Thermal analysis of mems-based thermoelectrically controlled micronozzle

Abstract

A new technique which implements heating upstream of the micronozzle throat and cooling downstream of the throat through the side-walls of the micronozzle is proposed. Thermoelements are used to pump heat from the cold section (supersonic) to the hot section (subsonic) of the micronozzle using Peltier effect. The proposed micronozzle is given herein the name Thermo-electrically Controlled Micronozzle (TECMN). A generalized quasi-one-dimensional model is developed to solve the flow of gaseous propellant inside the micronozzle in the presence of heat pumping from the supersonic to the subsonic through the side walls. The improvement in the efficiency due to using TECMN is verified, which is more significant for reduced divergent wall temperature and mass flow rate. The model also involves the thermoelectricity effects in the solid walls. A general energy equation of one-dimensional heat transfer in a non-uniform wall subjected to a longitudinal electrical field and lateral heat convection is developed and solved analytically for uniform wall and numerically for non-uniform walls. A set of non-dimensional parameters which affects the performance of the TECMN are identified and studied for better heat exchange with the flowing gas. It is found that the uniform TE wall performs better than non-uniform wall in heating-cooling process. The two-dimensional laminar Navier-Stokes equations are solved numerically for gas flow in a micronozzle for different thermal boundary conditions; isothermal divergent wall, uniform heating, and non-uniform heating-cooling in uniform side-walls. The non-uniform heating-cooling boundary condition is a imitation of the thermoelectric wall. It is found that heating upstream the throat always affect mass flow rate, while heating downstream the throat increases the thrust which may decrease with any mass flow reduction, however the thrust per unit mass flow and viscous losses increase always with heating. It is found that heat supply in the convergent-divergent side-wall results in enhancement of thrust level, specific impulse, mass consumption saving, and efficiency of specific impulse. Outcome of heat developing to/absorbing from a gas flowing into a convergentdivergent micronozzle for a range of Reynolds numbers below 103 is investigated assuming one-dimensional thermal analysis of a uniform side-wall. It was found that the improvement in the specific impulse efficiency increases with decreasing Reynolds number. This improvement reaches up to 9.35% at Re = 15 during the heating-cooling process through the side-walls. Heating process and heating-cooling process through the wall are more useful to improve efficiency at low Reynolds numbers below 100. This research concludes that the utilization of thermoelectricity to supply heat upstream of micronozzle throat and remove heat downstream of throat through thermoelement side walls is very useful to improve the micronozzle efficiency and reduces propellant consumption.