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An efficient thermal regulation strategy is of great significance in ensuring the safe operation of electric vehicles (EVs). However, the commonly used thermal management systems suffer from the problem of not being able to accurately and uniformly control the temperature distribution of lithium-ion batteries (LIBs), which poses great risks to the thermal safety control of batteries. In this paper, an advanced thermal management system for LIBs based on thermoelectric cooler (TEC) was designed to overcome the above problems. First, a temperature regulation mechanism model for LIB was constructed. Then, a novel temperature distribution modeling method for TEC was developed by using spectral method. This modeling process took into account the unsteady heat transfer characteristics, which can achieve high modeling accuracy. Next, a state space model of temperature control was constructed by combining a differential model of LIB with the proposed cooler model. On this basis, a temperature control strategy for LIB using nonlinear model predictive control (NMPC) method was proposed to optimize the cooling process because of its superior processing ability to constraints and nonlinearity. A various of experiments and verifications demonstrated that the presented thermal regulation strategy was effective and feasible. • An advanced thermal regulation system for lithium-ion battery based on thermoelectric cooler is designed. • A novel temperature distribution modeling method for TEC is proposed. • A regulation strategy is developed to control the uniformity of temperature distribution. • The paper provides a good guidance for the application and further study of advanced thermal management system in electric vehicle. [ABSTRACT FROM AUTHOR]

Conventional online evaluation methods for the mechanical/thermal behaviour of lithium-ion batteries fall short in terms of efficiency and accuracy, especially under extreme conditions coupling high-temperature and fast charging/discharging. This paper proposes an electrochemical/thermal/mechanical analytical model for prismatic lithium-ion batteries to assess their temperature, stress, deformation, and gas evolution. An electrochemical submodel is formulated, covering the lithium intercalation/deintercalation, solid-electrolyte interphase (SEI) decomposition/regeneration, and electrolyte decomposition. A thermal submodel is created to simulate heat transfer between the cell and its environment, considering reaction and Joule heating as heat sources. A mechanical submodel is developed to reveal the effects of nonlinear elastic constitutive properties and the mechanical/thermal/electrical states on cell deformation and stress, incorporating the reaction gas evolution. A coupled multidisciplinary analytical model is formed, using the state variables of temperature, stress, and deformation to link the submodels. The model's performance was validated against numerical and experimental results under high-temperature charge/discharge cycle conditions, demonstrating efficiency at the level of seconds, temperature errors below 0.6 %, and pressure errors below 4.6 %. The advantages in efficiency, accuracy, and applicability highlight its excellent prospects in energy storage and electric vehicle applications. This paper proposes an electrochemical/thermal/mechanical analytical model for prismatic lithium-ion batteries to assess their temperature, stress, deformation, and gas evolution. The temperature/pressure/SOC-dependent cell deformation is analyzed based on the nonlinear elastic property. [Display omitted] • A mechanical/thermal analytical model for prismatic lithium-ion cells is proposed. • The model integrates submodels of electrochemistry, heat transfer, and mechanics. • The mechanical submodel incorporates a nonlinear elastic constitutive equation. • The approach evaluates the state evolution in temperature, stress, and deformation. • The accuracy is validated by high-temperature charge/discharge cycle experiments. [ABSTRACT FROM AUTHOR]

Humidity plays a significant role in both daily life and industrial manufacturing. Adsorption-based dehumidification attracts considerable attention due to advantages of temperature and humidity independent control and great energy-saving potential. For adsorption-based dehumidification systems, desiccants are the basis for optimizing heat transfer and moisture adsorption performance. Despite the rapid advancements in materials science, few systematic classifications concerning composite materials are available. The primary objective of this paper is to provide a holistic and explicit roadmap of recent developments in composite desiccants, directing at its application in adsorption-based dehumidification for energy efficient utilization. Improvements in heat transfer can be achieved by adding high thermal conductivity materials or by reasonably designing structures of dehumidification components. Moisture adsorption is enhanced by combining different desiccants to maximize their functions. Three main categories are classified, that is, salt-embedded composites, porous matrix-polymer composites and polymer-polymer composites. This paper can help to identify the research gaps and explore promising approaches for future study to further enhance the energy efficiency of adsorption-based dehumidification technologies. [Display omitted] • A review of composites for adsorption-based dehumidification was completed. • High thermal conductivity additives and heat exchanger types can boost heat transfer. • Three main categories are classified for moisture adsorption improvement. • A comparative study was conducted on composites. [ABSTRACT FROM AUTHOR]

Porous surfaces are a common modified surface used to enhance boiling heat transfer. In this paper, a method for preparing gradient porous surfaces is presented, that is, magnetic stirring is added to the electrolyte and the cathode surface to be deposited is placed vertically downward. Within the Cl ion concentration range of 30–140 mg/L, increasing the Cl ion concentration results in lager pore sizes. When the Cl concentration was greater than 120 mg/L, the average pore size of the surface gradually increased from the center to the edge, and the number of pores gradually decreased from the center to the edge. All surfaces showed superhydrophilicity. The critical heat flux of Sample#3 is 158.72 W/cm2, which is 67% higher than the smooth surface. The wall superheat of Sample#3 was only 15 °C in the critical state. This porous surface has plenty of nucleation sites. These nucleation sites are gradually activated when the heat flux increases. At low heat fluxes, heat transfer on these porous surfaces presents a disadvantage because the nucleation sites are not fully activated. At high heat fluxes, these porous surfaces show a decrease in wall temperature. Consequently, the porous surface prepared in this paper has good boiling heat transfer at high heat flux. [Display omitted] • An inverted deposition method was designed to prepare gradient porous surfaces. • The gradient porous surface is superhydrophilic and provides a large number of nucleation sites. • An appropriate increase in Cl-ion concentration increases the pore size and pore wall thickness. [ABSTRACT FROM AUTHOR]

New materials and designs have been developed and proposed to enhance the thermal and electrical performance of photovoltaic-thermal (PV/T) systems in recent years. Despite the significant attention received by PV/T technology, the available PV/T modules are scarce due to complex system designs, environmentally unfriendly working fluids, and low thermal efficiency. In this paper, a highly efficient water-based PV/T system is proposed by combining an innovatively designed cooling system with a PV module. An experimental evaluation of the designed PV/T system was carried out in laboratory conditions. The test results of the PV/T system showed that when the inlet mass flow rate and temperature were 0.0458 kg/s and 11.90 °C, the PV/T system reached the maximum thermal efficiency of 96.47 ± 1.40 %. The increase in mass flow rate from 0.0042 kg/s to 0.0375 kg/s and the decrease in inlet temperature from 17.70 °C to 11.40 °C led to a 12 % improvement in thermal efficiency of the PV/T system showing that the inlet mass flow rate and temperature have a significant influence on thermal efficiency. The developed 3-D numerical model accurately estimated the outlet temperature of the PV/T system. A maximum of 3.43 % error occurred between the experimental results and model output. • The paper proposes a novel, highly efficient, state-of-the-art PV/T system. • The designed PV/T system achieves a maximum thermal efficiency of 96.47 ± 1.40 %. • The designed cooling system reduces the PV module temperature by 40.72 °C. • The electrical conversion efficiency of the PV module is enhanced by 18.32 %. [ABSTRACT FROM AUTHOR]

Consideration of roughness effects in the flow in a minichannel has been a major scientific problem for many decades. Roughness can alter the momentum diffusion, heat transfer conditions or laminar-turbulent transition. These effects are even more pronounced in minichannel flows where the roughness can occupy a large part of the cross-section. Modelling methods applied so far usually fall short in internal flows with high relative roughness. The presented paper pertains to the analytical flow model in Tesla turbine components with consideration of roughness on the rotor walls. The model uses the equivalent sand grain approach to modify dynamic viscosity in the governing equations to achieve a desired downward shift of the dimensionless velocity profile. The model solves two-dimensional equations of continuity, momentum and energy. The semi-empirical function was derived to consider the change in the shape of the radial velocity. The applied model incorporates Euler's turbomachinery equation to determine the influence of roughness on the turbine performance under varied operating conditions. Roughness shortens the streamlines inside the rotor, but the overall turbine's performance is improved. The roughness equal to 10−5 m increased the power generated and isentropic efficiency by factors of 3 and 2.5, respectively, compared to the smooth rotor. • Modification of fluid viscosity is used to account for roughness in the Tesla turbine. • Blockage effect of roughness elements in microchannels is considered. • Semi-empirical function for velocity profile is used to improve modelling accuracy. • Roughness can increase power three-fold and efficiency two-fold. [ABSTRACT FROM AUTHOR]

This paper describes the heat transfer performance of plate-fin-tube heat exchangers (PFTHE) using computational fluid dynamics (CFD) simulation. Air-side Nusselt number correlations obtained from CFD simulations are compared to existing empirical correlations found in the literature. The geometries and boundary conditions are presented and compared with previous studies. The results indicate relative differences in mean Nusselt numbers between CFD-based methods and empirical correlations for different Reynolds numbers. Several factors contributing to these differences are discussed, including thermal resistance issues and assumptions about fluid-side heat transfer coefficients. The proposed CFD-based methods provide insight into the heat transfer mechanisms on individual tube rows, with acceptable differences compared to experimental correlations. Comparison of these methods shows consistent results with relatively small average relative errors, indicating the effectiveness of CFD simulations in predicting the heat transfer performance of PFTHE. Moreover, the average relative errors between individual methods range from 5.1% to 6.9%, with some individual errors ranging from 0.1% to even 17.1%. These results demonstrate the potential of CFD simulations to accurately predict heat transfer characteristics in complex heat exchanger systems. • Developed three CFD-based methods for predicting Nusselt numbers in plate fin and tube heat exchanger. • Validated CFD results with experimental data, achieving relative errors of 5.1% to 6.9%. • Identified significant variations in air-side heat transfer coefficients for different tube rows. • Presented a universal methodology applicable to various plate fin and tube heat exchangers' geometries. [ABSTRACT FROM AUTHOR]

The isothermal compressed air energy storage (I-CAES) technology boasts the advantages of high theoretical round-trip efficiency and zero carbon emissions. In order to rapidly and efficiently assess the thermodynamic performance of I-CAES, and addressing the limitations of the overly complex thermodynamic model for spray heat exchanged closed-loop I-CAES (CI-CAES), this paper establishes a dimensionless evaluation model related to container size and initial state a * , spray water quantity b * , start or end spraying time c * , and the ratio of liquid level to droplet velocity u *. The expressions for evaluation indicators such as round-trip efficiency, indicated efficiency, compression exergy efficiency, and expansion exergy efficiency are summarized, revealing the impact patterns of dimensionless numbers on the thermodynamic performance of CI-CAES. The results show that the relative difference in the percentage of air enthalpy change calculated using the real gas model versus the ideal gas model during the expansion stage is 88.26 %. The indicated efficiency and round-trip efficiency of CI-CAES simulated by the real gas model were 88.18 % and 60.51 %, respectively, for the design parameters, and the variable condition operation of the hydrodynamic machinery was the main reason for the lower round-trip efficiency. The larger the values of a * and b * , the closer to the isothermal process, and the greater the effect of b * on the performance of the CI-CAES system compared to the two. When b * is 50, the polytropic indices of the compression and expansion stages reach 1.03 and 1.01, respectively. The round-trip, compression exergy efficiency and expansion exergy efficiency all vary parabolically with c * , suggesting that there is an optimal c * that optimizes the system performance. The change in pressure ratio has a greater effect on round-trip efficiency and on the percentage change in air enthalpy during compression and expansion, and u * has a lesser effect on system performance. The results of the research can provide theoretical guidance for the efficient operation of CI-CAES. • A CI-CAES dimensionless assessment model for spray heat transfer is developed. • Comparison of the effects of real and ideal gases on system performance is made. • The effect of dimensionless numbers on system performance is explored. • The developed dimensionless model simplifies the calculations. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the combustion behavior of lateral continuous leakage of heptane and gasoline on a steel substrate. The flame shape characteristics of the two fuels at different leakage rates were recorded and described. Variation trends in burning area and flame height with leakage rate were analyzed, and variations in flame width against the flame height were formulated. The mass loss rate was lower than that of the pool fire at the same equivalent diameter. Based on the fuel layer heat feedback and heat loss analysis, the mass loss rate for thin fuel layer combustion was calculated and verified to be about 0.013 kg/(m2‧s). Then, a multi-layer inclined cuboid flame model was established. Compared with the classical point source model and the cuboid flame model, the new model has better accuracy in predicting the external radiation of the combustion of thin-layer fuel. We hope to gain insights into the dynamics of such fires to inform fire prevention and control in initial spill scenarios. • The variation of thin-layer fuel flame shape with height was characterized. • Burning rate model for pool fires was not applicable to thin-layer fuel combustion. • The constant mass loss rate was verified based on heat transfer calculations. • A multi-layer cuboid flame model was developed to calculate the external radiation. [ABSTRACT FROM AUTHOR]

Excessive carbon emissions are one of the global challenges. Promoting the optimization of high-efficiency heat transfer systems and improving the analysis and evaluation methods of heat exchangers is one of the effective ways to save energy and reduce carbon emissions. The traditional thermal resistance analysis method treats the fluid domain as a uniform whole, which makes it difficult to regulate the heat transfer characteristics in local regions, especially in the near-wall region. To address this problem, this paper obtained the thermal resistance mathematical equation for different regions in the flow field by magnitude analysis. The thermal resistance delamination method for dividing the thermal resistance field is proposed from the channel flow, and the conduction, mixing and advection zones in the flow field are identified. The delamination factor (α) is defined to determine the boundaries of thermal resistance zones. The α values which meet the delamination factor independence under forced convection and natural convection conditions are investigated. By studying the mechanism of the thermal resistance in conduction zone of the enhanced heat transfer structure, the critical value of fin height to achieve maximum enhancement efficiency is determined. The thermal resistance delamination facilitates a comprehensive analysis of heat transfer processes and structure optimization in the near-wall region. • Thermal resistance delamination method based on flow characteristics is proposed. • The expression of each thermal resistance zone was determined by sensitivity analyses and delamination factor. • Analysis of heat transfer in enhanced double-sided channel flow based on thermal resistance delamination method. • Critical fin height for maximum enhancement efficiency determined by local thermal resistance. [ABSTRACT FROM AUTHOR]

Using earth air tunnel heat exchangers (EATHE) to pre-treat air entering underground space is an effective measure for energy-saving. This paper addresses the scarcity of numerical model for heat and mass transfer in long, separated air intake tunnels by establishing a three-dimensional model that considering condensation, specifically analyzing the heat transfer process in tunnels with separated ventilation earth air tunnel heat exchanger (SV-EATHE). The accuracy of the model was verified by engineering measured data. The heat transfer performance of EATHE and SV-EATHE is compared and analyzed by using the model. The results indicate that the annual heat exchange of SV-EATHE is approximately 80 % of that of EATHE, with the latent heat exchange from March to September accounting for 77.2 % of EATHE's. SV-EATHE significantly reduces condensation in traffic tunnels. Increasing ventilation will correspondingly increase the heat exchange and reduce dehumidification, but the rate of change will gradually decrease. The change in partition wall thickness has an approximately linear relationship with the amount of heat exchange. For every 0.1 m increase in diaphragm wall thickness, the heat exchange in the intake duct in August is reduced by approximately 1500 kWh and the dehumidification is reduced by approximately 0.6 kg/h. • A numerical model of separated ventilation with long air intake tunnels is proposed. • The model accounts for heat and mass transfer within the tunnels. • The effects of separated ventilation on heat and mass transfer are analyzed. • An analysis of how partition walls affect heat and mass transfer is conducted. [ABSTRACT FROM AUTHOR]

A comprehensive comprehension of the intricate heat transfer mechanisms pertaining to supercritical fluids within U-bend tubes holds paramount significance in the optimization design of submerged combustion vaporizers and other water-bath heating heat exchangers. This paper employs a combined approach of experimental analysis and numerical simulation to explore the complicated heat transfer processes of supercritical liquefied natural gas in the U-bend tube. For a careful consideration of similarity and safety, the N 2 –Ar mixture is used as the alternative experimental media. Upon validating the model's accuracy using experimental data, this study unveils the mechanism of the coupling effect between centrifugal force and buoyancy on heat transfer based on simulation results. The results show that the internal circulation flow field structure caused by centrifugal force weakens the heat transfer on the inner side within an angle range of approximately 60°. Along the entrance region of downstream straight tubing, secondary flow continues to be predominantly governed by centrifugal forces due to inertia-driven effects. Subsequently, buoyancy-driven secondary flow impels compression upon centrifugally-induced secondary flow towards the inner side, thereby instigating significant augmentation in fluidic heat transfer resistance in both the viscous sub-layer and buffer layer of the inner side. Overall, the downstream straight tube section exhibits a special heat transfer variation pattern characterized by an initial strengthening, followed by deterioration, and ultimately recovery due to the influence of centrifugal force, with a maximum influence distance extending to 175.5 d. • Heat transfer performance of supercritical LNG in U-bend tubes is investigated. • Coupling mechanism of buoyancy and centrifugal force on heat transfer is analyzed. • Secondary flow intensity generated by centrifugal force is much higher than buoyancy. • Bend section significant influence heat transfer of downstream straight tube section. • Heat transfer initially improved, then deteriorated and eventually recovered in downstream straight tube section. [ABSTRACT FROM AUTHOR]

Sediment compression during submarine hydrate depressurization production causes changes in physical and mechanical characteristics, which in turn affects production results. In this paper, based on geological conditions of SHSC-4 well in Shenhu area, a theoretical model considering sediment compression effects is established by COMSOL, and the effects on the evolution of reservoir physical and mechanical characteristics within 60 days during depressurization production is simulated. The results show that model dimension effects can be ignored when the size l ≥ 100 m within 60 days. The effects of sediment compression on the physical characteristics of the reservoir are mainly realized by affecting the evolution of porosity, and the porosity reduction leads to permeability reduction. The larger the sediment compression coefficient, the higher the pore pressure in the reservoir. Sediment compression hinders the propagation of low pore pressure and heat transfer in the reservoir, which is unfavorable for hydrate decomposition favorable to hydrate reformation. A larger or smaller sediment compression coefficient selected in the simulation can lead to under- or over-estimate of reservoir gas production, so choosing an appropriate sediment compression coefficient when considering sediment compression is necessary for rational assessment of reservoir production behavior. In the production test site, when the production pressure is higher than 3 MPa, the pore pressure gradient is the key factor to promote gas production from the reservoir. When the production pressure is lower than 3 MPa, the sediment compression is the key factor to impede gas production from the reservoir. [Display omitted] • Dimension effects can be ignored when model size l ≥ 100 m within 60 days. • Compression hinders production by affecting physical and mechanical characteristics. • An incorrect compression coefficient can lead to unreasonable production assessment. • When production pressure is below 3 MPa, compression becomes hindrance to production. [ABSTRACT FROM AUTHOR]

The segmented cooling thermal management system based on the closed-Brayton-cycle (CBC) is an excellent technology for thermal protection and power generation of scramjets. In this paper, a comparative study is conducted to investigate the system performance under different supercritical carbon dioxide CBC layouts. A zero-dimensional thermodynamic model was established to analyze the effects of compressor inlet temperature (T 1), turbine inlet temperature (T 3), and compressor outlet pressure (p 2) on fuel mass flow rate for cooling (m f) and net power (P net). A quasi-one-dimensional flow and heat transfer model was developed to study the cooling effectiveness. Results indicate that higher T 3 and p 2 reduce m f while increasing P net in the simple layout (SL) and simple recuperated layout (SRL). However, in the recompressing layout (RCL), the effects of T 1 , T 3 , and p 2 on m f are more complex due to the split ratio. Moreover, RCL has the lowest maximum wall temperature among the three layouts. Finally, after optimization, RCL has the lowest m f about 0.332 kg/s, which is a 19.8 % reduction compared to the regenerative cooling system. Correspondingly, RCL achieves the highest P net , reaching 109.89 kW. In general, the recompressing layout is most suitable for the CBC-based segmented cooling thermal management system for scramjets. [Display omitted] • Different layouts in the segmented cooling thermal management system are compared. • Models address the effects of key parameters on fuel mass flow rate and net power. • Recompressing layout achieves the highest net power, reaching 109.89 kW. • Recompressing layout is most suitable because of the smallest fuel mass flow rate. [ABSTRACT FROM AUTHOR]

The calculation of the temperature fields in solid state transformers is a critical step of the design process in order to ensure the stable and efficient operation of the device. Transformers operating in high frequencies can develop increased temperatures that potentially may result in the failure of the components due to the associated thermal stresses. This paper investigates the heat transfer mechanisms of a novel inductive power transfer (IPT) system submerged in a dielectric oil and operating at 50 kHz, in the context of SSTAR, a Horizon Europe project. The commercial software ANSYS is employed to implement a one-way coupled electromagnetic-thermal finite element simulation model in order to calculate the temperature field of the IPT components based on the electromagnetic losses. To cross-validate the model, the results obtained from ANSYS are benchmarked against the COMSOL software, revealing accepted temperature deviations between the two software. A comprehensive parametric analysis explores the impact of rated power, operating frequency, and dielectric gap on generated heat, highlighting their direct correlation with temperature increase. The findings underscore increased temperature levels, approximately reaching 224 °C under nominal operating conditions, with the temperature distribution concentrated around the transformer's windings. • Design of a novel high frequency 50 kHz Inductive Power Transfer system. • Assessment of the heat transfer mechanism of an Inductive Power Transfer system. • Development of a comprehensive coupled electromagnetic-thermal simulation model and validation. • Parametric analysis on the effect of rated power, frequency and dielectric gap on power loss and temperature. [ABSTRACT FROM AUTHOR]

Highly dense and integrated data centers face key challenges of realizing efficient cooling and improved energy efficiency. To overcome these challenges, this study experimentally investigated the flow and heat transfer characteristics of single-phase immersion liquid cooling (SPILC) systems. The influence of two opposite coolant flow directions on the SPILC performance was examined. Furthermore, a correlation mechanism between coolant thermal properties and SPILC performance was established, along with a control chart for regulating the working conditions of SPILC systems. The results indicate that compared to a pro-gravity flow, an anti-gravity flow scheme reduces the chip case temperature and thermal resistance by 33.8% and 55.6%, respectively, while decreasing the power usage effectiveness (PUE) by 1.4%. Using coolant with the lowest viscosity reduces the chip case temperature and thermal resistance by 9.3% and 10.5%, respectively, while decreasing the PUE by 0.4%. Moreover, the cooling water temperature has a greater impact on the performance of SPILC systems than the volume flow rate of coolants. Additionally, this paper provides control charts for the cooling water temperature and coolant flow rate to improve the PUE while ensuring the safe operation of SPILC systems, with the highest chip temperature and total electricity consumption as indicators. • Immersion cooling performance of system-level data center servers is experimentally studied. • PUE of the anti-gravity flow decreases by 1.4% compared to the pro-gravity flow. • Correlation between coolant properties and immersion cooling performance is established. • Energy-efficient control charts for cooling water and immersion coolant are provided. [ABSTRACT FROM AUTHOR]

In the process of biomass gasification syngas waste heat recovery, water and organic compounds in the syngas will condense at the same time, resulting in immiscible condensates adhering to the wall, which can reduce the heat exchanger heat transfer efficiency and working life. Changing the wettability of the wall surface can affect the condensate flow state on the wall surface, thus affecting the condensation heat transfer performance. Water and organic cyclohexane were used as immiscible working fluids in this paper, the condensation flow and heat transfer characteristics of the mixed vapors on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces were experimentally investigated. The results showed that cyclohexane in immiscible condensates existed as a liquid film on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces, while the water existed in droplets on the hydrophilic and super-hydrophobic wall surfaces, and there were two forms of channels and droplets on the super-hydrophilic wall surface. The condensation heat transfer coefficient on the super-hydrophobic wall surface was higher than that on the hydrophilic wall surface and the super-hydrophilic wall surface, with a maximum of 34% higher than hydrophilic and 45% higher than super-hydrophilic, which was related to the smaller droplet departure diameter on the super-hydrophobic surface. In addition, the super-hydrophilic wall surface had better heat transfer performance than the hydrophilic wall surface only when the immiscible condensate was a "film-channel" flow pattern. The results can provide guidance for enhancing the condensation heat transfer of the water and organic compounds binary mixed vapors. • Wall wettability can change the immiscible condensates flow behavior and thus affect condensation heat transfer. • The smaller the condensate droplets departure diameter on the wall, the greater the condensation heat transfer performance. • The condensation heat transfer coefficient on the super-hydrophobic wall surface was the highest. [ABSTRACT FROM AUTHOR]

The heat transfer and pressure drop (Δ P) of supercritical fluid are crucial for the safety of advanced power cycles. Here, experiments were performed for sCO 2 in a horizontal tube with inner diameter (d in) of 10 mm, covering in the ranges of (G): 496.7–1346.2 kg/m2, heat flux (q w): 97.4～400.3 kW/m2 and pressure (P): 7.53–23.51 MPa. Inspired by the similarity of the outer wall temperature (T ow) distributions between the sCO 2 flow and those of stratified-wavy-flow in subcritical pressures, the multiphase flow theory is introduced in subcritical pressures to deal with the sCO 2 heat transfer. In the two-phase-like (TPL) regime, heat transfer coefficients (HTC) and friction factors (f) of sCO 2 are found to significantly deviate from the correlations based on the single-phase flow theory. Further, the vapor-like Froude number Fr VL is proposed to develop new correlations for both the heat transfer and the flow resistance covering the whole data range. The present paper establishes a connection between the flow resistance and heat transfer in supercritical pressures, which is important for the design and operation of sCO 2 power cycles. • Supercritical heat transfer and flow characteristics of CO 2 is investigated in a horizontal tube. • Thick vapor-like film can reduce the frequency of negative temperature differences occurring. • Flow resistance and heat transfer in the two-phase-like regime both strongly deviates from the single-phase convection. • Fr VL was proposed to be the similarity criterion number to connect flow resistance and heat transfer for horizontal flow. • The new correlations with Fr VL number for heat transfer and friction factor are established. [ABSTRACT FROM AUTHOR]

Fouling is an important factor affecting the heat transfer performance of condensers in nuclear power plants. In response to the lack of experience in the current cleaning of condensers in nuclear power plants, this paper proposes a particle swarm optimization based LSTM method for predicting fouling thermal resistance and a dynamic optimization theory for condenser cleaning cycles. On the basis of LSTM and the PSO algorithm, compared with the prediction results of LSTM, the MAE, RMSE and MAPE values of PSO-LSTM decreased by 43.3%, 47.3% and 42.1%, respectively, while R2 increased by 26.4%. Considering the load loss and maintenance loss of the unit, as well as the economic loss caused by condenser scaling, the optimal cleaning time of the condenser glue ball system under different fouling rate and circulating water temperature was analyzed, and a calculation theory based on the unit output, the running loss cost of the glue ball and the minimum optimal cleaning cycle of the condenser was proposed. Results show that at rated flow, optimizing the cleaning cycle, with an annual operating time of 300 days, can save $0.45 million in operating costs per year. • Particle swarm optimization based LSTM method for predicting fouling thermal resistance of condenser of nuclear power plant are proposed. • Condenser health index of nuclear power plant based on dynamic power loss is established. • Condenser cleaning cycles of a practical power unit is optimized to show the trade-off. [ABSTRACT FROM AUTHOR]

Many industrial processes belong to complex thermal system coupled by multiple heat sources, in which the energy distribution and transmission for each heat source is closely related to its adjacent neighbors, and the thermal dynamics have obvious nonlinear time-series characteristics, these factors limit the modeling and predict accuracy for this type of systems in actual practice. In this paper, a convolution and memory network-based spatiotemporal modeling approach is proposed to model the nonlinear spatial features and temporal dynamics of these heating systems. First, a deformation convolutional neural network (D-CNN) strategy is developed to extract the spatial features, it designs a deformable kernel matrix for convolution layer to obtain the spatial multi-scale context information of the DPS, and the feature order is reduced by pooling operation. Then, a cascade long-short time memory network (LSTM) model is constructed to model the temporal dynamics of the time-series data. In this model, the sliding window method is used to obtain the sequential dataset for several sampling time, which is taken as the input of each LSTM unit to reconstruct the nonlinear temporal dynamics in this type of systems. The effect of the proposed model for spatiotemporal dynamics is verified by the experiment of serial-connected lithium batteries (S-LIBs), and the result shows that the proposed model has smaller modeling errors for spatiotemporal dynamics than the other two methods. • A convolution and memory network-based modeling approach is proposed to model the spatiotemporal dynamics in thermal processes. • A deformation convolutional neural network strategy is developed to extract the spatial features using a deformable kernel matrix. • A cascade long-short time memory network model is constructed for the temporal dynamics of the time-series data. • The effect of the modeling approach is verified by the experiment of serial-connected lithium batteries (S-LIBs). [ABSTRACT FROM AUTHOR]

Optimizing conjugate heat transfer in laminated configurations is pivotal for efficiently cooling turbine blades. The traditional approaches have limitations in achieving rapid optimization when design conditions change. The emergence of reinforcement learning offers an opportunity to address this issue. However, there is currently a notable scarcity of research on the application of reinforcement learning in the optimization of laminated cooling configurations. This paper presents a novel method using the Deep Q-Network (DQN) model for real-time optimization of laminated cooling configurations. A dataset comprising 246 sets of historical design data was generated through conjugate simulations and augmented with the incorporation of physical information. After undergoing off-policy reinforcement learning, the intelligent model was employed to address optimization problems associated with temperature levels and coolant usage. Results indicate that the intelligent model achieves accurate and real-time optimization for laminated cooling configuration, with an average time of 3 ms. The ability to identify the correct optimization direction is attributed to the formulation of reward and penalty mechanisms in reinforcement learning. Real-time optimization is enabled by establishing a forward computational path from design conditions to optimization results. The findings of this study are easily transferrable and contribute to cost savings in design. • The model learns optimization insights from raw data through reinforcement learning. • Optimization objectives and constraints are achieved through a reward mechanism. • The forward computational path of decision-making facilitates real-time optimization. • Integrating physical information enhances optimization process stability. [ABSTRACT FROM AUTHOR]

In the processes of modeling, optimization, heat transfer analysis, and thermal power conversion analysis in large-scale complex systems, challenges are encountered regarding intricate design and optimization. In this paper, a global heat flow topology is proposed that reveals the synergistic effect of heat transfer and thermal power conversion in large-scale systems. The approach involves the construction of a heat flow topology, mathematical model development, analysis of specific parameters, and multi-objective optimization. It integrates various methods and tools, including heat flow topology, numerical simulation tool, entransy transfer analysis, global thermal resistances visualization, genetic algorithm (GA), and technique for order preference by similarity to ideal solution (TOPSIS). By using the LNG cold energy recovery and regasification process in floating storage and regasification units (FSRU) as a case study, the methodology provides a comprehensive understanding of the interactions and conversions between heat transfer and thermal power within the system. The results demonstrate that the optimal configuration achieves a maximum thermal efficiency of 21.73 % and a maximum cold recovery efficiency of 58.48 %. Additionally, the interaction between LNG pressure and seawater temperature exhibits limited synergistic impact on both LNG cold exergy efficiency and entransy transfer efficiency. Similarly, the combined influence of LNG pressure and evaporator temperature shows weak synergistic effects on parameters such as supply/demand ratio, thermal efficiency, and entransy transfer efficiency. The analysis of the global thermal resistance bubble chart reveals the significant impact of evaporator temperature and seawater temperature on the evaporator resistance, as well as the notable impact of LNG pressure on the condenser resistance. [Display omitted] • Proposed a global modeling and optimization method for large-scale system. • Constructed heat flow topology to describe heat transfer and heat-work conversion. • Energy, exergy, entransy analysis and multi-objective optimization are carried out. • The global overall thermal resistances change is visualized by bubble diagram. [ABSTRACT FROM AUTHOR]

This paper presents experimental and theoretical research on ceiling jet, burn-through, and flame spread behaviors of the combustible ceiling with the impingement of an incipient fire source. Medium-density fiberboard was utilized as the combustible ceiling in experiments, and the ceiling height above the fire source was varied. The flame radial length (r f), ceiling surface temperature, flame shape and spread rate after burn-through, and radiative heat flux were measured. Results showed that r f beneath the combustible ceiling was significantly longer than that of the non-combustible ceiling. Theoretical analysis was conducted for r f based on energy distribution, and an expression of r f beneath combustible ceiling was proposed. The burn-through behavior of the combustible ceiling was explored by combining the ceiling temperature, small-sized experiment and Fourier law. The advancement of char front along the ceiling thickness was calculated, which was the key point during burn-through. Upper surface flame spread in a circular shape after burn-through, and an expression of spread rate was obtained. A three-dimensional radiation model was adopted to calculate the radiative heat flux received by the unburned ceiling surface during the dynamic flame spread process, the calculated results agreed well with the experimental data. • Ceiling jet, burn-through, flame spread behaviors of timber ceiling are researched. • The mechanism of the flame extension beneath the combustible ceiling is revealed. • Burn-through process and char front advancement are explored. • The flame spread behavior and heat radiation after burn-through are clarified. • Expressions of the flame radial length and flame spread rate are proposed. [ABSTRACT FROM AUTHOR]

Grate boilers are widely applied in biomass combustion for heat and energy generation. However, grate-firing systems often suffer from low efficiency and high emission. Computational fluid dynamic (CFD) becomes increasingly popular as a flexible method to obtain the detailed combustion behaviors in the furnace, and to optimize the performance of existing grate boilers. This paper presents efforts toward a reliable baseline CFD model for an industrial biomass-fired grate boiler, where the structure of the fuel-bed was sufficiently considered. The combustion performances in the furnace were investigated experimentally and numerically by coupling the fuel bed and freeboard, to clarify the impact of bed structure on the simulation accuracy. Results show that when the bed structure has been taken into account, the predictions are in better agreement with the various measurements, as the deviations between them are all within 10 %. Moreover, the flame center drops, the total heat transferred to the water-cooled walls increases, and the residence time of flue gas is greatly prolonged from 2.76 s to 3.90 s, resulting in a distinct difference of the temperature and species patterns in the freeboard. The simulations will provide valuable theoretical guidance for the accurate modeling of grate-fired boiler. [Display omitted] • A baseline model is proposed for accurate modeling of biomass-fired grate boiler. • Effect of fuel-bed structure on the simulation of grate boiler is clarified in detail. • Bed structure greatly affects the predicted temperature and species patterns. • Flue gas residence time and heat transfer are also highly impacted by bed structure. [ABSTRACT FROM AUTHOR]

Natural cooling energy and high-efficient radiant cooling techniques are essential to mitigate energy resources shortage crisis, breakthrough on traditional convective air-conditioning systems in isolation between indoor and outdoor environment with high indoor air quality. In this paper, a polyethylene aerogel (PEA) and phase change material (PCM) integrated novel Trombe wall was proposed, involving natural cooling energy harvesting, cooling energy storage, indoor ventilation and radiant cooling. A two-dimensional unsteady numerical model based on surface-to surface (S2S) radiation model and effective specific heat capacity method was developed in the commercial software Ansys Fluent to evaluate the cooling performance and dynamic heat-transfer mechanism of the novel Trombe wall. Subsequently, climate-responsive operation strategies on ventilation modes were proposed to maximize natural cooling energy utilization and fresh air supply. Parametrical and comparative studies were conducted on optimal structural design and robust operation. Our results showed that, with the novel design and advanced operation strategies, passive cooling capacity of 0.64 kWh/m2·day can be provided, together with fresh air supply of 2705.2 kg/day (1.4 m2 Trombe wall), corresponding to air change rate per hour (ACH) of 1.15. In terms of active cooling system, the integration of PEA and PCM can effectively prevent moisture condensation and shift peak cooling load. Hence, radiant cooling capacity of 0.99 kWh/m2·day and radiant cooling ratio of 47 % can be achieved by the novel Trombe wall, with electricity consumption only at valley period. Moreover, economic saving of 55.0 CNY/day and decarbonization potential of 23.8 kg CO 2,e /day can be achieved when the novel Trombe wall is integrated into a typical office building in subtropical climate Guangzhou. This study provides a novel structural design and optimal operation strategies on a Trombe wall, together with guidelines on techno-economic-environmental performance improvement, promoting effective natural cooling energy utilization and energy-flexible/efficient radiant cooling for decarbonization of buildings in cooling-dominant regions. • A novel Trombe wall for natural cooling energy harvesting and radiant cooling. • An unsteady numerical model for thermodynamic analysis. • Passive cooling capacity of 0.64 kWh/m2.day and fresh air supply of 2705.2 kg/day. • Radiant cooling capacity of 0.99 kWh/m2·day and radiant cooling ratio of 47 %. • Daily CO 2 reduction of 23.8 kg and economic saving of 55.0 CNY in a typical office building. [ABSTRACT FROM AUTHOR]

A multitude of uncertainties intertwined within the manufacturing and functioning of gas turbines has often been overlooked in numerous prior investigations regarding the aerothermal performance of blade tips. Consequently, the actual lifespan of the blades falls considerably short of the initially anticipated duration. This study proposes an efficient parallel turbo robustness analysis framework and aims to delve into the uncertain characteristics exhibited by various multi-cavity squealer tips during real-world gas turbine operations. The findings of this research reveal that the inclusion of ribs has an adverse impact on the flow field, leading to heightened chaotic tendencies and a considerable reduction in the expected aerodynamic efficiency of the multi-cavity squealer tip. The leakage flow experiences a notable increase, reaching values of 22.30%, 17.88%, and 24.51% for the three distinct multi-cavity configurations, surpassing the corresponding value of 13.63% observed for the conventional squealer tip. However, integrating the flow field uncertainty into the thermal field uncertainty proves challenging due to the disruption of the cavity vortex system caused by the pressure side ribs. Thus, the heat transfer performance of the multi-cavity squealer tip exhibits superior robustness compared to that of the conventional squealer tip. Furthermore, this paper introduces a novel evaluation index, based on comprehensive uncertainty flow and thermal analyses, to assess the robustness of the aerothermal performance. The present work makes a valuable contribution to the development of digital twins for turbomachinery systems. • The robustness of the aerothermal performance of squealer tips with and without ribs is investigated and compared comprehensively. • The presence of the ribs makes it difficult to transfer the uncertainty of the flow field to the heat exchange field. • The existence of large heat flux gradients and sharp fluctuations in the region around the ribs is distinguished. • The shortcomings of conventional sensitivity measures are analyzed and one with engineering relevance is derived. [ABSTRACT FROM AUTHOR]

The application of phase change materials (PCMs) in renewable energy storage and building temperature regulation is considered an effective method to reduce the use of fossil fuels and carbon emissions. However, issues concerning the utilization of PCMs in high-humidity environments remain to be addressed to fill the gap in real-world applications. This paper establishes a simplified novel two-zone model, comprehensively considering the natural convection on the surface of the PCP in high-humidity environments, as well as the formation, movement, and evaporation of water films on the surface. Subsequently, numerical solutions and experimental validation are conducted, and the influence of high-humidity environments on the heat and moisture transfer is elucidated. The results indicate that a high-humidity environment can significantly suppress the sensible heat transfer with a ratio range of latent heat to sensible heat typically around 1–4. Furthermore, the increase in the height of PCP leads to an increase in the proportion of sensible heat transfer. On the contrary, increasing the thermal conductivity of the PCM can amplify the latent heat transfer. The results can help further study the thermal storage and the dehumidification potential of phase change units in application on a large scale under high humidity conditions. [Display omitted] • A simplified model for PCM thermal storage prediction in high humidity environments is established. • The variation of water film on the PCP surface is considered. • Sensitivity analysis for PCM thermal storage in high humidity environments is investigated. • A high-humidity environment can lead to a ratio range of latent heat to sensible heat typically around 1–4. [ABSTRACT FROM AUTHOR]