Maximum Heat Transfer Research Articles

Performance improvement in a heat exchanger tube using discrete X–V baffle (DXVB) turbulators

Thermal performance improvement in a heating tube (HT) using discrete X–V baffle (DXVB) as turbulators is presented. The DXVB is designed with three main goals: 1. To decrease the pressure drop in the tested tube and 2. To increase the mixing quality in the heat exchanger tube and 3. To produce powerful vortex flows. Lower pressure drop, generated vortex flows and higher mixing quality will augment a heat transfer rate and thermo-hydraulic efficiency. This study examines effects of DXVB structures, DXVB distances and placements on laminar air flow and thermal structure with Reynolds number from 100 to 2000. The current problem is numerically investigated using the finite volume technique of a commercial program/code (ANSYS-FLUENT V.2022). The created model of the HT fitted with the DXVB is numerically validated. From the numerical results, the DXVB installed affects the air flow structure in the tested tube. The vortex streams are observed. The change in fluid flow influences thermal characteristics. The vortex streams destroy some parts of the thermal boundary layer and help to increase mixing quality. These perturbed thermal boundary layer (TB-layer) and better mixing quality are two important factors that contribute to convective heat transfer enhancement. In addition, the maximum heat transfer rate and pressure loss are 10.17 and 45.75 times upper than that in the circular plain tube, respectively, while the best thermal enhancement factor (TEF) of 3.09 is observed at 15b5g, +x at Re = 2000.

Numerical study on mixed convection heat transfer of copper-water nanofluid in a porous cavity with an isothermal solid block in local thermal non-equilibrium

This manuscript reports a numerical study on mixed convection heat transfer of Cu-water nanofluid in a porous cavity with an isothermal solid block in the state of local thermal non equilibrium. The set of governing equations are solved by finite volume method combined with SIMPLE algorithm. Through streamlines and isothermal contour plots as well as the average Nusselt number, the impact of various parameters like the nanoparticle concentration, Richardson number, Darcy number, and inter phase heat transfer coefficient is highlighted. The main findings indicate that the Local thermal non-equilibrium state (H = 1, 10) produces the maximum heat transfer rate than the local thermal equilibrium state (H = 1000).

Enhanced heat transmission in a triangular enclosure with a rotating cooled wall using Nano-Encapsulated Phase Change Material nanofluid under mixed convection

Maximizing heat transfer rates within enclosed cavities is of paramount importance in various engineering applications. This study focuses on enhancing heat transmission efficiency through forced convection within a triangular cavity containing a rotating cylinder. The approach involves incorporating Nano-Encapsulated Phase Change Material (NEPCM), applying a uniform magnetic field, and introducing a cold, dynamically rotating cylinder. The cavity's configuration maintains an elevated temperature on the upper wall while the inclined side walls remain cold. The investigation also explores the impact of varying the position of the rotating cylinder within the cavity. Mathematical modeling is undertaken using the Galerkin finite element methodology. Numerical results reveal a direct proportionality between the Nusselt number (Nu) and the Darcy number (Da), as well as an inverse proportionality between Nu and the Hartmann number (Ha). Elevating the Darcy number from 10−5 to 10−2 leads to a 54% increase in the Nusselt number, while increasing the Hartmann number from 0 to 100 results in a 12.5% decrease in Nu. Intriguingly, positioning the cold rotating cylinder in the upper enclosure leads to a 240% enhancement in Nu. This study highlights the intricate interplay of geometry and external fields in optimizing heat transfer within complex cavities.

Constructal Solid and Perforated Fin Installation in a Combined Microchannel Heat Sink for Maximum Heat Transfer

Constructal Solid and Perforated Fin Installation in a Combined Microchannel Heat Sink for Maximum Heat Transfer

Eksperimentalno ispitivanje performansi ključanja u bazenu na hibridnim površinama

The issue of excessive heat generation is present in the current electrical gadgets. Consequently, the task at hand is to devise a novel and effective cooling mechanism for them. To disperse the heat produced, the pool boiling method may provide a high heat transfer coefficient. The performance of the pool boiling process on the microchannel surfaces using saturated deionized water at atmospheric pressure has been experimentally investigated in this work. To examine the impact of coating deposited on the microchannel surface, ten surfaces were utilized. Four hybrid surfaces were manufactured: CNT (1 g), (CNT-GNPs (1:0.5) g), (CNT-GNPs (1:1) g), and (CNT-GNPs (1:1.5) g) on a rectangular micro-channel with 0.2 mm fin width, 0.4 mm channel depth and 0.8 mm channel width. Four plain surfaces were coated with the same material and concentrations mentioned above. And, for comparison, one microchannel surface of same dimension mentioned above and one bare plain surface were used. The results revealed that the hybrid surface with high concentration resulted in a higher performance. The maximum critical heat flux (CHF) augmentation is 125.5%, while the maximum heat transfer coefficient (HTC) enhancement is 312%. The outcomes are contrasted with previous work and have a good agreement.

DEVELOPMENT OF HEAT EXCHANGER WITH TWO-PASS DIVERGING MICROCHANNELS FOR EVAPORATION COOLING SYSTEMS

This study developed a two-pass diverging microchannel heat exchanger to avoid flow reversal and partial dry out of HFC-245fa flow boiling in the evaporation cooling systems. It is aimed to improve the diverging microchannel heat exchangers designed by previous studies and to effectively accommodate diverging channels on a limited heating base surface. The test results showed that the maximum heat transfer coefficients in a diverging channel heat exchanger were as much as 20% higher than those in straight channel heat exchanger, while the maximum partial dry-out heat flux is 42% higher in diverging channel heat exchanger. There is no significant difference for the pressure drops in two heat exchangers at low heat fluxes before it reached the partial dry-out condition. For higher flux, the pressure drops in straight channels were higher than those in divergent channels while partial dry out. It is concluded that the two-pass diverging channel design provided higher maximum heat transfer coefficients and higher maximum heat fluxes with lower penalties of pressure drops. It could be a good design to replace the conventional straight channel heat exchanger for evaporation cooling systems.

Effects of Nanoparticle Size on Natural Convection Pattrns of Nanofluids with the Lattice Boltzmann Method

In this work, numerical simulation of natural convection of nanofluids within a square enclosure were investigated by using the non-dimensional lattice Boltzmann method (NDLBM). The effects of key governing parameters Knudsen number ($10^{-6} \le Kn_{f,s} \le 10^4$), Rayleigh number ($10^3 \le Ra_{f,L} \le 10^6$), and nanoparticle volume fraction ($10^{-2} \le \phi_s \le 10^{-1}$) on the heat and mass transfer of nanofluids were discussed. The results show that in the low $Ra_{f,L}$ conductive domited regime, the nanoparticle size has little effect on heat transfer, whereas in the high $Ra_{f,L}$ convective dominated regime, larger nanoparticle sizes significantly enhance flow intensity and heat transfer efficiency. As fixed $Ra_{f,L}$ and $\phi_s$, the heat transfer patterns change from conduction to convection dominated regimes with increasing $Kn_{f,s}$. The influence of nanoparticle volume fraction was also investigated, and in convection dominated regime, the maximum heat transfer efficiency was achieved when $\phi_s = 8 \%$, balancing both thermal conduction and drag fore of nanofluids. Additionally, by analyzing the full maps of mean Nusselt number ($\overline {Nu}_{f,L}$) and the enhancement ratio related to the base fluid ($Re_{n,f}$), the maximum values of $\overline {Nu}_{f,L}$ and $Re_{n,f}$ occur when the nanoparticle size is $Kn_{f,s} = 10^{-1}$ for both conductive and convective dominated regimes. To capture the effects of all key governing parameters on $\overline {Nu}_{f,L}$, a new empirical correlation has been derived from the numerical results, providing deeper insights into how these parameters influence heat transfer performance.

Thermo-hydraulic performance investigation of double pass solar air heater integrated with PCM-based thermal energy storage

The solar air heater (SAH) is one of the ways to utilize solar energy for the purpose of drying, greenhouse heating and air conditioning. However, the SAHs are unable to deliver reliable thermo-hydraulic performance as a result of the intermittent nature of solar energy and the low convective heat transfer coefficient. Thus, in the present study, a three-dimensional numerical investigation is performed to study the thermo-hydraulic performance of the double pass solar air heater (DPSAH) having semi-cylindrical PCM tubes and perforated baffles as roughness geometry. The parameters selected for this study include baffle height ratio (eb/H) from 0.4 and 0.8, tube radius ratio (rt/H) from 0.2 and 0.5, and Reynolds numbers (Re) from 3000 and 13,000. Experimental validation has been conducted to verify the numerical results, and it has been found to be well-validated with mean absolute errors of 6.5 % and 1.2 % for the Nusselt number (Nur) and friction factor (fr), respectively. The maximum Nusselt number (Nur) is found to be 200.08 at Re of 13,000, while the maximum friction factor (fr) is measured to be 0.6290 at Re of 3000, which corresponds to eb/H of 0.8 and rt/H of 0.3. The maximum heat transfer enhancement (Nur/Nus) in comparison to the smooth duct is found to be 5.08 times with a maximum friction factor increment (fr/fs) of 65.80 times, which corresponds to eb/H of 0.8, Re of 13,000 and rt/H of 0.3. The maximum thermo-hydraulic performance parameter (THPP) is observed to be 1.83 at Re of 13,000, rt/H of 0.2 and eb/H of 0.4. This study contributes to the design and optimisation of SAHs by incorporating thermal energy storage and roughness geometries.

Maximizing heat transfer and minimizing entropy generation in concentric cylinders with CuO[sbnd]MgO[sbnd]TiO2 nanoparticles

Heat transfer is crucial because it has industrial uses. A novel type of nanofluids dubbed “ternary nanofluid” is being utilized to boost the ability of conventional fluids to transmit heat since it has a greater heat transfer capacity than solo and hybrid nanofluids. This work investigates the heat transfer capabilities and entropy generation in the cylindrical flow of a ternary nanofluid in the presence of a magnetic field. Minimizing the entropy generation and maximizing the heat transfer of a fluid using ternary nanoparticles (CuOMgOTiO2) is the aim of this work. The finite difference method is used by the MATLAB computer program to solve the problem numerically. The results reveal that the entropy generation minimizes in the presence of CuOMgOTiO2. The heat transfer rate of the fluid increased by 9.9%, 10.8%, and 11.2% on adding TiO2, MgOTiO2, and CuOMgOTiO2 nanoparticles, respectively.

Convective heat transport and entropy generation in butterfly-shaped magneto-nanofluidic systems with bottom heating and top cooling

PurposeThe purpose of this study is to carry out a comprehensive analysis of magneto-hydrodynamics (MHD), nanofluidic flow dynamics and heat transfer as well as thermodynamic irreversibility, within a novel butterfly-shaped cavity. Gaining a thorough understanding of these phenomena will help to facilitate the design and optimization of thermal systems with complex geometries under magnetic fields in diverse applications.Design/methodology/approachTo achieve the objective, the finite element method is used to solve the governing equations of the problem. The effects of various controlling parameters such as butterfly-shaped triangle vertex angle (T), Rayleigh number (Ra), Hartmann number (Ha) and magnetic field inclination angle (γ ) on the hydrothermal performance are analyzed meticulously. By investigating the effects of these parameters, the authors contribute to the existing knowledge by shedding light on their influence on heat and fluid transport within butterfly-shaped cavities.FindingsThe major findings of this study reveal that the geometrical shape significantly alters fluid motion, heat transfer and irreversibility production. Maximum heat transfer, as well as entropy generation, occurs when the Rayleigh number reaches its maximum, the Hartmann number is minimized and the angle of the magnetic field is set to 30° or 150°, while the butterfly wings angle or vertex angle is kept at a maximum of 120°. The intensity of the magnetic field significantly controls the heat flow dynamics, with higher magnetic field strength causing a reduction in the flow strength as well as heat transfer. This configuration optimizes the heat transfer characteristics in the system.Research limitations/implicationsFurther research can be expanded on this study by examining thermal performance under different curvature effects, orientations, boundary conditions and additional factors. This can be accomplished through numerical simulations or experimental investigations under various multiphysical scenarios.Practical implicationsThe geometric configurations explored in this research have practical applications in various engineering fields, including heat exchangers, crystallization processes, microelectronic devices, energy storage systems, mixing processes, food processing, air-conditioning, filtration and more.Originality/valueThis study brings value by exploring a novel geometric configuration comprising the nanofluidic flow, and MHD effect, providing insights and potential innovations in the field of thermal fluid dynamics. The findings contribute a lot toward maximizing thermal performance in diverse fields of applications. The comparison of different hydrothermal behavior and thermodynamic entropy production under the varying geometric configuration adds novelty to this study.

Micro/nanostructuring of metal additively manufactured aluminum alloy for enhanced pool boiling of dielectric fluids

Surface micro/nanotextures have the potential to increase bubble nucleation and promote capillary liquid wicking to enhance pool boiling heat transfer significantly. Despite past studies implementing surface micro/nanofabrication strategies to enhance boiling, the role of structure length scale and morphology on boiling heat transfer coefficient (h) and critical heat flux (CHF) of low-surface-tension dielectric fluids remains unclear. In this study, we systematically tune the surface microstructures on additively and conventionally manufactured aluminum alloys (AM AlSi10Mg and Al6061) from 1 µm to 5 µm to study the influence of microstructure length scale on boiling performance. In addition, to further understand the effect of submicron structures on boiling, nanostructures of 300 nm length were generated on a plain AM surface and hierarchically incorporated atop the microstructures. Dielectric fluid, HFE-7100, was used to investigate the effects of surface morphology on pool boiling heat transfer coefficient (h) and critical heat flux (CHF). Our results show that the 5 µm microstructured AM surface, AM-H(400)E(5), attained a CHF of 19.44 W/cm2 and a maximum heat transfer coefficient (hmax) of 2.89 W/cm2·K, which represents a reduction in CHF of 28.5 % and an enhancement in hmax of 103.8 %, as compared to the plain Al6061 surface. In addition, AM-H(400)E(5) achieved a large enhancement ratio of 2.2 as compared to the plain Al6061 at a heat flux of 20 W/cm2, and the highest h value amongst all structured surfaces, indicating its cavity size is optimal for bubble nucleation. Through the systematic tuning of micro/nanostructures length scale and morphology, this study found that the micro/nanostructures of 1 µm size and below are too small to serve as bubble nucleation sites. Additionally, micro/nanostructure wickability plays a negligible role in affecting pool boiling performances of highly wetting dielectric fluids, while surface morphology plays a dominant role in bubble nucleation to enhance boiling. Lastly, high-speed immersion microscopy was performed to understand the effects of micro/nanostructures on bubble characteristics such as bubble departure diameter and growth period. In summary, this work not only reports the first micro/nanostructured AM surfaces utilizing scalable fabrication techniques for enhanced boiling, but it also demonstrates the potential of tunning the micro/nanostructure length scale to optimize the bubble nucleation site density, resulting in significantly improved pool boiling performances.

Development of Electrodeposited Hierarchical Dendritic Wick Structure for Ultra-Thin Vapor Chamber Applications

Compact and light-weight electronic systems have posed stringent dimensional criteria for heat-dissipation components such as heat pipes and vapor chambers. An ultra-thin vapor chamber (UTVC) with an overall thickness below 1 mm requires an interior capillary wick structure less than 100 μm. The capillary wick layer provides a flow path for fluid circulation in an operational UTVC. The maximum UTVC heat transfer rate normally depends on liquid permeability (K) and capillary pressure (∆P) of the wick structure. Large K and ∆P values are rarely realized in typical homogeneous porous structure. In this study, a novel hierarchical dendritic copper wick was prepared to achieve large K and ∆P simultaneously by one-step electrodeposition and thermal sintering process. The effects of electrodeposition parameters, such as current density, deposition time, and solution conditions on the capillary performance of the dendritic copper wicks were investigated. The results indicate that the wicking capability is modulated by the dendritic morphology of Cu deposits. Moreover, a post-deposition sintering process can improve further the structural integrity of the Cu dendrites and the capillary performance of the electrodeposited wicks. An optimal dendritic copper wick of 30 μm in thickness possesses a promising capillary performance K/R eff of 0.811 μm, which is the thinnest wick reported in the literature.

Enhancement of pool boiling performance through an asymmetric dual V-groove microchannel structured surface

In pool boiling, microchannels on the heated surface change the bubble dynamics and consequently improve the heat transfer. In this study, two new microchannel configurations, i.e., asymmetric dual V-groove microchannels (VM) and orthogonally intersecting asymmetric dual V-groove microchannels (OIVM) have been introduced to study enhancement in pool boiling. The heat transfer enhancement due to the modified surfaces was established by comparing the heat transfer rates from the reference flat surface. Experiments have been performed using deionized water under saturation temperature at one atmosphere to evaluate the steady state heat transfer characteristics. The bubble dynamics and interface morphology at various heat flux levels have been captured using high-speed camera. The experimental observations have revealed that both the microchannel configurations exhibit a substantial improvement in heat transfer compared to that of flat surfaces. The OIVM surface demonstrates the highest rates of heat transfer and increase of 5.3 times in the maximum heat transfer coefficient (HTC) and 2.4 times in the critical heat flux (CHF) were observed compared to that of flat surfaces. Similarly, the VM surface demonstrates an improvement of 2.2 fold in HTC and 1.7 fold in CHF compared to the flat surface. Moreover, the OIVM surface demonstrates better heat transfer rates than that of modified surfaces investigated in the past studies. The increased heat transfer rate with the OIVM surface can be ascribed to large area for heat exchange, increased bubble initiation sites, bubble motion promoted macroconvection and efficient rewetting mechanism.

Tailoring Substrate Topography to Enhance Wicking Performance of Electrodeposited Cu Porous Films

Porous metallic films have received emerging interests in the fields of catalysts, fuel cells, lithium batteries, and phase-change heat transfer devices. Substrate topography is known to have a strong impact on adhesion and morphology of porous coating layers prepared by electrodeposition. In this study, we have tailored the topography of a Cu substrate by wet etching in a sodium persulfate/sulfuric acid (SPS) solution prior to electrodeposition of porous Cu films. An analytic approach is proposed to quantitatively analyze nucleation and growth of dendritic Cu deposits on the SPS-treated Cu substrates. Such a dendritic porous Cu film can serve as a capillary wick to complete recirculation of condensed liquid in the phase-change heat transfer devices. The maximum heat transfer rate of a heat pipe or vapor chamber indeed is proportional to the capillary performance (K/Reff ) of the wick structure, where K and Reff stand for liquid permeability and effective pore radius of the wick, respectively. A large K/Reff value of 0.975 µm has been attained for the electrodeposited dendritic Cu film on a Cu substrate with an optimal SPS etching treatment. The influence of dendritic deposits on the wicking performance of the electrodeposited Cu film is investigated. Figure 1

Two-phase flow condensation heat transfer characteristics of R-134a inside three-dimensional cylindrical micropillar enhanced tube

This paper presents an experimental investigation for evaluation of heat transfer coefficient, frictional pressure drops and flow regimes with their transitions during the condensation of R-134a inside a smooth, two microfins (MF1 and MF2) and a newly developed micropillar (MP) tubes. The experiments are carried out for a range of mass flux at an average saturation temperature of 35°C. Micropillar tube has produced the maximum heat transfer coefficient, while the microfin (MF1) tube resulted the highest frictional pressure gradient compared to other tubes. The experimental observations of microfin and micropillar tubes are plotted on the mass flux versus vapor quality flow map and Taitel and Duckler flow map to discuss the transitions within different flow patterns achieved. Visual inspection of the flow regimes with varying mass flux and vapor quality showed stratified-wavy, intermittent, and annular flow regimes. The occurrence of annular flow is found to be more in MF1 and MP tube. A performance evaluation factor (PEF) is defined to evaluate the thermal-hydraulic performance of the tubes. Using the same, it has been observed that the newly developed MP tube has a PEF value greater than unity which suggest augmentation of heat transfer coefficient at the expense of lesser pressure drop penalty.

Thermohydraulic and Irreversibility Analyses of Swirl Flows Utilizing Distorted Radial Fins: Entropy Generation and Entransy Dissipation Evaluation

The current investigation analyses the convective heat transfer performance, entropy generation, and entransy evaluation of swirl flows generated by distorted radial fins (DRF). As swirl flows and various vortical structures induce large temperature gradients, second law and entransy analyses are necessary to thoroughly evaluate their true thermodynamic influence on heat transfer enhancement. The results indicated that due to the influence of swirl flows and vortices, all angles of the DRF were capable of inducing intense fluid mixing, thinner thermal boundary layers, and turbulent eddies. It was found that overaggressive swirl flows may hinder local heat transfer performances, by enclosing low-velocity heated fluids within the thermal boundary layers. However, as these overaggressive swirl flows and strong vortices propagate downstream, beneficial fluid mixing was eventuated, favouring heat transport over large regions. In terms of thermal performances, the maximum heat transfer enhancement was exhibited by the α=45° DRF, improving the Nusselt numbers up to 59.3%. Accordingly, the highest performance evaluation criterion (PEC) of 1.269 was obtained by the α=45° DRF at the Reynolds number 2389, attributed to the centrifugal effects of the swirl flows. Optimal entropy generation numbers were also exhibited by the α=45° DRF at the highest studied Reynolds number, reducing total entropy generation by 36.81%. Lower entransy thermal resistances were also accredited to greater DRF angles due to the intense swirl effects. In essence, the study concludes that the effects of swirl flows and vortices significantly enhance heat transfer, whilst reducing both entropy generation and entransy dissipation rates, leading to optimal thermal performances.

Subcooled Pool Boiling on Hierarchical Micro- and Nanostructure-Modified Copper Surfaces in HFE-7100 Dielectric Liquid

ABSTRACT Hierarchical surfaces comprised both microscale and nanoscale structures have been previously studied as a means of targeting multiple length scales to achieve superior pool boiling performance. However, preceding studies have focused almost exclusively on high surface tension working fluids, while technologically important low surface tension fluids have remained largely unexplored. Due to their significantly lower surface tension these liquids tend to push out the air trapped in surface cavities of the heating surface, resulting in fewer nucleation sites compared to the same surface in water at low to moderate superheats. Thus, developing effective surface modification techniques for pool boiling in dielectric liquids and understanding the multiphase physics behind them is a pressing need in order to overcome these performance limitations and accelerate their adoption. In this work, we utilize scalable manufacturing techniques to realize four separate surface types (planar, nanoscale-modified, microscale-modified, and hierarchical) and experimentally determine their respective pool boiling performance within the low surface tension commercial working fluid HFE-7100. A maximum heat transfer enhancement of 125% at 38 K of superheat was observed for the best performing samples, which interestingly were nanoscale-modified and not those of the hierarchical type. Visual observations via high-speed video analysis of vapor bubble behavior are utilized to explain the underlying multiphase physics as to why these samples performed so well and future directions for achieving surface optimization across multiple length scales.

Impacts of entropy generation in second-grade fuzzy hybrid nanofluids on exponentially permeable stretching/shrinking surface

The present investigation aims to use entropy analysis to analyze the unsteady Magnetohydrodynamic (MHD) flow in a second-grade fuzzy hybrid Al2O3-Cu/SA\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left( {{\ ext{Al}}_{{2}} {\ ext{O}}_{{3}} - {\ ext{Cu/SA}}} \\right)$$\\end{document} nanofluid over an exponentially shrinking/stretching surface. The model for hybridization of the mixture of alumina Al2O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left( {{\ ext{Al}}_{{2}} {\ ext{O}}_{{3}} } \\right)$$\\end{document} and copper (Cu) nanoparticles in the sodium alginate (SA) base fluid under heat source/sink, nonlinear thermal radiation, and viscous dissipation. The fundamental partial differential equations (PDEs) are simplified using an appropriate similarity conversion to generate the ordinary differential equations (ODEs). The analytical computation occurs in the MATHEMATICA program implementing the homotopy analysis method (HAM). In terms of code validity, our results are preferable to previous findings. The features of several parameters against the velocity, surface friction coefficient, entropy, temperature, and Nusselt number are described through graphs. According to our findings, the rise in the Brinkman and Reynolds numbers enhanced the total entropy of the system. Furthermore, the nanoparticle volume fraction and viscus dissipation magnifies the fluid temperature while retards the flow profile throughout the domain. Fluid velocity declined due to the Lorentz force using magnetic impact applications. The imprecision of nanofluid and hybrid nanofluid volume fractions was modelled as a triangular fuzzy number (TFN) [0%, 1%, 2%] for comparison. The double parametric approach was applied to deal with the fuzziness of the associated fuzzy parameters. The nonlinear ODEs convert into fuzzy differential equations (FDEs) and use HAM for the fuzzy solution. From our observation, the hybrid nanofluid displays the maximum heat transfer compared to nanofluids. This important contribution will support industrial growth, particularly in the processing and manufacturing sectors. The percentage increase in skin friction factor is 18.3 and 15.0 when α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} and β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document} take input in the ranges of 0 ≤ α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} ≤ 0.8 and 0 ≤ β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document} ≤ 1, respectively.

Accelerating melting time in a triplex tube heat exchanger thermal energy storage unit with micro-channels

This article studies optimal conditions to maximize heat transfer efficiency within a triplex tube heat exchanger (TTHX) filled with phase-change material. In this context, micro-channels (MCs) incorporated into TTHX for the first time for acceleration melting time. A two-dimensional numerical model has been developed, and pure conduction and natural convection are both simulated. The Reynolds numbers range from 1 to 100. The types of temporal velocity profiles into micro-channels were uniform, step, elliptic, sinusoidal, and power. The effect of gravity states, namely no gravity, with gravity, and (MCHE), has been studied with different numbers of microchannels (4, 6, 8, 10, 12, and 14). The results showed that there was no variation in melting duration observed when increasing the Re number from 50 to 100. Thus, the maximum reduction in melting period occurred at Re = 50. Moreover, sinusoidal velocity profiles were more effective and could help the process finish sooner. In addition, micro channel tube exchanger (MCTE) fitted or equipped with 10 micro-channels has an optimum condition considering pressure drop and complete melting time. Using the sinusoidal profile reduced the total fusion time by 325 s compared to uniform flow (8.47 % reduction). This indicates that the sinusoidal profile is an effective way to reduce the melting period.

Study on the heat transfer characteristics of CO2 and liquid desiccant CaCl2 aqueous solution in the gas cooler and evaporator

The heat exchangers are essential components in the CO2 heat pump-driven liquid desiccant dehumidification system since the heat transfer performance of heat exchangers directly affects the energy efficiency of the system. However, the heat transfer characteristics of CO2 and liquid desiccant in the heat exchanger have yet to be fully revealed, resulting in a lack of appropriate strategies to improve the heat transfer performance. To address this issue, numerical gas cooler and evaporator models are developed and verified. The effects of parameters such as the weight concentration of the CaCl2 aqueous solution, the CO2 inlet pressure, mass flow rates, and the length of the heat exchanger on the heat transfer performance are investigated respectively under various operating conditions. Results show that the heat exchange load of the gas cooler can be significantly impacted by various inlet parameters of both fluids. In particular, the increase in the weight concentration from 36 to 54 wt.% deteriorates the heat exchange load by over 15 %. Nevertheless, the heat exchange load of the evaporator is hardly influenced by the weight concentration. This is attributed to a great gap in the two fluids’ heat capacity rates, causing the evaporator to be in the maximum heat transfer state. The sign of the maximum heat transfer state of the heat exchanger is whether the thermal effectiveness is close to 1, which is related to the heat transfer area. Therefore, modifying the heat exchanger length could avoid the thermal effectiveness approaching 1. Results indicate that the appropriate length of the evaporator is 3–4 m under the designed operating conditions.