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  • HEAT TRANSFER

    LAB MANUAL

    NIRMA UNIVERSITY

    INSTITUTE OF TECHNOLOGY

    CHEMICAL ENGINEERING DEPARTMENT

  • Chemical Engineering Department

    Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual

    List of Experiments:

    1. Thermal conductivity apparatus

    2. Thermal conductivity of metal rod

    3. Thermal conductivity of insulating powder

    4. Heat Transfer in natural convection

    5. Heat Transfer in forced convection

    6. Extended surface equipment

    7. Parallel flow heat exchanger

    8. Counter flow heat exchanger

    9. Shell and Tube heat exchanger

    10. Finned tube heat exchanger

    11. Emissivity measurement apparatus

    12. Drop wise and film wise condensation apparatus

  • Chemical Engineering Department

    Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual

    Date: Roll No:

    Practical No:

    THERMAL CONDUCTIVITY APPARATUS

    Objective: After this experiment student will able to understand how to determine the Thermal

    Conductivity of given specimen.

    Apparatus: Two slab guarded hot plate thermal conductivity apparatus, Specimen, Insulation

    (Glass wool) Packets.

    Utility: Water, Electric Supply.

    Theory:

    Principle of the guarded hot plate method:

    A sketch of the apparatus is shown in Fig. (1). The essential parts the Hot plate, the cold plate,

    the heater assembly, thermocouples and the specimen, in position, are shown in the same figure.

    For measurement of the thermal conductivity K what is required is to have one dimensional heat

    flow through the flat specimen, an arrangement for maintaining its faces at the constant

    temperature and metering method to measure the heat flow through a known area.

    To eliminate the distortion caused by the edge losses in unidirectional heat flow from the central

    plate, it is surrounded by a guard ring heater separately. Temperatures are measured by calibrated

    thermocouples, attached to the plates or to the specimen at the hot and the cold faces. Two

    specimens are used to ensure that all the heat comes out to the specimen only.

    Knowing the heat input to the central plate heater, the temperature difference across the

    specimen, its thickness and the area, one can calculate the K by the following formula.

    Where,

    K Thermal Conductivity of the sample, W /m C

    q Heat flow rate in the specimen, W

    A Area of the specimen, m2

    Th Hot plate temperature, C

    Tc Cold plate temperature, C

    L Thickness of the specimen, m

    If the specimen thickness are different and the respective hot and cold temperatures are

    different than,

    Where suffix 1 stands for upper specimen and 2 stands for lower specimen.

    )(*2

    *

    ch TTA

    LqK

    c2h2

    2

    c1h1

    1

    T - TT - T2

    LL

    A

    qK

  • Chemical Engineering Department

    Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual

    Apparatus description:

    The heater plate is surrounded by a guard heater for stabilising the temperature of the primary

    heater and to prevent heat loss radially around the edges. The primary and guard heaters are made

    of Nichrome wire packed between upper and lower mica sheets. These heaters together with

    upper and lower copper plates and rings from the heater plate assembly.

    Two thermocouples (1 & 2) are used to measure the hot face temperature at the upper and lower

    central plate assembly copper plates. Two more thermocouples (3 & 4) are used to check balance

    in both the heater inputs (see figure 1).

    Specimens are held between the heater and cooling unit on each side of the apparatus.

    Thermocouples (5 & 6) measure the temperature of the upper cooling plate and lower cooling

    plate respectively.

    The cooling chamber is a composite assembly of spiral grooved Aluminium casting and

    aluminium cover with entry and exit adopters for water inlet and outlet.

    Procedure:

    The specimens are placed on either side of the heating plate assembly uniformly touching the

    cooling plates. The outer container is filled with loosely filled insulation such as glass wool

    supplied in small packets. The cooling circuit is started. Then calculated heat input is given to the

    central and guard heaters through separate single phase power supply lines with dimmerstat in

    each line and it is adjusted to maintain the desired temperature (For ensuring no radial heat

    transfer, generally outer heater input is 2.5 to 3.0 times more than the central heating input). The

    guard heater input is adjusted in such a way that there is no radial heat flow, which is checked

    from thermocouples readings are recorded accordingly. The input of the central heater (current &

    voltage, watts) and the thermocouple readings are recorded every 10 minutes till a reasonably

    steady state condition is reached. The readings are recorded in the observation table. The final

    steady state values are taken for calculations.

    Precautions:

    Keep the dimmerstat to 0 voltage position at start.

    Increase the voltage gradually of the two heaters during initial set-up experimentation.

    Start the cooling circuit before switching on the heaters and adjust the flow rates so that

    practically there is no temperature rise in the circulation fluid.

    Keep the heater plate undisturbed and adjust the cooling plates after keeping the samples with

    the help of nuts gently.

    Keep the loose filled in insulation (glass wool) packets gently and remove them slowly so that

    they do not disturb the thermocouples terminals and heater wires.

  • Chemical Engineering Department

    Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual

    Observation table:

    Sr.

    No.

    Central Heater Guard Heater Cooling Plate

    T1(0C) T2(0C) T3(0C) T4(0C) T5(0C) T6(0C)

    The difference between the temperatures of central heater and guard heaters should not be more

    than 1 0C.

    V (volts)

    I (amp)

    q(watt)

    L (m) 0.019 0.019 0.019

    D (m) 0.18 0.18 0.18

    A (m2)

    K (Watt / m oC)

    Calculation:

    1. Area of Heat transfer A = ( / 4) * D2

    2. Thermal Conductivity of specimen

    Where,

    Th, av = (T1 + T2 ) / 2

    Tc, av = (T5 + T6 ) / 2

    L = Thickness of slab

    Result:

    Conclusion:

    )av Tc, - av Th,(2

    *

    A

    LqK

  • Chemical Engineering Department

    Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual

    Quiz:

    1. Write the Fourier rate equation for heat transfer by conduction. Give physical significance of

    each term.

    2. Why there is a negative sign in the Fouriers law of heat conduction?

    3. What is meant by one-dimensional steady state heat conduction?

    4. List some good conductors of heat; some poor conductors.

    5. What is the function of guard heater in Two Slab Guarded Hot Plate Method?

  • Chemical Engineering Department

    Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual

    Date: Roll No:

    Practical No: THERMAL CONDUCTIVITY OF METAL ROD

    Objective: After this experiment student will able to understand how to determine the thermal

    conductivity of given metal rod.

    Apparatus: Thermal conductivity apparatus, metal rod.

    Utility: Water, Electric Supply.

    Theory:

    The thermal energy is conducted in solids by the following modes:

    (i) Lattice vibration

    (ii) Transport by free electrons

    In good electrical conductors a large number of free electrons move about in the lattice structure

    of the material. They carry thermal energy from a high temperature region to a low temperature

    region. Energy may also be transmitted as vibrational energy in the lattice structure of the

    material. In general, this latter mode of transfer is not as large as the electron transport. With

    increase in the temperature, however the increased lattice vibration come in the way of the

    transport by free electrons and for most of the pure metals the thermal conductivity decreases

    with increase in temperature.

    Apparatus Description:

    The experimental set up consists of metal bar, one end of which is heated by an electric heater

    while the other end of the bar projects inside the cooling water jacket. The middle portion of the

    bar is surrounded by cylindrical shell filled with asbestos magnesia insulating powder. The

    temperature of the bar is measured at different sections (figure1) from 1 to 7 while the radial

    temperature distribution is measured by separate thermocouples at two different sections in the

    insulating shell.

    The heater is provided with a dimmerstat for controlling the heat input. Water under constant

    heat condition is circulated through the jacket and its flow rate and temperature rise is noted.

    Procedure:

    Start the electric supply. Adjust the room temperature in the temperature indicator by means of

    rotating knob, for compensation of the temperature equal to the room temperature (normally this

    is readjusted). Give input to the heater by slowly rotating the dimmerstat and adjust it