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Isothermalization of satellite panels contributes positively to system thermal performance. Although technology innovations provide one solution path, an alternative method that has not received much attention is simply optimized component placement. The present approach provides a fast method for determining optimized component placement over a rectangular surface that approaches a uniform distribution of heat flux. The approach presented in this paper is especially useful in situations in which limited or no thermophysical properties and/or environmental conditions are readily available. The resulting methodology can be used in a variety of industries, including microelectronics and satellite development. A companion Technical Note (Hengeveld, D., Braun, J., Groll, E., and Williams, A., "Optimal Distribution of Electronic Components to Balance Environmental Fluxes," Journal of Spacecraft and Rockets, Vol. 484, 2011, pp. 694-697. doi:10.2514/1.51063) addresses the problem of distributing individual components to individual panels of a satellite. When combined, the two methodologies provide an overall approach for minimizing temperature distribution across an entire satellite structure. [ABSTRACT FROM AUTHOR]

The article presents a study about achieving a balance distribution of heat flux in a spacecraft. The idea is to determine the optimal distribution of electronic components in the exterior panels through a simplified computational tool. Explanation of the optimization problem and the algorithm employed are provided. Conclusion show figures for reduced maximum temperatures, increased minimum temperatures, and range of difference between them.

Abstract: Dynamic models of vapor compression systems are useful tools in developing feedback controllers and are gaining increasing attention in recent years. The dominant dynamics are typically those of the evaporator and condenser, which are difficult to model. Accuracy and execution speed of system models therefore are highly dependent on the modeling approach of the heat exchangers. The two common approaches are the finite-volume (FV) and the moving-boundary (MB) methods. Both have been used successfully and reported in the literature, but there is little discussion presented for either choice. This paper presents the development and comparative study of shell-and-tube heat exchanger dynamic models using both the FV and the MB approaches. Detailed model formulations are provided and stability is demonstrated as components and within a complete centrifugal chiller system model. The system models are validated using data from a 300kW R134a centrifugal chiller test stand. The FV formulation is found to be more robust through start-up and all load-change transients, but executes slower. The moving-boundary method can handle all load-change transients but start-up stability is more sensitive to compressor and expansion valve formulations. The moving-boundary formulation also executes about three times faster than the finite-volume while maintaining nearly identical accuracy. With the homogenous two-phase assumption, charge prediction is seen to be less accurate in the moving-boundary approach. [Copyright &y& Elsevier]

This paper presents a detailed experimental validation of a simple transient model for cooling and dehumidifying coils that is developed in a companion paper (Zhou and Braun 2007). In all cases, the model provided very accurate predictions of exit air and water states. This appears to be the first experimental validation of a transient coil model under conditions where moisture condensation occurs. [ABSTRACT FROM AUTHOR]

Dynamic coil models are useful in the development and evaluation of feedback controllers and fault detection and diagnostics algorithms. Existing models in the literature have not been validated fully using experimental data and have not been evaluated in terms of trade-offs between model accuracy and computational requirements. This paper develops a computationally fast, distributed model for the transient behavior of cooling and dehumidifying coils. The model utilizes several steady-state performance indices that simplify dynamic modeling, including fin efficiency, air-side effectiveness, and water-side effectiveness. Predictions from the simplified model were compared with a detailed reference model and with other simplified models from the literature. Comparisons with detailed experimental measurements are given in a companion paper (Zhou and Braun 2007). The model provides very accurate predictions of coil transient performance and executes more than 1000 times faster than real-time on a 1.2 GHz personal computer. As a result, it is very practical for implementation within system simulation programs that execute over long time periods, such as a year. [ABSTRACT FROM AUTHOR]

Fin efficiencies are used within cooling coil models to simplify heat and mass transfer calculations associated with the use of air-side fins. These models utilize relationships developed for dry fins (i.e., no condensation) in determining convective heat transfer and modified fin efficiencies for estimating combined heat and mass transfer. However, the fin temperature distribution is different for wet and dry fins and, therefore, the use of a dry fin efficiency relationship for convective heat transfer is not strictly correct under wet conditions. This paper develops a correction factor for existing fin efficiency relationships that allows a better estimate of convective heat transfer fin efficiencies under wet conditions. The improved method is validated using results obtained from a two-dimensional numerical analysis and experiments performed on an eight-row cooling coil. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents results of experiments performed on different combinations of five types of filters of varying efficiencies (MERV4, 6, 8, 11, and 14) and four types of evaporator coils with depths and fin geometries under clean and fouled conditions. The fouled conditions were obtained after injection of 600g (1612g/m2 of coil face area) of dust upstream of the filter–coil combination, which was meant to simulate a year of operation in the field. The air-side pressure drops of the coils and filters and air-side effective heat transfer coefficients of the coils were determined from the measurements under the clean and fouled conditions. Depending upon the filter and coil, the coil pressure drops increased in the range of 6–30% for an air velocity of 2.54m/s. The impact was significantly greater for tests performed without an upstream filter (the coil pressure drops increased from 43% to 200%). The largest relative effect of fouling on pressure drop occurs for coils with fewer rows, primarily due to higher fin densities. The impact of fouling on air-side effective heat transfer coefficients was found to be relatively small, which ranged from −14% to 4%. In some cases, heat transfer was actually enhanced due to additional turbulence caused by the presence of dust. However, with large dust deposits, heat transfer is degraded because the dust also acts as insulation and creates an uneven air velocity. [Copyright &y& Elsevier]

Abstract: The problem of calculating transient heat transfer in concrete floor slabs is complicated due to ground coupling, which can require the numerical solution of two or three-dimensional transient conduction equations. This paper presents a simplified method for calculating transient slab-on-ground heat transfer that can be incorporated within hourly simulation programs. The method assumes that there are two primary one-dimensional paths for heat transfer from a ground-coupled floor slab: (1) one-dimensional heat transfer from the perimeter of the slab to the ambient and (2) one-dimensional heat transfer between the slab interior surface and a portion of the soil beneath the slab. The perimeter heat transfer is assumed to occur at quasi-steady state and is characterized in terms of a perimeter heat loss factor (Fp). Transient heat transfer within the slab and ground are modeled using a simple thermal circuit employing three nodes with an adiabatic boundary condition at a specified depth within the soil underneath the slab. Although some simulation models consider this type of two-path model, there appears to be no validation of this approach and there is no guidance for specifying perimeter heat loss factors and underfloor soil depths and node locations for the thermal circuit. In the current paper, results from detailed two-dimensional finite-element models for typical floor constructions and soil properties were used to identify (1) locations for nodes within the slab and soil, (2) correlations for soil depth as a function of soil properties associated with the underfloor adiabatic boundary condition, and (3) correlations for perimeter heat loss factor as a function of soil properties and edge insulation levels for different constructions. Transient heat transfer results from the simple model compared well with results from the finite-element program for different floor constructions, edge insulation, soil properties, locations, and times of year. [Copyright &y& Elsevier]

The thermal performance of heat exchangers within a thermoacoustic cooler was investigated. Experimental procedures and calculation methods to evaluate the oscillating flow heat transfer coefficients were developed. Dimensionless heat transfer coefficients, or Colburn-j factors, were estimated based on the oscillating-flow variables and compared with results from steady-flow measurements. The results were also compared with heat transfer coefficients predicted from a boundary-layer conduction model, and methods that utilize steady-flow correlations with Reynolds numbers that characterize oscillating flow conditions. Although the boundary layer model is commonly employed for thermoacoustic calculations, it did not accurately predict heat transfer coefficients and the influence of Reynolds number on heat transfer performance. However, accurate predictions were obtained using a steady-flow correlation and a modified Reynolds number that accounts for the oscillating flow field, assuming a half-cycle Reynolds number correction value of 0.109. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive model for a hermetic scroll compressor. The model combines models of the compression process including leakage and local heat transfer within the scrolls, frictional losses, motor inefficiencies, and heat transfer within the shell and to the ambient. The model is useful for investigating the impact of design changes on compressor performance. Some sample results are presented in this paper. Detailed validation and an investigation of compressor design improvements are described in a companion paper. [ABSTRACT FROM AUTHOR]

In this paper, the first open-source generalized simulation framework for positive displacement machines (PDSim) reported in literature is employed to model different compressor and expander types. In particular, it is shown how PDSim handles specific numerical and modeling aspects common to positive displacement machines such as stiffness of differential equations, discontinuous volume curves, leakage flow models, in-chamber and shell heat transfer models, mechanical and frictional losses. A control volume approach based on a set of differential equations is used to predict the performance of different positive displacement machines under steady-periodic operations. Reciprocating, scroll, and two rotary compressors as well as a single-screw expander have been considered as examples. The source code of PDSim with examples are provided as an electronic annex. [ABSTRACT FROM AUTHOR]

Metal hydrides have been studied for use in energy storage, hydrogen storage, and air-conditioning (A/C) systems. A common architecture for A/C and energy storage systems is two metal hydride reactors connected to each other so that hydrogen can flow between them, allowing for cyclic use of the hydrogen. This paper presents a nonlinear dynamic model and multivariate control strategy of such a system. Each reactor is modeled as a shell-and-tube heat exchanger connected to a circulating fluid, and a compressor drives hydrogen flow between the reactors. We further develop a linear state–space version of this model integrated with a model predictive controller to determine the fluid mass flow rates and compressor pressure difference required to achieve desired heat transfer rates between the metal hydride and the fluid. A series of case studies demonstrates that this controller can track desired heat transfer rates in each reactor, even in the presence of time-varying circulating fluid inlet temperatures, thereby enabling the use of a two-reactor system for energy storage or integration with a heat pump. • A nonlinear dynamic model of a two-reactor metal hydride system is derived. • The nonlinear model is linearized analytically and validated. • A model predictive controller is designed to track desired heat transfer rates. • Successive linearization is used to track setpoints across a large operating region. • The controller enables use of two-reactor systems for continuous heating or cooling. [ABSTRACT FROM AUTHOR]