Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
5
5
2013
RADIATION AND CHEMICAL REACTION EFFECTS ON UNSTEADY MHD FREE CONVECTION FLOW OF A DISSIPATIVE FLUID PAST AN INFINITE VERTICAL PLATE WITH NEWTONIAN HEATING
355-367
V.
Rajesh
Department of Engineering Mathematics, GITAM University Hyderabad Campus, Rudraram, Patancheru Mandal, Medak Dist.-502 329, Andhra Pradesh, India
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
D.
Bhanumathi
Department of Mathematics, S.V. University, Tirupati 517502, A.P, India
S. Vijaya Kumar
Varma
Department of Mathematics, Sri Venkateswara University, Tirupati-517 502, A.P., India
This paper focuses on the study of the effects of radiation and chemical reaction on unsteady magnetohydrodynamic free convection flow of a dissipative fluid past an impulsively started infinite vertical plate in the presence of Newtonian heating and uniform mass diffusion. The dimensionless governing equations are unsteady, coupled, and nonlinear partial differential equations. An analytical method fails to give a closed-form solution. Hence, the implicit finite difference scheme of the Crank-Nicolson method is employed. The influence of the magnetic field parameter, radiation parameter, and chemical reaction parameter on the velocity field and skin friction for both air (Pr = 0.71) and water (Pr = 7) are extensively discussed with the help of graphs.
EFFECT OF VARIABLE PROPERTIES ON HEAT TRANSFER IN A MICRO-CHANNEL WITH A SYNTHETIC JET
369-388
Ann
Lee
School of Engineering, Macquarie University, NSW 2109 Australia
Guan Heng
Yeoh
School of Mechanical and Manufacturing Engineering University of New South Wales, NSW 2052, Australia; Australian Nuclear Science and Technology Organisation (ANSTO), PMB 1, Menai, NSW 2234, Australia
Victoria
Timchenko
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney 2052, Australia
John
Reizes
School of Mechanical and Manufacturing Engineering, UNSW-Sydney, Sydney 2052, Australia
The effect of variable properties on thermal enhancement in a micro-channel due to synthetic jet and cross-flow fluid interaction is examined. Three-dimensional simulation is performed for low Reynolds number flow of water subjected to localized heating at the top surface of the micro-channel when a silicon wafer is etched. The complex conjugate heat transfer between the silicon substrate and water flow is analyzed. Axial conduction introduced by the thermal conductivity, density, and heat capacity temperature dependence of silicon is included. Computational results for the case of variable properties are compared against those of constant properties in both steady-state and transient conditions. The velocity field in the channel is found to be greatly influenced by the temperature distribution when the variable transport properties of water are taken into account. Numerical results of 30 full cycles of the actuator are simulated in order to track the development of the fluid flow and heat transfer. Quasi-steady results, which indicate the maximum cooling potential of a single synthetic jet actuator, are presented. The maximum, minimum, and average temperature profiles show a consistent reducing trend between the solutions of the variable and constant properties.
INFLUENCE OF GOERTLER VORTICES SPANWISE WAVELENGTH ON HEAT TRANSFER RATES
389-400
Vinicius
Malatesta
Laboratory of Applied Mathematics and Scientific Computing, Department of Applied Mathematics and Statistics, ICMC - University of Sao Paulo, Sao Carlos, Sao Paulo; Mobility Engineering Center, Federal University of Santa Catarina, Santa Catarina, Brazil
L. F.
Souza
Laboratory of Applied Mathematics and Scientific Computing, Department of Applied Mathematics and Statistics, ICMC - University of Sao Paulo, Sao Carlos, Sao Paulo, Brazil
Joseph T. C.
Liu
School of Engineering and Center of Fluid Mechanics, Brown University, Providence, RI
The boundary layer over concave surfaces can be unstable due to centrifugal forces, giving rise to Goertler vortices. These vortices create two regions in the spanwise direction−the upwash and downwash regions. The downwash region is responsible for compressing the boundary layer toward the wall, increasing the heat transfer rate. The upwash region does the opposite. In the nonlinear development of the Goertler vortices, it can be observed that the upwash region becomes narrow and the spanwise−average heat transfer rate is higher than that for a Blasius boundary layer. This paper analyzes the influence of the spanwise wavelength of the Goertler the heat transfer. The equation is written in vorticity-velocity formulation. The time integration is done via a classical fourth-order Runge-Kutta method. The spatial derivatives are calculated using high-order compact finite difference and spectral methods. Three different wavelengths are analyzed. The results show that steady Goertler flow can increase the heat transfer rates to values close to the values of turbulence, without the existence of a secondary instability. The geometry (and computation domain) are presented.
TRANSIENT ANALYSIS OF MIXED CONVECTION IN A BOTTOM-HEATED SQUARE CAVITY IN THE PRESENCE OF SURFACE RADIATION
401-423
Sikata
Samantaray
Siksha 'O' Anusandhan University
Swarup Kumar
Mahapatra
Indian Institute of Technology Bhubaneswar
Sofen K.
Jena
Department of Flows and Materials Simulation, Fraunhofer Institute for Industrial Mathematics (ITWM), Kaiserslautern, Germany, D-67663; Department of Mechanical Engineering, Jadavpur University, Kolkata, India-700032
Amitava
Sarkar
Department of Mechanical Engineering, Jadavpur University, Kolkata, India-700032
The present analysis reports interesting results regarding the effect of surface radiation on the transient behavior of mixed convection in a bottom-heated cavity having gray and diffuse walls. Movement of the walls causes shear-induced flow within the cavity, which either augments or attenuates the buoyancy-induced flow and results mixed convection. The effect of various influencing parameters such as the Rayleigh number (Ra), Richardson number (Ri), wall movement direction, and emissivity of the walls (ε) on the flow and heat transfer characteristics has been analyzed. Weak conservative form of governing equations are solved using the modified Marker and Cell method. A gradient-dependent consistent hybrid upwind scheme of the second order is used for discretization of the convective terms in the flow equation. An operator splitting algorithm is used to solve the energy equation. The surface radiation transport equation has been solved using the net radiation method. It is noticed from the present analysis that the dominance of shear-induced flow is more compared to buoyancy-induced flow in the case of horizontal wall movement. The time required to attain steady state is more for vertical wall movement in mixed convection regimes. The oscillating behavior of the average heat transfer with time; increases with the increase in the Rayleigh number and emissivity. Unicellular and multi-cellular flow structures are observed depending on the type of wall movement and other controlling parameters.
NUMERICAL STUDY OF RADIATION AND AIRPREHEATING EFFECT ON THE VELOCITY, TEMPERATURE, AND SPECIES DISTRIBUTION IN A CONFINED LAMINAR COFLOW DIFFUSION FLAME
425-440
A. K.
Chowdhuri
Department of Mechanical Engineering, Bengal Engineering and Science University, Shibpur, Howrah 7111103, India
Somnath
Chakrabarti
Department of Mechanical Engineering, Indian Institute of Engineering Science and Technology Shibpur, Howrah, 711103, West Bengal, India
Bijan Kumar
Mandal
Department of Mechanical Engineering, Bengal Engineering and Science University, Shibpur, Howrah 7111103, India
The effect of gas-band and soot radiation has been numerically investigated in a coflow laminar confined methane-air buoyant jet diffusion flame using non-preheated and preheated air. A specially developed computer code based on the SOLA algorithm is used to solve the overall mass, species mass concentration, momentum (Navier Stokes), and energy conservation equations along with appropriate boundary conditions. A two-equation semiempirical soot model for the estimation of soot, and an optically thin radiation model for the radiative heat loss from the gas band and soot have also been incorporated into the algorithm. The code has been run with and without incorporating the radiation model for air inlet temperatures of 300 K (non-preheated) and 400 K (preheated). The fuel temperature is kept constant at 300 K. The code has been validated with the experimental results available in the literature. Radiation heat loss decreases the temperature in the computational zone, but does not change the temperature distribution pattern in the case of non-preheated. But when preheated air is used, the decrease in temperature due to radiation heat loss becomes more, and the distribution pattern also changes to some extent. Maximum velocity decreases due to radiation in both cases. There is an ingress of ambient air near the wall in the case of non-preheated which results in higher velocity near the axis. No such recirculation is observed with preheated air and hence the velocity near the axis is also less compared to the non-preheated case. The variation of centerline temperature, velocity, and bulk temperature with axial height has also been shown and discussed for clarification of the abovementioned facts. The effects of radiation are found to be small in both the cases of non-preheated and preheated air. The CO2 and H2O distributions are almost not affected by radiation, although the air preheat affects the distributions of those two species.