Forced Convection Heat Transfer Characteristics Research Articles

Effect of SiO2 nanoparticles on the heat transfer characteristics of refrigerant and tribological behaviour of lubricant

Scientists and researchers are enthusiastically utilizing novel technologies that can substantially reduce energy consumption in diverse thermal systems. The foremost aim of the present investigation is to exploit the potential of nanoparticles on the enhancement of heat transfer characteristics of refrigerant and tribological capabilities of lubricant. Experimental investigations on the forced convection heat transfer characteristics of R134a/SiO2 nanorefrigerant (R134a + SiO2-polyalkylene glycol nanolubricant) are carried out. The effect of particle concentration, heat flux, mass flux, and vapour quality are investigated. The friction reduction and anti-wear properties of the nanolubricant are evaluated using four-ball tribo-tester. The results reveal that the presence of nanoparticles in the refrigerant significantly enhances the heat transfer coefficient of refrigerant and the tribological behaviour of lubricant. The maximum increase in heat transfer coefficient is 163.2% corresponding to a particle concentration of 0.4%. The presence of nanoparticles in refrigerant results in a marginal increase in pressure drop. However, the penalty in pressure drop is insignificant compared to the enhancement in heat transfer. Excellent friction reduction and anti-wear performance are also manifested by the nanolubricant. The maximum reduction in the friction coefficient is 37.76% and that of wear scar diameter is 40.83%. Considering the heat transfer and tribological characteristics, the optimum value of the particle volume fraction is 0.4%. SiO2-PAG nanolubricant can be considered as a potential energy-saving alternative to refrigerant compressor oils.

Numerical Investigation of Forced Convection Heat Transfer on a Circular Finned tube with AL2O3-Water Nano Fluid

This paper presents a three-dimensional numerical analysis to study the laminar forced convection heat transfer and flow characteristics of AL2O3–water Nano fluid with Solid particles less than 100 nm through a tube with 1m Length and 25 mm inner diameter and 30mm outer diameter contains circular fins with 30mm inner diameter and 50mm outer diameter with thickness of 2mm , investigated numerically by using finite volume method, models using ANSYS 14.5 Based on the single-phase approach, The flow of fluid is assumed to be incompressible, steady and laminar with various thermo physical properties according to volume concentration of Nano particles The Navies Stokes equations along with the energy equation have been solved by using SIMPLE algorithm Technique. The effects of different parameters such as nanoparticle volume concentration (1%, 3% and 5%), and Reynolds number are varied from (500 - 2100) for various axial locations of tube with AL2O3–water fluids and the effect of different values of velocity at the tube inlet will be studied during this paper. Where the results showed that the coefficient of heat transfer increases when the concentration of Nano fluid increase.

Experimental analysis for heat transfer of nanofluid with wire coil turbulators in a concentric tube heat exchanger

Abstract Nanofluids are a novel class of heat transfer suspensions of metallic or nonmetallic nanopowders with a size of less than 100 nm in base fluids and they can increase heat transfer potential of the base fluids in various applications. In the last decade, nanofluids have become an intensive research topic because of their improved thermal properties and possible heat transfer applications. For comparison, an experiment using water as the working fluid in the heat exchanger without wire coils was also performed. Turbulent forced convection heat transfer and pressure drop characteristics of Al2O3-water nanofluids in a concentric tube heat exchanger with and without wire coil turbulators were experimentally investigated in this research. Experiments effected particle volume concentrations of 0.4–0.8 to 1.2–1.6 vol% in the Reynolds number range from 4000 to 20,000. Two turbulators with the pitches of 25 mm and 39 mm were used. The average Nusselt number increased with increasing the Reynolds number and particle concentrations. Moreover, the pressure drop of the Al2O3-water nanofluid showed nearly equal to that of pure water at the same Reynolds number range. As a result, nanofluids with lower particle concentrations did not show an important influence on pressure drop change. Nonetheless, when the wire coils used in the heat exchanger, it increased pressure drop as well as the heat transfer coefficient.

Numerical investigation of 3D turbulent forced convective heat transfer and friction characteristics of a square duct

Numerical investigation of 3D turbulent forced convective heat transfer and friction characteristics of a square duct

Experiments on laminar cooling characteristics of a phase change nanofluid flow through an iso-flux heated circular tube

In the present work, the laminar forced convection heat transfer characteristics of using the Eicosane-in-water Nano-PCM emulsion as the phase change nanofluid in a circular tube heated with constant heat flux have been investigated experimentally. A circular oxygen-free copper tube, for which the inner and outer diameters are 3.4 mm and 4.0 mm, respectively, is fabricated with an iso-flux heated section of length 40 cm. Forced convection heat transfer experiments have been performed for the horizontal tube using the pure water, the water-based phase change nanofluids containing various mass fractions of Nano-PCM particles (ωpcm = 1, 2, 5, and 10 wt%) as the coolant under the following operating conditions: the volume flow rate Q̇ = 12.5–180 cm3/min, the heating power applied at the outer wall of the tube qo = 20, 30, 40, 50, 60 W, with the inlet fluid temperature Tin near 27 °C. Experimental results show that when the flow rate and the heat flux are in an appropriate range, the tube wall temperature along the iso-flux heated section can be effectively suppressed with increasing mass fraction of the Nano-PCM particles in the water based phase change nanofluid compared with that of the pure water. Meanwhile, a penalty of pressure drop increase of using the phase change nanofluids to replace the pure water in the tube was found to greatly uplift with the mass fraction of Nano-PCM particles.

UNSTEADY NUMERICAL SIMULATION OF TURBULENT FORCED CONVECTION IN A RECTANGULAR PIPE PROVIDED WITH WAVED POROUS BAFFLES

Numerical simulations of flow and heat transfer in a serpentine heat exchanger configuration are presented to demonstrate application of porous media techniques in heat exchanger analyses. In this study, steady-state 3D turbulent forced convection flow and heat transfer characteristics in a rectangular pipe with baffles attached inside pipe have been numerically investigated under constant wall heat flux boundary condition. Numerical study has been carried out for Reynolds number of 20000-50,000, Prandtl number of 0.71, baffle distances h/D h of 1/3 and 2/3, and baffle thickness e of 1/12, 2/3. It is observed that rectangular pipe having waved baffles has a higher Nusselt number and friction factor compared to the smooth rectangular pipe without baffles. Periodically fully developed conditions are obtained after a certain module. Maximum thermal performance factor is obtained for the baffle waved. Results show that baffle distance, waved porous baffle, and Reynolds number play important role on both flow and heat transfer characteristics. All the numerical results are correlated within accuracy of ±2% and ±2.5% for average Nusselt number and friction factor, respectively.

Periodically fully developed laminar flow and heat transfer in a two-dimensional horizontal channel with staggered fins

The 2-D periodically fully developed laminar forced convection fluid flow and heat transfer characteristics in a horizontal channel with staggered fins are investigated numerically under constant wall heat flux boundary condition. Study is performed using ANSYS Fluent 6.3.26 which uses finite volume method. Air (Pr @ 0.7) and Freon-12 (Pr @ 3.5) are used as working fluids. Effects of Reynolds number, Prandtl number, fin height, and distances between two fins on heat transfer and friction factor are examined. Results are given in the form of non-dimensional average Nusselt number and average Darcy friction factor as a function of Reynolds number for different fin distances and Prandtl numbers. The velocity and temperature profiles are also obtained. It is seen that as the fin distance increases, behavior approaches the finless channel, as expected. Also, thermal enhancement factors are given graphically for working fluids. It is seen that heat transfer dominates the friction as both the distance between two fins and Prandtl number increase. It is also seen that fins having blockage ratio of 0.10 in 2-D periodically fully developed laminar flow is not advantageous in comparison to smooth channel without fins.

Comprehensive Analysis of Convective Heat Transfer in Parallel Plate Microchannel with Viscous Dissipation and Constant Heat Flux Boundary Conditions

This paper reports the hydrodynamically and thermally fully developed, laminar, incompressible, forced convective heat transfer characteristics of gaseous flows through a parallel plate microchannel with different constant heat flux boundary conditions. The first order velocity slip and viscous dissipation effects are considered in the analysis. Here, three different thermal boundary conditions such as: both plates kept at different constant heat fluxes, both plates kept at equal constant heat fluxes and one plate kept at constant heat flux and other one insulated are considered for the analysis. The deviation in Nusselt number between the model that considers both first order velocity slip and temperature jump and the one that considers only velocity slip is reported. Also, the effect of various heat flux ratios on the Nusselt number is reported in this analysis. In addition, the deviation in Nusselt number between first and second order slip model is discussed in this study.

Flow drag and heat transfer characteristics of drag-reducing nanofluids with CuO nanoparticles

A new kind of aqueous CuO nanofluid with drag-reducing performance was developed. The new working fluid was an aqueous CTAC (cetyltrimethyl ammonium chloride) solution with CuO nanoparticles added and has both special effects of drag-reducing and heat transfer enhancement. An experiment was carried out to investigate the forced convective flow and heat transfer characteristics of conventional drag reducing fluid (aqueous CTAC solution) and the new drag-reducing nanofluid in a test tube with an inner diameter of 25.6 mm. Results indicated that there were no obvious differences of the drag-reducing characteristics between conventional drag reducing fluid and new drag-reducing nanofluid. However, their heat transfer characteristics were obvious different. The heat transfer characteristics of the new drag-reducing nanofluid significantly depend on the liquid temperature, the nanoparticle concentration and the CTAC concentration. The heat transfer enhancement technology of nanofluid could be applied to solve the problem of heat transfer deterioration for conventional drag-reducing fluids.

Experimental study of heat transfer and pressure drop of supercritical CO2 cooled in metal foam tubes

An experiment was conducted to investigate the forced convective heat transfer and pressure drop characteristics of supercritical CO2 cooled in tubes partially filled with metal foam. The effects of CO2 inlet pressure, mass flow rate and mean bulk temperature on the heat transfer and pressure drop were analyzed. Moreover, the parametric study was performed with different porosities (void fraction, 0.85/0.9/0.95) and pore densities (number of pores per inch, 20/40/60). The heat transfer coefficient decreases at first and then increases as porosity increases, and decreases as pore density decreases and finally approaches to a near constant value. The pressure drop monotonously increases as porosity decreases and finally approaches to a near constant value, and increases at first and then decreases as pore density increases. Based on the experimental data, both correlations for heat transfer and friction factors were proposed. The maximum error between the results predicted by new correlations and measured is ±15%.

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.

Laminar Forced Convection Heat Transfer Characteristics from a Heated Cylinder in Water Based Nanofluids

Laminar Forced Convection Heat Transfer Characteristics from a Heated Cylinder in Water Based Nanofluids

Numerical simulations of forced convection heat transfer and flow characteristics of nanofluids in small tubes using two-phase models

Laminar and turbulent forced convection heat transfer and flow characteristics of nanofluids in small smooth tubes are numerically simulated using two kinds of multiphase-flow models. The simulated results are compared with the experimental results from the published papers and the traditional predicting correlations to investigate the applicability of these models for nanofluids. The multiphase-flow models including mixture model and Eulerian model, and both of them belong to the well-known Euler–Euler model. The effects of various parameters such as Reynolds number and nanoparticles concentration on the heat transfer and flow characteristics are investigated and discussed in each model. The study results show that little deviation exists between the simulated results and the traditional predicting correlations for low concentration nanofluid, which indicates that low concentration nanofluid has no meaningful nano-effect on forced convection heat transfer. While, non-traditional fluid characteristics occur and increase with increasing the nanoparticles concentration, and the simulated results using special models of multiphase flow are closer to the experimental data than that of the traditional correlations, which means the multiphase flow models are more accurate than traditional correlations for high concentration nanofluid. Moreover, the numerical results also indicate that the drag coefficients of simulated results have only little difference less than 0.4% with that of experimental results for nanofluids in the laminar flow region. However, the drag coefficients of simulated results have a increase by about 60–22% compared with the experimental results in the turbulent flow region. As conclusion, the present study indicates that the two-phase models, including mixture model and Eulerian model, can predict the forced convection heat transfer and flow characteristics of nanofluid well, and have important implications for the application of nanofluid.

Heat transfer in Bingham plastic fluids from a heated elliptical cylinder

The forced convection heat transfer characteristics in Bingham plastic fluids from a heated elliptical cylinder of various aspect ratios E(=a/b) have been investigated numerically. The momentum and energy equations have been solved here by using the finite element method over wide ranges of rheological and kinematic parameters as: 0.01⩽Bn⩽100 (Bingham number), 0.01⩽Re⩽40 (Reynolds number), 1⩽Pr⩽100 (Prandtl number) and 0.1⩽E⩽10 (aspect ratio) thereby approaching the limiting conditions of a plate aligned with and transverse to the direction of mean flow. Furthermore, the influence of the type of thermal boundary condition, i.e., constant wall temperature (CWT) and constant heat flux (CHF) prescribed on the surface of the elliptical cylinder has also been examined. Extensive numerical results are reported herein in terms of the isotherm contours, variation of the Nusselt number on the surface of the cylinder for the two above-noted thermal boundary conditions and finally, the overall results are presented in terms of the surface averaged Nusselt number. Irrespective of the boundary condition prescribed on the surface of the cylinder, the Nusselt number shows a positive dependence on the both Reynolds number and Prandtl number while the effect of Bingham number is somewhat dependent on the Reynolds number range. The average Nusselt number has also been interpreted and correlated in terms of the Colburn heat transfer factor (j). Empirical correlations for the Colburn factor as functions of the Bingham number and aspect ratio have been proposed based on the present numerical results.

Experimental investigation of flow and heat transfer in rectangular cross-sectioned duct with baffles mounted on the bottom surface with different inclination angles

In this study, steady-state forced convection heat transfer and pressure drop characteristics in a horizontal rectangular cross-sectioned duct, baffles mounted on the bottom surface with different inclination angles were investigated experimentally in the Reynolds number range from 1 × 103 to 1 × 104. The study was performed under turbulent flow conditions. Effects of different baffle inclination angles on flow and heat transfer were studied. Results are also presented in terms of thermal enhancement factor. It is observed that increasing in baffle inclination angle enhances the heat transfer and causes an increase in pressure drop in the duct.

Experimental convective heat transfer studies in a turbulent flow regime using alumina-water nanofluids

The present work investigates forced convective heat transfer characteristics of alumina-water nanofluids in a turbulent flow regime. Nanofluids are dilute colloidal suspensions with nano-sized particles ( < 100 nm) dispersed in a basefluid. The thermal conductivity values are measured by a steady state method, using a guarded hot plate (GHP) apparatus customized for liquids. The forced convective heat transfer characteristics are evaluated with the help of a test loop maintained in a constant heat flux condition. Controlled experiments under a turbulent flow regime are carried out using four particle concentrations (0.5vol%, 1vol%, 2vol% and 4vol %). The experimental results show that, the thermal conductivity of nanofluids increases with an increase in particle concentration and closely follow effective medium theories. However, the enhancement of heat transfer coefficients in the turbulent regime is observed to be within the measurement uncertainty.

Determination of the Single-Phase Forced Convection Heat Transfer Characteristics of TiO2Nanofluids Flowing in Smooth and Micro-Fin Tubes by Means of CFD and ANN Analyses

A numerical study including a validation process with experimental data was performed on the forced convection flows of nanouids; the object of study was water containing TiO 2 nanoparticles in smooth and micro-fin tubes at a constant wall temperature. Constant heat flux and temperature-dependent properties were used to determine the hydrodynamics and thermal behaviors of the nanouid flow;a single-phase numerical model was used to solve two-dimensional equations by means of a CFD program for the water flow, contained in a smooth tube and in various micro-fin tubes having various helix angles (0 o , 18 o ). An extensive literature review on the determination of the physical properties (k, �, �, Cp) of nanofluids is given in this paper. Multilayer Perceptron (MLP), one of thearti- ficial neural network (ANN) methods, was used to determine the most agreeable physical propertiesof TiO 2 nanofluids among correla- tions. The inputs ofthe ANN analyses were the correlations of physical properties, the average temperature and velocity of water in the test tubes, and the nanoparticle concentrations, while the outputs were shear stress, friction factor, heat flux, convective heat transfer co- efficient, and pressure drop. After obtaining the best combination of physical properties of TiO 2 nanofluids from the ANN analyses, the numerical model was validated by means of a CFD program,with the experimental smooth tube data as a case study; it was also validate- das a simulation studyfor several micro-fin tubes through a CFD program. This paper shows temperature, pressure, and velocity distribu- tions in the investigated tubes; in addition, average and local experimental, theoretical, and numerical values in the smooth and micro-fin tubes are compared with oneanother in terms of friction factors, shear stresses, convective heat transfer coefficients, and pressure drops, according to various nanoparticle concentrations.

Determination of the Single-Phase Forced Convection Heat Transfer Characteristics of TiO2Nanofluids Flowing in Smooth and Micro-Fin Tubes by Means of CFD and ANN Analyses

A numerical study including a validation process with experimental data was performed on the forced convection flows of nanofluids; the object of study was water containing TiO2 nanoparticles in smooth and micro-fin tubes at a constant wall temperature. Constant heat flux and temperature-dependent properties were used to determine the hydrodynamics and thermal behaviors of the nanofluid flow;a single-phase numerical model was used to solve two-dimensional equations by means of a CFD program for the water flow, contained in a smooth tube and in various micro-fin tubes having various helix angles (0o, 18o). An extensive literature review on the determination of the physical properties (k, μ, ρ, Cp) of nanofluids is given in this paper. Multilayer Perceptron (MLP), one of theartificial neural network (ANN) methods, was used to determine the most agreeable physical propertiesof TiO2 nanofluids among correlations. The inputs ofthe ANN analyses were the correlations of physical properties, the average temperature and velocity of water in the test tubes, and the nanoparticle concentrations, while the outputs were shear stress, friction factor, heat flux, convective heat transfer coefficient, and pressure drop. After obtaining the best combination of physical properties of TiO2 nanofluids from the ANN analyses, the numerical model was validated by means of a CFD program,with the experimental smooth tube data as a case study; it was also validatedas a simulation studyfor several micro-fin tubes through a CFD program. This paper shows temperature, pressure, and velocity distributions in the investigated tubes; in addition, average and local experimental, theoretical, and numerical values in the smooth and micro-fin tubes are compared with oneanother in terms of friction factors, shear stresses, convective heat transfer coefficients, and pressure drops, according to various nanoparticle concentrations. Keywords: Heat transfer coefficient, Pressure drop, ANN, Nanofluid, Single-phase flow, CFD

Forced Convective Heat Transfer Characteristics in Micro/Minicylinders Group at Low Reynolds Number

As an effective method for heat transfer enhancement, mini- or microscale pin fin arrays with different arrangements have been employed and studied in heat exchangers for next-generation cooling technology. A forced convective heat transfer characteristic of deionized water flowing through in-line and staggered array micro/minicylinders group plates of microcylinders was experimentally studied. Using an electricity heater, the flow rate and temperature difference between the inlet and outlet of micro/minicylinders group were measured and the Nusselt numbers were obtained over low Reynolds numbers ranging from 8 to 100. The results indicate that the experimental Nu number was less than that of the classical correlation. The height of the cylinder plays a role due to the appearance of the sluggish regions in micro/minicylinders at low Reynolds number and the combined actions of some dimensional effects, such as the conjugate heat transfer effect, the end wall effect, and the thermophysical properties with temperature variation effect, etc. The distance between the outermost cylinders and the wall of the micro/minicylinders group plate affects the experimental Nu number of a staggered array more apparently than that of an in-line array when Re > 20, which resulted from a stronger brim effect according to the present experimental results.

FORCED CONVECTION THERMAL BOUNDARY LAYER DEVELOPMENT IN A POROUS MEDIA NEAR A WALL WITH VARIABLE TEMPERATURE BOUNDARY CONDITION

The behavior of forced convection heat transfer characteristics through and over porous layer near aheated flat plate at variable temperature has been investigated numerically. Two cases of variable walltemperature boundary condition are studied. The first case is of linear temperature variation with positionalong the flat plate and the second case is of sinusoidal temperature variation with time of heating. The flow field in the porous region is governed by the Darcy-Brinkman-Forchheimer equation, the thermal field in the porous region by the energy equation and the part over the porous matrix includes flow and heat transfer equations. Solutions of the problem have been carried out using a finite difference method through the use of a stream function-vorticity transformation. The effects of various governing dimensionless parameters, Darcy number, Reynolds number, Prandtle number as well as the inertia parameter are thoroughly explored. The variation of the non-dimensional period and amplitude values of the sinusoidal temperature distinction with time was also studied. Good results were obtained and reported graphically. It was found that the local Nusselt number on the flat plate increases with the increasing of the increasing non-dimensional values of period and amplitude individually.