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NIRMA UNIVERSITY INSTITUTE OF TECHNOLOGY CHEMICAL ENGINEERING DEPARTMENT LAB MANNUAL CH302- HEAT TRANSFER OPERATION

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  • NIRMA UNIVERSITY

    INSTITUTE OF TECHNOLOGY

    CHEMICAL ENGINEERING DEPARTMENT

    LAB MANNUAL CH302- HEAT TRANSFER OPERATION

  • Chemical Engineering Department Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual 2

    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. Emissivity measurement apparatus

    11. Drop wise and film wise condensation apparatus

    12. Finned tube heat exchanger

  • Chemical Engineering Department Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual 3

    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 TTALqK

    =

    +=

    c2h2

    2

    c1h1

    1

    T - TT - T2LL

    AqK

  • Chemical Engineering Department Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual 4

    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 5

    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*

    ALqK =

  • Chemical Engineering Department Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual 6

    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 to voltage equal to 80 to 120 volts. Start the cooling water supply through the jacket and adjust it about 350 cc/ minute. Go on checking the temperatures at some specified time intervals say 5 minutes and continue this till a satisfactory steady state condition is reached. Note the mass flow rate of water in kg/ min. and temperature rise in it and also note the temperature readings from 1 to 11 using temperature indicators.

  • Chemical Engineering Department Institute of Technology, Nirma University

    Heat Transfer Operation- Lab Manual 7

    Observations: 1. Length of the metal bar (total) 450 mm 2. Size of the metal bar (diameter) 38 mm 3. Test length of the bar 230 mm 4. No. of thermocouples mounted on the bar 7 5. No. of thermocouple in the insulation shell 4 6. Heater coil (band Type) Nichrome 7. Cooling Jacket Diameter 90 mm 8. Radial distance of thermocouple in insulating shell ro = 55 mm=r2

    ri = 35 mm =r1 9. Mass flow rate of water m = ___________litre/ minute ___________kg/ minute 10. Inlet temperature of water Ti = ___________0C 11. Outlet temperature of water To= ___________0C

    Observation Table:

    Sr. No: V ( volt ) I ( amp )