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Dual Solutions on Thermosolutal Marangoni Forced Convection Boundary Layer with Suction and Injection
R. A. Hamid,N. M. Arifin,R. Nazar,F. M. Ali,I. Pop
Mathematical Problems in Engineering , 2011, DOI: 10.1155/2011/875754
Abstract: This paper considers the extended problem of the thermosolutal Marangoni forced convection boundary layer by Pop et al. (2001) when the wall is permeable, namely, there is a suction or injection effect. The governing system of partial differential equations is transformed into a system of ordinary differential equations, and the transformed equations are solved numerically using the shooting method. The effects of suction or injection parameter 0 on the velocity, temperature, and concentration profiles are illustrated and presented in tables and figures. It is shown that dual solutions exist for the similarity parameter less than 0.5.
Effects of Hydromagnetic and Thermophoresis of Unsteady Forced Convection Boundary Layer Flow over Flat Plates  [PDF]
Md. Jashim Uddin, Md. Yeakub Ali
Journal of Applied Mathematics and Physics (JAMP) , 2016, DOI: 10.4236/jamp.2016.49182
Abstract: In this paper, we analyze unsteady two dimensional hydromagnetic forced convection boundary layer flow of a viscous incompressible fluid along flat plates with thermophoresis. The potential flow velocity has been taken as a function of the distance x and time t. The governing partial differential equations are transformed to ordinary differential equation by applying local similarity transformation. The resulting similarity equations are then solved numerically for unsteady case, applying Nachtsheim-Swigert shooting iteration technique with six order Runge-Kutta method. The variations in fluid velocity, fluid temperature and species concentration are displayed graphically and discussed for different material parameters entering into the analysis. The effects of the pertinent parameters on the skin-friction coefficient, wall heat transfer coefficient and wall deposition flux rate are also displayed in tabulated form and discussed them from the physical point of view. An analysis of the obtained results shows that the flow field is influenced appreciably by the magnetic field parameter and the thermophoresis particle deposition.
Mean-field equations for weakly nonlinear two-scale perturbations of forced hydromagnetic convection in a rotating layer  [PDF]
V. Zheligovsky
Physics , 2008, DOI: 10.1080/03091920802137573
Abstract: We consider stability of regimes of hydromagnetic thermal convection in a rotating horizontal layer with free electrically conducting boundaries, to perturbations involving large spatial and temporal scales. Equations governing the evolution of weakly nonlinear mean perturbations are derived under the assumption that the alpha-effect is insignificant in the leading order (e.g., due to a symmetry of the system). The mean-field equations generalise the standard equations of hydromagnetic convection: New terms emerge -- a second-order linear operator representing the combined eddy diffusivity, and quadratic terms associated with the eddy advection. If the perturbed CHM regime is non-steady and insignificance of the alpha-effect in the system does not rely on the presence of a spatial symmetry, the combined eddy diffusivity operator also involves a non-local pseudodifferential operator. If the perturbed CHM state is almost symmetric, alpha-effect terms appear in the mean-field equations as well. Near a point of a symmetry-breaking bifurcation, cubic nonlinearity emerges in the equations. All the new terms are in general anisotropic. A method for evaluation of their coefficients is presented; it requires solution of a significantly smaller number of auxiliary problems than in a straightforward approach.
Theoretical analysis of free convection between parallel, isothermal plates  [cached]
Andrzej K?opocki
Bulletin of the Institute of Heat Engineering , 1969,
Abstract: The energy equation for free convection flow between parallel, isothermal plates was intagrated and general relationship describing heat transfer was found.The discrepancies between the author's results and the earlier results of Blenbaas and Bodoia and Osterie do not exceed 10% for GrPr·s/l < 200.It was found that free convection heat transfer in the investigated conditions can be replaced with a non-steady heat conduction-process in a thin rod with isolated side surfaces.
Evaporation of a binary liquid film by forced convection  [PDF]
Nasr Abdelaziz,Debbissi Chokri,Nasrallah Ben Sassi
Thermal Science , 2011, DOI: 10.2298/tsci100427076n
Abstract: This paper deals with a numerical analysis of the evaporation of a thin binary liquid film by forced convection inside a channel constituted by two parallel plates. The first plate is externally insulated and wetted by a thin water ethylene glycol film while the second is dry and isothermal. The liquid mixture consists of water (the more volatile component) and ethylene glycol while the gas mixture has three components: dry air, water vapour and ethylene-glycol vapour. The set of non linear and coupled equations expressing the conservation of mass, momentum, energy and species in the liquid and gas mixtures is solved numerically using a finite difference method. Results concerns with the effects of inlet ambience conditions and the inlet liquid concentration of ethylene glycol on the distribution of the temperature, concentrations profiles and the axial variation of the evaporation rate of species i.
Numerical Analysis of Water Forced Convection in Channels with Differently Shaped Transverse Ribs
Oronzio Manca,Sergio Nardini,Daniele Ricci
Journal of Applied Mathematics , 2011, DOI: 10.1155/2011/323485
Abstract: Heat transfer enhancement technology has the aim of developing more efficient systems as demanded in many applications. An available passive method is represented by the employ of rough surfaces. Transversal turbulators enhance the heat transfer rate by reducing the thermal resistance near surfaces, because of the improved local turbulence; on the other hand, higher losses are expected. In this paper, a numerical investigation is carried out on turbulent water forced convection in a ribbed channel. Its external walls are heated by a constant heat flux. Several arrangements of ribs in terms of height, width, and shape are analyzed. The aim is to find the optimal configuration in terms of high heat transfer coefficients and low losses. The maximum average Nusselt numbers are evaluated for dimensionless pitches of 6, 8, and 10 according to the shape while the maximum friction factors are in the range of pitches from 8 to 10.
Extinction transition in bacterial colonies under forced convection  [PDF]
T. Neicu,A. Pradhan,D. A. Larochelle,A. Kudrolli
Physics , 2000, DOI: 10.1103/PhysRevE.62.1059
Abstract: We report the spatio-temporal response of {\it Bacillus subtilis} growing on a nutrient-rich layer of agar to ultra-violet (UV) radiation. Below a crossover temperature, the bacteria are confined to regions that are shielded from UV radiation. A forced convection of the population is effected by rotating a UV radiation shield relative to the petri dish. The extinction speed at which the bacterial colony lags behind the shield is found to be qualitatively similar to the front velocity of the colony growing in the absence of the hostile environment as predicted by the model of Dahmen, Nelson and Shnerb. A quantitative comparison is not possible without considering the slow dynamics and the time-dependent interaction of the population with the hostile environment.
Studies on forced convection nanofluid flow in circular conduits  [PDF]
Harikrishna Vishwanadula,Emmanuel C. Nsofor
Journal of Engineering and Applied Sciences , 2012,
Abstract: An experimental system was developed and used to study the nanofluid flow and heat transfer in circular conduits. Experiments were performed for a variety of nanofluid flow features in the system. Results obtained from the study show that the heat transfer rate for flow of the base fluid is less than that of the nanofluid used in the study. It was also found that the observed relationship between molecular diffusivity of momentum and the molecular diffusivity of thermal energy at the macroscale may not necessarily be the same at the nanoscale. A heat transfer correlation for turbulent forced convection flow in circular pipes was developed from the results in terms of Nusselt number, Reynolds number and Prandtl number. The correlation developed was compared to related correlations in the literature. Important factors that affect nanofluid flow and heat transfer in circular conduits were also determined. This type of study is essential for heat exchanger applications.
Unsteady free convection of a stagnation point of attachment on an isothermal surface
D. B. Ingham,J. H. Merkin,I. Pop
International Journal of Mathematics and Mathematical Sciences , 1984, DOI: 10.1155/s0161171284000648
Abstract: The time development free convection flow near a three-dimensional stagnation point of attachment on an isothermal surface is studied at large Grashof numbers. A small time solution and an accurate numerical method is described for determining the solution of the time-dependent boundary-layer equations. For a range of values of parameter c, which describes the local geometry, the development of the various physical properties of the flow are calculated and compared with their values at small and large values of time. In another range of values of c the numerical results suggest the development of a singularity in the boundary-layer equations at a finite value of time. An anlysis is presented which is consistent with the numerical results and confirms the presence of this singularity.
Mechanistic Multidimensional Modeling of Forced Convection Boiling Heat Transfer  [PDF]
Michael Z. Podowski,Raf M. Podowski
Science and Technology of Nuclear Installations , 2009, DOI: 10.1155/2009/387020
Abstract: Due to the importance of boiling heat transfer in general, and boiling crisis in particular, for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems, extensive efforts have been made in the past to develop a variety of methods and tools to evaluate the boiling heat transfer coefficient and to assess the onset of temperature excursion and critical heat flux (CHF) at various operating conditions of boiling channels. The objective of this paper is to present mathematical modeling concepts behind the development of mechanistic multidimensional models of low-quality forced convection boiling, including the mechanisms leading to temperature excursion and the onset of CHF.
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