1. Measure the thermal conductivity Measure the thermal conductivity of silicon off-set with the stable state law School of Electronics & Applied Physics, Hefei University of Technology

2. Primary Content  The necessity of measure the thermal conductivity  The brief conduction of common measuring method  The principles and guiding idea of measuring the thermal conductivity of silica gel with stable state law  Data form and data processing

3. λ is one of important parameters that can reflect the heat conduction performance of material.Both estimate the heat characteristic of material and the design application on the material need to know the size of λ. Measuring λ and the daily life are inseparable ： The knitting underwear that can maintain warmth, the thermos, the refrigerator, the radiator, the heater, the smelting furnace, the heat insulation pipeline and the development of thick oil in oil field must consider their heat conduction degree. Therefore it is necessary to research and measure thermal conductivity 。 The application of thermal conductivity

4. Stable state law ： Forms a stable temperature distribution through the heat source in the sample interior, measure its temperature with the thermo-element, then extract the material thermal conductivity. Dynamic method ： In the testing sample the temperature distribution along with the time assumes the periodic variation and the testing time is very short. The synopsis of commonly measuring method

5. The heat conduction law result: only demand we can aquire Experimental principles

6. Must solve two actual problems ： How to create a gradient of temperature in the material and measure its value ； How to measure the speed of transfering heat from the high temperature area to the low temperature area in the material ； The dynamic change of temperature and thermal are not easy to obtain,so we design the system to achieve the stable state and begin to measure under the stable state. Stable state description A B C

7. Under stable state ： λ=λ= A B C Side + bottom surface =－=－ side ＋ bottom surface

8. In the experiment measure the temperature in stable state and the free cooling temperature with the thermo-element thermoelectromotive force t > t 0 The temperature difference is not too big To solve the problem of measuring temperatur e is not precise enough Copper Constantan

9. Experimental equipment ： Electric stove Dewar's flask (thermo couple) copper plateA rubber plateB Copper plateC switch for heating power source gating switch replacemen t timer gib screw

10. Data form 1.Calculate the mean value of D B,h B,D c,h C by form1. order 1 2 3 4 5 Mean value e(cm) h B (cm) Form 1 Note ：（ Measure the thickness and diameter of rubber plate B with vernier caliper several times,then calculate the mean value of R B and h b ）

11. 2.Calculate the value of E 10 and E 20 in the stable state by the data in Form2. E 1 (mv) E 2 (mv) Form 2 Note ：（ Read the value of E1 and E2 every two minutes.When the value of sensor Ⅰ and Ⅱ is no longer rises in ten minutes ， it means having reached the stable state ， then begin to record the value of E 10 and E 20. ） 3.Calculate the rate of cooling by method of difference with the data in Form 3. t(s) 0 30 60 90 120 150 180 210 E 2 (mv) Form 3 Note ：（ Heating copper tray C, when the temperature is 0.4mV higher than the value of E20,let it cooling natural ly again, record the value of E2 every 30 seconds. The value of each four groups can be used in the method of difference computationonly when it isin the four groups around E20. ）

12. Final measuring formula ： λ=λ= In the formula, R B is radius of the sample, h B is the height of the sample, m is the mass of the copper plate, c (0.385KJ/kg.k) is the specific heat capacity of copper, Rc and hc are the radius and thickness of the copper plate,they can be read directly.E1 and E2 are respectively the stable state voltage (temperature)of the plateB and plateC.

13. Matters for attention in the experiment ： 1 、 The reading of digital voltmeter is changing.It indicates that the cold end and hot of the thermo-element must be stained in the silicon fat and be inserted to the bottom. 2 、 When we move the copper tray and the sample after heating,we must use the glove to prevent scald. 3 、 Must make the sample and copper plate contact precisely.

14. 1Calculates the radiation speed of plateC by the method of difference. 2Measure the size of error with the relative uncertainty. The revelation by the experiment ： What is the design idea of the experiment ？ Why do we choose the value nearby stable state temperature T2 when we measure the rate of cooling ？ What is the important source of experimental error ？ The request of processing the experiment report ： 100 ％