Non-steady-state Method To Measure The Thermal Conductivity Of Poor Conductor

Thermal conductivity is defined to represent the conductibility of material. It is a kind of thermo-physical properties which need to be measured in many cases. Steady state methods and transient methods are two different measure methods according to thermo-current state. Transient methods have following advantages: consuming short time, high precision, wide ranges of temperature and measuring scale. Therefore, transient methods are developed quickly in resent years.Since time and output voltage of temperature sensor must be repetitiously recorded, using conventional instruments to measure thermal conductivity is a tough task and can not be generalized. In case of measuring poor conductor using hot-wire method, temperature climbing time is only a few seconds, so it is difficult to measure temperature and time simultaneously and precisely and bring more distinct error. Thus conventional instrumentalities need to be improved.After expatiating principles, the paper presents characteristics and applications of different methods in measuring thermal conductivity and discusses hot-wire method in depth. Mathematical model is established and solution of which is accomplished. Measuring formula is subsequently inferred. A few influencing factors on measuring result are also debated.Measuring principles of temperature, thermo-current density and time, circuit diagrams and its performance are both offered in the article. Finally a archetypal specimen machine based on hot-wired method is developed. The equipment uses C8051F040, a high performance MCU as its kernel component. It consists of the following seven parts: MCU and its peripheries, material container, measurement module of temperature, measurement module of thermo-current density, regulating module of hot-wire power, human-machine interfaces module and communication module. High exact electronical elements and advanced measuring arithmetic are used to guarantee the unitary precision of the measuring system. The software consists of two parts: software on the side of MCU and PC. The former fulfills control of measuring course whereas the latter one performs storage, management and print of the result data.The article then presents the process of software exploitation of the measure system in detail. Flow charts of apiece part of the system are offered and some source code based on C language is given in appendix.Several experimentations undertaken by the equipment are given at the tail of the article. The experimental subjects are three poor conductors: dry atmosphere, granule sands and dry cement. The laboratorial condition is in normal temperature and normal air pressure. Experimental data show that the equipment reaches absolute precision of 5 percent, as well as repetitious precision. If used to measure thermal conductivity of solid and liquid material, it can bring out high coherence result. In comparison with conventional instrumentalities proposed in literature [34], measuring precision is more improved and measuring process is made more convenient. Since the sample is slightly affected, the equipment reaches really crossing-over measurement.The theoretical and experimental study of the dissertation provides a systematic and applied approach to intellectualize and generalize hot-wire technique in measuring thermal conductivity, which has some referenced worthiness.