Question

In: Physics

A heating system is designed to keep the inner wall surface temperature of a room at...

A heating system is designed to keep the inner wall surface temperature of a room at

25C. Only one wall of the room is contacted with the outer environment. The crosssectional view of the wall is schematically shown in Fig. H1. The height, width and

thickness of the wall are 2.5 m, 10 m and 0.2 m, respectively. The wall is made from red

bricks with a thermal conductivity of 0.72 W/m.K and solar absorptivity of s = 0.63.

The temperature and velocity of the ambient air stream are 1C and 20 km/h,

respectively at the outside. In addition, solar irradiation coming to the wall surface is

40 W/m2. Considering the given “day” conditions of winter,

a. Make an energy balance on the outer surface of the wall (show all input and output

streams). [3pts]

b. What is the outer surface temperature of the wall? [10pts]

c. What is the total heat loss from the wall? [2pts]

d. If an insulating material with a thickness of 3 cm and a thermal conductivity of

0.05 W/m.K is mounted to the adjacent of the wall (from room side), how is the outer

surface temperature and heat loss from the wall changed? What effect would such

an application have? [5pts]

e. How is the total heat loss from the wall with no insulation changed if the wind speed

increases to U= 40 km/h at the outside environment. Determine the percentage

increase/decrease in the heat loss, when compared to heat loss found in (c.). [5pts]

Expert Solution

genius_generous answered 2 years ago

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