Analysis of Close Contact Melting

This report presents a numerical transient analysis of Close Contact Melting (CCM), intended to help in accurate prediction of melt rate and interface configuration, which is to be utilized for a prospective frozen propellant based propulsion system. Three different substrate shapes namely- Flat, Cylindrical and Wedge, are chosen for the study. The domain discretization is based on generation of boundary fitted mesh and the time varying physical domain is transformed to a fixed computational domain, wherein the associated governing equations are solved. Apart from the conventional linear system solvers, an algebraic multigrid based solver is implemented. A non-iterative implicit/explicit melt interface tracking method is utilized, for determining the interface position at increasing time points. The problem is studied on materials of three different Prandlt number, in order to understand the advective and convective effects. Both Dirichlet and Neumann boundary conditions are utilized for the study. A seperate analytical analysis is conducted for the steady state solutions, for all the three different substrate shapes. For high Prandlt number materials, the steady state solution obtained as a limit of the transient analysis compares well with the simplified analytical solution, for all the substrate conditions. For low Prandlt number materials, the advective effects are to be included to get an accurate prediction of melt parameters. Accordingly, a closed form solution for a simplified system of momentum equations, including the transverse advective effects, is developed for flat plate substrate. For the cylindrical and wedge shaped substrate, a simplified iterative procedure is developed for accurate prediction of the melt parameters, with the inclusion of the advective effects. The steady state solution of low Prandlt number material based on the above procedure, has a close agreement to the steady state solution obtained as a limit of the numerical transient analysis. Even for a transient analysis (with no expected steady state), which includes the effect of undercooling in the solid phase, it is observed that the melt rates reach a quasi steady state. By the inclusion of gradients from the solid phase numerical results, in the interfacial heat balance, it is observed that the steady solution, at a particular time point, obtained by a simplified procedure has a good agreement to the results of a complete transient analysis. A separate parametric data fitting is carried out for the numerical results corresponding to the tested input values

Search full text options here 1 of 6 Droplet Evaporation-Based Approach for Microliter Fuel Property Measurements

Small-volume, high-throughput screening techniques are sought to enable downselection from a large candidate pool of bio-blendstocks to a select few, having physical properties consistent with requirements of downsized, turbo-boosted internal combustion engines. This work presents a droplet evaporation-based approach to predict heat of vaporization, vapor pressure, diffusion coefficient, and Lennard-Jones parameters for an unknown fuel. Two different schemes, considering the isothermal evaporation of a moving droplet in ambient air, are proposed, which combine droplet velocity and temperature measurements, with some known properties to predict unknown properties. The schemes utilize an inverse solution of a transient model of droplet evaporation solved in an iterative fashion. A baseline scheme, which only requires droplet size change measurements, is evaluated using test data for three liquid fuels, comprising of alkanes and alcohols, as obtained in a temperature-controlled chamber. Results yield temperature-dependent heat of vaporization and vapor pressure predictions within 10 % and 22 %, respectively, of reference values. The advanced scheme, which additionally requires droplet temperature measurement, is numerically evaluated in the current work and will be experimentally validated in future efforts. The advanced scheme is found to significantly improve prediction quality, with deviations less than 2 % and 1 % for heat of vaporization and vapor pressure, while also predicting diffusion coefficient and Lennard-Jones parameters within 5 % and 8 %, respectively. The combined set of approaches, which primarily track droplet evaporation, can be incorporated into a small-volume, high-throughput fuel screening process