A. High viscosity
B. High co-efficient of thermal expansion
C. Low temperature gradients
D. Low density change with temperature
Related Mcqs:
- Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the________________?
A. Surrounding temperature
B. Average temperature of the fin
C. Temperature of the fin end
D. Constant temperature equal to that of the base - A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be__________________?
A. Greater than that for un-insulated steam pipe
B. Less than that of the un-insulated steam pipe
C. Equal to that of the un-insulated steam pipe
D. Less than the steam pipe with 5 cms insulation - Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the_________________?
A. Existence of thermal boundary layer
B. Temperature gradient produced due to density difference
C. Buoyancy of the bubbles produced at active nucleation site
D. None of these - Nusselt number is a function of Prandtl number and ______________ number of fluid in natural convection heat transfer?
A. Grashoff
B. Biot
C. Stanton
D. Reynolds - In natural convection heat transfer, the correlating parameter is the_______________________?
A. Graetz number
B. Eckert number
C. Grashoff number
D. Bond number - Heat transfer occurs by natural convection because change in temperature causes difference in__________________?
A. Viscosity
B. Density
C. Thermal conductivity
D. Heat capacity - The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as______________?
A. (ΔT)1/4
B. (ΔT)1/2
C. (ΔT)5/4
D. (ΔT)3/4 - Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer cannot take place____________________?
A. Between two bodies in physical contact with each other
B. Between two bodies not in physical contact with each other
C. From one part of a body to the another part of the same body
D. Both B & C - Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface) ?
A. U1 – U2
B. 1/U1 – 1/U2
C. 1/U2 – 1/U1
D. U2 – U1 - For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area___________________?
A. Increases
B. Decreases
C. Remain constant
D. Passes through a maxima
