Heat Transfer Mock Test 8

10%

Question 1 of 10

1. The bubble diameter has been expressed by Fritz as

D _b= C _d β [2 σ/g (p _f– p_g)]^5/2

D _b= C _d β [2 σ/g (p _f– p_g)]^1/2

D _b= C _d β [2 σ/g (p _f– p_g)]^3/2

D _b= C _d β [2 σ/g (p _f– p_g)]^7/2

Question 1 of 10

Question 2 of 10

2. The local film coefficient for laminar flow past a flat plate may be obtained from the correlation

Nu = 0.332 (Re) ^0.5 (Pr) ^0.33

Nu = 0.332 (Re) ^0.5 (Pr) ^0.63

Nu = 0.332 (Re) ^0.5 (Pr) ^0.43

Nu = 0.332 (Re) ^0.5 (Pr) ^0.53

Question 2 of 10

Question 3 of 10

3. The correlation for liquid metal is given by

Nu = 0.465 (Re) (Pr)

Nu = 0.765 (Re) (Pr)

Nu = 0.665 (Re) (Pr)

Nu = 0.565 (Re) (Pr)

Question 3 of 10

Question 4 of 10

4. Boiling refers to a change from the

Solid to a liquid phase

Liquid to a solid phase

Liquid to a vapor phase

Vapor to a liquid phase

Question 4 of 10

Question 5 of 10

5. Consider the following statements regarding nucleate boiling
(i) The temperature of the surface is greater than the saturation temperature of the liquid
(ii) Bubbles are created by the expansion of entrapped gas oil vapor at small cavities in the surface
(iii) The temperature is greater than that in film boiling
(iv) The heat transfer from the surface to the liquid is greater than that in the film boiling
Which of these statements are correct?

i, ii and iii

i, ii and iv

ii, iii and iv

i and iii

Question 5 of 10

Question 6 of 10

6. Consider the following phenomena
(i) Boiling
(ii) Free convection in air
(iii) Forced convection in air
(iv) Conduction in air
Identify the correct sequence (heat transfer coefficient)

iii – iv – i – ii

iv – ii – iii – i

iv – i – iii – ii

iv – iii – ii – i

Question 6 of 10

Question 7 of 10

7. Which of the following is true for turbulent flow?

G _rP _r > 10¹⁵

G _rP _r > 10³

G _rP _r > 10⁹

G _rP _r > 10⁸

Question 7 of 10

Question 8 of 10

8. A nuclear reactor with its core constructed of parallel vertical plates 2.25 m high and 1.5 m wide has been designed on free convection heating of liquid bismuth. Metallurgical considerations limit the maximum surface temperature of the plate to 975 degree Celsius and the lowest allowable temperature of bismuth is 325 degree Celsius. Estimate the maximum possible heat dissipation from both sides of each plate. The appropriate correlation for the convection coefficient is
Nu = 0.13 (Gr Pr) ^1/3

153 MW

173 MV

163 MW

143 MW

Question 8 of 10

Question 9 of 10

9. Air at atmospheric pressure and 20 degree Celsius flows with 6 m/s velocity through main trunck duct of air conditioning system. The duct is rectangular in cross-section and measures 40 cm by 80 cm. Determine heat loss per meter length of duct corresponding to unit temperature difference. The relevant thermos-physical properties of air are
v = 15 * 10 ^-6 m²/s
α = 7.7 * 10 ^-2m²/hr
k = 0.026 W/m degree

32.768 W

62.768 W

52.768 W

42.768 W

Question 9 of 10

Question 10 of 10

10. Milk spills over when it is boiled in an open vessel. The boiling of milk at this instant is referred to as

Saturated nucleate boiling

Interface evaporation

Sub-cooled boiling

Film boiling

Question 10 of 10