of 
the inlet/outlet manifold. 
According to the present invention, the inlet/outlet manifold 10 and return 
manifold 12 are connected with the tubes so there is only the minimum 
number of outlet tubes 30 required to establish an acceptable velocity 
therein from the erosion standpoint (i.e., no allowance for plugging) and 
a substantially greater number of inlet tubes 29 as a sacrifice to 
anticipated plugging. This is simply accomplished by positioning of the 
partition 26 so that the desired larger group of tubes is open to the 
inlet chamber 27 than to the outlet chamber 28. In the embodiment shown 
which has been released for production, there is a total of twenty-one 
(21) tubes with twice the number of tubes connected in the inlet pass than 
in the outlet pass, i.e. fourteen (14) of the tubes connected in the inlet 
pass 29 and only the remaining seven (7) tubes connected in the outlet 
pass 30. As a result, the fluid velocity in the individual tubes in the 
inlet pass is half that of the tubes in the outlet pass where initially 
installed in a motor vehicle and there is in effect a seven (7) tube 
sacrificial offering. 
The foregoing description of a preferred embodiment of the invention has 
been presented for purposes of illustration and description. It is not 
intended to be exhaustive or to limit the invention to the precise form 
disclosed. Obvious modifications or variations are possible in light of 
the above teachings. For example, while a ratio of 2:1 between the number 
of inlet tubes and outlet tubes is disclosed, this ratio may be higher or 
lower based on plugging projection studies for the intended end use. The 
embodiment was thus chosen and described to provide the best illustration 
of the principles of the invention and its practical application to 
thereby enable one of ordinary skill in the art to utilize the invention 
in various embodiments and with various modifications as is suited to the 
particular use contemplated. All such modifications and variations are 
within the scope of the invention as determined by the appended claims 
when interpreted in accordance with the breadth to which they are fairly, 
legally and equitably entitled.