Two-phase flow pressure-drop type instabilities in a two-phase upflow boiling system has been stu... more Two-phase flow pressure-drop type instabilities in a two-phase upflow boiling system has been studied theoretically. The drift-flux model is adopted in predicting the steady state characteristics of the boiling system, using the finite difference method. The dynamic simulation of the quasi-static pressure-drop type instability in the boiling system is presented. The thermal non-equilibrium effect between the two phases is included by assuming the temperature profile in the subcooled boiling region. By comparing the equilibrium theory, non-equilibrium theory and experiments, it is concluded that the models including the nonequilibrium effects fit better the experimental results of the steady state characteristics of the system, as well as the system stability boundary and oscillations characteristics (amplitude and period).
In this work, two-phase flow boiling instabilities in vertical and horizontal system are presente... more In this work, two-phase flow boiling instabilities in vertical and horizontal system are presented. The stead-state system pressure-drop characteristics are determined by a numerical solution of the governing equations as derived from the Drift-Flux model. The transient characteristics of the two-phase flow are obtained for various parameters and the results are presented in tabular form. The numerical solutions are determined using an explicit finite difference scheme. A satisfactory agreement between the theory and experiments is obtained
Transient laminar forced convection within the thermal entrance region of parallel-plate chennels... more Transient laminar forced convection within the thermal entrance region of parallel-plate chennels is analytically solved for by making use of the Generalized Integral Transform Technique (GITT) and mixed symbolic-numerical computation (Mathematica 3.0 system). ...
International Journal of Heat and Mass Transfer, 1998
The problem of condensation of vapors flowing with high velocity around a horizontal tube is solv... more The problem of condensation of vapors flowing with high velocity around a horizontal tube is solved for the case of isothermal condition of the wall of a condenser tube. The interfacial shear at the vapor conderLsate film is assessed with the help of Colburn analogy. Extension of these results in the estimation of average condensation heat transfer coefficients is found to be successful. The present theoretical results are further compared with the recent experimental data and the agreement between the two is found to be very satisfactory.
... Membrane Fuel Cells Vladimir Gurau, Hongtan Liu, and Sadik Kakac; Dept. ... The resulting equ... more ... Membrane Fuel Cells Vladimir Gurau, Hongtan Liu, and Sadik Kakac; Dept. ... The resulting equations are a gen-eralized form of Darcy's law (Dagan, 1989) and in nondimen-sional form read as (Gurau, 1998) with the last terms in Eqs. ...
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 2, 2010
A nanofluid is defined as the suspension of nanoparticles in a base liquid. Studies in the last d... more A nanofluid is defined as the suspension of nanoparticles in a base liquid. Studies in the last decade have shown that significant amount of thermal conductivity and heat transfer enhancement can be obtained by using nanofluids. In the first part of this study, classical forced convection heat transfer correlations developed for pure fluids are used to predict the experimental values of heat transfer enhancement of nanofluids. It is seen that the experimental values of heat transfer enhancement exceed the enhancement predictions of the classical correlations. On the other hand, a recent correlation based on the thermal dispersion phenomenon created by the random motion of nanoparticles predicts the experimental data well. In the second part of the study, in order to further examine the validity of the thermal dispersion approach, a numerical analysis of forced convection heat transfer of Al2O3/water nanofluid inside a circular tube in the laminar flow regime is performed by utilizin...
Microscale Heat Transfer Fundamentals and Applications
... (58) W#R' C0 +1 4 KnEv R2/, where C0 1 s +2 s +n 3/ 4 KnEv/ where n=0 fo... more ... (58) W#R' C0 +1 4 KnEv R2/, where C0 1 s +2 s +n 3/ 4 KnEv/ where n=0 for parallel plate micro channel, and n=1 for micro tube. ... (59) +1 4 KnEv R2/ T#R, Z' cccccccccccccccccccccc Z 2 T#R, Z' cccccccccccccccccccccccc R2 n cccc R T#R, Z' cccccccccccccccccccccc R The eqs. ...
Two-phase flow pressure-drop type instabilities in a two-phase upflow boiling system has been stu... more Two-phase flow pressure-drop type instabilities in a two-phase upflow boiling system has been studied theoretically. The drift-flux model is adopted in predicting the steady state characteristics of the boiling system, using the finite difference method. The dynamic simulation of the quasi-static pressure-drop type instability in the boiling system is presented. The thermal non-equilibrium effect between the two phases is included by assuming the temperature profile in the subcooled boiling region. By comparing the equilibrium theory, non-equilibrium theory and experiments, it is concluded that the models including the nonequilibrium effects fit better the experimental results of the steady state characteristics of the system, as well as the system stability boundary and oscillations characteristics (amplitude and period).
In this work, two-phase flow boiling instabilities in vertical and horizontal system are presente... more In this work, two-phase flow boiling instabilities in vertical and horizontal system are presented. The stead-state system pressure-drop characteristics are determined by a numerical solution of the governing equations as derived from the Drift-Flux model. The transient characteristics of the two-phase flow are obtained for various parameters and the results are presented in tabular form. The numerical solutions are determined using an explicit finite difference scheme. A satisfactory agreement between the theory and experiments is obtained
Transient laminar forced convection within the thermal entrance region of parallel-plate chennels... more Transient laminar forced convection within the thermal entrance region of parallel-plate chennels is analytically solved for by making use of the Generalized Integral Transform Technique (GITT) and mixed symbolic-numerical computation (Mathematica 3.0 system). ...
International Journal of Heat and Mass Transfer, 1998
The problem of condensation of vapors flowing with high velocity around a horizontal tube is solv... more The problem of condensation of vapors flowing with high velocity around a horizontal tube is solved for the case of isothermal condition of the wall of a condenser tube. The interfacial shear at the vapor conderLsate film is assessed with the help of Colburn analogy. Extension of these results in the estimation of average condensation heat transfer coefficients is found to be successful. The present theoretical results are further compared with the recent experimental data and the agreement between the two is found to be very satisfactory.
... Membrane Fuel Cells Vladimir Gurau, Hongtan Liu, and Sadik Kakac; Dept. ... The resulting equ... more ... Membrane Fuel Cells Vladimir Gurau, Hongtan Liu, and Sadik Kakac; Dept. ... The resulting equations are a gen-eralized form of Darcy's law (Dagan, 1989) and in nondimen-sional form read as (Gurau, 1998) with the last terms in Eqs. ...
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 2, 2010
A nanofluid is defined as the suspension of nanoparticles in a base liquid. Studies in the last d... more A nanofluid is defined as the suspension of nanoparticles in a base liquid. Studies in the last decade have shown that significant amount of thermal conductivity and heat transfer enhancement can be obtained by using nanofluids. In the first part of this study, classical forced convection heat transfer correlations developed for pure fluids are used to predict the experimental values of heat transfer enhancement of nanofluids. It is seen that the experimental values of heat transfer enhancement exceed the enhancement predictions of the classical correlations. On the other hand, a recent correlation based on the thermal dispersion phenomenon created by the random motion of nanoparticles predicts the experimental data well. In the second part of the study, in order to further examine the validity of the thermal dispersion approach, a numerical analysis of forced convection heat transfer of Al2O3/water nanofluid inside a circular tube in the laminar flow regime is performed by utilizin...
Microscale Heat Transfer Fundamentals and Applications
... (58) W#R' C0 +1 4 KnEv R2/, where C0 1 s +2 s +n 3/ 4 KnEv/ where n=0 fo... more ... (58) W#R' C0 +1 4 KnEv R2/, where C0 1 s +2 s +n 3/ 4 KnEv/ where n=0 for parallel plate micro channel, and n=1 for micro tube. ... (59) +1 4 KnEv R2/ T#R, Z' cccccccccccccccccccccc Z 2 T#R, Z' cccccccccccccccccccccccc R2 n cccc R T#R, Z' cccccccccccccccccccccc R The eqs. ...
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