A. (r1 – r2)/ln(r1/r2)
B. (r1 – r2)/ln(r2/r1)
C. (r2 – r1)/ln(r1/r2)
D. (r1 – r2)/-ln(r1/r2)
Related Mcqs:
- What is the geometric mean of two heat transfer areas A1 and A2 ?
A. √(A1 . A2)
B. √(A1 + A2)
C. ½ √(A1 . A2)
D. 2 √(A1 . A2) - In case of heat transfer by conduction in a hollow cylinder, ______________ mean area is used to calculate the heat transfer rate?
A. Geometric
B. Arithmetic
C. Logarithmic
D. Either A., B. or C. - Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3/min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately ?
A. 32
B. 37
C. 45
D. 50 - Harmonic mean temperature difference is given by_________________?
A. √(ΔT1 . ΔT2)
B. 2 (ΔT1 . ΔT2)/(ΔT1 + ΔT2)
C. 2 (ΔT1 . ΔT2)/(ΔT1 – ΔT2)
D. (ΔT1 – ΔT2)/(ΔT1 . ΔT2) - Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is ____________________?
A. Thin walled having the value of Ao Ai/< 2
B. Thick walled
C. Having the value of Ao/Ai > 2
D. Both B. and C. - In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is_________________?
A. Minimum
B. Maximum
C. Zero
D. Infinity - Log mean temperature difference (LMTD) cannot be used, if ___________________?
A. Heat transfer co-efficient over the entire heat exchanger is not constant
B. There exists an unsteady state
C. The heat capacity is not constant and there is a phase change
D. None of these - Which of the following is the most widely used heat insulating material for pipelines carrying steam ?
A. Tar dolomite bricks followed by asbestos
B. Fireclay refractory followed by aluminium sheet
C. Cotton followed by aluminium foil
D. 85% magnesia cement and glass wool - Nucleate boiling is promoted ___________________?
A. On polished surfaces
B. On rough surfaces
C. In the absence of agitation
D. None of these - Indirect contact heat exchangers are preferred over direct contact heat exchangers, because_________________?
A. Heat transfer co-efficient are high
B. There is no risk of contamination
C. There is no mist formation
D. Cost of equipment is lower
