| Thermal conductivity is important thermal parameter, symbols the ability of heat exchanging. It is widely used in the designing of heat exchanger, in the choice of the working medium of the thermal processing, it is the important gist. But the parameters are little in the literatures and all though for one material there are big differences between the different literatures. So it is very important to measure the thermal conductivity soon and accurately. Now the instruments to measure the solid thermal conductivity are used in the factual working, but apparatus to measure the fluid thermal conductivity haven't appeared.This thesis aims to design one instrument to measurement of the fluid thermal conductivity by used the hot-wire method (HWM). Firstly expatiated on the theory of this method, got the academic solution by analyzing the ideal model, and then amended the ideal solution to satisfy the factual situations.For verify the test theory, we used the numerical method the simulated the instrument heat exchanging. Thus we checked the axial heat disturbing how to influence the test results, and checked the test time's influence the test result, finding the time limit to avoid the natural convection influence.Lastly we measured the distilled water thermal conductivity on the twelve temperature point, and every temperature point measured sit times. From the test results we founded that the biggest relative errors is -1.01%, the smallest relative is -0.01%, and the average relative errors is 0.47% (relative errors absolute value average). On 8℃, we measured the distilled water by using different electrical current 100 mA and 200 mA to define the electrical current influence on the result, and founded that the electrical current hasn't distinct influence on the test if the test time can be controlled out of the natural convection. And we measured the ethanol thermal conductivity. All the test results showed that the apparatus is good accuracy.
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