Painting the surface black
Painting the surface white (with aluminium paint)
Giving the surface a mirror finish
Roughening the surface
✅ The correct answer is option B.
Engineering MCQs
For a perfectly transparent surface (like gases), the
Absorptivity = 0
Transmissivity = 1
Reflectivity = 0
All of the above
✅ The correct answer is option B.
Graetz number is given by
mCp/kL
kL/mCp
mCp/kμ
kμ/mCp
✅ The correct answer is option A.
Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone.
Laminar
Transition
Both A & B
Highly turbulent
✅ The correct answer is option D.
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.
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.
Heat exchanger tubes are never made of
Plain carbon steel
Stainless steel
Lead
Copper
✅ The correct answer is option C.
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.
Prandtl and Reynold’s analogies are identical for Prandtl number value of
0
0.5
1
5
✅ The correct answer is option C.
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.