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Item type:Publication, Access status: without files , Surface radiative transfer in gas-to-gas cocurrent microheat exchangerThe influence of surface radiative transfer in parallel flow microheat exchanger is numerically studied for its importance at high temperatures and for small flow dimensions. For these heat exchangers, the role of radiation is beneficial when the convective heat transfer to the annulus flow exceeds the convective heat transfer from the core flow. For this case, radiation improves the heat exchanger performance by decreasing the logarithmic mean temperature difference and by increasing the capacity, effectiveness, and volumetric heat transfer coefficient. Additional surface area is made available for convection to the annulus flow, thereby increasing the specific heat transfer surface for fixed geometry. Therefore, a high emissivity layer over the surfaces of microheat exchanger can improve the heat exchange performance. The active heat transfer area weighted by the convective heat flow rates is introduced as the true measure of heat exchanger compactness.Publicationtype: Journal Article13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Efficient methods to account for variable property effects in numerical momentum and heat transfer solutionsNumerical solutions of complex turbulent flows that have been achieved under the assumption of constant properties can be corrected with respect to the influence of variable properties for arbitrary (small) heat transfer rates and arbitrary (Newtonian) fluids with an asymptotic approach. It is based on the Taylor series expansion of all properties with respect to temperature. Two methods, one with a special manipulation to circumvent higher order equations are introduced and discussed in detail. Finally it is shown, how DNS and LES solutions, which need extremely large CPU-times, can be treated with respect to the influence of variable properties, at least approximately.Publicationtype: Journal Article18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Second law analysis of momentum and heat transfer in unit operations(2011); Momentum and heat transfer in complex systems always is the sum of single and simple transfer elements here called unit operations. They are usually characterised by head loss coefficients and Nusselt numbers as far as the flow and the heat transfer aspect is concerned. In our study we show that this is insufficient for a complete assessment and that additional parameters should be introduced. They take into account that energy, its use and conversion always is subject to the constraints set by the second law of thermodynamics.Publicationtype: Journal Article12