Forced Convection Heat Transfer Research Articles

Effect of particle size on second law of thermodynamics analysis of Al2O3 nanofluid: Application of XGBoost and gradient boosting regression for prognostic analysis

In this study, the current research delves into the influence of nanoparticle size on turbulent forced convective heat transfer, entropy generation, and friction factor. The investigation focused on three different sizes (30 nm, 50 nm, and 80 nm) of Al2O3 nanoparticles (NPs) suspended in a water-based nanofluid (NF) with a 1 vol% concentration flow in a circular tube. The nanoparticles (NPs) were characterized using various characterization techniques. The stability and pH of the NF were determined, and its viscosity (VST) and thermal conductivity (TC) were measured at a temperature of 60 °C. Heat transfer experiments were conducted with varying particle sizes and Reynolds number (Re), maintaining a fluid inlet temperature of 60 °C. The results indicated that the NF containing 30 nm particles exhibited higher VST and TC compared to the other samples and the base fluid. The maximum enhancement in Nu for Al2O3 (30 nm) and Al2O3 (80 nm) NFs is 60.7 and 18.5 % greater than that of base fluid, respectively. The maximum and minimum total entropy generation (Sgen,T) value of 0.499 and 0.286 observed for base fluid and Al2O3 NF (30 nm), respectively at low Re. The highest friction factor enhancement for Al2O3 NF (30 nm) exceeded by 9.4 % compared to the base fluid, and the maximum thermal performance factor observed for Al2O3 NF (30 nm) was 1.57. Finally, regression analysis was employed to establish correlations for estimating Nu and friction factor values. Prognostic models were developed using two sophisticated machine learning algorithms, XGBoost and Gradient Boosting Regression (GBR). Both models demonstrated exceptional prediction abilities, achieving over 99 % accuracy rates based on the experimental data.

Effect of the Slinger Ring on the Forced Convection Heat Transfer in a Window Air Conditioner

The present study evaluates the effect of the slinger ring on the forced convection heat transfer in window air conditioners. Slinger rings are fitted around condenser fans to spread the condensate onto the condenser to achieve additional cooling. The single-phase forced convection is simulated to compare the thermal performance of the multiphase flow by the slinger ring. Experiments are performed to validate the numerical results. The numerical results well reconstruct the experimental ones, showing the regional dependent distribution and the discharge of the sprayed condensates by the slinger ring. The slinger ring causes a considerable heat transfer on the condenser coils by spraying the condensates, compared with the single-phase flow. However, the inner region of the slinger ring and the fan is almost the dead zone for the condensate spray, since the strong axial flow protects the entrainment of the splashed condensate, which is explained by the isotherms and velocity vectors. The regions of the occurrence of the additional heat transfer are almost overlapped to those exposed to the condensates sprayed by the slinger ring. The slinger ring contributes to a substantial increase of approximately 17% in the heat transfer on the condenser coils, compared with the single-phase flow.

Machine learning-assisted high precision predictive modelling of convective heat transfer in fluid channels fabricated by laser powder bed fusion

Laser powder bed fusion (LPBF) has proven to be an effective tool in fabricating heat transfer devices with improved efficiency. However, the accurate prediction of convective heat transfer in LPBF-fabricated fluid channels remains a challenge. The classical Gnielinski model is regarded as the most accurate correlation for predicting forced convective heat transfer in traditional pipes. However, whether it is applicable to LPBF-fabricated pipes is yet to be determined. To address this challenge, in this study, pipe samples with diameters of 3 mm, 4 mm, and 5 mm were designed and fabricated using LPBF along the building angles of 0°, 45°, and 90°. The pressure loss and heat transfer characteristics of these samples were experimentally measured. Results showed that there was a maximum prediction error of 72.1 % between the classical Gnielinski model and experimental results. To improve the prediction accuracy, a corrected Colebrook model with improved prediction accuracy of the friction factor was developed, introduced into the classical Gnielinski model, and reduced the maximum prediction error down to 36.8 %. To further improve the prediction accuracy, a gradient descent-based machine learning method was adopted to reconstruct the Gnielinski model, which achieved a high prediction accuracy with prediction errors of below 10 %. With the assistance of machine learning, a high precision predictive model of convective heat transfer in LPBF-fabricated fluid channels was established.

Experimental investigation of forced convection heat transfer for different models of PPFHS heatsinks with different fin-pin spacing

Cooling of electronic components is one of the most important concerns of manufacturers. Using heatsinks with different models is one of the recommended methods for cooling. To compare 12 types of heatsinks, including 3 types of fin-pin heatsinks with rectangular pins, 3 types of fin-pin heatsinks with circular pins, 3 types of fin-pin heatsinks with conical pins, and 3 types of simple fin heatsinks in 5, 7, and 9 fin types regarding forced displacement heat transfer, an experiment was conducted. A special setup designed and built for these types of heatsinks was used to conduct the test. The setup had dimensions of 100 cm × 12 cm x 3 cm with an opening of 120 cm × 120 cm for placing a fan to create airflow with variable speeds and a place for placing the heatsink at the end of the wind tunnel under variable temperatures. The test results showed that the maximum error in the two experimental tests was 6 %. Also, the results showed that in all 4 types of heatsinks, 7-fin pin types had 4 to 20% lower thermal resistance and 20 to 100% higher convection heat transfer coefficient compared to the 5- and 9-fin pin types respectively. When comparing the heatsinks with the same number of fins, it was observed that the 7 and 9-fin types of heatsinks with conical fins have lower thermal resistance and higher convection heat transfer coefficient than other types of heatsinks with the same number of fins, The conical fins having more than 81 % convection heat transfer coefficient compared to the plate fin heatsink. It was also observed that in the 5-pin fin heatsink design, the plate-fin heat sink had the lowest amount of heat resistance due to its higher surface area with the flowing air current.

COMBINED FORCED AND NATURAL CONVECTION FROM A SINGLE TRIANGULAR CYLINDER

Unsteady laminar confined and unconfined fluid flow and mixed (forced and free) convection heat transfer around equilateral triangular cylinders are investigated numerically. The computation model is a two-dimensional domain with blockage ratios of BR=0.5, 0.25, 0.2, 0.1, 0.05, and 0.0333, with the Reynolds numbers ranging from 100 to 200. The working fluid is water (Pr = 7). The effects of aiding and opposing thermal buoyancy are incorporated into the Navier-Stokes equations using the Boussinesq approximation. The Richardson number, which is a relative measure of free convection, is varied in the range -2 ≤ Ri ≤ 2. The governing equations are solved by using the Finite Volume Method with a second-order upwind scheme used for differencing of the convection terms, and the SIMPLE algorithm is used for the velocity-pressure coupling. A discussion of the effect of the blockage ratio on the mean drag, mean rms lift coefficients, the Strouhal number, and the mean Nusselt number is also presented. The iso-vorticity contours and dimensionless temperature field are generated to interpret and understand the underlying physical mechanisms. The results reveal that, in addition to the Richardson and Reynolds numbers, the blockage rate is effective in the vortex distribution in the channel. It has been determined that the vortices formed behind the cylinder spread to the channel with a decreasing blockage rate. Especially at high Reynolds numbers, both the drag coefficient and the mean Nusselt number are significantly affected by the blockage ratio. For Ri=0, the drag coefficients for BR=0.25 in comparison to the BR=0.05 case are about 9% and 29% larger for Re= 100 and 200, respectively. For BR

Experimental study on heat transfer from rectangular fins in combined convection

Combined natural and forced convective heat transfer arise in many transport processes in engineering devices and in nature, which is frequently encountered in industrial and technical processes, including electronic devices cooled by fans, heat exchangers placed in a low-ve-locity environment, and solar receivers exposed to winds. In this study, the effects of design parameters have been experimentally investigated for the air-side thermal performance under combined (natural and forced) convection of the rectangular plate heat sinks, and the values of optimum design parameters were sought. Many ideas for improving cooling methods have been proposed, one of which is the heat sink. In this work, the average Nusselt number (Nu) and thermal resistance of a simple base rectangular plate and five vertical rectangular plate heat sinks with different numbers of fins under natural and combined convection were exper-imentally investigated to obtain the maximum average Nu and minimum thermal resistance for various Reynolds numbers (Re) from 2300 to 40000, Rayleigh numbers (Ra) from 1300000 to 13000000, and Richardson numbers (Ri) from 0.4 to 3. Also, in this experiment, fin spacing (P) was varied from 2.8 mm to 14.6 mm and the dimensionless P/H ratio was varied from 0.1 to 0.49. The flow velocity varied in the range of 2 to 8 m/s under combined convection. Based on the effects of Ri and Re, two empirical equations for natural and also for combined con-vection heat transfer were derived to calculate the average Nu. The average deviation for these two equations is about 7%. The outcomes of this research can be beneficial for engineers who work on electronics cooling systems.

Analysis of heat transfer characteristics of sandwich cylindrical shell with an aerogel-metal-rubber composite core

Metal-rubber sandwich cylindrical shell displays a broad range of potential applications in the field of thermal insulation due to its advantages of lightweight, high-temperature stability, and superior high-temperature thermal insulation properties. To optimize the thermal insulation performance of a sandwich cylindrical shell with a metal-rubber core, this study proposes the idea of filling the pores of the metal-rubber with aerogel, thereby forming a composite structure of aerogel and metal-rubber (AMR). Through finite element analysis, the law of internal temperature changes in the AMR composite structure and the distribution laws of the velocity field, viscosity field, and pressure field of the sandwich cylindrical shell under varying wind speeds are investigated. These findings are further verified through heat transfer and forced convection tests. The results reveal that the thermal conductivity of the AMR composite structure at the same density is lower than that of the metal-rubber, and the thermal insulation performance of the AMR composite structure is directly proportional to its density. Meanwhile, through the analysis of forced convection heat transfer in the cylindrical shell, it is found that wind speed has a direct relationship with the pressure field, velocity field, and viscosity field. In addition, there is a relatively high viscosity and a low flow rate near the wall of the cylindrical shell, with a higher flow rate at the axis of the cylindrical shell. At the same wind speed, the temperature rise of the sandwich cylindrical shell shows a positive correlation with an increase in density, and the maximum stable temperature also increases correspondingly. Moreover, at the same density, the thermal conductivity demonstrates a negative correlation with increasing temperature.

Computational fluid dynamics analysis of PCM-based ocean thermal engine with external rib turbulators

The concept of extracting energy from ocean thermal gradients for the long-term deployment of underwater profiling vehicles is promising. One potential method to capture ocean thermal energy is leveraging the volume change of phase-change materials (PCMs). However, the low thermal conductivity of PCMs and the low heat transfer coefficient between heat exchangers and seawater limit the performance of PCM-based ocean thermal engines (OTEngs). In this paper, a new type of heat exchanger structure with external rib turbulators is proposed. Detailed computational fluid dynamics analysis is conducted for the external forced convection heat transfer process of the heat exchanger with Reynolds number in the range of 240,000 to 600,000. In addition, a solver for calculating the phase-change process of the PCM inside the heat exchanger was developed based on OpenFOAM. The influence of the ribs on the heat transfer and energy conversion processes of the OTEng was analyzed. Results show that (i) the heat transfer coefficient of the ribbed heat-exchanger wall significantly improves, especially at low Reynolds numbers; (ii) 2.5–5 mm high ribs can effectively enhance heat transfer through the wall. When rib weight exceeds 5 mm, the heat transfer coefficient does not increase with the height; (iii) increasing the rib spacing reduces the water resistance and heat transfer coefficient of the wall; and (iv) the ribbed OTEng has a higher net power output compared with the conventional engine.

Flow-induced vibration and heat transfer in arrays of cylinders: Effects of transverse spacing and cylinder diameter

This two-dimensional numerical study investigates flow-induced vibration (FIV) and heat transfer in 3 × 3 arrays of nine heated circular cylinders of equal and unequal diameter configurations at a constant Re = 100. Six out of the nine cylinders are stationary, while three are elastically supported in the vertical direction. The computations are carried out using the commercial software ANSYS Fluent loaded with user-defined function (UDF). The effects of transverse spacing ratio (G* = 2, 3, and 4), diameter (D) and reduced velocity (2 ≤ Ur ≤ 20) on time histories of cylinder displacements, vorticity contours, oscillation amplitudes, mean pressure coefficient and Nusselt number (Nu) are investigated by considering forced convection heat transfer. Results show that lower oscillation amplitudes of elastically supported cylinders are noticed in arrays of cylinders when all cylinders are placed closely, i.e., at G* = 2. Furthermore, as G* increases, the oscillation amplitudes also increase due to the formation of vortex shedding. A better heat transfer performance is observed for arrays of cylinders with varying diameters at G* = 2 compared to those with the same diameter. For G* = 4, arrays of cylinders with the same diameter possess better heat transfer for all Ur. FIVs affect the Nu of elastically supported cylinders as well as stationary cylinders.

Impact of forced convective heat transfer on temperature uniformity and frequency doubling efficiency in large aperture ammonium dihydrogen phosphate (ADP) crystals

With advancements in optical technology, the large-aperture ADP crystals have grown significantly used in high-power laser systems. Ensuring their optimal performance in such applications necessitates effective control over the temperature uniformity of crystals, this research primarily delves into the influence of forced convective heat transfer on the temperature uniformity of ADP crystals and examines the subsequent effects on the frequency-doubling efficiency of crystals. Thus, this study developed a fan-forced convective heating scheme that was tailored for large-aperture ADP crystals and scrutinized pivotal factors impacting the temperature distribution of the crystal. By integrating numerical simulations with experimental approaches, the flow field and temperature field distribution patterns were discerned at varying fan tilt angles. Additionally, the distribution of the crystal's frequency doubling efficiency was determined. The results showcased that with a fan tilt angle set at 30.0°, the ADP crystal's temperature uniformity achieved a measure of 0.03 °C, and the frequency doubling conversion efficiency peaked at 87.0 %. A reduction in the cavity length to 800 mm further refined the crystal's temperature uniformity, bringing it down to 0.02 °C. This study demonstrated that forced convection can markedly augment the temperature uniformity of the crystal. These insights are invaluable to the domains of optical applications and crystal engineering, paving the way for enhanced performance and application of ADP crystals in controlled nuclear fusion reaction devices.

Thermophysical characteristics and forced convective heat transfer of ternary doped magnetic nanofluids in a circular tube: An experimental study

This experimental study investigated the influence of ternary-doped magnetic nanoparticles (NPs) on the thermophysical characteristics and forced convective heat transfer (FCHT) of nanofluids. Ternary-doped magnetic NPs were synthesized by combining multi-walled carbon nanotubes (MWCNTs) doped with zinc oxide (ZnO) and manganese ferrite (MnFe2O4) NPs to form a new composite material. The laminar FCHT and pressure drop were also measured in a circular tube under constant wall flux with and without a magnetic field (MF). The findings showed that increasing NP concentration improved the thermal conductivity (TC) of the nanofluid, and the inclusion of magnetic NPs enhanced the Nusselt number (Nu). The nanofluid with a concentration of 0.2 wt% in the field of 400 G and a Reynolds number (Re) of 2200 showed the highest improvement in the Nu, with an increase of 40 %. The highest increases in pressure drop were achieved in the presence of a 400G MF and at a Re of 800 for nanofluids containing 0.2 wt%, which was 8.2 %. The study's results can contribute to the design and optimization of nanofluid-based heat transfer (HT) systems, particularly in the field of magnetic nanofluids under the influence of MF.

Flow and heat transfer characteristics of microencapsulated phase change material slurry in bonded triangular tubes for thermal energy storage systems

Three nanoscale metal oxides composed of nano TiO2, nano Al2O3, and nano MgO were added to the phase change microcapsule slurry for optimising the heat transfer behaviour. The thermal and rheological properties of the resulting microencapsulated phase change materials (MPCMs) and microencapsulated phase change material slurries (MPCSs) were characterized to determine the effects of added metal oxides in optimising the performance of MPCSs. The impacts of factors like metal oxides, concentrations, and flow rates on the heat transfer behaviour of MPCSs were investigated by forced convective heat transfer experiment with various working conditions. Compared to 6 wt% MPCSs, the heat transfer coefficients (hx) of 6 wt% slurries containing 1 wt% TiO2, 1 wt% Al2O3, and 1 wt% MgO increased by 4.0 %, 2.5 %, and 7.13 %, respectively. Nano-MgO showed the most significant heat transfer enhancement effect on MPCSs. Moreover, the heat transfer performance gradually enhanced as a function of the concentration for nano MgO. Overall, the addition of metal oxides enhanced heat transfer by increasing the thermal conductivity of the slurry, as well as improved the micro-convection effect. The proposed MPCSs are promising for applications in solar photovoltaic/thermal (PV/T) systems, chip cooling, thermal management, buildings, and automotive cooling.

Effect of Nanoparticle Material, Porosity and Thermal Radiation on Forced Convection Heat Transfer of Cu-Water and CuO-Water Nanofluids over a Stretching Sheet

Effect of Nanoparticle Material, Porosity and Thermal Radiation on Forced Convection Heat Transfer of Cu-Water and CuO-Water Nanofluids over a Stretching Sheet

Designing of Evaporator Length in Very Low Temperature Chest Freezer by using Environmentally Friendly Refrigerant R290

Chest freezers generally use R600a or R134a as working fluids. When using R600a, the minimum cabin temperature is only -10oC, whereas when using R134a, it can reach -25oC. The purpose of this study is to calculate the evaporator length of a chest freezer that uses R290 as a refrigerant so that its cabin temperature can reach below 35 oC, lower than the cabin temperature of a typical chest freezer. Calculation of the evaporator pipe length is done using the forced convection heat transfer equation to calculate the heat transfer coefficient inside the evaporator pipe and natural heat transfer to calculate the heat transfer coefficient outside the evaporator pipe. Based on the calculations, the chest freezer has a compressor capacity of 200 W, an evaporator length of 3.57 m, and a diameter of 3/8 inch or 9.52 mm. The test results show that the temperature of the chest freezer cabin can reach -36oC in the 36th minute with a cooling capacity of 289 W, while the input power and COP are 198 watts and 1.46, respectively. Compared to R134a, the use of R290 is more advantageous. In addition to lower cabin temperatures, it is also much more environmentally friendly, because the GWP (global warming potential) value of R134a is much higher than that of R290. It means that the use of R290 as a working fluid in the chest freezer will significantly reduce emissions of gases that cause global warming.

Finite Element Modeling for HEAT Transfer of FORCED CONVECTION in INSULATED TUBE With EES Analytical Validation at different Operating conditions

Finite Element Modeling for HEAT Transfer of FORCED CONVECTION in INSULATED TUBE With EES Analytical Validation at different Operating conditions

Experimental study on heat transfer performance using a hybrid cooling method combined of a flat-plate heat pipe and spray cooling

A hybrid cooling system consists of spray cooling as condensing end and flat-plate heat pipe (FPHP) as heat-transfer medium was previously studied on the effects of the volume flow rate and the inlet temperature. As an extension, this paper using multi-nozzle arrays to promote the forced convection heat transfer and changing the surface roughness of the FPHP to improve the phase change heat transfer. It was found that the impinging energy and drainage channel formed by multi-nozzle arrays were the main reasons for the enhancement in convection region. However, in the phase-change section, a uniform thin liquid film and surface roughness apparently improved the evaporation and nucleate boiling. Relative to our previous study, a maximum heat flux removal was increased from 70 W/cm2 to 90 W/cm2 at surface roughness (Ra = 1.62 μm) with a surface superheat only 4.17℃, the heat transfer coefficient of 21.6 W·cm-2·K-1 and an enhancement of 28.6 % were obtained. Furthermore, the transition temperature and the temperature change rate were studied to explore the vapor flow modes and thermal response characteristics of the FPHP. As the transition temperature Ttr = 251 K, and the Knusden number＜0.01, the FPHP consistently maintained a continuum flow regime during startup, stabilization, and dry-out processes. Impressively, the temperature change rate of the FPHP remained below 0.015℃/s, resulting in a temperature change of only 0.9℃ within one minute. This exceptional temperature stability ensured reliable operation for electronic components.

Influence of inclined magnetic field and cross diffusion on transient forced convective heat and mass transfer flow along a porous wedge with variable Prandtl number

The unsteady 2-D forced convective mass and heat transfer flow of an incompressible, viscous and electrically conducting fluid along a porous wedge is examined in this article using numerical analysis to survey the effects of a magnetic field and thermophoresis. This is done in the existence of temperature-dependent thermal conductivity, a variable Prandtl number, and the effect of cross diffusion. The governing nonlinear PDEs have been converted into nonlinear ODEs by using a similarity transformation. The modified ODEs are solved for similar solutions using the shooting technique and the Runge–Kutta fourth-order method. The temperature, velocity, concentration, thermophoretic velocity, and thermophoretic particle deposition velocity results for various parameters are provided. The Dufour number’s effect enhances the temperature profile and rate of heat transfer. Moreover, it is noted that the rate of mass transfer is meaningfully influenced by the variation of the thermophoresis parameter and Soret number. Thus, in any physical model where the thermal conductivity of the fluid is temperature dependent, the Prandtl number within the BL have to be treated as variable rather than constant.

Etude numérique de l’effet des générateurs de vortex longitudinaux sur le transfert thermique d’un écoulement laminaire traversant un micro-canal

We conducted, in this work, a three-dimensional numerical study of forced convection heat transfer of a laminar flow of water passing through micro-channels with and without longitudinal vortex generator, using the CFD code “Ansys- Fluent”. This work aimed to elucidate the effect of vortex generators on the dynamic and thermal behavior of the micro-fluidic flow. The results obtained show that the increase in the Reynolds number leads to an improvement in the quality of heat transfer in both cases of the study. Rectangular micro-channel with LVG can improve heat transfer compared to smooth rectangular micro-channel while consuming more pressure drop. In the range of Reynolds numbers between 200 and 1200, a 2-21% increase in the mean Nusselt number was observed for micro-channels with LVG compared to smooth micro-channels. This occurs through better mixing of the fluid, reduction in the thickness of the thermal boundary layer, and increased heat transfer area. In addition, the friction factor has been increased by more than 50% compared to smooth micro-channels, due to the local resistance of LVGs and the presence of secondary flows.

A new modeling method to evaluate effective forced-convective heat transfer rate of pipe flow with endothermic chemical reactions

Heat transfer correlation describes the relationship between heat transfer and factors such as fluid properties and flow conditions. The establishment of heat transfer correlations is of paramount importance in the design and calculation of heat exchangers and reactors in various chemical engineering fields as well as in certain aerospace applications. In this study, we present a theoretical derivation of a heat transfer correlation model for fully developed flow with gas-phase homogeneous chemical reactions. By means of theoretical derivations, the modeling of complex multi-physics coupling problems can be significantly simplified, and the impact of chemical reactions can be effectively demonstrated. The concept of effective specific heat and effective thermal conductivity are generalized to finite-rate chemically reacting flow. Modifications are proposed for Nusselt number correlation. It is shown by preliminary verification that evaluating error of new correlation has been significantly decreased by the modification. The enhancement factor can be evaluated by specific ratio cpr,x/cp*. To demonstrate the reliability of the derived correlation, we carry out numerical simulations and compare the results with derived formulations. The simulations show good agreement with the theoretical values, demonstrating that the derived correlation is both theoretically grounded and practically usable.

Experimental Investigation and Comparison of Natural and Forced Convective Heat Transfer Enhancement Using Water -Cuo Nano Fluid

Free and forced convective heat transfer along a vertical cylinder immersed in water– CuO nanofluid for numerous concentrations (0, 0.05, 0.1, 0.15, 0.2vol %) below consistent heat flux circumstance turned into investigated experimentally with and without vibrations and compared the effects. The vibrational movement is acquired by way of placing vibratory motor beneath the experimental setup. The accelerometer is used to measure the vibration frequencies 100HZ-220HZ. Thermal stratification become discovered out of doors the boundary layer in the ambient fluid after steady-state condition is done as the fluid temperature is going on growing alongside the axial course. It is found that the temperatures of the cylinder and the fluid increases alongside the axial route and the fluid temperature decreases inside the radial route. Experiments had been conducted for various heat inputs (30 W, 40 W, 45 W and 50 W) and quantity concentrations and determined that the addition of Copper oxide nanoparticles as much as 0.15 vol. % complements the thermal overall performance and then the further addition of nanoparticles ends in deterioration. The most enhancement in the free convection (without vibration) i.e., the heat transfer coefficient is 478.4214 w/m2 k at 0.15 vol. % and in forced convection (with vibration) i.e., the heat transfer coefficient is 489.4614 w/m2 k at 0.15 vol. %. Thus it is observed that for the same heat input, the heat transfer enhancement is greater for forced convection in comparison to free convection due to vibratory impact.