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C A Dorao - One of the best experts on this subject based on the ideXlab platform.

  • detailed experimental investigations on frictional pressure drop of r134a during Flow boiling in 5 mm diameter channel the influence of acceleration pressure drop component
    International Journal of Refrigeration-revue Internationale Du Froid, 2017
    Co-Authors: Tomasz Muszynski, Rafal Andrzejczyk, C A Dorao
    Abstract:

    Abstract This article presents detailed two-phase diabatic pressure drop data for refrigerant R134a at a saturation pressure of 5.5 bar corresponding to the saturation temperature of 19.4 °C. Study cases have been set for a mass flux varying from 100 to 500 kg m −2  s −1 . The obtained data are used as a validation of the void fraction literature models, a set of graphs shows comparisons, for a representative set of experimental conditions, of the two-phase frictional pressure gradients for the Adiabatic and diabatic Flow. Verification of the acceleration pressure drop predictions for two-phase Adiabatic Flow showed that all correlations predict that over 60% of experimental data fit in the range of ±30%. The model proposed in this article predicts 63% of presented data within 10% error, and 96% of the data are predicted within 30% error.

  • experimental investigations on Adiabatic frictional pressure drops of r134a during Flow in 5 mm diameter channel
    Experimental Thermal and Fluid Science, 2017
    Co-Authors: Rafal Andrzejczyk, Tomasz Muszynski, C A Dorao
    Abstract:

    Abstract The article presents detailed two-phase Adiabatic pressure drops data for refrigerant R134a at a saturation pressure of 5.5 bar corresponding to the saturation temperature of 19.4 °C. Study cases have been set for a mass flux varying from 100 to 500 kg/m2 s. The frictional pressure drop was characterized for the refrigerant R134a, for vapor qualities ranging from 0 to 1. Long-time thermal stability of test facility allowed to gather a comprehensive experimental database for two-phase frictional pressure drop including multiple data points in transition and dryout Flow regions. The effect of transition region on the peak value of two-phase frictional pressure drop, for literature models and experiment, is recognized. A systematic assessment of predictive techniques for two-phase frictional pressure drop in Adiabatic Flows for varying vapor quality was conducted. Both qualitative and quantitative analysis of gathered data vs. literature models was presented. Verification of the pressure drop for two-phase Adiabatic Flow showed that for Zhang and Webb correlation 93% of experimental data fits in the range of ±30%. The model proposed by Thome et al. in other hand predicts almost 33% of data within 10% error, but only 80% of the data is predicted within 30% error. Additional prediction of the peak value of two-phase frictional pressure drop with literature models and the experiment was made.

Christopher F Mckee - One of the best experts on this subject based on the ideXlab platform.

  • the expulsion of stellar envelopes in core collapse supernovae
    The Astrophysical Journal, 1999
    Co-Authors: Christopher D Matzner, Christopher F Mckee
    Abstract:

    We examine the relation between presupernova stellar structure and the distribution of ejecta in core-collapse supernovae of Types Ib, Ic, and II, under the approximations of Adiabatic, spherically symmetric Flow. We develop a simple yet accurate analytical formula for the velocity of the initial forward shock that traverses the stellar envelope. For material that does not later experience a strong reverse shock, the entropy deposited by this forward shock persists into the final, freely expanding state. We demonstrate that the final density distribution can be approximated with simple models for the final pressure distribution, in a way that matches the results of simulations. Our results indicate that the distribution of density and radiation pressure in a star's ejecta depends on whether the outer envelope is radiative or convective, and if convective, on the composition structure of the star. Our models are most accurate for the high-velocity ejecta cast away from the periphery of a star. For stellar structures that limit to a common form in this region, the resulting ejecta limit to a common distribution at high velocities because the blast wave forgets its history as it approaches the stellar surface. We present formulae for the final density distribution of this material as a function of mass, for both radiative and efficiently convective envelopes. These formulae limit to the well-known planar, self-similar solutions for mass shells approaching the stellar surface. However, the assumption of Adiabatic Flow breaks down for shells of low optical depth, so this planar limit need not be attained. The event of shock emergence, which limits Adiabatic Flow, also produces a soft X-ray burst of radiation. Formulae are given for the observable properties of this burst and their dependence on the parameters of the explosion. Motivated by the relativistic expansion recently inferred by Kulkarni et al. for the synchrotron shell around SN 1998bw, we estimate the criterion for relativistic mass ejection and the rest mass of relativistic ejecta. We base our models for the entire ejecta distribution on the high-velocity solution, on our shock-velocity formula, and on realistic radiation pressure distributions. We also present simpler, but less flexible, analytical approximations for ejecta distributions. We survey the ejecta of the polytropic hydrogen envelopes of red supergiants. Our models will be useful for studies of the light curves and circumstellar or interstellar interactions of core-collapse supernovae, and of the birth of pulsar nebulae in their ejecta.

  • the expulsion of stellar envelopes in core collapse supernovae
    arXiv: Astrophysics, 1998
    Co-Authors: Christopher D Matzner, Christopher F Mckee
    Abstract:

    We examine the relation between presupernova stellar structure and the distribution of ejecta in core-collapse supernovae, assuming Adiabatic, spherically symmetric Flow. We develop a simple yet accurate formula for the blastwave shock velocity, and demonstrate that the entire final density distribution can be approximated with simple models for the final pressure distribution, along with the approximate shock-deposited entropy, in a way that matches the results of simulations. We find that the distribution of density in a star's ejecta depends on whether its outer envelope is radiative or convective, and if convective, on the composition structure of the star; simple approximate forms are presented for red and blue supergiant ejecta. Our models are most accurate for the high-velocity ejecta from the periphery of a star, where the shock dynamics are predictable. We present formulae for the final density distribution of this material, for both radiative and efficiently convective envelopes. These formulae limit to the well-known planar, self-similar solutions for mass shells approaching the stellar surface. But, the assumption of Adiabatic Flow fails at low optical depth, so this planar limit need not be attained. Formulae are given for the observable properties of the X-ray burst accompanying shock emergence, and their dependence on the parameters of the explosion. Motivated by the relativistic expansion recently inferred by Kulkarni et al. (1998) for the synchrotron shell around SN1998bw, we estimate the criterion for relativistic mass ejection and the rest mass of relativistic ejecta.

Ravi Kumar - One of the best experts on this subject based on the ideXlab platform.

  • Adiabatic Flow characteristics of R-600a inside a helically coiled capillary tube
    Applied Thermal Engineering, 2018
    Co-Authors: Santhosh Kumar Dubba, Ravi Kumar
    Abstract:

    Abstract This paper presents an experimental investigation of a helically coiled capillary tube with an Adiabatic Flow of R-600a. The details of experimental facility for testing a capillary tube with different inlet sub-cooling degree and varying pressure are discussed. The effect of coil diameter, capillary length, capillary tube diameter, sub-cooling degree and inlet pressure on mass Flow rate are described. The degree of sub-cooling at the inlet of both straight and helical capillary tube is varied from 3 to 15 °C. The experimental results confirm that, the mass Flow rate in the straight capillary tube is 1.5–16 percent higher than the coiled capillary tube. A non-dimensional correlation to predict the mass Flow rate through a straight and helical coiled capillary tube has been developed with a good agreement of ±20 percent of measured mass Flow rate.

  • numerical analysis of Adiabatic Flow of refrigerant through a spiral capillary tube
    International Journal of Thermal Sciences, 2009
    Co-Authors: M K Mittal, Ravi Kumar, Akhilesh Gupta
    Abstract:

    In the present work, a homogenous model including the metastable liquid region has been developed for the Adiabatic Flow of refrigerant through the spiral capillary tube. In order to develop the model, both liquid region and two phase region have been discretized into infinitesimal segments to take into account the effect of varying radius of curvature of spiral tube on the friction factor. The effect of the pitch of spiral on the mass Flow rate of refrigerant and capillary tube length has been investigated. A comparison of Flow characteristics of refrigerant R22 and its alternatives, i.e., R407C and R410A has been made at different operating conditions at the inlet of the capillary tube and it has been found that the Flow characteristics of R22 and R407C are almost similar for a given condenser pressure and degree of subcooling at the inlet of capillary tube.

Akhilesh Gupta - One of the best experts on this subject based on the ideXlab platform.

  • numerical analysis of Adiabatic Flow of refrigerant through a spiral capillary tube
    International Journal of Thermal Sciences, 2009
    Co-Authors: M K Mittal, Ravi Kumar, Akhilesh Gupta
    Abstract:

    In the present work, a homogenous model including the metastable liquid region has been developed for the Adiabatic Flow of refrigerant through the spiral capillary tube. In order to develop the model, both liquid region and two phase region have been discretized into infinitesimal segments to take into account the effect of varying radius of curvature of spiral tube on the friction factor. The effect of the pitch of spiral on the mass Flow rate of refrigerant and capillary tube length has been investigated. A comparison of Flow characteristics of refrigerant R22 and its alternatives, i.e., R407C and R410A has been made at different operating conditions at the inlet of the capillary tube and it has been found that the Flow characteristics of R22 and R407C are almost similar for a given condenser pressure and degree of subcooling at the inlet of capillary tube.

Rafal Andrzejczyk - One of the best experts on this subject based on the ideXlab platform.

  • detailed experimental investigations on frictional pressure drop of r134a during Flow boiling in 5 mm diameter channel the influence of acceleration pressure drop component
    International Journal of Refrigeration-revue Internationale Du Froid, 2017
    Co-Authors: Tomasz Muszynski, Rafal Andrzejczyk, C A Dorao
    Abstract:

    Abstract This article presents detailed two-phase diabatic pressure drop data for refrigerant R134a at a saturation pressure of 5.5 bar corresponding to the saturation temperature of 19.4 °C. Study cases have been set for a mass flux varying from 100 to 500 kg m −2  s −1 . The obtained data are used as a validation of the void fraction literature models, a set of graphs shows comparisons, for a representative set of experimental conditions, of the two-phase frictional pressure gradients for the Adiabatic and diabatic Flow. Verification of the acceleration pressure drop predictions for two-phase Adiabatic Flow showed that all correlations predict that over 60% of experimental data fit in the range of ±30%. The model proposed in this article predicts 63% of presented data within 10% error, and 96% of the data are predicted within 30% error.

  • experimental investigations on Adiabatic frictional pressure drops of r134a during Flow in 5 mm diameter channel
    Experimental Thermal and Fluid Science, 2017
    Co-Authors: Rafal Andrzejczyk, Tomasz Muszynski, C A Dorao
    Abstract:

    Abstract The article presents detailed two-phase Adiabatic pressure drops data for refrigerant R134a at a saturation pressure of 5.5 bar corresponding to the saturation temperature of 19.4 °C. Study cases have been set for a mass flux varying from 100 to 500 kg/m2 s. The frictional pressure drop was characterized for the refrigerant R134a, for vapor qualities ranging from 0 to 1. Long-time thermal stability of test facility allowed to gather a comprehensive experimental database for two-phase frictional pressure drop including multiple data points in transition and dryout Flow regions. The effect of transition region on the peak value of two-phase frictional pressure drop, for literature models and experiment, is recognized. A systematic assessment of predictive techniques for two-phase frictional pressure drop in Adiabatic Flows for varying vapor quality was conducted. Both qualitative and quantitative analysis of gathered data vs. literature models was presented. Verification of the pressure drop for two-phase Adiabatic Flow showed that for Zhang and Webb correlation 93% of experimental data fits in the range of ±30%. The model proposed by Thome et al. in other hand predicts almost 33% of data within 10% error, but only 80% of the data is predicted within 30% error. Additional prediction of the peak value of two-phase frictional pressure drop with literature models and the experiment was made.