Heat transfer enhancement with nanofluid in an open enclosure due to discrete heaters mounted on sidewalls and a heated inner block

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Endalkachew Getachew Ushachew ◽  
Mukesh Kumar Sharma ◽  
Mohammad Mehdi Rashidi
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Heat Convection ◽  
Physical Parameters ◽  
Transfer Enhancement ◽  
Temperature Zone ◽  
Content Type ◽  
Rectangular Enclosure

Purpose The purpose of this study is to explore the heat transfer enhancement in copper–water nanofluid flowing in a diagonally vented rectangular enclosure with four discrete heaters mounted centrally on the sidewalls and a square-shaped embedded heated block in the influence of a static magnetic field. Design/methodology/approach Four discrete heaters are mounted centrally on each sidewall of the rectangular enclosure that embraces a heated square block. A static transverse magnetic field is acting on the vertical walls. The Navier–Stokes equations of motion and the energy equation are modified by incorporating Lorentz force and basic physical properties of nanofluid. The derived momentum and energy equations are tackled numerically using the successive over-relaxation technique associating with the Gauss–Seidel iteration technique. The effects of physical parameters connected to dynamics of flow and heat convection are explored from streamlines and isotherms graphs and discussed numerically in terms of Nusselt number. Findings The effect of the embedded heated square block size and its location in the enclosure, nanoparticles volume fraction and the intensity of the magnetic field on flow and heat transfer are computed. Compared with the case when no heated block is embedded in the enclosure, in free convection at Ra = 106, the average local Nusselt number on the wall-mounted heaters is attenuated by 8.25%, 11.24% and 12.75% when the enclosure embraced a heated square block of side length 10% of H, 20% of H and 30% of H, respectively. An increase in Hartmann number suppresses the heat convection. Research limitations/implications The enhancement in the convective heat is greater when the buoyancy effect dominates the viscous effects. Placing the embedded heated block near the inlet vent, the lower temperature zone has reduced while the embedded heated block is at the central location of the enclosure, the high-temperature zone has expanded. The external magnetic field can be used as a non-invasive controlling device. Practical implications The numerically simulated results for heat convection of water-based copper nanofluid agreed qualitatively with the existing experimental results. Social implications The models could be used in designing a target-oriented heat exchanger. Originality/value The paper includes a comparative study for three locations of the embedded heated square. The optimal results for the centrally located heated block are also performed for three different sizes of the embedded block. The numerically simulated results are compared with the published numerical and experimental studies.

Effect of vibrator position and frequency on heat transfer enhancement in counter flow concentric pipe heat exchanger

2020 ◽  
Vol 17 (5) ◽  
pp. 751-760
Author(s):  
Shanmukh Sudhir Arasavelli ◽  
Ramakrishna Konijeti ◽  
Govinda Rao Budda
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Heat Transfer Enhancement ◽  
Hot Water ◽  
Transfer Enhancement ◽  
Counter Flow ◽  
Pipe Length ◽  
Content Type ◽  
Pipe Heat

Purpose This paper aims to deal with heat transfer enhancement because of transverse vibration on counter flow concentric pipe heat exchanger. Experiments were performed at different vibrator positions with varying amplitudes and frequencies. Design/methodology/approach Tests are carried out at 4 different vibration frequencies (20, 40, 60 and 100 Hz), 3 vibration amplitudes (23, 46 and 69 mm) and at 3 vibrator positions (1/4, 1/2 and 3/4 of pipe length) with respect to hot water inlet under turbulent flow condition. Findings Experimental results indicate that Nusselt number is enhanced to a maximum extent of 44% with vibration when compared to Nusselt number without vibration at a frequency of 40 Hz, an amplitude of 69 mm and at a vibrator position of one-fourth of pipe length with respect to hot water inlet. Originality/value Empirical correlation is developed from experimental data to estimate the heat transfer coefficient with vibration for experimental frequency range with an error estimate of approximately ±10%.

Effect of adding nanoparticle on squeezing flow and heat transfer improvement using KKL model

2017 ◽  
Vol 27 (7) ◽  
pp. 1535-1553 ◽  
Author(s):  
M. Sheikholeslami ◽  
D.D. Ganji
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Volume Fraction ◽  
Nanoparticle Volume Fraction ◽  
Transfer Enhancement ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Squeeze Number

Purpose Nanofluid flow which is squeezed between parallel plates is studied using differential transformation method (DTM). The fluid in the enclosure is water containing different types of nanoparticles: Al2O3 and CuO. The effective thermal conductivity and viscosity of nanofluid are calculated by Koo–Kleinstreuer–Li (KKL) correlation. The comparison between the results from DTM and numerical method are in well agreement which proofs the capability of this method for solving such problems. Effects of the squeeze number and nanofluid volume fraction on flow and heat transfer are examined. Results indicate that Nusselt number augment with increase of the nanoparticle volume fraction. Also, it can be found that heat transfer enhancement of CuO is higher than Al2O3. Design/methodology/approach The problem of nanofluid flow which is squeezed between parallel plates is investigated analytically using DTM. The fluid in the enclosure is water containing different types of nanoparticles: Al2O3 and CuO. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL correlation. In this model, effect of Brownian motion on the effective thermal conductivity is considered. The comparison between the results from DTM and numerical method are in well agreement which proves the capability of this method for solving such problems. The effect of the squeeze number and the nanofluid volume fraction on flow and heat transfer is investigated. The results show that Nusselt number increase with increase of the nanoparticle volume fraction. Also, it can be found that heat transfer enhancement of CuO is higher than Al2O3. Findings The effect of the squeeze number and the nanofluid volume fraction on flow and heat transfer is investigated. The results show that Nusselt number increase with increase of the nanoparticle volume fraction. Also, it can be found that heat transfer enhancement of CuO is higher than Al2O3. Originality/value This paper is original.

Multi-objective optimization of the dimple/protrusion channel with pin fins for heat transfer enhancement

2019 ◽  
Vol 29 (2) ◽  
pp. 790-813 ◽  
Author(s):  
Lei Luo ◽  
Wei Du ◽  
Songtao Wang ◽  
Weilong Wu ◽  
Xinghong Zhang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Dissipative Function ◽  
Transfer Enhancement ◽  
Nsga Ii ◽  
Content Type ◽  
Pin Fin ◽  
Geometry Model

PurposeThe purpose of this paper is to investigate the optimal geometry parameters in a dimple/protrusion-pin finned channel with high thermal performance.Design/methodology/approachThe BSL turbulence model is used to calculate the flow structure and heat transfer in a dimple/protrusion-pin finned channel. The optimization algorithm is set as Non-dominated Sorting Genetic Algorithm II (NSGA-II). The high Nusselt number and low friction factor are chosen as the optimization objectives. The pin fin diameter, dimple/protrusion diameter, dimple/protrusion location and dimple/protrusion depth are applied as the optimization variables. An in-house code is used to generate the geometry model and mesh. The commercial software Isight is used to perform the optimization process.FindingsThe results show that the Nusselt number and friction factor are sensitive to the geometry parameters. In a pin finned channel with a dimple, the Nusselt number is high at the rear part of the dimple, while it is low at the upstream of the dimple. A high dissipative function is found near the pin fin. In the protrusion channel, the Nusselt number is high at the leading edge of the protrusion. In addition, the protrusion induces a high pressure drop compared to the dimpled channel.Originality/valueThe originality of this paper is to optimize the geometry parameters in a pin finned channel with dimple/protrusion. This is good application for the heat transfer enhancement at the trailing side for the gas turbine.

scholarly journals A Study on the Mechanism of Convective Heat Transfer Enhancement Based on Heat Convection Velocity Analysis

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4175 ◽  
Author(s):  
Hui Xiao ◽  
Zhimin Dong ◽  
Rui Long ◽  
Kun Yang ◽  
Fang Yuan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Temperature Gradient ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Circular Tube ◽  
Heat Convection ◽  
Convection Velocity ◽  
Transfer Enhancement

This paper explores the mechanism of convective heat transfer enhancement in a new perspective. In this paper, a new parameter called heat convection velocity is proposed based on the field synergy principle. It is defined as the velocity projection on the temperature gradient vector and reflects the magnitude of the velocity component that contributes to heat convection. Three typical cases are taken into consideration to investigate the influence factors of Nusselt number theoretically. The results indicate that the Nusselt number can be enhanced by increasing the mean heat convection velocity and the dimensionless mean temperature difference. Through theoretical analysis, three suggestions are found for designing heat transfer enhancement components: (a) the overall synergetic effect should be improved; (b) the fluid with lower temperature gradient should be guided to the region where the temperature gradient is higher; (c) temperature distribution should be an interphase distribution of hot and cold fluid. Besides, the heat convection velocity is used to investigate the mechanism of convective heat transfer in the smooth tube. It is found that the increase of Nusselt number is due to the increase of heat convection velocity. In addition, according to design suggestions, a new insert is invented and inserted in the circular tube. With heat convection velocity analysis, it is found that there is much potential of increasing heat convection velocity for enhancing the convective heat transfer in the circular tube.

Magnetohydrodynamic thermal characteristics of water-based hybrid nanofluid-filled non-Darcian porous wavy enclosure: effect of undulation

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Nirmalendu Biswas ◽  
Dipak Kumar Mandal ◽  
Nirmal K. Manna ◽  
Rama Subba Reddy Gorla ◽  
Ali J. Chamkha
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Free Convection ◽  
Heat Transfer Enhancement ◽  
Hybrid Nanofluid ◽  
Wavy Wall ◽  
Transfer Enhancement ◽  
Volumetric Fraction ◽  
Content Type ◽  
Water Based

Purpose The aims of this study is to numerically investigate the thermal phenomena during magnetohydrodynamic (MHD) free convection in an oblique enclosure filled with porous media saturated with Cu–Al2O3/water hybrid nanofluid and heated at the left wavy wall. The thermophysical phenomena are explored thoroughly by varying the amplitude (λ) and undulation (n) of the wavy wall and the inclination of the enclosure (γ) along with other pertinent physical parameters. Darcy–Rayleigh number (Ram), Darcy number (Da), Hartmann number (Ha) and nanoparticle volumetric fraction (ϕ). The effect of all parameters has been analyzed and represented by using heatlines, isotherms, streamlines, average Nusselt number and local Nusselt number. Design/methodology/approach The finite volume method is used to work out the transport equations coupled with velocity, pressure and temperature subjected to non-uniform staggered grid structure after grid-sensitivity analysis by an indigenous computing code and the semi-implicit method for pressure linked equations (SIMPLE) algorithm. The solution process is initiated following an iterative approach through the alternate direction implicit sweep technique and the tridiagonal matrix algorithm (TDMA) algorithm. The iterative process is continued until successive minimization of the residuals (<1e-8) for the governing equations. Findings This study reveals that the increase in the heating surface area does not always favor heat transfer. An increase in the undulation amplitude enhances the heat transfer; however, there is an optimum value of undulation of the wavy wall for this. The heat transfer enhancement because of the wall curvature is revealed at higher Ram, lower Da and Ha and lower volume fraction of nanoparticles. In general, this augmentation is optimum for four undulations of the wavy wall with an amplitude of λ = 0.3. The heat transfer enhancement can be more at the cavity inclination   γ = 45°. Research limitations/implications The technique of this investigation could be used in other multiphysical areas involving partial porous layers, conducting objects, different heating conditions, wall motion, etc. Practical implications This study is to address MHD thermo-fluid phenomena of Cu–Al2O3/water-based hybrid nanofluid flow through a non-Darcian porous wavy cavity at different inclinations. The amplitude and number of undulations of the wavy wall, permeability of the porous medium, magnetic field intensity, nanoparticle volumetric fraction and inclinations of the enclosure play a significant role in the heat transfer process. This analysis and the findings of this work can be useful for the design and control of similar thermal systems/devices. Originality/value Many researchers have examined the problem of buoyancy-induced free convection in a wavy-porous cavity packed with regular fluids or nanofluids. However, the effect of magnetic fields along with the amplitude (λ) at different undulations (n) of the heated wavy wall of an inclined enclosure is not attended so far to understand the transport mechanisms. Most often, the evolutions of the thermo-fluid phenomena in such complex geometries invoking different multiphysics are very intricate. Numerical implementations for simulations and subsequent post-processing of the results are also challenging.

Study of the boundary layer heat transfer of nanofluids over a stretching sheet: Passive control of nanoparticles at the surface

2015 ◽  
Vol 93 (7) ◽  
pp. 725-733 ◽  
Author(s):  
M. Ghalambaz ◽  
E. Izadpanahi ◽  
A. Noghrehabadi ◽  
A. Chamkha
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Base Fluid ◽  
Stretching Sheet ◽  
Volume Fraction ◽  
Enhancement Ratio ◽  
Transfer Enhancement

The boundary layer heat and mass transfer of nanofluids over an isothermal stretching sheet is analyzed using a drift-flux model. The relative slip velocity between the nanoparticles and the base fluid is taken into account. The nanoparticles’ volume fractions at the surface of the sheet are considered to be adjusted passively. The thermal conductivity and the dynamic viscosity of the nanofluid are considered as functions of the local volume fraction of the nanoparticles. A non-dimensional parameter, heat transfer enhancement ratio, is introduced, which shows the alteration of the thermal convective coefficient of the nanofluid compared to the base fluid. The governing partial differential equations are reduced into a set of nonlinear ordinary differential equations using appropriate similarity transformations and then solved numerically using the fourth-order Runge–Kutta and Newton–Raphson methods along with the shooting technique. The effects of six non-dimensional parameters, namely, the Prandtl number of the base fluid Prbf, Lewis number Le, Brownian motion parameter Nb, thermophoresis parameter Nt, variable thermal conductivity parameter Nc and the variable viscosity parameter Nv, on the velocity, temperature, and concentration profiles as well as the reduced Nusselt number and the enhancement ratio are investigated. Finally, case studies for Al2O3 and Cu nanoparticles dispersed in water are performed. It is found that increases in the ambient values of the nanoparticles volume fraction cause decreases in both the dimensionless shear stress f″(0) and the reduced Nusselt number Nur. Furthermore, an augmentation of the ambient value of the volume fraction of nanoparticles results in an increase the heat transfer enhancement ratio hnf/hbf. Therefore, using nanoparticles produces heat transfer enhancement from the sheet.

HEAT TRANSFER ENHANCEMENT IN A CHANNEL PARTIALLY FILLED WITH A POROUS BLOCK: LATTICE BOLTZMANN METHOD

2013 ◽  
Vol 24 (09) ◽  
pp. 1350060 ◽  
Author(s):  
M. NAZARI ◽  
M. H. KAYHANI ◽  
R. MOHEBBI
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Lattice Boltzmann Method ◽  
Heat Transfer Enhancement ◽  
Lattice Boltzmann ◽  
Block Size ◽  
Blockage Ratio ◽  
Transfer Enhancement ◽  
Porous Block ◽  
Boltzmann Method

The main goal of the present study is to investigate the heat transfer enhancement in a channel partially filled with an anisotropic porous block (Porous Foam) using the lattice Boltzmann method (LBM). Combined pore level simulation of flow and heat transfer is performed for a 2D channel which is partially filled with square obstacles in both ordered and random arrangements by LBM which is not studied completely in the literature. The effect of the Reynolds number, different arrangements of obstacles, blockage ratio and porosity on the velocity and temperature profiles inside the porous region are studied. The local and averaged Nusselt numbers on the channel walls along with the respective confidence interval and comparison between results of regular and random arrangements are presented for the first time. For constant porosity and block size, the maximum value of averaged Nusselt number in the porous block is obtained in the case of random arrangement of obstacles. Also, by decreasing the porosity, the value of averaged Nusselt number is increased. Heat transfer to the working fluids increases significantly by increasing the blockage ratio. Several blockage ratios with different arrangements are checked to obtain a correlation for the Nusselt number.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

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