M. Kevin Drost

Measurement and use of bi-directional reflectance

Bi-directional reflectance is a fundamental surface property that has received a great deal of attention, particularly during the early years of the space program. Although the value of using accurate surface property data has always been recognized, bi-directional reflectance information is rarely used because of the sheer volume of data involved. Now, with powerful workstations readily available, large Monte Carlo codes can be run very quickly and full advantage can be taken of the detailed surface property description provided by bi-directional reflectance data. This paper provides a detailed description of a simple, compact, flexible apparatus for measuring bi-directional reflectance and a review of measurement considerations.

Monte Carlo simulation of radiative heat transfer in arrays of fixed discrete surfaces using cell-to-cell photon transport

An accurate simulation of radiative heat transfer in arrays of fixed discrete surfaces is challenging because of the complicated geometries that can shade and block many surfaces. This paper presents an innovative Monte Carlo scheme using cell-to-cell photon transport developed to simulate monochromatic radiation impinging on an array of fixed discrete elements. Results of the study show that cell-to-cell photon transport is an efficient method of simulating radiation heat transfer in complicated geometries. Sample calculations demonstrate the dependence of radiation heat transfer in the array on the geometry of the array elements.

Miniaturization Technologies for Advanced Energy Conversion and Transfer Systems

Microfabricationtechnologieshavemadepossiblethedevelopmentofmeso-scaleenergyconversionandchemical processing systems with microscale features. Scaling effects, such as the linear increase in surface-area-to-volume ratio that affects surface processes such as convection heat transfer, adsorption, and catalytic chemical conversion processes, provide some of the motivation for the miniaturization efforts. Other mechanical, thermal, and e uid scaling effects are presented. Fabrication and material limitations, as well as scaling effects, must be considered in the design process and may result in miniaturized systems that are considerably different than their full-scale prototypes. System and component development efforts at Battelle Pacie c Northwest National Laboratories are highlighted. A fuel atomizer for gas turbine engines and a multicomponent fuel processor for the production of on-demand hydrogen are microscale components that show potential for improving current large-scale systems. Complete miniaturized systems such as a gas turbine, a vapor-absorption heat pump, and a Joule ‐Thompson cryocooler could be used for mobile power production and cooling of electronics and individuals. Components for miniaturized systems include microbatteries with multiple dee nable voltage levels and a high degree of integratability and a combustor/evaporator for methane combustion with low levels of harmful emissions.

Recent Developments in Microtechnology-Based Chemical Heat Pumps

Pacific Northwest National Laboratory (PNNL) has an ongoing program focused on the development of compact chemical heat pumps based on the absorption cycle. Design and laboratory data suggest that, by taking advantage of the high rates of heat and mass transfer available in microstructures, we are able to radically reduce the size of a heat-actuated heat pump based on the absorption cycle. Current estimates suggest a size reduction of a factor of 60 compared with a conventional heat pump. High performance is achieved by using microchannel combustor technology, microchannel heat exchangers and ultra-thin-film micromachined contactors. Currently all of the components of the system have been demonstrated and PNNL is assembling a complete bench-scale version of the device. Successful development of this technology will enable a new class of compact, heat-actuated space conditioning systems that can be used for portable or distributed heating and cooling.

Process Intensification Through Miniaturization of Chemical and Thermal Systems in the 21st Century

The 21st century holds great promise for development of Micro Chemical and Thermal Systems (MICRO-CATS™). The quest for miniaturization will lead to greater process intensification. Miniaturization greatly reduces the resistances to heat and mass transfer. When heat and mass transfer rates are increased by orders of magnitude, revolutionary changes occur in technology.