Determination of Heat Transfer Coefficient in Forced Convention

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BACKGROUND

Convection is the process of heat transfer using the movement of fluids.1 In forced convection, externally induced flow is used for heat transfer. The fluid is forced to pump via external means, such as a pump or a fan over a surface or in a tube in such methods to increase the rate of heat transfer.

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Creating a forced convention is not a difficult task. This method is used in the ventilation system where the blower is used to push the heated air into the furnace through the house. The Nusselt number depends on the rate of heat transfer through a thermal body layer from a surface hotter or colder than air passing over it. Forced convection is caused by the dynamic flow (wind) only which corresponds to the turbulent movement.2

The heat transfer rate for a convection process is given by:

q = -h*A (Ts-Ta)

where      h= convection coefficient

A= Surface Area

Ts= Surface Temperature

Ta= Ambient Temperature3

The prime objective of this experiment is to determine the heat transfer coefficient in a forced convection process.

REQUIREMENTS

Materials:   

Test Pipe (33mm inner dia., 500mm long )

Band Heater

Thermocouple (Chromel/Alumel)

Ammeter (0-2 A)

Voltmeter (0-200 V)

Dimmer Stat (2A, 240V)

Orifice Meter with the water manometer

PROCEDURE

First of all switch ON the main supply, and adjust the input to the heater through a dimmer stat. Now, check the air flow with the valve after starting the boiler, and if needed adjust the blower accordingly. Keep waiting until the steady state is achieved, and after this take note of all the readings from the temperature T1 to T7. Note down the surrounding temperature in your notebook. Now, calculate the heat transfer coefficient with proper equations.

Determination of Heat Transfer Coefficient in Forced Convention

CONCLUSION

The method of determining the heat transfer coefficient through forced convection has been studied. Try to operate all the controls in a gentle manner, and do not obstruct the flow of air during the experiment.

REFERENCES

  1. Bejan, Convection Heat Transfer, Wiley.
  2. W. M. R. A. E. Bergles, “The Determination of Forced-Convection Surface-Boiling Heat Transfer,” Journal of Heat Transfer, vol. 86, no. 3, pp. 365-372, 1963.
  3. R. J. G. T. H. Kuehn, “An experimental and theoretical study of natural convection in the annulus between horizontal concentric cylinders,” Journal of Fluid Mechanics, vol. 74, no. 4, pp. 695-719, 1976.

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