Thermo-hydraulic Performance Research Articles

A facile design of porous heat sink optimized thermodynamically for thermo-hydraulic performance

Implementing active cooling through micro-channel heat sinks integrated with printed circuit heat exchangers demands a simultaneous enhancement of thermal and hydraulic performance, all while avoiding complex designs for ease of fabrication. We propose a porous wall embedded double-layered micro-channel heat sink, aiming to decrease the necessary pumping powers while maintaining a minimal impact on the heat transfer rate. Additionally, this design simplifies geometric complexities, enhancing ease of fabrication. We assessed the feasibility of different porous embedded double-layered micro-channel heat sink configurations by evaluating their thermal and hydraulic performance. Our analysis uniquely integrates the principles of the second law of thermodynamics with traditional first law analysis, providing novel insights into heat sink design. We discovered that configuring porous walls solely in the top layer of the double-layered micro-channel heat sink is the only viable option. Furthermore, our analysis reveals that embedding porous walls exclusively in the top layer reduces irreversibility due to frictional losses by 9.13 %, with a slight increase in irreversibility due to heat transfer by 1.55 %, in comparison to the solid double-layered micro-channel heat sink at a flow rate of 1000 ml/min. Moreover, at the same flow rate, compared to configuration with porous walls in both layers, the top layer configuration exhibits improved thermal performance by 17.28 %. Next, we demonstrate that while the first law analysis indicates the viability of the top porous configuration, the second law analysis limits its viability to a certain coolant flow rate range. Finally, we optimize the heat sink design and coolant flow rates, proposing a viable design by simply incorporating porous walls in only the top layer of double layered micro-channel heat sink, which otherwise proved to be non-viable.

Orientation effects on mixed convective performance of twisted pin fin heat sink: Experimental investigation

In the current work, an experimental study is carried out to examine the heat transfer performance and friction effects on a pin fin matrix of a heat sink for different design variables and operating conditions. This examination aims to assess the thermo-hydraulic performance of the heat sink with three orientations (90°, 180°, and 270°). In the presence of three heat loads (66 W, 91 W, and 121 W), each of these orientations is tested with three twisting angles (30°, 60°, and 90°) for different pin fins cross-sections of square and hexagonal at various ranges of air Reynolds number (Re) (3182 to 9971). The downward position of a heat sink achieves a higher Nusselt number (Nu) than the sideward and upward positions. The fin pin with a twisting angle 30° has superior efficiency for three orientation angles and hexagonal and square cross sections. Square pin fin records the lower thermal performance at Re = 3182, orientation angle (β) = 270˚, and pin twist angle (θ) = 30°, and the best at Re = 9971, β = 180°, and θ = 90°. Compared to 60˚ and 90˚, the pin fins had a reduced pressure loss at a twisting angle of 30°.

Experimental and Numerical Investigation of Single-Phase Liquid Cooling for Heterogeneous Integration Multichip Module

Abstract The variety of new electronic packaging technologies has grown significantly over the last 20 years as a result of market demands for higher device performance at lower costs and in less space. Those demands have pushed for heterogeneous packaging, where computer chips with different stack heights are closely packed, creating nonuniform heat flux and temperature and additional challenges for thermal management. Without implementing an appropriate thermal management strategy for heterogeneous packages, large temperature gradients can be observed within the package, which would increase the thermal stresses on the chip and raise reliability issues. To mimic this real-life scenario of such packaging, an experimental setup was designed and built. The design of the new experimental setup consists of four identical 1.2 cm × 1.2 cm ceramic heaters, each of which is connected to a separate power supply and can reach a heat flux of 140 W/cm2. Accordingly, this mock package is capable of delivering different power levels to mimic different multicore microprocessor conditions. To give the heater the ability to move precisely in the x-, y-, and z-directions, each heater is mounted to an XYZ linear stage. Deionized water (DI) was used as the working fluid, and a pin-fin heat sink was used to run the initial steady-state tests on the experimental rig. The tests showed how different flow rates at a constant fluid temperature and input power affect the temperatures of the heaters and the thermohydraulic performance of the heat sink. In addition, a three-dimensional numerical model has been developed and validated with experimental data in terms of heat sink pressure drop and the temperatures of the heaters.

Impact of hyperbolic-cut twisted tape on heat transfer, friction factor and thermohydraulic performance of heat exchanger tube: an experimental study using Internet of Things (IoT) approach

Impact of hyperbolic-cut twisted tape on heat transfer, friction factor and thermohydraulic performance of heat exchanger tube: an experimental study using Internet of Things (IoT) approach

Thermo-hydraulic Investigation of a Heat Exchanger Tube Equipped with 3D-Printed Swirl Flow Generators

AbstractHeat transfer capabilities of the heat exchangers require enhancements to save energy and decrease their size. For this purpose, the swirl generators have been widely preferred. However, the swirler inserts have not reached their optimum shape. Thus, this study experimentally and numerically investigates the impact of novel 3D-printed swirler inserts with varying twist angles in the range of 0°–450° on the thermo-hydraulic performance of solar absorber tube heat exchangers under laminar flow (Re = 513–2054) condition. Friction factor, Nusselt number, and performance evaluation criterion (PEC) were used to assess heat exchanger performance, and related correlations are provided. Tangential velocity components were also used to explore fluid flow characteristics in local analysis. Numerical investigation was done by using computational fluid dynamics adopting Finite Volume Method in ANSYS Fluent. Results show that 3D-printed swirlers considerably increase heat transfer compared to plain tube. The swirler with a twist angle of 450° led to the maximum enhancements of nearly 217% in average Nusselt number and around 1630% in friction factor at Reynolds number of 2054. Overall, increasing Reynolds number enhanced Nusselt number. The highest PEC of 1.15 was observed at a Reynolds number of 1031 using the swirler with 150° twist angle. Flow near the swirler has higher tangential velocities, hence contributing to local Nusselt number enhancement up to 453.8% compared to plain tube when swirler with twist angle of 450° utilized. It is anticipated that findings of this study can guide further related research and increase the usage of swirlers in heat exchangers.

Investigation on the thermal and hydraulic characteristics of the micro heat sinks with grooves and pin fins by Taguchi-based sensitivity analysis

The heat dissipation issue of the micro electronic devices seriously restricts their application in the aerospace, national defense, communication, etc. The novel heat sinks with trapezoidal grooves and rectangular pin fins are proposed to meet the cooling requirement of the high-power devices. The cooling effect, thermohydraulic characteristics, total efficiency and thermodynamic performance of the heat sinks are studied by three-dimensional numerical simulation. Firstly, the influence of the relative position between the grooves and the pin fins on the thermohydraulic performance is explored in detail. Secondly, Taguchi optimization and analysis of variance are adopted to quantitatively analyze the impact degree of the pin fin width, length and height on the Nusselt number, friction factor and total performance index. The optimal structures are obtained for different objectives. Lastly, the temperature performance, total performance and the irreversibility of the optimal structures are compared thoroughly. New findings include that: the best arrangement of the grooves and pin fins is obtained, which enhances the Nusselt number by 1.5 times compared to the smooth heat sink. The fin width is the most critical factor for the heat transfer and flow, while the fin length shows the greatest importance in the overall performance. The optimized heat sink with the fin width of 50 μm, length of 60 μm and height of 150 μm reduces the peak temperature by 12.3 ℃ compared to the smooth heat sink for Reynolds number of 303. This heat sink yields the highest total performance index with 1.43 for Reynolds number of 368 and significantly reduces the irreversible loss. Moreover, the optimized heat sink with the fin width of 10 μm, length of 60 μm and height of 100 μm reduces the friction factor by 61.39 % compared to the original structure for Reynolds number of 635, which is beneficial to reduce the energy consumption. The quantitative analysis of the parameter sensitivity for novel heat sinks reveals the mechanism of the heat transfer enhancement by modifying the geometric parameters and provides an effective solution for thermal management of the high-power devices.

Effective thermal performance assessment for prismatic triangular solar air heater integrated with fins and turbulators

A numerical study was conducted to explore the effective usability of prismatic triangular channel solar air heaters integrated with longitudinal fins and quadrilateral rib turbulators. Using the matrix inversion technique and MATLAB-developed code, the governing equations of the system were solved. The analytical model is confirmed, showing commendable agreement with an average discrepancy of 4.2%. For the constant value of quadrilateral rib conditions, the first law and the thermohydraulic performance of the novel air heating system are analyzed by considering the design and operating conditions of Reynolds number, fin height ratio, fin thickness ratio, and number of fins. The achieved results reveal that the provision of fins with rectangular rib roughness enhances the thermal and effective thermal performance by optimizing fin design parameters, leading to a maximum value of 85.48% and 78.58%, respectively. The comparison results reveal that the present work improves the effective thermal performance by 5.14% to 20.2% up to the Reynolds number of 21600. It is an attractive design, achieving a rise in temperature parameter up to 0.012 W/m2K.

Numerical analysis of the effect of wave amplitude on thermohydraulic performance in a heat exchanger with sinusoidal wavy channels

With the increasing application of heat exchangers, the research has become increasingly comprehensive. Previous studies mainly focused on comparing the amplitudes to investigate the performance of heat exchangers, while the study of variable amplitude channel structures was limited. This study investigated the thermal-hydraulic performance of seven different sinusoidal channels with inclination angles of 20° and 30°, and their combinations. Using the CFD solver, simulations were conducted to assess the heat transfer capabilities of sinusoidal channels under various Reynolds numbers and different amplitude conditions, compared to straight channels and single amplitude sinusoidal channels. The results indicated that within one period, both the pressure drop and temperature difference exhibited a ripple trend of gradually decreasing amplitude. When evaluating the comprehensive performance of the channels, three trends emerged across the seven models, with the performance of the cold fluid and the hot fluid within the same group showing opposite trends. This suggested that more variations could enhance the overall performance of the hot fluid while reducing the performance of the cold fluid. For structures with the same amplitude, in terms of amplitude variation frequency, models with six periods per group exhibited higher overall heat transfer performance than those with three periods per group, with an average increase of 36.37%. For the arrangement of amplitudes (taking the hot fluid inlet as an example), configurations with a smaller amplitude at the inlet outperformed those with a larger amplitude, indicating that in combined amplitude models, a structure with a larger group and a smaller amplitude at the inlet (taking the hot fluid as an example) should be designed.

Comparison of thermo-hydraulic performance among different 3D printed periodic open cellular structures

As additive manufacturing of periodic open cellular structures (POCS) is gaining interest in structured catalytic reactor research, this work seeks to thermohydraulically compare the well-known Kelvin lattice structure with the lesser-researched BCC and gyroid lattice structures. Using a combined CFD (Computational Fluid Dynamic) and experimental approach, the selected POCS are fabricated through Laser Powder Bed Fusion (LPBF), characterized, and subsequently subjected to numerical analysis. From the manufacturability point of view, the 3D printed samples closely matched their CAD designs, showing a maximum porosity deviation of 15% below design values. A CFD model, validated through pressure drop experiment, was employed to compare the POCS designs on shared geometric attributes such as specific surface area and porosity. While all structures exhibited comparable performance in term of heat and momentum transfer, our findings suggest that the Gyroid lattice may provide the optimal balance between momentum and heat transfer rates in low-velocity region. Conversely, the BCC configuration may be more favourable at higher velocity. An Ergun-like correlation was also developed and validated for each lattice type, with a Mean Absolute Percentage Error (MAPE) below 10%. Our pressure drop results align quite well with existing literature correlations, showing a MAPE under 20%. Concerning heat transfer, the values forecasted in this research show a reasonable alignment with literature’s results, though they tend to be on the lower spectrum.

Enhancement in thermo-hydraulic performance of ceramic-based disk heat sink with fractal micro-channels via double layering, hybrid nanofluids, and cross-sectional convergence

The focus of this paper is to further improve the thermo-hydraulic performance of a disk heat sink with fractal-like microchannels by introducing four distinct modifications: incorporating convergent cross-sections in microchannels, implementing double layering, utilizing a high-conductivity material (AlN ceramic) for the heat sink, and integrating hybrid nanofluids. Hybrid nanofluids, encompassing Aluminum Oxide-Graphene, Aluminum Oxide-Copper, and Copper-Graphene, each with varying volume fractions and an overall volume fraction of 2 % and 4 %, were systematically evaluated. The cumulative impact of these modifications on the four levels fractal-like microchannel heat sink's thermo-hydraulic performance was rigorously assessed through numerical simulations. The flow rate ranges from 300 to 600 ml/min, corresponding to an inlet Reynolds number in the range of 3014 to 6018.The findings reveal that the increase around 10 % in Nusselt number can be achieved through implementing converging cross-sections at levels 3 and 4. Substituting silicon with AlN ceramic leads to a reduction in maximum temperature from 1.85 to 2.58 ℃, depending on the flow rate. Under a heat flux of 40 W/cm2, double layering can reduce thermal resistance by 0.2. Most effective configuration involves a double-layered fractal microchannel with convergent cross-sections at levels 3 and 4, employing AlN ceramic as the material, and utilizing a hybrid water-based nanofluid with a volume fraction of Cu 3 %-Al2O3 1 %. This configuration achieves a notable reduction in maximum temperature by 11.1 °C and 17.97 °C under heat fluxes of 40 and 80 W/cm2, respectively, at a volumetric flow rate of 300 ml/min.

Thermohydraulic performance analysis and optimization of stripe patterned hybrid-wetting surface condensation by 3D steady simulation

The configuration parameters of stripe patterned hybrid-wetting surfaces (SPHWSs) had a significant effect on the thermohydraulic performance of condensation. By using Taguchi-GRA method modified by entropy weight for optimization, Nusselt number (Nu) and thermal performance factor (TPF) reached the highest increment of 225.9% and 252.8% at vapor mass fraction (ω) equal to 15%, respectively, and the maximum reduction of Fanning friction coefficient (f) was −41.7% at ω = 30%, as compared without SPHWSs. A 3D steady CFD-aided method based on pseudo transient under-relaxation model was developed to predict Nu, f, and TPF of SPHWSs for different configuration parameters, including oblique pattern angle (β), hydrophilic (Wi) and hydrophobic (Wo) pattern width, hydrophilic (θi), and hydrophobic (θo) contact angle. The result indicated that the simulation was in good agreement with the experimental data. θi had a more pronounced effect on the thermohydraulic performance compared to other factors. Notably, the droplet reached a specific dynamic force balance at θi = 60°, effectively restraining near-wall erratic flow and enabling cost-optimal heat transfer.

Thermohydraulic performance augmentation of triangular duct solar air heater using semi‐conical vortex generators: Numerical and experimental study

AbstractThermohydraulic performance augmentation using turbulence promotors is a commonly adopted technique in solar air heater (SAH) applications. This article presents the thermohydraulic performance augmentation of triangular duct SAH using semi‐conical vortex generators (SCVG) using computational fluid dynamics and experimental methodology for various flow Reynolds numbers ranging from 6000 to 21,000. An in‐depth parametric analysis is undertaken to establish the influence of flow attack angle, relative longitudinal pitch, relative transverse pitch and cone diameter of SCVG on the thermohydraulic performance as indicated by the thermohydraulic performance parameter (THPP). The results reveal that the SCVG generates longitudinal vortices and introduces flow impingement zones which significantly affects the flow and heat transfer characteristics of air heaters. Correlations for Nusselt number and friction factor are established, which predicts the performance outcomes with an average error of 6.74% and 4.46%, respectively. The optimal THPP is determined to be 1.74 using artificial neural network model and Bonobo Optimization algorithm. The SCVG produces THPP values well above unity for the entire flow Reynolds number range of 6000–21,000.

Investigation of heat transfer and friction characteristics of solar air heater through an array of submerged impinging jets

This research focuses on experimental and computational analysis of enhancement in thermal performance of a solar air heater with submerged impinging jets (SAHSIJ). The Application of submerged pipe jets generates a high impinging velocity and induces a significant degree of turbulence at the absorber plate, leading to elevated heat removal rates. This research investigates the effect of change in geometric parameters such as jet spacing ratio (Sj/Dh) from 0.108 to 0.433 at various jet angles (α) from 75° to 90° on the Nusselt number and frictional characteristics to improve the overall thermo-hydraulic performance parameter (THPP) of the system. The results obtained from SAHSIJ are compared with those of a smooth duct to determine the effectiveness in terms of the thermo-hydraulic performances parameter (THPP) of the system. It is found that the novel submerged pipe jet configuration in better in extracting heat from the absorber plate than the orifice jet and smooth duct solar air heater.

Numerical Investigation of Air-Steam Condensation in a Vertically Enhanced Tube with Concave and Convex Surfaces

Condensation heat transfer enhancement technology is an important problem for heat exchangers. The air-steam condensation inside a vertically enhanced tube with concave and convex surfaces is analyzed numerically, and the effects of relevant parameters on thermohydraulic performance are discussed. The numerical results show that the drop in steam and temperature between the inlet and outlet is improved by 53.8% and 96.8%, respectively, compared with smooth tubes. In the condensation process, the noncondensable gas accumulates near the wall, which leads to the deterioration of condensation. The structures of concave and convex surfaces disrupt the boundary layer flow and noncondensable gas film and promote flow mixing, leading to enhanced condensation heat transfer. All the numerical results provide guidance values for heat transfer enhancement technology in the applications of condensers.

Local entropy generation optimization and thermodynamic irreversibility analysis of oval-shaped coaxial ground heat exchangers: A detailed numerical investigation

Optimizing the heat transfer and thermodynamic efficiency of Ground Heat Exchangers (GHE) is crucial for maximizing the energy efficiency of Ground-coupled Heat Pump (GCHP) systems utilized in building heating and cooling applications. This study pioneers an effective approach of both the first and second laws of thermodynamics of the newly oval-shaped coaxial GHEs (oval-CGHEs), assessing heat transfer, thermohydraulic performance, and local entropy generation rate to explore the optimum design and operational conditions for heat exchange maximization and entropy generation minimization. Utilizing a three-dimensional numerical model validated by experimental results, this study examines the trade-offs between heat transfer improvements and entropy generation rate intensification of the oval-CGHEs in comparison to the typical circular-shaped CGHE (circle-CGHE) further than exploring the effect of key operational and design parameters and performing sensitivity analysis. The results reveal that oval-CGHEs exhibit higher irreversibility as a penalty for their superior heat transfer capabilities compared to traditional circular-shaped CGHEs (circle-CGHE), which can be mitigated by optimizing the position of the inner tube. Moreover, the study underscores the criticality of maintaining a balance between enhanced heat transfer and the associated rise in irreversibility, particularly concerning the factors of mass flow rates and installation depths.

Experimental investigation of the effects of graphene nano particle added water fluid on heat transfer in a smooth tube with double inserts

In this study, experimental studies were carried out to increase the performance of heat exchangers. The effects of two techniques (inserts and nanofluid) on thermohydraulic performance was investigated simultaneously. The twisted tape and the helically wire coil were originally created. The two separation ratios (0.1 and 0.05), the eight twisted tape pitch ratios (1.9/2.3/2.7/3 and 2.1/2.4/2.8/3.2), the four coil wire pitch ratios (0.8/1.2/1.5/1.6) and three weight fractions (0.5/0.75/1 %) for graphene-water nanofluids were used with the Reynolds number ranging from 5000 to 26,000. Experiments in which a coiled wire coil and twisted tape are used together have been found to increase both the heat transfer rate and the friction factor compared to experiments using distilled water in an empty tube. According to the results of all experiments, it was found that the highest heat transfer rate and friction factor were obtained with the model containing graphene-water fluid used at a weight fraction of 1 %. The highest performance evaluation criteria is found as 2.5 b y using the graphene-water mixture model with a wall separation ratio of 0.05, a twisted tape ratio of 2.1, a wire coil ratio of 0.8 and a 1 % weight fraction among all combinations.

Thermo-hydraulic performance evaluation of heat transfer tubes with different configuration forms

Fluid mixing induced by changes in tube direction is an effective method to enhance the heat transfer performance of heat transfer tubes. This study proposes three types of configuration forms for heat transfer tubes that improve their thermo-hydraulic performance, named cases 1, 2, and 3. Case 1 is distributed on the same plane and has the following configuration form: horizontal to vertical upward to horizontal to vertical downward to horizontal. Cases 2 and 3 transform the front and rear tubes into two parallel planes through the middle horizontal tube, with a 180° difference at the outlet direction. The thermo-hydraulic performance of heat transfer tubes with different configuration forms is evaluated by quantitative comparison of the Nusselt number (Nu), friction coefficient (f), and performance evaluation criterion (PEC), within a Reynolds number range of 5000–40 000. The distribution results of velocity, streamline, turbulent kinetic energy, skin friction coefficient, and so on are analyzed to reveal the underlying mechanisms of difference in the thermo-hydraulic performance of heat transfer tubes with different configurations. The results show that the thermo-hydraulic performance of heat transfer tubes with different configurations is better than that of a straight tube due to induced fluid mixing within the tube. In addition, case 1 rather than cases 2 and 3 has a more significant influence on the thermo-hydraulic performance of heat transfer tubes, especially at high Reynolds numbers, and the maximum PEC of case 1 exceeds cases 2 and 3 by 6% and 8.5%, respectively. Furthermore, the decrease in connection length of case 1 improves the heat transfer performance, which is more pronounced at high Reynolds numbers. These research findings serve as a valuable reference for designing heat transfer tube configurations to enhance heat transfer efficiency.

Optimization investigation for heat transfer enhancement of fins for plate-fin heat exchangers in cryogenic helium systems

In order to further improve heat transfer performance and high compactness of plate-fin heat exchangers (PFHEs) in cryogenic helium systems, a new type of perforated-serrated fins is proposed by combining traditional serrated and perforated fins. In this paper, the flow and heat transfer characteristics of helium in perforated-serrated fins and serrated fins channels at low-temperature are investigated using numerical simulations. The numerical model invokes the properties of low-temperature helium by NIST-Real-Gas-Model. Meanwhile, Colburn factor j, friction factor f and JF factor are qualitatively evaluated for pressure drop, heat transfer performance and thermo-hydraulic performance, respectively. The results show that new perforated-serrated fins have better heat transfer performance. The j factor of the new fins increases by 32.58% to 15.63% compared with serrated fins. The flow performance of perforated-serrated fins is slightly worse than that of serrated fins, but the overall thermo-hydraulic performance is better, especially at low Reynolds number. Compared with serrated fins, the JF factor of perforated-serrated fins is significantly higher and increase by 25.95% to 10.86%. The optimizing method of fins structure can be used in the actual design of PFHEs in cryogenic helium systems.

Flat plate solar collector networks: Design and retrofit considering fouling effects

This study presents the thermohydraulic principles for retrofitting existing flat plate solar collector networks with the aim of increasing energy capture using the installed capacity. The arrangement of a solar collector field influences its thermohydraulic performance and pumping costs. In this study, factors such as scaling-induced fouling, solar radiation, and flow distribution are considered. The case of an existing plant consisting of a total of 40 collectors is examined. It is concluded that the optimal arrangement should include 8 collectors per line connected in series as a limit to enhance thermohydraulic performance and reduce overall operating costs. The annual savings due to reduced natural gas consumption in the original plant structure (4Lx5px2s) amount to $17,522.72 USD per year; however, modifying the structure to 4Lx10s, the savings increase to $19,818.64 USD per year. Under fouling conditions, the new structure reaches savings of $19,512.41 USD per year. This suggests that, in design, the network configuration should prioritise the number of collectors in series per line, only limited by the increase in pressure drop.

CFD simulation and geometric optimization of a novel baffle heat sink for power electronics cooling

The electric drivetrain of an electric vehicle typically has two fluid circuits: an oil circuit for lubrication and a water-glycol circuit for cooling. Eliminating the water-glycol circuit can result in a more compact and lighter drivetrain. However, this requires the drivetrain components to be cooled with oil as coolant, which has inferior heat transfer properties compared to water-glycol mixtures. This is particularly challenging for the power modules in the power electronics unit, which exhibit some of the highest heat fluxes in the drivetrain. This study focusses on the design and optimization of a novel type of heat sink for laminar flows with baffles to guide the flow in four different directions. This has two main advantages: the baffles act as fins and increase the heat transfer area and they introduce a swirling motion in the oil thereby disturbing the boundary layers continuously. Computational fluid dynamics simulations using Ansys Fluent are performed to evaluate the thermohydraulic performance of the heat sink. The influence of design parameters such as the height and thickness of both fins and baffles and the baffle spacing in horizontal, upward and downward direction was evaluated by simulations with several combinations of the design space, considering manufacturing constraints. The optimization of the design showed that the fin thickness, horizontal baffle spacing and baffle length should be as small as possible, while there were optimal values for fin height, upward and downward baffle spacing, streamwise baffle spacing and baffle thickness. The simulations show that the thermal resistance of the baffle heat sink can be 19% lower than that of a benchmark pin fin heat sink at equal pumping power.