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Flow boiling heat transfer is a promising technology for thermal management. In this paper, flow boiling heat transfer characteristics in a rectangular vertical flow channel are experimentally and numerically investigated at low flow rate. Visualization results provide guidance for the prediction of flow patterns. The flow boiling correlation at low flow rates is improved with an error of less than 30%. Numerical results reveal vortices enhanced local heat transfer. Absolute vorticity is introduced to quantify the secondary flow. The results indicate that the secondary flow intensity increases with heat flux, verifying that boiling flow produces the local convection enhancement. [ABSTRACT FROM AUTHOR]

The erosion and sedimentation of bank slopes are important factors affecting the safety of wharf operations. The essence of bank slope monitoring is to identify the water–soil interface. This paper proposes a model for soil-and-water interface identification and monitoring equipment buried on the bank slope of the wharf, based on the difference in thermodynamic heat transfer between water and soil media, and presents the results of multi-condition numerical simulation. The comparison between numerical simulation results and indoor experimental results shows that the overall patterns are consistent, with an error of less than 11.4%, which is lower than the deviation between theoretical calculation results and indoor experiments. Based on the accuracy of the numerical calculation results, the temperature rise and propagation characteristics of linear heat sources made of iron and PVC in eight types of cohesive soils and six types of non-cohesive soils were studied. The results indicate that there are significant differences in the temperature distribution of linear heat sources made of iron and PVC in both water and soil media. The monitoring equipment model based on the difference in heat transfer between water and soil can be applied in practical engineering. This provides a foundation for the design and application of subsequent monitoring equipment. [ABSTRACT FROM AUTHOR]

The stability and performance of loess infrastructure in cold regions are often challenged by seasonal freezing–thawing action. The action of the foundation loess is a complex thermo-hydro-mechanical coupling process, and it is crucial to understand this process for the loess infrastructure in cold regions. A series of controlled tests were conducted to observe the changes in temperature, moisture, and frost heave variations within loess samples under freezing–thawing, and the influences of cycle period, freezing–thawing amplitude, and cycle number on the thermo-hydro-mechanical behavior of loess were investigated. The results reveal that freeze–thaw cycles significantly affect the heat transfer, water migration, and deformation of the loess. The temperatures of sample at different heights periodically vary under freezing–thawing. Water is absorbed to the samples, which undergoes a rapid water intake stage, a water drained stage, and a slow water intake stage under freezing–thawing, resulting in moisture redistribution in loess. Loess undergoes frost heave, thaw settlement, and consolidation processes during freezing–thawing, and a slight wetting collapse may occur after several freezing–thawing cycles. Within the same cycle, frost heave is the largest while consolidation deformation is the smallest. Frost heave and consolidation deformation reach their maximum values at the second cycle, whereas thaw settlement reaches its maximum value during the second or third cycle. Each stage deformation increases with an extended cycle period and almost decreases as the freezing–thawing amplitude increases. Freeze–thaw cycles can induce wetting collapse of loess, resulting in negative residual deformation. Furthermore, the thermo-hydro-mechanical coupling process and the deformation mechanism of loess have been elucidated. These insights contribute to a more comprehensive understanding of the failure mechanisms in loess engineering in cold regions. [ABSTRACT FROM AUTHOR]

In India, air conditioning is essential in the truck driver's cabin during the summer. An air conditioning system powered by the vehicle's engine adds to the engine's workload, resulting in higher fuel demand and more emissions. An adsorption chiller that runs on engine exhaust is designed here to lower the interior temperature of a truck cabin to address the above-mentioned issue. Here, an adsorption air conditioner system's effectiveness is forecast using a lumped analytical technique. During the adsorption process, heat from the adsorber bed is absorbed by cold water and released into the radiator. The desorber bed has been heated using hot water as a heat transfer medium from the engine exhaust heat. The analysis was carried out using the adsorption kinetic equation at adsorption equilibrium. The influence of inlet water flow rate, temperature and switching time (adsorber process to desorber process and vice versa) on adsorption chiller performance has been studied here. According to simulation results, the proposed adsorption chiller can be used to keep the driver cabin cool during summer for operational conditions adopted during the simulation. The adsorption air conditioner's highest coefficient of performance (COP), as determined by this investigation, was found to be 0.214. [ABSTRACT FROM AUTHOR]

The condensation of water vapor plays a crucial role in various applications, including combating water scarcity. In this study, by employing molecular dynamics simulations, we delved into the impact of graphene coatings on water vapor condensation on copper surfaces. Unique to this work was the exploration of various levels of graphene coverage and distribution, a facet largely unexplored in prior investigations. The findings demonstrated a notable increase in the rate of water vapor condensation and heat transfer performance as the graphene coverage was reduced. Using graphene coverages of 84%, 68%, and 52%, the numbers of condensed water molecules were 664, 735, and 880 molecules/ns, respectively. One of the most important findings was that when using the same graphene coverage of 68%, the rate of water vapor condensation and heat transfer performance increased as the graphene coating became more distributed. The overall performance of the water condensation correlated well with the energy and vibrational interaction between the graphene and the copper. This phenomenon suggests how a hybrid surface can enhance the nucleation and growth of a droplet, which might be beneficial for tailoring graphene-coated copper surfaces for applications demanding efficient water vapor condensation. [ABSTRACT FROM AUTHOR]

In order to investigate the dynamic process of the heat and mass transfer phenomenon of water vapor on activated carbon, a fixed‐column adsorption unit and two kinds of activated carbon were used as adsorbent for water vapor adsorption under the adsorption temperature 293.15 K, 303.15 K and 313.15 K, respectively. A coupled model was developed by mass and energy balance, mass transfer and simplified DO adsorption equilibrium equation. The effects of physical parameters on heat and mass transfer were theoretically investigated. Results show that the numerical model match well with the experimental data (R2>0.993). The axial diffusion coefficient (DL) increases from 1.226×10−6 m2 s−1 to 4.062×10−6 m2 s−1 for RAC and 1.425×10−6 m2 s−1 to 4.030×10−6 m2 s−1 for MAC, mass transfer coefficient (k) increases from 8.171 s−1 to 27.083 s−1 for RAC and 9.499 s−1 to 26.864 s−1 for MAC. Concurrently, the breakthrough time of adsorption water vapor gradually shorten from 1000 s to 780 s with temperature increasing from 293.15 K to 313.15 K. The effect of axial diffusion coefficient (DL) on mass transfer is not obvious. Furthermore, the influence of the mass transfer coefficient (k) on temperature variation rate surpasses that of the internal heat transfer coefficient (h). [ABSTRACT FROM AUTHOR]

The current work investigates the thermal characteristics of nanofluid flow (water and air as base fluids with Al2O3 nanoparticles) in a circular pipe at constant heat flux. Numerical simulations were performed using the Eulerian-Euleian two-phase model with an RNG k − ε turbulent model with enhanced wall function. Results showed that the two-phase approach reduced the error by about 3–5% in the prediction of the average heat transfer coefficient. Within the range of a volumetric fraction of nanoparticles from 1 to 5% and inlet velocity from 10 to 25 m/s, heat transfer performance increased significantly compared to pure fluid flow. For water, the particle motion from the wall to the center of the pipe was empowered by thermophoresis in addition to higher turbulent kinetic energy leading to a profit index of about 3.5, while for air; the Brownian motion of particles increased the viscosity and thermal conductivity near the wall leading to profit index of about 240 indicating high amount of heat transfer. For both fluids, the heat transfer effectiveness ratio increased at a higher volume fraction of nanoparticles (3.5 for water-based nanofluid and 140 for air-based nanofluid). These values indicate promising effects of nanoparticle addition, especially for air, where the volume fraction had a much more significant effect than water. [ABSTRACT FROM AUTHOR]

An accurate understanding of the heat transfer of water through rock fractures is essential for the extraction and utilization of thermal energy from high‐temperature rock masses. A systematic numerical simulation based on the double‐rough‐walled model has been presented to investigate the shear effect on convective heat transfer in rough rock fractures. On the basis of the modified successive random additions algorithm, four different self‐affine surfaces were generated and utilized to establish the 3D double‐rough‐walled fracture models. The fluid flow and heat transfer were simulated by directly solving the Navier–Stokes equation and energy conservation equation, respectively. The combined effects of shear and surface roughness on the heat transfer were investigated. The results show that the heat within rough‐walled fractures transfers preferentially along the main fluid flow channels, and the areas of fast and slow thermal transmission fit well with the high‐ and low‐flow regions, respectively. As shear advances, the heat transfer coefficient firstly increases, then decreases slightly and finally stabilizes within a certain range, in which stabilization occurs earlier in fracture with a larger joint roughness coefficient. The effect of surface roughness on heat transfer shows an opposite trend during shearing. When the shear displacement is small, the enhancement effect of surface roughness that provides larger heat transfer areas dominates the heat transfer. As shear displacement continues to increase, this enhancement effect will be gradually weakened until the decreasing effect that bumps on the rough‐walled surface hinder the fluid flow dominates the heat transfer. [ABSTRACT FROM AUTHOR]

In power applications, convection plays a dominant position in the transport of strength for the proper design to attain higher warmth transfer quotes. Where in the fluid movement is genuinely induced via density gradients. This has a look at what is involved with transient convection in an isosceles-superimposed triangular enclo sure. The walls were angled at θ = 45°. Critical Rayleigh numbers have been obtained: Ra = 106, especially for the fluid crushed between the two triangles where we can visualize the critical convection transaction between the air and water. The consequences in the quantitative dimension of average Nusselt quantity change and qualitative visualization of streamline and isotherms are examined. The air and water streamlines and the temperature fields had been obtained for the Rayleigh numbers 10³ ≤ Ra ≤ 108. Furthermore, the water fluid's natural convection case has the best heat transfer performance at the water fluid, whereas the dilatant fluid exhibits the lowest heat transfer performance. Heat transfer from the bottom to the top can be significantly improved by the triangle shape at first in a smooth and harmonious manner, and then it turns into a more complex and disorderly shape when the water reaches high temperatures. [ABSTRACT FROM AUTHOR]

In this paper, hydrophilic cotton (CO) yarn and hydrophobic cross-section polyester (PET) filaments were used to prepare single-layer interwoven fabrics (CO/PET fabrics) with plain, 3/1 twill, and 8/5 satin to formulate a hydrophobicity–hydrophilicity gradient across the fabric for obtaining a good water transfer ability. The CO fabrics and PET fabrics were prepared for comparison. The contact angle and thermo-physiology properties of the fabrics, including the wicking property, moisture management ability, drying property, air permeability and water vapor permeability, thermal property, and dynamic cooling property, were investigated. The results show that the asymmetric hydrophobicity–hydrophilicity characteristic can be formed across CO/PET fabric with 3/1 twill and 8/5 satin. This can improve the water transfer ability from the inside to the outside of the fabrics, and the longer the floating length of the fabric is, the stronger the water transfer ability is. These two fabrics also exhibit excellent wicking properties, overall moisture management capability, and thermal comfort, and have good permeability, drying properties, and dynamic cooling properties compared to the corresponding fabrics. As a result, these two CO/PET interwoven textiles are more suitable for application as clothes worn in summer. The interweaving technique combining hydrophilic and hydrophobic yarns is an easy and cost-effective method to prepare fabrics that meet summer requirements. This work provides insight into the thermal and moisture comfort property of interwoven fabrics for summer garments. [ABSTRACT FROM AUTHOR]

Supercritical water, known for its abrupt changes in fluid properties near the pseudocritical region, has always posed a design challenge, leading to enhancement or deterioration in heat transfer. Additionally, the lack of complete understanding of the thermodynamic behavior of supercritical water near the pseudocritical zone, unlike in the subcritical zone, highlights the necessity of a systematic study. Hence, this paper focuses on characterizing the convective upward flow and heat transfer characteristics inside a vertical smooth annular square channel. The numerical analysis uses a steady-state, pressure-based, compressible, Newtonian solver with body force term and two-equation turbulence model to study the influence of variation in pressure, heat flux, and heat-to-mass flux ratios. The flow characteristics and heat transfer behavior of deteriorated, normal, and enhanced heat transfer modes are studied. The heat transfer deterioration is suppressed with the increase in pressure; however, it increases with the increase in inlet bulk temperature. The supercritical boiling number that determines the heat transfer mode is calculated and analyzed for the square annulus section. The evolution of the flow in different heat transfer modes differs based on the effect of buoyancy on the velocity field and the turbulence. The calculated Nusselt numbers match the existing Jackson and Hall correlation well with a maximum absolute error of 9.91%. [ABSTRACT FROM AUTHOR]

Water vapor condensation is a key process for many applications. Existing studies in water vapor heterogeneous condensation have used different methods to modify the hydrophobicity of the water vapor condensation surface. One way to modify the surface properties is to use graphene coating. On a macroscale, surface modification using graphene coating can improve water vapor condensation heat transfer of various substrates. However, on the molecular scale, its effect is poorly understood. This work investigated the effect of graphene coating on water vapor condensation using molecular dynamics simulations (MDS). We examined the water vapor condensation on bare copper surfaces considering the effects of initial temperature difference, water model, and surface size, parameters that have not been investigated by previous studies employing MDS for the same water-surface configuration. One water model was then used to simulate the condensation on a copper surface with and without graphene coating. We then investigated the effect of graphene defect, the energy and vibration of graphene atoms, and the interaction between graphene and copper layers. The surface size notably influenced the condensation rate and heat transfer performance. The condensation rate and heat transfer performance were significantly reduced when the copper surface was coated by graphene. The number of water molecules condensed was 1253 molecules/ns on the bare copper surface, compared to 587 molecules/ns on the graphene-coated copper surface. Moreover, the water molecules condensed on the graphene-coated copper surface tended to return to the bulk vapor phase. Other important results are also provided. This study gives an insight into the water vapor condensation on graphene-coated copper surfaces, useful to pursuit the design and optimization of graphene-coated copper surfaces for applications that need efficient water vapor condensation, such as for industrial applications, like thermal, chemical, and nuclear. [ABSTRACT FROM AUTHOR]

There are several industrial applications where boiling is used, for example boilers, refrigeration systems, nuclear reactor cooling, and microelectronic chip cooling. Experimental research has been carried out to determine the flow boiling heat transfer capabilities of copper-alumina-coated surfaces for application in heat transfer equipment. De-ionized (DI) water is used as the coolant for experimentations in a minichannel with dimensions 10 × 1.5 × 10 mm. Copper surfaces coated with thin copper-alumina nanocomposite films are created using the electrodeposition process. The coated layer created using an electrochemical technique offers strong adhesiveness with the base copper and is therefore anticipated to be suitable for real-world heat transfer appliances as part of the ongoing scientific development in subcooled flow boiling. The electrochemical technique offers easier control over its various parameters, such as current density, duration and electrolyte composition, making it possible to easily achieve a variety of surface characteristics, such as crystallinity, wettability and porosity. as required in the coated surfaces. Additionally, the copper-alumina is a hydrothermally stable oxide material that is well suited for use in boiling heat transfer devices. The boiling (subcooled flow) heat transfer tests are carried out at various mass flows. The improvement in the two-phase heat transfer coefficient (HTC) and critical heat flux (CHF) can reach up to 90 % and 93 %, respectively. The coated surfaces have improved CHF and HTC because of improved wettability, increased surface roughness, and the existence of active nucleate sites in high-density. [ABSTRACT FROM AUTHOR]

In thermal convection of water, the movement of water as a whole includes movement of not only heated water but also the motion of the water that surrounds it. It is conceivable that confusion between the movement of water and the transfer of heat is caused by not paying attention to the movement of water around the heated water. In this study, we created a teaching tool that can observe time-dependent changes of both temperature and flow velocity distributions simultaneously and clarify the movement of water around heated water. In addition, the case of a cooling experiment was similarly clarified. Two particular flows were observed in the region of water around heated water: the "movement of water that rises with the upward flow generated from the heating part" and the "movement of flowing water such that it fills the area where there was a heating part-generated upward flow." Similarly, in the case of cooling, the "movement of water around cooled water" was revealed. By using this teaching tool in the unit "Heat Transfer in Matter" of fourth-grade elementary science, it is expected that confusion between heat transfer and movement of water can be prevented. [ABSTRACT FROM AUTHOR]

The solar‐driven interfacial evaporation system has attracted much attention in recent years due to its reduced heat loss and accelerated steam generation. As a low‐cost and readily available resource, wood is widely applied as photothermal materials in solar‐driven interfacial evaporation system because of its superior water transfer and heat loss prevention properties. Herein, a simple, mild, and cost‐effective method is employed to fabricate wood‐based photothermal materials. The results demonstrate that the solar absorption rate of wood‐nigrosine is more than 97.5% across a wide wavelength range (200–2500 nm), and an evaporation rate of 1.46 kg m−2 h−1 and evaporation efficiency (86.1%) are achieved under 1‐sun illumination (100 mW cm−2). The solar‐driven interfacial evaporation system based on wood‐nigrosine exhibits strong structural stability and processing capability for dyes and seawater. [ABSTRACT FROM AUTHOR]

• The structural model was constructed for a water evaporator operating in a low-pressure environment. • A multi-objective optimization method combining CFD simulations and the MO-SHERPA algorithm was proposed. • The offset strip fin structure and heat transfer performance of the water evaporator was optimized. The aim of this study was to investigate the optimal heat transfer performance and structure of airborne water evaporators in low-pressure environments. To achieve this, a multi-objective optimization design was performed on a plate-fin water evaporator with offset strip fins, operating in a low-pressure environment at an absolute pressure of 7 kPa. The multi-objective Simultaneous Hybrid Exploration that is Robust, Progressive and Adaptive (SHERPA) (MO-SHERPA) algorithm was used to optimize the structure of the plate–fin water evaporator under a low pressure of 7 kPa. There are three conflicting optimization objectives, including comprehensive performance factor (JF), entropy generation (S gen), and weight. The optimal Pareto frontier design points were compared and analyzed based on the three evaluation indicators. The optimization results showed that compared with the initial design point, the JF increased by 32.14% and the weight decreased by 48%, which indicated that the heat exchange performance has been significantly improved, and the weight of the heat exchanger was also reduced. The internal and external flow fields of the water evaporator, including temperature, pressure, and volume fraction of vapor, were qualitatively compared to prove the optimization effect. In addition, the influence of structural parameters on the heat transfer performance of the water evaporator were analyzed. The method proposed in this study can effectively optimize the fin structural design parameters, providing valuable guidance for the structural design of water evaporators operating in low-pressure environments. [ABSTRACT FROM AUTHOR]

In order to improve the heat transfer characteristics of miniature thermosyphons, a study of the processes of heat transfer by them using water and nanofluids as heat carriers was carried out. A water mixture based on nanoparticles of Ukrainian natural aluminosilicate – attapulgite with the addition of 0.1 % carbon nanotubes was used as nanofluids. The data of the study of the maximum heat flow and the minimum thermal resistance of copper thermosyphons with an internal diameter of 5 mm and a length of 700 mm are presented. Orientation of thermosyphons in space: vertical. The length of the heating zone varied from 50 mm to 200 mm, with the same amount of heat-carrier. The fill factor varied from 0.44 to 1.93. A comparison was performed of the heat transfer capabilities of thermosyphons with water and with a nanofluid with a mass concentration of 0.5 %. It has been shown that nanofluid thermosyphons transmit 53 % more heat flow compared to water, and thermal resistances are reduced by 25 %. The influence of the concentration of nanoparticles on the heat transfer characteristics of thermosyphons is shown. Nanofluids with concentrations (0.1 %, 0.5 %, 0.7 %) showed the same level of thermal resistances, with an increase in maximum heat flows compared to distilled water. Thus, when compared with the lowest concentration (0.1 %), the use of 0.5 % nanofluid gives an advantage of up to 40 %, and 0.7 % – an advantage of up to 51 %. This is explained by the appearance of a specific porous structure of anisometric nanoparticles on the heating surface, which contributes to the appearance of additional centers of vaporization during boiling and improves the heat transfer characteristics of thermosyphons. Thus, the use of such thermosyphons with nanofluids when cooling elements of electronic equipment could improve their functional characteristics. [ABSTRACT FROM AUTHOR]

• Refrigerant maldistribution of the novel heat exchangers is analyzed. • The decentered orifice plate creates nested loop flow to improve distribution. • The parallel multi-chamber forms separate chambers to improve distribution. • Significant reduction of refrigerant maldistribution after optimization design. The novel alternatively-laminated-microchannel-tube (ALMT) heat exchanger contains two pairs of vertical headers and alternatively laminated microchannel flat tubes, which realizes high-efficient heat transfer between water and refrigerant and shows energy-saving potential in large-scale air conditioners. However, the microchannel flat tubes are upright inserted into vertical headers and are susceptible to refrigeration maldistribution. In this article, two-phase refrigerant maldistribution and optimization design in ALMT heat exchangers with vertical headers are studied experimentally and numerically. Refrigerant maldistribution is experimentally measured and its flow behaviors are explored with CFD simulations. The R410A is used as the working fluid. Results show that more liquid refrigerant is supplied to middle tubes but less to both ends under phase separation and gravity. Therefore, the decentered orifice plate (DOP) and parallel multi-chamber (PMC) are designed to improve refrigerant distribution. Both DOP and PMC promote gas-liquid phase mixing by accelerating refrigerant flow. The DOP creates the nested loop flow and PMC forms separate chambers inside vertical header to distribute refrigerant to each flat tube uniformly. Moreover, the formation conditions for nested loop flow are established. The average standard deviation of refrigerant flow rate reduces from 0.21 to 0.07 with DOP, and to 0.03 with PMC, respectively. [ABSTRACT FROM AUTHOR]

Beyond photothermal conversion, the surface wettability of light-absorbing materials should be also determinative to the efficiency of solar-driven interfacial steam generation (SISG). Herein, by modifying hydrophobic Cu nanoparticles (NPs) with a hydrophilic carbon (C) shell, hydrophilic Cu@C core–shell NPs were successfully fabricated and used for constructing evaporation films for SISG. In comparison to the film constructed with Cu NPs, the evaporation films constructed with Cu@C core–shell NPs exhibit much increased SISG efficiency, reaching 94.6% as high. Except for the localized surface plasmon resonance (LSPR) effect of Cu NPs ensuring the excellent photothermal conversion, it is experimentally and theoretically revealed that the surface wettability switching from hydrophobicity to hydrophilicity, as induced by C coating, is beneficial to heat transfer at the solid/liquid interface and water transport at the evaporative surface, thus improving the thermal-evaporation conversion performance for efficient SISG. However, the further thickened C shells would weaken the LSPR effect and hinder the interface heat and water transfer, leading to the decreased photothermal and thermal-evaporation conversion efficiencies, and thus the lowered SISG performances. This demonstration gives an alternative and promising access to the rational design of photothermal materials featured with switchable surface wettability ensuring interface heat and water transfer enhancement for efficient SISG. Highlights: • Cu@C core-shell NPs with hydrophilic surface were successfully obtained via hydrothermal carbonization. • The C shells induced surface wettability switching from hydrophobicity to hydrophilicity benefited heat and water transfer. • The Cu@C core-shell NPs exhibited a high SISG efficiency reaching 94.6% under 1 sun illumination. With surface wettability of Cu nanoparticles switched from hydrophobicity to hydrophilicity by the coating of C shells, the obtained Cu@C core-shell NPs exhibit much increased SISG efficiency, reaching 94.6% as high, synergistically attributed to the excellent photothermal conversion, the strengthened heat transfer at the solid/liquid interface and the enhanced water transport at the evaporative surface. [ABSTRACT FROM AUTHOR]

Heat transfer coefficient (HTC) was experimentally measured for saturated and subcooled pool boiling of binary mixtures of water and glycerin. Saturated boiling was studied for mixtures with water mass fractions ω w from 100 % to 60 % on horizontal flat nickel-plated surfaces at heat fluxes from 50 to 650 k W m − 2 at atmospheric pressure. Subcooled boiling was investigated in the range of subcooling from 0 to 30 K at heat fluxes of approximately 250, 450 and 650 k W m − 2 . It was found that mixture effects have a significant impact on saturated boiling HTC even for mixtures with very low content of glycerin as significant drops of HTC were observed for subtle changes in composition for mixtures of high ω w . Measured HTC was successfully correlated with the combination of Yagov (1999) and Inoue and Monde (2009) correlations with a mean relative error of 12 %. A simple empirical HTC correlation is also proposed. For subcooled boiling, developed subcooled boiling regime was reached for all investigated heat fluxes. For this regime, correlations, which were able to predict HTC for saturated boiling, were employed to predict subcooled boiling HTCs for all investigated concentrations, heat fluxes and subcoolings. Effect of subcooling and effect of liquid composition on total HTC were of the same importance for mixtures with higher water content. With the increase in concentration of glycerin in the mixture, decrease in total HTC with increasing subcooling became more significant. [ABSTRACT FROM AUTHOR]

Domestically and internationally, the effect of fracture flowing water and transferring heat on the temperature field of surrounding rock in high-level radioactive waste repositories is a popular research area. Compared with straight fracture flowing water and transferring heat, there are few relevant literatures about the heat transfer of curved fracture water flow. Based on the conceptive model of flowing water and transferring heat in curved fractured rock mass, the influence of flowing water and transferring heat in "I", "L", , and shaped fractures on the temperature field of rock mass is calculated by using discrete element program. The findings indicate that: When the model goes into a stable state under four working conditions, the rock on the x = 0–2 m mostly forms a heat transfer path from left to right; the x = 2–4 m primarily forms a heat transfer path from bottom to top, and the temperature gradient reveals that the isotherm of 40–45 °C is highly similar to the shape of four different fractures, indicating that flowing water and transferring heat in the fracture configuration dominate the temperature field of the right side rock mass. The direction of the flowing water and transferring heat of the fracture exerts a dominant effect on the temperature of the rock mass than the length. [ABSTRACT FROM AUTHOR]

In recent years, the open microchannel has drawn increasing interest, but severe local dryout limited the heat transfer capability of flow boiling. It was anticipated that nanostructures with exceptional capillary wicking abilities would overcome this problem. In this study, blade-like CuO nanostructures were created in the copper open microchannels to experimentally investigate water flow boiling. Experiments were carried out in nanostructured open microchannels (NMCs), and smooth-surface open microchannels (SMCs), as a comparison, were examined under identical operating conditions. Four main flow patterns, including bubbly flow, slug flow, and two kinds of stratified flow, dominated successively in NMCs and SMCs. Although the flow patterns were similar in NMCs and SMCs, the heat transfer coefficient (HTC) of flow boiling was greatly enhanced by nanostructures under conditions of medium and high heat flux, while the nanostructures' influence on HTC was unnoticeable at low heat flux. At medium and high heat fluxes, the dependence of HTC on heat flux and flow rate indicated the joint contribution of nucleate boiling mechanism and convective evaporation mechanism to heat transfer. The enhanced effect of nanostructures on nucleate boiling and convective evaporation became more prominent as heat flux increased, leading to a higher HTC in NMCs than in SMCs at higher heat flux conditions. [ABSTRACT FROM AUTHOR]

In a proton exchange membrane fuel cell (PEMFC) system, proper management of water and heat transport is essential to improve its overall performance and durability. To comprehensively investigate the internal processes of PEMFCs, an improved two-phase non-isothermal model based on heat and water transfer mechanisms inside the fuel cell is developed. The results show that the model proposed in this work can predict the fuel cell's performance accurately and is capable of exploring water and heat transfer phenomena inside fuel cells. Additionally, the water and heat transfer of cathodes and anodes under different relative humidity and temperatures are studied. It can be concluded that when the PEMFC operates under a constant voltage, the anode water content gradually increases, while the cathode water content gradually decreases. The maximum water content occurs at the interface between cathode catalyst layer and cathode gas diffusion layer, while the minimum value is attained at the interface between anode catalyst layer and anode gas diffusion layer. When the fuel cell operates at 0.75 V, although the water content of CCL is the highest, no back-diffusion of dissolved water occurs. [ABSTRACT FROM AUTHOR]

A gravity-type heat pipe boiling characteristics test rig was constructed to solve the heat dissipation problem of fuel cells during operation. The boiling heat transfer characteristics of water in a parallel plate under negative pressure at different inclination angles and heat flow density input are investigated. The results show that: First, the gravity-type heat pipe can dissipate some heat and it is possible to use it for fuel cell heat dissipation. Second, with a certain range of heat flow density, the temperature of all parts of the plate is about 80 °C, with a small temperature difference, which is conducive to the safe operation of the fuel cell. Third, the heat flow density is in the range of 2222~3111 W·m−2, the temperature difference is large, and the outlet temperature is greater than 80 °C, which exceeds the operating temperature of the fuel cell, and the power-type heat pipe should be used for heat dissipation. Fourth, the average temperature of the plate placed at an inclination angle of 45°~60° is lower compared to other angles, and the temperature is evenly distributed. On the one hand, the conclusions reveal the characteristics of boiling heat exchange under negative pressure conditions of water inside the flat plate and, on the other hand, provide a reference for designing heat pipe systems for fuel cell heat dissipation. [ABSTRACT FROM AUTHOR]

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The thermal management of micro- and nano-electromechanical systems is closely related to maintaining optimal system performance and reliability. Heat dissipation through the phase transition of the working medium has emerged as an effective approach to these problems. In this study, the phase transition of liquid nanofilms over copper surfaces with various heat fluxes, nanoroughness, and wetting conditions is studied by means of molecular dynamics simulations. The results indicate that the phase transition mode of the water nanofilm is normal evaporation at low heat flux and explosive boiling at high heat flux. Two different nanorough surfaces with the same surface area have almost an identical effect on the water nanofilm phase transition. Explosive boiling occurs earlier on hydrophobic surfaces, which is consistent to the macroscopic phenomenon. The heat flux at which explosive boiling occurs on nanorough surface increases for hydrophobic and neutral surfaces compared with smooth surfaces and remains constant for hydrophilic surfaces. The onset of explosive boiling on nanorough surfaces is later than that on smooth surfaces. These findings on the mechanism of heat and mass transfer at the micro- and nanoscale are conducive to efficient utilization and energy conservation. [ABSTRACT FROM AUTHOR]

Hot water shower sterilization is a crucial part in the production of liquid pharmaceutical products. This work was conducted to experimentally investigate the heat transfer for hot water shower sterilizers by examining the effects of various parameter changes. Heating and cooling runs were performed using a lab-scale test bench for a 1000 ml glass bottle and 500 ml flexible polypropylene infusion bag. The temperature range under investigation spanned from 20 °C to 80 °C, covering a significant portion of the range for heating and cooling of the sterilization process as well as typical temperatures used in food pasteurization. Temperature measurements were taken at three distinct locations within the products. High-speed and infrared photography was employed to explore the varying film regimes on the products. The results indicated that increasing the surface-averaged volume flow rate from 20 m3 h-1 to 40 m3 h-1 per m2 of spraying surface reduced the cooling and heating rates for the bag. However, increasing the surface-averaged volume flow rate correlated to an increase in cooling and heating rates for the bottle. Additionally, configuring a distribution tray above the products with a greater number of smaller holes resulted in reduced sensitivity of the surface-averaged volume flow rate on the cooling rates and an overall decrease in cooling time. A higher hole plate porosity was identified to increase the heating rate of bags. In summary, this study offers valuable insights into how various parameter changes impact the heat transfer in bottles and bags during hot water shower sterilization. • Decreased heating and cooling rates for higher volume flow rates for bags identified. • Faster cooling with a greater number of smaller distribution tray holes achievable. • Agitation effect of flexible bag wall on temperature stratification in bags measured. • Importance of heat transfer of the bags' underside in sterilizers identified. • Increased hole plate porosity increased heating rate. [ABSTRACT FROM AUTHOR]

Work was done on the Tesla valve in this study with a coiled and three-dimensional shape, where a different number of these channels and a direct and reverse flow turbine were used to compare the changes that obtain the amount of pressure and temperatures. With the conception of the technology of transferring heat energy in various heat exchangers, it became necessary to develop our technologies that increase the transmission of this energy, and we must refer to the inventions that contributed to the development of the heat transfer system and the three energy laws. They contributed to the development of some mechanical systems, where the Tesla valve is considered one of the valves that have two directions of flow, the first is direct, in which the pressure value is low, and the other is reverse, which occurs when movement is disturbed due to the direction of the channel in which it can be used. This concept can be used to improve heat transfer. Where the results establish that an increase in the number of channels positively affects the pressure and thus gives more outlets for the passage of water, a study has shown. In the case of four channels an exit temperature of 304.14 K was obtained, which is the highest temperature reached in cases where the direction of flow is direct. The pressure value was in the case in which the channel is a quadrilateral, and the pressure value reached 209 pa. This data are useful and important because the direct exit score has reached 305.74 K for the Tesla valves, which are designed to give enough time for the heat to transfer to the water. The main principle of the Tesla valve is the reverse direction, which works to obstruct the movement of the fluid, and thus increases the pressure and reduces the velocity of the flow. [ABSTRACT FROM AUTHOR]

In this paper, the thermal insulation performance of the roof with water-retained bricks was first analyzed theoretically with respect to the thermal inertia, attenuation and delay time of the roof with water-retained bricks. Then, the experimental rig was established to carry out the experimental research on the thermal insulation performance of the roof with and without water-retained bricks on the sunny, overcast and rainy days in the summer and on the sunny day in the winter. The results showed that: (1) the surface heat storage coefficient is affected by the evaporating heat transfer of the water layer; (2) the thermal inertness, attenuation and delay time of the roof with water-retained bricks are 2.575, 21 and 6.94 h, respectively, when the water depth is 2 cm; (3) on the sunny, overcast and rainy days in the summer, laying water-retained bricks can enhance the heat insulation performance of the roof, and can improve the thermal comfort of the loft; and (4) on the sunny day in the winter, after laying water-retained bricks, the average temperature of the loft in 24 h increases by 2.3 °C, and the temperature fluctuation of the loft decreases by 56.0%. Therefore, the thermal insulation effect is significantly improved after laying water-retained bricks on the roof from the results of both the theoretical and experimental study. [ABSTRACT FROM AUTHOR]

The effect of frying temperature on heat transfer, water loss kinetic, oil uptake kinetic, and quality of French fries was evaluated. With increasing frying temperature, the core temperature of fries increased, and the Biot number and heat transfer coefficient (h) first decreased and then increased significantly (p < 0.05). The water loss rate (kw) and water effective diffusion of fries increased with the increasing frying temperature. The kw of fries fried at 150–190 °C were 0.2391, 0.2414, 0.3205, 0.3998, and 0.3931, respectively. The oil uptake rate (ko) first increased and then decreased with increasing frying temperature, and the ko of samples fried at 150–190 °C were 0.2691, 0.2564, 0.4764, 0.3387, and 0.2522, respectively. There were significant differences in the a*, L*, ΔE, and BI between fries with different temperatures (p < 0.05), while there was no significant difference in the b* (p > 0.05). The hardness and crispness of fries increased with increased frying temperature. The highest overall acceptability scores of fries were fried at 170 °C. Therefore, the changes in color, texture overall acceptability, and oil content were due to the Maillard reaction and the formation of porous structure, which was induced by h and water evaporation of fries when they changed. [ABSTRACT FROM AUTHOR]

A numerical study is conducted to investigate heat transfer characteristics of supercritical water flowing upward in an inclined smooth tube under uniform heating conditions. In this study, model verification was performed under the conditions of low heat flux and high heat flux to ensure the accuracy of experimental data. Inner wall temperature and heat flux distribute non-uniformly on the circumference due to the influence of natural convection. The increase of heat flux enhances the non-uniform circumferential distribution, while the increase of mass flux reduces the non-uniform circumferential distribution. Heat transfer of upward vertical and inclined flows is compared under low and high heat flux conditions. Radial distributions of fluid temperature, density, specific heat capacity, velocity, and turbulent kinetic energy are presented and analyzed. The analysis shows that the increase of heat flux reduces radial turbulence and heat-absorbing capacity of the boundary fluid, while increases radial temperature and density gradient. Three dimensionless buoyancy parameters are used to evaluate the buoyancy effect of inclined flow. [ABSTRACT FROM AUTHOR]

Volume of fluid（VOF） model and user-defined function were applied to simulate the flow boiling of water in microchannel with V-shaped, trapezoidal, square and dovetail-shaped cavities on the heating wall. The effects of cavity shape on the bubble behaviors of bubble nucleation, growth, detachment and coalescence were analyzed. The results show that when the heat flux on the wall is 300 kW· m-2, all cavities are activated as boiling nucleation sites. Compared with the other cavities with V, trapezoidal and square shapes, the onset of boiling time in microchannel with dovetailed cavities is relatively earlier when flow boiling occurs. In the nucleate boiling stage, compared with the trapezoidal cavity, the growth and detachment times of the bubble in the microchannel with dovetailed cavity are decreased by 7.50 ms and 6.70 ms, respectively, while the detachment frequency of the bubble is increased from 33.8 s-1 to 66.7 s-1, which is helpful to enhance the flow boiling heat transfer of water in microchannel. The coalescence and elongation of the detached bubbles in microchannel can increase the evaporation area of liquid film near the heating wall and improve the disturbance of the liquid phase simultaneously. However, it can cause local drying on the heating wall and reduce the stability and reliability of flow boiling heat transfer in microchannel. [ABSTRACT FROM AUTHOR]

To reveal the water and heat transfer characteristics of the orchard soil under water storage pit irrigation and to regulate the distribution of soil water and heat for improving apple quality and increasing yield, a 3D soil water and heat transfer model of orchards under water storage pit irrigation was established. The model not only considered the influences of root water uptake, precipitation, evaporation, and irrigation, but also simulated the infiltration process of the variable water head in the pit according to the principle of mass conservation and introduced the pit coefficient to simulate the difference in radiation in the pit to describe the influence of the pit on the model. Verify and analyze the simulation results. Results showed that the variation trend of simulated soil moisture and heat was consistent with that of measured data. The mean absolute percentage error, root mean square error, and mean absolute deviation were 3.23%, 0.9460, and 0.6984 for soil temperature and 10.05%, 0.0269, and 0.0214 for water content after irrigation, respectively. The simulation results have high accuracy and show that the soil moisture content centers on the pit with an ellipsoid distribution and tends to be uniform over time. The soil temperature was higher in the 4–5 cm area near the soil surface and the wall of pit, and it remarkably changed with time. The intraday variation of soil temperature was mainly affected by atmospheric temperature, but a certain lag was observed compared with the change of atmospheric temperature. With the increase of the irrigation amount, the distribution range of soil moisture content and water high value area increased, while the average and maximum soil temperature decreased. With the increase of irrigation water temperature to 18–24 h after irrigation, the soil temperature in the ellipsoidal area around the pit remarkably increased. The model established in this paper can be used to simulate the hydrothermal status of the soil in the field under water storage pit irrigation. The results prove that the water storage pit irrigation can effectively improve the hydrothermal status of the middle-deep soil and promote the root system of fruit trees to absorb water. [ABSTRACT FROM AUTHOR]

• Neutron physics, thermal–hydraulic and water chemistry are coupled to predict corrosion product growth and CIPS risk. • Boron hideout mass shows a parabolic tendency as CRUD depositions thicken and bulk coolant boron concentration decreases. • Power tends to shift to 0 % axial offset at EOC after the most negative axial offset of −5.07 % with 5.03 mg boron hideout. CRUD depositions on fuel cladding are the main cause of power shift and localized corrosion in nuclear power plants. This paper is the third of a three-part study concerning the prediction of CIPS risks during fuel burnup. In this paper, based on the coupling modules of CRUD growth and internal heat and mass transfer in Part 2, a multi-physics coupling method for high-fidelity simulation of CRUD growth and CIPS phenomenon is developed to better understand coupled physics and respective feedback mechanisms. Based on OpenMC, Fluent and self-developed CRUD-related code, this coupling method considers nuclide depletion, coolant flow, heat transfer and water chemistry, in which fine radial CRUD mesh in neutronic module and influences of CRUD surface characteristics on heat transfer in thermal–hydraulic module are introduced. The coupling method is applied to predict CIPS risk during a 360-day cycle depletion process reaching burnup of 22.04 MWd/kgHM. Corrosion products deposit on cladding to thicken CRUD, while flow erosion gets enhanced washing away more particles on CRUD surfaces, resulting in a slow-down net CRUD growth rate, reaching maximum values of 8.60 g in mass and 37.10 μm in thickness at EOC. As CRUD depositions thicken, boron hideout mass increases, while subsequently bulk coolant boron concentration decreases and boron diffuses out of CRUD depositions causing a decrease in boron hideout mass. The highest boron hideout mass and most negative AO both occur near MOC time. At EOC, net mass reduction of boron hideout and bottom-favored nuclide depletion contribute toward pushing power distribution closer to 0 % axial offset. The results of this study provide a precise method for understanding CIPS risk and its influencing factors to further predict and alleviate CRUD-related safety issues. [ABSTRACT FROM AUTHOR]

• 1 Flow and boiling heat transfer in a 5 mm tube were studied experimentally. • 2 Heat transfer enhancement is obviously founded in the region where x e < 0.05. • 3 New empirical correlations are developed based on the experimental data. • 4 New correlations have higher prediction accuracy than the existing correlations. Experimental investigation on flow boiling heat transfer in a small tube under high system pressure has been conducted in this study. The test-section is constructed with a 316L stainless steel tube. The inner diameter and heated length of the test-section are 5 mm and 930 mm, respectively. The working fluid is deionized water. The operating conditions of the experiments are as follows, the mass flux from 548 to 978 kg/(m2·s), the wall heat flux from 136 to 238 kW/m2, and the system pressure from 1.0 to 2.9 MPa. The experimental results showed that the inlet subcooling mainly affects the onset of nucleate boiling, but its impact on the heat transfer coefficient at the same vapor quality is almost negligible. The heat transfer coefficient increases with the increase of mass flux and wall heat flux, especially in the region where x e < 0.02. The average heat transfer coefficient is higher under high system pressure owing to the variation of the thermophysical properties. Additionally, the existing flow and heat transfer correlations cannot predict the flow boiling heat transfer coefficient and frictional pressure drop in the experiments accurately enough. Therefore, the new flow and heat transfer correlations are developed based on the experimental data in this paper, and the mean absolute deviation of the flow boiling heat transfer correlation and frictional pressure drop correlation are 13.3% and 12.1%, respectively. [ABSTRACT FROM AUTHOR]

• High level of heat transfer enhancement was obtained using a horn-type transducer. • Incident area under ultrasonic effects was exhibited by TLCs. • Velocity fluctuations from ultrasound were measured by a hot film sensor. • Predictive formula for Nusselt number was proposed relative to crucial parameters. The enhancement of heat transfer of water flow over a flat plate under 20 kHz ultrasound irradiated from a submerged horn-type transducer was investigated experimentally in a water tunnel. To examine the ultrasonic effects, the transducer emitted waves perpendicular to the mainstream direction, and the freestream velocity varied between 0.12 and 0.17 m/s. The transducer position was fixed at 0.45 m from the plate leading edge in a streamwise direction. This position was altered in a heightwise direction as dimensionless heightwise distances (Z) that were divided by the diameter of the horn-tip transducer (12 mm) at 1.5, 3.0, and 4.5 from the plate surface. A hot film sensor and thermochromic liquid crystals coated on the test surface were used to demonstrate the hydrodynamic and thermal characteristics, respectively. The maximum temperature reduction of 3.5 °C was observed in the case of Z = 1.5. By employing a horn-type transducer, the acoustic jet and cavitation phenomena played a key role in destabilizing the thermal and velocity boundary layers, which resulted in a decrease in surface temperature. The incident wave shape was triangular, with an enlarging lateral zone along the flow stream. When the waves were released at Z = 1.5, the local Nusselt number was increased up to 2.55 compared to without waves. Under ultrasonic effects, the near-wall flow velocity was detected to be decreasing upstream prior to the incident zone while increasing in the incident region. When waves existed, the highest turbulent intensity was up to 29 times more intense than it was in the absence of waves. Furthermore, a predictive formula for the Nusselt number with ultrasound was established depending on the local Reynolds number and the distance between the ultrasonic source and test surface. [ABSTRACT FROM AUTHOR]

• Developed laboratory closed loop CO2 circulation apparatus to verify the thermosiphon effect. • Demonstrated the thermosiphon effect at initial injection pressures of 8.5 to 18 MPa and heater temperatures of 80 to 200 °C. • The apparatus showed peak heat output at injection pressures of 12–14 MPa. • Changing the medium from water to CO 2 made the thermosiphon effect more feasible. The thermosiphon effect has been shown theoretically to exist in the closed loop CO 2 circulation geothermal power generation systems. We verified this effect based on previous numerical studies that determined the conditions under which the thermosiphon effect can be established and we developed laboratory experimental apparatus with conditions analogous to those in the previous studies. The results of laboratory closed loop CO 2 circulation experiments using this apparatus demonstrated the thermosiphon effect at initial injection pressures from 8.5 to 18 MPa and heater temperatures from 80 to 200 °C. With this experimental apparatus, higher heater temperatures produced higher heat output at the same injection pressures, and that the peak heat output was observed at injection pressures of 12–14 MPa. Furthermore, comparing CO 2 with water as the thermal transfer medium indicated that the feasibility of the thermosiphon effect was increased by changing the medium from water to CO 2. [ABSTRACT FROM AUTHOR]

In the nuclear fuel structure, most spacers are constructed with vanes that increase turbulence flow mixing downstream of the spacer and therefore enhance the heat transfer rate. The objective of this work is numerical evaluation of the effects of a spacer without a vane and a spacer with a vane (hereinafter referred to as spacer/spacer with vane) on the flow and heat transfer of water at supercritical pressure downstream to the spacer of the annular channel. In this study, computational fluid dynamics (CFD) models of the annular channel have been developed considering spacer/spacer with vane. Experimental data for the heated annular channel have been used to validate the same CFD model (as the geometry used for the experiment) using the CFD code ANSYS Fluent. The CFD results show good agreement with the experimental data used, and hence, the developed CFD models of the annular channel that consider spacer/spacer with vane can be simulated with adequate precision for the flow and heat transfer downstream to the spacer. The effects of spacer/spacer with vane on heat transfer and flow behavior of water have been studied with numerical simulations for the following parameters: mass fluxes of 500 and 1000 kg/m2·s, heat flux of 400 kW/m2, pressure of 25 MPa, and inlet water temperature of 350°C. The results obtained through the simulations show that the spacer with vane has a remarkable influence on flow and heat transfer downstream to the spacer vane against spacer without a vane in an annular channel. Raising the flow velocity is an effective approach to reduce wall temperature and enhance the heat transfer in the channel. The range of the spacer effect in the enhancement of heat transfer is observed from X/D = 0 to 45 in the downstream direction. In addition, the simulation results for the Nusselt number ratio of the present CFD models have been compared with correlation data established by several researchers in a downstream direction to the spacer/spacer with vane, and qualitatively proper agreement has been found. [ABSTRACT FROM AUTHOR]

In the present study, a membrane-based air-to-air planar humidifier (MAPH) with baffle-blocked flow channels and a common MAPH are fabricated, tested and compared. These MAPHs are well thermal insulated from their surroundings. Polyoxymethylene (POM) plates with some unique properties such as large tensile and flexural strength, high chemical resistance and high stiffness are used to create channels at dry and humid sides of MAPHs. The obtained findings revealed that the higher heat and water transfer rates and smaller dew point approach temperature (DPAT) in entire tested flow rates occurs in baffle-blocked MAPH. To evaluate the MAPH performance with considering the pressure drop, a dimensionless parameter, performance evaluation criteria (PEC), is introduced. At flow rates less than 1 m3/h, PEC is less than 1, indicating a decline in MAPH performance with considering the pressure drop. In baffle-blocked MAPH using water trap in the inlet of dry side leads to the performance deterioration. Additionally, the increased relative humidity (RH) of humid side inlet causes an increase in DPAT, consequently, the performance deterioration. • A membrane-based air-to-air planar humidifier (MAPH) with new design is fabricated. • To evaluate the pressure drop, performance evaluation criteria (PEC), is introduced. • Insulation thermal boundary condition is applied. • Using water trap in the inlet of dry side leads to the performance deterioration. [ABSTRACT FROM AUTHOR]

The search for materials with high thermal resistance has promising applications in thermoelectric devices and boiling crisis retardation. In this paper, we study the interfacial heat transfer between water and gold, nanostructuring the gold surface and coating it with graphene. By trapping air (or vacuum in our simulations) between graphene and the nanopatterned surface, we observe a considerable increase in the interfacial resistance compared to the planar gold situation, which is shown to scale with the effective graphene–gold contact surface for both monolayer and multilayer graphene. With the massive thermal resistances we predict (up to 200 nm in terms of Kapitza length), the system proposed here represents a robust alternative to superhydrophobic Cassie materials. Moreover, since the low thermal conductance is achieved primarily due to geometry (vacuum trapping), it is straightforward to extend our results to any material with a structure equivalent to that of the nanopatterned gold wall considered here. [ABSTRACT FROM AUTHOR]

The effect of doping distilled water with MgSO4 on the boiling flow regime and heat transfer on a vertical surface at low pressures was experimentally determined. The experiments were performed in a sealed 20 mm x 20 mm square cross section, 300 mm long vertical pipe. Two opposing walls were made of copper and the other two walls were made of polycarbonate for flow visualization. The tube was filled to 100 mm and heat was applied at the lower end of one copper wall and cooled at the upper end. The boiling dynamics on the heated copper vertical wall and the resulting two phase flow was visualized using a high speed camera for pure distilled water and 0.1 M, 0.2 M and 0.4 M concentrations of MgSO4. The presence of MgSO4 significantly changed the boiling dynamics, with a suppression of bubble coalescence and a promotion of nucleate boiling. The two phase flow exiting the heated section changed from slug to bubbly with the addition of the MgSO4. There was a significant increase in the heat transfer coefficient with the addition of the MgSO4. [ABSTRACT FROM AUTHOR]

This study focuses on the investigation of the predictive capability of the Clausius–Clapeyron (C–C) equation in conjunction with soil–water retention characteristics to estimate soil-freezing curves (SFC). The Clausius–Clapeyron equation together with soil–water retention (SWR) models can provide a quick estimation of SFCs. However, the validity of the equilibrium assumption may not be applicable in all scenarios of freezing and thawing. The overall goal of this study is to provide a comprehensive assessment of SWRC-derived soil-freezing curves for different types of soils under varying environmental conditions. An extensive set of data obtained from studies reported in the literature pertaining to thermally induced hydraulic properties of sand, silt, and clay soils from multiscale experiments was analyzed. In addition, in-house laboratory freeze–thaw experiments were performed using silty soil. The SFCs derived from the SWRC were in good agreement with the measured SFCs for sands, whereas significant discrepancies were noted for silt and clay soils. Intensified discrepancies were noted when the results from different experimental methods and changing boundary conditions were compared. A significant hydraulic hysteresis was observed and possible controlling mechanisms were explained. A reliable method to predict SFC from SWRC will enable accurate modeling of coupled heat transfer and water flow processes in the Arctic subsurface for sustainable built and natural environments. [ABSTRACT FROM AUTHOR]

In this paper, we experimentally and theoretically study the effect of external induced convection on heat transfer from horizontal heaters under conditions of pool boiling of saturated water at atmospheric pressure. The induced convection is shown to significantly affect the heat transfer in the natural convection mode and hardly affects the heat transfer in the nucleate boiling mode. The proposed model for calculating the heat transfer coefficient at the heat transfer intensification due to external induced convection is in good agreement with the experimental data. The results of the study can be used in the design of heat exchange equipment for the needs of the nuclear power industry. [ABSTRACT FROM AUTHOR]

The Leidenfrost phenomenon entails the levitation of a liquid droplet over a superheated surface, cushioned by its vapor layer. This vapor layer can obstruct boiling heat transfer in heat exchangers, thereby compromising energy efficiency and safety. For water, superhydrophobic surfaces are believed to reduce the Leidenfrost point (TL)—the temperature at which this phenomenon occurs. Therefore, superhydrophobic surfaces are not commonly utilized in thermal machinery despite their benefits such as reducing frictional drag. Here, we demonstrate that it is possible to achieve superhydrophobicity without lowering TL by surface engineering and fine-tuning liquid–solid adhesion. We demonstrate that TL of water on superhydrophobic surfaces comprising doubly reentrant pillars (DRPs) can exceed that on hydrophilic and even superhydrophilic surfaces. Via theory and computation, we disentangle the contributions of microtexture, heat transfer, and surface chemistry on the onset of the Leidenfrost phenomenon. Remarkably, coating-free and superhydrophobic DRP architecture can facilitate ∼300% greater heat transfer to water droplets at 200 °C in comparison with conventional superhydrophobic surfaces. These findings advance our understanding of the Leidenfrost phenomenon and herald technological applications of superhydrophobic surfaces in thermal machinery. [ABSTRACT FROM AUTHOR]

A detailed experimental work on the convective heat transfer characteristics of water based hybrid nanofluids with Graphene Nanoplatelets and Multi Walled Carbon Nanotubes in the ratio 1:1 has been performed. Volume concentrations viz., 0.01%, 0.05%, 0.1%, 0.15% and 0.2% were considered. The hybrid nanofluid was passed through the micro channel heat sink which was electrically heated to simulate the heat load. The heat load was varied from 50W to 200 W while the flow rate of nanofluid was varied from 5 g/s to 30 g/s. The thermal conductivity of the 0.2 vol% nanofluid was 25% higher than the base fluid while the convective heat transfer coefficient was enhanced by 85% leading to a reduction of heat sink temperature by 12 °C. Variations of friction factor during nanofluid flow were nearly constant with respect to Reynolds number and volume concentration of the nanomaterials. This shows the absence of any penalty in the pressure drop with the addition of nanomaterials. The results showed the hybrid nanofluid (Graphene Nanoplatelets /Multi Walled Carbon Nanotubes-water) as an effective coolant for the replacement of the conventional coolant for electronic cooling applications. [Display omitted] • Functionalized GnP/MWCNT-water hybrid nanofluids was prepared and characterized. • Thermal conductivity of nanofluid increased by ~25% at 0.2 vol%. • Heat transfer coefficient and pressure drop of hybrid nanofluids are reported. • Heat transfer coefficient enhanced by ~85% with 0.2 vol%. • There is a limited penalty in pressure drop increment with 0.2 vol%. [ABSTRACT FROM AUTHOR]

A snowpack has a profound effect on the hydrology and surface energy conditions of an area through its effects on surface albedo and roughness and its insulating properties. The modeling of a snowpack, soil water dynamics, and the coupling of the snowpack and underlying soil layer has been widely reported. However, the coupled liquid–vapor–air flow mechanisms considering the snowpack effect have not been investigated in detail. In this study, we incorporated the snowpack effect (Utah energy balance snowpack model, UEB) into a common modeling framework (Simultaneous Transfer of Energy, Mass, and Momentum in Unsaturated Soils with Freeze-Thaw, STEMMUS-FT), i.e., STEMMUS-UEB. It considers soil water and energy transfer physics with three complexity levels (basic coupled, advanced coupled water and heat transfer, and finally explicit consideration of airflow, termed BCD, ACD, and ACD-air, respectively). We then utilized in situ observations and numerical experiments to investigate the effect of snowpack on soil moisture and heat transfer with the abovementioned model complexities. Results indicated that the proposed model with snowpack can reproduce the abrupt increase of surface albedo after precipitation events while this was not the case for the model without snowpack. The BCD model tended to overestimate the land surface latent heat flux (LE). Such overestimations were largely reduced by ACD and ACD-air models. Compared with the simulations considering snowpack, there is less LE from no-snow simulations due to the neglect of snow sublimation. The enhancement of LE was found after winter precipitation events, which is sourced from the surface ice sublimation, snow sublimation, and increased surface soil moisture. The relative role of the mentioned three sources depends on the timing and magnitude of precipitation and the pre-precipitation soil hydrothermal regimes. The simple BCD model cannot provide a realistic partition of mass transfer flux. The ACD model, with its physical consideration of vapor flow, thermal effect on water flow, and snowpack, can identify the relative contributions of different components (e.g., thermal or isothermal liquid and vapor flow) to the total mass transfer fluxes. With the ACD-air model, the relative contribution of each component (mainly the isothermal liquid and vapor flows) to the mass transfer was significantly altered during the soil thawing period. It was found that the snowpack affects not only the soil surface moisture conditions (surface ice and soil water content in the liquid phase) and energy-related states (albedo, LE) but also the transfer patterns of subsurface soil liquid and vapor flow. [ABSTRACT FROM AUTHOR]