Engineering Archives

1321. Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is

Finned tube heat exchanger with air inside and steam outside

Finned tube heat exchanger with air outside and steam inside

Shell and tube heat exchanger with air inside tubes and steam on shell side

Shell and tube heat exchanger with air on shell side and steam inside tubes

✅ The correct answer is option B.

1322. Natural convection is characterised by

Grashhoff number

Peclet number

Reynolds number

Prandtl number

✅ The correct answer is option A.

1323. Radiation heat transfer rates does not depend upon the

Type of absorbing surface

Distance between the heat source and the object receiving the heat

Surface area and temperature of the heat source

None of these

✅ The correct answer is option D.

1324. A multiple effect evaporator as compared to a single effect evaporator of the same capacity has

Lower heat transfer area

Lower steam economy

Higher steam economy

Higher solute concentration in the product

✅ The correct answer is option C.

1325. In a shell and tube heat exchanger, square pitch compared to triangular pitch

Gives a higher shell side pressure drop

Gives a lower shell side pressure drop

Can pack more surface area into a shell of given diameter

None of these

✅ The correct answer is option A.

1326. For an ideal black body

Absorptivity = 1

Reflectivity = 1

Emissivity = 0

Transmissivity = 1

✅ The correct answer is option A.

1327. The driving potential for the crystal growth during crystallisation is the __________ of the solution.

Concentration

Viscosity

Super-saturation

Density

✅ The correct answer is option C.

1328. Calburn analogy is applicable for the value of Prandtl number from

0.001 to 1

0.6 to 120

0.5 to 5

120 to 400

✅ The correct answer is option B.

1329. 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

Greater than that for uninsulated steam pipe

Less than that of the uninsulated steam pipe

Equal to that of the uninsulated steam pipe

Less than the steam pipe with 5 cms insulation

✅ The correct answer is option B.

1330. Prandtl number is the ratio of

Momentum diffusivity to mass diffusivity

Momentum diffusivity to thermal diffusivity

Thermal diffusivity to mass diffusivity

Thermal diffusivity to momentum diffusivity

✅ The correct answer is option B.