Richard N. Smith

Mushy zone modeling with microstructural coarsening kinetics

A key element of mushy zone modeling is the description of the microscopic evolution of the lengthscales within the mushy zone and the influence of macroscopic transport processes. This article describes some recent progress in developing a mean-field statistical theory of phase coarsening in adiabatic mushy zones. The main theoretical results are (1) temporal scaling laws that indicate that the average lengthscale increases as time1/3, (2) a self-similar distribution of mushy zone lengthscales based on spherical solid particle shapes, and (3) kinetic rate constants which provide the dependences of the coarsening process on material parameters and the volume fraction of the solid phase. High precision thermal decay experiments are described which verify aspects of the theory in pure material mushy zones held under adiabatic conditions. The microscopic coarsening theory is then integrated within a simple macroscopic heat-transfer model of one-dimensional alloy solidification. The method demonstrates an ability to predict the influence of macroscopic heat transfer on the evolution of primary and secondary dendrite arm spacings in Al-Cu alloys.

Development of a required international experience for undergraduate engineering students

The School of Engineering at Rensselaer has recently announced the REACH Program (Rensselaer Engineering Education Across Cultural Horizons) as a component of our undergraduate engineering degree that we envision will become a requirement for every student. The major feature of this experience will be a bilateral semester abroad with partner international universities, whereby students will spend a full semester studying abroad as a part of their educational program, and students from the partner university will likewise spend a semester at Rensselaer. The Program will begin in 2009 with approximately 25% of the then junior class growing to virtually 100% by 2015. The critical issues in developing and scaling up to such a large program of exchange will be discussed, along with the alternative international experiences that are also under development. We envision that this program will radically alter the culture of our undergraduate programs and our campus environment and will establish Rensselaer as unique among major engineering universities in terms of commitment to providing such an expansive global perspective for all of our students.

Experimental investigation of freezing inside a thick-walled cylinder

A series of experiments were performed to investigate the effects of a thick wall on the freezing process occurring inside a cylindrical container. Two cylinders with different thermal diffusivity (k/ϱc) values were compared. To isolate the effects of the wall sensible energy, experiments were run for both a subcooled wall and the wall initially at the phase change material (PCM) fusion temperature. The PCM was initially at its fusion temperature for all cases. The base of the cylinder was maintained at a constant temperature in all but one case, where the lower boundary was approximately adiabatic. At several time steps, the mass fraction solidified and the phase front profile were determined. Measurements of the base heat flux and mean cylinder temperature were also obtained as functions of time. The fraction frozen vs time curves and the shape of the phase front profiles are compared for each set of conditions. The energy content of the wall can significantly affect both results. The data are presented in such a way as to encourage comparison with numerical computations of a similar complex-boundary freezing problem.

An experimental study of waste heat recovery from a residential refrigerator

This paper describes the design, construction, and testing of an integrated heat recovery system which has been designed both to enhance the performance of a residential refrigerator and simultaneously to provide preheated water for an electric hot water heater. A commercial, indirect-heated hot water tank was retrofitted with suitable tubing to permit it to serve as a water cooled condenser for a residential refrigerator. This condenser operates in parallel with the air-cooled condenser tubing of the refrigerator so that either one or the other is active when the refrigerator is running. The refrigerator was housed in a controlled-environment chamber, and it was instrumented so that its performance could be monitored carefully in conjunction with the water pre-heating system. The system has been tested under a variety of hot water usage protocols and the resulting data set has provided significant insight into issues associated with commercial implementation of the concept.

Thermal recalescence and mushy zone coarsening in undercooled melts

Precision adiabatic recalescence experiments on both pure and binary undercooled melts have been conducted. The adiabatic constraint limits the amount of net phase transformation from the metastable under-cooled state (creating a mushy zone) and also sets bounds on the microstructural parameters of the mushy zone, namely the volume fraction of the phases, their length scales, and the interfacial compositions. As many as three distinct kinetic time scales are observed in these experiments: a short time scale (less than ∼1 s) of rapidly increasing temperature from the initial nucleation temperature, associated with the propagation of the dendrites and release of latent heat; an intermediate time scale (∼103–104 s) of slowly rising temperature, associated with coarsening of the mushy zone; and a long time scale (days) of steadily falling temperature, associated with solid-state diffusional adjustments near the solid-liquid interface.