# UPTU Previous Year Question Papers

## Heat Transfer Operation

Note : (i) Use of steam table is allowed.

(ii) Attempt all parts of a question at one place.

1. Attempt any four parts of the following :

(a) What is critical insulation thickness and how it differs from optimum insulation thickness? Explain for a pipe.

(b) Derive the expression for a heat flow in cylinder of radius ‘r^ and ‘r0’ as inner and outer radius respectively and length ‘Z’, having a thermal conductivity ‘k’.

(c) Find the heat loss per square meter through a brick wall 0.5m thick. Let the inner surface be at 400 K and the outside temp, be 300 K. The thermal conductivity of brick is 0.7 W/mK.

(d) What are fins and what is their practical application?

(e) Derive the expression for heat loss in series through composite walls of thickness tj, t2 and t3 having thermal conductivities kj, k2 and k3.

(f) What is unsteady state heat transfer? Write the expression for one dimensional unsteady state heat conduction.

2. Attempt any four of the following :

(a) What is overall heat transfer coefficient? Explain it.

(b) What are the significance of the following:

(i) Reynold number

(ii) Nusselt Number

(iii) Prandtl number.

(c) What is forced convection and how it is different from natural connection? Explain with an example.

(d) What is dirt factor? How its affect the overall heat tasnfer coeff?

(e) Using dimensional analysis, show that for convective heat transfer Nu = f (Re, Pr, Gr).

(f)  With the help of temperature vs. heat flow rate curve, derive the expression for LMTD.

3. Attempt any two of the following :

(a) Heat is transferred by radiation between two large grey surfaces of emissivities ej and e2 respectively. By what fraction will the heat transfer rate be reduced by the introduction of a thin metal shield (having emissivity esh) between the radiating surfaces? Neglect any temp, gradient across the shield.

(b) Two concentric tubes A and B with diameters 30 cm and 25 cm resp. are maintained at temp, of 540°C and 200°C. The emmissivity of tube A is 0.87 and that of tube B is 0.26. Determine the net heat transfer by radiation between the surface of the tubes (ct =4.875 x io-8 kcal/ hr m2K4)

(c) (i) Differentiate between grey body and black

body giving example of each.

(ii) What is Kirchoffs law ?

(iii) Explain the term ‘Emissivity’.

4. Attempt any two of the following :

(a) A continuous single effect evaporator is to be fed with 5000 kg/hr of solution containing 17 (by weight) solute. The feed is at a temperature of 303 K. It is to be cons, to a solution of wt. to solute. The evaporation is at atmosphere pressure (101.3 kPa) and the area of the evaporator is 69.7 m2 saturated steam is supplied at 143.3 kPa for heating. Calculate the amounts of vapor and liquid product.

(b) What are the various types of evaporator ? Describe the uses of them. Also discuss the working of any one of them.

(c) (i) What do you understand by film wise condensation and drop wise condensation? — Explain.

(ii) What is boiling? Explain the nucleate boiling with neat sketch.

5.  Attempt any two of the following :

(a) Explain versatility of shell and tube heat exchanger. Explain the principle and working of 2-4 shell and tube heat exchanger with neat labelled sketch.

(b) In a water to water heat exchanger with counter flow arrangement and having a heating surface of 2m2, the inlet temperature and flow rate of heating water were 85°C and 2000 kg/hr. The flow rate and inlet temp, of the water being heated were 1500 kg/hr and 25°C. Calculate rate of heat transfer from the hot to the cold water and give their final temperature U = 1200 kcal/hr m2 °C.

(c) (i) What are boilers and how they differ from calandrias?

(ii) Explain the working of Kettle type Boiler with neat sketch.