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    Heat Convection Exercise

    Uploaded by

    Layike Alemayehu
    This document contains 7 questions related to heat transfer via convection. The questions cover topics such as: 1) The differences between laminar and turbulent flow and which has a higher heat transfer coefficient. 2) The physical significance and definition of the Reynolds number for external flow over a plate. 3) Calculating the heat transfer rate from a flat plate with given conditions. 4) Determining the maximum power rating of electronic devices in a duct given cooling conditions. 5) Calculating the power required to heat water in a pipe with an electric resistance heater. 6) Finding the exit temperature and heat loss rate for hot air passing through an uninsulated duct.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    Heat Convection Exercise

    Uploaded by

    Layike Alemayehu
    37 views2 pages
    This document contains 7 questions related to heat transfer via convection. The questions cover topics such as: 1) The differences between laminar and turbulent flow and which has a higher heat transfer coefficient. 2) The physical significance and definition of the Reynolds number for external flow over a plate. 3) Calculating the heat transfer rate from a flat plate with given conditions. 4) Determining the maximum power rating of electronic devices in a duct given cooling conditions. 5) Calculating the power required to heat water in a pipe with an electric resistance heater. 6) Finding the exit temperature and heat loss rate for hot air passing through an uninsulated duct.

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    Heat

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    Heat convection Exercise

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    This document contains 7 questions related to heat transfer via convection. The questions cover topics such as: 1) The differences between laminar and turbulent flow and which has a higher heat transfer coefficient. 2) The physical significance and definition of the Reynolds number for external flow over a plate. 3) Calculating the heat transfer rate from a flat plate with given conditions. 4) Determining the maximum power rating of electronic devices in a duct given cooling conditions. 5) Calculating the power required to heat water in a pipe with an electric resistance heater. 6) Finding the exit temperature and heat loss rate for hot air passing through an uninsulated duct.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    37 views2 pages

    Heat Convection Exercise

    Uploaded by

    Layike Alemayehu
    This document contains 7 questions related to heat transfer via convection. The questions cover topics such as: 1) The differences between laminar and turbulent flow and which has a higher heat transfer coefficient. 2) The physical significance and definition of the Reynolds number for external flow over a plate. 3) Calculating the heat transfer rate from a flat plate with given conditions. 4) Determining the maximum power rating of electronic devices in a duct given cooling conditions. 5) Calculating the power required to heat water in a pipe with an electric resistance heater. 6) Finding the exit temperature and heat loss rate for hot air passing through an uninsulated duct.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 2

    ADDIS ABABA UNIVERSITY

    AAiT
    School of Mechanical and Industrial Engineering
    Heat Transfer (MEng 3171): Exercise on convection

    1. How does turbulent flow differ from laminar flow? For which flow is the heat transfer coefficient
    higher?

    2. What is the physical significance of the Reynolds number? How is it defined for external
    flow over a plate of length L?

    3. The local atmospheric pressure in Denver, Colorado (elevation 1610 m), is 83.4 kPa. Air at this
    pressure and 20°C flows with a velocity of 8 m/s over a 1.5 m x 6 m flat plate whose temperature
    is 140°C. Determine the rate of heat transfer from the plate if the air flows parallel to the (a) 6-m-
    long side and (b) the 1.5-m side.

    4. The components of an electronic system are located in a 1.5m-long horizontal duct whose cross
    section is 20 cm X 20 cm. The components in the duct are not allowed to come into direct
    contact with cooling air, and thus are cooled by air at 30°C flowing over the duct with a velocity
    of 200 m/min. If the surface temperature of the duct is not to exceed 65°C, determine the total
    power rating of the electronic devices that can be mounted into the duct.

    Page 1 of 2
    5. Water is to be heated from 15°C to 65°C as it flows through a 3-cm-internal-diameter 5-m-long
    tube. The tube is equipped with an electric resistance heater that provides uniform heating
    throughout the surface of the tube. The outer surface of the heater is well insulated, so that in
    steady operation all the heat generated in the heater is transferred to the water in the tube. If the
    system is to provide hot water at a rate of 10 L/min, determine the power rating of the resistance
    heater. Also, estimate the inner surface temperature of the pipe at the exit.

    6. Hot air at atmospheric pressure and 80°C enters an 8–m-long uninsulated square duct of cross
    section 0.2 m x 0.2 m that passes through the attic of a house at a rate of 0.15 m3/s. The duct
    is observed to be nearly isothermal at 60°C. Determine the exit temperature of the air and the
    rate of heat loss from the duct to the attic space.

    7. A type-302 stainless steel tube of inner and outer diameters Di = 22 mm and Do = 27 mm,
    respectively, is used in a cross-flow heat exchanger. The fouling factors, Rƒ, for the inner and
    outer surfaces are estimated to be 0.0004 and 0.0002 m2 K/W, respectively.

    Determine the overall heat transfer coefficient based on the outside area of the tube, Uo. Compare the thermal
    resistances due to convection, tube wall conduction, and fouling.

    Page 2 of 2

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