STUDY OF THE REACTION RATE OF MH_High (MHTAL HYDRIDE: Ti_0.18Zr_0.84Cr_1.0Fe_0.7Mn_0.3Cu_0.057) TO BE USED FOR COMPACT MH REFRIGERAION SYSTEMS

Our purpose is to develop the compact MH refrigeration system for the vending machine and the show case, and to attain a refrigeration temperature of 243 K by using a heat source of about 423K. The reaction rate of the MH to use for the heat source, MH_High is studied first though the MH refrigeration system consists of two MHs, one is used for the heat source and the other is used for the cooling load extracting. As for the reaction rate in the hydriding process, initially, a rapid surface reaction, governed by the relation 1−(1−F)^1/3 =k_ht. After the MH surface has been covered by hydride, the reaction becomes diffusion controlled with the relation 1−3(1−F')^2/3 +2(1−F') = k'_h t. The reaction rates, k_h, k'_h are exponentially proportional to the pressure difference and increase with temperature. And, As for the dehydriding process, it is found out that the rate-controlling step is uniquely diffusion reaction. The dehydriding reaction rate is exponentially proportional to the pressure difference and the initial reacted fraction, and increases with temperature. Finally, on the basis of these experimental results, the brand new rate correlations are reasonably derived. The calculated results are in agreement with the experimental ones.