Thermo-fluid Characteristics Research Articles

Detailed thermo-hydraulic investigation of 3D octet lattice structure integrated heat sink

The present research work examined the thermo-fluidic characteristics of a heat sink packed with octet-structured periodic metal foam having varying porosity (0.83–0.93) and unit cell lengths (UCL) of 2.5–5 mm for electronic cooling application. AlSi10Mg material is considered for the octet lattice structure with water as the cooling medium, with the inlet velocity ranging from 0.02 to 0.05 m/s and a steady heat flux of 10 W/cm2 applied at base of the substrate. The effect of the porosity, unit cell length, and inlet velocity on pressure gradient, friction factor, Nusselt number, wall temperature, heat transfer coefficient, and thermo-hydraulic performance parameter is analyzed. Larger pressure gradients are observed for lower values of porosity and unit cell length, with a maximum value of approximately 5000 Pa/m for the thermal system having 0.83 porosity, 2.5 mm UCL, and 0.05 m/s inlet velocity. The wall temperature drops with a rise in inlet velocity and a reduction in porosity and UCL, with the lowest value of 311 K for the case of 0.83 porosity, 2.5 mm UCL, and 0.05 m/s inlet velocity. The case of 0.83 porosity, 5 mm UCL, and 0.02 m/s velocity was determined as optimum design based on thermo-hydraulic performance parameter.

Thermo-fluid characteristics and exergy analysis of a twisted tube helical coil

In the present investigation, the exergy of an innovative technique involving the integration of curved helical tubes with twisted passages was experimentally presented. This technique aims to improve the thermofluid characteristics by involving the swirl intensity of fluid flow in a twisted tube helical coil (TTHC). Six identical geometries with different pitch ratios \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Upsilon$$\\end{document} of 36 mm, 54 mm, and ∞ (smooth/no twisted) were experimentally explored at two different inner tube profiles of triangular and square cross-sections in counter flow arrangements. The experimental runs were carried out at 10,300 ≤ Rei ≤ 37,800 and 2400 ≤ Reo ≤17,600 for both the inner and annulus fluids, respectively. The results showed that the Nusselt number, Nu, increased by 39.6% and 41.5% for triangular and square inner twisted cross-section profiles, respectively, at a \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\it \\Upsilon$$\\end{document} of 36 mm at the expense of increasing f by 37.6% and 60.7%, respectively. The results also showed that the thermal performance factor reached 1.3 and 1.25 for a \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\it \\Upsilon$$\\end{document} of 36 mm for the triangular and square inner twisted tube profiles, respectively. A comprehensive study is performed to analyze the TTHC from thermal, frictional, and exergetic viewpoints. New correlations for expecting the annulus Nuo and fo are presented.

Thermo-fluidic and entropy generation analysis of MPCMS in straight, segmental, and rib-groove microchannel heat sinks: A numerical investigation

The efficient management of thermal systems is crucial for various technological applications, necessitating innovative cooling strategies to enhance performance and reduce entropy generation. Microchannels have emerged as a promising solution due to their high heat transfer rates and compact size. This study investigates the thermofluidic characteristics and entropy generation in straight, segmental, and rib-groove microchannels utilizing de-ionized water and microencapsulated phase change slurry (MPCMS) as working fluids. Employing numerical analysis, the investigation integrates a mixture model for the base fluid and micro-encapsulated phase change material (MPCM) using an equivalent heat capacity approach to incorporate the phase transition of the MPCM (composed of paraffin with a Ti shell). Operational parameters include an inlet fluid velocity ranging from 0.575 to 3.45 m/s, heat flux varying between 15 and 30 W/cm2, and MPCM volume fractions of 5% to 20%. The ANSYS Fluent Solver, a finite volume method using a multigrid solver, was used to control the simulation by species transport. Notably, segmental channels exhibit a notable decrease in wall temperature of 29.7% and 26.3% compared to straight and rib-groove channels, respectively, under constant heat flux and flow rate. However, the effectiveness of MPCM in enhancing thermal performance was greater in straight and rib-groove channels, surpassing segmental channels by 2.5% and 3.28%, respectively, under constant heat flux. On analyzing the irreversibility, segmental channels exhibit higher frictional entropy but lower thermal entropy generation due to the fin structure, resulting in an overall reduction in total entropy generation. Moreover, segmental microchannels, when utilizing MPCMS, demonstrate superior performance in reducing irreversibility by 60.66% and 49.6% compared to straight and rib-groove channels, respectively. Total entropy generation increases with higher velocity and heat flux, while it diminishes with higher MPCM concentration across all configurations.

Thermo-fluid characteristics and lock-on range efficiency of infrared suppression (IRS) devices with diathermic funnels in the presence of surface radiation: A comparative study

This investigation examines the influence of surface radiation on the thermo-fluid characteristics of three distinct infrared suppression (IRS) mechanisms employing diathermic funnels. Managing the flow and heat transfer attributes within an IRS apparatus becomes increasingly intricate owing to the convergence of frigid ambient mass entering via inter-funnel apertures and the high-temperature flue gas generated by the turbine on naval or cargo vessels. Conducting a three-dimensional analysis involving conical, louvered conical, and louvered cylindrical funnels, computational simulations based on the Navier-Stokes equation, encompassing the energy and radiative transfer equations, are conducted. This study offers a comprehensive elucidation of how the Reynolds number (ranging from 6.1 × 105 to 3.18 × 106), FOL (negative, zero, and positive), and NOL collectively influence the temperature variations at the system’s exit. Louvered cylinder-shaped funnels, specifically in zero-overlap scenarios, emerge as the optimal configuration for the IRS system. The computations undertaken aim to gauge the ship’s lock-on range, accounting for the presence or absence of the IRS system.

Comparative thermo-fluidic analysis of condensation characteristics inside smooth and enhanced tubes

Three-dimensional simulations are performed to investigate the thermo-fluidic characteristics during the flow condensation of representative R134a refrigerant inside smooth and enhanced tubes. Along with a perfectly smooth surface, four different surface structures, i.e., hemispherical ribs, conical fins, axial, and circumferential continuous protrusions (tunnels and huddles) on the inner surface of the tube are tried to understand the heat transfer enhancement mechanism. Simulations are carried out for the mass flux ranging from 100 to 200 kg m−2 s−1 and inlet vapor quality of 0.8 at a phase change temperature of 40 °C. The effect of structures on the flow behavior is analyzed, and the presence of directional condensate drainage near the protrusions is observed. The qualitative and quantitative examinations of interfacial structures at different axial and longitudinal sections are also presented to better understand the distinctive condensation phenomenon for smooth and enhanced tubes. The spatial and time-averaged vapor fraction and liquid film thickness show lower values in the case of enhanced tubes compared to the smooth surface for all tested operating conditions. Furthermore, the hemispherical rib structure showed the highest heat transfer coefficient among the tested structures, whereas a tube with circumferential protrusions (huddles) results in maximum pressure drop during flow condensation. The benefits of heat transfer enhancement appear to be more than the pressure drop penalty for tubes with a conical fin structure and axial tunnels.

Study on convective melting heat transfer of a solid-liquid phase change slurry in U-shaped curved tubes

As a phase change material, ice slurry has been successfully applied in HVAC&R systems due to its high energy storage density. The heat exchangers are the key equipment realizing energy conversion of ice slurry. In HVAC&R systems, U-tubes are frequently used in shell and tube heat exchanger. However, there are few studies on thermo-fluidic characteristics of ice slurry in U-tubes. Therefore, the thermo-fluidic characteristics of ice slurry in U-tubes are numerically studied in this paper using Euler-Euler approach. The results indicated that as enlarging the inlet ice content and velocity, the ice concentration distribution becomes more uniform along in vertical profile. Due to the secondary flow in bend section, the ice concentration decreases in the inner wall and increases in the outer wall as the inlet velocity increases; At the high Reynolds number, the inlet ice content and ice particle diameter have a more significant fluence on pressure drop (Δp). The local heat transfer coefficient (hlo) in bend section exhibits a tendency of first increasing and then decreasing, with the maximum value of hlo occurs at θ = 90° of the bend section. Finally, a correlation is suggested between the average resistance coefficient (fave) and local Nusselt number (Nulo).

An experimental investigation on the influence of Strouhal number and amplitude on the flow and heat transfer behavior of synthetic jet impingement

ABSTRACT Here, tests are performed to analyze the effect of Strouhal number (St) and amplitude on thermo-fluid characteristics of synthetic jet (SJ) impingement for varied range of Reynolds numbers (Re = 3000–6000) and three different SJ actuation amplitudes (Vrms = 4, 6, 8 V). The hot wire anemometer and the infrared thermal imaging camera are used to measure the flow velocity and surface temperature, respectively. At a constant amplitude of the SJ actuation, discrete pairs of Strouhal numbers, i.e. low St ( S t L ) and high St ( S t H ), are found to exhibit the same Re. The heat transfer characteristics are expressed in three different regions such as the region of recirculation, the region of high Strouhal number dominance, and the region of low Strouhal number dominance. At lower orifice-to-surface spacings (z/d < 6), the thermal efficacy of SJ with S t H is found to be lower compared to the SJ with S t L . At z/d = 2, SJ with S t H exhibits the decrease in the average Nusselt number upto 53.4% corresponding to S t L at Re = 4000 and 4 Vrms. However, at intermediate spacings (z/d ≥ 6 ), the SJ with S t H tends to outperform the S t L , which may be due to vortex pairing at high St synthetic jets. At larger z/d, the dominance of S t L is reestablished due to matching of the SJ actuation frequency with the natural frequency of a steady jet. Correlations have been proposed for the average Nusselt number at both S t L and S t H as a function of Re, St, and z/d. The results of the study provide information on the selection of the operating frequency of SJ to achieve higher heat transfer at varied orifice-to-surface spacings.

Understanding Thermo-Fluidic Characteristics of a Triangular Solar Air Heater Having W-Shaped Rib-Turbulators: A 3D Computational Fluid Dynamics Study

Abstract A solar air heater duct with W-shaped rib-turbulators on the collector plate disrupts the flow that enhances the heat transfer from the hot surface due to turbulence in the flow. In this analysis, a three-dimensional fluid domain of the W-shaped ribbed triangular solar air heater duct is numerically simulated to analyze the impact of roughness and flow parameters on thermo-fluidic performance; also, the turbulence behavior near the rib surfaces is presented. Roughness variables like non-dimensional pitch and non-dimensional height varied from 6.23 to 17.85 and 0.04 to 0.053, respectively. In contrast, the flow parameter, like the Reynolds number, is kept in the range of 4×103 to 18×103. A maximal performance evaluation criterion of 1.51 is attained for the W-shape ribs with a non-dimensional pitch of 7.14 and a non-dimensional height of 0.047 at a Reynolds number of 15×103. For the W-shaped rib-turbulators with a non-dimensional pitch of 7.14 and a non-dimensional height of 0.047 at a Reynolds number of 15×103, the maximum heat transfer is found to be 1.826 times that of a smooth duct. Accordingly, in the parametric range, the maximum friction penalty is 2.63 times that of a smooth duct. Some useful correlations are established considering the computational data.

Parametric Influence on the Thermofluidic Characteristics of the Branched Wavy Heat Sink

Abstract The branched wavy heat sink (BWHS) is found as a novel design for heat sink application. The aim of this paper is first to investigate the optimum branch angle by varying the branch angle while keeping the constant parametric value such as pitch, wavelength, and secondary width; the idea was established, and we found that a 45-deg branch angle is the best among other branch angles. After that, we varied the next important parametric value, i.e., secondary width, to know the optimum secondary width. Four secondary pass angle (branch angle) configurations (25 deg, 35 deg, 45 deg, and 55 deg) were proposed and numerically investigated by keeping the constant parametric value. The RNG k–ɛ model has been employed with the full domain model approach in the computational analysis. Further, the optimum branch angle has also been investigated with the varying secondary width. The secondary flowrates were strongly affected in all the cases. The pressure loss increases as the secondary pass angle increases. However, a secondary pass maintains pressure uniformity in the spanwise direction through flow migration. It is clear that raising the secondary pass angle reduces the hot spot region. Finally, the optimum branch angle has also been investigated with varying secondary widths of 0.5 mm, 0.25 mm, and 0.20 mm. According to the thermofluidic study, the BWHS design with 45-deg angle and 0.25-mm secondary width has better heat convection performance among all. With a 2% volumetric concentration of nanofluid, the heat transfer rate improves by about 10% compared to water. As a result, the 45-deg BWHS presents a viable avenue for further study. The heat transfer rate of the microchannel heat sink (MCHS) is greatly aided by secondary flow mixing. The branched wavy heat sinks (BWHSs) under forced convection with water/Al2O3 under the Re = 100–500 have been investigated.

NUMERICAL INVESTIGATIONS OF THERMO-FLUIDIC CHARACTERISTICS IN INNOVATIVE PARALLEL PLATE-FIN HEAT SINK DESIGN SUBJECTED TO PARALLEL FLOW: EXPLORING THE STAGGERING EFFECT

NUMERICAL INVESTIGATIONS OF THERMO-FLUIDIC CHARACTERISTICS IN INNOVATIVE PARALLEL PLATE-FIN HEAT SINK DESIGN SUBJECTED TO PARALLEL FLOW: EXPLORING THE STAGGERING EFFECT

Numerical modelling and analysis of porous surface-enhanced jet cooling using copper inverse opals in single-phase flow

Abstract In this study, we propose a novel cooling scheme that utilizes copper inverse opals (CIOs) for surface enhancement in a single-phase impingement jet cooling system. We perform computational fluid dynamics simulations to evaluate the cooling performance of the CIO jet coolers. Our modelling results indicate that the proposed CIO-coated cooler can significantly reduce the average temperature and improve the temperature uniformity across the entire chip surface. The average Nusselt number of the CIO-coated cooler can reach up to 2.8 times that of the flat surface jet cooler. However, the porous structure of the CIO-coated cooler increases the total pressure drop. To determine designs with high cooling performance and low energy consumption, we investigate two crucial design factors, namely the inlet velocity and the nozzle-to-CIO distance. Our analysis reveals that increasing the inlet velocity further enhances the heat transfer, but at the expense of high pressure drop. On the other hand, a larger nozzle-to-CIO distance results in a lower pressure drop but also reduces the heat transfer coefficient. The effects of nozzle-to-CIO distance are further understood by studying the flow resistance network. Furthermore, we present a reduced-order model that accurately captures the thermofluidic characteristics of the proposed design.

A PARAMETRIC AND COMPARATIVE STUDY ON BARE-TUBE BANKS AND NEW CAM-SHAPED TUBE BANKS FOR WASTE HEAT RECOVERY APPLICATIONS

The present study numerically examines the effects of tube diameter (12 to 35 mm), arrangement, pitch-to-diameter ratio (1.25 to 2.5), length (300 to 1500 mm), and passage number (1-4 passes) on the thermofluidic characteristics of cross-flow tube bundles. Especially, five new cam-shaped tubes are proposed in comparison with the conventional round tube. The air temperatures at the cold and hot side inlets are kept constant at 25&amp;deg;C and 600&amp;deg;C, respectively. The numerical method is verified by the existing experimental results. The findings show that a cam-shaped tube with an equal diameter (Cam_1818) is a promising tube for tube bundles, which apply in waste heat recovery. Indeed, it can offer the same minimum gap as that of the round tube; however, it improves the total thermal resistance up to about 28&amp;#37; and enhances the heat-transfer rate up to an average of 42.3&amp;#37; compared to that of the round tubes at the same pumping power.

Experimental and numerical study on thermofluidic characteristics of microchannel heat sinks with various micro pin-fin arrays arrangement patterns

Targeting at improving the comprehensive performance of microchannel heat sink, microchannel heat sinks integrated with various arrangements of micro pin-fins arrays are proposed in this paper. The thermofluidic characteristics and heat transfer enhancement mechanism of different pin-fins arrangement patterns is investigated by experimental test and numerical simulations. It is found that the partially uniform/gradient stagger pin-fins arrangement patterns present largest pressure drop with moderate heat dissipation performance, while the patterns with overall pin-fins distribution demonstrate superior heat transfer performance than all partial pin-fins distribution modes. Thus, overall gradient stagger pin-fins arrangement with moderate pressure drop yields optimal heat transfer capacity, achieving 4.8∼6.1 times enhancement than smooth channel. Furthermore, the partially uniform/gradient stagger pin-fins arrangement patterns indicate best temperature uniformity and thermal resistance with 26.2 K and 47.6% reduction than smooth channel at 80 ml/min, 100 W/cm2, respectively. The temperature trend in the longitudinal direction shows peaks and troughs for arrangements with partial pin fins distribution, while patterns of gradient pin fins distribution exhibit wavy curves of temperature rise. Additionally, the performance evaluation plot is adopted to describe the comprehensive performance of heat sinks with different pin fins patterns. It is observed that the overall gradient stagger pin-fins arrangement shows optimal comprehensive performance among all patterns, achieving heat transfer enhancement ratio greater than 4 in contrast with smooth channel. Finally, the correlations of Nusselt number and apparent friction factor for patterns are established. This study provides feasible insights on the performance improvement of microscale liquid cooling technologies for thermal management of electronic devices.

A numerical investigation into thermo-fluid characteristics of pulsating jet impingement on a dimpled surface

A two-dimensional axisymmetric numerical model is employed to study the flow and heat transfer attributes of the pulsating air jet impingement on a dimpled surface. The results are compared with the steady jet impingement. The results are examined at a fixed Reynolds number of 5000, over a Strouhal number range of 0.1–0.5, and pulsation amplitude of 15% and 25% for three different nozzle-to-surface separations (z/d = 2, 6, and 10). The pulsation amplitude of 15% has a minor effect on heat transfer from the dimpled surface. However, at 25% pulsation amplitude, significant improvements in the heat transfer rates are obtained in many combinations of jet Strouhal number and jet surface spacing. The value of the optimum Strouhal number provides conditions for the maximum heat transfer rate, which varied with nozzle-to-surface separation distances. Combinations of higher separations and lower Strouhal numbers (and vice versa) produced optimum heat transfer among the cases considered in the present study. The maximum improvement (17.41%) in the average heat transfer over the steady jet was found at z/d = 10 for pulsation at St = 0.1, while at z/d = 6, St = 0.2 provides the highest heat transfer rate. It is urged that the vortices formed in pulse jet close to the natural frequency of vortex formation provide a conducive environment for the vortex growth and their existence, significantly affecting the jet entrainment, mixing, and jet spread, which eventually play the decisive factor in determining the overall heat transfer rates on the dimpled surface.

Thermo-fluidic characteristics of an aerodynamic swirl nozzle with low-concentration nanofluids

Thermo-fluidic characteristics of an aerodynamic swirl nozzle with low-concentration nanofluids

Effect of nucleation frequency and compressible buffer volume on the thermofluidic characteristics for flow boiling through a microchannel heat sink

A 1-D transient model of flow boiling in a rectangular microchannel is developed to assess the pressure drop and heat transfer characteristics, particularly emphasizing the impacts of nucleation frequency and compressible buffer volume. The combined influence of nucleation frequency with channel height, inlet velocity and heat flux is also studied. The increased nucleation frequency reduces the pressure drop amplitude and enhances the heat transfer coefficient. As the buffer volume is increased, the pressure drop and heat transfer coefficient are reduced due to the predominant occurrence of reverse flow in the channel. The amplitude and duration of reverse flow are identified as two important key parameters. As the reverse flow strongly affects the thermal-hydraulics of the channel, a sensitivity analysis is performed to assess the variation of these two key parameters over a range of operating conditions. The variation of amplitude and duration of reverse flow strongly depends on the trends of channel pressure drop, which is the consequence of the competing effects of bubble growth rate and reverse flow. Lastly, the effect of variable vapor properties on pressure drop and heat transfer characteristics of the channel has been discussed.

CFD Thermo-Hydraulic Evaluation of a Liquid Hydrogen Storage Tank with Different Insulation Thickness in a Small-Scale Hydrogen Liquefier

Accurate evaluation of thermo-fluid dynamic characteristics in tanks is critically important for designing liquid hydrogen tanks for small-scale hydrogen liquefiers to minimize heat leakage into the liquid and ullage. Due to the high costs, most future liquid hydrogen storage tank designs will have to rely on predictive computational models for minimizing pressurization and heat leakage. Therefore, in this study, to improve the storage efficiency of a small-scale hydrogen liquefier, a three-dimensional CFD model that can predict the boil-off rate and the thermo-fluid characteristics due to heat penetration has been developed. The prediction performance and accuracy of the CFD model was validated based on comparisons between its results and previous experimental data, and a good agreement was obtained. To evaluate the insulation performance of polyurethane foam with three different insulation thicknesses, the pressure changes and thermo-fluid characteristics in a partially liquid hydrogen tank, subject to fixed ambient temperature and wind velocity, were investigated numerically. It was confirmed that the numerical simulation results well describe not only the temporal variations in the thermal gradient due to coupling between the buoyance and convection, but also the buoyancy-driven turbulent flow characteristics inside liquid hydrogen storage tanks with different insulation thicknesses. In the future, the numerical model developed in this study will be used for optimizing the insulation systems of storage tanks for small-scale hydrogen liquefiers, which is a cost-effective and highly efficient approach.

Numerical investigation of mixed convection through an infrared-suppression (IRS) device

The flow through an infrared-suppression (IRS) device, installed on a warship, is often subject to various thermal regimes, including forced, natural, and mixed convection. When the ship becomes stationary/idle in the middle of a sea or in a port, mixed convection flow through the IRS device becomes noteworthy. In this paper, we numerically investigate the thermo-fluid characteristics through a cylindrical IRS device in mixed convection regime. Computations are performed for turbulent flow mixed convection with Richardson number in the range 0.1 ≤ Ri ≤ 10 to analyze the entrainment ratio (ER), flow field, and temperature variations in the IRS device. For a parametric study, dimensionless parameters such as nozzle-exit temperature, diameter ratio, nozzle protrusion, and funnel overlap are varied over the range of 1.91 ≤ T* ≤ 2.577, 1.05 ≤ DR ≤ 1.25, −1.5 ≤ NP ≤ 1.5, and − 22% ≤ OL ≤ 22% respectively. Temperature-dependent fluid properties are considered to obtain accurate results at higher temperature scales. The computed ER fairly agrees with the benchmark experimental results. With increase in Ri, the ER rises, whereas the actual mass suction diminishes. The centerline plume temperature at the exit of the IRS device is around 0.53 times the nozzle-exit temperature for Ri = 10, whereas it is almost identical at Ri = 0.1. The optimal Ri (=0.75) is obtained based on the maximum cooling efficiency. Finally, an empirical correlation for the ER is developed as a function of the above pertinent parameters.

Experimental Investigation of Thermo-Fluid Characteristics in Air Flow Through Corrugated Tubes with Various Configurations

Experimental Investigation of Thermo-Fluid Characteristics in Air Flow Through Corrugated Tubes with Various Configurations

Advancing Diffusion Bonded Compact Heat Exchangers for High Temperature Applications

Abstract Enhancement of the diffusion bonding process for the development of compact heat exchangers (CHXs) provides an energy efficient solution for high-temperature applications in advanced nuclear reactors and other technologies. However, available information is limited concerning the diffusion bonding (and manufacturing) of CHXs in high temperature applications and associated selection of bonded materials, bonding conditions, mechanical performance, and thermo-fluid characteristics. This article reviews the available knowledge and the ongoing research being conducted to address gaps in information and application.