In the present study, a direct simulation Monte Carlo solver is utilized to simulate the effects of heater plates on the performance parameters of microelectromechanical propulsion devices. The simulation is two dimensional. Proper cell dimensions, number of particles per cell, and grid study are used to guarantee the accuracy of simulations. Three types of microthrusters including cold gas as type 1, a propulsion device with heaters in the walls as type 2, and a microthruster with heater plates inside the domain as type 3 are studied. Type 1 is considered as a reference case and two other types are compared with type 1. It is observed that heater plates inside the microelectromechanical thruster enhance the downstream temperature due to conversion of pressure drop occurred by plates into temperature. In type 3, the specific impulse is enhanced but the thrust force is decreased in comparison with type 1. Heating the walls in type 2 accelerates the flow while there is no considerable pressure reduction. Moreover, all performance parameters are increased in this type. It is also demonstrated that increasing of wall temperature increases thrust and specific impulse and decreases the sensitivity of thruster due to rarefaction effects.

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In the current paper, downstream flow field of a propeller at low Reynolds numbers and at static conditions (zero flight speed) is investigated experimentally. This propeller can be utilized in UAVs. Propeller diameter is 56 centimeter and it is investigated at 2550 to 5670 rpm experimentally. Experiment results show that propeller rpm increasing, increases induction velocity. Flow swirl ratio and axial flow coefficient decrease along propeller radius at different propeller rpm. Experimental results of absolute velocity of swirl flow at the propeller airfoil trailing edge downstream is fairly similar to the free vortex flow theory at static condition along the blade radius. At static condition for r/R<0.8, semi-empirical equations are suggested for variation of flow swirl ratio and axial flow coefficient at downstream of propeller. The propeller is also simulated with numerical simulations. Relative standard deviation of numerical and experimental results for propeller thrust and power are 0.4 and 4.1, respectively. The exponential coefficient (n) which predicts numerical axial flow downstream of propeller for r/R<0.8 has a 7.7 relative standard deviation with experimental results at static condition.

In the present paper, effects of pre-heated walls/plates on microthrusters performance are studied using a DSMC/NS solver. Three microthruster configuration types are studied. Type 1 is a cold gas microthrster. Microthruster type 2 has pre-heated walls. Pre-heated plates are inserted inside the chamber of microthruster type 3. It is observed that in microthruster type 2 the flow is accelerated and the specific impulse is elevated. However, by insertion of the pre-heated plates in microthruster type 3, viscous effects have stronger negative influence and the thrust is decreased. By implementing temperature gradients on walls in type 2 and on plates in type 3, it is observed that a higher temperature gradient enhances performance parameters of microthruters. Among all types of microthrusters, microthruster type 2 with pre-heated walls has the highest thrust and specific impulse. Microthruster type 3 with a temperature gradient of 300-500 K has the minimum thrust due to a considerable decrease in the mass flow rate.