An experimental investigation of heat transfer to hydrogen peroxide in microtubes

Abstract

Because of its strong oxidizing properties, high density, low-toxicity and environmentally friendly decomposition products, concentrated hydrogen peroxide has regained popularity as a propellant in many rocket applications. The MEMS-based MIT micro-rocket engine is one such application where 98% liquid hydrogen peroxide and JP7 are proposed as a propellant combination. Like other micro-thrusters concepts, the MIT micro-rocket engine uses its propellants to regeneratively cool the combustion chamber and the nozzle. Although JP7 has been proven to be an effective coolant under such conditions, hydrogen peroxide becomes unstable at high temperature and may explode, thus adding a critical constraint to the cooling scheme. To address this issue, heat transfer experiments in 95 [mu]m inside diameter, 4 mm long, electrically heated stainless steel microtubes have been performed to define the stability limit and explosion condition associated with 98% hydrogen peroxide thermal decomposition. Conditions such as pressures, temperatures, heat fluxes and length scale found in the engine were replicated. Tests were conducted whereby heat transfer to the hydrogen peroxide was increased until an explosion occurred. For each test, prior to the explosion, an experimental forced convective heat transfer coefficient has been obtained and compared to standard empirical correlations. Experimental results indicate that 98% hydrogen peroxide has limited cooling capacity for a regeneratively-cooled rocket engine. Independent of pressure and mass flow, results show that a local fluid temperature of approximately 150⁰C consistently yields an explosion in stainless steel microtubes. In addition, standard macro-scale heat transfer correlations were found to significantly

(cont.) underestimate the heat transfer rates obtained experimentally. Instead, a correlation developed for forced convective heat transfer in microtubes is presented and provides a more accurate estimate.