King Saud University
College of Engineering
Chemical Engineering Dept.
ChE 313
Tutorial # 1
10/1/1426
Heat Transfer Operations
Dr. M Al Ahmed, Eng. M Gaily
1. Find the heat loss per m2 of surface through a brick wall 0.5 m thick when the
inner surface is at 400 K and the outside at 310; the thermal conductivity of
the brick may be taken as 0.7 W/m.K.
2. *The outer surface of a 0.2-m- thick concrete wall is kept at a temperature of 5 ºC, while the inner surface is kept at 20 ºC. The thermal conductivity of the
concrete is 1.2 W/m.K. Determine the heat loss through a wall 10 m long and
3 m high.
3. A square silicon chip 7 mm by 7 mm in size and 0.5 mm thick is mounted on a
plastic substrate. The top surface of the chip is cooled by a synthetic liquid
flowing over it. Electronic circuits on the bottom of the chip generate heat at a
rate of 5 watts that must be transferred through the chip. Estimate the steadystate temperature difference between the front and the back surfaces of the
chip. The thermal conductivity of silicone is 150 W/ m K.
4. *In determining the thermal conductivity of an insulating material, the
temperatures were measured on both sides of a flat slab of 25 mm of the
material and were 318.4 and 303.2 K. The heat flux was measured as 35.1
W/m2 . Calculate the thermal conductivity of the material.
5. A heat flux meter at the outer (cold) wall of a concrete building indicates that
the heat loss through a wall of 10 cm thickness is 20 W/m2. If a thermocouple
at the inner surface of the wall indicates a temperature 22 ºC while another at
the outer surface shows 6 ºC, calculate the thermal conductivity of the
concrete.
6. *Calculate the heat loss through a 1-m by 3-m glass window 7 mm thick if the
inner surface temperature is 20 ºC and the outer surface temperature is 17 ºC.
Comment on the possible effect of radiation on your answer.
7. *A warehouse is to be designed for keeping perishable foods cool prior to
transportation to grocery stores. The warehouse has an effective surface area
of 20000 ft2 exposed to an ambient air temperature of 90 ºF. The warehouse
wall insulation (k = 0.1 Btu/hr ft ºF) is 3 in. thick. Determine the rate at which
heat must be moved (Btu/hr) from the warehouse to maintain the food at 40
ºF.