#### Heat Transfer

26

Pick out the correct equation.

A. jH = (St)(Pr)2/3 = f/2
B. jH = (St)(Pr)1/3 = f/2
C. jH = (St)2/3(Pr) = f/2
D. jH = (St)1/3(Pr) = f/2

27

The unit of heat transfer co-efficient is

A. BTU/hr. ft^2circF
B. BTU/hr.circF. ft.
C. BTU/hr. circF
D. BTU/hr. ft

28

The value of Stefan-Boltazman constant in SI unit is

A. 5.6697 x 10^-8 W/m^2circ K^4
B. 0.171 x 10^-8 W/m^2circ K^4
C. 5.6697 x 10^-8 kcal/m^2circ K^4
D. 0.1714 x 10^-8kcal/m^2circ K^4

29

The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface)

A. K/h0
B. 2K/h0
C. h0/K
D. h0/2K

30

A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when

A. CPA > CPB
B. CPA < CPB
C. kA < 0.5kB
D. kA>2 kB