Improved Heat Transfer Research Articles

INVESTIGATION OF FLOW AND HEAT TRANSFER PERFORMANCE OF GYROID STRUCTURE AS POROUS MEDIA

There are active and passive methods used to improve heat transfer. One of the passive methods is utilising porous media with high heat transfer surface area. Porous media are divided into two groups: regular and irregular structures. One of the regular structures is triply periodic minimal surfaces (TPMS), which have been studied quite frequently recently. In this study, heat transfer and flow analysis of a Gyroid geometry, one of the most used TPMS in the literature, is investigated numerically considering the conjugate heat transfer conditions. A single porosity is considered (ε = 0.6), and aluminium, ceramic and PLA are selected for the heat exchanger material to examine the temperature change in the heat exchanger. To understand the different flow characteristics, Reynolds numbers (Reh) are assumed to be 19.12, 95.61 and 172.09. The fluid inlet temperature is assumed to be constant at 298.15 K, and the initial temperature of the heat exchanger is assumed to be constant at 278.15 K to be consistent with the regenerative heat recovery temperature difference in ventilation standards. Nu numbers under different operating conditions are compared, and it is the ceramic material with low thermal diffusivity is at the highest level despite its low thermal conductivity. At the highest Re number, it provided approximately 6% better heat transfer than the aluminium heat exchanger.

Heat transfer analysis of nanofluid flow with entropy generation in a corrugated heat exchanger channel partially filled with porous medium

AbstractHeat exchanger research is mainly exploited to develop and optimize new engineering systems with high thermal efficiency. Passive methods based on nanofluids, fins, wavy walls, and the porous medium are the most attractive ways to achieve this goal. This investigation focuses on heat transfer and entropy production in a nanofluid laminar flow inside a plate corrugated channel (PCC). The channel geometry comprises three sections, partially filled with a porous layer located at the intermediate corrugate channel section. The physical modeling is based on the laminar, two‐dimensional Darcy–Brinkman–Forchheimer formulation for nanofluid flow and the local thermal equilibrium model for the heat equation, including the viscous dissipation term. Numerical solutions were obtained using ANSYS Fluent software based on the finite volume technique and the appropriate meshed geometries. The numerical results are validated with theoretical, numerical, and experimental studies. The simulations are performed for CuO–water nanofluid and AISI 304 porous medium. The coupled effects of porous layer thickness (δ), Reynolds number (Re), and nanoparticle fraction (φ) on velocity, streamlines, isotherm contours, Nusselt number (Nu), and entropy generation (S) are analyzed and illustrated. The simulation results demonstrate that heat transfer enhancement in clear PCC can be achieved using a porous layer insert. For the porous thickness range of [0.1–0.6], the corresponding range of average Nusselt number increase is [35.7%–176.9%], and the average entropy generation is [105.4%–771.9%]. The effect of the Reynolds number is more important in a porous duct than in a clear one. For δ = 0.4 and φ = 5%, the increase of Re in the range of [200–500] induces an increase in average Nusselt number in the range of [80.9%–108.4%] and average entropy in [222.9%–309.1%] comparatively to clear PCC. The effect of φ is practically the same for porous and clear channels. For φ = 5%, the increase on average Nu is about 9%, and entropy generation is 5%. Accordingly, important improvements in heat transfer in PCC can be achieved through the combined effect of flow Reynolds number and porous layer thickness.

3D printable phase change based thermal interface material with lower total thermal resistance at operating temperature

Thermal interface materials (TIMs) play a crucial role in addressing the heat dissipation challenges of electronic components, which needing high thermal conductivity and low thermal resistance to effectively improve heat transfer between chip and heat sink. This work focuses on the design of a 3D printable phase change based TIMs, which can be integrated with 3D printing technology to provide shapes suitable for quickly filling the gap between the chip and the heat sink in actual automated production. The optimized sample exhibits a total thermal resistance of 0.0012 m2K/W at operating temperature, with a through-plane thermal conductivity of 0.48 W/mK and an in-plane thermal conductivity of 1.24 W/mK. In practical thermal management, the resulting samples demonstrated a temperature reduction of 22 °C comparison with commercial TIM, highlighting its superior heat dissipation capability.

A parametric study on hydrogen storage in AB5 hydride alloys: Heat and mass transfer, thermodynamics, and design

The design of heat exchangers plays an important role in the performance of solid-state hydrogen storage devices. In this study, three different designs of hydrogen storage devices were investigated, incorporating phase change material (PCM), specifically, RT25HC into their walls in various shapes. A mathematical model, validated using previous experimental data, was employed to calculate heat and mass transfer and determine the reaction time period. The calculations were conducted using ANSYS Fluent, with a constant hydrogen supply pressure of 10 bars and a temperature of 295 K. The absorption properties of the storage reactor were investigated through various parameters such as liquid fraction, hydrogen concentration, and natural convection heat transfer coefficients. Results showed that the geometric structure and PCM distribution significantly impacted the performance of the hydrogen storage devices. Design 1, with a centralized PCM distribution, demonstrated moderate heat transfer rates and a longer reaction time. Design 2, featuring a more distributed PCM layout, improved heat transfer rates and reduced hydrogen kinetics time by 40%. Design 3, which optimized the geometric structure with advanced PCM shapes, achieved the highest heat transfer rates and improved hydrogen kinetics time by 50%. This design also enabled the storage of thermal energy at a high density, ranging from 10.2 J/g to approximately 190.5 J/g. The study provides critical information on the design of efficient solid hydrogen storage processes. The findings suggest significant potential for improved performance in industrial applications such as electric vehicles and domestic energy supply. The high efficiency of the large-scale reactor is due to its well-designed system, which effectively converts chemical energy into thermal energy. Optimizing the reactor geometry and PCM distribution is crucial for achieving superior hydrogen storage and retrieval performance.

Improving heat transfer performance in serpentine microchannel with carbon nanotube-embedded PVDF coating

This paper examines the impact of a polyvinylidene fluoride (PVDF) and carbon nanotube (CNT) hybrid coating on the heat transfer and hydraulic performance of serpentine microchannel heat sinks. In an aluminum serpentine microchannel heat sink using deionized water as the working fluid, the heat transfer performance and flow resistance were analyzed for different mass fluxes (G) in both PVDF-CNT coated (PSMC) and uncoated (TSMC) heat sinks under different heat flow densities. The results demonstrate that the PVDF-CNT coating enhances the heat transfer and hydraulic performance of the serpentine flow channel. Compared to the TSMC, the convective heat transfer coefficient of the PSMC increased by up to 61.9%, while the flow resistance coefficient decreased by up to 33.8%. The PVDF-CNT coating offers a superior balance of heat transfer performance and pressure drop compared to the addition of fins. A critical interval for the inlet mass flux G was identified, beyond which the heat transfer efficiency improvement of PSMC over TSMC was more pronounced.

Numerical investigation on heat transfer and pressure drop characteristics of Micro-Pillar array surface

The array surface structure can improve heat transfer efficiency and achieve large heat transfer area per unit of volume. In this study, a numerical simulation using CFD method was carried out to construct a dual-channel three-dimensional mathematical model with micro-pillar array surface. The characteristic of heat transfer and flow resistance for the arrayed surface structure have been studied. In addition, four different array configurations, including cylindrical, elliptical, quadrangular and herringbone, were considered to compare the thermal performance and flow behavior. The configuration with the best overall performance was obtained as cylindrical by comparison. The effects of different heights, arrangement methods and pitches on the system performance were analyzed. The velocity distribution on the array surface was also obtained. It is found that the cylindrical array structure has obvious advantages in overall performance, with more uniform surface velocity distribution and better overall performance at lower Re conditions.

Mitigation effects of lattice structure arrays on heat transfer deterioration of supercritical CO2

This study numerically investigates the suppression mechanism of heat transfer deterioration (HTD) of supercritical carbon dioxide (SCO2) in heated vertical channels with lattice structure arrays (LSA). The influences of lattice structure parameters on the velocity field, temperature field, heat transfer coefficient, buoyancy effect and flow acceleration effect are analyzed. The results demonstrate that compared to smooth channels, the tri-claw LSA can significantly reduce the maximum peak wall temperature by up to 57 K. The heat transfer coefficient substantially increases, and the fluid turbulent kinetic energy (TKE) quintuples. The vortex structures generated by lattice structures can enhance turbulence intensity and heat transfer, which effectively mitigates buoyancy effect and ultimately suppresses HTD. Increasing the lattice claws number can create more complex vortex structures, lengthening the lattice disrupts the laminar flow within the boundary layer, increasing the lattice diameter can produce a composite vortex that enhances the strength of flow mixing. An increase lattice number across the cross-section strengthens the suppression effect, but an excessive number may lead to instability. A dense lattice arrangement can continually suppress HTD, achieving an overall improvement in heat transfer within a certain range. This paper could support the design of heat exchangers in SCO2 Brayton cycles.

Experimental performance analysis of methanol adsorption in granular activated carbon packed bed through design of a double pipe heat exchanger with longitudinal fins

Activated carbon (AC) is essential for its exceptional adsorption properties and high surface area in various applications. Adsorption/desorption (A/D) processes with AC can be exothermic or endothermic, necessitating improved heat exchanger (HE) designs due to AC's low thermal conductivity. This study presents an A/D HE design with longitudinal fins in the sorption bed to enhance heat transfer during methanol A/D in AC. Bed heating/cooling uses water flowing through pipes inside the HE. Experimental investigations focus on thermal characteristics and A/D efficiency under diverse conditions, comparing results to a base non-finned HE design. Various experiments measured HE shell temperatures at different water flow rates while varying the sorption bed condition (vacuumed, filled with air, or methanol). The finned HE design showed a 1.8 °C increase in maximum bed surface temperature and a 3-h, 40-min reduction in process time compared to the non-finned HE. Subsequent tests with the finned HE at different water flow rates (5, 10, and 15 l/min) demonstrated superior heat transfer at 15 l/min due to turbulent flow enhancement. Additionally, adsorption ceased at a bed temperature of 54 °C. These findings highlight the efficacy of finned HE for optimizing methanol A/D processes, offering insights into improving heat transfer in AC-based systems.

An in‐depth comparative analysis of entropy generation and heat transfer in micropolar‐Williamson, micropolar‐Maxwell, and micropolar‐Casson binary nanofluids within PTSCs

AbstractSolar energy holds promise as a sustainable and environmentally friendly source of power. In this study, we focus on improving the thermal efficiency of parabolic trough solar collectors (PTSCs) by investigating the performance of three different binary micropolar nanofluids – micropolar‐Casson, micropolar‐Maxwell, and micropolar‐Williamson – when used as heat transfer fluids within these collectors, with engine oil as the base fluid. The problem studied revolves around enhancing the heat transfer characteristics within PTSCs, crucial for maximizing energy conversion efficiency in solar power generation. By exploring the behavior of these nanofluids under various flow conditions, we aim to optimize the design and operation of PTSC systems for improved performance and sustainability. The importance of this research lies in its potential to significantly enhance the efficiency of solar energy harvesting, thereby contributing to the transition toward cleaner energy sources and reducing dependence on fossil fuels. Additionally, the findings have implications for diverse applications, including solar aviation, solar‐powered maritime vessels, solar thermal power plants, industrial process heating, and solar‐driven water pumping mechanisms, where improved heat transfer efficiency is paramount for enhancing overall system performance and reducing operational costs. Furthermore, the investigation delves into the influence of various factors governing the flow of these binary micropolar nanofluids within PTSC setups, including aspects such as velocity, thermal characteristics, entropy generation, skin friction, drag force, and local Nusselt number. The results notably reveal substantial enhancements in thermal efficiency, with maximal relative enhancements quantified as 22.1768%, 19.3662%, and 17.7349% for micropolar‐Casson, micropolar‐Maxwell, and micropolar‐Williamson nanofluids, respectively.

A detailed thermohydraulic performance assessment of surface-modified silver nanofluids in turbulent convective heat transfer

This study investigates the thermohydraulic performance of surface-modified silver nanofluids in turbulent convective heat transfer applications. The primary objective is to evaluate the impact of citrate, lipoic acid, and silica surface modifications on heat transfer coefficients, pressure drops, and friction factors under turbulent flow conditions. Silver nanoparticles (50 nm) with the specified surface modifications were synthesized and dispersed in deionized water, ensuring stable nanofluid preparations. Experimental evaluations were conducted in a smooth brass tube with a uniform heat flux, covering Reynolds numbers from 3400 to 21,800, mass flow rates of 32 to 78 g s−1, and inlet temperatures of 26 °C, 31 °C, and 36 °C. Key findings indicate that the silica-shelled nanofluid (Ag/S) exhibited a significant 35% increase in the heat transfer coefficient compared to DI water, while citrate-coated (Ag/C) and lipoic acid-coated (Ag/L) nanofluids showed slight decreases of 0.2% and 2%, respectively. The mean Nusselt number for Ag/S also increased by 9%, demonstrating enhanced heat transfer capabilities. Surface-modified nanofluids experienced higher pressure drops and friction factors than the base fluid. Ag/C showed a 7.7% increase in pressure drop, Ag/L a 12.3% increase, and Ag/S a 12.5% increase, correlating with an 11.9% rise in viscosity. While surface-modified silver nanofluids, particularly silica-shelled, can significantly improve heat transfer performance, the associated increases in pressure drops and friction factors must be carefully balanced for specific applications. Future research should explore long-term stability, varying nanoparticle concentrations, and more complex geometries to optimize nanofluid formulations for targeted heat transfer applications.

Mass transfer and RTD studies in 3D printed serpentine and wavy serpentine millireactor

This study investigates the performance of serpentine and wavy serpentine millireactors. Millireactors, with their microscale features, offer advantages such as heightened surface-to-volume ratio, improved heat transfer coefficients, and reduced mass transfer pathways. The serpentine and wavy serpentine millireactors, characterized by their channel structures, demonstrate superior energy efficiency, reaction speed, and scalability compared to conventional reactors. The focus of this research is on understanding the mass transfer rates and residence time distribution (RTD) in these millireactors, crucial for optimizing their design and operation. The residence time distribution studies providing insights into the mixing characteristics and overall flow behavior. The (RTD) data was fitted to different models. Mass transfer studies examine the movement of acetic acid between aqueous and organic phases, with the volumetric mass transfer coefficient (KLa) as a key parameter. Results from the serpentine millireactor indicate a partially mixed flow behavior with a dispersion number of 0.611, while the wavy serpentine millireactor exhibits a dispersion number of 0.130, indicating improved mixing efficiency. The mass transfer studies yield KLa values in the range of 0.31–1.42 min−1 and 0.49–2.71 min−1 for serpentine and wavy serpentine millireactors, respectively. Efficiency assessments reveal 72.31% and 83.21% for serpentine and wavy serpentine millireactors, respectively. The study concludes that the use of serpentine and wavy serpentine millireactors represents an effective method for process intensification, offering valuable insights for chemical engineering and process optimization applications. The results contribute to advancing the millireactor technology and its potential in continuous flow chemical manufacturing.

Enhancing thermal-hydraulic performance in heat exchangers with metal foam inserts: a comprehensive experimental investigation

ABSTRACT This research investigates the use of metal foam inserts to enhance the thermal-hydraulic performance of double-tube heat exchangers, relevant for energy-efficient systems such as solar flat plate collectors. Motivated by the need for improved heat transfer efficiency, this study hypothesizes that metal foam integration can significantly boost performance. Through systematic experimental study, the impact of metal foam inserts on heat transfer and pressure drop characteristics is comprehensively evaluated across various configurations, spanning horizontal and vertical orientations. Experimental evaluations were conducted on four configurations, including both conventional and metal foam-integrated heat exchangers in horizontal and vertical orientations, using water as the working fluid and Nickel metal foam with 0.9 porosity and 10 PPI in the annular space. The findings highlight significant enhancements in heat transfer performance with metal foam integration across both horizontal and vertical heat exchanger configurations compared to conventional counterparts, particularly showcasing superior effectiveness and efficiency in the horizontal configuration. Results show that metal foam integration substantially enhances heat transfer, with horizontal configurations exhibiting a 14.56% higher heat transfer coefficient than vertical ones. Additionally, the comprehensive performance index improved by 1.17 times, indicating a better balance between heat transfer enhancement and pressure loss. These findings were validated against established correlations from the literature, confirming the superior effectiveness of horizontal metal foam heat exchangers.

Effects of mass ratio and rotation speed on flow induced vibration of a rotating cylinder with two degrees of freedom

Rotating cylinders submerged in the fluid have many practical applications such as offshore wind turbines and drilling pipes. These rotating cylinders are usually subjected to vortex-induced vibrations, and heat transfer has a great effect on their efficiency. Therefore, it is very important to investigate the heat transfer from the rotating cylinder undergoing vortex-induced vibrations. The present study investigates the flow-induced vibration (FIV) of a rotating circular cylinder, along with the related convective heat transfer, for various mass ratios (mr), rotating rates (α), and a range of reduced velocity (3.0 ≤ ur ≤ 15). The cylinder is modeled as a two-degree-of-freedom system, whereby it is free to oscillate both in the streamwise and transverse directions. The results indicate that the rotational motion of the cylinder significantly enhances the cylinder's displacements in both directions. Furthermore, the displacement amplitude in both directions decreases with an increase in mr. For higher reduced velocities, the displacement amplitude becomes constant. Also, it is observed that increasing mr leads to an improvement in heat transfer for high reduced velocities. Also, the maximum value of the Nusselt number is 15.25 for the non-rotating cylinder and 14 for the rotating cylinder with α=1. The FIV of a rotating circular cylinder exhibits several vortex patterns, including 2S, 2P, P + S, and 2T.

Large eddy simulations of flow over additively manufactured surfaces: Impact of roughness and skewness on turbulent heat transfer

Additive manufacturing creates surfaces with random roughness, impacting heat transfer and pressure loss differently than traditional sand–grain roughness. Further research is needed to understand these effects. We conducted high-fidelity heat transfer simulations over three-dimensional additive manufactured surfaces with varying roughness heights and skewness. Based on an additive manufactured Inconel 939 sample from Siemens Energy, we created six surfaces with different normalized roughness heights, Ra/D=0.001,0.006,0.012,0.015,0.020, and 0.028, and a fixed skewness, sk=0.424. Each surface was also flipped to obtain negatively skewed counterparts (sk=−0.424). Simulations were conducted at a constant Reynolds number of 8000 and with temperature treated as a passive scalar (Prandtl number of 0.71). We analyzed temperature, velocity profiles, and heat fluxes to understand the impact of roughness height and skewness on heat and momentum transfer. The inner-scaled mean temperature profiles are of larger magnitude than the mean velocity profiles both inside and outside the roughness layer. This means, the temperature wall roughness function, ΔΘ+, differs from the momentum wall roughness function, ΔU+. Surfaces with positive and negative skewness yielded different estimates of equivalent sand–grain roughness for the same Ra/D values, suggesting a strong influence of slope and skewness on the relationship between roughness function and equivalent sand–grain roughness. Analysis of the heat and momentum transfer mechanisms indicated an increased effective Prandtl number within the rough surface in which the momentum diffusivity is larger than the corresponding thermal diffusivity due to the combined effects of turbulence and dispersion. Results consistently indicated improved heat transfer with increasing roughness height and positively skewed surfaces performing better beyond a certain roughness threshold than negatively skewed ones.

Bioconvective variable viscosity flow of Carreau nanofluid with external heat source and nonlinear radiation: Analysis with convective heat and mass constraints

In this study, an unsteady model for Carreau nanofluid with microorganism decomposition is developed. The viscosity and thermal conductivity of the Carreau nanofluid are considered variable. Magnetic and porosity effects are included using a magneto-porosity parameter. An additional heat source is introduced to improve heat transfer. Nonlinear analysis is applied for radiative applications. The flow is modeled using an oscillatory stretching surface. Convective mass and heat constraints are used to analyze the problem. Analytical computations are performed on the developed model. The significance of various parameters for the thermal problem is discussed. The results may enhance the performance of transport problems, heat transmission, energy systems, and thermal devices.

Optimal Design Of The Concentric Annulus For The Solar Collectors And Energy Storage

Heat exchangers with uniform heating ensure even heat distribution, improving heat transfer efficiency and lowering thermal stress. It contributes to increasing the effectiveness of solar energy conversion into thermal energy in solar collectors, improving system performance and sustainability. It is essential for enhancing performance in both home and industrial applications because of these advantages. An experimental investigation was conducted to study the natural convective flow between two isothermal concentric cylinders filled with porous media (silica sand) and equipped with annular fins attached to the inner cylinder. The fins varied in length (Hf = 3, 7, and 11 mm), and the radius ratios (Rr) between the cylinders were also considered during the study. This work examines and discusses the effects of independent characteristics, such as fin height (Hf), radius ratio (Rr), and Rayleigh number (Ra) from 10 to 500, on heat transfer outcomes. As the distance between the two cylinders expands, the average Nu remains relatively constant for low values of Ra. However, as Ra approaches 100, the average Nu increases. These values also rose when Rr decreased for the hot cylinder and vice versa for the cold cylinder. The average Nusselt number versus Ra was analyzed in graphical form to show the effect of the fin number on the average Nusselt number. The analysis includes a range of fin numbers. It is found that as the amount of fins increases from n = 12 to n = 23 and eventually to n = 45, there is a decrease in the average Nusselt number. The decrease in average Nusselt number can range from 19.2% to 26.6% for the same value of Ra.

Two-phase analysis of heat transfer of nanofluid flow in a wavy channel heat exchanger: A numerical approach

The heat transfer improvement by using CuO/water nanofluid (NF) in a wavy channel is evaluated numerically using the turbulent two-phase mixture and the κ - ε models. The numerical work is a 2-dimensional model created and analyzed in Gambit and Ansys Fluent software, respectively. The flow Reynolds (Re) numbers of 8000 – 40,000, wavelength ranging from 0 – 0.4 m, and solid volume fraction (SVF) of 0 % to 4 % are investigated. In all cases, a constant heat flux of q′′=5000 W/m2 is applied on the outer surface of the heat exchanger. The heat transfer and fluid flow were analyzed by the flow visualization method and heat transfer evaluation indexes. The results show that by increasing the Re number, the vortices increase and more turbulence are generated in the vicinity of the waves near the channel inlet. As the amplitude of the channel waves increased, the velocity at the top of the wave increased, and the resulting pressure gradient behind the wave is intensified and the reverse flow is generated. The improving effect of using NF is more prominent where the effect of other enhancing factors is weak. For wall amplitude of 0.1 m, by increasing the SVF from 1 – 4 % the average Nu number (Nuavg) increased by 35 % and 22 % in Re = 8,000 and 40,000, respectively.

A Comprehensive Evaluation of Recent Studies Investigating Nanofluids Utilization in Heat Exchangers

This comprehensive review critically examines recent research concerning the application of nanofluids in heat exchangers. The utilization of nanofluids, which are colloidal suspensions of nanoparticles in a base fluid, has garnered significant attention in enhancing heat transfer performance. Various studies have explored the potential benefits and challenges associated with incorporating nanofluids into heat exchanger systems. Through a systematic analysis of recent literature, this review assesses the effectiveness of nanofluids in improving heat transfer efficiency and overall performance of heat exchangers. Key parameters such as nanoparticle concentration, size, and type are thoroughly evaluated to understand their influence on heat transfer characteristics. Additionally, factors such as stability, flow behavior, and thermal conductivity enhancement are scrutinized to provide a comprehensive understanding of nanofluid behavior in heat exchangers. The review also addresses potential limitations and areas requiring further investigation to optimize the utilization of nanofluids in heat exchanger applications. By synthesizing recent findings, this review aims to contribute to the advancement of knowledge in the field of heat exchanger technology and nanofluid applications. Ultimately, the insights provided in this review offer valuable guidance for researchers and engineers seeking to enhance heat transfer processes through the implementation of nanofluid-based heat exchangers. Nanofluids offer advantages like enhanced thermal conductivity and tailored properties, promising optimized heat exchanger designs, leading to energy efficiency and reduced costs. However, challenges remain, such as nanoparticle dispersion and cost-effectiveness, necessitating further research for refinement. Interdisciplinary collaboration is crucial for advancing nanofluid applications, fostering innovation to meet demands for sustainable heat transfer solutions.

Heat transfer and visualization of flow boiling on nanowire surfaces in the microchannel

Enhancing heat transfer efficiency is crucial in heat exchange equipment. Although previous studies have focused on developing micro/nano-structured surfaces, further exploration into how surface structure can improve heat transfer efficiency (H) by altering bubble dynamics is still needed. This study aimed to innovatively analyze the impact of titanium carbide (TiC) nanowire heights—specifically 4 µm and 12 µm—on boiling heat transfer performance. Conducted under varying heat flux (Q) (50–200 W/m2) and mass flux (G) (200–300 kg/m2·s), our experiments assessed H, pressure drop (P), and local boiling curves. Using a high-speed camera, we observed complex periodic flow patterns on the 4 µm nanowire surface, including elongated bubble formation, expansion, local dryout, and subsequent fluid rewetting. Results showed that the 12 µm nanowire surface increased H by up to 19.84 % in single-phase conditions, while the 4 µm nanowire surface increased H by up to 27.9 % in two-phase conditions. These findings highlight the significant role of nanowire length and arrangement in optimizing boiling heat transfer performance. This work lays a foundation for further investigations into diverse nanowire materials and configurations.

Numerical study on a new spiral fin heat Exchanger's thermal-hydraulic performance

This study presents a numerical investigation of a novel spiral finned heat exchanger (SFHE). The primary objective is to optimize the heat transfer efficiency of micro gas turbine recuperators by employing a spiral fin model. Through computational simulations (CFD), the study examines the variations in the Colburn j factor and Fanning friction f factor as the spiral fins alter. The results demonstrate that the SFHE exhibits superior heat transfer capacity and overall heat transfer performance compared to wavy fin models. At a Reynolds number of 1000, the JF factor of the spiral fin 35_125 is 70.47 % higher than that of a wavy fin at the same Reynolds number, and 34.03 % higher when the Reynolds number increases to 5000. The study also reveals that the cutting thickness of the top and bottom, denoted as C1, does not significantly impact the variable j, f. However, increasing the cut thickness C2 on the left and right sides results in a more compact model, leading to higher values of f, but the j-factor is almost unchanged. While decreasing the wavelength of the spiral fins can improve heat transfer efficiency, it also increases pressure loss, necessitating careful selection of wavelength for optimal SFHE design.