A Heat exchanger may be defined as equipment which transfers the energy from a hot fluid to a cold fluid, with maximum rate and minimum investment and running cost. It is a very common device and widely used in our life now days. The simple definition of a heat exchanger is: A Heat Exchanger is a mechanism built for efficient heat transfer from a fluid to another, whether the fluids are divided by a solid wall so that they never mix, or the fluids are directly contacted with each other. Objective • To determine heat transfer coefficient and friction factors in a smooth tube.
• To use this information to size a simple heat exchanger. Apparatus The apparatus is a double-tube heat exchanger. • Air compressor. • A smooth tube made of copper (20mm diameter and 2m length). • A Pressure gauge (manometer) to measure the pressure drop. • A thermocouple. • A barometer to measure atmospheric pressure. Procedure • Use the barometer to read out the atmospheric pressure (mm Hg) • Switch the water system • Switch on the air blower and let the system be stable. • Measure the temperature of air at inlet and outlet.
• Measure the temperature of water at inlet and out let. • Measure the pressure drop across the tube Errors do occur even after performing an experiment with utmost care accuracy. The way the experiment was conducted and the noting of readings will have a great effect on the accuracy. The apparatus used, whether it is perfect or not and the calibration is very much important to obtain accurate results. Taking the readings of the pressure change and the temperature are the main factors which affect the accuracy of an experiment.
The constants used depend on many empirical formulae which affect the accuracy of the results. In laboratory experiments, human errors cannot be avoided. Proper care can be taken to attain accuracy but 100% perfection is impossible. These errors could happen in reading the gauges, setting up the experiments and doing the calculations. Another thing that might affect the accuracy is the materials that have been used in the lab experiment. From the calculations and the standard correlations Nusselt Number increased by increasing Reynolds number, which does not apply on the friction factor.
When increasing Reynolds Number in the calculation the friction factor increases but by the standard correlation it decreases. 16. Comment of the effect of roughening the tube on the heat transfer, pressure drop, and pumping power. Obviously, the roughening of tube does have affects on heat transfer, pressure drop and pumping power. The pressure drop increases with increase in roughening. As much as the roughening increases the pressure drop increases. And the same applies on the pumping power. Conclusion Considering the limited range of Reynolds number, specific relationships were obtained.
The range of the Reynolds number considered was 10000 to 31000. This is supposed to be a highly turbulent flow. The Nusselt number relation obtained matches that of the standard. However, the friction coefficient did not match and gave almost linear relation with Reynolds number and indicated slightly increasing value as the theoretical calculations were only for low range of Reynolds number and the considered were not of low range. More times the lab is conducted the more accurate results we get.
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