421. Finned tube heat exchangers
Give larger area per tube
Use metal fins of low thermal conductivity
Facilitate very large temperature drop through tube wall
Are used for smaller heat load
✅ The correct answer is option A.
Heat Transfer MCQs
422. Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the
Existence of thermal boundary layer
Temperature gradient produced due to density difference
Buoyancy of the bubbles produced at active nucleation site
None of these
✅ The correct answer is option D.
423. Heat exchanger tubes are never made of
Plain carbon steel
Stainless steel
Lead
Copper
✅ The correct answer is option C.
424. Heat transfer by natural convection is enhanced in system with
High viscosity
High co-efficient of thermal expansion
Low temperature gradients
Low density change with temperature
✅ The correct answer is option B.
425. Prandtl and Reynold’s analogies are identical for Prandtl number value of
0
0.5
1
5
✅ The correct answer is option C.
426. Boiling point elevation of a solution of NaOH
Increases rapidly with temperature rise
Is almost independent of temperature
Is almost independent of pressure
Both B and C
✅ The correct answer is option D.
427. At constant temperature, the thermal conductivities of gases __________ with rise in pressure.
Decrease
Increase
Remain unchanged
May increase or decrease; depends on the pressure
✅ The correct answer is option A.
428. Which has the lowest Prandtl number?
Liquid metal
Aqueous solution
Water
Lube oil
✅ The correct answer is option A.
430. In counter flow compared to parallel flow,
LMTD is greater
Less surface area is required for a given heat transfer rate
Both A and B
More surface area is required for a given heat transfer rate
✅ The correct answer is option C.