JNTU B.Tech III PROCESS HEAT TRANSFER Previous Question Paper (November/December - 2017 - R13)

State Fourier’s law.

What is Biot’s number? State its significance.

Define critical radius of insulation.

Write the energy balance equations for heat exchangers and condensers.

What are various types of fluid flow?

Write a note on eddy diffusivity during heat transfer.

What is Peclet number?

What is drop wise and film type condensation?

What is the limitation of 1-1 heat exchanger?

Classify the various types of evaporators.

A tube of 60 mm outer diameter (O.D.) is insulated with a 50 mm layer of a silicon foam layer, for which the conductivity is 0.055 W/m°C, followed with a 40 mm layer of cork with a conductivity of 0.05 W/m°C. If the temperature of the outer surface of the pipe is 150°C and the temperature of the outer surface of the cork is 30°C, calculate the heat loss in W/m of pipe.

A sudden cold wave drops the atmospheric temperature to -20°C for 12 h. (i) If the ground was initially at 5°C, how deep would a water pipeline have to be buried to be in no danger of freezing? (ii) What is the penetration distance under these conditions? The thermal diffusivity of soil is 0.0011 m²/h.

A layer of pulverized cork 152 mm thick is used as a layer of thermal insulation in a flat wall. The temperature of the cold side of the cork is 4.4°C, and that of warm side is 82.2°C. The thermal conductivity of the cork at 0°C is 0.036 W/m°C and that at 93.3°C is 0.055. The area of the wall is 2.32 m². What is the rate of heat flow through the wall in Watts?

Derive an expression for logarithmic mean radius for flow of heat through thick walled cylinder.

Calculate the overall heat transfer coefficient based on both inside and outside areas for the following cases. Case 1: Water at 10°C flowing in a 3/4 inch 16 BWG condenser tube and saturated steam at 105°C condensing on the outside. hi = 12 kW/m²°C, ho = 14 kW/m²°C and km = 120 W/m°C. Case 2: Benzene condensing at atm. pressure on the outside of a 25 mm steel pipe and air at 15°C flowing within at 6 m/s. The pipe wall is 3.5 mm thick. hi = 20 W/m²°C, ho = 1200 W/m²°C and km = 45 W/m°C.

With a neat sketch, explain the construction and working principle of a single–pass tubular condenser.

In a counterflow heat exchanger, the hot stream is cooled from 120°C to 30°C, while the cold stream temperature changes from 20°C to 60°C. If the same exchanger were operated with parallel flow, what would be the exit temperatures of the two streams?

Write a note on (i) fouling factors (ii) classification of individual heat transfer coefficients.

Oil at 60°F is heated in a horizontal 2-in schedule 40 steel pipe 60 ft long having a surface temperature of 120°F. The oil flow rate is 150 gal/h at inlet temperature. What will be the oil temperature as it leaves the pipe and after mixing? What is the average heat transfer coefficient?

Discuss the thermal and hydrodynamic boundary layers on a flat plate.

Glycerine is flowing at the rate of 700 kg/h through a 30 mm ID pipe. It enters a heated section 2.5 m long, the walls of which are at a uniform temperature of 115°C. The temperature of the glycerine at the entrance is 15°C. (i) If the velocity profile is parabolic, what will be the temperature of the glycerine at the outlet of the heated section. (ii) What would the outlet temperature be, if flow were rodlike (iii) How long would the heated section have to be, to heat the glycerine essentially to 115°C?

Write a note on heating and cooling of fluids in forced convection outside tubes.

A shell and tube condenser with vertical 3/4 inch (19 mm) BWG 16 copper tubes has chlorobenzene condensing at atm.pressure in the shell. The latent heat of condensation of chlorobenzene is 324.9 J/g. The tubes are 1.52 m long. Cooling water at an average temperature of 79°C flowing in a tubes. The water side coefficient is 4540 W/m²°C. (i) What is the coefficient of the condensing chlorobenzene. (ii) What would be the coefficient in a horizontal condenser with the same number of tubes if the average number of tubes in a vertical stack were six. Neglect fouling factor and tube wall resistance.

Describe with a neat sketch the construction of a Kettle type reboilers.

Air at 1 atm pressure is passed through a horizontal 2-inch (51 mm) Schedule 40 steam jacketed steel pipe at a velocity of 1.5 ft/s (0.457 m/s) and an inlet temperature of 68°F (20°C). The pipe wall temperature is 220°F (104.4°C). If the outlet air temperature is to be 188°F (86.7°C), how long must be the heated section be?

Write a note on absorption of radiation by opaque solids.

Describe the working principle of a outside packed dehumidifying cooler condenser.

List the important properties of evaporating liquids used in an evaporator.

Describe the working principle of a plate type exchanger with a neat sketch.

Discuss the various types of jacket design used in heat transfer of agitated vessels.