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che309-H1 report - Abstract This report discuses heat...

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Abstract: This report discuses heat transfer by conduction in four different units which are: unit #1, unit #2, unit #3, and unit #4. In this experiment we study unit #4 twice: 1. Unit #4a, where the power input was about 750 watts 2. Unit #4b, where the power input was reduced to half of that used in unit #4a. Our objective in this experiment is to calculate the mass flow rate of water and thus the rate of heat transfer for each unit can be also calculated, and to find the barrier resistance between different joint metals. This was achieved by heating one end of the conducting bar. Water was passed over the bar and its incoming and leaving temperature was recorded. For example, the flow rate at which heat transfer in all units ware: 10.500 W - for unit 1 18.906 W - for unit 2 26.679 W - for unit 3 185.35 W - for unit 4a 72.926 W - for unit 4b The % of error results from comparing Q exp. and Q ther . In units # (3, 4a,4b) were : 4.30 % - for unit 3 1.01 % - for unit 4a 0.615 % - for unit 4b In unit # [1 and 2 ], the barrier resistance were as follows: For the 2-in barrier the result was: 1.428 C.s/K in unit 1 1.111 C.s/K in unit 2 For the 9.75-in barrier the result was: 0.381 C.s/K in unit 1 0.158 C.s/K in unit 2 1
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Introduction: Heat transfer occurs in three ways: either by conduction, convection or radiation. Heat transfer by conduction is the best done in solid where the thermal conductivity is high. When a temperature gradient exists in a body , experience has shown that there is an energy transfer from the high temperature region to the low temperature region. So, heat moves from the higher temperature to the lower temperature object. Heat transfer by conduction when temperature gradient exist in the body, and in this case heat transfer from the place where the temperature is higher. It results from molecular interaction between adjacent molecules. Also , there I another mechanism which is caused free electron which occur in free metallic solid Material differs in their ability to conduct heat due to their differences in their thermal conductites. As the thermal conductivity increases, the ability of each material to conduct heat increases as well. However, energy transfer by conduction is accomplished in tow ways. The first mechanism is heat of moleculear interaction, in which the grater motion of a molecule at a higher energy level (temperature) imimpart energy to adjacent molecules at lower energy level. Theoretical Background: The process of heat transfer by conduction is described by Fourier’s low: Where K is the thermal conductivity , aphysical properrty of the conducting material.for many practical appliaction it is considered a constant. However in case ofsolid , K is pften assumed to change lineraly with Temperature. 2 dx dT AK q x - = ) 1 ( 0 T K K β + =
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Where K 0 is the thermal conductivity at a reference temerature, and B is a propertey of the conducting material.
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