Surface Heat Transfer Coefficient Research Articles

Study on Temperature Field Distribution of a High-Speed Double-Helical Gear Pair with Oil Injection Lubrication

The temperature field distribution of high-speed double-helical gears under oil injection lubrication is investigated by obtaining heat flux density and convective heat transfer coefficients through theoretical calculations and CFD (computational fluid dynamics) simulations. Based on the CFD method, fluid simulations are performed to obtain the distribution of lubricating oil on the surface of the double-helical gears, the velocity streamline diagram of the lubricating oil, and the convective heat transfer coefficients of different surfaces of the gears. The friction heat flux density is calculated using Hertzian contact theory and theoretical formula of heat generation. The double-helical gears’ steady-state temperature field simulation uses this heat flux density as a boundary condition. The correctness of the calculation method is verified through experiments. The study shows that increasing the jet velocity allows the jet to reach the tooth surface more effectively, improving the cooling effect and reducing the maximum gear temperature. However, the relationship between the jet velocity and the minimum gear temperature is non-linear. Within a certain range, increasing the jet diameter makes the jet wider, and the area covered by the lubricating oil becomes larger as the jet spreads around the gear teeth, enhancing the cooling effect. An increase in gear speed leads to an increase in frictional heat flux density; moreover, the high-velocity airflow generated by the increased speed reduces the amount of lubricant entering the mesh zone, which in turn causes the maximum temperature of the gears to continue to rise.

Numerical study of heat transfer and pressure drop characteristics in helical tubes based on OpenFOAM

Due to the structural characteristics of the helical tube, centrifugal force complicates the flow boiling phenomenon inside the tube. How to accurately describe and predict the parameter distributions involved in helical tube flow and heat transfer is a concern for scientists. Based on the OpenFOAM, this paper combines the wall boiling model, the interphase model, other closed models with the Eulerian two-fluid model, analysed changes of void fraction, surface heat transfer coefficient, pressure drop with working conditions in the single-phase to nuclear boiling section in the tube. The results show that this solver and the corresponding empirical relational model have the ability to accurately simulate the boiling of the flow in helical tube; In nuclear boiling section at the working conditions of P=4–8 MPa, q = 200–350 kW/m2, Re = 66827–89103, The degree of gas-phase buildup near the inner wall surface of the spiral tube decreases with the increase of Re number, increases with the increase of heat flux and pressure, and the ratio of friction pressure drop to total pressure drop decreases with the increase of Re number, heat flux, and pressure by a maximum of 1.4 %, 4.26 %, and 17.35 %. This paper can provide a reference for adding new models and developing new solvers in the OpenFOAM to simulate boiling in helical tube flows.

Comparative Study on Heat Dissipation Performance of Pure Immersion and Immersion Jet Liquid Cooling System for Single Server

Heat dissipation has emerged as a critical challenge in server cooling due to the escalating number of servers within data centers. The potential of immersion jet technology to be applied in large-scale data center server operations remains unexplored. This paper introduces an innovative immersion jet liquid cooling system. The primary objective is to investigate the synergistic integration of immersion liquid cooling and jet cooling to enhance the heat dissipation capacity of server liquid cooling systems. By constructing a single-server liquid cooling test bench, this study compares the heat dissipation efficiencies of pure immersion and immersion jet liquid cooling systems and examines the impact of inlet water temperature, jet distance, and inlet water flow rate on system performance. The experimental outcomes show that the steady-state surface heat transfer coefficient of the immersion jet liquid cooling system is 2.6 times that of the pure immersion system, with increases of approximately 475.9 W/(m2·K) and 1745.0 W/(m2·K) upon adjustment of the jet distance and flow rate, respectively. Furthermore, the system model is streamlined through dimensional analysis, yielding a dimensionless relationship that encompasses parameters such as inlet water temperature, jet distance, and inlet water velocity. The correlation error is maintained below 18%, thereby enhancing the comprehension of the immersion jet cooling mechanism.

Effects of solar energy absorbed by south wall on carbon emission from space heating in hot summer-cold winter region

Carbon emission caused by space heating (CEH) in hot summer and cold winter climate zone has increased dramatically. Taking advantage of the solar energy absorbed by south wall (SEASW) can effectively reduce CEH, however, the accurate quantification of its impact remains a challenge. The study investigates the potential of SEASW in mitigating CEH. Key parameters affecting CEH, such as sunny day ratio, insulation form, and outer surface heat transfer coefficient of south wall (h), were analyzed. Results show the reduction in carbon emissions caused by the solar energy absorbed by each unit area of the south-facing wall (ΔCreduction) can be as high as 18.61 kgCO2⋅m−2 for the wall employing internal insulation and smaller h. A prediction model of ΔCreduction was further developed by using multivariate nonlinear regression, which can estimate the reduction in CEH for different fuels as heating source by a south wall in different sizes. Besides, the potential of SEASW on the reduction of carbon emission per unit floor area can reach 12.2 %. This study underscores the importance of SEASW as a carbon-neutral heating strategy, particularly for regions characterized by short winter heating periods and lower heating loads compared to colder climates. It provides valuable insights for sustainable energy practices and policy formulation.

Modelling of evaporative falling-film heat transfer over a horizontal tube

This article focuses on evaporative falling film heat transfer through numerical simulations. A two-dimensional symmetric liquid film flowing outside a single horizontal tube was simulated using the open-source CFD software OpenFOAM. The Tanasawa model was employed to consider mass transfer at the liquid–vapour interface, and the isoAdvector VOF method was used for interface tracking. The simulations explored the impact of film flow rate, tube surface heat flux, and tube diameter on the liquid film thickness and surface heat transfer coefficient. Additionally, the critical heat flux and operational limits were considered. The results demonstrate the accurate reproduction of evaporative falling film heat transfer performance by the present model. The film thickness exhibits a similar profile to adiabatic and sensible falling film heat transfer but provides smaller values. Similarly, the evaporative heat transfer coefficient exhibits significantly higher values and a gentle peripheral variation. The influence of heat flux on evaporative falling film heat transfer is contingent on the film flow rate; it can either enhance or weaken the process. Notably, a larger tube diameter negatively affects heat transfer, suppressing the impact of heat flux, and also increases the risk of liquid film dryout. For a given film flow rate, the average heat transfer coefficient increases initially, reaches a maximum value, and then decreases as the wall heat flux is increased. The peak heat flux, termed critical heat flux, increases with film flow rate but decreases with tube diameter. An operational limit exists where the heat flux is lower than the critical heat flux and the film flow rate is higher than the critical film flow rate; under these conditions, evaporative falling film heat transfer operates in a fully wetting status.

Thermal management of lithium-ion batteries with direct and counter flow channels: A comparative study of different cooling fluids

The study addresses the crucial issue of thermal management in lithium-ion batteries (LIBs) and the maintenance of safe operational temperatures. It emphasizes the importance of efficient cooling mechanisms in preventing damage. A comparative analysis was conducted to assess the impact of various cooling fluids on the thermal performance of LIBs using direct and counter fluid flow channels. The study involved the use of different cooling fluids including water, water-glycol, Novec7000, mineral oil, and silicon oil. The researchers examined temperature variation, surface Stanton number (SN), surface Nusselt number (Nu), surface heat transfer coefficient (HTC), battery surface temperature, and pressure drop to evaluate the battery cooling process with different cooling configurations. The battery cooling part proved highly effective in managing heat, achieving a significant maximum temperature reduction of 30.70 % and 37.43 % for direct and counter flow channels, respectively. The Nu values of various fluids showed notable differences, with water-glycol showing a 3.76 % increase, Novec 7000 with an 11.39 % increase, mineral oil with a 15.46 % improvement, and silicon oil with a 20.09 % increase. The HTC values in the direct flow channel proved a consistent decrease from 16.09 to 57.73 to 11.07–25.69 W/m2K, respectively. Similarly, the HTC values for the counter flow channel ranged from 15.88 to 55.38 to 11.07–25.69 W/m2K. Additionally, it was seen that silicon oil outperformed other cooling fluids with a 6.0 % improvement in HTC in both direct flow and counter flow channels. The SN showed increases of 17.34 %, 20.11 %, 26.76 %, 29.57 %, and 29.60 %, respectively, at all five liquid flow velocities through the direct channel, and 19.39 %, 22.18 %, 28.34 %, 36.58 %, and 37.64 %, respectively, through the counter flow channel. These findings clearly show the superior heat transfer capabilities of silicon oil compared to other coolants. However, it is important to note that the use of silicon oil also resulted in a lower pressure drop, a critical consideration for ensuring efficient cooling. These findings have significant implications for the advancement of battery thermal management systems for electric vehicles, as designers can optimize the cooling process by considering different cooling configurations to enhance the thermal performance of battery packs while ensuring safe and stable operation.

Simulation and verification of cylinder head’s temperature field for marine low-speed engine

Abstract The high load capacity of marine low-speed engines poses a challenge to the thermal load of the cylinder head and temperature field simulation can guide its structural design and optimization. The 3-dimensional models of the fluid domain for the cooling water and the solid domain for the cylinder head are established and meshed, the fluid domain model is simulated to research the heat transfer pattern by Fluent software, and the surface temperature and heat transfer coefficient of the cooling water is calculated. The thermal boundary conditions of the gas in the cylinder are simulated through the analysis of the engine working process. The temperature of the cylinder head is calculated based on the fluid-structure interaction model with the thermal boundary conditions by Workbench software. The validation of the model is carried out by comparing the simulated and measured temperature data in the heated inner wall of the cylinder head. The research results show that compared with the measured value, the error of simulation results is small, which shows that the model and method are reasonable. The temperature in the inner wall of the combustion chamber is low, which can provide possibilities to appropriately improve the power density of the low-speed engine and reduce the risk of low-temperature corrosion.

Numerical investigation of multiple affecting parameters on mixed convective heat transfer for arrays of buildings

This study aims to explore relationships between wind speed, wind direction, exterior surface roughness, temperature difference, plan area density and convective heat transfer coefficients (CHTCs) for external surfaces of arrays of buildings. The present investigation provides correlations for CHTCs at the windward, leeward, top, left, and right lateral surfaces. Three different plan area densities of 0.25, 0.111 and 0.027 are considered and 249 numerical simulations are conducted to investigate the influential parameters including density (λp), wind angle (θ), wind speed (U10), temperature difference (ΔT), and surface roughness (ε). Findings reveal that higher plan area density results in lower CHTC due to heightened airflow obstruction. Increase of the wind angle amplifies CHTC on leeward and right lateral facades while reduces it on the left lateral side. With increased wind speed, CHTC experiences significant increase. The results also shows that the temperature difference's impact is pronounced at lower air velocities, leading to heightened CHTC. Besides, increased surface roughness enhances heat transfer coefficients. Finally, the present study employs extensive simulations to present correlations for different facades of the buildings in the studied arrays offering insights into CHTC variations in terms of plan area density, wind angle, speed, temperature difference, and roughness height.

Improving defect detection capability of pulse and pulse phase thermography method for CFRP plates by enhancing rear surface heat transfer coefficient

Infrared pulse thermography (PT) is a noncontact and convenient nondestructive inspection method, and its application to various objects has been reported in many papers. However, conventional PT is not suitable for detecting deep- or near-rear-surface defects. This study focuses on PT inspections of CFRP plates and improvements in their defect detection capabilities. To improve the capability of detecting near-rear-surface defects, a method for enhancing the heat transfer coefficient (HTC) of the rear surface during PT inspection was examined in this study; this would increase the temperature difference in the defective areas observed in thermal images. To investigate the effectiveness of the proposed method, experiments were conducted on CFRP specimens with artificial defects. The CFRP specimens were inspected using the PT method, during which water was brought into contact with the rear surfaces of the specimens to enhance the HTC. The experimental results showed that the capability of detecting near-rear-surface defects improved when the rear surfaces were in contact with water with forced convection. In addition, obtaining phase images by applying a Fourier transform to the experimentally obtained temperature data (that is, pulse phase thermography: PPT) was examined. Consequently, the combination of the enhancement of the rear-surface HTC and the use of phase images was significantly effective in improving the defect detection capability.

Impact of Different Protrusions in Energy Transfer and Fluid Flow Characteristics Using Al₂O₃ Nanofluid in Pipe Flow

The study investigates how the protruded surface (the part sticking out of an otherwise flat surface) over the small channel affects flow characteristics and heat transfer within a circular flow regime, utilizing computational methods. This investigation uses an alumina nanofluid to compare and analyze the thermo-physical parameters of protruding pipes such as boxes, cylinders, dimples, and pyramids in pipe flow. Alumina nanofluid with varying volume fractions was evaluated as a thermo-fluid under laminar flow conditions, exploring its ability to enhance energy transmission (heat) over the protruded channels. The protruded surface induces turbulence around the protruded region, altering the coolant's physical characteristics. Since heat transfer predominantly occurs on surfaces, the alteration in surface geometry due to the protruded shape increases detectable heat transfer and the Nusselt number. With an increase in the volume percentage of nanofluids, there's a tendency for pressure loss to rise along the flow direction's centerline. The dimpled channel exhibits the highest Nusselt number among all protruding channels, indicating that increasing the Reynolds number also increases the surface heat transfer coefficient for all protrusions. When compared to the base fluid, cylindrical protrusions show the greatest pressure drop. Additionally, comparing a protruded channel with base fluid to one with a 4% volume of alumina nanofluid, it can be observed that the latter significantly improves heat transfer, followed by volume fractions of 1% to 3%.

Parametric investigation of the effects of variables controlling thermal characteristics during continuous and high-speed cold stamping processes with active cooling structures

Knowledge of the thermal phenomena that occur during stamping is important for improving the design and performance of stamping die thermal structures. A new mathematical full-scale model for energy and carbon flows is established based on operational data from a cold stamping production line in China. Moreover, numerical simulations of the thermal-fluid–solid coupling field for a cooling medium in an asymmetrically heated rectangular channel with high heat flux and strong wall superheating are carried out with a suitable CFD solver. The results are discussed in detail and compared with theoretical calculations, and the deviation of the surface heat transfer coefficient is ± 11.9 %. Emphasis is placed on parametric effects of variables controlling thermal characteristics on cold stamping with an active cooling structure. The effects of heat flux, and ambient temperature on temperature rise, pressure drops, and heat transfer coefficients are limited less than 7 °C, 167 Pa and 45.11 % under specific operating conditions, respectively. While the heat transfer coefficient and pressure drops are increased hundreds of times with inlet velocity. The fluid cooling performance, threshold value, and approaches for heat transfer enhancement are obtained. Finally, the CO2 emissions rates is assessed as approximately 1.8 g per piece associated with stamping operations, as well as major contributors, CO2 reduction potential, and economic impacts. Negative energy consumption can be achieved with active cooling. These results can help to improve production quality in the future application and provide theoretical support for determining the causes of metal sheet tensile cracking accidents.

Consequences of higher order chemical reaction on bioconvective carbon nanotubes flow implementing Buongiorno's model

In recent years, carbon nanotubes have been extensively explored based on numerous applications in fields such as carbon nanotube based electrodes, super capacitors, nanowires, sensors, coating with polymers, biomedical, and mechanical applications. Keeping in view the significance of carbon nanotubes in the heat transfer process in micro-electrochemical systems, this study is conducted to examine the heat transfer attributes of the carbon nanotubes using the mixture base working fluid. The focus of this investigation is to elaborate the consequence of higher chemical reactions on the bioconvective flow of carbon nanotubes. Additionally, modified Buongiorno's nanofluid model has been used, which undertakes thermophoresis and Brownian motion effects. Heated boundary condition has also been incorporated with the migration of motile microorganisms. The hybrid nanofluid mechanism has been followed in this work. Carbon nanotubes of single-layer and multi-layer have been used simultaneously with different working fluids, such as ethylene glycol (EG) and ethylene glycol/water (EG-water). Non-dimensional flow model equations have been tackled with the bvp-4c package. The obtained outcomes have been presented for distinct profiles and tabulated data sets for the surface skin friction and heat transfer coefficient. It has been observed that when the level of Brownian motion increases, the velocity profile decreases abruptly for SWCNT-MWCNT/EG as compared to SWCNT-MWCNT/EG-water hybrid nanofluid. Opposite behavior has been seen with raising values of magnetization. High Prandtl number decrease thermal boundary layer thickness for both types of hybrid nanofluids. The motile microorganism profile expands by raising the level of bioconvective Lewis number. Moreover, the outcomes of drag force and Nusselt number have been compared, and good agreement has been found.

Temperature distribution analysis and mechanical property prediction of wire loops in the Stelmor air-cooling system

During the Stelmor air-cooling process, the temperature distribution has a significant impact on the wire loops' final mechanical properties. The temperature distribution during air-cooling process is accurately solved by establishing three-dimensional model and Computational Fluid Dynamics (CFD) simulation. It is also found that the heat transfer coefficient on the cross section of the wire loop is very different, with a difference of 70–100 Wm−2K−1. The average value of the surface heat transfer coefficient of the wire loops section is used to replace the surface heat transfer coefficient of the wire loops, which improves the temperature distribution calculation accuracy, which is not considered by previous scholars. The finite difference method is used to calculate the mathematical model of the temperature distribution during the Stelmor air-cooling process. It is found that the maximum temperature difference of the wire during the cooling process is 90–110 K. The prediction model of mechanical property of wire after air-cooling was established, and distribution of mechanical property of the wire loops was obtained, and the reason for the uneven distribution of mechanical property of the wire loops was found.

Thermal Environment Analysis and Optimization for Large Space Buildings with Radiant Cooling Floors: A Case Study of Xianyang International Airport

Radiant cooling floors combined with ventilation systems have been widely applied in large space buildings. However, there has been a lack of research on system control strategies for their adaptation to weather changes. This study aimed to find control strategies for radiant cooling floors combined with displacement ventilation systems used in large space buildings in order to achieve energy conservation and environmental improvement. Supply air temperature and cooling surface temperature were determined to be the control variables. It was found that cooling capacity of the combined system and the comfort index, PMV (predicted mean vote), were linear in relation to the supply air temperature and cooling surface temperature. The linear equations regarding cooling capacity and PMV were established separately using environment data, and then the optimal region was determined. A case study on Terminal 3 of Xi’an Xianyang International Airport was conducted. The thermal environment was investigated through on-site measurements, questionnaires, and numerical simulations with CFD (computational fluid dynamics). It was found that supply air temperature and cooling surface temperature had a significant impact on PMV, and less impact on the cooling capacity. Therefore, it was determined that the supply air temperature should be altered first when the indoor temperature exceeds the upper limit, and then the cooling surface temperature should be changed if the indoor environment continues to overheat with the supply air temperature set to 18 °C. Thus, the supply air temperature was kept at 18 °C, and the floor surface temperature was set to be 22 °C on a high-temperature day. The average PMV was 0.87, and the cooling capacity of the combined system was 200 W/(m2·K), according to the CFD simulation. In addition, the surface heat transfer coefficient of the cooling floor was found to be 10.26 W/(m2·K). This research provides important references for the design and operational management of radiant cooling floors in large space buildings.

Coupling analysis of cylinder block for two-stroke aviation piston engine

The aluminum alloy block is a component of aircraft piston engine, and it is prone to fatigue cracks when working in a thermal mechanical coupling state for a long time. Establish a GT-POWER simulation model for a certain type of engine, verify the accuracy of the model, obtain boundary parameters such as temperature and pressure of the engine block under harsh operating conditions through the model, and divide the cylinder wall into gradients based on the engine operating conditions to obtain the surface heat transfer coefficient of the block, and then obtain the temperature field distribution of the engine body. The coupling analysis of the cylinder burst pressure and temperature field of the engine block under harsh working conditions showed that the maximum stress of the engine block was 292.55 MPa and the maximum deformation was 0.39 mm, with thermal load being the main factor causing deformation. Conduct a complete engine bench test, and under the 1000 h bench durability test, there are no cracks on the engine block, indicating that the design and analysis meet the requirements.

Heat transfer measurements on a flat plate and cylinders at high velocity conditions: Comparison of calculation models with infrared thermography

In this study, various heat transfer measurement models using infrared (IR) thermography were applied to a flat plate and cylinders to examine the accuracy and suitability of the measurements in a transonic blow-down test facility recently developed at Korea Aerospace University. Experiments were performed under three inlet velocity conditions for the flat plate, and for the cylinders, two diameters, two turbulence intensity levels, and five inlet velocity conditions. The surface temperature distribution during the experiment was acquired using an IR camera, and the surface heat transfer coefficient (HTC) was calculated using four HTC calculation models based on the one-dimensional semi-infinite (1D SI) solid assumption: step change (STEP), Duhamel's superposition (DUH), 1D finite volumetric model (1D FVM), and linear regression model (LRM). The LRM showed minimum deviation with reference correlation for the flat plate heat transfer measurements, while STEP, DUH, and 1D FVM showed increased deviations at higher mainstream velocity conditions. The measurements by LRM at the cylinder stagnation location showed the most comparable value with the reference correlation, whereas STEP and FVM showed about 10% deviation from the reference. It is concluded that the LRM is the most suitable heat transfer calculation model for high velocity tests because the model excludes the ramping data during the transient tests, and it can also obtain the local adiabatic wall temperature experimentally.

Effect of Different Control Strategies on the Heat Transfer Mechanism of Helical Energy Piles

In this paper, numerical simulations of a special energy pile, which constitutes a spiral-injected pipe and one straight discharge pile for Geothermal Heat Pump Systems (SGHEs-P(parallel)), were conducted by Fluent software. The effects of the spiral pitches on the heat transfer rate based on the G-function method and peripheral soil temperature of the pile were investigated under continuous and intermittent operation strategies. The impact of spiral tube sizing on the surface heat transfer coefficients was studied. The results indicated that SGHEs-P may be preferred for office buildings under intermittent operation conditions. For a short period, the temperature profiles and heat transfer efficiency of SGHEs-P were mainly influenced by the fluid type, length of the spiral tube, and spiral pitch. The smaller the spiral pitch, the more uniform the temperature distribution, and the better the heat transfer effect, but the heat transfer per unit depth of pile decreased. The average temperature variation curve of the soil around the energy pile with different spiral pitches was simulated and obtained over time. Meanwhile, the impact of spiral radius, spiral pitch, and spiral tube radius on the convective heat transfer coefficient was also presented. Through data fitting, the formulas for the correction coefficients of spiral radius, spiral pitch, and spiral tube radius on convective heat transfer coefficient were obtained, respectively.

Heat of Hydration Analysis and Temperature Field Distribution Study for Super-Long Mass Concrete

In this study, the combination of ordinary cement concrete (OCC) and shrinkage-compensating concrete (SCC) was utilized to pour super-long mass concrete. The temperature and strain of the concrete were continuously monitored and managed actively after pouring. The investigation focused on the temporal and spatial distribution patterns of the temperature field, the temperature difference between the core and surface, and the strain evolution. Based on the constructed hydration exothermic model of layered poured concrete, the effects of the SCC, molding temperature, and surface heat transfer coefficient on the temperature field were analyzed. The results show that the temperature of super-long mass concrete rises quickly but falls slowly. SCC exhibits higher total hydration heat than OCC. The temperature field is symmetric along the length but asymmetric along the thickness due to varying efficiency of heat dissipation between the upper and lower parts of the concrete. After final setting of the concrete, the strain varies opposite to the temperature and peaks at −278 με. A few short cracks are observed on the end of the upper surface. Moreover, the numerical simulation results are in good agreement with the measured results. Increasing the molding temperature and surface wind speed increases the temperature difference between the core and surface. Conversely, increasing the thickness of the insulation layer is an effective way to curtail this difference. Thermal stress analysis is carried out and shows that lowering the molding temperature of SCC and increasing the thickness of insulation material can effectively reduce thermal stress.

Effects of cross-sectional shape on flow and heat transfer of the laminar flow of supercritical carbon dioxide inside horizontal microchannels

Supercritical carbon dioxide (sCO2) flow at the micro scale provides an excellent heat transfer solutions for a range of microelectronics cooling applications. The cross-sectional shape of the microchannel (in combination with the abruptly changing thermophysical properties of sCO2) affects the heat transfer and flow characteristics, but these effects are not well understood at constant wall temperatures as most of the previous studies were performed at constant surface heat fluxes. Current study numerically investigated, using CFD, the effects of different cross-sectional shapes, such as circle, equilateral triangle, semi-circle, and square, in zero gravity (space) and in terrestrial conditions, at constant wall temperatures.In all cases, the hydraulic diameter of the microchannel was 100 μm, the total length was 27 mm, and the heated length was 25 mm. A total of 216 cases were analyzed to predict the effects of surface temperature ranging from 310 to 330 K, pressures ranging from 8 to 10 MPa, and Reynolds numbers from 100 to 500 on the heat transfer and flow. It was revealed that the microchannel with triangular cross-section has the highest heat transfer rate, highest mass flow rate, and lowest pressure drop both in zero gravity and in terrestrial conditions. The total surface heat transfer rate for the triangular microchannel was about 49% higher than the circular microchannel at a pressure of 8 MPa, around 53% higher at 9 MPa, and about 55% higher at 10 MPa. However, the average surface heat transfer coefficient displayed a complex behavior, and it depends on the combination of surface temperature, Reynolds number, and operating pressure. The surface heat transfer rate and pressure drop were increased for all shapes at terrestrial conditions, emphasizing that the effects of buoyancy cannot be neglected. Overall, this study revealed a complex behavior of the flow of sCO2 inside microchannels of different cross-sectional shapes, and the triangular cross-section performed better than other shapes.

Enhancing the performance of thermal energy storage by adding nano-particles with paraffin phase change materials

Abstract Phase change materials (PCMs) are now being extensively used in thermal energy storage (TES) applications. Numerous researchers conducted experiments using various circumstances and materials to optimize storage performance. A study was conducted to compare the numerical research of the melting process of paraffin wax using a hybrid nano-integrated paraffin PCM with graphene oxide (GO) and single-walled carbon nanotubes (SWCNTs) in a TES unit. Hence, this research focuses on a sustainable TES system using hybrid nanomaterials (PCM + GO, PCM + SWCNTs, PCM + GO + SWCNT) with varying concentrations of nanoparticles. The objective is to improve the thermal characteristics of PCMs. The main aim of this study is to examine the numerical analysis of the system inside a TES that has a rectangular form. The numerical experiments were conducted using the finite-volume solver Ansys Fluent. The obtained findings show the thermophysical characteristics fluctuations with respect to the solid volume fractions, liquid fraction, temperature, and velocity inside the TES system. Implementing an effective heat transfer mechanism from the point of capture to storage and later consumption necessitates the employment of a heat transfer fluid. The inclusion of SWCNT particles at a concentration of just 10% has been seen to expedite the melting phenomenon. Furthermore, incorporating GO in conjunction with SWCNT alleviates this phenomenon, resulting in a melting behavior that resembles that of unadulterated paraffin. Additionally, the introduction of just 1% GO, combined with SWCNT, leads to a rapid alteration in surface heat transfer coefficient compared to the scenario with single SWCNT and paraffin. These insights hold practical relevance for the development of TES systems in various applications.