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[en] The contribution under consideration reports on a gamma denitometric measurement of gas concentrations in a vertical heated tube bundle which is flowed around by a fluid. Two measurement positions, two flow rates of the circulating fluid, two subcooling values and eleven heat fluxes were selected for the measurement. The authors of this contribution describe the test facility, measurement methodology, results and their interpretation. The measurement uncertainty is described in detail.
[en] The objective of this research is to estimate ablating and charring of heat shield materials in severe aero thermal / erosive environments. This requires an accurate and rapid technique for its serious heat transfer with moving boundary. Aerodynamic heating is obtained by an explicit relation. Fully implicit method is used for heat transfer calculation. Moving boundary is captured by VOF method. Thickness of heat shield, temperature of moving surface and radiation heat is presented. The results are in good agreement with other calculations. (author)
[en] A mathematical model of radiative heat exchange in the throats of wide-necked helium cryostats is analyzed. A comparison of the numerical results with known calculated and experimental data shows their good agreement
[en] Compared to the pure refrigerants, the zeotropic refrigerant mixtures have the obvious temperature glide during phase change. Therefore, the Lorenz cycle can be approached with this special attribute. By analysing the heat transfer in the counter flow heat exchanger, a new evaluation method for zeotropic refrigerant mixtures based on the variance of the temperature difference between the refrigerant and heat transfer fluid (HTF) is proposed in this paper. For approaching to the Lorenz cycle and perfect glide matching, the zeotropic mixture which has smaller variance in the heat exchanger should be chosen in the refrigeration cycle. The variance of temperature difference is affected by two factors which are the temperature difference between the inlet and outlet of HTF and the linear relationship between the refrigerant temperature and enthalpy, respectively. The smallest variance of the zeotropic refrigerant can be obtained by setting the temperature difference of HTF to be the optimal temperature difference.
[en] The effect of radiation in combining with turbulent natural convection on the rates of heat transfer in volumetrically heated fluid layers characterized by high temperatures has been considered in this study. It is demonstrated that even at high Rayleigh numbers the radiation mode is as effective as the turbulent natural convection mode in removing the heat from the upper surface of molten pools with adiabatic lower boundary. As a result of this improved heat transfer, it is shown that considerably thicker molten pools with internal heat generation can be supported without boiling inception. The total Nusselt number at a moderate but fixed value of conduction-radiation parameter, can be represented as a function of Rayleigh number in a simple power-law form. As a consequence of this relationship it is shown that maximum nonboiling pool thicknesses vary approximately inversely as the 0.9 power of internal heat generation rate. A comparison between exact analysis using the integral formulation of radiation flux and Rosseland approximateion shows that the latter approximation bears out very adequately for optically thick pools with conduction-radiation parameter > or approx. =0.4 inspite of the fact that individual components of Nusselt number due to radiation and convection, respectively, are grossly in error. These errors in component heat fluxes are compensating due to the total heat balance constraint. However, the comparison between Rosseland approximation and exact formulation gets poorer as the value of conduction-radiation parameter decreases. This increase in error is principally incurred due to the error in estimating wall temperature differences
[en] This paper discusses a laboratory model that is employed for the experimental investigation of ground heat exchange problems, and it has been utilized to measure the three dimensional Shape Factors and heat losses from buried spherical geometries. This study simulates the modes by which heat is transferred in the actual problem, that is: a) from the buried sphere to the ground surface by conduction, and b) from the surface to the ambient by the combined modes of conduction, natural convection and radiation