The goals of this paper are to develop and demonstrate an efficient modeling technique for the thermal analysis of compact heat exchangers for integration into more complex systems. The proposed simplified heat exchanger model can take advantage of an existing library of heat exchanger perfoimance data, or alternatively, it can use existing heat exchanger performance curves. The ultimate utility of this methodology is to allow quick and accurate design decisions at system-level during package development by enabling the analyst to construct models and perform system-level thermal (and CFD) analyses in a matter of a few hours, rather than a few days (or weeks). The developed procedure has been demonstrated on a typical military aircraft electronics application, where the components are cooled by conduction of heat from the boards to "cold-plated" sidewalls. The proposed procedure is integrated into a thermaVCFD model of the above system.Heat transfer between the sidewall and the working fluid is modeled using a fluid network. Each section in the network denotes a heat exchanger section and is linked to a corresponding section of the coldplate through using the "UA" of the heat exchanger. Index Terms
This paper describes an approach based on coupled electrical, thermal and CFD analysis to predict the thermal performance of Bussed electrical centers and junction blocks. Typically from 200 to 400 amps flow trough various circuitries, which lead to a significant amount of Joule heat dissipation that is responsible for the majority of heat loss in the system. The Joule heat dissipation distribution is not known prior to the solution and must be evaluated by simultaneously solving the electrical field. This can be accomplished through a "coupled electrical, thermal solution" scheme, where the voltage field is solved throughout the region using the electrical loads and boundary conditions (in addition to thermal and flow fields) during each iteration. The most recent temperature field is used to update the electrical resistivity of the conductors in the model. The power dissipation is then calculated and updated for all conductor elements.In this paper, a thermal/electrical/CFD model of a typical Bussed Electrical Center (BEC) consisting of several relays, diodes and switches is discussed. The procedure for coupling the electrical and thermal effects is presented using 3D views of various circuitries. A discussion relating to the application of electrical boundary conditions (voltage and current BC's) is presented, followed by a detailed discussion of flow, thermal and voltage fields.
This study investigates the impact of the adjustment times of the atmospheric boundary layer (ABL) on the control of low-cloud coverage (LCC) climatology by large-scale atmospheric conditions in the subtropics. Using monthly data, we calculate back-trajectories and use machine learning statistical models with feature selection capabilities to determine the influence of local and upstream large-scale conditions on LCC for four physical cloud regimes: the Stratocumulus (Sc) deck, the along-flow transition into the Sc deck (“Inflow”), the Sc-to-cumulus transition, and tradecumulus clouds. All four regimes have unique local and upstream relationships with the large-scale meteorological variables within our parameter space, with upstream controls of LCC being the dominant processes in Sc deck and Sc-to-cumulus transition regimes. The timescales associated with these upstream controls across all regimes are consistent with known adjustment timescales of the ABL, determined in both modeling and observational studies. We find that low-level thermodynamic stratification (estimated inversion strength) is not the most important large-scale variable for LCC prediction in transition and trade-cumulus regimes despite its ubiquitous use as a proxy for LCC throughout the subtropics. Including upstream control provides significant improvements to the skill of statistical models predicting monthly LCC, increasing explained variance on the order of 15% in the Inflow, Sc deck, and transition regimes, but provides no improvement in the trade-cumulus regime.
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