Improved design methodology for the development of electrically actuated MEMS structures

A comprehensive design flow is proposed for the design of Micro Electro Mechanical Systems that are fabricated using SOIMUMPs process. Many of the designers typically do not model the temperature dependency of electrical conductivity, thermal conductivity and convection coefficient, as it is very cumbersome to create/incorporate the same in the existing FEM simulators. Capturing these dependencies is very critical particularly for structures that are electrically actuated. Lookup tables that capture the temperature dependency of electrical conductivity, thermal conductivity and convection coefficient are created. These look up tables are taken as inputs for a commercially available FEM simulator to model the semiconductor behavior. It is demonstrated that when temperature dependency for all the above mentioned parameters is not captured, then the error in estimation of the maximum temperature (for a given structure) could be as high as 30%. Error in the estimated resistance value under the same conditions is as high as 40%. When temperature dependency of the above mentioned parameters is considered then error w.r.t the measured values is less than 5%. It is evident that error in temperature estimates leads to erroneous results from mechanical simulations as well.

Experimental studies on evaporation of fuel droplets under forced convection using spray in crossflow methodology

Experimental data on evaporation of droplets of decane, Jet-A1, and Jet-A1 surrogate are generated using a spray in crossflow configuration. The advantage of a crossflow configuration is that it enables us to study droplet evaporation under forced convective conditions involving droplet diameters of size relevant in practical combustors. Specifically, spray from an airblast atomizer is injected into a preheated crossflow of air and the resulting spray is characterized in terms of spray structure along with droplet size and velocity. An existing correlation for the spray trajectory is modified to incorporate the effect of elevated temperature, and is found to be in good agreement with the experimental data. Droplet sizes and velocities are measured at different locations along the crossflow direction to assess droplet evaporation. Specifically, droplets having size less than 25-mu m are selected for further analysis since these droplets are observed to exhibit velocities which are aligned with the crossflow. By comparing the droplet diameter profiles at upstream and downstream locations, the evaporation constant k for the d(2)-law is obtained iteratively. To assess the efficacy of the values of k obtained, the calculated droplet size distribution using the proposed k values at the downstream location is compared with the measured droplet size distribution at that location. A reasonably good match is found for all the three liquids confirming the validity of the analysis. (C) 2015 Elsevier Ltd. All rights reserved.