Heat transfer through foam. 3

[kmasine]

I currently have a design to heat an automobile seat by placing a copper coil under the foam of the seat and piping hot engine coolant through the coil. How can I model the amount of heat transfer to the top of the seat if the bottom and sides of the coil are insulated so the heat can only go up. I realize I'll need to know the conduction coefficient of the seat foam and the flowrate, but how do I go about calculating the heat transfered upward?

 

[vpl]

sailoday

A typical car heater/defroster blows hot air into the passenger compartment. The heating (and cooling in the summer) is done in the engine compartment. The two compartments are separate (usually by a metal wall). The piping for heating system does not directly interact with the passenger.

In so far as "providing constructive input on why an idea may not work," I obviously mistakingly thought that providing input as to the dangers and liabilities associated with having someone sit on a seat with a pipe under him/her and behind his/her legs holding 180°F - 196°F (82°C - 91°C) was sufficient. Perhaps my wording was a mite too terse to properly get the concept across that even a minor pinhole leak inside the passenger compartment could release that hot fluid directly onto the driver/passenger or that even a minute quanity of fluid at those temperatures might cause damage to human skin, much less distract the driver leading to an accident.

Furthermore, because it appears that the hot fluid piping would be encased in foam, there is a danger that the fluid might be adsorbed by the foam, depriving the engine of coolant while also causing the above-mentioned damage.

Additionally, because of the possibility of an automobile being involved in an accident, there is a danger of a coolant pipe being severed (especially due to sudden seat movement.) This could lead to a large quantity of extremely hot fluid being suddenly released unto the human occupants of the car. This could result in 2nd or 3rd degree burns.

I should also point out that, at least, the American Justice system has taken a dim view of manufacturer's whose products end up hurting people, especially when such hurt could be avoided through a reasonable design.

Finally, and to interject a somewhat humorous note: It's not my bottom that gets cold, it's my feet! Perhaps kmasine would do better to turn his inventive gaze onto a way of running all that engine coolant underneath the automobile to heat the underside and provide a warm floorboard.

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[IRstuff]

Car seats have to move, so flexible hose is required. Break in hose means passengers get sprayed with scalding coolant, real nice.

TTFN

 

[magicme]

vpl

i agree with 99.9% of what you say.

but my wife really really likes her car seat warmers.

magicme

------------------------------------
"not all that glitters is gold"

 

[rmw]

Patricia,

Au contraire. At least not in a Ford. The heater core is easily accessible from the inside of the passenger compartment, and luckily so. Fords are notorious for leaking heater cores. (in my opinion.) If it leaks, it leaks right onto the carpet in the passenger foot well. I've replaced several. They are not hard to get to.

rmw

PS: the air conditioning evaporator is also inside the 'airspace' of the passenger compartment meaning that if it leaks, freon enters the passenger air. Those systems are not isolated from the passenger area.

 

[kenvlach]

I believe car seat heaters are electrical resistance wires embedded within silicone rubber: Flexible and instant-on (don't have to wait for thermal mass of cold coolant & piping to warm), plus have a temperature sensor to prevent overheating.

 

[MedicineEng]

kmasine:
I believe that you already understood how potentialy dangerous your idea is.
This should give you an indication which way your idea should take...

 

[torpen]

Hello,

This AIAA paper seems to be interesting:

http://www.box.net/public/qsbegq1b75

Regards,

Torpen.

 

[kenvlach]

The AIAA paper covers seat cooling, but on page 5 a figure shows a thin electric 'Heater mat construction' just below the top fabric.

See some basic electric heater details in 'Thermal Simulation of Textile Heating, e.g. Car Seat' here:

http://www.ltnt.ethz.ch/teaching/Master-Sc-LTNT.pdf

You can buy a 'GM & Mopar Licensed Car Seat Heater Kit - Model Specific' here:

http://www.sportsimportsltd.com/heatelcarsea.html

Some details:
"Power requirements vary by kit and range between 51W (3.7A @ 13.8V) & 84W (6.1A @ 13.8V).
Temperature: High - 113 to 119 degree F
Temperature: Medium - 110-116 degree F
Temperature: Low - 97 to 103 degree F
Heating Element: .25" thick Polyester Foam w/Nylon Scrim"

Why anyone would want to sit on a rigid seat containing a cold metal-coolant heat sink that doesn't heat up until the engine warms is beyong the understanding of the OEM's & myself.