How to choose insulation materials for IVD reagent cold chain (1) A formula that must be recognized In vitro diagnostic reagents have strict requirements for production, transportation and storage. How to choose insulation materials for IVD reagent cold chain packaging, we must first understand the Fourier equation: Q=KA△T/d, R=A△T/Q Q: heat, W; K: thermal conductivity, W/mk; A: contact area; d: heat transfer distance; △T: temperature difference; R: thermal resistance value (2) Correct understanding of thermal conductivity Unprofessional solutions will focus on the thermal conductivity of the material; professional solutions will focus on the thermal resistance of the material. K is an inherent performance parameter of the material itself and is used to describe the thermal conductivity of the material. This property has nothing to do with the size, shape and thickness of the material itself, but only with the composition of the material itself. Therefore, the thermal conductivity of the same materials is the same, and will not change because of the different thickness. Combine the above two formulas to get K=d/R. Since the K value is constant, it can be seen that the thermal resistance R value is proportional to the material thickness d. In other words, the thicker the material, the greater the thermal resistance. However, if you look closely at some materials of thermal conductive materials, you will find that the thermal resistance value R of many thermal conductive materials is not completely proportional to the thickness d. This is because The thermal material is not a single component, and there will be a nonlinear change. As the thickness increases, the thermal resistance value will increase, but it is not necessarily a linear relationship that is completely proportional, and may be a steeper curve relationship. According to R=A△T/Q This formula, in theory, can test and calculate the thermal resistance value R of a material. But this formula is only a basic idealized formula. The condition is that the contact surface is completely smooth and flat, and all the heat passes through the material through heat conduction and reaches the other end. Actually this is an impossible condition. Therefore, the thermal resistance value tested and calculated is not completely the thermal resistance value of the material itself, and should be: the thermal resistance value of the material itself + the thermal resistance value of the contact surface. Because of the flatness, smoothness or roughness of the contact surface and the different pressures of the mounting and fastening, different contact surface thermal resistance values ​​are generated, and different total thermal resistance values ​​are also obtained. (3) Test method of thermal resistance The international popularization will recognize the setting of a standard test method and condition, which is ASTM D5470. This test method will indicate how much contact area A, how much heat value Q, and the amount of pressure applied to the contact surface when the thermal resistance test is performed. Everyone uses the same method to test different materials, and the results are comparable. The thermal resistance R value obtained by the test is not completely the true thermal resistance value. The physical science is like this. Many parameters cannot be truly quantified, just a "fuzzy" mathematical concept. Through such "fuzzy" data, One can quantify some of the data for practical use. The term "fuzzy" as used herein is a mathematical term, and "fuzzy" means the closest approximation to reality. For the same reason, according to the thermal resistance value and the thickness, the calculated thermal conductivity K value is not completely the true thermal conductivity value. (4) Suggestions on the design of temperature control packaging to users The Fourier equation is a completely idealized formula. We can use it to understand the principle of thermal materials. However, the practical application and thermal resistance calculation are complex mathematical models, and there are many correction formulas to improve the problems that may occur in all links. Yuanda recommends: a. The same material, the thermal conductivity is a constant value, and the thermal resistance value will vary with thickness. b. The same material, the greater the thickness, can be easily understood as the more heat travels through the material, the more time it takes, and the less effective it is. c. For thermal materials, the choice of proper thermal conductivity and thickness is highly dependent on performance. Choose a material with a high thermal conductivity, but the thickness is very large, too Performance is not good enough. The most ideal choice is: high thermal conductivity, thin thickness, perfect contact pressure to ensure the best interface contact. d. What kind of thermal conductive material is used for the customer is theoretically a very difficult thing. It is difficult to accurately calculate which material is suitable by using some simple data. More depends on testing and comparison, as well as experience. Testing is the most suitable material to achieve the desired results. This article was compiled and uploaded by Shenzhen Yuanda Innovation Technology Co., Ltd., which is used to advocate passive temperature control packaging, industry technology exchange and user training. 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