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MG MGA - Shifting The Heater Box Air

The Nose Surrounds thread has got me thinking about the size of the ducting and the power of heater motor.

The air outlet vent on top of the tunneling has a surface area of about 68 sq cm. If this is closed off, the combined air outlet to the windscreen vents is 110 sq cm. With both open, we have a surface area of up to 178 sq cm.

Why then do we have a massive pipe running from the front of the car with a cross-sectional area of 353 sq cm?

I somehow cannot believe that the heater fan is so efficient that it can compress the air by between 2:1 and 3:1. Many jet engine types that have rows and rows of dynamic and static compressor vanes only compress air between 3 to 12 times its original pressure.

Any aerodynamicists out there who can educate me?


Steve
Steve Gyles

Steve-
There is a lot of loss of flow in long pipes, especially long accordion pipes with bends.
That said, the real reason is to slow down the flow and give lots of time and surface area for the air in the pipe to get to the same temperature as the air outside the pipe, thus ensuring that all this tomfoolery does not interfere with your natural discomfort, hot or cold! A secondary reason is to keep people from monkeying with all the gubbins hidden by the pipes.
FRM
FR Millmore

This thread was discussed between 21/01/2006 and 22/01/2006

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