Forced Convection Heat Transfer Characteristics Research Articles

Evaluation of nanoparticle shape factor on a laminar forced convective heat transfer characteristics of various nanofluids flow in a tube using single-phase numerical model

Nanotechnology is advantageous in improving thermophysical properties and enhancing heat transfer rate compared with conventional fluids due to their superior thermophysical properties. These properties vary with many parameters such as concentration and shape. In this study, the effect of nanoparticles shape is numerically explored on heat transfer performance under a laminar flow regime (Re=500 and 2000) through the smooth tube. Heat transfer enhancement capability of the nanoparticle shapes with targeted reference to average Nusselt number, average Darcy friction factor, pumping power, and performance evaluation criterion have been investigated. Three types of nanofluids (Fe3O4/water, Al2O3/water, and GO/water) with various nanoparticle shapes (brick, cylindrical, platelet, and spherical) and different nanoparticle volume fractions (φ=1.0, 2.0, 3.0, and 4.0%) have been used as heat transfer fluid in analyzes. Numerical results show that heat transfer performance was greatly influenced by changing nanoparticle shapes. The highest average Nusselt number was obtained for GO/water nanofluid with platelet nanoparticle shape and φ=4.0%. Compared to water, Fe3O4/water, and Al2O3/water, the average Nusselt number in GO/water increased by 64.34%, 54.02%, and 43.41%, respectively. The highest performance evaluaton criterionwas obtained for the GO-water nanofluid with platelet nanoparticle shape at Re=2000. On the other hand, it is found that the Fe3O4/water nanofluid with platelets nanoparticle shape causes the highest pumping power compared with other analyzed nanofluids.

Natural and Forced Convective Heat Transfer Enhancement for Solid Cylinders with Different Geometrical Shapes

Enhancing heat transfer for both natural and forced convection is a common issue for any heat transfer process. Experimental studies have been carried out for six different geometrical shapes of solid bars for natural convection and forced convection with four different air velocities while keeping the same perimeter and length of the solid bars, which means the lateral surface area of the bars is the same. Results reveal that both the natural and forced convective heat transfer characteristics are greatly influenced by the geometrical shape in terms of Nusselt number (Nu), heat transfer coefficient (h), and heat transfer rate (q). In addition, isosceles and cylindrical shape geometry contribute to the lowest and highest heat transfer, respectively. As well, it is obtained from the results that convective heat transfer characteristics are directly related to the cross-sectional area, even if the perimeters are the same. Moreover, among the different geometrical shapes, the isosceles and hexagonal shapes take the shortest and longest duration to attain the steady-state condition in the conductive heat transfer process. The convective heat transfer characteristics are well-validated, with available results for both natural and forced convection heat transfer.

Forced Convection Heat Transfer Characteristics of Developed Laminar Flow in the Octagonal Channels of Octo-Square Asymmetric Particulate Filters

Forced Convection Heat Transfer Characteristics of Developed Laminar Flow in the Octagonal Channels of Octo-Square Asymmetric Particulate Filters

Magnetohydrodynamic forced convection and heat transfer of a Casson fluid flow in an anisotropic porous channel with Isoflux boundaries

Theoretical analysis of magnetohydrodynamic fully developed forced convective flow and heat transfer characteristics of a non-Newtonian electrically conducting Casson fluid through a porous channel filled with anisotropic porous material bounded by two impermeable horizontal walls subject to constant heat flux applied to the outer walls is investigated. The extended Darcy-Brinkmann model govern the flow inside the porous channel and accounts for the presence of the inertia term, which allows for the no-slip boundary conditions at the walls. The principal axis of anisotropic permeability is oriented from to radians. The equations governing the system are solved using the inbuilt “DSolve” in Mathematica 11.1 for the velocity and temperature profiles as well as the Nusselt number (Nu), which characterizes the rate of heat transfer in the system. The effects of various parameters on the velocity, temperature and heat transfer profiles are displayed through graphs and discussed quantitatively. From the results we observed that the velocity profile reduced as the Casson parameter (ß), anisotropic ratio (Kr), orientation angle (), and Hartmann number (Ha) increased, whereas the velocity profile increased when the Darcy number (Da) and apparent viscosity () increased. Similarly, these variables also had similar effect on the temperature profile of the fluid. On the other hand, the heat transfer profile, as measured by Nusselt number, increased when the Casson parameter (ß), anisotropic ratio (Kr) and Hartmann number (Ha) increased, while increasing the orientation angle () and apparent viscosity ( ) decreased the Heat Transfer Profile. Upon further investigation, the heat transfer profile was shown to be maximum along the path of least permeability in the anisotropic porous media under investigation.

Forced convection heat transfer characteristics of aviation kerosene in a horizontal tube under electric field

The electrohydrodynamic (EHD) technique can considerably improve the performance of aviation heat exchangers. In this study, the forced convection heat transfer characteristics of aviation kerosene in a horizontal wire-tube structure under electric field were investigated. The influences of positive and negative high voltages on the heat transfer in test section were compared. Key factors affecting EHD heat transfer enhancement, such as fuel inlet temperature, mass flow, heat flux and operating pressure were explored. Furthermore, the cause of electrode corrosion was investigated using Scanning Electron Microscope (SEM) and Energy Disperse Spectroscopy (EDS). The experimental results showed that the circumferential temperature distribution of the test section was uneven owing to buoyancy in the absence of electric field. As the applied voltage increased, temperature heterogeneity decreased. Negative voltage improved the heat transfer more effectively than positive voltage. The electric field enhanced the heat transfer of high-temperature fuel more effectively. In the charge injection mechanism voltage range, the numerical simulation results were more similar to the negative voltage experimental results. The heat transfer enhancement ratio was reduced by an increase in the fuel mass flow and operating pressure. A higher heat flux led to a more substantial buoyancy effect, which inhibited the electric field force effect. Finally, the corrosion rate of positive high voltage electrode was the highest, resulting in rapid loss of metal elements from the electrode surface.

Natural and forced convection heat transfer characteristics of single-phase immersion cooling systems for data centers

Improving power usage effectiveness (PUE) in data centers becomes a key challenge for carbon neutrality and carbon peaking strategies. In this context, this paper investigates the single-phase immersion cooling (SPIC) system that promises to improve PUE. Three-dimensional mathematical models of pump-driven and buoyancy-driven immersion cooling tanks are established and numerically solved. The thermal characteristics, flow resistance, and energy consumption levels of immersion cooling tanks in three operating modes are investigated. Moreover, the roles of volume flow rate, inlet temperature, and device power in immersion cooling characteristics are analyzed. The results indicate that the heat dissipation of buoyancy-driven SPIC systems is less effective than pump-driven ones. Compared to buoyancy-driven SPIC systems, the average temperature of immersion coolants and PUE in pump-driven SPIC systems reduces by 55.5 and 11.6%, respectively. Interestingly, although natural convection in mixed convection operation enhances convective disturbance, it induces temperature stratification that weakens temperature homogeneity. Increases in inlet temperature and device power both worsen the immersion cooling performance. However, increasing inlet temperature improves temperature uniformity and reduces flow resistance losses, while increasing device power has the opposite effect. Besides, the increased flow rate enhances the convective heat transport and temperature uniformity but increases the flow resistance loss.

Experimental study on the forced convection heat transfer characteristics of airflow with variable thermophysical parameters in a circular tube

The heat transfer of fluids in pipelines under conditions with variable thermophysical parameters is ubiquitous in engineering applications, but effective methods to predict the heat transfer parameters are scarce. To address this issue, an experimental method was proposed to measure the heat transfer parameters in a circular tube by considering the effect of the insufficient development of turbulence in the inlet region and a Robin boundary on the wall. The variation of the Nusselt number of the inner wall was calculated by measuring the temperature distribution of the outer wall, and a temperature-related Gnielinski correlation was developed for conditions under which the thermophysical parameters vary with the fluid temperature. The results demonstrated that the deviations between the experimental Nusselt numbers and the values predicted using the traditional Gnielinski correlation became larger and larger as the flow distance increased. The temperature-related correlation generally improved the prediction accuracy by more than 25%, and the accuracy was better with increasing inlet temperature and decreasing airflow velocity. This study provides an important empirical reference for the prediction of the convective heat transfer parameters in pipelines and related engineering applications under strong heating or cooling conditions.

Review on Thermal Performance of Nanofluids With and Without Magnetic Fields in Heat Exchange Devices

Addition of nanoparticles into a fluid can improve the heat transfer performance of the base fluid in heat exchangers. In this work, the preparation method and process of nanofluids are introduced, and thermal properties of nanofluids, such as thermal conductivity and viscosity, are discussed deeply. This paper summarizes various theoretical models of thermal conductivity and viscosity of nanofluids. A comprehensive literature survey on applications and limitations of nanofluids has been compiled. This paper also aims to review the natural and forced convective heat transfer characteristics of nanofluids with and without magnetic fields. The discussion for the natural convective heat transfer of nanofluids focuses on the heat transfer performance of non-conventional enclosures and electric heaters. The effects on heat transfer due to variations of heated walls are also investigated. Specific applications of nanofluids in a tube with trapezoidal ribs, double-tube heat exchangers, and plate heat exchangers have been reviewed and presented in a discussion about forced convective heat transfer. The previous results show that the inlet temperature of nanofluids obviously affects the heat transfer characteristics of double-tube heat exchangers, whereas a multi-walled carbon nanotube–water nanofluid shows significant advantages in plate heat exchangers. Finally, this paper studies natural convective heat transfer of magnetic fluids in a square cavity and forced convection heat transfer in a straight tube and a corrugated structure under the action of magnetic fields. It is found that the heat transfer performance of an Fe3O4–water nanofluid is enhanced when a magnetic field is applied to the corrugated plate heat exchangers, and the pressure drop can be reduced by around 10%. It is recommended that natural convection of magnetic fluids needs to be investigated experimentally in a real cavity and a corrugated channel under the influence of a magnetic field. In addition, studies of alternating magnetic field are recommended to reveal any improvements of thermal performance of magnetic fluids in heat exchange devices. This review puts forward an effective solution for improvement of the thermal performance of heat transfer equipment and serves as a basic reference for applications of nanofluids in heat transfer fields.

A Comparative Study of Multiple Regression and Machine Learning Techniques for Prediction of Nanofluid Heat Transfer

Abstract The aim of this article is to introduce and discuss prediction power of the multiple regression technique, artificial neural network (ANN), and adaptive neuro-fuzzy interface system (ANFIS) methods for predicting the forced convection heat transfer characteristics of a turbulent nanofluid flow in a pipe. Water and Al2O3 mixture is used as the nanofluid. Utilizing fluent software, numerical computations were performed with volume fraction ranging between 0.3% and 5%, particle diameter ranging between 20 and 140 nm, and Reynolds number ranging between 7000 and 21,000. Based on the computationally obtained results, a correlation is developed for the Nusselt number using the multiple regression method. Also, based on the computational fluid dynamics results, different ANN architectures with different number of neurons in the hidden layers and several training algorithms (Levenberg–Marquardt, Bayesian regularization, scaled conjugate gradient) are tested to find the best ANN architecture. In addition, ANFIS is also used to predict the Nusselt number. In the ANFIS, number of clusters, exponential factor, and membership function (MF) type are optimized. The results obtained from multiple regression correlation, ANN, and ANFIS were compared. According to the obtained results, ANFIS is a powerful tool with a R2 of 0.9987 for predictions.

Forced convection heat transfer of aviation kerosene enhanced by electric field in a circular channel

• Using EHD technique to enhance avionics system heat dissipation is proposed. • Electrical properties of aviation kerosene in wire-tube EHD structure are studied. • Inlet parameters affecting the EHD heat transfer enhancement is investigated. • Flow, temperature and electric fields are captured by numerical simulation. Coolant heat transfer capacity determines the security of avionics system operation. Electrohydrodynamics (EHD), as an enhanced heat transfer technology, can be applied to the avionics cooling system. In this paper, the forced convection heat transfer characteristics of aviation kerosene enhanced by the EHD technique were investigated by both experimental and numerical simulation methods for the first time. One kind of wire-tube structure heat exchanger was designed and the heat dissipation performance of aviation kerosene was tested experimentally at different inlet parameters and electric potentials. A 3D mathematical model was established based on Maxwell and Navier-Stokes equations and the finite volume method was used for conservative discretization of the governing equations. The experimental and numerical simulation results are in good agreement. In the range from 128 to 900 of Reynolds number, the EHD heat transfer enhancement effect becomes weaken with the increase of mass flow. The charge migration along the electric field is suppressed due to the increasing axial velocity. However, the heat transfer enhancement effect is more obvious with the increasing inlet temperature of aviation kerosene. Due to the low viscosity and high ion mobility of high-temperature aviation kerosene, the charge migrating ability is enhanced and the viscous resistance is easier to overcome to produce the secondary flow. The maximum heat transfer enhancement ratio can reach 1.9 times. This paper expanded the EHD application to aviation fuels as the coolant in avionics systems and provided a deeper understanding on inlet parameters affecting the EHD heat transfer enhancement.

Forced convective flow and heat transfer past a blunt headed cylinder with corner modification

A numerical analysis is performed to elucidate the forced convective fluid flow and heat transfer characteristics past a blunt-headed cylinder. Simulations are carried out employing air (Pr = 0.71) as an operating fluid in a Reynolds numbers range 40≤Re≤200. The curvature ratio is varied from 0 to 0.5. The flow and heat transport features are elucidated in detail for different curvature ratios. Important flow parameters such as boundary layer thickness, vortex strength, wake width, drag, lift, skin friction coefficient, pressure coefficient, Strouhal number, and recirculation length are computed. Also, a primary stability analysis has been carried out using the Landau equation, whereas secondary stability analysis has been done implementing dynamic mode decomposition (DMD) to compute the critical Reynolds number at each curvature ratio. Calculating local and time-averaged values of Nusselt numbers, heat transfer characteristics are studied. An entropy generation analysis is done to investigate the effects of corner modification on the efficacy of thermofluid transport characteristics.

Forced convection and entropy generation past a series of porous bodies with internal heat generation

A numerical investigation of forced convective heat transfer and entropy generation characteristics around a series of heat-generating permeable bodies, placed in a confined domain, has been carried out in the present study. Considering air as an operating media, simulations have been performed for the range of Reynolds number, and Darcy number, The simulations have been carried out by using the finite volume method and implementing the Darcy-Brinkman-Forchheimer model to solve the momentum equations in the porous domain. The local thermal equilibrium model (LTE) is adopted to model the thermal behavior between the solid and fluid phases of the porous media. It is observed that the heat transfer rates from the bodies to the clear fluid domain increase with an increase in either or The flow from the preceding body modifies the heat transfer characteristics of the succeeding body. An increased amount of fluid flow results in the tempering of recirculation zones while decreasing the transverse spread of isotherms. The total entropy generation increases with an increase in or However, an increment in either of these parameters results in the increased dominance of fluid friction irreversibilities over heat transfer irreversibilities. Observed findings could be helpful to understand, design, and operate a similar porous multibody embedded system. One very common example of a such system is the cooling of electronic chips which may be relevant for high-performance computing applications.

Coupling effect of heat transfer in plate heat exchanger filled with porous media

The forced convection heat transfer characteristics in plate heat exchanger filled with porous media are semi-analytically investigated in this paper. The Darcy-Brinkman model is utilized to describe the fluid flow, and the local thermal non-equilibrium model is employed to establish the energy equations. The solutions of the temperature and velocity distributions are validated in limiting case. The coupling heat transfer characteristics are studied in parallel flow and counter flow under different conditions. The influences of the heat capacity ratio, the Darcy number, the Biot number, the porosity, and the thermal conductivity, on heat transfer are discussed. The results show the coupling effect in plate heat exchanger filled with porous media since the thermal boundary conditions of each channel of the plate heat exchanger are dependent on the flow and heat transfer parameters of both the two channels. The heat capacity ratio is found to have the most important influence on the coupling effect. The coupling effect should be considered when designing the plate heat exchanger filled with porous media.

Effect of Magnetic Field on the Forced Convective Heat Transfer of Water–Ethylene Glycol-Based Fe3O4 and Fe3O4–MWCNT Nanofluids

This paper discusses the forced convective heat transfer characteristics of water–ethylene glycol (EG)-based Fe3O4 nanofluid and Fe3O4–MWCNT hybrid nanofluid under the effect of a magnetic field. The results indicated that the convective heat transfer coefficient of magnetic nanofluids increased with an increase in the strength of the magnetic field. When the magnetic field strength was varied from 0 to 750 G, the maximum convective heat transfer coefficients were observed for the 0.2 wt% Fe3O4 and 0.1 wt% Fe3O4–MWNCT nanofluids, and the improvements were approximately 2.78% and 3.23%, respectively. The average pressure drops for 0.2 wt% Fe3O4 and 0.2 wt% Fe3O4–MWNCT nanofluids increased by about 4.73% and 5.23%, respectively. Owing to the extensive aggregation of nanoparticles by the external magnetic field, the heat transfer coefficient of the 0.1 wt% Fe3O4–MWNCT hybrid nanofluid was 5% higher than that of the 0.2 wt% Fe3O4 nanofluid. Therefore, the convective heat transfer can be enhanced by the dispersion stability of the nanoparticles and optimization of the magnetic field strength.

Experimental and computational determination of heat transfer, entropy generation and pressure drop under turbulent flow in a tube with fly ash-Cu hybrid nanofluid

The purpose of this research is to study the forced convection heat transfer and flow characteristics of water base fly ash-Cu (80:20% by volume) hybrid nanofluid (HNF) flow through a copper tube under a constant heat flux (CHF) of 7962W/m2 experimentally and numerically. The present work presents results for the concentrations of 0.5–2.0 vol% at a fluid inlet temperature of 30 °C in the flow rate range of 5–16 LPM. HNF stability, thermal conductivity, and viscosity were experimentally analyzed and compared with the established correlations. The maximum augmentation in Nusselt number (Nu) was 57.1% and 8.95% at a concentration of 2.0% relative to water for HNF and fly ash nanofluid (FANF), respectively. The total entropy generation varies inversely with the Reynolds number (Re). The pressure drop (Δp) of HNF is greater than the FANF and water. The development of correlations with experimental data is for determining Nu and friction factors of HNF. Bejan number (Be) of HNF and FANF varies inversely with concentration and Re improvement. The values of thermal performance factor (TPF) enhance with concentration, and a maximum TPF value observed is 1.52 at 2% concentration. The performance of the computational analyses is with ANSYS software gives a reasonable agreement between them.

Friction and Forced Convection Heat Transfer Characteristics in Tubes by Use of Helical-Wire-Coil Inserts.

This work summarizes the results of experimental investigation of convective heat transfer and friction loss characteristics of air flow in a horizontal circular copper tube of diameters 13.5/22 mm., using helical wire-coils , of diameter 1.4 mm, inserted in. The helix angle (a) of the helical-wire-coil is varied from 65° to 86.7o. The outer surface of the test tube is heated by superheated steam (degree of superheat 2:3 oC) at atmospheric pressure. During the experimental work, Reynold's number is changed from 6000 to 120000 and Prandti number is about 0.7. The heat transfer enhancement of the inserted helical-wire-coil is ranging from 30 % to 145 %. However, A quantitatively increase in hydrodynamics resistance is noticed. Correlations of Nusselt number and friction factor has been made. It was found that the nusselt number and friction factor were dependent on both Reynold's number and helix angle.

Thermo-hydraulic performance of nanofluids in enhanced tubes - a review

Technological developments are continuously growing to improve the efficiency of thermal systems on the demand of present era. To get rid of the scientists and engineers from traditional heat transfer intensification methods and to miniaturize thermal transport devices, novel and innovative techniques are obligatory. In this whole drive, the effective tube geometries and efficient working fluids perform vital role in the betterment of heat exchange devices. Geometrical argumentations/surface modifications impose on smooth tubes are called as enhanced tubes. These tubes contribute towards high rate of heat transfer by reducing the formation of boundary layer near the wall surfaces of the tube. Also, nanofluids with superior thermo-physical properties compared to conventional fluids also assist the rate of heat exchange in various heat transfer applications. This article begins with the introduction of enhanced tubes and nanofluids and followed by overview of nanofluid synthesis and different tube geometries. An attempt has been made to summarize last decade research contributions in the field of forced convection heat transfer and flow characteristics (HTFC) with employing the combined effect of enhanced tubes and nanofluids. Additional heat transfer enhancement techniques (swirl flow devices, magnetic field, agitation, rotation and pulsation) brace with present ones, are also discreetly deliberated. Proposed correlations by authors are also represented which shows the good agreement with experimental data. Important findings and outcomes from reviewed studies are compiled in discussion section. A number of suggestions and guidelines are highlighted to intensify the heat transfer rate as well as to mitigate the effects of pressure losses in fluid flow pipes.

Particle-resolved numerical study of the forced convection heat transfer characteristics of an endothermic-biomass particle placed in supercritical water crossflow

Abstract Biomass gasification in supercritical water (SCW) for high energy density gas fuel is a promising method for the efficient usage of biomass resource. Researches have indicated that the gasification efficiency is greatly depended on the heat transfer rate during the practical process of cold biomass particle injected into SCW. So the study of the forced convection heat transfer characteristics of an endothermic-biomass particle placed in SCW crossflow is of great significance. Moreover, the study of the particle surface local heat transfer rate distribution is also necessary for the complete gasification of biomass particles in SCW. Therefore, this work performs particle-resolved direct numerical simulation study on SCW flow past an endothermic sphere. Results demonstrate that the heat transfer gets great enhancement when the heat transfer temperature range comprises the large specific heat capacity zone. For the particle surface local heat transfer distribution, the enhancement at the front of particle is much stronger than that at the rear. Furthermore, the heat transfer characteristics under different pressures are also studied. In the end, a new forced convection heat transfer correlation applicable for SCW flow past an endothermic sphere is obtained.

Forced convective flow and heat transfer past an unconfined blunt headed cylinder at different angles of incidence

In the present paper, a numerical investigation has been carried out to study the forced convective flow and heat transfer characteristics past a blunt-headed cylinder in crossflow. Employing air as an operating fluid, calculations are carried out for a range of Reynolds number (Re) from 40 to 160. The angle of incidence is varied in the range of 0∘ ≤ α ≤ 180 ∘. The thermofluid features of flow and heat transport are analysed in detail for different angles of incidence. To analyse the aerodynamic characteristics, several parameters such as drag and lift coefficients, moment coefficient, Strouhal number, recirculation length, and local time-averaged vorticity flux have been calculated. Furthermore, a stability analysis has been undertaken by using the Stuart Landau equation to enumerate the critical Reynolds number at each angle of incidence. Heat transfer characteristics are studied by computing local and time-averaged values of Nusselt numbers. When compared to a rectangular cylinder, a blunt-headed cylinder exhibits an enhanced heat transfer rate. In the end, an entropy generation analysis has been carried out to study the effects of Re and angle of incidence on the efficiency of thermofluid transport characteristics.

Convective heat transfer performance of hybrid nanofluid in a horizontal pipe considering nanoparticles shapes effect

In this paper, the problem of steady forced convection heat transfer and fluid flow characteristics of a hybrid nanofluid flowing through an isothermally heated horizontal tube considering various nanoparticle shapes has been investigated numerically. The three dimensionless cylindrical coordinate equations are discretized using the finite volume method and solved via a FORTRAN program. A numerical parametric investigation is carried out for a tube filled with regular water, (TiO2/water) nanofluid and (Ag–TiO2/water) hybrid nanofluid. Four different types of nanoparticle shapes are considered in this study, spherical, cylindrical, platelets and blades, with different volume fractions ranging from 0 to 8% using water as a base liquid. The influence of nanoparticle shape, nanoparticle concentration and Reynolds number on the local Nusselt number and the friction factor is essentially examined. The results showed that the friction factor of both nanofluid and hybrid nanofluid flow was increased as the nanoparticle volume fraction increased for all kinds of nanoparticle shapes, whereas it decreased as the Reynolds number increased. Nusselt number increased with increase in the nanoparticle concentration and Reynolds number. The highest heat transfer rate was acquired for the maximum nanoparticle volume concentration by using blade nanoparticle shape followed by platelet shape, cylindrical shape and lastly the sphere shape. It was found that the maximum values of the friction factor were registered for platelet-shape nanoparticles.