Laminar Convection Heat Transfer Research Articles

Experimental investigation of substrate board orientation effect on the optimal distribution of IC chips under forced convection

ABSTRACT Steady-state experiments are conducted under the laminar forced convection heat transfer mode for the cooling of seven asymmetric IC chips (heat sources) mounted at different positions on the substrate board. The board is oriented at different angles, i.e., at 0° (horizontal), 30°, 60°, and 90° (vertical) to study its effect on the cooling of the IC chips. The goal is to determine the optimum configuration (arrangement of these seven IC chips on the board) leading to minimize their maximum temperature. The optimal configuration is determined by employing a hybrid optimization strategy that combines the Artificial neural network (ANN) with Genetic algorithm (GA) which is further validated with suitable experiments. Different correlations are proposed to study the effect of the substrate board orientation on the Nusselt number (cooling rate) and temperature of the IC chips. The results suggest that the temperature of the IC chips is a strong function of their size, positioning on the substrate board, input heat flux, and the substrate board orientation. The temperature of the IC chips is least for the 30° oriented board, as for this case, the maximum surface area of the board is in contact with the flowing air. This helps in cooling the chips effectively in lowering their temperature. The surface area available to dissipate the heat from the IC chips keeps on decreasing after the 30°. For the vertical orientation, the air entering the inlet section of the substrate board hits perpendicular to it. Hence, the temperature of the IC chips is maximum for the vertical substrate board. Air velocity is also crucial for the cooling of the IC chips. There is a temperature drop of 1.42–17.33% for the higher velocity (8 m/s) as compared to the lower one (4.5 m/s).

Assessment of Fe3O4–water nanofluid for enhancing laminar convective heat transfer in a car radiator

Increasing the heat transfer rate in car radiators by using nanofluids leads to better control of engine temperature at hard working conditions and reduces the required radiator dimensions. However, due to the possibility of disposal of radiator coolants in the environment, use of an eco-friendly nanofluid coolant is of particular importance. Therefore, in the current research, Fe3O4–water nanofluids with the nominal particle diameter of 28 nm were synthesized. The experiments were performed at vol% ranging from zero to 0.9, three radiator input temperatures (72, 80 and 88 °C) and four radiator fan speeds (1000, 1500, 2000 and 2500 rpm). Although the fluid flow rate was constant in this study, Re number varied in a narrow range (30–100) according to the change in the nanofluid concentration. It is interesting to say that the best working condition of the radiator obtained at 0.1 vol% and more increase in the nanoparticle concentration deteriorated the heat transfer. At 0.1 vol%, the heat exchanging performance of the radiator is improved by an average of 21% in comparison with the pure water. At this concentration, maximum Re number was also obtained according to the measured density and viscosity of the nanofluids. It can be concluded that at higher nanofluid concentrations (> 0.1 vol%), not only the particle agglomeration but also Re number reduction may lead to heat transfer deterioration. Moreover, at 0.1 vol% of nanoparticles, the outlet coolant temperature from the radiator decreased with increasing the radiator fan speed from 1000 to 2500 rpm. However, for temperatures more than 80 °C, the difference between the output fluid temperature at the fan speeds of 2000 and 2500 rpm was not significant. Therefore, as an overall conclusion, the concentration of 0.1 vol% and fan speed of 2000 rpm could be recommended in the car radiator with inlet temperatures at the range of 80–88 °C.

Numerical simulation of convective heat transfer of microencapsulated phase change material slurrys in a circular tube

For the Microencapsulated Phase Change Materials slurry(MPCMs)having a large latent heat during the phase change period and having a higher heat convection coefficient than the single-phase fluid, it has become a new thermal fluid of widespread investigation. In this paper, the model of equivalent specific heat is presented to numerical simulate the laminar convective heat transfer performances of MPCMs in a tube under the condition of constant heat flux. The heat transfer of MPCMs in a tube is investigated under various concentrations of MPCMs and heat flux and the correlation of the convective heat transfer with MPCMs in a tube is obtained.

A numerical study of mixed convection heat transfer in a lid-driven cavity using Al2O3-water nanofluid

This study aims a numerical investigation of steady, laminar mixed convection heat transfer in a two-dimensional cavity by employing a finite volume method with a fourth-order approximation of convective terms, when nanoparticles are present. With the aim of solving two-dimensional momentum and energy conservation equations, a finite volume method on a non-uniform staggered grid is utilized. Second-order central differences are utilized to approximate diffusion terms in momentum and energy equations, while the development of a non-uniform four-point fourth-order interpolation (FPFOI) scheme is performed for the convective terms. Continuity and momentum equations are solved using the SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) algorithm. In order to evaluate heat transfer enhancement, various viscosity and thermal conductivity models were employed. Numerical solution results were obtained in different models in cases where Gr number is between 103 and 105, Re number is 10-100-1000 and nanoparticle volumetric fraction is 0-5%.

Study of Laminar Convection Heat Transfer of Non-Newtonian Nanofluids in a Tube under Constant Heat Flux Using New Power-Law Relation

Study of Laminar Convection Heat Transfer of Non-Newtonian Nanofluids in a Tube under Constant Heat Flux Using New Power-Law Relation

The mechanism of laminar convective heat transfer enhancement enforced by twisting of elliptical tube

Nusselt number has unique characteristics under uniform wall temperature (UWT) and uniform wall heat flux (UWHF) thermal boundary conditions in twisted elliptical tube. Twisting of elliptical tube produces larger local Nusselt number under UWT than that under UWHF in some regions. In order to discover the mechanisms to form such characteristics in twisted elliptical tube, the velocity contribution and velocity gradient contribution to the transport of the heat flux defined by Fourier's law, q, are numerically investigated in this paper. Velocity gradient under UWHF contributes more greatly to the transport of the heat flux under UWHF than under UWT, which results larger local Nusselt number under UWHF than under UWT in straight elliptical tube. Velocity and its gradient contributions to the transport of the heat flux nearly normal to the wall surface have larger values under UWHF than under UWT in most regions, which produces larger local Nusselt number in twisted elliptical tube under UWHF than under UWT in these regions. In some regions velocity and its gradient contributions to the transport of the heat flux nearly normal to the wall surface have larger values under UWT than under UWHF produces larger local Nusselt number in twisted elliptical tube under UWT than under UWHF in these regions.

Study of Heat Transfer through Radially Buffled Rotating Annulus

This paper presents an experimental study of laminar forced convection heat transfer for cold water flows through annular tube. The test section consisted of two annular spaces the inner of which for the tested cold water while the outer for the heating water flow that heated in a tank by electrical heaters. The inner tube of the annulus is rotated with rotational speeds which varied from 175 to 650 p.m. The outer tube of the annulus have a constant diameter of 54.5mm but the diameter of inner tube of the annulus is equal to 21, 26.7 and 33.5 mm so as to give diameter ratios of 0.62, 0.49 and 0.386. Variable numbers of semi-circle of buffles are used circumferentially around the rotating tube. The diameter of buffle is equal to 52 mm and 2 mm thickness. Cold water flowed axially through the annular space with velocities that ranged from (0.0192 to 0.0666 m/s), to give axial Reynolds numbers in the range (612 ≤ Re ≤ 2175), to cover the laminar flow regime. In the present work the effects of radius ratio, axial Reynolds number and rotational Reynolds number on the heat transfer are investigated. The results show that, the rate of heat transfer of the rotational annular tubes is higher than that of the stationary one of the same radius ratio and axial Reynolds numbers, and the rate of heat transfer of rotational annular tubes with baffles higher than rotational annular tubes without baffles of the same radius ratio and axial Reynolds numbers. 1- Rotation without buffle, Produces a maximum increase in Nusselt number of the order of 79% at Rea= 2080, Reω= 21545 and rotational speed= 480 r.p.m, (increase of only 11% in Nusselt number at Rea=646.2, Reω=7808 ,( rotational speed of 175 r.p.m), compared to the results of the stationary annular tube of the same radius ratio . 2- Rotation with buffle, Produces a maximum increase in Nusselt number of 200% at Rea= 2175, Reω= 21884 and rotational speed= 480 r.p.m, and increase of only 84% in Nusselt number at Rea=634, Reω=21778, ( rotational speed of 175 r.p.m) compared to the results of the stationary annular tube of the same radius ratio . Two correlations are made to describe the relation between Nusselt numbers and axial Reynolds number, diameter ratio, pitch to diameter ratio P/D and rotational Reynolds number and Reynolds number for stationary, rotating and buffled rotating annuli.

Experimental Investigation on Laminar Forced Convective Heat Transfer of Ferrofluid under Different Modes of Magnetic Field.

In this paper, the effects of constant, alternating and rotating magnetic fields on the laminar forced convective heat transfer of /water nanofluid (ferrofluid) in a uniformly heated copper tube are investigated experimentally. The local convective heat transfer coefficients are measured in the hydrodynamically fully developed region. The experiments are conducted using ferrofluid with 2.5% mass concentration. A quadrupole magnetic field system has been designed and constructed to generate the constant, alternating and rotating magnetic fields. For the magnetic field system, different operation modes were also examined and the most efficient mode was obtained. The effects of alternating magnetic field frequency and rotating magnetic field speed were also studied. The primary experiments showed that Uni-pole magnetic field system provides the maximum heat transfer enhancement. A significant enhancement in the local convective heat transfer of ferrofluid was observed by application of constant magnetic field. It was observed that constant magnetic field has provided a maximum local heat transfer enhancement of 119.6% compared to the case without magnetic field for ferrofluid with 2.5% mass concentration and at Re = 2000. This value is decreased to 106.7% and 96.8% by application of rotating and alternating magnetic field, respectively. Additionally, increasing the alternating magnetic field frequency and the rotating magnetic field speed adversely affect the heat transfer enhancement.

Heat Transfer Augmentation

This article presents a brief review of various methodologies applied for heat transfer enhancement in laminar flow convection regime. Experimental setup for laminar flow convection heat transfer enhancement using insertions has been explained along with the associated results. Nusselt’s number is found to be a key parameter for investigatigation in order to perceive the enhancement in heat transfer. Similarly, the magnetohydrodynamic mixed convection heat transfer enhancement technique has also been explored. The results of isotherms and fluid flow parameters are discussed which directly affect the heat transfer coefficient. This review article complements the literature in related field and thus will be helpful in order to carry out further experiments in heat transfer enhancement in future.

Heat Transfer Augmentation

This article presents a brief review of various methodologies applied for heat transfer enhancement in laminar flow convection regime. Experimental setup for laminar flow convection heat transfer enhancement using insertions has been explained along with the associated results. Nusselt’s number is found to be a key parameter for investigatigation in order to perceive the enhancement in heat transfer. Similarly, the magnetohydrodynamic mixed convection heat transfer enhancement technique has also been explored. The results of isotherms and fluid flow parameters are discussed which directly affect the heat transfer coefficient. This review article complements the literature in related field and thus will be helpful in order to carry out further experiments in heat transfer enhancement in future.

A complex evaluation of [C2mim][CH3SO3]– alumina nanoparticle enhanced ionic liquids internal laminar flow

This paper involves a numerical study of several water – ionic liquids mixtures and nanoparticle enhanced ionic liquids starting from a less studied ionic liquid: 1-Ethyl-3-methylimidazolium Methanesulfonate, [C2mim][CH3SO3]. The research start point was several previous published experimental results in regard to the water – ionic liquid mixtures and alumina based nanoparticle enhanced ionic liquids thermophysical properties. Consequently, all the considered fluids are completely described and can be successfully implemented in a numerical analysis using the single phase approach. The numerical analysis was performed in a cylindrical enclosure considering laminar steady state and results were collected in terms of Nusselt number, convective heat transfer coefficient, pressure drop and temperature on tube exit. Results were discussed in terms of heat transfer enhancement and pumping power requirement variation, as well as field synergy. Concluding, it can clearly say that mixing water with [C2mim][CH3SO3] ionic liquid it gets a decrease in laminar convective heat transfer coefficient, while adding nanoparticles the heat transfer is enhanced by maximum 50%, depending on the alumina mass concentration.

Numerical analysis of 2-D laminar natural convection heat transfer from solid horizontal cylinders with longitudinal fins

Proper thermal management through an effective cooling mechanism is essential for improving the reliability of operation of various electronic devices. A number of cooling methods are available among which passive cooling by natural convection has been deemed appropriate since it has distinctive advantages over active cooling or forced convection like high reliability, low maintenance cost, energy efficiency and noise-free nature. In the present study, natural convection from solid horizontal cylindrical heat sources of the geometry and dimensions of heat sinks of LED bulbs with external longitudinal plate fins have been modelled. Numerical computations of continuity, momentum and energy equations to solve the two dimensional incompressible natural convection conjugate heat transfer from such cylinders has been studied in the laminar regime (4.5×105<RaD<5.2×105). The diameter of the cylinder is kept at 60 mm whereas the length is kept at 50 mm. The number of fins has been varied from three to 36, the height of fins kept at 10, 20 and 30 mm and thickness at one mm. The effect of fin geometry parameters and Rayleigh number on total heat transfer, heat transfer exclusively from fin surface and from bare cylinder surface, heat transfer per fin and Nusselt number based on cylinder diameter have been studied in detail. Finally, optimum fin spacing for a particular fin height has been evaluated. Contour plots to capture temperature and velocity vectors around the heat source have also been developed. Numerical correlations of Nusselt number as a function of Rayleigh number, non-dimensional fin spacing and non-dimensional fin height reveal that the scaling laws of RaD1∕3 and RaD1∕4 are valid both for the computational data of our present analysis and experimental data even though the experiments are for a slightly different boundary condition.

Laminar entry region mixed convection heat transfer from an inclined rectangular fin array

Purpose The paper aims to investigate the influence of the angle of inclination on mixed convection heat transfer from rectangular plated shrouded fin array computationally. This study has got applications in the various thermal field such as cooling, solar thermal and so on. Design/methodology/approach A computational study is made to evaluate the thermal performance in an inclined channel. Findings Increase in clearance from 0.01 to 0.25 results in an increase of local Nusselt number by is as high as 15% near the exit. At a higher value of Gr with an increase in C* from 0.10, Nu is found to increase by 5.5%. Increase in Gr by 1.37 times results in enhancement of Nu by a maximum of 25-30%. Around 10% increase in overall Nu value is observed with an increase in inclination (i.e. from 30° to 60°). Practical implications This study has got applications in the various thermal field such as cooling, solar thermal and so on. Originality/value Entry region mixed convection in a shrouded inclined finned channel is performed.

Forced Convection Heat Transfer from a Pair of Circular Cylinders Confined in Ventilated Enclosure

This paper deals with a numerical simulation of laminar forced convection heat transfer from a pair of identical circular cylinders placed at the center of square cavity in the line array, the cavity is ventilated with single inlet and outlet ports, the inlet port is located at the middle of left vertical wall and the outlet port is located at the middle of right vertical wall. The work represents the effects of the distance between cylinders and Reynolds number on fluid flow and heat transfer rate. The governing equations of continuity, momentum and energy are solved by using finite-volume method. The obtained results are represented and discussed for following conditions: Reynolds number Re = 1 to 40, Prandtl number Pr = 7.01 and the gap distance S = 0.3L to 0.7L, where L is the cavity length. The main results are potted under the streamline and isotherm contours, the total drag coefficient and average Nusselt number of each cylinder is plotted versus studied parameters. It is found that the increase in the gap space distance between cylinders increases the heat transfer rate.

Numerical Study of Heated Tube Arrays in the Laminar Free Convection Heat Transfer

Laminar free convection heat transfer from a heated cylinder and tube arrays is studied numerically to obtain the local and average Nusselt numbers. To verify the numerical simulations, the Nusselt numbers for a single cylinder were compared to other authors for the Rayleigh numbers of 103 and 104. Furthermore, the vertically arranged heated tube arrays 4 × 1 and 4 × 2 with the tube ratio spacing SV/D = 2 were considered, and obtained average Nusselt numbers were compared to the existing correlating equations. A good agreement of the average Nusselt numbers for the single cylinder and the bottom tube of the 4 × 1 tube array is proved. On the other hand, the bottom tubes of the 4 × 2 tube array affect each other, and the Nusselt numbers have a different course compared to the single cylinder. The temperature fields for the tube array 4 × 4 in basic, concave, and convex configurations are studied, and new correlating equations were determined. The simulations were done for the Rayleigh numbers in the range of 1.3 × 104 to 3.7 × 104 with a tube ratio spacing S/D of 2, 2.5, and 3. On the basis of the results, the average Nusselt numbers increase with the Rayleigh numbers and tube spacing increasing. The average Nusselt number and total heat flux density for the convex configuration increase compared to the base one; on the other hand, the average Nusselt number decreases for the concave one. The results are applicable to the tube heaters constructional design in order to heat the ambient air effectively.

Numerical investigation of nanofluid laminar forced convection heat transfer between two horizontal concentric cylinders in the presence of porous medium

In this paper, the finite volume method is used to investigate the laminar forced convection of water–copper nanofluid between two porous horizontal concentric cylinders. The effects of Reynolds number, the volume fraction of nanoparticles, the geometry, and the porous medium porosity on heat transfer have been studied. The problem is investigated in two different geometries and Re = 10, 25, 50, 75,100, and volume fraction of nanoparticles 0, 0.2, 0.5, 2, and 5% that were related to Copper nanoparticles and the porous medium porosity of 0.5, 0.9. The results indicated that in each geometry, the corresponding Nusselt number increase in the porosity of 0.9 is greater than that of the case with the porosity of 0.5. The results show that the increase in the heat transfer coefficient in the second geometry is greater than the first geometry and in porosity 0.9 is greater than porosity 0.5. These increase values are 6 and 3%, respectively. The increase in the average temperature of the inner cylinder surface in the five mentioned Reynolds values and both geometries is investigated. This increase in temperature in Re = 10 is greater than other Reynolds numbers. The corresponding temperature increases of Re = 10, for the first and second geometries, are 1.8 and 2.2%, respectively. Investigation of the effects of volume fraction of nanoparticles on Nusselt number and heat transfer coefficient shows that both parameters increase by increasing in the volume fraction of nanoparticles. The results show that the increase in the volume fraction of nanoparticles causes the increase in average temperature of the surface. The results show that these increases of temperature that take place in the volume fractions of 0.5, 2, and 5% of nanoparticles are equal to 0.6, 1.14, and 2.3% and relative to the water, respectively.

Laminar convective heat transfer in helical tube with twisted tape insert

Tape insert has been commonly adopted as heat transfer enhancement method in a thermal system. Most studies dealing with tape insert have been focused on straight tube. Helical coil tube, on the other hand, has been proven to have higher heat transfer than straight tube. It is of interest to combine both enhancement methods and obtain the optimum heat transfer enhancement. The main objective of this study is, therefore, to numerically investigate flow behaviour and the corresponding heat transfer in helical tube with twisted tape insert subjected to constant wall temperature. A three-dimensional computational model is developed based on conservation equations of mass, momentum, and energy, and is validated against the established empirical correlations. Good agreement is achieved between the numerical prediction and the empirical correlation calculation within the considered range of Reynolds (Re=100−2000) and Dean Numbers (De=25−1200). The effects of twist ratio, inlet Reynolds number and wall temperature are evaluated and discussed in the light of numerical result. It is found that adding twisted tape insert in helical heat exchanger can enhance heat transfer performance by up to four times as compared to conventional straight tube heat exchanger, at a cost of higher frictional pressure drop. Lower twisting ratio gives rise to a higher heat transfer enhancement as it promotes higher secondary flow. At low Pr (air), heat transfer enhancement ratio increases as Re is increased; however, at high Pr (water), heat transfer enhancement ratio is higher at Re 500–1000. Finally, Nu and f correlations are developed to predict heat transfer and pressure drop for practical applications.

Optimization of laminar convective heat transfer of oil-in-water nanoemulsion fluids in a toroidal duct

This study presents numerical simulations, back propagation artificial neural networks and genetic algorithms for optimizing laminar convective heat transfer of oil-in-water nanoemulsion fluids having non-Fourier heat conduction characteristics. Firstly, a numerical study has been conducted on laminar flow and forced convective heat transfer of oil-in-water nanoemulsion fluids in toroidal ducts using Eulerian-Lagrangian two-phase approach. New correlations of drag coefficient, effective thermal conductivity and effective viscosity were adopted to improve the accuracy of simulation. Numerical results show that convective heat transfer can be enhanced by oil nanodroplets with thermal conductivity lower than that of the base fluid. Then regression models and artificial neural network models were developed based on simulation results for predicting convective heat transfer performances of nanoemulsions, considering effects of cross-sectional aspect ratio, Reynolds number, oil nanodroplet diameter and concentration. Artificial neural network models can predict mean Nusselt number and pressure drop better than the regression model. Finally, genetic algorithms was used to optimize convective heat transfer of nanoemulsions considering droplet migration. It can be found that low cross-sectional aspect ratio of width to height is beneficial for thermal performance factor. For single-objective optimization, mean Nusselt number reaches the maximum 32.3 at aspect ratio of 0.9677 and thermal performance factor reaches the maximum 1.305 at aspect ratio of 0.3935 under certain conditions. Pareto optimal set was obtained for two-objective optimization. This study would be useful for the optimal design of convective heat transfer of emulsions in toroidal ducts.

3D-printed tubes with complex internal fins for heat transfer enhancement—CFD analysis and performance evaluation

Additive manufacturing (AM), also known as 3D printing technology, is applied to fabricate complex fin structures for heat transfer enhancement at inner surface of tubes, which conventional manufacturing technology cannot make. This work considered rectangular fins, scale fins, and delta fins with staggered alignment at the inner wall of heat transfer tubes for heat transfer enhancement of internal flows. Laminar flow convective heat transfer at 500 < Re < 2000 has been numerically studied, and heat transfer performance of the tubes with 3D-printed interrupted fins has been compared to that with conventional straight continuous fins and smooth tubes. The benefit from heat transfer enhancement and the loss due to increased pumping pressure is evaluated using the total entropy generation rate in the control volume of heat transfer tube. The heat transfer coefficient in tubes with interrupted fins in staggered arrangement can have 2.6 times of that of smooth tube and 1.4 times of that with conventional continuous straight fins. The entropy generation in the tubes with interrupted fins in staggered arrangement only has 30–50% of that of smooth tube or tube with traditional continuous straight fins. The benefit of using interrupted fins in staggered arrangement is significant.

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.