Trying to understand convective heat transfer rate

[dmehling]

I am trying to understand the concept of convective heat transfer. I plugged in some values into the convective heat equation and ended up with q = 40. Now, I don't know what that means. What does that tell me about how long it would take to bring a given volume of air around a hot surface to a given temperature? I need a layman's explanation since my physics background is limited.

 

[Chestermiller]

You haven't provided enough detail for us to understand what you are talking about.

 

[dmehling]

Maybe I don't quite understand the point of the equation: q = hc A dT . I plugged in values of hc = 100, A = .01, dT = 40 and the answer was q = 40 w per second. I just want to know what that answer tells me about how much a given volume of air above a hot surface will increase over a given amount of time. Are there other values and factors that I need to know in order to figure this out.

 

[Chestermiller]

Maybe I don't quite understand the point of the equation: q = hc A dT . I plugged in values of hc = 100, A = .01, dT = 40 and the answer was q = 40 w per second. I just want to know what that answer tells me about how much a given volume of air above a hot surface will increase over a given amount of time. Are there other values and factors that I need to know in order to figure this out.

hc is called the heat transfer coefficient. This equation tells you how much heat is passing through the surface into the air above. If the air is pretty well mixed and you are heating it from the surface, you can determine the rate of temperature rise of the air by also knowing the mass and heat capacity of the air: $$MC_p\frac{dT_a}{dt}=h_cA(T_s-T_a)$$
where Ts is the temperature of the surface.