Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
11
5
2019
EFFECTS OF DISCRETE CONTROLLERS ON THE STABILIZATION OF NATURAL CONVECTION INDUCED BY INTERNAL HEAT GENERATION IN A SHALLOW CAVITY
387-400
10.1615/ComputThermalScien.2019026046
A.
Mebrouki
Departement de Genie Mecanique, Faculte de Technologie, Universite Mustapha Ben Boulaid Batna, Algerie; Laboratoire d'Innovation en Construction, Eco-Conception et Genie Sismique, LICEGS, Universite Mustapha Ben Boulaid, Batna, Algerie
Alloui
Zineddine
Departement de Genie Mecanique, Faculte de Technologie, Universite Mustapha Ben Boulaid Batna, Algerie; Laboratoire d'Innovation en Construction, Eco-Conception et Genie Sismique, LICEGS, Universite Mustapha Ben Boulaid, Batna, Algerie
Patrick
Vasseur
Ecole Polytechnique, Université de Montréal, C.P. 6079, Succ. "Centre ville", Montréal,
Québec H3C 3A7, Canada
natural convection
internal heat generation
feedback control
discrete controllers
The stabilization of natural convection in a horizontal fluid layer with internal heat generation is studied numerically. The horizontal boundaries of the system are cooled isothermally. The system is stabilized using multiple sensors and discrete individually controlled actuators that modify the local intensity of the heating power. Discrete controllers of finite length and spacing are located on the horizontal boundaries of the system. The thermal sensors are positioned at a given vertical height of the fluid layer. Upon using a feedback proportional control, the heating power of the system is modulated in order to postpone the onset of motion or annihilate the intensity of convection. Two-dimensional numerical simulations of the full governing equations are carried out. The results are used to determine the influence of the governing parameters, such as the length and spacing of the actuators, positions of the thermal sensors, and control gain on the control of the system. A correlation equation is proposed to predict the critical length of the actuators, above which the no-motion state cannot be maintained in the layer, as a function of the Rayleigh number.
LOCALIZED RADIAL BASIS FUNCTIONS AND DIFFERENTIAL QUADRATURE-MESHLESS METHOD FOR SIMULATING COMPRESSIBLE FLOWS
401-422
10.1615/ComputThermalScien.2019025846
Ebrahim
Nabizadeh
Department of Mechanical Engineering, Rice University, Houston, Texas 77005, USA
Darrell W.
Pepper
NCACM, Department of Mechanical Engineering, University of Nevada Las Vegas, Las Vegas, NV 89154, USA
meshless method
compressible flow
radial basis function
A numerical approach based on the meshless method is used to simulate compressible flow. The meshless, or mesh-free, method circumvents the need to generate a mesh. Since there is no connectivity among the nodes, the method can be easily implemented for any geometry. However, one of the most fundamental issues in numerically simulating compressible flow is the lack of conservation, which can be a source of unpredictable errors in the solution process. This problem is particularly evident in the presence of steep gradient regions and shocks that frequently occur in highspeed compressible flow problems. To resolve this issue, a conservative localized meshless method based on radial basis functions and differential quadrature (RBF-DQ) has been developed. An upwinding scheme, based on the Roe method, is added to capture steep gradients and shocks. In addition, a blended RBF is used to decrease the dissipation ensuing from the use of low shape parameters. A set of test problems are used to confirm the accuracy and reliability of the algorithm, and the method applied to the solution of Euler's equation.
PERFORMANCE PREDICTION AND COMPARATIVE ANALYSIS FOR A DESIGNED, DEVELOPED, AND MODELED COUNTERFLOW HEAT EXCHANGER USING COMPUTATIONAL FLUID DYNAMICS
423-443
10.1615/ComputThermalScien.2019028520
Shuvam
Mohanty
Department of Mechanical Engineering, Amity University Haryana, India
Rajesh
Arora
Department of Mechanical Engineering, Amity University Haryana, India
Om
Parkash
Department of Mechanical Engineering, Amity University Haryana, India
three-dimensional (3D) computational fluid dynamics (CFD) modeling
logarithmic mean temperature difference (LMTD)
renormalization group (RNG) k-e model
temperature distribution
velocity distribution
pressure drop
This paper presents a systematic approach for three-dimensional analysis of a counterflow heat exchanger, where hot water flows through a 12.7-mm-diameter tube and cold water flows through a 20-mm-diameter tube concurrently along the length of the heat exchanger. In particular, the flow and the temperature fields are resolved by using commercial computational fluid dynamics (CFD) software. The analysis and developments are made by working over a circular tube bank using different numerical methods and CFD simulations while considering turbulent models. Significant geometric optimization is made in the heat exchange between the circular tubes by limiting the cost since no polymers or additives are used and steering clear of flow separation, which has a greater impact on the flow phenomena. In order to analyze heat transfer characteristics, we carried out numerical analyses by altering the hot and cold fluid inlet temperatures. To simulate the flow, the renormalization group k-ε turbulence model was chosen. The simulated outcomes of the counterflow heat exchanger are compared with the existing literature to find the logarithmic mean temperature difference (LMTD). The following two factors were considered: (1) the effect of changing the temperature at one end and fixing it at the other end on the heat transfer and LMTD and (2) the effect of altering the mass flow rates at every step by fixing the temperature. There was a significant amount of change in the LMTD while increasing the hot fluid temperature (with an average of 31.41) rather than increasing the cold fluid temperature. However, by further decreasing the cold fluid inlet temperature the LMTD peaks at a value of 27.32. It was also observed that changing the cold fluid flow rate gives better insight into the heat transfer and LMTD with average of 28.94 and an average error of 8.455%, respectively.
EFFECT OF CONFINEMENT ON NATURAL CONVECTION IN POWER-LAW FLUIDS FROM A CIRCULAR CYLINDER
445-474
10.1615/ComputThermalScien.2019026115
S.
Gupta
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016,
India
A. K.
Gupta
Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208016, India
Rajenda P.
Chhabra
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016,
India; Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar
140001, India
natural convection
circular cylinder
confinement
power-law index
heatlines
Bejan number
In this work, free convection in power-law fluids from an isothermal horizontal cylinder confined between adiabatic vertical walls has been investigated numerically. The coupled governing equations have been solved over wide ranges of conditions such as Rayleigh number (103 ≤ Ra ≤ 106), Prandtl number (5 ≤ Pr ≤ 100), power-law index (0.3 ≤ n ≤ 1.5), channel height (5 ≤ L/D ≤ 20), and confinement ratio (2 ≤ W/D ≤ 10). The flow and heat transfer results have been interpreted in terms of streamlines and isotherm contours, heatlines, vertical velocity profiles, drag coefficient, and local and average Nusselt number. Furthermore, entropy production rates have been computed to evaluate the value of the Bejan number to delineate the individual contributions due to heat transfer and fluid friction. Depending upon the values of the power-law index and buoyancy-induced flow (Gr), the confinement may enhance or deteriorate heat transfer from the cylinder with reference to that from an unconfined cylinder. Overall, for Newtonian fluids, we may obtain up to 50% enhancement in heat transfer for the minimum confinement effect (W/D = 10), at the highest Rayleigh number (Ra = 106), and the shortest channel height (L/D = 5). At high Ra and Pr, shear-thinning viscosity exerts a positive influence on the Nusselt number while a reverse trend is seen for small values of Ra and Pr. The present results have been consolidated via a simple expression for the average Nusselt number as a function of W/D, L/D, n, and the Rayleigh number. In most cases, the overall entropy generation is mainly due to heat transfer, and it draws only a small contribution from fluid flow friction effects.
NANOFLUID ELECTROHYDRODYNAMIC FORCED CONVECTION AND RADIATION INSIDE A POROUS ENCLOSURE
475-487
10.1615/ComputThermalScien.2019027956
Mohsen
Sheikholeslami
Department of Mechanical Engineering, Babol Noshirvani University of Technology, Babol,
Iran; Renewable Energy Systems and Nanofluid Applications in Heat Transfer Laboratory, Babol
Noshirvani University of Technology, Babol, Iran
Muhammad Mubashir
Bhatti
College of Mathematics and Systems Science, Shandong University of Science and Technology,
Qingdao, Shandong, 266590, China; Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University Yanchang Road,
Shanghai 200072, China
Ahmad
Shafee
FAST, University Tun Hussein Onn Malaysia, 86400, Parit Raja, Batu Pahat, Johor State,
Malaysia; Public Authority of Applied Education and Training, College of Technological Studies, Applied
Science Department, Shuwaikh, Kuwait
Zhixiong
Li
School of Engineering, Ocean University of China, Qingdao 266110, China; School of Mechanical, Materials, Mechatronic and Biomedical Engineering, University of Wollongong, Wollongong, NSW 2522, Australia
nanofluid
electrohydrodynamic
porous media
EFD viscosity
forced convection
shape of nanoparticles
Radiative heat source impact on nanofluid electrohydrodynamic flow has been displayed numerically using CVFEM. Fe3O4-ethylene glycol nanofluid was employed considering the electric field effect on its viscosity. Different shapes of nanoparticles have been considered, i.e., spherical, platelet, cylinder, and brick. The positive electrode is the lower wall. The physical behavior of permeability, Coulomb forces, lid velocity, the volume fraction of nanofluid, and radiation parameter have been discussed numerically and graphically. A graphical comparison is also shown to ensure that the results obtained are correct. It is found that the Darcy number and Coulomb tend to enhance the distortion of isotherms. Furthermore, thermal radiation also tends to augment the temperature gradient closer to the lower wall.