Enhancement In Average Nusselt Number Research Articles

Thermo-fluid analysis on novel design of central impact-inlet double layered micro-channel heat sinks featured with bifurcation verified by experiments

CI-DL-MHCS represents designed central impact-inlet double layered microchannel heat sinks which shows the principal heat transfer feature, and the novel bifurcation is added on upper/lower deck in CI-DL-MHCS, namely CI-DL-MHCS-UB/LB, to explore the further overall thermal advantages numerically and experimentally. The internal located bifurcation parameters including position in CI-DL-MHCS and length have been investigated in the work with the coolant velocities in the range of 0.25–1.05 m/s. The calculated models in simulation is set as symmetric boundary condition, while the assumptions including RNG k-ε turbulence flow and incompressibility dominate in the paper. Bifurcation located lower deck of CI-DL-MHCS has been shown to be effective in controlling the substrate temperature, with a reduction in peak temperature of >18 K compared to referenced CI-DL-MHCS. Numerical simulations clearly demonstrate the enhancement of heat transfer caused by impingement jets and novel located bifurcations with experimental verification. Besides, CI-DL-MHCS with bifurcation have an average Nusselt number enhancement by 4.47% higher compared with CI-DL-MHCS without bifurcation. The bifurcation inevitably occupies the space in CI-DL-MHCS, resulting in a higher pressure drop penalty than the proposed bifurcated structure CI-DL-MHCS, but this can be balanced by an increase in heat transfer considering the overall thermal performance factor. Thus, CI-DL-MHCS featured with bifurcation located in CI-DL-MHCS-LB_3 outperforms significantly in overall thermal performance and thermal uniformity on substrate among all the designed tested models.

Numerical investigation of the thermal-hydraulic performance of a novel parabolic trough wavy tubular receiver by using FMWNCT/oil-nanofluid coupled with fins

This study employs a computational fluid dynamics (CFD) approach to assess the performance of a novel wavy profile tube receiver. It integrates rectangular fins and an Oil-based nanofluid, specifically utilizing Thermodyne GG-03 synthetic oil combined with Functionalized Multi-Wall Carbon Tubes (FMWNCT). The synthesis involves rigorous experimental procedures to characterize the thermophysical properties of the oil and nanofluid. Empirical correlations, validated against Bitam et al.'s model [1], guide the numerical analysis. The investigation, utilizing a steady-state κ - ω SST turbulence model with a non-uniform Gaussian thermal flux distribution, explores thermohydraulic performance in fully developed turbulent flow (Reynolds number range: 2 × 104 – 5 × 104). Comparative analysis with Bitam et al.'s work, employing Syltherm 800 oil as a reference, reveals a 25.76% average Nusselt number enhancement with Thermodyne GG-03. Additional improvements are observed: 124.69% with FMWNCT/oil-nanofluid, 137.04% with fins, and 236.54% with combined FMWNCT/oil-nanofluid and fins. These enhancements lead to increased heat transfer coefficients and rates. The friction coefficient rises by less than 60%, mainly attributed to the Nusselt number improvement. At RE = 20000, the Maximum Performance Evaluation Criteria (PEC) is 5.5, signifying significant improvement. Notably, a 300% PEC enhancement is observed compared to Roger and Mayhew's curved tube model [1]. In conclusion, these findings offer valuable insights for efficiently designing wavy tubular receivers in PTR collectors.

Heat transfer and hydraulics for a novel receiver pipe of solar parabolic trough: a computational approach.

The effect of symmetrical convex-concave corrugations on receiver pipe of a parabolic trough solar collector is numerically investigated. Twelve distinct geometrically configured receiver pipes with corrugations have been examined for this purpose. The computational study is conducted for varying corrugation pitch (4mm to 10mm) and height (1.5mm to 2.5mm). Heat transfer enhancement, flow behavior, and overall thermal performance of fluid moving through a pipe under non-uniform heat flux condition are all determined in this work. The Reynolds number ranges from 5000 to 50,000. The findings reveal that presence of corrugations leads to axial whirling and vortices in the receiver pipe, thus enhancing the heat transfer. The receiver pipe having corrugations of 8mm pitch and 2mm height gave the best results. The maximum enhancement in average Nusselt number over smooth pipe has been observed as 28.51%. In addition, relationships of Nusselt number and friction factor against selected design parameters and operating conditions are also displayed as correlations.

Heat transfer in a conical gap using H2O–Cu nanofluid and porous media. Effects of the main physical parameters

Heat transfer around a conical antenna is quantified in this work. Cooling of this active electronic component is ensured by a medium of high porosity saturated by a H2O–Cu nanofluid with a volume fraction varying between 0% and 5%. The ratio between the thermal conductivity of the porous materials and that of the water (base fluid) ranges from 4 to 41.2, the null value corresponding to a heat transfer without porous media (only nanofluid). The conical enclosure's aspect ratio varies in the 0.2–0.6 range, being its base inclined between 0° (horizontal base with cone's top oriented upwards) and 180° range (horizontal base with cone's top oriented downwards). The associated Rayleigh number varies within the 3.32x105-6.74x107 range. Heat transfer by natural convection is quantified for any configuration combining these five parameters and presented via a correlation allowing determination of the average Nusselt number. This study shows that heat transfer increases when the cone is tilted. For a given aspect ratio, the maximum is reached when the cone is vertical with the top pointing down. This observation remains valid in the overall Rayleigh number range. The average Nusselt number enhancement varies between 20 and 70%, according on the considered cavity's aspect ratio. This study complements a recent one restricted to the case of a cone whose horizontal base is located at the bottom, being 0.2 the aspect ratio of the enclosure.

Investigation on Circular Array of Turbulent Impinging Round Jets at Confined Case: A CFD Study

Jet impingement has immense applications in industrial cooling, such as glass tempering, turbine blades, electrical equipment, etc. The interplay in-between several jet arrangements and the effect of swirl intensity require enormous study to achieve steady heat transfer. This paper numerically investigates an inline array of 25 circular confined swirling air jets impinging vertically on a flat surface. In this regard, three-dimensional simulations are executed using the finite volume method for a number of control parameters, such as Reynolds number (Re = 11600, 24600, and 35000), impinging distance (H/D = 0.25, 0.5, 1), swirl number (S = 0.3 and 0.75) and jet-to-jet separation distance (Z/D = 2.5), where, D is the nozzle diameter. Impinging pressure distribution, flow velocity, surface Nusselt number, and Reynolds stresses are investigated for different operating conditions. The results reveal that both the wall pressure and surface Nusselt number are comparatively uniform in the case of high swirl flow. Moreover, distinct heat transfer behavior is observed from the unconfined condition for high swirl flow in which the heat transfer is constant after a certain radial distance. The Reynolds normal stress adjacent to the nozzle exit is more rigorous than the downstream regions while Reynolds shear stress varies unpredictably along the radial direction. In addition, an estimated 102 % enhancement in average Nusselt number is observed for high swirl flow, at a Reynolds number increment from 11600 to 35000. This enhancement is evident by 23 % in terms of thermal performance factor. Besides, the average Nusselt number and thermal performance factor augmented by 19 % and 8 %, respectively, for an increased swirl intensity at low a Reynolds number (Re =11600).

Numerical investigation into heat transfer augmentation in a square minichannel heat sink using butterfly inserts

Heat transfer augmentation in a square minichannel heat sink through introduction of various butterfly insert configurations is numerically investigated for a range of Reynolds numbers (200 – 900). The present study also examines the individual effects of insert, pitch of the insert, and perforations in the wings of the butterfly insert on the thermohydraulic performance of minichannel heat sinks. Incorporating any kind of insert in a typical square minichannel is found to have a positive influence on the overall thermohydraulic performance, yielding performance evaluation criteria consistently over unity for the whole range of tested Reynolds numbers. The effect of pitch is tested for unperforated inserts, wherein a reduction of pitch distance from 10 mm to 5 mm is found to increase heat transfer performance by 15.08 - 46.39% for the studied range of Reynolds numbers. Perforations in the wings of butterfly inserts are found to result in a reduction of friction factor, with a 4.01 – 20.78% decrease, when compared with an unperforated insert having an identical pitch. However, this reduction is achieved at the cost of a lower heat transfer performance (5.07 – 16.17%). Therefore, unperforated butterfly inserts are deemed to be superior in terms of the overall thermohydraulic enhancement. In all enhanced minichannel configurations, a redistribution of velocity and temperature fields due to the formation of a primary vortex pair and thinning of thermal boundary layers due to a second pair of secondary vortices are thought to be the major contributors behind the observed thermohydraulic enhancement. • Introduction of a butterfly insert with 10 mm pitch is found to enhance heat transfer performance in MCHS by 42.02% to 109.31% for the tested range of Reynolds numbers. • A reduction in pitch from 10 mm to 5 mm in an MCHS with unperforated butterfly inserts is observed to yield an augmentation of average Nusselt number by 15.08% to 46.39% for the studied range of Reynolds numbers. • Perforation on insert wings is found produce a reduced enhancement in average Nusselt number, i.e., 5.07%–16.17%, for the investigated range of Reynolds numbers. • Observed thinning and disruption of thermal boundary layers and enhanced fluid mixing at the central region of the minichannel due to a pair of primary vortices are thought to be the major reasons for enhanced thermal performance. • A maximum performance evaluation criterion of 1.66 is observed for the case of unperforated butterfly inserts with 5 mm pitch at a Reynolds number of 900.

Natural Thermo-Bio Convection of gyrotactic micro-organisms in a square cavity with two heaters inside: application to ocean ecosystems

ABSTRACT The paper reports the natural thermo-bio-convection of gyrotactic microorganisms in a square cavity with two smaller square heat sources inside the cavity. The flow is assumed to be two-dimensional, steady, buoyancy-driven, and Newtonian. The work investigates the influences of thermal Rayleigh number, bio-convection Rayleigh number, Lewis number, and Peclet number on the natural convection heat transfer, entropy generation, and micro-organism concentration. The governing equations are discreted by finite element method. The diffusion equation is used for the motion of microorganisms, and the energy equation is considered for the effects of temperature. The main finding of this study is that both thermal and bio-convection Rayleigh number improve thermo-bio-convection performance of gyrotactic microorganisms in a square cavity with two square heaters inside the cavity. For high thermal Rayleigh numbers (Rat = 105), increasing Rab from 10 to 100 causes 4.5% enhancement in average Nusselt number and average Sherwood number decreases by 4.5%. These findings are applicable in various fields of expertise such as ocean ecosystems, oil recovery and fuel cells.

Thermal efficiency of eco-friendly MXene based nanofluid for performance enhancement of a pin-fin heat sink: Experimental and numerical analyses

MXenes are an eco-friendly innovative type of graphene-like nanomaterials and are proven to exhibit remarkable thermal, electrical, mechanical and optical properties. This study is aimed at evaluating the thermal efficiency of novel Ti3C2Tx MXene-based nanofluid in a pin-fin heat sink was via experimental and numerical analyses. The aqueous-based 2D Ti3C2Tx MXene nanofluid was synthesised in a two-step process, followed by their characterisation and experimental testing. For the numerical analysis, the forced convection of the nanofluid was simulated through multiphase Lagrangian–Eulerian approximation by incorporating the interphase interactions of Brownian motion, thermophoresis, drag and Saffman lift forces, gravity, virtual mass and pressure gradient-induced forces. The thermal performance of the MXene nanofluids was assessed in terms of log mean temperature difference, average Nusselt number, local temperature and local Nusselt number distribution at the base of the heat sink and thermal contours. Their fluid flow characteristics were probed by analysing the coolant pumping power, flow streamlines distribution and performance evaluation criteria of the heat sink. Results demonstrated that utilising the MXene-based coolant resulted in a significant average Nusselt number enhancement at the expense of a small increase in coolant pumping power. Maximum improvements of 29.8 and 40.5% in the average Nusselt number were observed for nanoparticle concentrations of 0.013 vol% and 0.027 vol% respectively.

Heat transfer enhancement using elliptical fin microchannel

AbstractThermal performance and fluid flow characteristics of elliptical fin microchannel are numerically investigated by varying fin orientation in the laminar flow region. Six distinctly oriented elliptical fins ranging 0°–12° along channel length are numerically examined for inlet Reynolds number (Re) ranging 174–748. The same is compared with the conventional straight fin microchannel. It is found that continuous straight fin when replaced with a series of short length elliptical fins leads to re‐establishment of the thermal boundary layer and results in thinning of boundary layer thickness. By varying the fin angle, fluid is directed from primary channel to secondary channel which finally flows into the primary channel. These secondary flows disrupt the boundary layer and show better fluid mixing in the channel. Among all the orientations considered, elliptical fin oriented at 2° yields better cooling performance ensuing an optimum average Nusselt number enhancement of 116% (7.68–16.64) with a very less pressure penalty (15%). Besides this, the rise in wall temperature is reduced by 25.39% in comparison to straight fin microchannel.

Effect of Rib Shape on Flow Regime and Heat Transfer

In current study, flow behavior and heat transfer properties in a square channel roughened with square, right triangle, isosceles triangle and circular ribs were examined. The validation test was performed for an experimental square rib case with a pitch ratio (P/e) of 9 and a blockage ratio (e/H) of 0.1. Only to examine the rib shape factor; height, base width, and rib spacing were taken the same in all cases. The study investigated the effect of various rib shapes on flow characteristics, overall thermal performances, normalized heat transfer distributions, and friction factors (pressure losses) at Reynolds numbers of 30,000 and 60,000. As a result of the numerical study, it was found that the rib shape effect did not cause as big differences in the flow properties as the blockage ratio (rib height) and pitch ratio (rib spacing) effect. In terms of the average Nusselt number enhancement, the right triangular ribbed case performed best, circular ribbed case performed worst, while the isosceles ribbed case performed better than square ribbed case. The isosceles ribbed case and right triangular ribbed case cause higher friction factor and pressure loss, while minimum friction is obtained in circular ribbed case and then in square ribbed case. As a result, in terms of overall thermal performances, right triangular ribbed case provided the best performance, followed by isosceles triangular ribbed case. The circular ribbed case produced less friction than the square ribbed case. The thermal performance of the square ribbed case was slightly higher than that of circular ribbed case.

Experimental study on heat transfer and pressure drop characteristics utilizing three types of water based nanofluids in a helical coil under isothermal boundary condition

• Three types of nanofluids TiO 2 /water, ZnO /water and Ag /water through helical coils are experimentally investigated. . • Increasing the coil pitch reduces both Nusselt number and pressure drop. • Nusselt number enhancement up to 28.7 %, 17.8 % and 11.8 % was achieved for TiO 2 /water, ZnO /water and Ag /water respectively. • Pressure drop increasing up to 28.5%, 23.5% and 25.4% was observed for TiO 2 /water, ZnO /water and Ag /water respectively. • Novel correlations are introduced for Nusselt number and pressure drop. Nanofluids are an innovative attractive challenging field suitable for many heat transfer applications. The helical coil is preferred due to compactness and additional curvature flow disturbance. Heat transfer and pressure drop characteristics of Ag, ZnO and TiO 2 water based nanofluids through helical coil tubes under isothermal boundary conditions are experimentally investigated with 0.25% nanoparticles volume concentration Ag /water, ZnO /water and TiO 2 /water nanofluids. Five coils are constructed with different coil pitches of 2, 4, 6, 8 and 10 cm. The flow rate of the nanofluid varies between 1 to 3.5 L/min with inlet temperature from 30 °C to 60 °C. The results showed that increasing the coil pitch reduces Nusselt number and pressure drop. The nanofluids have a positive impact on the enhancement of heat transfer but with a pressure drop penalty. Average Nusselt number enhancement up to 11.8 %, 17.8 % and 28.7 % was achieved at Ag /water, ZnO /water and TiO 2 /water with average pressure drop increasing up to 25.4%, 23.5% and 28.5% respectively. The results showed that an increase in coil pitch decreases hydrothermal performance index ( HTPI) and utilizing nanofluids increases HTPI for all types of nanofluids Ag /water, ZnO /water and TiO 2 /water. Novel correlations were developed to predict Nusselt number and pressure drop. Graphical Abstract .

NUMERICAL STUDY OF VARIATION IN DRAG AND VIRTUAL MASS FORCES FOR A NANOFLUID FLOW THROUGH A MICROCHANNEL USING EULERIAN-EULERIAN TWO-PHASE MODEL

Laminar forced convection of copper oxide (CuO) and titanium oxide (TiO2 ) water-based nanofluid flow through a microchannel has been studied numerically using a Eulerian–Eulerian two-phase model. The governing equations of the liquid phase and solid phase are solved using sixth-order compact finite difference schemes. The effects of Reynolds number and nanoparticle volume concentrations on drag and virtual mass forces are reported. Estimation of thermal conductivity for nanofluid has been discussed here using two-phase results. Results show that significant heat transfer enhancement is observed with an increase in Reynolds number and nanoparticle volume concentrations compared with pure water. The 2 vol % CuO nanofluid has shown 3.44% and 18.65% enhancement in average Nusselt number compared to pure water for Re = 50 and Re = 600, respectively. An increase in particle concentration from 1% to 3% leads to a 4.45% increase in the average Nusselt number at Re = 200 for CuO nanofluid. A significant change of 26.5% is found in the dimensionless drag force with an increase in Reynolds number from 50 to 600. A negligible change in dimensionless drag force is observed with an increase in nanoparticle concentrations for Re ≥ 200. The virtual mass force is less significant than the drag force for nanofluid flows. Present results show a small deviation between the obtained and experimental thermal conductivity of nanofluid. The developed two-phase numerical model is validated with the numerical and experimental results available in the literature.

Effects of a rotating tube bundle on the hydrothermal performance for forced convection in a vented cavity with Ag–MgO/water hybrid and CNT–water nanofluids

In this study, effects of rotating tube bundle on the hydrothermal performance for the forced convection in a vented cavity are numerically studied with a mixture of Ag and MgO nanoparticles suspended in water, forming a hybrid nanofluid and CNT–water nanofluid. The finite volume method is used for the numerical simulations. The simulation study is performed for various values of Reynolds number (between 100 and 1000), rotational Reynolds number (between − 100 and 100), size (between 0.01H and 0.12H), vertical (between 0.3H and 0.65H) and horizontal locations (between 0.3H and 0.65H) of the cylinder in the tube bundle and nanoparticle volume fraction (between 0 and 0.02). An experimental correlation was used for the description of the Ag–MgO/water hybrid nanofluid. Results indicated that the rotational effects of the tube bundle contribute to the hydrothermal performance. The average Nusselt number enhancements are 8.95% and 40% when CNT–water is used for solid volume fraction of 0.02 at the highest speed, while these values are 31.5% and 37.7% for hybrid nanofluid. The pressure coefficients are higher for negative value of $${\text {Re}}_{\upomega }$$ and hybrid nanofluid. The size of the tube bundle is effective at the highest size, while the increment amount is 16.8% both for CNT–water and for hybrid nanofluids. The center location of the tube bundle resulted in heat transfer enhancement which is in the range of 11% and 18%. As the solid volume fraction of nanoparticles becomes higher, discrepancies between the average Nu values of CNT–water nanofluid and Ag–MgO/water hybrid nanofluid become higher which is also observed for the pressure coefficient. It is advantageous to use CNT particles since higher heat transfer coefficients with lower values of pressure coefficient are obtained.

RETRACTED: MRT lattice Boltzmann simulation of free convection in a symmetrical annulus combined with experimental data of TiO2-H2O nanofluid's properties

Abstract The axisymmetric nanofluid flow and heat transfer in a two-dimensional vertical annulus are investigated. The Multi-Relaxation-Time lattice Boltzmann model is used to simulate the flow and temperature fields. Hence, the macro cylindrical energy equation is exactly recovered using Chapman-Enskog analysis. The numerical results of the present numerical approach are compared with those existed researches, and it is found that there are close agreements between the results. In addition, the thermo-physical properties of TiO2-H2O nanofluid are measured in the laboratory. The Rayleigh number, nanoparticle concentration of nanofluid and aspect ratio of annulus are governing parameters. It is found that the maximum enhancement of average Nusselt number are about 45% and 94%, respectively; when the volume fraction of nanofluid and Rayleigh number change from their minimum values to maximum values. On the other hand, the maximum increment of total entropy generation is about 57% as the Rayleigh number enhances.

Analysis of coiled tube waste heat storage tank under water injection

Abstract In this paper, attempts are made to increase the heat transfer in the hot water storage tank via water injection into the storage water. With new water injection system, increasing mixing effect especially around the coiled tube was aimed. The experimental study was conducted to obtain the effect of different velocity (0.03 ≤ V ≤ 1.3), different flow pressures and different outlet hole diameters on dimensionless temperature distribution, Nusselt number and second law efficiency. The results showed, depending on the velocity, water injection into the tank provided an increase in the range of 15–60% for the Nusselt number. The highest enhancement in average Nusselt number occurred when the V = 1.3 m/s. The highest decrease in the second law efficiency was observed around 5% for the 1 mm hole diameter. In addition, the water injection method compared with air bubble injection method in the literature. The comparison indicated, average Nusselt number of the air bubble method 0.6% higher than the water injection method but second law efficiency and average dimensionless temperature 1.7% and 25.7% respectively less than the water injection method.

Forced convection in a branching channel with partly elastic walls and inner L-shaped conductive obstacle under the influence of magnetic field

In this study, forced convection in a branching channel with partly elastic walls is examined under the effects of magnetic field. Also, a conductive L-shaped obstacle is used to control flow field. Galerkin weighted residual finite element method is used for the solution of the governing equations. The Arbitrary-Lagrangian-Eulerian method is utilized for the description of the fluid motion with the elastic walls in the bifurcating channel in the fluid-structure interaction model. Effects of various pertinent parameters such as Reynolds number (between 100 and 500), elastic modulus of flexible wall (between 106 and 109), size of the elastic part (between 2H and 32H), Hartmann number (between 0 and 20), size of the obstacle (d1 between 0.1H and 0.45H), inclination of the obstacle (between −90 and 90) on the fluid flow characteristics and convective heat transfer features are examined. It was observed that the size and elastic modulus of the flexible wall are effective on the redistribution of separated zones for the horizontal branching channel. The average Nusselt number reduces with the bigger size of the elastic wall and the amount of reduction is in the range of 8% and 9%. Magnetic field suppresses the separated flow regions and increases the average heat transfer rate. The average Nusselt number enhancements are 33.9% and 12.5% for lower and upper hot walls of the horizontal bifurcating channel when configurations in the absence and presence of magnetic field (at the highest strength) are compared. It was observed that the size and orientation of the L-shaped obstacle have significant effects on separated flow regions and heat transfer rate and therefore can be used as an excellent control tool.

Forced Convection of Fe3O4-Water Nanofluid in a Bifurcating Channel under the Effect of Variable Magnetic Field

In this study, forced convection of Fe 3 O 4 –water nanofluid in a bifurcating channel was numerically studied under the influence of variable magnetic. Galerkin residual finite element method was used for numerical simulations. Effects of various values of Reynolds number (between 100 and 500), Hartmann number (between 0 and 3), and solid nanoparticle volume fraction (between 0% and 4%) on the convective heat transfer characteristics were analyzed. It was observed that location and size of the re-circulation zones established in the walls of the bifurcating channel strongly influenced by the variable magnetic field and Reynolds number. Average Nusselt number versus Hartmann number showed different characteristics for hot walls of the vertical and horizontal branching channels. The average Nusselt number enhancements were in the range of 12–15% and 9–12% for hot walls of the branching channel in the absence and presence of magnetic field (at Hartmann number of 3).

Effect of uniform/non-uniform magnetic field and jet impingement on the hydrodynamic and heat transfer performance of nanofluids

Abstract Effect of uniform and non-uniform magnetic field and jet impingement on the hydrodynamic and heat transfer performance of nanofluids has been investigated numerically. Five types of magnetic field with different strengths (Ha = 0–40) are applied externally to the flow domain under direct and transverse jet (cross-flow) impingement conditions. The effect of Reynolds number (Re = 200–600), nanoparticle type (Cu, Al, TiO2, and hybrid (Cu + TiO2)), nanoparticle diameter (dp = 20 nm–80 nm) and concentration (O = 1 vol% to 3 vol%) on the hydrodynamic and heat transfer behavior under uniform and non-uniform magnetic field are predicted. The presence of magnetic field introduced a Lorentz force responsible for higher values of flow velocity particularly near the walls resulting in the enhancement of average Nusselt number. Moreover, the direct and transverse jet against the applied uniform/non-uniform magnetic field also enhanced the local flow velocity near the impingement region leading to enhancement in the local Nusselt number. Transverse jet exhibits higher average Nusselt number in comparison with direct jet. A maximum heat transfer enhancement of 173% is obtained for 3 vol% Cu nanofluid under magnetic field. Moreover, two equivalent nanofluid pairs are also identified that will provide a better switching option in thermal management of high power electronic devices and nuclear reactors.

MHD mixed convection of nanofluid due to an inner rotating cylinder in a 3D enclosure with a phase change material

PurposeThe purpose of this study is to numerically examine the mixed convection of CuO-water nanofluid due to a rotating inner hot circular cylinder in a 3D cubic enclosure with phase change material (PCM) attached to its vertical surface. Heat transfer and fluid flow characteristics were examined for various values of pertinent parameters.Design/methodology/approachFinite element method was used in the numerical simulation. Influence of various pertinent parameters such as Rayleigh number (between 10$^5$ and 10$^6$), Hartmann number (between 0 and 100), angular rotational speed of the cylinder (between −50 and 50), solid nanoparticle volume fraction (between 0 and 0.04) and PCM parameters (height-between 0.2H and 0.8H, thermal conductivity ratio- between 0.1 and 10) on the convective heat transfer characteristics are numerically studied.FindingsIt was observed that local heat transfer variations along the hot surface differ significantly for the cases with and without magnetic field where three distinct hot spots of peak Nusselt number are established when magnetic field is imposed. The average Nusselt number enhancement with the nanofluid at the highest particle volume fraction is 52.85 per cent at Hartmann number of 100, whereas its value is 39.76 per cent for the case in the absence of magnetic field. When the inner cylinder rotates, flow and thermal fields are affected within the cavity. The local heat transfer variations spread over the hot surface with cylinder rotation and 16.43 per cent of reduction in the average heat transfer is obtained with counter-clockwise rotation at 100 rad/sec. An enhancement in the PCM height and a reduction in the thermal conductivity of the PCM result in average heat transfer deterioration for the 3D cavity. The amount of the reduction is 43 per cent when the PCM height is increased from 0.2H to 0.8H, whereas 19.10 per cent enhancement in the heat transfer is achieved when thermal conductivity ratio (PCM) to the base fluid is increased from 0.1 to 10.Originality/valueSuch configurations can be designed for convection control, and in our case, various methods are available. Some of the investigated methods can be used in applications where magnetic field already exists. Convection control study in 3D cavity gives more realistic results as compared to 2D configurations, and results of the current investigation may be used for the design, optimization and flow control of many thermal applications involving magnetic field effects.

Forced Convection of Pulsating Nanofluid Flow over a Backward Facing Step with Various Particle Shapes

In this study, numerical analysis of forced convective pulsating nanofluid flow over a backward-facing step with different nanoparticle shapes was performed by the finite volume method. The effects of the Strouhal number (between 0.1 and 2), solid nanoparticle volume fraction (between 0 and 0.04) and nanoparticle shapes (spherical, blade and cylindrical) on the heat transfer and fluid flow were examined with the aid of numerical simulation. It was observed that the average Nusselt number is a decreasing function of the Strouhal number for the considered range, and it enhances for higher solid particle fractions. Using nanofluids with spherical particles is advantageous in pulsating flow, whereas cylindrically-shaped particles are preferred in steady flow configurations. Average Nusselt number enhancements up to 30.24% and 27.95% are achieved with cylindrical- and spherical-shaped particles at the highest volume fraction.