Additively manufactured vaporizing liquid microthruster with micro pin fins for enhanced heat transfer

Vaporizing liquid microthruster is a relatively new concept for evaporation based propulsive system. The research interest in vaporizing liquid microthruster mainly comes from its simplicity and the use of green propellant: water. This paper presents the study of a highly compact additively manufactured vaporizing liquid microthruster of 38 × 22 × 8 mm in dimension. The heat transfer enhancement effect of micro pin fins for vaporizing process has been investigated using modeling and computational fluid dynamics simulation, followed by experiments to validate the results. It has been shown that all micro pin fins (square, diamond, circular) with different array arrangements (staggered and inline) can enhance heat transfer. Square shaped pin fin exhibited the best heat enhancement performance with an increase in dimensionless total thermal resistance of 14.65% (as compared to blank vaporizing liquid microthruster) due to its large contacting area, while the circular shape was least effective. Meanwhile, the inline arrangement was found to induce a significant fluctuation in transverse flow velocity between the columns, which promotes heat convection. The vaporizing liquid microthruster prototype was produced using a specialty resin of good heat resistance up to 350 °C as confirmed by the thermogravimetric analysis. Thrust performance of the prototype was measured using a torsional thrust stand in a vacuum chamber. The vaporizing liquid microthruster with square micro pin fins and in inline configuration has produced the highest thrust of 740.2 μN at 2 μl/s flow rate, giving a specific impulse of 37.7s. The developed prototype could be implemented as micropropulsion system for nanosatellites, such as CubeSat and PocketQube.