Search results
1 – 10 of 854Pradeep Hegde, K.N. Seetharamu, G.A. Quadir, P.A. Aswathanarayana, M.Z. Abdullah and Z.A. Zainal
To analyze two‐phase flow in micro‐channel heat exchangers used for high flux micro‐electronics cooling and to obtain performance parameters such as thermal resistance, pressure…
Abstract
Purpose
To analyze two‐phase flow in micro‐channel heat exchangers used for high flux micro‐electronics cooling and to obtain performance parameters such as thermal resistance, pressure drop, etc. Both uniform and non‐uniform micro‐channel base heat fluxes are considered.
Design/methodology/approach
Energy balance equations are developed for two‐phase flow in micro‐channels and are solved using the finite element method (FEM). A unique ten noded element is used for the channel descritization. The formulation also automatically takes care of single‐phase flow in the micro‐channel.
Findings
Micro‐channel wall temperature distribution, thermal resistance and the pressure drop for various uniform micro‐channel base heat fluxes are obtained, both for single‐ and two‐phase flows in the micro‐channel. Results are compared against data available in the literature. The wall temperature distribution for a particular case of non‐uniform base heat flux is also obtained.
Research limitations/implications
The analysis is done for a single micro‐channel and the effects of multiple or stacked channels are not considered. The analysis needs to be carried out for higher heat fluxes and the validity of the correlation needs to be ascertained through experimentation. Effects of flow mal‐distribution in multiple channels, etc. need to be considered.
Practical implications
The role of two‐phase flow in micro‐channels for high flux micro‐electronics cooling in reducing the thermal resistance is demonstrated. The formulation is very useful for the thermal design and management of microchannels with both single‐ and two‐phase flows for either uniform or non‐uniform base heat flux.
Originality/value
A simple approach to accurately determine the thermal resistance in micro‐channels with two‐phase flow, for both uniform and non‐uniform base heat fluxes is the originality of the paper.
Details
Keywords
Manash Protim Boruah, Pitambar R. Randive and Sukumar Pati
The purpose of this study is to numerically analyze the thermal and entropy generation characteristics on two-dimensional, incompressible, laminar single-phase flow of Al2O3-water…
Abstract
Purpose
The purpose of this study is to numerically analyze the thermal and entropy generation characteristics on two-dimensional, incompressible, laminar single-phase flow of Al2O3-water nanofluid in a micro-channel subjected to asymmetric sinusoidal wall heating with varying amplitude, length of fluctuation period and phase difference of applied heat flux for Reynolds number in the range of 25-1000.
Design/methodology/approach
The numerical computation is based on the Finite Element Method and the Lagrange finite element technique is used for approximating the flow variables within the computational domain.
Findings
The average Nusselt number increases with increasing Reynolds number (Re) for all the volume fractions of nanofluid. However, the total entropy generation decreases up to a critical value of Re and increases thereafter. Increase in volume fraction shifts the critical Re towards the lower Re regime. The average Nusselt number and total entropy generation increase with amplitude and length of fluctuation period of heat flux. The optimal choice of volume fraction for lesser entropy generation and higher heat transfer is found to be 3 per cent independent of the value of amplitude, length of fluctuation period and phase difference of the heat flux.
Originality/value
To the best of authors’ knowledge, the interplay of various parameters concerning non-uniform heating in achieving the maximum heat transfer with minimum irreversibility has not been investigated. Focusing on this agenda, the results of this study would benefit the industrial sector in achieving the maximum heat transfer at the cost of minimum irreversibilities with an optimal choice of inlet Reynolds number, volume fraction of nanofluid, amplitude, length of the period of fluctuation of heat flux and phase difference of applied heat flux.
Details
Keywords
Davood Toghraie, Ramin Mashayekhi, Hossein Arasteh, Salman Sheykhi, Mohammadreza Niknejadi and Ali J. Chamkha
This is a 3D numerical study of convective heat transfer through a micro concentric annulus governing non-uniform heat flux boundary conditions employing water-Al2O3 nanofluid…
Abstract
Purpose
This is a 3D numerical study of convective heat transfer through a micro concentric annulus governing non-uniform heat flux boundary conditions employing water-Al2O3 nanofluid. The nanofluid is modeled using two-phase mixture model, as it has a good agreement to experimental results.
Design/methodology/approach
Half of the inner pipe surface area of the annulus section of a double pipe heat exchanger is exposed to a constant heat flux which two models are considered to divide the exposing surface area to smaller ones considering the fact that in all cases half of the inner pipe surface area has to be exposed to the heat flux: in model (A), the exposing surface area is divided radially to two parts (A1), four parts (A2) and eight parts (A3) by covering the whole length of the annulus and in model (B) the exposing surface area is divided axially to two parts (B1), four parts (B2) and eight parts (B3) by covering half of the annulus radially.
Findings
The results reveal that model (B) leads to higher Nusselt numbers compared to model (A); however, at Reynolds number 10, model (A3) exceeds model (B3). The average Nusselt number is increased up to 142 and 83 per cent at models (A3) with Reynolds number 10 and model (B3) with Reynolds number 1000, respectively.
Originality/value
This paper is a two-phase investigation of water-Al2O3 nanofluid in a micro concentric annulus under non-uniform heat flux boundary conditions.
Details
Keywords
Lahcen El Moutaouakil, Zaki Zrikem and Abdelhalim Abdelbaki
This work is devoted to the numerical analysis of laminar natural convection in two-dimensional vertical cavities, filled with air and of high aspect ratios. One of the sidewalls…
Abstract
Purpose
This work is devoted to the numerical analysis of laminar natural convection in two-dimensional vertical cavities, filled with air and of high aspect ratios. One of the sidewalls is cooled isothermally while the other is heated by a uniform or linear heat flux whose average is located at mid-height of the wall. The paper aims to discuss these issues.
Design/methodology/approach
The governing equations are discretized by the finite volume method and solved, in transient regime, by using the SIMPLE algorithm.
Findings
The flow structure, air temperature field, local convective heat flux on the cold wall, variation of the temperature along the heated wall as well as its average and its maximum are analyzed for various combinations of the controlling parameters. These parameters are the linear heat flux slope γ (γ=0, 1 and −1, for a uniform, increasing and decreasing heat flux, respectively), the average Rayleigh number Ra m (103Ra m 3×104) and the aspect ratio A (10A80). It was found that for a given A and Ra m , the highest (lowest) mean temperature of the hot wall is obtained when the linear heating is descending (ascending). While the maximum temperature increases with the three controlling parameters.
Practical implications
Accurate correlations which allow calculating the average and maximum temperatures of the heated wall are developed for each type of heating. Also, an empirical relationship for the position of the maximum temperature is provided for γ=−1.
Originality/value
Despite its fundamental and practical interest, natural convection in cavities with 10A80 and submitted to non-uniform heat flux was not examined before. Development of original correlations.
Details
Keywords
G.A. Quadir, Anvar Mydin and K.N. Seetharamu
A finite element method is applied to evaluate the performance of microchannel heat exchangers that are used in electronic packaging. The present approach is validated against the…
Abstract
A finite element method is applied to evaluate the performance of microchannel heat exchangers that are used in electronic packaging. The present approach is validated against the CFD data available in the literature. A comparison of the predicted results with other available results obtained from different concepts shows that the present method is able to predict the surface temperature, the fluid temperature and thus the total thermal resistance of the microchannel heat sink satisfactorily. The present methodology has an added advantage in that non‐uniform surface heat flux distribution over the package base can also be analysed easily. The method used in the present analysis is an alternative to massive CFD calculations.
Details
Keywords
Lahcen El Moutaouakil, Zaki Zrikem and Abdelhalim Abdelbaki
A detailed numerical study is conducted on the effect of surface radiation on laminar natural convection in a tall vertical cavity filled with air. The cavity is heated and…
Abstract
Purpose
A detailed numerical study is conducted on the effect of surface radiation on laminar natural convection in a tall vertical cavity filled with air. The cavity is heated and cooled, through its two vertical walls, by a linear or uniform heat flux q(y) and by a constant cold temperature, respectively. The horizontal walls are considered adiabatic. The paper aims to discuss these issues.
Design/methodology/approach
The radiosity method is employed to calculate the net radiative heat exchanges between elementary surfaces, while the finite volume method is implemented to resolve the governing equations of the fluid flow.
Findings
For each heat flux q(y) (ascending, descending or uniform), the effect of the emissivity ε (0ε1) on the local, average and maximum temperatures of the heated wall is determined as a function of the average Rayleigh number Ram (103Ram 6×104) and the cavity aspect ratio A (10A80). The effect of the coupling on the flow structures, convective and radiative heat transfers is also presented and analyzed. Overall, it is shown that surface radiation significantly reduces the local and average temperatures of the heated wall and therefore reduces the convective heat transfer between the active walls.
Practical implications
The studied configuration is of practical interest in several areas where overheating must be avoided. For this purpose, a simple design tool is developed to estimate the mean and the maximum temperatures of the hot wall in different operating conditions (Ram, A et ε).
Originality/value
The originality lies in the study of the interaction between surface radiation and natural convection in tall cavities submitted to a non-uniform heat flux and a constant cold temperature on the active walls. Also, the development of an original simplified calculation procedure for the hot wall temperatures.
Details
Keywords
M. A. Hossain, M.K. Chowdhury and R.S.R. Gorla
We determine the effects of micro‐inertia density and the vortex viscosity on laminar free convection boundary layer flow of a thermomicropolar fluid past a vertical plate with…
Abstract
We determine the effects of micro‐inertia density and the vortex viscosity on laminar free convection boundary layer flow of a thermomicropolar fluid past a vertical plate with exponentially varying surface temperature as well as surface heat flux. The governing nonsimilarity boundary layer equations are analyzed using: first, a series solution for small ξ (a scaled streamwise distribution of micro‐inertia density), second, an asymptotic solution for large ξ and, third, a full numerical solution implicit finite difference method together with Keller‐box scheme. Results are expressed in terms of local skin friction and local Nusselt number. The effects of varying the vortex viscosity parameter, Δ, surface temperature and the surface heat flux gradient n and m respectively against ξ for fluids having Prandtl number equals 0.72 and 7.0 are determined.
Details
Keywords
Ramadevi B., Sugunamma V., Anantha Kumar K. and Ramana Reddy J.V.
The purpose of this paper is to focus on MHD unsteady flow of Carreau fluid over a variable thickness melting surface in the presence of chemical reaction and non-uniform heat…
Abstract
Purpose
The purpose of this paper is to focus on MHD unsteady flow of Carreau fluid over a variable thickness melting surface in the presence of chemical reaction and non-uniform heat sink/source.
Design/methodology/approach
The flow governing partial differential equations are transformed into ordinary ones with the help of similarity transformations. The set of ODEs are solved by a shooting technique together with the R.K.–Fehlberg method. Further, the graphs are depicted to scrutinize the velocity, concentration and temperature fields of the Carreau fluid flow. The numerical values of friction factor, heat and mass transfer rates are tabulated.
Findings
The results are presented for both Newtonian and non-Newtonian fluid flow cases. The authors conclude that the nature of three typical fields and the physical quantities are alike in both cases. An increase in melting parameter slows down the velocity field and enhances the temperature and concentration fields. But an opposite outcome is noticed with thermal relaxation parameter. Also the elevating values of thermal relaxation parameter/ wall thickness parameter/Prandtl number inflate the mass and heat transfer rates.
Originality/value
This is a new research article in the field of heat and mass transfer in fluid flows. Cattaneo–Christov heat flux model is used. The surface of the flow is assumed to be melting.
Details
Keywords
Iman Rashidi, Lioua Kolsi, Goodarz Ahmadi, Omid Mahian, Somchai Wongwises and E. Abu-Nada
This study aims to investigate a three-dimensional computational modelling of free convection of Al2O3 water-based nanofluid in a cylindrical cavity under heterogeneous heat fluxes…
Abstract
Purpose
This study aims to investigate a three-dimensional computational modelling of free convection of Al2O3 water-based nanofluid in a cylindrical cavity under heterogeneous heat fluxes that can be used as a thermal storage tank.
Design/methodology/approach
Effects of different heat flux boundary conditions on heat transfer and entropy generation were examined and the optimal configuration was identified. The simulation results for nanoparticle (NP) volume fractions up to 4 per cent, and Rayleigh numbers of 104, 105 and 106 were presented.
Findings
The results showed that for low Ra (104) the heat transfer and entropy generation patterns were symmetric, whereas with increasing the Rayleigh number these patterns became asymmetric and more complex. Therefore, despite the symmetric boundary conditions imposed on the periphery of the enclosure (uniform in Ɵ), it was necessary to simulate the problem as three-dimensional instead of two-dimensional. The simulation results showed that by selecting the optimal values of heat flux distribution and NP volume fraction for these systems the energy consumption can be reduced, and consequently, the energy efficiency can be ameliorated.
Originality/value
The results of the present study can be used for the design of energy devices such as thermal storage tanks, as both first and second laws of thermodynamics have been considered. Using the optimal design will reduce energy consumption.
Details
Keywords
Gongnan Xie, Shian Li, Bengt Sunden and Weihong Zhang
With the development of electronic devices, including the desires of integration, miniaturization, high performance and the output power, cooling requirement of chips have been…
Abstract
Purpose
With the development of electronic devices, including the desires of integration, miniaturization, high performance and the output power, cooling requirement of chips have been increased gradually. Water-cooled minichannel is an effective cooling technology for cooling of heat sinks. The minichannel flow geometry offers large surface area for heat transfer and a high convective heat transfer coefficient with only a moderate pressure loss. The purpose of this paper is to analyze a minichannel heat sink having the bottom size of 35 mm×35 mm numerically. Two kinds of chip arrangement are investigated: diagonal arrangement and parallel arrangement.
Design/methodology/approach
Computational fluid dynamics (CFD) technique is used to investigate the flow and thermal fields in forced convection in a three-dimensional minichannels heat sink with different chip arrangements. The standard k-e turbulence model is applied for the turbulence simulations on the minichannel heat sink.
Findings
The results show that the bottom surface of the heat sink with various chip arrangements will have different temperature distribution and thermal resistance. A suitable chip arrangement will achieve a good cooling performance for electronic devices.
Research limitations/implications
The fluid is incompressible and the thermophysical properties are constant.
Practical implications
New and additional data will be helpful as guidelines in the design of heat sinks to achieve a good thermal performance and a long lifetime in operation.
Originality/value
In real engineering situations, chips are always placed in various manners according to design conditions and constraints. In this case the assumption of uniform heat flux is acceptable for the surfaces of the chips rather than for the entire bottom surface of the heat sink.
Details