PE Problem #43

7/31/2018

An atrium houses furniture in varying arrangements at the floor level, of which heat transfer is a primary concern between combustible objects. Determine the rate of convective heat transfer (in kW) between a 31 sqft section of wood-faced wall at 22 deg C with an effective heat transfer coefficient of 0.54 kW/m^2K and a burning surface at 425 deg C.
a. 218 kW
b. 627 kW
c. 6746 kW
d. 7115 kW

Solution | Posted 08/01/18

4 Comments

FPE

7/31/2018 08:16:31 am

b. 627 kW
Ref. Qc = hc x A x (Tg-Ta)

7/31/2018 08:58:22 am

B. 627kW

Q = h*A*(T_1-T_2)

keeping mindful of unit conversions between imperial and metric

Colleen

7/31/2018 10:43:48 am

Concur, B. 627 kW

per FPH 2-9, Qdot=h*A*deltaT=(0.54 kW/m^2*K)*[(31 ft^2)*(0.3048 m/1 ft)^2]*(425-22)=627.7 kW

looks like answer A is a distractor since that's what you get if you use q_dot''=h*deltaT (but that is the flux, kW/m^2). Also looks like C is a distractor answer if you forget to convert feet to meters.

Brian

7/31/2018 06:15:21 pm

Q’’ = A *h (T2K-T1K)
=(31*.2909) * .54 * ((425+273) - (22+273))
=626.7kw

=B
Looking for specific information about the value of the T’s. FPH 2-9 says Kelvin, Meyers 2017 & 18 show C. Hopefully the solution speaks to the correct units.

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