Rectangular Heat Research Articles

Numerical analysis of mono and hybrid nanofluids-cooled micro finned heat sink for electronics cooling-(Part-II)

This study investigates the thermal and hydraulic performance of heat sinks with micro pin-fins in circular and rectangular configurations using mono and hybrid nanofluids. Motivated by the need for efficient cooling solutions in high-performance electronic devices, the research explores novel combinations of metallic oxide (Ag, MgO) and carbon-based nanoparticles (GNP, MWCNT) in nanofluids. A constant volume fraction of micro pin-fins and nanoparticles was maintained to assess their effects on thermohydraulic performance. The method involved experiments with aqueous nanofluids as coolants, measuring pressure drops (Δp) at the inlet and outlet. Thermal performance was evaluated using metrics like thermal resistance (Rth), Nusselt number (Nuavg), pumping power (PP), volumetric flow rate (Q), overall performance (OP), and performance evaluation criterion (PEC). Results showed that GNP-based mono nanofluids significantly reduced Rth by 46.41 % and increased Nuavg by 60.54 % and PEC by 62 % in rectangular heat sinks compared to conventional water cooling. Comparisons between rectangular and circular configurations revealed minimal Rth differences of 2.54 % and 3.57 %. GNP-dispersed nanofluids outperformed other coolants, with the rectangular configuration achieving a higher PEC of 1.62 versus 1.52 for the circular configuration at 820 Pa. The conclusions suggest that rectangular pin-fins with GNP-based nanofluids offer superior thermohydraulic performance. The key outcomes from current study have significant contribution in enhancing the cooling efficiency of advanced electronic systems.

Partitions influence on rectangular latent heat thermal energy storage unit performance during melting and solidification

The growing use of renewable energy sources demands efficient storage solutions due to their variability. Thermal energy storage systems utilising phase change materials are emerging as viable options to address this challenge. This study evaluates the impact of various partition types on phase change duration in thermal energy storage systems. The well-known and validated enthalpy-porosity algorithm implemented in the Fluent 2021R2 software was used. The shortest melting time was observed in the case with four vertical tubes and three horizontal partitions, which was 82 % shorter than in the reference case. The highest change in specific enthalpy of phase change material (252.5 kJ/kg) during melting was also noted for this system. The shortest solidification time was observed for the case with four tubes and two diagonal partitions, which was 72 % shorter than in the reference case. The greatest increase in the specific enthalpy of phase change material (240.4 kJ/kg) during the solidification process was also observed in this system. In conclusion, due to the thermal conductivity of the partitions, the temperature distribution throughout the domain becomes more homogeonous, thus contributing to more uniform heat flux extraction and supply throughout the process.

Numerical analysis of enhanced heat transfer and nanofluid flow mechanisms in fan groove and pyramid truss microchannels

A combined groove and truss structure is designed for rectangular microchannel heat sinks with 4 % Al2O3 nanofluid as the working fluid to address the heat dissipation requirements of high heat flux density electronic devices. The effects of fan shape, elliptical, waterdrop, rectangular, trapezoidal and triangular grooves on the heat transfer characteristics and mechanical properties of microchannels are investigated. The fan-shaped groove microchannels with the best overall heat transfer performance and excellent mechanical properties. The stress of the fan-shaped grooved truss microchannel is reduced by 76.41 % compared to the smooth microchannel. Three structural parameters were investigated, including the length of the truss in the spreading direction (Lx), the ratio of truss flow downstream length to upstream length (e) and truss rod diameter (d). The performance of the microchannels is reflected by the integrated heat transfer factor and the field coordination number. The individual structural parameters were analysed in a single-factor comparison. The microchannels exhibited the best hydrothermal performance in the Reynolds number range of 500 ∼ 1300 at Lx = 0.8 mm, e = 3, d = 0.2 mm. When the Reynolds number is 900, the microchannel with the optimal parameter combination exhibits a remarkable enhancement of 234 % in the Nusselt number and an 80 % increase in the integrated heat transfer factor compared to the rectangular microchannel.

Experimental study on heat storage characteristics of an air-sand moving bed heat exchanger

The air-sand moving bed heat exchanger, designed for storing fluctuating medium-temperature gas waste heat, offers significant potential for energy conservation and carbon reduction in industrial settings. However, its operational characteristics are insufficiently explored. This study investigates the heat storage process involving direct contact and cross-flow of air and quartz sand within a rectangular heat exchanger chamber. Comprehensive analyses were conducted to explore flow resistance characteristics, temperature response, and heat storage performance. Results indicate that pressure drop increases with higher air velocity and temperature, and lower air pressure, particle diameter. The relative discrepancy between fitted pressure drops and experimental data is below 10%. The primary heat transfer zone exists during particle descent. As the air-particle mass flow ratio increases, the descent rate of this zone along the airflow direction slows. Additionally, higher air temperatures elevate the optimal air-particle mass flow ratio. With inlet temperatures for air and particles set at 350 °C and 30 °C respectively, and a mass flow ratio of 0.81, an exergy efficiency of 58.93% and a power density of 600.64 kW·m−3 are achieved. These findings offer crucial insights for air-sand moving bed heat exchangers for medium-temperature gas waste heat recovery.

The time‐fractional ISPH method for fin circular rotation on MHD bioconvection flow of oxytactic microorganisms and NEPCM within a hexagonal‐shaped cavity

AbstractThis work investigates the bioconvection flow of oxytactic microorganisms and nanoparticle‐enhanced phase change material (NEPCM) within a hexagonal‐shaped cavity containing a rotated cross fin, utilizing the incompressible smoothed particle hydrodynamics (ISPH) method based on a time‐fractional derivative. The study considers the circular rotation of an inner cross fin and the presence of two rectangular heat sources on the plane walls inside the hexagonal cavity. The novelty of this work is its integration of a hexagonal‐shaped cavity with a rotated cross fin and the use of a time‐fractional derivative in the ISPH method to analyze bioconvection flow, offering new insights into the interaction between microorganism motion and heat transfer dynamics in complex geometries. The effects of Darcy, Hartmann, Lewis, Peclet, Rayleigh, and bioconvection Rayleigh numbers on isotherms, heat capacity ratio, microorganism density, velocity fields, and average Nusselt number are analyzed. The key findings demonstrate the significant impact of Rayleigh and bioconvection Rayleigh numbers in enhancing heat distribution and velocity fields, thereby significantly influencing microorganism motion. Due to Lorentz forces, the velocity field decreases by with an increase in the Hartmann number from 0 to 50. The resistance of the nanofluid's velocity becomes apparent as the Darcy number decreases. Increasing Lewis and Péclet numbers cause the microorganisms to shift towards the cavity's boundaries.

CFD and ANN analyses for the evaluation of the heat transfer characteristics of a rectangular microchannel heat sink with various cylindrical pin-fins

CFD and ANN analyses for the evaluation of the heat transfer characteristics of a rectangular microchannel heat sink with various cylindrical pin-fins

Modeling of Rectangular Microchannel Heat Sink with Non-Uniform Channels and Multi-Objective Optimization

Modeling of Rectangular Microchannel Heat Sink with Non-Uniform Channels and Multi-Objective Optimization

Computational fluid dynamics based multi-species transport simulation of auxiliary energy systems for friction stir welding of dissimilar materials

This research compares auxiliary energy-assisted friction stir welding (FSW) techniques with conventional FSW when joining dissimilar materials. Specifically, it conducts numerical modeling and experimental validation for the effectiveness of plasma-assisted FSW and induction-assisted FSW for DH36 steel and 6061-T6 aluminum alloy. Fully coupled 3D computational fluid dynamics (CFD) models, incorporating the multi-species transport method, were developed, where the species mass fractions of the workpieces are transported through diffusion, convection, and reaction sources for individual species. Based on the temperature validation, the dedicated heat flux based on the rectangular heat flux and Gaussian heat flux distribution were considered for induction coil and plasma arc heating on the DH36 steel side, respectively. The established conventional and auxiliary energy-assisted FSW models were validated against experimentally observed temperature fields and the joints’ material features. Results indicate that the assistance of plasma and induction auxiliary energy sources increased the temperature field, strain rate, and flow velocity without forming stagnant zones on the steel side caused by reduced dynamic viscosity. In plasma arc-assisted FSW, the steel could not extrude effectively from the base steel sheet due to deficient heat and flow velocity input; therefore, defect-prone coarse steel fragments were blended with the Al matrix. In induction-assisted FSW, the uninterrupted steel layer was extruded from the steel side and placed on the Al side, which was caused by enhanced heat build-up and flow velocity. Moreover, induction-assisted FSW achieved symmetric material flow on both advancing and retreating sides, resulting in defect-free welds.

Constructal design for H-shaped compound heat transfer path in a rectangular heat generation body

An H-shaped compound heat transfer path (HSCHTP) model in a rectangular heat generation body (RHGB) is built in present article. With specified total volumes of HSCHTP and RHGB, constructal design for HSCHTP model is conducted by varying path length ratios and radius. The minimum complex functions composed of thermal and flow performances are acquired, and the multi-objective optimizations are performed furtherly. Three decision-making approaches are introduced to obtain the optimal design scheme (ODS) from Pareto-optimal frontiers. It indicates that complex function after triple-optimization is reduced by 14.7 % compared with that of initial design. Compared with performance of RHGB with no heat conduction path, complex function after optimization is reduced by 77.5 %. Thus, performance of the HSCHTP is apparently superior to that with no heat conduction path in this case. The complex function minimization is a special case of the multi-objective optimization (MOO). The fifth order path radius, adjacent order and internal order length ratios acquired by MOO are distributed within the ranges of 1.50mm-1.60 mm, 1.39–1.47 and 0.066–0.90, respectively. By chasing for the smallest deviation-index, optimal structure of HSCHTP acquired by LINMAP decision-making method is taken for the ODS when multiple requirements are considered in the heat dissipation designs.

Experimental and Numerical Study of a Trapezoidal Rib and Fan Groove Microchannel Heat Sink.

A novel microchannel heat sink (TFMCHS) with trapezoidal ribs and fan grooves was proposed, and the microchannel was manufactured using selective laser melting technology. Firstly, the temperature and pressure drop at different power levels were measured through experiments and then combined with numerical simulation to explore the complex flow characteristics within TFMCHSs and evaluate the comprehensive performance of microchannel heat sinks based on the thermal enhancement coefficient. The results show that, compared with rectangular microchannel heat sinks (RMCHSs), the average and maximum temperatures of TFMCHSs are significantly reduced, and the temperature distribution is more uniform. This is mainly caused by the periodic interruption and redevelopment of the velocity boundary layer and thermal boundary layer caused by ribs and grooves. And as the heating power increases, the TFMCHS has better heat dissipation performance. When P=33 W and the inlet flow rate is 32.5 mL/min, the thermal enhancement factor reaches 1.26.

Subcooled flow boiling in multiple parallel rectangular micro-channel heat sink: Development of heat transfer correlation

This study experimentally evaluated and presented the heat transfer performance of FC-72 flow boiling in a rectangular micro-channel heat sink under subcooled conditions. The hydraulic diameter of the rectangular micro-channel under investigation is 666 µm, and the heat sink has twenty-four parallel mico-channels machined on an oxygen-free copper block. The width and height of the rectangular micro-channel are 400 µm and 2000 µm, respectively. The experimented mass flux and fluid inlet temperature to the heat sink range between 103–1026 kg/m2s and 20–50℃, respectively. Furthermore, a consolidated subcooled flow boiling database is developed by using the FC-72 flow boiling data of the present experimental study and the subcooled flow boiling database with four different micro-channel heat sinks with HFE-7100 as the coolant by Lee and Mudawar (2008). Nine prominent predictive heat transfer correlations for subcooled flow boiling are methodically assessed and contrasted against the combined database comprising 631 data points. The evaluation resulted in significant variations in the predictions by the correlations with the current consolidated database. The conventional correlations in the literature for flow boiling under subcooled conditions are inadequate for foreseeing the heat transfer during subcooled flow boiling in the micro-channel heat sink as they are developed based on conventional tubes and annuli with channel hydraulic diameters greater than 3 mm. A new subcooled flow boiling heat transfer correlation rooted in dimensionless group terms is then developed from the consolidated database. Compared to prior correlations, better predictive performance is observed for the new subcooled flow boiling correlation against the consolidated database. The newly developed correlation has a mean absolute error of 21.9%, with 74.9% of data points forecasted within ±30%.

Numerical study of the melting process of a novel phase change material using a rectangular shell-coil heat exchanger

This paper presents the numerical study of the melting process of hydrogenated palm stearin as a new phase change material (PCM) using a shell-coil heat exchanger. A phenomenological model was proposed and validated using experimental results. After model validation, numerical simulation was used to study the influence of natural convection on the melting process and stored energy in a rectangular shell-coil heat exchanger. The influence of operational variables such as the inlet velocity and the temperature of the heat transport fluid (HTF) on the melting time was studied with an analysis of variance (ANOVA) with inlet temperatures of 65 °C, 75 °C and 85 °C and inlet velocities of 1 l·min−1, 2 l·min−1 and 3 l·min−1. The ANOVA indicated that the inlet temperature has the greatest influence on the melting time, while the inlet velocity has no significant effect. For the study of the influence of natural convection, the natural convection heat transfer coefficient was determined, showing that the upper zones have the greatest influence of natural convection, achieving coefficients of 61.8, 39.1 and 66.8 W·m−2·°C−1. In addition, using a rectangular shell-coil heat exchanger presents a more uniform melting process in the lower zones, allowing the melting of all the PCM. According to simulations, two streams of movement of the liquid phase of the PCM are formed in the center of the system. These results shows that hydrogenated palm stearin has a high capacity for energy store, reaching 306.46 kJ·kg−1.

Sizing horizontal metallic inclusions in insulators using lock-in inductive infrared thermography

We present a methodology to size the area and depth of horizontal metallic inclusions of unknown geometry, embedded in insulators, using lock-in inductive thermography. The method is based on averaging the amplitude and phase thermograms along circles concentric with the center of the heated region. We present an analytical calculation of the surface temperature distribution produced by a horizontal circular heat source, taking into account conductive coupling with the air, and we propose to fit the averaged data to this model. We present lock-in thermography data on resin samples containing embedded calibrated circular and rectangular Cu slabs that we excite inductively. The results indicate that it is possible to determine the area and depth of rectangular heat sources with aspect ratio below 1.5 with accuracy better than 10 %.

Numerical Simulation of Rapid Heat Storage in Plate-Fin Phase Change Heat Exchanger

Rapid phase change heat storage has significant application value in high-power density thermal management systems. This paper presents a comparative numerical simulation study of the rapid heat storage and release dynamics of two types of finned plate heat exchangers with different fin shapes. The study reveals that, under the same fin thickness and volume fraction, the contact surface area of triangular fins is 1.6 times that of rectangular fins, but the heat storage rate of triangular fin heat exchangers is 2 times that of rectangular fin heat exchangers. Due to the small characteristic scale and high material viscosity of the heat exchanger, the natural convection velocity of the liquid phase during the heat storage process is low, and its influence on enhancing the heat storage rate is weak.

Improved model for thermal transmission in evacuated tubes: Effect of non-uniform heat flux and circumferential conduction

Evacuated tubes are extensively utilized for converting solar energy into thermal energy owing to their exceptional thermal properties and affordability. The circumferential temperature gradient of the evacuated tube is significant to the heat and mass transfer inside, but it is often neglected. This research proposed an improved model incorporating non-uniform heat flux and circumferential conduction to obtain the temperature distribution. In the experiment, A thermal insulation material was inserted inside the inner tube to create an adiabatic boundary. Various conditions (non-uniform, rectangular, and uniform heat fluxes, circumferential conduction of the coating) were numerically compared. The enhanced combined thermal transmission model was validated, demonstrating a relative error of 6.45 % in temperature increase calculation and increasing the prediction accuracy by 42.15 % at least. The distribution of the heat flux and the thermal conduction of the coating were identified as the primary factors affecting the heat transfer properties of the evacuated tube. An imbalanced distribution of heat flux resulted in non-uniform heat transfer, whereas the circumferential conduction within the coating effectively modulated the temperature distribution to achieve uniformity. The local heat transfer coefficient exhibited non-uniformity, with calculated values ranging from 0.23 to 3.25 W/(m2∙K), and an error range of −16 to +3 %.

Experimental study of embedded manifold staggered pin-fin microchannel heat sink

High-heat-flux thermal management of high-power chips in electronic devices is becoming more and more critical. Manifold microchannel heat sink is one of the effective choices. In order to improve the heat dissipation capacity of manifold microchannel heat sink, a silicon-based thermal test chip including staggered pin-fin microchannels is designed and fabricated. Staggered pin-fin microchannels and rectangular microchannels with the same area size are embedded on the opposite side of the silicon-based thermal test chip for liquid-cooled heat dissipation. The experiments are conducted using HFE7100 as the working fluid. The heat transfer performance and the flow characteristic of two distinct microchannel structures are evaluated. It is found that the differences in temperature, convection heat transfer coefficient and pressure drop caused by different microchannel structures are greatly related to the mass flow rate. The heat transfer performance of the staggered pin-fin microchannel heat sink is better than that of the rectangular microchannel heat sink at a larger mass flow rate, but it also brings greater flow pressure drop. The bubble effect caused by the transition from single-phase to two-phase flow in microchannels makes the monotonicity of the convection heat transfer coefficient decrease significantly and the monotonicity of the pressure drop increase significantly. Compared to rectangular microchannel heat sinks, staggered pin-fin microchannel heat sinks reach the two-phase flow at higher heat flux. At the mass flow rate of 5 mL/s and the heat flux of 700 W/cm2, the staggered pin-fin microchannel heat sink can reduce the chip surface temperature by 8 K compared with the chip surface temperature of the rectangular microchannel heat sink.

Enhanced heat transfer study of microchannel heat sink with periodically arranged triangular cavities and arc‐shaped ribs

AbstractThe microchannel heat sink with periodically arranged triangular cavities and arc‐shaped ribs (MC‐ARTC) is investigated numerically under the conditions of Reynolds number 147–736. The effects of triangular cavities and arc‐shaped ribs on velocity, pressure, and temperature distribution in the channel are analyzed in comparison with a rectangular microchannel heat sink, microchannel heat sink with arc‐shaped ribs, and microchannel heat sink with triangular cavities. The results show that the triangular cavity and the arc‐shaped rib have important effects on the flow and heat transfer characteristics in the microchannel heat sink. Both rib and cavity can cause a change in fluid flow direction and disturb the development of the flow boundary layer. The fluid flow and heat transfer characteristics of microchannels are improved. Among the four microchannels, the MC‐ARTC has the optimum comprehensive performance for the combined effect of the rib and cavity. Relative cavity width () and relative rib height () are also defined to study the effects of cavity width ( = 89–200 μm) and rib height ( = 8.9–28.9 μm) on the flow and heat transfer characteristics. It is found that the heat transfer of MC‐ARTC is enhanced with increasing and , while lead to higher pressure drop. When and are 252 and 249 μm, respectively, the comprehensive performance factor () of MC‐ARTC reaches 1.76.

Computational investigation on the energy efficiency of heat exchangers using Al2O3 nanofluids

In this research, we perform a numerical investigation to examine the dynamic and thermal properties of a rectangular counterflow heat exchanger under forced convection. Our specific focus is on a novel category of heat transfer fluids referred to as nanofluids, and we investigate their performance in conditions of steady-state laminar flow. The analysis is conducted through the application of the finite volume method within the Ansys-Fluent software. The findings obtained reveal that the heat exchanger attains its peak efficiency of 35% when operated with reduced flow rates ( m ̇ c = 0.08 kg s and m ̇ h = 0.03 kg / s ) and a significant nanoparticle volume fraction of 3%. Furthermore, it has been detected that the use of steel as a material enhances the overall efficiency of the thermal transfer device. These results highlight the enhanced efficiency of nanoparticle-infused fluids in improving the heat exchanger’s performance.

Conjugate gradient method with regularization in estimating mold surface heat flux during continuous casting

The reconstruction of the boundary heat flux between solidifying steel and water-cooled mold wall using measured temperature data is recognized as an inverse heat conduction problem (IHCP). A Tikhonov spatial regularization approach to enhance the smoothness of the Conjugate Gradient Method (CGMr) was proposed which incorporates three different orders of spatial regularization: zeroth, first, and second order. The optimal regularization parameter was selected using a modified L-curve method. The accuracy of the CGMr is investigated with Case 1: a triangular time-spatial variation heat flux, and Case 2: a step change in the form of rectangular variation heat flux. The effects of measurement noise, grid points and time-step size are investigated. The results show that the minimum relative error (eRMS) of the predicted Case 1 heat flux is 1.98%, 7.64%, and 8.02% for zeroth-, first-, and second-order spatial regularization, respectively. The corresponding values for the predicted Case 2 heat flux are 3.82%, 13.42%, and 14.91%. Subsequently, CGMr algorithm is applied to calculate the heat flux in a mold simulator experiment. By comparing the relationship between heat fluxes reconstructed by CGMr after different iteration numbers, it is observed that the recovered heat flux of 2.14 MW/m2 with zeroth regularization remains highly stable.

Pressure drop correlation for subcooled flow boiling in micro-channel heat sink

This study experimentally explores the subcooled flow boiling pressure drop of FC-72 in a multiple parallel rectangular micro-channel heat sink with a channel hydraulic diameter of 666 µm (width 400 µm and height 2000 µm). Detailed experimental procedures and data reduction methodology are presented. The study analyzes and reports the impact of inlet subcooling on the total pressure drop during subcooled flow boiling of FC-72 in rectangular micro-channels heat sink. Additionally, a consolidated subcooled flow boiling pressure drop database is created by incorporating the additional data points assimilated from the study of Lee and Mudawar (2008), which used HFE-7100 as the coolant fluid. The consolidated database is methodically reviewed and evaluated using the seminal pressure drop correlations described in the literature for pressure drop during subcooled flow boiling. For the micro-channels heat sink adopted in this study, existing subcooled flow boiling pressure drop correlations fail to predict the consolidated database. Based on the consolidated pressure drop data points, a new subcooled flow boiling pressure drop correlation for the rectangular micro-channels heat sink is suggested. The new pressure drop correlation well predicts the consolidated subcooled flow boiling pressure drop database with a mean absolute error of 16.6 % and 86.3 % of data points predicted inside ±30 %.