Begell House Inc.
Journal of Porous Media
JPM
1091-028X
5
4
2002
Convective Boiling Phenomena in a Sintered Fibrous Channel: Study of Thermal Non-Equilibrium Behavior
11
Lounes
Tadrist
Aix-Marseille Universite, CNRS, Laboratoire IUSTI, UMR 7343, Marseille 13453, France
Marc
Miscevic
Laboratoire Plasma et Conversion d'Energie (Laplace), UMR5213, Institut National Polytechnique-Universite Paul Sabatier-Centre National de la Recherche Scientifique (INP-UPS-CNRS), Toulouse, France
Frederic
Topin
Polytech Marseille, Laboratoire IUSTI, UMR CNRS 7343, Technopole de Chateau Gombert, 5 rue Enrico Fermi, 13453 Marseille Cedex 13, France
Convective boiling and heat transfer are studied experimentally in a vertical sintered fibrous channel heated on the walls. For given values of the operating parameters, several zones, corresponding to different fluid states, appear in the channel. A thermal non-equilibrium state between the liquid and its vapor is observed for critical operating conditions. The transition corresponds to a dry out of the heated wall. The heat transfer between the walls and the fluid is systematically studied. A boiling curve, taking into account the presence of a thermal nonequilibrium zone, is derived for the sintered porous channel.
Estimation of Thermal Moisture Diffusivity from Liquid Redistribution Measurements
12
S. K. Saiful
Islam
Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
Nihal E.
Wijeysundera
Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
S. K.
Chou
Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
K.
Srinivasan
Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560 012, India
Experiments are performed to estimate the thermal liquid diffusivity of water in cork. The isothermal liquid diffusivity, the moisture content dependent thermal conductivity and the sorption isotherm are measured in separate experiments. A heat and moisture transfer model is used to interpret the experimental data. The error between the measured and predicted moisture distributions is minimized to obtain the best estimate of the thermal liquid diffusivity.The value obtained is 2.1·10-9 kg/m·s·K. The dominant mode of moisture redistribution is the transfer due to the temperature gradient in the material. The ratio of the effective thermal moisture diffusivity to the thermal vapor diffusivity varies from about 2 to 4. The material property that has the most significant impact on the heat flux is the moisture content-dependent thermal conductivity. The contribution of condensation/evaporation processes associated with vapor diffusion to the effective thermal conductivity is less than 5 percent.
Combined Method of Hydrocarbon Conversion in a Tubular Reactor with a Catalyzing Box, and Its Mathematical Model
9
Abdumumin
Sharifov
Tajik Technical University, 6 Nozim Khikmet, 734001, Dushanbe, Tajikistan
This article describes a method of combining hydrocarbon conversion in one reactor, where the endothermic conversion of hydrocarbon with water vapor is carried out in the reactor tubes, and the oxygen conversion of hydrocarbons is carried out in a catalyzing box surrounding the tubes. This method does not require burning fuel to heat the reactor, so it is highly efficient, because there is no contamination from smoke. The mathematical model of the proposed method includes equations of material and thermal balances, equilibrium of chemical responses, heat transfer, speeds of chemical reactions and mass hyphen reacting substances, and products of the reactions in a porous layer of catalyst. This model is used to calculate the technological parameters of the combined method of hydrocarbon conversion in a tubular reactor with a surrounding catalyzing box.
Measurement of Diffusivity of Water in Corc
11
S. K. Saiful
Islam
Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
Nihal E.
Wijeysundera
Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
S. K.
Chou
Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
The diffusivity of water in cork samples from a commercial corkboard was measured using three experimental techniques. These are the liquid intake method, electrical resistive method and the full-immersion method. The cork samples for the different tests were taken from the same corkboard. The diffusivity estimated from the electrical resistive method and the full-immersion method showed good agreement. Although the moisture concentration-dependent diffusivity obtained from the liquid intake method showed some fluctuations, the general trend is an increase of the diffusivity with concentration.
Implications of Alternative Macroscopic Descriptions Illustrated by General Balance and Continuity Equations
12
Faruk
Civan
Mewbourne School of Petroleum and Geological Engineering, The University of Oklahoma, 100 East Boyd, SEC Room 1210, Norman, Oklahoma, USA
This article demonstrates the outstanding challenges of the application of well-established averaging procedures and rules, and shows that the results are not universal and alternative forms differ by inherent realization, difficulties, and conveniences for implementation in practical analyses of processes in porous media. Two alternative forms of the general macroscopic balance equation are derived by means of the representative elementary volume and mass-weighted-volume averaging rules and illustrated for the equation of continuity. Differences in the resulting mathematical expressions and their implications for practical problems are delineated. The macroscopic equation of continuity derived by combining the volume and mass-weighted-volume averaging rules may be convenient for conforming to the mathematical form of the microscopic equation of continuity. Using only the volume averaging rules yields an additional term compared to the conventional microscopic equation of continuity, which is referred to as transport by hydraulic dispersion due to convective mixing and spreading in porous media and contains a hydraulic dispersion parameter. An equation for empirical determination of the hydraulic dispersion parameter is also derived. Both averaging approaches are shown to be equally applicable when used with proper designations of various quantities as being the volume or mass-weighted-volume averaged. The macroscopic equation of continuity using only the volume-averaged quantities and conforming to the mathematical form of the microscopic equation of continuity is proven to involve an inherent error.