Heat Transfer Practice Test 8

1. The free convection coefficient is given by
h = C ₁ d t ^m/l ^{1 – 3m}
The value of exponent for turbulent flow is

2. When evaporation takes place at the liquid-vapor interface, the heat transfer is solely due to free convection and the film coefficient follows the relation

3. A 1.0 mm diameter and 300 mm long nickel wire is submerged horizontal in water at atmospheric pressure. At burnout, the wire has a current of 195 A. Calculate the voltage at burnout. The relevant thermos-physical properties are
p _f (fluid) = 959.52 kg/m³
p _g (vapor) = 0.597 kg/m³
h _{f g} = 2257000 J/kg
σ = 0.0533 N/m

4. A thin walled duct of 0.5 m diameter has been laid in an atmosphere of quiescent air at 15 degree Celsius and conveys a particular gas at 205 degree Celsius. Base your calculations on one meter length of the duct, estimate the convective coefficient of heat transfer

5. Which number establishes the relation between convective film coefficient, thermal conductivity of the fluid and a significant length parameter?

6. The product of buoyant force and inertia force to the square of the viscous force is known as

7. Natural convection heat transfer coefficients over surface of a vertical pipe and a vertical flat plate for same height. What is/are the possible reasons for this?
(i) Same height
(ii) Both vertical
(iii) Same fluid
(iv) Same fluid flow pattern
Select the correct answer

8. Which of the following is true for laminar flow?

9. A hot plate of 15 cm² area maintained at 200 degree celsius is exposed to still air at 30 degree Celsius temperature. When the smaller side of the plate is held vertical, convective heat transfer rate is 15 per cent higher than bigger side of the plate is held vertical. Find size of the plate. The appropriate correlation for the convection coefficient is

Nu = 0.60 (Gr Pr) ^0.25

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