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This paper summarizes the phenomena and challenges in regenerative cooling, including transcritical thermophysical properties, fuel pyrolysis, and surface coking. The corresponding numerical methods are classified according to their characteristics, including the fuel surrogate, pyrolysis, surface coking, and turbulence models. The scope of application and the advantages and disadvantages of the models are discussed. Currently, only the differential global reaction method achieves model generality over a wide range of continuous pressures (3–7 MPa) and conversion rates (up to 75%), and it is recommended to adopt non-invasive methods and direct cooling unit to improve the accuracy of pyrolysis models. Future surface coking studies should focus on two-way coupling and consider coking and species concentration interaction. The actual coking distribution and porous effects need to be investigated simultaneously, and more kinetic models are urgently required to meet a wide range of pressures. Besides, an overview of parameterized studies in recent years is presented, including operating pressure, heat flux, mass flux, flow direction, flight acceleration and channel configuration. The weaknesses of existing parametrical studies are analyzed from a practical point of view. Heat transfer correlations of endothermic hydrocarbon fuels are also summarized and classified. Establishing heat transfer correlations for the hot spot of the heated side is essential for designing the regenerative cooling system, and the surface coking effect should be introduced. • Kinetic models of fuel pyrolysis and pyrolysis effects on cooling performance are discussed. • Surface coking studies are summarized and divided into one-way and two-way coupling. • Recommended turbulence models for regenerative cooling studies with EHFs are summarized. • Numerical progress on parametric studies of regenerative cooling technology with EHF is reviewed. • Shortcomings of parametrical studies are discussed from a practical point of view. [ABSTRACT FROM AUTHOR]

Accurate heating load prediction is essential to supply-demand collaboration in district heating systems and energy sustainability. With the development of the Internet of Things technology, massive monitoring data is collected that provides abundant data sources for the prediction models. However, the missing data from equipment anomalies, network transmissions and the complexity of heat load changing cause difficulty in realizing accurate heat load prediction. Therefore, the hybrid model based on bidirectional long short-term memory network and temporal convolutional network proposed in this paper to improve the accuracy of the heat load prediction from the aspects of reconstruction of missing values and extraction of complex features. The bidirectional long short-term memory algorithm imputes missing values based on bi-directional features of existing data and provides solid data foundation for subsequent training of predictive models. The temporal convolutional network achieves high-level feature extraction and parallel computation, which contributes to the effective modeling of complex changes in heat load and the realization of accurate heat load prediction. Comparative study was conducted with four heat exchange stations of actual environment to evaluate the performance of the prediction model. The results showed the mean absolute percentage error of the hybrid model decreased to 2.47% which is lower than the State-of-the-Art models, such as long short-term memory, temporal convolutional network, and support vector regression etc. The superior results further validated the feasibility of this hybrid model in heat load prediction. • The missing values in heating system were reconstructed by deep learning model. • A hybrid heating load prediction model was proposed considering missing values. • Detailed experiments were conducted to validate the model's superiority. [ABSTRACT FROM AUTHOR]

This review paper presents an overview of transpired solar collectors (TSCs) - a clean energy technology that has gained considerable attention due to its potential to minimise building energy demand and contribute to achieving net zero emissions. The review is mainly focused on scrutinising the disparities in heat and mass transfer mechanisms, specifically the impact of homogeneous and inhomogeneous suction flow distributions on the TSC, encompassing performance improvement methods, performance assessment, and optimisation strategies for TSCs. The inconsistency between the theoretical and real-world performance of TSCs was observed, attributed to the high turbulence wind with non-uniform speed distribution and suction flow interactions with the main flow in the plenum. Corrugations on the absorber improved thermal performance but increased wind heat loss on the exterior surface, which could be mitigated by adding glazing to corrugated TSCs. The review highlighted the flexibility of integrating TSCs with other technologies, including coupling with separate phase change material (PCM) thermal energy storage units, which outperformed those placing the PCM plate into the plenum. Moreover, integrating TSCs with desiccant wheel cooling systems showed some interesting results in terms of cost and payback period, while integration with heat pump systems could reduce electricity consumption, but it was not recommended in cold climates. Exergetic analysis has been frequently used to determine thermodynamic losses of TSCs and it could provide a more accurate performance assessment when integrating TSCs with power generation systems. The review identified several research gaps in related study fields and provided recommendations, encompassing dimensionless analysis of the relationships between wind effect and heat transfer of TSC absorbers, the development of convective heat transfer correlations for TSC's absorber, and the exploration of cost-effective design and optimisation strategies for hybrid TSCs. • Heat and mass transfer mechanisms of transpired solar collectors (TSCs) were analysed. • TSCs can be integrated with different energy technologies to improve flexibility. • Various designs of TSC systems and their main design parameters were discussed. • It provides some insights into developing convective heat transfer correlations. [ABSTRACT FROM AUTHOR]

To improve the water production of the disc solar still (SS), this paper proposed a new type of membrane distillation enhanced SS by installing an air-gap membrane module vertically inside the SS, and its technical feasibility was confirmed by experiments. An unsteady heat and mass transfer mathematical model of the new SS was also constructed. MATLAB was used to program and solve it, realizing the theoretical prediction of the operation and output characteristics of the new SS, and revealing the change rule and interaction mechanism between the operation parameters and water production. Tests have shown that it is feasible to install membrane modules vertically to increase water production in the SS. The hourly water production per unit area of membrane distillation is at least 3.7 times higher than that of the disc distillation, and the addition of the membrane module can enhance the water production of the SS during the weak period of water production, and realize the continuous water production day and night. The hydrophobic membrane area of 0.08 m2, which is less than one-eleventh of the disc evaporation area, can increase the SS's daily water production by 7.6% to 3457.8 g. The efficiency is 33.4%, which is about 10.2% higher than that of SS. • A new type of solar still called a membrane distillation enhanced disc solar still was designed. • The air gap membrane module was installed inside the disc solar still and was vertically mounted. • An unsteady heat and mass transfer mathematical model of the new solar still was constructed. • Theoretical prediction of the operational characteristics of the device was realized. • The change rule and interaction mechanism between the operating parameters and water production of the device were revealed. [ABSTRACT FROM AUTHOR]

With industrial informatization, rich data frameworks provide the possibility of efficient design and global optimization of methane to hydrogen processes. However, the high coupling between mixed variables leads to the difficulty of first-principles modeling (FPM) to capture the optimal Pareto front in infeasible domains. In this paper, a machine learning proxy (MLP) method is proposed to minimize economic, exergy destruction, CO 2 emissions, and maximize hydrogen production. First, process simulation as FPM is built using physical properties, energy balance, and reaction kinetics to analyze single variable effects and objective trade-offs. Then, datasets consisting of feed, heat transfer, and design variables are built by sampling the FPM in design and extended spaces. The eXtreme Gradient Boosting (XGBoost) with hyperparameter optimization is built as a proxy FPM, capturing the complex mapping between variables and objectives. Finally, the Pareto front is searched in design and extended spaces by combining the proxy model and genetic algorithm. The proposed method benefits 20.2%, 37.2%, 46.7%, and 2.3% in economic, exergy destruction, CO 2 emissions and hydrogen production respectively compared to the heuristic design. XGBoost not only can effectively proxy FPM to capture the complex behavior of reforming techniques, but also can perform better in infeasible domains that are difficult to explore with FPM. [Display omitted] • A MLP optimization method is proposed to explore the trade-offs for four objectives. • The R2 score of XGBoost is above 98.4% for four objective values. • Proxy model exhibits effective exploration of the space far beyond the FPM boundaries. • TAC, exergy destruction, CO 2 emissions, and H 2 production benefits 20.2%, 37.2%, 46.7% and 2.3%. [ABSTRACT FROM AUTHOR]

Particle-based moving bed heat exchangers are increasingly playing a significant role in industrial energy conservation and solar energy utilization. However, the moving bed heat exchanger used for cohesive granular materials still needs to be developed. This paper investigates the feasibility of indirect heat transfer of cohesive granular materials through a moving bed heat exchanger. A vibrating moving bed heat exchanger is developed for the metallurgical slag of vanadium-titanium (MSVT) from industry. The experiment demonstrates that the vibrating moving bed heat exchanger can establish an approximate mass flow regime of MSVT in the experimental section. The vibration device designed for the experimental and discharge section effectively resolves bridging and the intermittent collapse of arching in cohesive granular materials. The outer side of the tube is tightly wrapped by MSVT with vibration. Significant differences are observed in the flow and heat transfer behavior of MSVT between the aligned and staggered tubes. The local heat transfer coefficient at the top and bottom of the aligned tubes exhibits much lower sensitivity to flow velocity compared to the staggered tubes. The relationship between Nu −1 and Pe −0.5 or MSVT around the aligned and staggered tubes follows a linear correlation. Compared to aligned tubes, Nu −1 for MSVT in staggered tubes shows an average reduction of 28%. [Display omitted] • A vibrating moving bed heat exchanger is developed for cohesive granular materials. • Special experimental design can resolve bridging and arching between tubes. • Rheological properties of vanadium-titanium granular are quantitatively evaluated. • The heat transfer of granular flow is tested around different tube arrangements. • The heat transfer correlations are built to predict the heat transfer. [ABSTRACT FROM AUTHOR]

The rapid advancement of micromachining technology has led to the proliferation of micro-combustors in both civilian and military applications, and the actual operation process requires the ability to adapt to complex working conditions. The sudden change of the operating conditions poses a huge threat to the flame stability in micro-combustion, but the flame regulation, especially the adaptive regulation, has proved to be challenging under the sudden change of inlet velocity. In this paper, we report a novel method that significantly improves combustion performance, including heat transfer enhancement under steady-state conditions and adaptive stable flame regulation under velocity sudden increase. We successfully harnessed the synergistic benefits of both the front and rear baffles, investigated the angle matching of the baffles at various inlet velocities, and employed nitinol memory metal as the baffle material to examine its impact on enhancing heat transfer and flame control behavior. According to the results, under the synergic action, the combustion efficiency reaches to 96.92%, and the baffle angle matching 60° + 30° shows good combustion performance at medium-low velocity, and a flame breaking limit of 92 m/s is obtained at 0° + 0° with high-velocity condition. In addition, nitinol alloy is selected as the deformation baffle material, the flame breaking limit is further extended by 6 m/s, and the combustion efficiency can still be maintained at 0.45 ms by a velocity sudden increment of 60 m/s, and the pressure loss is reduced by more than 70%. This study is helpful to provide a reference for the steady combustion under the sudden change of micro-scale conditions, and provides a new idea for the adaptive control of flame. [ABSTRACT FROM AUTHOR]