Begell House Inc.
Heat Transfer Research
HTR
1064-2285
45
8
2014
NUMERICAL STUDY OF THE SHELL−SIDE PERFORMANCE OF THE TRISECTION BAFFLED AND QUARTERN BAFFLED HEAT EXCHANGERS
701-723
Yongli
Sun
School of Chemical Engineering and Technology; National Engineering Research Center for Distillation Technology, Tianjin University, Tianjin, P. R. China
Feiyang
Li
School of Chemical Engineering and Technology, Tianjin University, Tianjin, P. R. China
Luhong
Zhang
School of Chemical Engineering and Technology, Tianjin University, 92, Weijin Road, Tianjin 300072, China
Bin
Jiang
School of Chemical Engineering and Technology; National Engineering Research Center for Distillation Technology, Tianjin University, Tianjin, P. R. China
Xiaoming
Xiao
School of Chemical Engineering and Technology, Tianjin University, Tianjin, P. R. China
In this article, the heat transfer performance and the resistance loss of a trisection baffled heat exchanger
and a quartern baffled heat exchanger with 20°, 30°, 40°, and 50° helical angles are analyzed comparatively by using the commercial codes GAMBIT 6.4 and FLUENT 14.0. With the same helical angle and under the same shell side volume flow rate, both the average heat transfer coefficient and the pressure drop of the trisection baffled heat exchanger are larger than those of the quartern baffled heat exchanger because of the longer helical line in the former. However, the heat transfer coefficient per pressure drop of the trisection baffled heat exchanger is lower than that of the quartern baffled heat exchanger. So the comprehensive performance of the quartern baffled heat exchanger is better than that of the trisection baffled heat exchanger. It is also observed that the comprehensive performance of a quartern baffled heat exchanger with the 40° helical angle is the best. A series of simulations on the trisection baffled heat exchanger and the quartern baffled heat exchanger with the same helical pitch are also carried out, with the simulation results demonstrating that with the same helical line, the outlet temperature and the pressure drop of the trisection baffled heat exchanger are similar to those of the quartern baffled heat exchanger. According to two simulation results for the former we can conclude that the major influencing factor on the heat transfer performance and resistance loss in a helically baffled heat exchanger is the helical line. The research achievement of heat transfer and flow distribution in this investigation will provide theoretical basis for further optimization of the helically baffled heat exchanger.
NATURAL CONVECTION HEAT TRANSFER IN A SQUARE CAVITY CONTAINING A NANOFLUID WITH A BAFFLE UNDER A MAGNETIC FIELD
725-748
M.
Davoudian
Department of Mechanical Engineering, Faculty of Engineering, Shahrekord University, Shahrekord, Iran
Alireza
Arab Solghar
Department of Mechanical Engineering, Faculty of Engineering, Vali-e-Asr University, Rafsanjan, Iran
A buoyancy-driven fluid flow and heat transfer in a square cavity with a vertical plate at the center and filled with Al2O3−water nanofluid is examined numerically. The left and the right side walls of the cavity are maintained at temperatures Th and Tc, respectively, with Th > Tc.
The enclosure's top and bott om walls are adiabatic. The transport equations are discretized using the finite volume method. Comparisons with previous works are presented and found to be in excellent agreement. The heat and fluid flow structures are fully investigated via streamlines and
isotherms. A parametric study is carried out and the effects of the Rayleigh number, Hartmann number, and Joule heating on the fluid flow and heat transfer inside an enclosure are studied. The results show that the average Nusselt number increases with the Rayleigh number. Finally, it is
found that a magnetic field has strong influence on the rate of heat transfer while the role of the Joule heating is marginal.
NUMERICAL SIMULATION OF ELECTRICALLY CONDUCTING FLUID FLOW AND FREE CONVECTIVE HEAT TRANSFER IN AN ANNULUS ON APPLYING A MAGNETIC FIELD
749-766
Masoud
Afrand
Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
Said
Farahat
Department of Mechanical Engineering, University of Sistan and Baluchestan, Zahedan, Iran
Alireza Hossein
Nezhad
Department of Mechanical Engineering, University of Sistan and Baluchestan, Zahedan, Iran
Ghanbar Ali
Sheikhzadeh
Department of Mechanical Engineering, University of Kashan, Kashan, Iran
Faramarz
Sarhaddi
Department of Mechanical Engineering, University of Sistan and Baluchestan, Zahedan, Iran
The presence of free convective heat transfer in an enclosure filled with a congealing melt leads
to the output of a product with a nonuniform structure involving large grains. On applying a proper magnetic field to the melt in the enclosure, the convective flows are decreased and uniform and small grain structures are obtained. In this work, using the finite volume method, we investigated the application of a magnetic field to the convective heat transfer and temperature fields in
steady and laminar flows of melted gallium in a long annulus between two horizontal cylinders at the Prandtl number 0.02. The inner and outer walls of the annulus are at TC and TH temperatures,
respectively, with TH > TC. We also investigated the effect of the magnetic field intensity and the Hartmann number on the flow and temperature fields, the influence of the variation of
other parameters, like the Rayleigh number, the angle of magnetic field application, the ratio of the inner to outer radii of the annulus on the flow and temperature field. It has been reveales that on changing the field angle to the horizon, the Nusselt number (Nu) is increased, which is of
importance in a specific range of Hartmann numbers. Also with increase in the Rayleigh number, the change in Nu with the magnetic field intensity does not occur. In studying the influence of the outer radius to inner radius ratio on Nu at a fixed Rayleigh number, we have found that with
increase in the diameter ratio, the Nu number increases.
EFFECT OF INTERNAL HEAT GENERATION ON THE APPLICABILITY OF DIFFERENT LUMPED MODELS WITH UNSTEADY ONE-DIMENSIONAL CONDUCTION
767-793
Behrooz
Abbasi Souraki
Chemical Engineering Department, Faculty of Engineering, University of Guilan, Rasht, Iran
N.
Assareh
Chemical Engineering Department, Faculty of Engineering, University of Guilan, Rasht, Iran
M.
Omidi
Chemical Engineering Department, Faculty of Engineering, University of Guilan, Rasht, Iran
In this study, the effect of internal heat generation as well as the Biot number on the accuracy and applicability of lumped models in unsteady one-dimensional heat transfer problems is investigated. The simple classical lumped capacity approach and also improved lumped models
based on the Hermite and polynomial approximation approaches were used to obtain the average temperature and heat flux in the spatial direction. The applicability of the lumped models was quantified using the dimensionless number B = hR/k and dimensionless heat source G = R2q°/(T0 − T∞) that depend on the objects geometry, thermal and physical properties, the value of internal heat generation, and on the environmental conditions they are subjected to. The range of application of different lumped models was analyzed by evaluation of the average relative error between
the solution of approximate lumped models and a reference exact solution of the original partial differential equation for a whole time domain at B and −G numbers equal between 0 and 20. The results show that at the B numbers lower than 13, the variations of the relative error with the internal heat generation passes through a minimum at a dimensionless internal heat generation lower than 5, and, thus, in these ranges of B and G, the internal heat generation has increasing effect on the precision of the lumped models.
EFFECTS OF RADIATION AND CHEMICAL REACTION ON HEAT AND MASS TRANSFER BY NATURAL CONVECTION IN A MICROPOLAR FLUID-SATURATED POROUS MEDIUM WITH STREAMWISE TEMPERATURE AND SPECIES CONCENTRATION VARIATIONS
795-815
Ahmed M.
Rashad
Department of Mathematics, Aswan University, Faculty of Science, Aswan, 81528, Egypt
Ali J.
Chamkha
Department of Mechanical Engineering, Prince Sultan Endowment for Energy and
Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952, Kingdom of Saudi
Arabia; RAK Research and Innovation Center, American University of Ras Al Khaimah, United Arab Emirates, 10021
S.M.M.
EL-Kabeir
Department of Mathematics, Salman bin Abdulaziz University, College of Science and Humanity Studies, Al-Kharj, 11942, Saudi Arabia; Department of Mathematics, Aswan University, Faculty of Science, 81528, Egypt
In this paper, the problem of coupled heat and mass transfer by a natural-convection boundary-layer flow of a micropolar fluid past a vertical flat plate in a saturated porous medium with streamwise sinusoidal variations of both the surface temperature and species concentration in the presence of thermal radiation and chemical reaction effects is investigated. A suitable set of dimensionless variables is used to transform the governing equations of the problem into a nonsimilar form. The resulting nonsimilar equations have the property that they reduce to various special cases previously considered in the literature. An adequate and efficient implicit, tridiagonal finite difference
scheme is employed for the numerical solution of the obtained equations. Various comparisons with previously published work are performed, and the results are found to be in excellent agreement. A representative set of numerical results for the velocity, temperature, and concentration profiles as well as the surface shear stress, rate of heat transfer, and the rate of mass transfer is presented
graphically to show interesting features of the solutions.
Contents Volume 45, 2014
817-820
Index Volume 45, 2014
821-823