Analysis and testing of a silicon intrinsic-point heater in a micropropulsion application

Abstract

Efficient heating of a fluid is demonstrated using a novel heat exchanger in which bulk silicon forms both the heater structure and the resistive heating elements. Current passed through the heater raises the temperature of the heater fins and this energy is transferred to a fluid flowing between adjacent fins. By exploiting the change in sign of the temperature coefficient of resistivity of the heavily doped silicon, the temperature of the system is stably maintained at the intrinsic point. A heat exchanger of this nature is integrated with a nozzle, resulting in a microthruster with elevated chamber temperature, which greatly improves the specific impulse, or thrust per unit weight flow of propellant. A numerical model is presented to optimize the heater design. Benchtop tests demonstrate the inherent stability of the intrinsic point heater design, while thrust tests demonstrate the improved fuel economy of the micropropulsion system.