Download AKTU B-Tech 5th Sem 2018-2019 RME 502 Heat And Mass Transfer Question Paper

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Paper Id: 140507

ME-502

Time: 3 Hours

Code:

Roll No:

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B. TECH.

(SEM V) THEORY EXAMINATION 2018-19

HEAT AND MASS TRANSFER

Total Marks: 70

Note: Attempt all Sections. If require any missing data, then choose suitably.

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SECTION A

1. Attempt all questions in brief. 2×7=14

   1. Define three different modes of heat transfer. Give a practical example where all three modes are occurring simultaneously.
   2. What do you mean by the term thermal conductivity? Why good electrical conductor materials are also good heat conductors?
   3. What do you understand by overall heat transfer coefficient?

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   4. Write down the significance of critical radius of insulation.
   5. State the assumptions made in lumped heat capacity method for analysis of transient heat conduction problems.
   6. Define Nusselt number and Prandtl number.
   7. Explain black body, white body, gray body and opaque body.

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SECTION B

1. Attempt any three of the following: 7×3=21

   1. A gas filled tube has 2mm inner diameter and 25cm long, the gas is heated by an electrical wire of diameter 50 microns located along the axis of the tube, the current and voltage drop across the heating element are 0.5A and 4V respectively. If the temperature of wire is 175°C and inside tube wall temperature is 150°C respectively. Find the thermal conductivity of the gas filling the tube.
   2. Derive the expression for temperature distribution and heat dissipation in a straight fin of rectangular profile when fin is of infinite length.
   3. Explain the physical mechanism of free convection with the help of example and neat sketch. Discuss the significance of various dimensionless numbers with respect to natural convection.

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   4. Define the following terms: Total emissivity, Monochromatic emissive power and Monochromatic emissivity.
   5. Differentiate between dropwise and filmwise condensation. Which type has higher heat transfer film coefficient and why?

SECTION C

1. Attempt any one part of the following: 7×1=7

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   1. Derive the 3-D steady state generalized heat conduction equation (without internal heat generation) in Cartesian coordinate system. Write the assumptions used.
   2. An exterior wall of a house may be approximated by a 0.1m layer of common brick (k = 0.7 W/m°C) followed by a 0.04m layer of gypsum plaster (k = 0.48 W/m°C). What thickness of loosely packed rock wool insulation (k = 0.065 W/m°C) should be added to reduce the heat loss (or gain) through the wall by 80 percent?

2. Attempt any one part of the following: 7×1=7

   1. A steel rod (k = 32 W/m°C), 12mm in diameter and 60mm long, with an insulated end, is to be used as spine. It is exposed to surroundings with a temperature of 60°C and a heat transfer coefficient of 55 W/m²C The temperature at the base of fin is 95°C. Determine:
      1. The fin efficiency

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