# Practice Test: Question Set - 16

**1. The left face of a one dimensional slab of thickness 0.2 m is maintained at 80°C and the right face is exposed to air at 30°C. The thermal conductivity of the slab is 1.2 W/m.K and the heat transfer co-efficient from the right face is 10 W/m**

^{2}.K. At steady state, the temperature of the right face in °C is- (A) 77.2

- (B) 71.2

- (C) 63.8

- (D) 48.7

**2. In forced convection, the heat transfer depends on**

- (A) Re, Pr

- (B) Re, Gr

- (C) Mainly Gr

- (D) Re only

**3. Agitated film evaporator is suitable for concentrating __________ liquids.**

- (A) Foaming

- (B) Viscous

- (C) Very thin

- (D) Corrosive

**4. A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material 'A' is**

- (A) 125

- (B) 133

- (C) 150

- (D) 160

**5. Kirchoff's law is applicable to**

- (A) Monochromatic radiation only

- (B) Total radiation only

- (C) Both (a) and (b)

- (D) Only volumes and not to surfaces

**6. The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m**

^{2}. The flux, when the element temperature is increased to 1000°C for the same furnace temperature is- (A) 11.2 kW/m

^{2}

- (B) 12.0 kW/m

^{2}

- (C) 14.6 kW/m

^{2}

- (D) 16.5 kW/m

^{2}

**7. With increase in temperature, the thermal conductivity of non-metallic amorphous solids**

- (A) Decreases

- (B) Increases

- (C) Remain constant

- (D) First decreases upto certain temperature and then increases

**8. The Dittus-Boelter equation for convective heat transfer [(i.e.**

*h*= 0.023 (*K*/*D*) (*Re*)^{0.8}(*Pr*)^{0.4}] cannot be used for- (A) Low Reynold's number

- (B) Very low Grashoff number

- (C) Molten metals

- (D) All (a), (b) and (c)

**9. A black body when hot, emits heat radiation of __________ wavelengths.**

- (A) Small

- (B) Large

- (C) All

- (D) One fixed

**10. Tube pitch is the __________ of tube diameters and the clearances.**

- (A) Sum

- (B) Difference

- (C) Ratio

- (D) None of these

**11. In Joule's experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms**

^{-2}. Neglecting the heat capacity of agitator, the temperature of water (in °C) is- (A) 40.5

- (B) 34.4

- (C) 26.8

- (D) 25

**12. Heat transfer rate per unit area is called**

- (A) Thermal conductivity

- (B) Heat flux

- (C) Heat transfer co-efficient

- (D) Thermal diffusivity

**13. The unit of heat transfer co-efficient is**

- (A) BTU/hr. ft

^{2}°F

- (B) BTU/hr. °F. ft

- (C) BTU/hr. °F

- (D) BTU/hr. ft

**14. The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)**

_{R}and the co-efficient of performance as a heat pump (COP)_{HP}are- (A) (COP)

_{R}= (COP)

_{HP}= 0.6

- (B) (COP)

_{R}= 2.5; (COP)

_{HP}= 1.5

- (C) (COP)

_{R}= 1.5; (COP)

_{HP}= 2.5

- (D) (COP)

_{R}= (COP)

_{HP}= 2.5

**15. For what value of Prandtl number, the Col-burn analogy is valid?**

- (A) 0.06 to 120

- (B) 0.6 to 120

- (C) 1 to 103

- (D) 1 to 50

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