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Heat-transfer Coefficient (heat-transfer + coefficient)
Selected AbstractsHeat-Transfer Coefficient for Cellular Materials Modelled as an Array of Elliptic Rods,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Marcelo J. S. de Lemos Convective heat-transfer coefficients in foam-like materials, modelled as an array of elliptic rods, are numerically determined. An incompressible fluid is considered, flowing through an infinite foam-like material with an arbitrary solid temperature. A repetitive cell is identified and periodic boundary conditions are applied. Turbulence is handled with both low and high Reynolds number formulations. The interfacial heat-transfer coefficient is obtained by volume integrating the distributed variables obtained within the cell. The results indicate that, for the same mass-flow rate, materials formed by elliptic rods have a lower interfacial heat-transfer coefficient compared to other media modelled as staggered arrays of square rods. [source] Heat-transfer coefficient in viscous liquid,solid circulating fluidized bedsAICHE JOURNAL, Issue 2 2005K. S. Shin First page of article [source] Heat-Transfer Coefficient for Cellular Materials Modelled as an Array of Elliptic Rods,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Marcelo J. S. de Lemos Convective heat-transfer coefficients in foam-like materials, modelled as an array of elliptic rods, are numerically determined. An incompressible fluid is considered, flowing through an infinite foam-like material with an arbitrary solid temperature. A repetitive cell is identified and periodic boundary conditions are applied. Turbulence is handled with both low and high Reynolds number formulations. The interfacial heat-transfer coefficient is obtained by volume integrating the distributed variables obtained within the cell. The results indicate that, for the same mass-flow rate, materials formed by elliptic rods have a lower interfacial heat-transfer coefficient compared to other media modelled as staggered arrays of square rods. [source] Numerical Analysis of Heat Transfer during Surface Pasteurization of Hot Dogs with Vacuum-Steam-Vacuum TechnologyJOURNAL OF FOOD SCIENCE, Issue 9 2004L. Huang ABSTRACT: The objective of this study was to validate the fundamental heat-transfer mechanism governing the process of vacuum-steam-vacuum surface pasteurization of hot dogs. It was hypothesized that the steam could not directly flow into the pores below the surface of hot dogs, and the heat was transferred into these areas by conduction. A numerical analysis program was first developed to estimate the heat-transfer coefficient between steam and hot dogs and was then used to simulate the temperature distribution at different locations below the surface. The hypothesis and computer simulation model were successfully validated using hot dogs surface-inoculated with Listeria innocua. Results showed that the heat from saturated steam must be conducted into the interior to kill L. innocua harboring in the pores and irregularities below the surface of hot dogs. Results of computer simulation and biological validation also suggested that heating must be maintained at 138 °C for at least 25 s to achieve a complete elimination (> 8 log colony-forming units per gram) of L. innocua from hot dogs. [source] Theoretical study of a membrane reactor for the water gas shift reaction under nonisothermal conditionsAICHE JOURNAL, Issue 12 2009Marķa E. Adrover Abstract A simulation of a membrane reactor for the water gas shift reaction is carried out by means of a 1D pseudo-homogeneous nonisothermal mathematical model. The composite membrane consists of a dense layer of Pd (selective to H2) supported over a porous ceramic layer. The effect of temperature, overall heat-transfer coefficient, and mode of operation on the membrane reactor performance and stability are analyzed, and the results obtained are compared with those corresponding to a reactor with no hydrogen permeation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Comparing flow-reversal and inner recirculation reactors: Experiments and simulationsAICHE JOURNAL, Issue 7 2003Moshe Ben-Tullilah The operation of reactors with flow reversal operate similar to a reactor with internal recirculation, which the feed enters through one (say, inner) reactor and then turns around and flows out through (the outer) another, when the heat-transfer coefficient between the tubes is large. In this study, we compare the behavior of a packed-bed reactor operating in flow-reversal or internal-recirculation modes, using ethylene oxidation on Pt/Al2O3 as a model reaction. The reactor was built from two concentric tubes (with 28.5 and 42.5 mm in diameter), both packed with a 20 cm catalytic bed and 10 cm inert beds (of alumina-pellets) on each side. An adjustable opening between the tubes allowed for an internal recycle mode and the whole system could be operated with periodic flow reversal. The reactor can be employed then either as a simple once-through bed or as a bed with flow reversal in the inner tube or as bed with internal recirculation flowing from the inner to outer tube, or in the opposite direction, as well as an internal-recirculation reactor with flow reversal. Due to heat losses, the latter two modes were inferior to the others. The experiments, backed by simulations using a homogeneous model with independently determined parameters, showed that the technically-simpler inner-outer internal-recycle reactor operated better at low flow rates, than that with flow reversal, but the conclusion is reversed at high flow rates. The domain where the internal-recirculation reactor is superior depends on the heat-transfer coefficient between the streams. By lowering the feed concentration, the extinction point was determined for each mode highlighting again the conclusions drawn above that inner-recirculation operation may be superior to flow reversal at low flow rates. Simulations revealed also the existence of solutions with stationary fronts or oscillatory fronts. [source] Heat-Transfer Coefficient for Cellular Materials Modelled as an Array of Elliptic Rods,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Marcelo J. S. de Lemos Convective heat-transfer coefficients in foam-like materials, modelled as an array of elliptic rods, are numerically determined. An incompressible fluid is considered, flowing through an infinite foam-like material with an arbitrary solid temperature. A repetitive cell is identified and periodic boundary conditions are applied. Turbulence is handled with both low and high Reynolds number formulations. The interfacial heat-transfer coefficient is obtained by volume integrating the distributed variables obtained within the cell. The results indicate that, for the same mass-flow rate, materials formed by elliptic rods have a lower interfacial heat-transfer coefficient compared to other media modelled as staggered arrays of square rods. [source] Condensation of steam in the presence of air on a single tube and a tube bankINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2003Adrian Briggs Abstract Data are presented for condensation of steam in cross-flow with and without the presence of air on the outside of a single tube and a bank of tubes. The tube bank consisted of ten staggered rows of two and one tubes per row. For pure steam the experimental results for both the single tube and tube bank gave good agreement with single-tube theory when account was taken of the reduction in vapour velocity due to condensation. There was some evidence, however, that condensate inundation may play a minor role in reducing heat-transfer coefficients on the lower tubes in the bank. For the case of condensation from steam,air mixtures, the single-tube data gave good agreement with theory. For condensation from steam,air mixtures on the bank of tubes, the data were significantly under predicted by single-tube theory, possibly because of mixing and re-circulation due to the complex flow pattern around the tubes. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||