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A novel solid-state elastocaloric cooling device is presented, making use of a bistable actuation mechanism for loading of a natural rubber (NR) foil refrigerant. The thicknesses of the foil refrigerants are 290 and 650 μm in an initial undeformed state, while their lateral size is 9 × 26.5 mm2. Owing to the large surface-to-volume ratio of the NR foils, heat transfer to the heat sink and source is accomplished by a solid–solid mechanical contact. The loading mechanism consists of a rotating lever arm providing for stable positions at contact to the heat sink and source, which allows for significant power saving during elastocaloric cycling. In addition, the negative biasing associated with bistability favors good thermal contact at the end positions, which improves heat transfer resulting in a maximum temperature span ΔTdevice of 4.2 K in the strain range of 300%–700% under adiabatic conditions. The coefficient of performance of the device COPdevice reaches values up to 5.7 for foil refrigerants of 290 μm thickness. The maximum cooling power is 214 mW corresponding to a specific cooling power of 3.4 Wg−1. [ABSTRACT FROM AUTHOR]

Blocking phonon transport via localized resonance is a crucial method for controlling heat transfer and enhancing thermoelectric performance in nanostructures. However, the effects of disorder and asymmetrically distributed side branches on thermal transport and local resonant hybridization in two-dimensional materials remain insufficiently understood. In this work, we investigate the influence of symmetric and asymmetric disordered side branches on phonon transport in branching graphene superlattices. Our results demonstrate that aperiodic superlattices (ap-SL) can reduce thermal conductivity by up to 21% compared to periodic superlattices. The reduction in thermal conductivity in ap-SL is primarily due to phonon Anderson localization caused by disordered side branches. Interestingly, the localization lengths of symmetric and asymmetric ap-SLs are comparable, resulting in similar thermal conductivity in both cases. This finding suggests that the randomness in the upper and lower branches of asymmetric graphene superlattices does not significantly affect phonon transmission. Consequently, our work indicates that differences in symmetry between the upper and lower edge branches of graphene nanoribbons can be disregarded during experimental preparation without influencing their thermal conductivity. [ABSTRACT FROM AUTHOR]

Liquid metal phase change materials have the advantages of high thermal conductivity and high volumetric latent heat, which are expected to address the growing challenges of thermal management of advanced electronics. In previous studies, the effect of radiative heat transfer from fins of a phase change heat sink on thermal management performance has rarely been considered. In this study, radiative coating materials with high emissivity were prepared and coated on the fins of the liquid metal phase change heat sink. The effect of radiative heat transfer on the performance of liquid metal phase change heat sink was investigated. The experimental results of continuous heating under natural convection conditions show that the introduction of the radiative coating with an emissivity of 0.9298 can extend the time for the surface temperature of the heat source to reach 100 °C by 9.4%, while shortening the recovery time of the phase change heat sink by 14.9%. The results of high-power cyclic heating indicate that the high emissivity coating can reduce the peak temperature by 16.6 °C in the tenth working cycle. A simplified numerical model was subsequently developed and validated to determine the specific effects of phase change and radiative heat transfer on the overall thermal control performance. The radiation-enhanced liquid metal phase change heat sink proposed in this study is simple and maintenance-free. It is expected to address the thermal management issues of electronic devices that cannot use active cooling or operate in thin-air environments. [ABSTRACT FROM AUTHOR]

Thermoelectric generators (TEGs) are a promising solution for waste-heat-recovery system as they can generate power when there is a temperature difference, i.e., temperature difference between the waste heat, Tsource, and heat sink, Tsink. While there are many studies on TEGs for waste-heat recovery, most works optimize their performance based on the hot- and cold-side temperatures, Thot and Tcold, respectively, of the TEGs which are different than those of the available waste-heat and coolant temperatures, i.e., Tsource and Tsink. This work proposes a model for estimating the maximum power output of TEGs based on heat-source and heat-sink conditions without taking extra steps to extract Thot and Tcold out of the conditions. From given heat-source and heat-sink conditions, i.e., temperature and flow rate, the model can determine the optimal TEG and heat exchanger geometry for maximum power generation. This model is valid for cases where the heat transfer rate of the heat sink is much greater than that of the heat source. Finally, a TEG system is optimized for marine engine waste-heat recovery, generating about 157% more power than an unoptimized system. This newly proposed model offers a simple and quick estimation of the maximum power generation of a TEG system for waste-heat recovery. [ABSTRACT FROM AUTHOR]

The thermal conductivity of glasses is well-known to be significantly harder to theoretically describe compared to crystalline materials. Because of this fact, the fundamental understanding of thermal conductivity in glasses remain extremely poor when moving beyond the case of simple glasses, e.g., glassy SiO2, and into so-called "modified" oxide glasses, that is, glasses where other oxides (e.g., alkali oxides) have been added to break up the network and alter, e.g., elastic and thermal properties. This lack of knowledge is apparent despite how modified glasses comprise the far majority of known glasses. In the present work, we study an archetypical series of sodium silicate [xNa2O–(100 − x)SiO2] glasses. Analyses of modal contributions reveal how increasing Na2O content induces increasing vibrational localization with a change of vibrations to be less ordered and a related general decrease in modal contributions to thermal conductivity. We find the vibrational phases (acoustic vs optical) of sodium vibrations to be relatively disordered compared to the network-forming silicon and oxygen species, explaining how increasing Na2O content decreases thermal conductivity. Our work sheds new light on the fundamentals of glassy heat transfer as well as the interplay between thermal conduction and modal characteristics in glasses. [ABSTRACT FROM AUTHOR]

Owing to charge free property, magnon is highly promising to achieve dissipationless transport without Joule heating and, thus, potentially applicable to energy efficient devices. In this paper, using the non-equilibrium Green's function, we present the bulk-boundary correspondence for magnonic Kagome lattices by studying the edge magnons transport. With staggered exchange interaction and Dzyaloshinskii–Moriya interaction in the Kagome lattices, one can observe valley contrasting magnon Hall effect, which endows magnon transport with the valley degree of freedom and adds a new dimension to regulate magnon excitation. In particular, we demonstrate that the valley splitting in the Kagome lattice enables a tunable single edge chiral transport. Thermal rectification is a direction-dependent asymmetric heat transfer phenomenon; here, we report the tunable thermal rectification by asymmetric nonlinear effect, and it is, indeed, regulated by the Dzyaloshinskii–Moriya interaction direction (D → − D) and the exchange of J 1 and J 2 (J 1 ↔ J 2). Moreover, we show that the topological edge state mainly localizes around edges and leaks into the bulk with oscillatory decay. These give full play to spin and valley degrees of freedom and provide various avenues for information encoding and manipulation based on valley related magnonic flux. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies were performed on the vibrational energy relaxation in shock-heated CO/N2/Ar mixtures. A laser absorption technique was applied to the time-dependent rovibrational temperature time-history measurements. The vibrational relaxation data of reflected-shock-heated CO were summarized at 1720–3230 K. In shock-tube experiments, the rotational temperature of CO quickly reached equilibrium, whereas a relaxation process was found in the time-dependent vibrational temperature. For the mixture with 1.0% CO and 10.0% N2, the vibrational excitation caused a decrease in the macroscopic thermodynamic temperature of the test gas. In the simulations, the state-to-state (StS) approach was employed, where the vibrational energy levels of CO and N2 are treated as pseudo-species. The vibrational state-specific inelastic rate coefficients of N2–Ar collisions were calculated using the mixed quantum–classical method based on a newly developed three-dimensional potential energy surface. The StS predictions agreed well with the measurements, whereas deviations were found between the Schwartz–Slawsky–Herzfeld formula predictions and the measurements. The Millikan–White vibrational relaxation data of the N2–Ar system were found to have the most significant impact on the model predictions via sensitivity analysis. The vibrational relaxation data of the N2–Ar system were then modified according to the experimental data and StS results, providing an indirect way to optimize the vibrational relaxation data of a specific system. Moreover, the vibrational distribution functions of CO and N2 and the effects of the vibration–vibration–translation energy transfer path on the thermal nonequilibrium behaviors were highlighted. [ABSTRACT FROM AUTHOR]

Coagulational growth in an aerosol is a multistep process; first particles collide, and then they coalesce with one another. Coalescence kinetics have been investigated in numerous prior studies, largely through atomistic simulations of nanoclusters (102–104 atoms). However, with a few exceptions, they have either assumed the process is completely isothermal or is a constant energy process. During coalescence, there is the formation of new bonds, decreasing potential energy, and correspondingly increasing internal kinetic (thermal) energy. Internal kinetic energy evolution is dependent not only on coalescence kinetics but also on heat transfer to the surrounding gas. Here, we develop and test a model of internal kinetic energy evolution in collisionally formed nanoclusters in the presence of a background gas. We find that internal kinetic energy dynamics hinge upon a power law relationship describing latent-to-sensible heat release as well as a modified thermal accommodation coefficient. The model is tested against atomistic models of 1.5–3.0 nm embedded-atom gold nanocluster sintering in argon and helium environments. The model results are in excellent agreement with the simulation results for all tested conditions. Results show that nanocluster effective temperatures can increase by hundreds of Kelvin due to coalescence, but that the rise and re-equilibration of the internal kinetic energy is strongly dependent on the background gas environment. Interestingly, internal kinetic energy change kinetics are also found to be distinct from surface area change kinetics, suggesting that modeling coalescence heat release solely due to surface area change is inaccurate. [ABSTRACT FROM AUTHOR]

The time-periodic modulation of a temperature gradient can alter the heat transport properties of a physical system. Oscillating thermal gradients give rise to behaviors such as modified thermal conductivity and controllable time-delayed energy storage that are not present in a system with static temperatures. Here, we examine how the heat transport properties of a molecular lattice model are affected by an oscillating temperature gradient. We use analytical analysis and molecular dynamics simulations to investigate the vibrational heat flow in a molecular lattice system consisting of a chain of particles connected to two heat baths at different temperatures, where the temperature difference between baths is oscillating in time. We derive expressions for heat currents in this system using a stochastic energetics framework and a nonequilibrium Green's function approach that is modified to treat the nonstationary average energy fluxes. We find that emergent energy storage, energy release, and thermal conductance mechanisms induced by the temperature oscillations can be controlled by varying the frequency, waveform, and amplitude of the oscillating gradient. The developed theoretical approach provides a general framework to describe how vibrational heat transmission through a molecular lattice is affected by temperature gradient oscillations. [ABSTRACT FROM AUTHOR]

Thermal transport plays a pivotal role across diverse disciplines, yet the intricate relationship between amorphous network structures and thermal conductance properties remains elusive due to the absence of a reliable and comprehensive network's dataset to be investigated. In this study, we have created a dataset comprising multiple amorphous network structures of varying sizes, generated through a combination of the node disturbance method and Delaunay triangulation, to fine-tune an initially random network toward both increased and decreased thermal conductance C. The tuning process is guided by the simulated annealing algorithm. Our findings unveil that C is inversely dependent on the normalized average shortest distance L n o r m connecting heat source nodes and sink nodes, which is determined by the network topological structure. Intuitively, the amorphous network with increased C is associated with an increased number of bonds oriented along the thermal transport direction, which shortens the heat transfer distance from the source to sink node. Conversely, thermal transport encounters impedance with an augmented number of bonds oriented perpendicular to the thermal transport direction, which is demonstrated by the increased L n o r m . This relationship can be described by a power law C = L n o r m α , applicable to the diverse-sized amorphous networks we have investigated. [ABSTRACT FROM AUTHOR]

The main target of this article is to analyze the role of activation energy and thermal radiation effects on the bioconvective peristaltic transport of Sutterby nanofluid in a two-dimensional flexible porous channel with heat and mass transfer. Also, the consequences of Hall current, heat source, and complaint wall properties along with an inclined magnetic field are taken into consideration. The proposed system of governing equations is simplified by using lubrication approximation and solved numerically using MATLAB's bvp5c solver. Further, numerical observations are analyzed to figure out the consequence of different physical parameters on the flow characteristics. According to the observations, it is identified that the Sutterby nanofluid velocity declines with the climb in the damping force parameter, while it enhances with the upsurge in the Darcy number. The Sutterby fluid temperature profile strengthens when the influence of the heat generation and Brinkman number increase, while it depicts the reverse effect with the elevation in the fluid parameter and radiation parameter. The temperature ratio and activation energy parameters were found to have a significant impact on the fluid concentration. The volume of the trapped fluid bolus is an enhancing function of the channel's non-uniformity parameter. Moreover, current work reveals its applicability to recognize the hemodynamic flow analysis and other biofluid movements in the human body and industrial sectors. [ABSTRACT FROM AUTHOR]

Purpose: To measure and compare the mean temperature values due to heat generated during the grinding of different prosthetic materials with diamond burs using a high-speed instrument with and without water cooling. Materials and Methods: In total, 120 disk-shaped specimens (10 × 2 mm), each with a smaller disk in the center (3 × 2 mm), were fabricated from yttrium-stabilized zirconia, monolithic zirconia, glass-ceramic, indirect composite, polyetheretherketone (PEEK), and cast metal (Ni-Cr alloy). The specimens were divided into six groups (n = 20) according to material type. The specimens in each group were ground continuously with a high-speed handpiece and diamond burs with (n = 10) and without (n = 10) water cooling until the smaller disks were removed. Two different methods (thermocouple and thermal camera) were used to measure the temperature during the grinding process. Results were analyzed using two-way ANOVA and paired-samples t test (P < .05). Results: PEEK had the lowest mean temperature and metal had the highest values, both with and without water cooling, according to data measured with a thermocouple. Zirconia and monolithic zirconia samples without water cooling had the highest mean temperature when measured with a thermal camera. Both with and without water cooling, composite samples had the lowest mean temperatures for thermal camera measurements. Conclusions: Water cooling is strongly recommended when grinding all prosthetic materials. The heat transferred to the supporting teeth may depend on the thermal conductivity of the material used. [ABSTRACT FROM AUTHOR]

In order to solve the problems of low energy utilization and poor structural stability of photothermal conversion materials, a graphene-based photothermal conversion material was prepared, which was structurally integrated with a light-absorbing upper layer and a heat insulating base. During the preparation process, a tightly arranged nanotube array upper layer was constructed on the basis of graphene films by microimprinting technology, and a porous aerogel base was molded by a fixed-point titration and multiple-foaming method. The results show that the light trap constructed from graphene hollow nanotubes can significantly increase the number of light reflections and reduce light reflectivity. Meanwhile, the length of the nanotubes is directly proportional to the light-absorbing capacity of the material, which can increase the light-absorbing rate to more than 98% under the embossing conditions of 85 kN and 8h. In addition, the porous aerogel insulation base can effectively improve the photothermal conversion effect, and a photothermal conversion efficiency of 87% and a water evaporation rate of 1.3 kg/(m2 h) can be achieved at a base thickness of 6 mm. [ABSTRACT FROM AUTHOR]

In this study, laser Directed Energy Deposition technology is employed to fabricate internal structures within the hollow interiors of rotating parts such as tubes and cylinders. A three-dimensional transient multiphysics model for C276 material was developed, which anticipated the impact of angular velocity from tube rotation on various aspects. This model, validated by experiments, focused on the melt pool morphology, Marangoni convection, oriented crystal microevolution, and deposited material microhardness. It was found that at 150 ms deposition, the dimensions of the melt pool stabilized. With an increase in the Peclet number, heat transfer within the melt pool transitioned from conduction to convection. A rise in angular velocity reduced the melt pool deposition height, limited by the volume of the deposited material. Additionally, this angular velocity generated tangential forces, leading to an asymmetric melt distribution in the longitudinal section of the melt pool and a movement of the melt toward the melting front. At the bottom of the melt pool, the growth of C276 columnar crystals was notably inclined toward the center of Marangoni convection. The microhardness of the deposited material showed a stable distribution along the inclined crystal direction, whereas significant fluctuations were observed perpendicular to the cylinder substrate. These findings highlighted the considerable effect of Marangoni convection on microstructural evolution. [ABSTRACT FROM AUTHOR]

Flow of a fluid past a body is a very complicated phenomenon. Computational fluid dynamics is used for studying the characteristics of flow past an array of hemispherical protrusions that is disposed on the wall surfaces of a millisecond microchannel reactor. Protrusions can be used to improve the transport processes involved, but the causes of the phenomena are still incompletely understood. Parametric analyses are performed under different sets of circumstances to delineate the role of geometric features and operation conditions in reactor performance. Dimensionless quantities are used to simplify the characterization of the reactor system with multiple interacting transport phenomena. The mechanisms involved in the intensified processes are analysed, and performance improvement recommendations are presented. The results indicate that the protruded reactor behaves effectively and good yields can be obtained with only milliseconds residence of the mixtures within the channels. The reactor offers the unique advantage for hydrogen production from methanol in that process intensification is realized while preserving the energy balance between the exothermic and endothermic processes. However, the flow rates must be adjusted as needed to maximize production of hydrogen and minimize pressure drops. The momentum diffusivity is more dominant around the protrusion regions than in the other regions. The thermal diffusivity is more dominant in the protruded channels than in the flat channels. The results have implications for hydrogen production and beyond for the study of transport phenomena in microchemical systems.

The thermal conductivity of group IV elements—germanium, silicon, and diamond—is described in order to demonstrate various important and interesting aspects of the mechanism of phonon heat transfer in single-crystalline semiconductors and dielectrics. The measured temperature dependence of thermal conductivity κ (T) for these materials reveals different phonon scattering processes that determine thermal conductivity. In addition to the intrinsic processes of phonon–phonon scattering, scattering by isotopes, dopants, free electrons, sample surfaces, the effects of phonon focusing, irradiation with high-energy particles, and phonon hydrodynamics are discussed. [ABSTRACT FROM AUTHOR]

We demonstrate a non-monotonic evolution of in-plane thermal conductivity of large-area hexagonal boron nitride films with thickness. Wrinkles and defects/impurities are present in these films. Raman spectroscopy, an optothermal non-contact technique, is employed to probe the temperature and laser power dependence property of the Raman active E2ghigh phonon mode, which, in turn, is used to estimate the rise in the temperature of the films under different laser powers. As the conventional Fourier law of heat diffusion cannot be directly employed analytically to evaluate the thermal conductivity of these films with defects and wrinkles, finite-element modeling is used instead. In the model, average heat resistance is used to incorporate an overall near-surface defect structure, and Voronoi cells with contact resistance at the cell boundaries are constructed to mimic the wrinkled domains. The effective in-plane thermal conductivity is estimated to be 87, 55, and 117 W/m K for the 2, 10, and 30 nm-thick films, respectively. We also present a quantitative estimation of the thermal resistance by defects and wrinkles individually to the heat flow. Our study reveals that the defects/impurities render a much higher resistance to heat transfer in the films than wrinkles. [ABSTRACT FROM AUTHOR]

Pharmaceutical fluid processing is a procedure of medication manufacturing, utilizing a particular kind of heat transfer in a biofluid designed to maintain the desired temperature for extended periods. Choosing a suitable fluid can have a positive effect on the operating efficacy of the system and lengthen the fluid's and system's life spans. As an outcome of this development, we investigate the influence of the partial slip and gyrotactic microorganisms on the peristaltic transport of a magnetohydrodynamic Ree–Eyring nanofluid via an aligned porous conduit with thermal radiation, energy generation, along with cross and double diffusion effects. By invoking suitable nondimensional parameters, the proposed dimensional governing equations are transformed into a system of dimensionless partial differential equations. The analytical solutions for the system of partial differential equations are obtained by incorporating the homotopy perturbation method. Further, tabular and graphical presentations are used to examine the characteristics of the various sundry parameters on the temperature, concentration, motile microorganism density, axial velocity, trapping, and other relevant flow quantities. The observations of this study indicate that the Darcy number and thermal Grashof number have the capability to enhance the velocity distribution of the Ree–Eyring nanofluid in the presence of bioconvection. The trapped bolus size and the skin friction coefficient increase noticeably because of an enhancement in the Ree–Eyring fluid parameter. Also, the Darcy number and the Hall current parameter increase the skin friction coefficient. Furthermore, validation of the results is carried out to examine the consistency between the current and the previous findings for some special cases and excellent agreements are found. [ABSTRACT FROM AUTHOR]

Water dissociation on TiO2 surfaces has been known for decades and holds great potential in various applications, many of which require a proper understanding of thermal transport across the TiO2–H2O interface. Molecular dynamics (MD) simulations play an important role in characterizing complex systems' interfacial thermal transport properties. Nevertheless, due to the imprecision of empirical force field potentials, the interfacial thermal transport mechanism involving water dissociation remains to be determined. To cope with this, a deep potential (DP) model is formulated through the utilization of ab initio datasets. This model successfully simulates interfacial thermal transport accompanied by water dissociation on the TiO2 surfaces. The trained DP achieves a total energy accuracy of ∼238.8 meV and a force accuracy of ∼197.05 meV/Å. The DPMD simulations show that water dissociation induces the formation of hydrogen bonding networks and molecular bridges. Structural modifications further affect interfacial thermal transport. The interfacial thermal conductance estimated by DP is ∼8.54 × 109 W/m2 K, smaller than ∼13.17 × 109 W/m2 K by empirical potentials. The vibrational density of states (VDOS) quantifies the differences between the DP model and empirical potentials. Notably, the VDOS disparity between the adsorbed hydrogen atoms and normal hydrogen atoms demonstrates the influence of water dissociation on heat transfer processes. This work aims to understand the effect of water dissociation on thermal transport at the TiO2–H2O interface. The findings will provide valuable guidance for the thermal management of photocatalytic devices. [ABSTRACT FROM AUTHOR]

Heat exchangers are made of metals because of their high heat conductivity and mechanical stability. Metal surfaces are inherently hydrophilic, leading to inefficient filmwise condensation. It is still a challenge to coat these metal surfaces with a durable, robust, and thin hydrophobic layer, which is required for efficient dropwise condensation. Here, we report the nonstructured and ultrathin (∼6 nm) polydimethylsiloxane (PDMS) brushes on copper that sustain high-performing dropwise condensation in high supersaturation. Due to the flexible hydrophobic siloxane polymer chains, the coating has low resistance to drop sliding and excellent chemical stability. The PDMS brushes can sustain dropwise condensation for up to ∼8 h during exposure to 111 °C saturated steam flowing at 3 m·s-1, with a 5-7 times higher heat transfer coefficient compared to filmwise condensation. The surface is self-cleaning and can reduce the level of bacterial attachment by 99%. This low-cost, facile, fluorine-free, and scalable method is suitable for a great variety of heat transfer applications.

This paper focuses on the study of Blasius–Rayleigh–Stokes nanofluid dusty flow with generalized Fourier and Fick laws under the influence of a transitive magnetic field. The Blasius–Rayleigh–Stokes nanofluid dusty flow has significant applications in various fields, including the design of heat exchangers, microfluidic devices and industrial processes involving the transportation of suspended particles in fluids. This paper considers the impact of melting heat transfer at the surface boundary. By employing relevant transformations, the mathematical model is transformed into a system of self-similar equations. The solution to this set of highly nonlinear equations is obtained using the bvp4c numerical method in combination with the response surface methodology (RSM) statistical approach. The results are presented through graphical illustrations and numerically calculated tabulated values. It is observed that the fitted model for the skin friction coefficient Re x 1 ∕ 2 C f optimal. Moreover, the model parameters Pr , Q, β v , M and L are linearly and quadratically significant in explaining the variation presented for skin friction coefficient Re x 1 ∕ 2 C f . This indicates the response skin friction coefficient Re x 1 ∕ 2 C f is minimized to 0.005 at Pr = 2. 2 0 2 7 , Q = 0. 2 5 2 , β v = 0. 2 2 , M = 0. 2 1 7 and L = 0. 2 5 2 and is maximized to 1.387 at Pr = 2. 0 6 6 , Q = 0. 2 5 4 , β v = 0. 0 2 1 , M = 0. 0 5 6 and L = 0. 2 5 2. [ABSTRACT FROM AUTHOR]

Deep within coal gangue hills, there is a substantial amount of wasted thermal energy. Prolonged accumulation of these hills leads to significant damage to the atmosphere and soil. Gravity heat pipes, as efficient heat transfer components, can safely, efficiently, and conveniently extract the accumulated heat in gangue hills to achieve effective thermal control. In this study, we first analyzed the optimal height of the heat dissipation fins through a single fin heat dissipation model. Then, we determined the optimum spacing between the heat dissipation fins through analysis with multiple fins. The results showed that when the height of the heat dissipation fins was 80 mm and the spacing between fins was 80 mm, the heat dissipation performance and economic costs were most reasonable. Through an engineering trial conducted for 143 days at the Maotergou coal mine gangue hill, it was found that the average heat dissipation rate of a single gravity heat pipe ranged from 243.52W to 494.32W. The total heat dissipation during the entire experimental process was 54.39 kJ, and the total heat dissipation at the elevation of 890 meters was 1087.71 kJ. This indicates that managing the internal temperature accumulation in coal gangue hills using gravity heat pipes is entirely feasible. [ABSTRACT FROM AUTHOR]

The current investigation focuses on improving the performance of a single slope solar still integrated with Phase Change Material as energy storage media. The problem of low thermal conductivity of PCM which hinders the energy storage capability has been addressed by incorporating fins with different profiles into the energy storage unit. Initially, an experimental investigation was conducted and analyzed to assess the effective performance of a Conventional Single Slope Solar Still (CSS) using various water depth levels: 1–4 cm. The optimal basin water depth for testing solar still with energy storage material along with fins was identified as 2 cm. Subsequently, the CSS was subjected to performance enhancement investigation under three different conditions: Case 1 – Solar Still (SS) with PCM storage unit, Case 2 – SS with fins at the PCM storage unit, and Case 3 – SS with fins at the storage unit and a parallel plate attached to the other end of the fins. The experimental results demonstrated the production of fresh water and efficiency improvements are as follows 26.95%, 55.86%, 69.14% and 24.34%, 52.83%, 68.83% for cases I, II, and III, respectively. Further, it was observed that Case III exhibited a lower cost of water production and a shorter payback period compared to CSS. The enviro-economic analysis revealed that the net CO2 emissions (NCEM) and Carbon Credits Earned (CCE) for Case III were 15.60 tons and 312.07 USD respectively against 9.22 tons and 184.31 USD for CSS. [ABSTRACT FROM AUTHOR]

Thermal conductivity of the coolant for liquid cooling fuel cell, which is one of the key factors determining the cooling performance of the cooling system. Nanofluid is considered as desirable coolant due to their high thermal conductivity property, but its electrical property also cause leakage current. In this study, the supersonic plasma spraying technique was used to spray Al 2 O 3 on the inner wall of the cooling channels to make an insulating coating to eliminate leakage current. However, the rough coating surface possibly affect the flow and its thermal resistance also affect the heat transfer. Heat transfer characteristics and pump power of deionized water, alumina nanofluids, and graphene nanofluids were investigated. The results show that, before spraying insulation coating, graphene nanofluid has lowest maximum temperature and index of uniform temperature (IUT) at different pump power conditions, and it has the optimal cooling performance. As the pump power increasing, the effect of pump power on IUT gradually diminishes, the method of increasing pump power consumption to improve temperature uniformity is ineffective. The effective cooling coefficient of graphene nanofluid is highest at the same Re, and the convective heat transfer coefficient increases approximately linearly but not uniformly with increasing Re. After spraying the insulating coating, the maximum temperatures of the cooling plate are slightly reduced at different Re, the average reduction is 0.3 K, heat conduction from heat source by cooling channels slightly decreased, and the pump power of graphene nanofluid slightly increases, it increases by up to 2.7% at Re = 1500. It indicates that insulating coating do not have a significant effect on heat transfer and flow. • Al 2 O 3 insulating coatings are prepared using supersonic plasma spraying technology. • Graphene nanofluid has the best thermal performance and thermal conductivity ability. • Increasing pump power method is inefficient for the IUT at high pump power. • Al 2 O 3 insulating coatings do not have a significant effect on heat transfer and flow. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the heat transfer mechanism while considering the attributes of viscous dissipation, Joule heating, and nonlinear thermal radiations in the three-dimensional steady incompressible flow of Carreau liquid on an extendable rotating disk. By using the similarity transformation, the governed equations were converted into the nonlinear coupled ordinary differential equations. The essential characteristics of various variables like Prandtl number, Lewis number, Carreau liquid parameter, Brownian motion, thermophoresis parameter, radiation parameter, Eckert number and Hartmann number on velocity, thermal, and concentration are discussed through graphs and tables. The presented investigation divulges that the thermal and mass transfer rates enhance when Brownian motion and thermophoresis processes extended and manifest as opposing features on the concentration field. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases (CVDs) are recognized as a significant threat to global health. The rapid, sensitive, and precise measurement of relevant biomarkers is essential for the timely diagnosis of CVDs. Molecularly imprinted polymers (MIPs), which act as artificial receptor recognition materials, have been extensively utilized in the detection of CVD biomarkers. Their widespread application is due to their cost-effectiveness, physical and chemical stability, straightforward preparation processes, and excellent compatibility with various sensor types. This review introduces the principles of MIP sensors in combination with electrochemical, optical, thermal transfer, and acoustic detection techniques for detecting CVD-related biomarkers. It then discusses methods developed over the past decade for detecting biomarkers of three major CVDs—coronary artery disease (CAD), acute myocardial infarction (AMI), and heart failure (HF)—using MIP sensors. Finally, the review summarizes the potential of MIP sensors in CVD biomarker detection and provides an outlook on future research directions. [ABSTRACT FROM AUTHOR]

This study focuses on a four-cylinder, four-stroke hydrogen engine equipped with a passive pre-chamber (PC). The effects of excess air ratio (λ) on the performance of the turbulent jet ignition (TJI) hydrogen engine are investigated through experimental and numerical simulations. The hydrogen engine operates at 1600 rpm with an intake manifold pressure of 70 kPa. The results show that λ values significantly influence the internal flow field, energy distribution, and flame development in the PC, affecting the combustion in the main chamber (MC). The experiment found that as λ decreases, the BMEP and BTE gradually increase. Due to the influence of jet and multi-point ignition, the heat transfer loss in lean combustion is also relatively high. The jet oscillation caused by the TJI hydrogen engine has high controllability and low destructiveness, and λ is one of the main factors controlling the jet oscillation. The influence of spark timing (ST) on engine performance is explored through experiments. The results show that as λ increases, the sensitivity of BMEP to ST gradually decreases. With the delay of ST, BTE increased first and then decreased. However, the cyclic variation is less affected by ST. For the TJI hydrogen engine, an appropriate delay in ST under the close stoichiometric ratio condition can not only ensure power output and combustion stability but also reduce emissions. [Display omitted] • Pre-chamber gas-flow movement, mixture distribution, and flame propagation are analyzed • The pre-chamber exhibits stratification of the mixture under lean combustion conditions. • The BMEP and BTE continue to decrease with the increase of lambda. • The jet oscillations in TJI engines are highly sensitive to the excess air ratio. • The spark timing has a smaller effect on lean combustion than rich mixtures. [ABSTRACT FROM AUTHOR]

Inspired by natural bifurcated systems, a bionic microchannel system with tree-like topological structure is proposed, and applied for thermal management of proton exchange membrane fuel cell (PEMFC). The tree-like microchannel is optimized based on the minimization of flow resistance under steady laminar and pulsating flow conditions, respectively. Finite element simulations and microfluidic experiments are carried out for pulsating flow in the tree-like microchannel to determine its heat transfer performance. The results show that the optimized successive diameter ratio for the pulsating flow in a symmetric and dichotomous tree-like network is 0.707 (≈2−1/2), which is different from that of steady laminar flow (0.794≈2−1/3) known as Murray's law. Compared with steady flow, the application of sinusoidal-wave and rectangular-wave pulsating flow in a tree-like microchannel can further improve both the heat transfer efficiency and temperature uniformity. The tree-like microchannel with a length ratio of 2−2/3≈0.630 and diameter ratio of 2−1/3≈0.794 shows best performance under steady and pulsating flow modes. The present work has important theoretical significance for understanding the mechanism of natural bifurcated systems, and may provide theoretical basis and technical support for the industrial applications of bionic tree-like microchannel in thermal management of fuel cell and microelectronic device cooling etc. [Display omitted] • Bionic tree-like microchannel is designed for thermal management of PEMFC. • Optimized successive ratio of tree-like microchannel with pulsating flow is derived. • Thermal-hydraulic performance of bionic microchannel is investigated by FEM. • Mathematical model of bionic microchannel is validated by microfluidic experiment. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) dissociation is of an initial and very important step during its combustion process. This study therefore systematically investigates the effect of reaction temperature (650–950 °C), fluidisation number (0.83–2.50) and static bed depth (0–25 mm) on NH 3 dissociation in a laboratory-scale Bubbling Fluidised Bed (BFB). By analysing the concentrations of H 2 and N 2 in the effluent using gas chromatography, results show that the conversion ratio of NH 3 in BFB was merely 0.26%–0.29% at 650 °C but increased significantly to 18.1%–25.3% at 950 °C. This highlights the importance of temperature in promoting NH 3 dissociation. However, as fluidisation number increased from 1.0 to 2.5, attributing to a decrease in gas – solid contact time, the conversion ratio of NH 3 decreased correspondingly from the highest 20.7%–5.7%. Moreover, as static bed depth increased from 15 mm to 25 mm, the conversion ratio of NH 3 increased slightly from 21.5% to 26.8%, both of which were found to be higher than that without bed particles. Clearly, NH 3 dissociation is enhanced by the bed material depth but is also dependent on the gas – solid contact time. In addition, by measuring the temperature distribution in the BFB reactor, a temperature drop of ca. 20 °C near the distributor was confirmed, showing a strong effect of endothermicity during NH 3 dissociation. These would provide an improved comprehension on the mechanisms of NH 3 dissociation and offer theoretical guidance for optimising the combustion processes in BFB burning NH 3. [Display omitted] • NH 3 dissociation at different temperatures and fluidisation numbers in BFB studied. • NH 3 conversion increased with temperature due to enhanced kinetic and heat transfer. • Increasing bed depth promotes NH 3 dissociation by increasing gas-solid contact time. • NH 3 conversion was the highest at incipient fluidisation but decreased at higher FN. • The endothermic NH 3 dissociation decreases bed temperature and hinders conversion. [ABSTRACT FROM AUTHOR]

This study examines the stability of double-diffusive convection in a Kuvshiniski viscoelastic nanofluid, in which the fluid is affected by two fields (such as temperature and salinity) that influence its density. The classical Fick's law, which assumes an immediate response of temperature to the heat flux gradient, is not entirely correct because it suggests an instantaneous reaction at all points, which is not entirely accurate since information propagates at a finite speed. This shortcoming of Fick's law leads us to consider the Maxwell–Cattaneo effect (MC effect). Thus, our research focuses on Maxwell–Cattaneo double-diffusive convection in a horizontal layer of a porous medium saturated with viscoelastic nanofluid. Here, the fluid's small dimensions result in its relaxation time being comparable to its thermal diffusion time, necessitating the use of the Maxwell–Cattaneo relationship. The behavior of viscoelastic nanofluids is described by a constitutive equation of the Kuvshiniski kind, and for the porous medium, Brinkman–Darcy model is considered. The nanofluid model includes the effects of Brownian diffusion and thermophoresis, with the assumption that the flux of the nanoparticle volume fraction is zero at the isothermal boundaries. The framework of linear and nonlinear stability theory leads the analysis. By applying linear stability theory with the help of normal mode technique, the conditions for the occurrence of both stationary and oscillatory convective motions are found in terms of a critical thermal Rayleigh number. The Kuvshiniski viscoelastic fluid exhibits Newtonian behavior in a state of stationary convection. We have discussed two cases for oscillatory convection that are when (i) Maxwell–Cattaneo coefficient for temperature (CT) = 0 and (ii) Maxwell–Cattaneo coefficient for salinity (CC) = 0. Convective heat and mass transfers are determined using a weakly nonlinear stability analysis. The effects of various factors on oscillatory and stationary states as well as the mass and heat transport are depicted graphically. It is found that with increase in the value of Kuvshiniski parameter F, thermal Rayleigh number Ra also increases for both cases CT = 0 and CC = 0. Ra drops with increasing values of modified diffusivity ratio NA and thermosolutal Lewis number Ls for both stationary as well as oscillatory convection. With increase in the value of Darcy number Da, an interesting pattern can be seen. For stationary convection, Ra increases with Da, but it has reverse effect on oscillatory convection (for both the cases). Streamlines, isotherms, and isohalines are also examined. [ABSTRACT FROM AUTHOR]

Single‐particle reactors in lab‐scale are a promising technology to gain an in‐depth understanding of the intricate reaction and transport processes that occur in catalyst particles under operando conditions. It is not described whether the effect of the bounding walls in such narrow flow channels influence the processes at the particle. Therefore, this work applies three‐dimensional (3D) computational fluid dynamics (CFD) simulations to analyze the drag coefficient CD alongside the local and average particle Nusselt number Nup as characteristic local and integral quantities in the range of particle Reynolds numbers 10 ≤ Rep ≤ 103. An equation is derived to correct for the wall effects on CD and Nup and assist the experimenter in the interpretation of measured results. [ABSTRACT FROM AUTHOR]

This study presents numerical simulations of the convective heat transfer on wavy microchannels to investigate heat transfer enhancement in these systems. The objective is to propose a methodology based on local and global energy balances in the device, instead of the commonly used Nusselt number, as an alternative for the thermal analysis. This investigation is carried out on a single-wave microchannel model of size 0.5 mm by 0.5 mm by 20 mm length, with water flowing inside the channel, exposed to a heat influx of 47 W/cm 2 at the bottom. The governing equations for an incompressible laminar flow and conjugate heat transfer are first built, and then solved, for representative models, with copper as the solid-block material under a number of operating conditions (cold-water flowrates of R e = 50 , 100, and 150), by the finite element technique. From computed velocity, pressure and temperature fields, local and global energy balances based on cross-section-averaged velocities and temperatures enable calculating the heat rate at each section of the corresponding device. Results from this study for two different designs, namely, serpentine and divergent-convergent layouts, show that this so-called averaged energy-balance methodology enables higher accuracy than that based on Nusselt numbers since neither transfer coefficients nor characteristic temperatures are needed. [ABSTRACT FROM AUTHOR]

Additive manufacturing has received significant interest in the fabrication of functional channels for heat transfer; however, the inherent rough surface finish of the additively manufactured channels can influence thermal performance. This study investigates the impact of roughness on the thermo-fluid characteristics of laminar forced convection in rough minichannels. A numerical model was developed to create 3D Gaussian roughness with specified root-mean-square height. The finite volume method was used to solve the conjugate heat transfer of developed laminar flow in square minichannels. For Reynolds numbers ranging from 200 to 1600, the simulation results indicated enhanced heat transfer and increased flow resistance as Reynolds number increases, compared to a smooth minichannel, where effects on heat transfer and flow friction were negligible. For channels with relative roughness (root-mean-square height to channel hydraulic diameter) of 0.0068, 0.0113, and 0.0167, increasing the Reynolds number led to increased friction factor by 1.56, 1.71, and 2.91%, while the Nusselt number was enhanced up to 0.03%, 32.74%, and 46.05%, respectively. Heat transfer reduced in roughness valleys due to the presence of local low-velocity fluid in these regions; however, recirculation regions can occur in deep valleys of high roughness, increasing heat transfer and flow friction. Heat transfer was enhanced over roughness peaks due to flow impingement on the windward face of roughness as well as intensified energy transfer to the channel wall from roughness. Moreover, surfaces with higher roughness have a greater number of high peaks providing a thermal-flow path of a larger area and a thermal conductivity greater than that of the fluid. [ABSTRACT FROM AUTHOR]

The rotary compressors are currently witnessing a trend towards high-speed operation, resulting in an increased frequency of valve motion and a higher mass flow rate through the discharge valve. Consequently, high-speed operation leads to intensified impact between the valve and both the valve stopper and valve seat, thereby posing challenges to the reliability of the valve. Simultaneously, the dynamic characteristics of the valve at high operating speeds exert a significant influence on the compressor's performance. This paper develops a three-dimensional fluid-structure interaction (FSI) model to investigate the dynamic characteristics and reliability of the valve in a high-speed rotary compressor while considering heat transfer during the flow process within the cylinder. The proposed model shows better agreement with the experiment. The study revealed that as the rotational speed increases, there is an obvious rise in over-compression loss and a pronounced valve closure delay, which increases the impact velocity of the valve. The valve experiences two peaks of equivalent stress within one cycle, rendering it susceptible to fail at high speeds. The adoption of a double-valve structure at a rotational speed of 12,000 rpm leads to a significant reduction in over-compression loss by 62.9 %, an increase in volumetric efficiency by 6.7 %, a maximum decrease in impact velocity by 54.5 %, and a maximum decrease in equivalent stress by 25.6 %. The reliability of the double-valve structure under 12,000 rpm was proved by an endurance experiment. Besides, the asymmetry in the opening process of the two valves has been unveiled for the first time. [ABSTRACT FROM AUTHOR]

• The countercurrent hollow fiber membrane module is proposed for cold water generation. • A 3-D numerical model is developed accounting for irregular fiber filling. • Channeling effect and flow dead zones degrade the heat and moisture transport. • Irregular fiber filling increases the air side heat transfer resistance by >158 %. • Irregular fiber filling offers the potential to improve energy efficiency under certain conditions. The countercurrent hollow fiber membrane-based evaporative water cooler (MEWC) offers an eco-friendly and compact solution for cold water generation. This study introduces a random sequential addition algorithm to model the real-world irregular fiber filling within the MEWC. Inspired by the honeycomb structure, the developed 3-D numerical model adopts a calculation unit featuring a hexagonal prism comprising multiple fibers. Validation against experimental data reveals an average relative error of 2.81 % concerning outlet water temperature. The effects of fiber filling patterns (regular layout and random layout) on the velocity and temperature fields of the MEWC are investigated. Comparisons of outlet water temperature, cooling efficiency, consumptive electric power ratio, and heat and mass transfer resistance composition between these layouts under various operating conditions are conducted. The results indicate that the random layout fosters severe channeling effect and large flow dead zones, impairing air side heat and moisture transfer. The random layout exhibits over 15.9 % reduction in cooling efficiency and 36.3 % decrease in consumptive electric power ratio compared to the regular layout. Irregular fiber filling leads to a notable 158.6 % increase in air side heat transfer resistance and a 35.9 % rise in mass transfer resistance. Although irregular filling compromises the cooling performance, it demonstrates potential for energy savings under certain conditions. Design schemes should be carefully tailored to meet specific application requirements by considering these trade-offs. [ABSTRACT FROM AUTHOR]

Maldistribution seriously impacts the heat transfer performance of the microchannel heat exchanger (MCHX). Fully understanding the two-phase distribution in the heat exchanger is important for advancing academic research and engineering applications. This study introduces a novel method for quantifying two-phase distribution in a microchannel heat exchanger. An experimental setup was developed to measure the local vapor mass fraction in the heat exchanger header. Capacitance signals were measured under inlet vapor mass fractions from 0 to 1, and inlet flow rates of 10, 15, and 25 g s−1 corresponding to a mass flux of 17.47, 26.2, and 43.66 kg m−2s−1, respectively. The local vapor mass fraction in the header was estimated using the capacitance measurements. The mass flow rate in the header, the microchannel tube, and the vapor mass fraction in the tube were calculated using the proposed model. The calculation model was validated against literature data, and the results were analyzed. The analysis reveals the characteristics of vapor mass fraction and mass flow rate distribution in the MCHX and further elaborates on the effects of phase separation, entrainment ratio, and pressure drop balance on the distribution. The proposed method can evaluate distribution in the header and tubes of microchannel heat exchangers, and it is also applicable to other types of two-phase flow devices. [ABSTRACT FROM AUTHOR]

• Boiling heat transfer of ammonia in a vertical rectangular microchannel at high pressure of 354–615 kPa was investigated. • The wake at lower end of the primary bubbles increases the local flow rate significantly. • Influence of saturation temperature on bubble growth and heat transfer performance was analyzed. Ammonia boilers are commonly used as expendable radiators during the return phase of spacecraft. The aim of this study is to investigate the bubble behavior and heat transfer characteristics within a vertical rectangular microchannel of a plate-fin ammonia boiler under gravity at an absolute pressure of 354–615 kPa. In order to achieve this, a single rectangular microchannel unit was intercepted from the ammonia boiler structure to construct a simulation model, and the high-pressure boiling process of ammonia in the rectangular microchannel was numerically investigated using the VOF model. Good agreement was obtained by comparing the numerical results with the experimental data with the error within 8 %. The results show that the wake flow at the lower end of the primary bubbles has an enhanced effect on the heat transfer, which is about 50–60 %. The maximum horizontal dimension of primary bubbles increases with increasing superheat, and significant bubble coalescence occurs when 45 % of the rectangular microchannel spacing is exceeded. In addition, the effect of different saturation temperatures on the heat transfer performance on the hot high temperature wall was investigated. Significant heat transfer deterioration was found to occur at saturation temperatures below 4 °C (superheat above 15 °C). The reason found in this study was that bubble coalescence significantly increases the percentage of gas-phase contact area on the high-temperature wall (from 25 % to 54 %) and weakens the wake enhancement effect. [ABSTRACT FROM AUTHOR]

• Yu & Koyama (1998) and Cavallini et al. (2009) overpredict heat transfer coefficients. • Han & Lee (2005) and Kedzierski & Goncalves (1997) show similar average performance. • Correction factor significantly improves model prediction accuracy. • Variable metric method cuts MAD for Kedzierski & Goncalves (1997) to 13.1 %. • Cavallini et al. (1997) best predicts frictional pressure gradient. To mitigate global warming, the world is transitioning to refrigerants with low global warming potential (GWP). Supporting this shift requires a model that can accurately predict the heat transfer and pressure drop of new refrigerants, crucial for designing efficient heat exchangers. Existing models, however, are largely based on currently deployed refrigerants and primarily developed for unexpanded micro-fin tubes with spiral angles of 6° to 30°. Their applicability to new refrigerants, especially in expanded micro-fin tubes, is uncertain. This study assesses the performance of four well-known condensation models for six emerging refrigerants—R-32, R-454B, R-454C, R-455A, R-1234yf, and R-1234ze(E)—against experimental data. Initially, the Han and Lee (2005) model shows the best prediction accuracy with a mean absolute deviation (MAD) of 22.1 %. To enhance the accuracy of heat transfer models for new refrigerants and geometries with large temperature glides, two approaches are proposed. The first approach applies a simple correction factor, reducing the MAD of the Cavallini et al. (2009) model from 68.2 % to 15.4 %. The second approach uses the variable metric method for minimization, fitting new constants to the data. This optimization results in the Kedzierski and Goncalves (1997) model achieving the highest accuracy, with a MAD of 13.1 %. For pressure drop models, the Cavallini et al. (1997) model is the most accurate with a MAD of 6.4 %, followed by the Haraguchi et al. (1993) model with a MAD of 9.4 %. Due to its simplicity, the Haraguchi et al. (1993) model is a practical option for predicting frictional pressure drop. [ABSTRACT FROM AUTHOR]

Currently, although significant advancements have been made in understanding heat transfer coefficients and pressure decreases in different tube shapes, there is still a noticeable lack of detailed studies on the generation of entropy under flow boiling conditions. In this work, the entropy generation in micro-fin tubes (MFT1 and MFT2) and smooth tubes (ST1 and ST2) in flow boiling conditions experimentally investigated with refrigerant R513A. Research focused on evaluating influence of different input parameters on entropy generation, specifically contribution of heat transfer coefficient (HTC) and total pressure drop (TPD) on entropy generation for all testing tubes. As at a heat flux of 6 kW· m −² and a saturation temperature of 12 °C, MFT1 shows HTC contributions to entropy generation ranging from 0.032 to 0.156 W· K −1, while MFT2 ranges from 0.03 to 0.14 W· K −1. TPD contributions for both MFT1 and MFT2 range from 0.001 to 0.04 W· K −1. Hence, MFT2 shows better results than MFT1 as low entropy generation required for a good heat exchanger. Among input parameters, heat flux displays the highest sensitivity, indicating its significant influence on total entropy generation variations, while vapor quality, mass flux, and saturation temperature also demonstrate notable sensitivity. This research helps us design systems that transfer heat more effectively while using less energy. Understanding these factors can lead to more efficient heat exchangers and other thermal systems. [ABSTRACT FROM AUTHOR]

• 1mm chevron depth W-shaped plate has no favor to R32 and slight benefit to R410A. • Convective boiling occurs earlier with decreasing of chevron depth. • Several correlations predict well to R32/R410A flow boiling in microscale plate channel. Brazed plate heat exchanger (BPHE) has gained more advantages of refrigerant inventory reduction and high efficiency due to smaller chevron channel. This paper experimentally investigates the heat transfer and pressure drop of R32 and R410A flow boiling in BPHEs with 1 mm chevron depth and W– and V– chevron patterns. Variations in heat transfer coefficient (HTC) and frictional pressure drop (FPD) with mass flux (15 − 40 kg m−2 s−1 for R32 and 25 − 60 kg m−2 s−1 for R410A) and imposed heat flux (from 6 − 14 kW m−2) are analyzed for each combination of the two refrigerants and two types of plate patterns. The HTC of R32 is approximately 10 % and 30 % higher than that of R410A at same mass flux in W– and V–shaped plates, respectively, which has an equivalent friction factor. The V–shaped plate is found more suited for R32 compared to the W–shaped plate. The existing available transition criterions fail to predict the flow boiling heat transfer mechanism in microscale channel, and convective boiling seems dominant in 1 mm chevron depth channel under the present working conditions, particularly for R32. The HTC correlations of Hsieh and Lin, and Palmer et al. fit the measured data relatively well with 96 and 80 % data within the deviation of ±20 %, respectively. Huang et al. correlation exhibits fare predictability for FPD, with more than 80 % data within the deviation of ±25 %. [ABSTRACT FROM AUTHOR]

• Four common latent heat functional fluids are described and compared. • Summarizes the current methods for determining the stability of PCMEs. • The mechanism and solution to the stability of PCMEs are analyzed. • The mechanism, inhibition method and research on PCME supercooling are concluded. • An overview of the latest research progress of PCMEs in various fields. As the global environment continues to deteriorate and temperatures gradually rise, it has been realized that the utilization of renewable energy is one of the most effective measures to mitigate global warming. Thermal energy storage plays a crucial role in the energy mix, and phase change materials are among the most significant and effective methods of thermal energy utilization. Phase change material emulsions, as fluid-phase phase change materials, play a significant role in thermal energy storage and heat transfer. However, issues related to stability and supercooling hinder the practical application of phase change material emulsions. Consequently, this paper explores the current research status of stability and supercooling mechanisms and technologies. Firstly, this paper provides a brief overview of the fundamental concepts of phase change material emulsions. Then, it addresses the challenges related to controlling the stability of phase change material emulsions and the issue of significant supercooling. The paper elaborates on relevant research findings in detail, mechanisms, evaluation criteria, and potential solutions. Finally, the paper outlines the research progress of phase change material emulsions in the fields of solar energy, construction, and thermal management, demonstrating their potential to advance renewable energy and various industrial sectors. [ABSTRACT FROM AUTHOR]

• A heat-dynamic network model is developed for FPSCs with reasonable accuracy. • A miniature FPSC prototype is developed for HOT infrared detector. • The non-ideal heat exchange is dominant loss in the expander of miniature FPSCs. High Operating Temperature (HOT) infrared detectors with a miniature Stirling cryocooler, operating at 150 K and above, will become smaller size and more popular in applications with the development of infrared detector technology. In this paper a miniature free-piston Stirling cryocooler (FPSC) is developed for the application of HOT infrared detectors. Allowing for the active properties of the regenerator, actual thermal process in each chamber of the Stirling cryocooler, and the heat-dynamic coupling, the two-port network model is derived for each component of the FPSC, and then a heat-dynamics network analysis model is established for the entire cryocooler. Meanwhile, the performance prediction with the experimental verification is performed for the cryocooler prototype developed. Then analyses of energy losses are carried out, and the studied results shows that main loss for the expander of miniature cryocooler is ascribed to the non-ideal heat transfer of the regenerator. For the miniature cryocooler prototype developed, the cooling capacity of 1.35 W@150 K is achieved, at room temperature of 23 °C and the input power of 10 W AC. The relative Carnot efficiency of the prototype is 13.5 %, and the maximum input power is 20 W AC and the weigh is 200 g. The achieved performance is quite appropriate for the application of high operating temperature infrared detectors. [ABSTRACT FROM AUTHOR]

• Stratified annular flow including oil-poor layer and oil-rich layer is observed. • Heat transfer of R32-partially miscible oil is enhanced by the stratification. • Heat transfer correlation reflecting stratification of R32-oil is developed. R32 commonly applied in room air-conditioners has flammability, and the ways to decrease the charging amount, e.g. reducing the dissolution of refrigerant in the lubricating oil, are important to reduce combustion risk. The application of partially miscible oil rather than completely miscible oil can decrease R32 solubility but may deteriorate the heat transfer by the forming of pure oil layer, and thus the understanding of the stratification and flow boiling heat transfer characteristics of R32-partially miscible oil mixture is necessary. The purpose of this study is to experimentally investigate the stratification and flow boiling heat transfer characteristics of a mixture of R32 and partially miscible POE oil, and to propose a new heat transfer correlation. The experiments are carried out at evaporation temperature varying from -5 °C – 15 °C, total oil concentration varying from 1 % to 5 %, vapor quality varying from 0.1 – 0.9 and mass flux varying from 200 kg m-2 s-1 to 400 kg m-2 s-1.The results indicate that the stratification of R32-partially miscible oil mixture occurs at the high liquid oil concentrations, and an oil-poor layer and an oil-rich layer are involved in the stratified annular layer. R32-partially miscible oil mixture has higher flow boiling heat transfer coefficients than R32-completely miscible oil mixture due to the low viscosity of the oil-poor layer. A new flow boiling heat transfer correlation reflecting the effect of stratification is developed, and the predicted results agree with 91 % of the test results as the relative deviation ranges in ±20%. [ABSTRACT FROM AUTHOR]

• One-dimensional Kalman Filter was used to reduce pressure drop estimation errors. • Kalman Filter initialization equation were developed based on pressure drop parameters. • Significant improvements were observed, particularly for mini tubes. • Kalman Filter approach MARD decreased from 62.90 to 12.12 for mini tubes. The estimation of pressure drop in systems involving two-phase fluids holds a substantial influence over system design, energy efficiency, heat transfer dynamics, and the overall system performance. Existing correlations in the current literature exhibit considerable errors, primarily attributable to the diverse characteristics of flow patterns inside the pipe. This work presents a discussion on the pressure drop of the R-407C fluid in horizontal pipes during two-phase flow, along with the application of the Kalman Filter to improve the estimations produced by well-known correlations. The initialization data used were obtained through equations created based on experimental data and considering the influence that diameter, mass velocity, and saturation pressure have on the pressure drop. The correlations used as a basis for the calculations were selected from the literature, considering the lowest percentage error observed in the pressure drop estimation. Experimental data of pressure drop where compared with the results the obtained by using the correlation alone and in combination with a Kalman Filter. For tubes with a diameter greater than 1.5 mm, applying the correlation together with the Kalman Filter resulted in a Mean Absolute Relative Deviation (MARD) of 15.71, whereas using the correlation alone yielded a MARD of 28.26. For tubes with diameters of 1.5 mm or less, the MARD values were 12.12 and 62.90, for the combination of correlation and the Kalman Filter and for the correlation alone, respectively. These results underscore the viability of the Kalman Filter as an effective tool for improving the accuracy of pressure drop calculations in horizontal tubes. [ABSTRACT FROM AUTHOR]

This paper aims to study the nanofluids with peristaltic flow motion in a confined length of non-uniform horizontal tube with an endoscope. In addition to wall properties and velocity slip effect, three geometries (i.e., sphere, cylinders, and blades) of Gold – blood MHD nanoparticles are also considered. To peruse the realistic study of the model, equations and boundary conditions are modeled and formed in dimensionless control equations. Expressions for the exact solutions of velocity, nanoparticle shape effects for temperature, heat transfer, and stream function are obtained. Visual depiction of these solutions is also demonstrated by carrying out various parameters. After analyzing, a few observations illustrate that platelet-shaped nanoparticles attain the highest thermal conductivity. The maximum temperature is experienced for sphere-shaped nanoparticles and the increasing behavior is also observed for higher values of thermal slip parameter. The conduct of velocity profile increases for greater values of the slip parameter. Sphere-shaped nanoparticles also show dominance compared to brick- and platelet- shaped particles. A trapping phenomenon is also discussed in the current study. The presented model can useful for applications associated with the metabolic structures that play a vital role in heat sources inside the human body. [ABSTRACT FROM AUTHOR]

The transport properties of solids are better compared to liquids or base fluids. Thus, when solid nanoparticles are added to a base fluid, the resultant nanofluid is more efficient for cooling or heating phenomena compared to the base fluid. The study will help thermal engineers in predicting the transmission of thermal energy. In this aspect, Cattaneo-Christov heat flux is used to compute the rate of transferring heat in a material. Cattaneo-Christov heat flux, also known as heat paradox, is used in the flow for heat transfer. Ag-silver is taken as the nanoparticles with the ethylene glycol C $ _{2} $ 2 H $ _{6} $ 6 O $ _{2} $ 2 the base fluid. Heat transfer is analyzed for the two-phase flow when the heated rod is placed vertical as well as horizontal in the cavity. The simulation is made in Open-source Field Operation And Manipulation. The projection method and the finite volume method (FVM) are used for the computation of the model developed for the flow of nanofluid. A comparison between the projection method and the FVM is made. The transmission of thermal energy via the FVM in OpenFOAM better suits compared to the results obtained via the projection method shown in the figures. [ABSTRACT FROM AUTHOR]