Heat Transfer (Set 5) Flashcards
As one of the transport phenomena, the concepts in heat transfer are crucial for design, operation, and maintenance of heat transfer equipment such as heat exchangers and insulation.
In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid
varies directly as the area and the LMTD.
With increase in temperature, the total emissivity of conductors
increases
Loss of heat from untagged steam pipe to the ambient air is by
all (a), (b) & (c)
Conduction, Convection & Radiation
Fruit juice (a heat sensitive material) can be concentrated in a ____ evaporator.
falling film
Tubes are held between top and bottom tube sheets in Calenderia type evaporator by keeping
both the tube sheets fixed.
A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of
2^0.8
Heat sensitive materials can be concentrated in an evaporator employing
vacuum
A concentric double pipe heat exchanger as compared to the shell and tube heat exchanger for the same heat load requires
more space.
In a shell and tube heat exchanger, floating head is used for
large temperature differentials.
Steam trap is used to
remove water resulting from partial condensation of steam.
The average heat transfer co-efficient over the entire length of the plate (ha) and the local heat transfer co-efficient (hL), in case of heat transfer over a flat plate in lminar zone is related as
ha = 2hL
What is the logarithmic mean of r1 and r2 ?
(r1-r2/ln(r1/r2))
Maximum heat transfer rate is achieved in ____ flow.
turbulent
Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is ____ law.
Wien’s
Three material A, B and C of equal thick-nes and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of ____ °C.
70
Which of the following parameters of the fluid is not very important, while deciding its route in a shell and tube heat exchanger?
density
Corrosiveness of steam condensate is due to the presence of
a. CO2
b. dissolved O2
both (a) & (b)
The equation, (NSt x N2/3Pr) = f/2, is the ____ analogy.
Colburn
The driving potential for the crystal growth during crystallisation is the ____ of the solution.
super-saturation
jH factor for heat transfer depends upon the ____ number.
Reynolds
Kg of liquid evaporated per hour in an evaporator is defined as its
capacity
Pick out the correct statement.
In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity.
Open pan evaporators are preferred to be used, when the solution to be concentrated is
highly viscous
Cp.μ/K is termed as the ____ number.
Prandtl