2016 年 82 巻 844 号 p. 16-00232
This paper presents an experimental and analytical investigation of the thermal characteristics in a layer of exothermic powder mixture that is utilized in body warmers, hot compresses, thermotherapy, etc. The research objective is to develop a manufacturing method that enables the exothermic temperature to be controlled in order to prevent cases of low-temperature burns. The exothermic powder mixture generally comprises metal powder, catalyst powder, and vermiculite particle absorbing some saline solution. The exothermic powder mixture is put into a mini-autoclave, and then placed in a constant temperature bath after the atmosphere inside the mini-autoclave has been replaced with pure oxygen. The degradation of oxygen pressure inside the mini-autoclave shows that the reaction rate of corrosion depends on the reaction temperature, the volume of the saline solution, and the conversion of iron powder into oxide, in addition to the ambient oxygen concentration; a correlation is suggested for the reaction rate. The variation over time of the temperature distribution in a layer of the exothermic powder mixture is evaluated analytically using this empirical correlation for the reaction rate, and compared with the experimental results. In the analysis, the mass, momentum, energy and oxygen component equations are solved numerically for a layer of the exothermic powder mixture, which is regarded as a porous medium. The analysis does not predict the temperature distribution accurately, but the analytical and experimental results are in accordance qualitatively.
