Janardan Rai Nagar Rajasthan Vidyapeeth 2006 B.Tech Chemical Engineering HEAT TRANSFER - Question Paper

Model Question Paper

BSCH9-BSMR9-BSM9- HEAT TRANSFER

Time : 3 hrs Maximum marks : 75

 

Instruction:

1. Question paper is divided into Group A, Group B and Group C

2. Each Group is 25 Marks

3. Figure to the right in bracket indicates marks.

4. Good Handwriting is expected

5. Assume suitable data if necessary.

 

Group A (25 Marks)

Answer any three questions (Question 1 is compulsory)

	(5)

 

Q.1 Explain Newtons law of cooling for convection ?

(10)

Q.2 Describe heat transfer from a fin insulated at the tip ?

(10)

Q.3 Derive an expression for the heat flow through radial cylindrical surface ?

	(10)

 

Q.4 Explain (a) Fouriers law of heat conduction ? (b) Newtons law of cooling for

(10)

Convection ?

 

Q.5 What is hydrodynamic boundary layer ? Explain laminar and Turbulent Flows ?

 

Group B (25 Marks)

Answer any three questions (Questions 6 is compulsory)

(5)

(10)

Q.6 A container with outside surface area 0.36m² and outside temperature of 0⁰C

Contain ice at 0⁰C. The container is placed in ambient air at 24⁰c and the surface

Coefficient of heat transfer between the container surface and the surrounding air

is estimated to be 6.25 w/m² . Calculate the rate at which ice would be changed into

liquid water. Take latent heat of fusion of ice as 340 J/KG.

Q.7 Air at 200⁰ c and 2 bar is heated as it flows through a 2.5 cm diameter tube at a velocity

of 10 m/s. A constant flux is maintained at the wall and the wall temperature is 20⁰c above

the air temperature. How much will the bulk temperature of air increase over a 5m length

of the tube ?

 

Q.8 The wall of a large rectangular combustion chamber for a furnance are to be of 20 cm common

Brick (CB), lined on the inside with 20cm thick layer of magnesite brick (MB) Given :

Temperature of combustion products = 1355⁰c

Surrounding air temperature = 45⁰c

Radiation coefficient, inside surface = 17.6 w/m² / k

Radiation coefficient , inside surface = 16.5 w/m² / k

Radiation coefficient , outside temperature = 7.4 w/m²/k

Radiation coefficient , outside temperature = 11.9 w/m²/k

Thermal conductivity of MB = 3.8 w/m/k

Thermal conductivity of CB = 0.66 w/m/k

Estimate

(a)    Rate of heat loss through the wall per square meter area.

(b)   Maximum temperature to which common brick is subject.

 

Q.9 A dry and wet bulb temperature records the following reading Dry Bulb temperature , t₁ = 44⁰c

Wet bulb temperature, t₂ = 28⁰c

Determine the relative humidity of the air.

 

Q.10. (a) The suction line of a refrigeration system has refrigeration flowing inside a copper tube

1.25 cm O.D and 2 m long. The temperature of the tube wall is -22⁰c. The surrounding

air is at a temperature of 40⁰c. Calculate the heat gain of the line by natural convection.

(b) If air is blown across the line at a velocity of 5m/s, what will be the heat gain ?

Group C (25 Marks)

All Questions are Compulsory.

Q.11 Fill in the blanks ( each question carry 2 marks)

1. Units of thermal conductivity in M.K.S. units is __________

2. The law which relates the diffusion rate a species to its driving potential is _________

3. The device which transfer heat from a low temperature region to a high temperature region is

called a ________

4. Reynolds number = ___________

5. For a black boby, the radiation emitted is given by ___________.

 

Q.11 Multiple choice question. (Each question carry 2 marks)

1. Decreasing order of thermal conductivity is

a) Metals, non-metals, liquids , gates.

b) Metals, Gases, liquids, non-metals.

c) Non-metals, metals, liquids, gases

d) None

2. Rayleigh number =

a) b) c) Gr.Pr d) None

3. The speed of C is equal to

a) C = b) V = c) C = d) None

4. SI unit of heat transfer coefficient is

a) Wm^-2k^-1 b) Wmk^-2 c) W²mk d) None

5. The ration of emissive power of a body to the emissive power of a perfectly black body is

called

a) Absorptivity b) Emissivity c) Diffusivity d) Conductivity

 

Q.11 True or false (each question carry 1 marks).

1. All radiations in a black body are reflected.

2. Heat transfer coefficient is a measure of the temperature.

3. Thermal radiation emitted by a body is proportional to the fourth power of its absolute

temperature

4. Critical radius of insulation for a spherical shell is .

5. Units of kinematic viscosity is m²/s .

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