Enhancement Of Forced Convection Heat Transfer Research Articles

Enhancing laminar forced convection heat transfer by using Al2O3/PCM nanofluids in a concentric double-tube duct

In this study, a tube with a smaller diameter was inserted in an isoflux heated circular tube to form a concentric double-tube duct. The forced convection heat transfer enhancement efficacy of using concurrent flows of Al 2 O 3 /PCM nanofluids through outer annulus/inner tube of this resulting double-tube duct to replace its parent single-tube (with water) was experimentally investigated. The results showed that a high total flow rate combined with a high concurrent flow ratio could effectively increase heat transfer effectiveness. When heating power = 200 W, Reynolds number = 1700, and the concurrent flow ratio = 2.38, for 1% Al 2 O 3 -water nanofluid in the outer annulus and 4.63% phase-change nanofluid in the inner tube, the convective heat transfer increased by 32%. Due to the excessive pressure drop, the figures of merit of the investigated objectives are all less than 1.

Role of Three-Dimensional Swirl in Forced Convection Heat Transfer Enhancement in Wavy-Plate-Fin Channels

Abstract The influence of wall-corrugation-induced swirl flow on enhanced forced convection in wavy-plate-fin cores has been investigated. Three-dimensional computational simulations were carried out for steady-state periodically developed air flow (Pr ∼ 0.71; 50 ≤ Re ≤ 4000) with channel walls subject to constant-uniform temperature conditions. The recirculation that develops in the wall troughs and grows to have an axially helical character is scaled by the Swirl number Sw. As Sw increases with higher flowrate and/or corrugation severity, tornado-shaped vortices appear in the wave trough region midway of the interfin channel height, then extend longitudinally to encompass majority of the flow channel. The local wall-shear and heat transfer coefficient variations indicate that boundary-layer thinning upstream of the wave peak aids in intensifying momentum and heat transfer. However, the flow recirculation in wall trough impedes heat transfer at low Sw due to flow stagnation but promotes it at high Sw because of the vortices-induced augmented fluid mixing. The effects of this secondary flow are quantified by Φf(or j), which is seen to increase log-linearly as fin corrugation aspect ratio γ and/or fin spacing ratio ζ increases; the influence of cross section aspect ratio α is marginal. Moreover, the pressure drag penalty due to swirl critically affects overall pressure loss, and its proportion remains nearly constant when α varies, but grows as Sw, γ, and/or ζ increases and can be as much as 80% of the total pressure drop.

Experimental study for laminar forced convection heat transfer enhancement from horizontal tube heated with constant heat flux, by using different types of porous media

Forced convective heat transfer for water flowing through a circular pipe oriented horizontally has been investigated experimentally. the pipe was heated at constant heat flux and also packed with two different types of particles (steel and mixture of steel & plastic) as a porous media.The flow features are an internal, laminar, incompressible and steady flow for a wide range of Reynolds numbers (500,1000 and 1500) with variable heat flux (200, 400 and 600 W) for each case and three times for each number.The experimental results comprehended temperature recording on different positions of test sections at steady state depending on the effect of the porous media type and Reynolds number employed (which indicate to the mass flux) in addition to the value of heat flux. The results of the study are represented in terms of temperature distribution to show temperature behaviors in the pipe, besides other diagrams uptake relation of the local and average Nusselt number with data aforementioned above. For each porous type, the results show an increase in local and average Nusselt number with increasing of the Reynold number for steel and mixture porous media respectively. It has obverse from this study that in a porous steel media the heat transfer will occur mainly by conduction, while in the other types of porous media that the heat transfer will occur mainly by forced convection.

Application of electromagnets for forced convective heat transfer enhancement of magnetic fluids

The current research aims to numerically investigate the effect of a three-dimensional magnetic field generated by four electromagnets on the convective heat transfer of Fe3O4 /Water ferrofluid in a parallel plate channel. Simulations have been carried out for different ferrofluid flow rates and concentrations, magnetic field intensities, and the electromagnets locations. The obtained numerical results have been compared with the experimental data of our previous work and accuracy of the numerical method has been determined at different conditions. Results show that the external magnetic field induces a quasi-oscillatory fluid motion between the surfaces of the channel that disturbs the thermal boundary layer and increases the heat transfer rate. A maximum of 24% heat transfer enhancement has been obtained at the optimum conditions. It is also concluded that the magnetic field has both increasing and decreasing effect on the fluid local pressure according to the sign of the magnetic field gradient. However, the overall pressure drop does not vary too much with the magnetic field intensity. Moreover, the accuracy analysis implies that the numerical method is more reliable in low magnetic field strengths and low Reynolds numbers.

Heat Transfer Enhancement of an Automobile Engine Radiator using ZnO Water Base Nanofluids

In this research paper, the forced convective heat transfer enhancement of a Suzuki Mehran (VXR) 2016 radiator (heat exchanger) along with pressure drop and friction factor by utilizing Zinc oxide (ZnO) water based nanofluids has been experimentally studied. Three types of nanofluids with different volumetric concentrations of ZnO nanoparticles (0–0.3%) were employed in order to understand its effect on heat transfer enhancement. The experimental setup was completely designed as closely as possible to the car cooling system. The experimentation has been done under laminar flow conditions (186≤Re≤1127) at different fluid volume flow rates (2–12 L/min) and constant fluid inlet temperature (70°C) to the automobile radiator. A maximum enhancement in heat transfer rate, overall heat transfer coefficient and Nusselt number was obtained up to 41%, 50% and 31% by using nanofluid with 0.2% volumetric concentration of nanoparticles respectively. On the other hand, the mean enhancement in pressure drop and friction factor was obtained up to 47% and 46% by using nanofluid with the same volumetric concentration of nanoparticles i.e. 0.2% respectively. The experimental results also revealed that the heat transfer rate, overall heat transfer coefficient and Nusselt number of nanofluids increases by increasing the volume flow rates and volumetric concentration of nanoparticles. However, these thermal performance parameters of nanofluids started to decline when the volumetric concentration of nanoparticles was increased from 0.2% to 0.3%. Furthermore, pressure drop and friction factor of nanofluids increase by increasing the volumetric concentration of nanoparticles, while pressure drop increases and friction factor decreases by increasing the volume flow rate of nanofluids respectively. At the end, the thermal efficiency of automobile radiator with high cooling rates was obtained by using nanofluid with 0.2% volumetric concentration of nanoparticles.

Forced convection heat transfer enhancement using a coaxial wire-tube corona system

Laminar forced convection heat transfer enhancement in a coaxial wire-tube corona system is numerically examined. Governing equations were solved using the finite volume method implemented in a developed solver using the OpenFOAM platform. The proposed corona system could change the flow pattern pushing the central high-velocity flow towards the hot surface. For a specific wire length, an enhancement of 100% in heat transfer could be achieved at a Reynolds number of 600 and the applied voltage of 8 kV. Finally, considering both heat transfer enhancement and electrical power consumption, the most effective case was recommended among scenarios considered in this study.

Forced Convective Air-Cooling Effect on Electronic Components of Different Geometries and Orientations at Flow Shedding Region

The recent technological developments in electronics and product miniaturization demand high-performance thermal management to secure the reliability and the operating characteristics of the components. The present 2-D numerical study investigates heat transfer characteristics of different geometries of electronic components such as capacitors, resistors, condensers, and pin fin heat sinks and the additional effect of their optimized orientation in the confined forced convective air-cooling arrangement. The flow confinement effect is induced by preferring the blockage ratio (channel height/characteristic length of various geometries) to be 4. A finite volume-based flow solver is used to solve flow and energy equations. The resulting flow and heat transfer characteristics of various geometries studied from pressure contour, temperature contour, total drag coefficient, total pressure drop, Strouhal number, and volume goodness factor, and local and average Nusselt numbers for various Reynolds numbers such as 200, 400, 600, and 800. The average forced convection heat transfer enhancement depends on profoundly attached flow velocity, not on flow shedding. As per the thermal hydraulic performance, 45° tilted square front cum segment is the best among geometries considered for the analysis at this confinement.

Performance evaluation of nanofluid for heat transfer enhancement and pumping power reduction through a semicircular corrugated pipe

Implementing nanofluid in heat transfer enhancement application is a modern and accessible method. In this present investigation Al2O3-water and CuO –water nanofluid with 1 % - 5 % volume fraction was chosen to study forced convective heat transfer enhancement through a semicircular corrugated pipe. 5000 W/m constant heat flux was considered as subjected to the pipe wall. The improvement was observed in both heat transfer rate and required pumping power with increased volume fraction of nanofluid comparing with base fluid water. The numerical simulation was analyzed in the range of Reynolds number 10,000 to 20,000. Effect of using nanofluid on total wall shear stress was also studied. 2% Al2O3-water and 1% CuO-water nanofluid were selected as they exhibit superior performances in enhanced heat transfer with optimum pumping power than water. Finally, the power advantage for both nanofluid was performed under prescribed flow condition.

Effects of Phase Shift and Wavy Amplitude on the Laminar Forced Convection Heat Transfer Enhancement in Corrugated Channels Using Copper-Water Nano-Fluid

Effects of Phase Shift and Wavy Amplitude on the Laminar Forced Convection Heat Transfer Enhancement in Corrugated Channels Using Copper-Water Nano-Fluid

CFD study of forced convective heat transfer enhancement in a 90° bend duct of square cross section using nanofluid

In this paper, the forced convective heat transfer enhancement with nanofluids in a 90° pipe bend has been presented. Numerical investigation is carried out for the turbulent flow through the pipe employing finite volume method. The governing differential equations are discretized using hexahedral cells, and the resulting algebraic equations are solved using Commercial solver Fluent 6.3. In order to close the time averaged Navier–Stokes equations, the two-equation k–ɛ turbulence model with a standard wall function have been used. The duct Reynolds number is varied in the range of 2,500–6,000. It is observed that the heat transfer is enhanced significantly by varying the volume fraction of the nanofluid. It is also found that the heat transfer is increased with Reynolds number. A strong secondary flow is observed due to the presence of the wall. Turbulent kinetic energy near outer wall is found to be higher than the inner wall of the bend. A comparative assessment for the heat transfer enhancement with different types of nanofluids is also presented. The computed results of area weighted average Nusselt numbers are validated with some of the existing literature.

Improved gas heaters for supercritical CO2 Rankine cycles: Considerations on forced and mixed convection heat transfer enhancement

To improve heat transfer performance of the gas heater in the supercritical CO2 Rankine cycle, heat transfer characteristics of supercritical CO2 heated in Internally Ribbed Tubes (IRT) was experimentally and numerically investigated over a wide range of buoyancy effect. Experiments reveal that for IRT with a geometric parameter of β=109, serious local heat transfer deterioration did not occur and buoyancy consistently improved heat transfer. IRT showed far superior performance over smooth tubes. Empirical Nusselt correlations were recommended for both upward and downward flows. A numerical model was then developed and verified against experimental data from IRT with different geometries. Further numerical studies on 7 different IRT demonstrate that buoyancy effect relates closely to rib geometries. For IRT with β=0.48–4, heat transfer to supercritical CO2 in upward flow was impaired when Bo is around 10−4, though the impairment became weaker as β increased. When β reached 16, buoyancy-induced impairment disappeared and Nusselt number increased gradually as buoyancy became stronger. Further increase in β up to 109 didn’t lead to obvious heat transfer enhancement of supercritical CO2, indicating that rib geometries play a smaller role in heat transfer than buoyancy for IRT with β>16. Finally, design strategy for IRT was provided for the optimization of gas heaters.

Numerical investigation for enhancement of heat transfer in internally finned tubes using ANSYS CFX program

In this study, a numerical investigation has been carriedout for single phase flow behavior for thirty six internally finnedtubes to demonstrate the effect of axial pitch to fin height ratio(p/e) for 0.8≤p/e≤6.345, helix angle of internal fins (β) for30°≤β≤70°, apex angle of internal fins (α) for 0°≤α≤53.13°, internalfin height (e) for 0.6mm≤e≤1.0mm, internal tube diameter (di)with 14 mm and Reynolds number (Re) of single-phase flow for10000≤Re≤50000 on enhancement of forced convection heattransfer and reduction of friction factor by using ANSYS CFXprogram. It solves the three-dimensional Navier-Stokes equationsfor steady state turbulent with SST model and enhance walltreatment. The numerical analysis provided at fully developedvelocity and temperature. Numerical results showed that thesmallest axial pitch to fin height ratio (p/e) =0.8 and with apexangle α=10 degree provided enhancement of heat transfer of 2.8 to3.55 times higher than of smooth tube. Finally, present numericalresults are seen to be in good agreement with literatureexperimental correlations.

Experimental investigation of forced convective heat transfer enhancement of γ-Al2O3/water nanofluid in a tube

The effect of nanofluids on heat transfer inside circular tubes under uniform constant heat flux boundary condition was investigated. The working nanofluid was a suspension of γ-Al2O3 nanoparticles of average diameter 20 nm. The heat transfer coefficients were calculated experimentally in the range of 1057 < Re < 2070 with different particle volume concentrations of 0.1%, 0.3% and 0.9%. Increasing the particle volume fraction led to enhancement of the convective heat transfer coefficient. The results show that the average heat transfer coefficient increased 16.8% at 0.9% volume concentration and Reynolds number of 2070 compared with distilled water. In addition, the enhancement of the convective heat transfer was particularly significant in the entrance region and decreased with axial distance. Finally, an empirical correlation for Nusselt number has been proposed for the present range of nanofluids. The mean deviation between the predicted Nusselt number and experimental values for the new correlation is 3.57%.

A comprehensive review of experimental investigations of forced convective heat transfer characteristics for various nanofluids

Abstract Nanofluids are suspension of nanoparticles (less than 100 nm) in the conventional base fluids. The dispersed solid metallic or non-metallic nanoparticles change the thermal properties like thermal conductivity, viscosity, specific heat, and density of the base fluid. Past studies focused on measuring the thermal properties of nanofluids. These suspended nanoparticles effectively improve the transport properties and heat transfer characteristics of the base fluids. Recently, heat transfer augmentation using suspensions of nanometre-sized solid particles in base liquids have been investigated by various research groups across the world. This paper reviews the state-of-the-art nanofluid studies in the area of forced convection heat transfer enhancement. The results for the heat transfer characteristics in internal flow with constant heat flux and constant wall temperature boundary conditions reported by various researchers have been compiled and reviewed. Further, in heat exchangers, the real boundary conditions are different from the constant heat flux and constant wall temperature boundary conditions. Over a span of 2 decades, the literature in this field is widespread; hence, this review would be useful for researchers to have a precise screening of a wide range of investigations in this area.

Forced Convection Heat Transfer Enhancement by Porous Pin Fins in Rectangular Channels

The forced convective heat transfer in three-dimensional porous pin fin channels is numerically studied in this paper. The Forchheimer–Brinkman extended Darcy model and two-equation energy model are adopted to describe the flow and heat transfer in porous media. Air and water are employed as the cold fluids and the effects of Reynolds number (Re), pore density (PPI) and pin fin form are studied in detail. The results show that, with proper selection of physical parameters, significant heat transfer enhancements and pressure drop reductions can be achieved simultaneously with porous pin fins and the overall heat transfer performances in porous pin fin channels are much better than those in traditional solid pin fin channels. The effects of pore density are significant. As PPI increases, the pressure drops and heat fluxes in porous pin fin channels increase while the overall heat transfer efficiencies decrease and the maximal overall heat transfer efficiencies are obtained at PPI=20 for both air and water cases. Furthermore, the effects of pin fin form are also remarkable. With the same physical parameters, the overall heat transfer efficiencies in the long elliptic porous pin fin channels are the highest while they are the lowest in the short elliptic porous pin fin channels.

Investigation of forced convective heat transfer enhancement in the presence of an electric field – a finite element analysis

The effect of electro‐convection in a cylindrical flow annulus on heat transfer enhancement has been investigated numerically. Weakly ionized air is considered to be the working fluid throughout this work. The effect of exit boundary condition, considered to be the main hindrance for the numerical solution, has been discussed in detail. The present work shows interesting flow field characteristics, which are in excellent agreement with some other established experiments. The heat transfer enhancement, as reported in this work, appears to be small in view of the low magnitude of the applied voltage but it clearly and surely delineates the trend, i.e. with increase in the strength of the electric field, heat transfer enhances.

Forced Convection Heat Transfer Enhancement Using a Self-Oscillating Impinging Planar Jet

Impinging jets are widely used in the local enhancement of heat removed from internal passages of gas turbine blades. Arrays of stationary jets are usually impinged on surfaces of internal cooling passages. The current practice is to benefit from the high heat transfer coefficients existing in the vicinity of the jet impingement region on a target wall. The present study shows that a self-oscillating impinging-jet configuration is extremely beneficial in enhancing the heat removal performance of a conventional (stationary) impinging jet. In addition to a highly elevated stagnation line Nusselt number, the area coverage of the impingement zone is significantly enhanced because of the inherent sweeping motion of the oscillating coolant jet. When an oscillating jet (Re=14,000) is impinged on a plate normal to the jet axis (x/d=24 hole to plate distance), a typical enhancement of Nu number on the stagnation line is about 70 percent. The present paper explains detailed fluid dynamics structure of the self-oscillating jet by using a triple decomposition technique on a crossed hot wire signal. The current heat transfer enhancement levels achieved suggest that it may be possible to implement the present self-oscillating-impinging-jet concept in future gas turbine cooling systems, on rotating disks, glass tempering/quenching, electronic equipment cooling, aircraft de-icing, combustors and heat exchangers.

Evaluating the performance of forced convection heat transfer enhancement

Two methods for assessing thermal performance were evaluated for four kinds of forced convective heat transfer augmentations. On method uses the first law of thermodynamics, i.e., the heat transfer improvement at (1) constant Reynolds number, (2) constant pressure loss, and (3) constant pumping power. The other method uses the second law of thermodynamics, i.e., the entropy generation. The first method restricts the effective region and the second method supplies the condition for achieving the minimum entropy generation rate. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(2): 142–154, 1998

Evaluating the performance of forced convection heat transfer enhancement

Two methods for assessing thermal performance were evaluated for four kinds of forced convective heat transfer augmentations. On method uses the first law of thermodynamics, i.e., the heat transfer improvement at (1) constant Reynolds number, (2) constant pressure loss, and (3) constant pumping power. The other method uses the second law of thermodynamics, i.e., the entropy generation. The first method restricts the effective region and the second method supplies the condition for achieving the minimum entropy generation rate.

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