Heat Transfer MCQs Archives

411. Tubes are held between top and bottom tube sheets in Calenderia type evaporator by keeping

Both the tube sheets fixed

Both the tube sheets floating

The top tube sheet floating and bottom tube sheet fixed

The top tube sheet fixed and the bottom tube-sheet floating

✅ The correct answer is option A.

412. Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer.

Grashoff

Reynolds

Both A & B

Prandtl & Grashoff

✅ The correct answer is option D.

413. What is the absorptivity of a black body?

0.78

0.95

✅ The correct answer is option A.

414. Kg of liquid evaporated per hour in an evaporator is defined as its

Capacity

Economy

Steam load

None of these

✅ The correct answer is option A.

415. 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

Directly proportional to LMTD and inversely proportional to the area

Varies as square of the area

None of these

✅ The correct answer is option A.

416. Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer.

Grashoff

Biot

Stantan

Reynolds

✅ The correct answer is option A.

417. The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by

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.

418. For a perfectly transparent surface (like gases), the

Absorptivity = 0

Transmissivity = 1

Reflectivity = 0

All of the above

✅ The correct answer is option B.

419. Graetz number is given by

mCp/kL

kL/mCp

mCp/kμ

kμ/mCp

✅ The correct answer is option A.

420. 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.