PH1004_Experiment_6

PH1004_Experiment_6 - PH1004 Exp 6: Thermal Conductivity PH...

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PH1004 Exp 6: Thermal Conductivity 1 h T 1 T 2 PH 1004 Laboratory Instructions Experiment 6 Thermal Conductivity Introduction Heat is thermal energy, which is transferred from one place to another due to a temperature difference. In the SI system of measurement, the unit of heat is called “joule” (J). Heat can be transferred from one point to another by three common means: conduction, convection, and/or radiation. Thermal conduction is heat transport due to the interaction between ions, atoms and molecules of a substance without the transfer of ions, atoms or molecules themselves. For example, in a solid substance the atoms in the region of higher temperature have greater energy of vibration than the atoms in the region of lower temperature. In collisions with neighboring atoms, this extra energy is transferred to the atom of another region, with lower initial temperature. In the terms of thermodynamics, this energy transfer produces a heat flow from the higher temperature to the lower. Free electrons, existing in metals, aid thermal conduction. In this experiment, you will investigate the rate of thermal conduction through two transparent materials used in building construction, ordinary or silica glass and acrylic glass (Lexan). The amount of heat conducted through a slab of material, Q , is given by: ( ) h t T T A k Q = 1 2 (6-1) In this equation, A is the area through which conduction takes place, T 2 -T 1 is the temperature difference between the top and bottom surfaces of the sample, t is the time during which the conduction occurs, h is the thickness of the material and k is a coefficient, which is known as the thermal conductivity for a given material. The value of the thermal conductivity depends on the composition of the material. You can see from equation (6-1) that the unit of k in the SI system is Watt per meter-
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PH1004 Exp 6: Thermal Conductivity 2 Kelvin (W/mK). The value of k is important to designers, builders, and homeowners. To prevent heat flow between buildings and surroundings, you need to use building materials with a small thermal conductivity. The same is true for the walls of refrigerators, freezers and so on. Inversely, if you want to accelerate heat flow, for example, when heating water in a container, you should build the container with materials of high thermal conductivity. Apparatus In this experiment you will use a steam generator like that shown in Figure 6-1. Figure 6-1. Steam Generator Sample Water channel for melted ice Thermocouple wire Figure 6-2. Experimental Setup Steam chamber Drain Spout
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PH1004 Exp 6: Thermal Conductivity 3 The one-liter tank must be approximately half to three-quarter full of water. You should set the dial of the steam generator to a value above 6 to produce steam. The entire experimental apparatus is shown in Figure 6-2. It operates in the
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PH1004_Experiment_6 - PH1004 Exp 6: Thermal Conductivity PH...

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