Forced Convection Heat Transfer Research Articles

Enhanced Air-Flow Forced Convection Through Metal Foams: Contrasting Compressed and Uncompressed Foams

Abstract The influence of complex pore architecture, its characteristic length, and the contrast between compressed and uncompressed open-cell foam structures in forced convection are explored experimentally. Air-flow (Pr ∼ 0.71; 300 < Re < 10,000) data is presented and a critical issue of the appropriate definition of the hydraulic diameter, especially with foams of different pores/inch (ppi) and compressions, is addressed. Instead of the usual characterization, fin theory is applied and for this, the foam void volume structure is precision mapped by micro-CT scans. The veracity of defining the hydraulic diameter as 4× void volume divided by wetted area is supported by forced convection heat transfer results for different uncompressed and compressed metallic (aluminum) foam cores. All foams promote higher heat transfer coefficients, albeit accompanied with greater pressure drop. While the latter increases with foam ppi and compression (decreasing porosity), the former has a more complex interplay with these factors along with surface area changes and ligament fin effects. This scales with thermally effective surface area density βe (product of area density and overall fin effectiveness), and the overall convective-conductance of the foam (product of empty-duct-based heat transfer coefficient ho and βe) increases. The consequent enhancement, when evaluated by a modified volume goodness factor figure of merit, shows that the 40 ppi compressed foam (×3-in-x) performance is the highest (∼ 15–45 times an empty duct for the same fan power) with significant reduction in the volume of a heat exchanger.

CFD Analysis for Improving Forced Convection Heat Transfer from Newly Designed Perforated Heat Sinks

CFD Analysis for Improving Forced Convection Heat Transfer from Newly Designed Perforated Heat Sinks

Experimental investigations of effects of nanoparticle size on force convective heat transfer characteristics of Al2O3 - MWCNT hybrid nanofluids in transitional flow regime

This study reports an experimental investigation of nanoparticle sizes effects on the heat transfer characteristics of hybrid nanofluids along the transitional flow regime. Four different particle sizes were used to prepare hybrid nanofluids of Al2O3 and MWCNT (i.e., 5 nm and 20 nm for Al2O3 and <7 nm and 30–50 nm for MWCNT nanoparticles). Three hybrid nanofluids with different particle combinations (i.e., Al2O3(5 nm) – MWCNT (<7 nm), Al2O3(20 nm) – MWCNT(<7 nm) and Al2O3(20 nm) – MWCNT (30–50 nm)) at a percentage weight composition (PWC) of 60:40 and 0.3 volume concentration were prepared. Results showed that particle sizes significantly affected the convective heat transfer characteristics of the nanofluids. Along the transition region, all three fluids were found to have different critical Reynold numbers 1152, 1172, and 1898 for Al2O3(20 nm) – MWCNT (<7 nm), Al2O3(5 nm) – MWCNT (<7 nm) and Al2O3(20 nm) – MWCNT (30–50) respectively. Al2O3(20 nm) – MWCNT (<7 nm) have shown better heat transfer performances. Its Nusselt number shows an enhancement of about 48.86 % along the transition region. And its coefficient of thermal performance (COP) was better than that of Al2O3(20 nm) – MWCNT (30–50 nm) and Al2O3(5 nm) – MWCNT (<7 nm) with 43.53 % and 21.89 %, respectively. While its friction factor and pressure drop were lower than that of Al2O3(5 nm) – MWCNT (<7 nm) nanofluid by 5.2 % and 12.78 %. It was concluded that for a 60:40 hybrid nanofluid of Al2O3 and MWCNT, particle sizes have influenced heat transfer characteristics and affected other flow characteristics along the transition regime.

Numerical investigation of thermal and entropy generation characteristics in a sinusoidal corrugated channel under the influence of sinusoidal wall temperature

The corrugated channels play a vital role in many engineering applications, such as electronic cooling and heat exchanger devices; thus, forced convection heat transfer and entropy generation within the corrugated channels are important subjects to investigate. This study numerically investigated the laminar forced convection heat transfer and entropy generation of water flow within a sinusoidal corrugated channel. The channel walls were subjected to sinusoidal wall temperature heating while varying the wave parameters. The finite element method had been employed to solve the governing equation, and the simulation results were conducted for Reynolds number 5 ≤ Re ≤ 500, dimensionless wall temperature wavelength 0.25 ≤ λth ≤ 2.25, and Prandtl number Pr = 6.93. The main findings were depicted in terms of Nusselt number, skin friction coefficient, heat transfer effectiveness, total entropy generation, and Bejan number contours, as well as the results being compared with the results of uniform heating. In addition, the results demonstrated that sinusoidal heating significantly improved heat transfer compared to uniform heating for λth < 1.75 and all ranges of Reynolds number, while a critical Reynolds number was found, where the uniform heating showed a higher heat rate compared to non-uniform heating at λth ≥ 1.75 . Besides that, it is found that the sinusoidal wall temperature has lower entropy generation than uniform heating, except with λth = 0.25. This investigation recommends that sinusoidal wall temperature heating is more effective in heat transfer than uniform heating by 7.5, 2.78, 1.9, 1.52, and 1.34 factors at λth = 0.25, 0.75, 1.25, 1.75 and 2.25, respectively.

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.

Numerical analysis of heat and mass transfer for forced convection radially magnetized Williamson nanofluid over a curved stretching surface

Present communication investigates the magnetohydrodynamics (MHD) bioconvection Williamson nanofluid with mass and thermal characteristics caused by the swimming of gyrotactic microorganisms subjected to a radially magnetic field and thermal radiation through a curved stretching surface. To emphasize the significance of thermal engineering processes, this novel mathematical model is designed to simulate the transportation of energy through the boundary layer flow of non-Newtonian nanofluid, taking into account the influences of thermophoresis, the density of motile microbes, and Brownian motion. Based on these assumptions, the fundamental governing equations are initially modeled in terms of partial differential equations (P DEs) through boundary layer theory and then formulated into a system of ordinary differential equations (ODEs) by utilizing similarity transformations. The numerical solution for the given nonlinear system, along with their respective boundary conditions, is computed using the BVP4c package in MAT LAB. To comprehensively evaluate the influence of various emerging parameters, results are discussed through graphs and tables for nanofluid’s temperature, concentration profile, local Sherwood number, skin fraction, axial velocity, heat transfer, and distribution of motile microorganisms. The nanofluid’s velocity experiences a decrease with the simultaneous increase of both curvature and magnetic parameters. As a primary finding, the motile microorganism profile exhibits a substantial increase concerning the curvature parameter. Similarly, the nanofluid parameters, including thermophoresis and Brownian motion, along with the radiation parameter, enhance the temperature of the nanofluid.

Forced convective heat transfer performance of foam-like structures – comparison of the Weaire-Phelan and the Kelvin structures with real metal foam

Real foam and foam-liked structures have been widely used in the field of flow and heat transfer but whether foam-like structures can be used as an alternative to metal foams for forced convective heat transfer needs to be further investigated. In this study, three foam structures (Weaire-Phelan, Kelvin and metal foam) were compared by simulation under turbulent conditions and the flow heat transfer characteristics have been evaluated. The 3D models of the two foam-liked structures were constructed using CAD software and the 3D model of the metal foam was scanned and reconstructed using CT. All three structures were constrained by the same pore size parameters. The results reveal that neither the Weaire-Phelan structure nor the Kelvin structure can serve as a substitute model for the real metal foam. The Weaire-Phelan structure demonstrates the best effective overall heat transfer performance (OHTP) while the Kelvin structure exhibits the worst. With an inlet velocity of 10 m/s, the area goodness factor (j/f) of the Weaire-Phelan structure is similar to the metal foam structure which is 12.3 % higher than that of the Kelvin structure. With an inlet velocity of 25 m/s, the j/f value of the metal foam structure becomes comparable to that of the Kelvin structure. However, the j/f value of the Weaire-Phelan structure exhibits 12.18% higher than the other two structures.

Thermal enhancement of couple stress fluid flow through anisotropic porous media

This study examines forced convective heat transfer via an anisotropic porous channel in a couple stress flow. The flow field is assumed to be fully developed and governed by the Darcy Brinkman Forchheimer equation. The thermal field is assumed to be developing. The channel walls are subjected to constant heat flux. Since the momentum equation is non-linear and the thermal energy equation is linear, coupled equations are solved numerically using the finite difference method. The variation in the bulk mean temperature is linear with the axial distance for all values of the couple stress parameter and Darcy number. In the absence of axial conduction and heat sources or sinks in the flow field, it is easy to see that the energy gained by the fluid up to an axial distance is twice the axial distance. The parameters, anisotropic permeability ratio, and anisotropic angle enhance the heat transfer. The couple stress parameter lessens the enhancement in heat transfer. Anisotropy is critical in heat transmission for Darcy number, DaH≤0.8. The heat transfer rate decreases by more than 40% due to couple stress fluid and anisotropic effects in the channel, as opposed to the Newtonian isotropic situation. This investigation's findings have been compared with previous experimental and numerical research.

Experimental and numerical studies of the effect of perforation configuration on heat transfer enhancement of pin fins heat sink

AbstractIn this study, experimental and computational studies of the impact of forced convective flow on the heat transfer characteristics of staggered pin fins with perforations are investigated in a rectangular channel at constant heat flux with Reynolds numbers (Re) of 2 × 103–12 × 103. In particular, cylindrical pin fins with circular longitudinal (L) perforation, longitudinal/transverse (LT) perforation, and longitudinal/transverse/vertical (LTV) perforation perforations are compared to solid pin fins to find out how adding different perforation arrays affects overall heat transfer performance and also to find the best perforation configuration for maximum performance. ANSYS‐FLUENT is employed for numerical simulation, validated by experimental data. Experimental validation is conducted by attaching the heat sink to a Peltier module, inducing heat generation through current on one face in the Armfield Free and Forced Convection Heat Transfer Service Units HT 19 and HT10XC. Results highlight significant increases in Nusselt number (Nu) for perforated pins compared to solid pins, with L perforations at 8%, LT perforations at 33%, and 67% for LTV perforated pins due to transverse perforations that act as slots, which stir up the primary flow and induce secondary flow generated by vertical perforations. Regarding pressure drops, L perforations reduce by 9%, LT by 19%, and LTV by 27% compared to solid pins. The overall enhancement ratio peaks at the minimum Reynold number, notably achieving a 38% increase in the LTV perforation pin fin array. This innovative study holds promise for diverse electronic applications, offering enhanced heat transfer performance in electronic cooling systems.

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.

Design study of a disruptive self-powered power plant prototype

This research work discusses a preliminary disruptive prototype design of a self-powered thermal power plant doing work by strictly isothermal closed processes using forced convection heat transfer both for adding and extracting heat. It includes useful work by expansion and vacuum-based contraction due to adding heat to and extracting heat from a working fluid. A cycle analysis considering useful work due to vacuum-based contraction is the core of the problem-solving methodology. The findings will be applied to the prototyping implementation task, which includes the cascade and series of cascade coupling of several regenerative power units. The empirical results of the case studies provide the data needed to carry out a prototyping task considering the results of real cases subjected to realistic irreversibilities and heat recovery factors that make the self-feeding power plant an interesting design option. This extraordinary result confirms the technical viability of real machines that exhibit the ability to provide more energy than they use, that is, second-class perpetual motion machines

Force convective heat transfer simulation in a rectangular channel with multiple square obstacles via finite element method

This study investigated fluid flow and forced convective heat transfer in rectangular microchannels with square barriers, as illustrated in Fig. 1 . In the first situation, three obstacles were positioned along the microchannel’s top wall. In the second scenario, obstacles were positioned along the microchannel’s bottom wall. In the final example, three square obstacles are placed symmetrically on either side of the microchannel wall. With the help of the Finite Element Method (FEM), we investigate the physicochemical behavior of the microchannel. The development of computer code within COMSOL multiphysics made it possible to simulate heat transport and fluid flow. The results include the implications of the rarefaction effect on fluid flow and heat transmission and decisions regarding the location of barriers and the shape of obstacles in squares. In addition, with the lowest value in skin friction and a lower Nusselt number, the third example, which has barriers on both sides, provides a valuable method for reducing the fluid temperature at the exit of the microchannel. This is because it has barriers on both sides. In the section under “Results and Discussion,” we provide an in-depth analysis of the numerical data derived from the microchannel. • Objective: This study aims to numerically investigate forced convective heat transfer in a rectangular channel featuring multiple square obstacles. The simulation employs the FEM to model fluid flow and temperature distribution. • Geometry and complexity: The channel geometry incorporates square obstacles, introducing geometric complexity. The FEM is chosen for its capability to handle intricate geometries accurately.

Experimental investigation of forced convective heat transfer and fluid flow in a mini heat pipe with rectangular micro grooves

In the present study, the convective heat transfer coefficient of water in a laminar flow regime under constant inlet temperature conditions inside a flat mini heat pipe was investigated ex-perimentally. Heat flux ranged from 20-50W and various horizontal heat sink temperatures (operating temperature) ranged from 15-35°C with liquid flow rate (3.563E-8 m3/sec) used during the experiments. The rectangular microchannels performance is evaluated in terms of the temperature profile, heat transfer coefficient, Nusselt number and thermal resistance. The results emphasized that the mini heat pipe temperature gradients are less than the tempera-ture of the copper plate and the heat resistance gradually decreases to its lowest value when the heat flux value reaches its highest value if it does not exceed the capillary limits. The data also demonstrated that the coefficient of heat transfer in the condensation zone is lower than in the evaporation zone at different heat sink temperatures. The augmentation rate for the flat mini heat pipe thermal conductivity reached about 240% at a heat load 30W for the positions of thermosyphon and horizontal, while the rate of increase in the case of the anti-gravity situ-ation at a heat load 30W reaches 210%, then the improvement percentage begins to decrease to 200%. A generalized regression equation is developed for the estimation of the Nusselt number valid for water in a flat mini heat pipe.

The investigation of anisotropic kelvin cells: Forced convective heat transfer

The skeleton shape of the Kelvin cell plays a significant role in influencing forced convective heat transfer behaviors, and it can be tailored to enhance overall heat transfer performance (OHTP). To this end, this study conducted a comprehensive experimental and numerical comparison of the Kelvin cells (KC), Kelvin cells with elliptical skeletons (ES), and Kelvin cells with reversed elliptical skeletons (RES) to elucidate the hydraulic and thermal characteristics. The findings indicated that the pressure drop and the overall Nuseelt number of the ES is 53.0 % and 8.2 % lower than those of the KC. Consequently, the area goodness factor, which serves as an indicator of the OHTP, is 105.5 % higher in the ES compared to the KC. Conversely, the RES does not exhibit a significant advantage in the aforementioned parameters. The reduced energy loss attributable to the presence of elliptical skeletons enhances the hydraulic performance of the ES. Furthermore, the smaller recirculation area on the leeward side of the elliptical skeleton promotes improved heat transfer near the heat substrate. The ES has advantage in the fin efficiency compared with KC. The 1.25 cell height is a significant reference value for the development of heat transfer device with Kelvin cell.

Numerical Study of Forced Convection Heat Transfer Across an Elliptic Cylinder in Laminar and Unsteady Nanofluid Flow

Numerical Study of Forced Convection Heat Transfer Across an Elliptic Cylinder in Laminar and Unsteady Nanofluid Flow

Investigation of forced convection of a novel hybrid nanofluid containing NEPCM in a square microchannel: Application of single-phase and Eulerian-Eulerian two-phase models

In the present study, laminar forced convection flow and heat transfer of novel hybrid nanofluid of Al 2 O 3 -n-octadecane/water through a horizontal microchannel under a constant wall heat flux condition are investigated. N-octadecane is regarded as a nano-encapsulated phase change material (NEPCM). Simulations are performed utilizing single-phase and Eulerian-Eulerian two-phase models. Governing equations are discretized by finite volume method and then solved using SIMPLE algorithm. Effects of nanoparticles volume fraction ( φ ), Reynolds number ( Re ), and melting range ( T mr ) on thermal and hydrodynamic parameters of hybrid nanofluid are evaluated. It is shown that predictions by Eulerian-Eulerian approach are more accurate than those by single-phase approach when compared to available experimental data. Addition of Al 2 O 3 and n-octadecane nanoparticles to water-based fluid leads to a reduction in fluid and wall temperatures, which is intensified at higher φ and Re . Also, these nanoparticles do not have a significant effect on hydrodynamic development of flow, while they delay its thermal development. NEPCM with a higher T mr only slightly improves thermal performance of hybrid nanofluid, which is more noticeable in single-phase procedure. Total efficiency of hybrid nanofluid ( η hnf ) is amplified by raising φ for both approaches. This augmentation is more evident in Eulerian-Eulerian model due to better thermal and hydrodynamic performances. Maximum increases in η hnf concerning single-phase and Eulerian-Eulerian models are 27% and 60%, respectively, occurring at φ Al 2 O 3 = 1 % and φ n ‐ octadecane = 10 % . Therefore, this type of hybrid nanofluids, because of its enhanced thermo-physical properties, can be considered as a suitable candidate for thermal energy storage, heat transfer, and renewable energy applications.

Modelling the effect of roughness density on turbulent forced convection

By examining a systematic set of direct numerical simulations, we develop a model which captures the effect of roughness density on global and local heat transfer in forced convection. The surfaces considered are zero-skewed three-dimensional sinusoidal rough walls with solidities, $\varLambda$ (defined as the frontal area divided by the total plan area), ranging from low $\varLambda = 0.09$ , medium $\varLambda = 0.18$ to high $\varLambda = 0.36$ . For each solidity, we vary the roughness height characterised by the roughness Reynolds number, $k^+$ , from transitionally rough to fully rough conditions. The findings indicate that, as the fully rough regime is approached, there is a pronounced breakdown in the analogy between heat and momentum transfer, whereby the velocity roughness function $\Delta U^+$ continues to increase and the temperature roughness function $\Delta \varTheta ^+$ attains a peak with increasing $k^+$ . This breakdown occurs at higher sand-grain roughness Reynolds numbers ( $k_s^+$ ) with increasing solidity. Locally, we find that the heat transfer can be meaningfully partitioned into two categories: exposed, high-shear regions experiencing higher heat transfer obeying a local Reynolds analogy and sheltered, reversed-flow regions experiencing lower and spatially uniform heat transfer. The relative contribution of these distinct mechanisms to the global heat transfer depends on the fraction of the total surface area covered by these regions, which ultimately depends on $\varLambda$ . These insights enable us to develop a model for the rough-wall heat-transfer coefficient, ${C_{h,k}(k^+, \varLambda, Pr)}$ , where $Pr$ is the molecular Prandtl number, that assumes different heat-transfer laws in exposed and sheltered regions. We show that the exposed–sheltered surface-area fractions can be modelled through simple ray tracing that is solely dependent on the surface topography and a prescribed sheltering angle. Model predictions compare well when applied to heat-transfer data of traverse ribs from the literature.

Study on the Cooling Performance of a Focused Ultrasonic Radiator for Electrical Heating Elements.

In this work, a focused ultrasonic radiator is proposed for cooling the electrical heating elements in the focal region, and its working characteristics are investigated. The analyses of the FEM computational and flow field visualization test results indicate that focused ultrasound can generate forced convective heat transfer by the acoustic streaming in the focal region, which can cool the heating elements effectively. Experiments show that when the input voltage is 30Vp-p and the ambient temperature is 25 °C, the focused ultrasonic radiator can cause the surface temperature of the heating element (high-temperature alumina ceramic heating plate with a diameter of 5 mm) in the focal region to drop from 100 °C to about 55 °C. When the diameter of the electrical heating element is changed from 5 mm to 30 mm, the cooling effect is similar in the focal region. Compared with a fan, the focused ultrasound radiator has a shorter cooling time and a more concentrated cooling area. The focused ultrasonic radiator proposed in this work is suitable for some special environments.

Low-Reynolds-number turbulent forced-convection flow over graded baffle plates

The thermo-hydraulic behaviors of turbulent forced-convection heat transfer flow over a rectangular cross section baffled channel are numerically examined in various graded baffle plate ratio configurations ‘GBR = 0.10, 0.11, 0.12, 0.13, 0.14, and 0.15) at different Reynolds numbers, ranging from 12,000 to 32,000. The governing equations that describe the flow are integrated by the finite volumes method, in two dimensions, employing the Commercial CFD software FLUENT 6.3 with low-Reynolds-number k-E model to describe the turbulence. The velocity and pressure terms of momentum equations are solved with SIMPLE-algorithm. In particular, axial velocity, turbulence intensity, pressure, and temperature fields, average Nusselt number and friction loss are obtained. The numerical runs are carried out for different values of Reynolds numbers and graded baffle ratios at constant wall temperature condition along the top and bottom walls. Results were compared with available experimental data from the literature and good agreement is obtained.

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