Efficiency and Effectiveness of Fins in Natural and Forced Convection

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BACKGROUND

Fins are the extended surfaces that are used to raise the heat transfer rate by means of an increase in convection to or from the environment. The fins broaden the surface area and thus provides an economical and efficient solution of heat transfer problems in both natural and forced convection. The efficiency of a fin is the ratio of actual heat transfer from the fin surface to the heat dissipated if the whole surface is maintained at its best temperature.¹

i.e, h_fin = Actual heat transferred by the fin (Q_fin)/ Maximum heat transferred from the whole surface (Q_max).

The concept of fin efficiency is based on the conduction along the fin and convection from or to the fin surface which causes reduction in temperature potential between the fin and the ambient fluid.² It is also known as the fin temperature effectiveness, and most of the real fins are treated as “one- dimensional (1 D)”, with standard idealisations used for analysis. This efficiency is a function of fin geometry, fin material, het transfer coefficient at the fin surface and fin tip boundary condition.³

A simple fin is used in the apparatus which is attached to a rectangular duct, and it is further connected to the suction end of a blower. An electrical heater is used to heat the one end of fin for proper heat transfer.⁴ A thermocouple is mounted over the fin length which notes the fluid duct temperature. When the top cover of the fin is opened, it is used for natural convection process, while when the top cover is closed, and the blower is opened, the process is used for forced convection.

The main objective of this experiment is to determine the efficiency and effectiveness of fins in a natural and forced convection process.

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REQUIREMENTS

Materials:   Electrical Heater

Dimmer Stat

Thermocouple

Voltmeter

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PROCEDURE

Natural convection

First of all, open the duct cover which is positioned over the fin, and then with the help of the dimmer stat, adjust the voltage to 80 V which is supplied to the heater. Note down the required readings such as manometer readings and temperatures after it reached a steady state.

Forced convection

In forced convection, first of all, close the duct cover which is positioned over the fin, and then start the blower. With the help of the dimmer stat, adjust the voltage to 100-110 V which is supplied to the heater. Note down the required readings such as manometer readings and temperatures after it reached a steady state.

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CONCLUSION

The process of finding the efficiency and effectiveness of fins in a natural and forced convection system has been discussed. With the data analysis, it has been observed that the actual temperature is slightly less than the calculated value due to the effect of thermal radiation.

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REFERENCES

1. M. M. Y. a. J. R. C. P. TEERTSTRA, “ANALYTICAL FORCED CONVECTION MODELING OF PLATE FIN HEAT SINKS,” Journal of Electronics Manufacturing, vol. 10, no. 4, pp. 253-261, 2000.
   
2. E. M. S. a. S. Acharya, “A Natural Convection Fin with a Solution-Determined Nonmonotonically Varying Heat Transfer Coefficient,” Journal of Heat Transfer, vol. 103, no. 2, pp. 218-225, 1981.
   
3. P. D. R.M. Warkhedkar, “Thermal performance of elliptical pin fin heat sink under combined natural and forced convection,” Experimental Thermal and Fluid Science, vol. 50, no. 6, pp. 61-68, 2013.
   
4. T. O. C.J. Kobus, “Development of a theoretical model for predicting the thermal performance characteristics of a vertical pin-fin array heat sink under combined forced and natural convection with impinging flow,” International Journal of Heat and Mass Transfer, vol. 48, no. 6, pp. 1053-1063, 2005.