Numerical Simulation And Experimental Study About Endothermic Reaction Applied To High Heat Flux Heat Dissipation

With the development of new high-techs, occasions due to high and even ultra high heatflux appear. So heat dissipation problem due to high heat flux becomes more and moreimportant. Some mature forced cooling methods at present which are based on physical heatsink, including forced air cooling, water phase change, pool boiling, spray cooling,micro-channel cooling and micro-jet array cooling et al., are limited by latent heat ofvaporization of working medium and can’t satisfy the heat dissipation requirements ofextreme physical situations due to high heat flux, such as super high temperature reactionkettle, super high temperature gas turbine engine, super mach number propeller, high powerlaser pump and so on.Therefore, since the1960s, the United States has into practice the study of chemical heatsink application as cooling method, many studies focused on how to make the chemicalendothermic reaction applied to heat-dissipation problem. For example, the reaction ofethanol dehydration to ethylene is an endothermic reaction with good thermal effect, in thepreparation of ethylene, by using the adiabatic tube reactor, heat could be removed from thereactor with the endothermic reaction, while coke formation is avoided; endothermicrecombination reaction of methane has been applied to internal cooling of gas turbine blade.With the study of large mach-number air vehicle, chemical heat sink has irreplaceable statuscompared with common methods. But most chemical heat sink methods focus on long-chainhydrocarbon fuel which is endothermic for decomposition of composite chain, so it is limitedto apply to other occasions. The study of chemical endothermic reaction starts pretty late, thestudy field is narrow. The theoretical study of instantaneous heat dissipation due to high heatflux don’t go deep, the problem of heat transfer time control is hardly ever involved and needtheoretical exploration and study from heat transfer aspect.Against above problems, a chemical/phase change compound heat dissipation method,which uses activated carbon powder and carbon dioxide hydrate as cooling materials,removes heat with chemical heat sink promptly, is put forward in this thesis. In this method,heat will be removed by3steps: gasification decomposition of carbon dioxide hydrate; phasechange of mixture and temperature rise to reaction point; the endothermic reactions of C-CO2and C-H2O (g). Among these, heat removed by the two endothermic reactions is the main partin all. From theoretical calculation, heat removed by per mole carbon dioxide hydrate is about10times than that of water phase change. In addition, CO and H2, the products, could be usedas high calorific value fuel for cycle, which is equivalent to transfer energy from one medium to the other and provides conditions for energy cycle, at the same time, for the controllabilityof reaction time, the problem of instantaneous heat removal will be solved fundamentally.The thesis combines theoretical calculation, numerical simulation and experimentalverification, focuses on the study of C-CO2endothermic reaction. The theoretical calculationresults indicate that heat dissipation potential of C-CO2endothermic reaction is far larger thanthat of water phase change, in the meantime, the reaction is very quick, the reaction timecould reach one percent second level at a certain temperature (about1400K). The numericalsimulation of applying C-CO2endothermic reaction for heat removal under high heat flux isperformed, the result is in accordance with that of theoretical calculation, which explains thevalidity. The results of numerical simulation of high temperature substrate spray cooling show:when CO2rate is certain, surface temperature of heat substrate reduces with the increase ofcarbon powder spray rate; when carbon powder spray rate is certain, surface temperature ofheat substrate reduces with the reduce of CO2rate. A spray cooling experimental platform isdesigned to verify the feasibility of applying C-CO2endothermic reaction for heat removal inreality. The experiment results show that, by using this endothermic reaction for heat removalunder high temperature, the purpose of heat removal largely and promptly can be achieved.