Question

# 1. Consider a 1.8-m high and 1.5 m-wide double-pane window consisting of two 4-mm thick layers...

1.

Consider a 1.8-m high and 1.5 m-wide double-pane window consisting of two 4-mm thick layers of glass (k = 0.78 W/m°C) separated by a 10-mm wide stagnant air space (k = 0.026 W/m°C). The room is maintained at 20°C while the temperature of the outdoors is -10°C. Take the convective heat transfer coefficients on the inner and outer surfaces of the window to be 10 W/m2°C and 40 W/m2°C, respectively.

Determine the steady rate of heat transfer through this double-pane window?

 A. 155.8 W B. 210.1 W C. 346.9 W D. 400.1 W

2.

A glass window measures 1 m x 2 m x 0.5 cm thick. The temperature on one side of the window is 10°C,

while the temperature on the opposite side is 2°C. The thermal conductivity of the glass is 0.78 W/m K.

Find the amount of heat loss through the window after 5 hours. Provide answer in J/s

3.

Compute the log mean temperature difference for a heat exchanger with the hot fluid entering at 150°C and leaving at 90°C. The cold fluid enters at 20°C and leaves at 110°C.

Assume countercurrent flow.

 A. 25.3°C B. 33.3°C C. 53.6°C D. 77.3°C

4.