Interaction of superadiabatic combustion and heat conversion waves in a porous medium with incorporated metal hydride elements

A new concept of coupling combustion and metal hydride heat conversion by means of superadiabatic thermal waves in a porous medium is suggested and investigated analytically and numerically. As an example of the concept implementation, the heat conversion cycle in a two-channel porous medium with metal hydride pairs incorporated in it is considered. The heat conversion is initiated by a superadiabatic combustion of extremely lean gaseous mixture and develops as a series of thermal waves induced by positive and negative heat sources corresponding to charge and discharge stages of metal hydride cycle. It is shown that the thermal effectiveness of heat conversion in a porous medium is provided by heat recirculation mechanism, similar to the superadiabatic effect of the lean fuel combustion. To analyze the concept and its effectiveness, two methods have been employed: (1) analytical study of possible quasi-steady-state structures of the coupled thermal waves and (2) numerical modeling of their dynamic interaction. It is demonstrated that the minimal temperature in the superadiabatic refrigerating wave and the maximal temperature in a combustion wave are attained when both of these waves move synchronously with the free thermal wave generated by convective heat transfer in the porous medium, that is, under the thermal resonance conditions. Modeling has revealed that the superadiabatic combustion wave with the maximal temperature ≈1000 °C (the adiabatic effect of the lean mixture is 100 K) can induce the refrigerating wave with the temperature down to −100 °C (the adiabatic effect of hydrogen phase transition in the porous medium is −20 K).