Thermal Performance Of System Research Articles

Experimental and economic evaluation on the performance improvement of a solar photovoltaic thermal system with skeleton-shaped fins

At elevated ambient temperatures, the production and efficiency of solar panels are degraded due to the overheating of the cells. Cooling photovoltaic cells at elevated ambient temperatures can prevent overheating, extend their life, and enhance overall efficiency, particularly in areas exposed to strong sunlight and elevated temperatures. In this study, an attempt was made experimentally to increase the performance of solar photovoltaic thermal systems with a novel cooling technique. The proposed system has an absorber plate coupled with novel skeleton-shaped fins used to create double-pass ambient air channels below the solar module for natural heat dissipation. Performance of the proposed photovoltaic thermal system with skeleton-shaped fins was designed, evaluated, and evaluated, under different climatic conditions of the southern Algeria city of Ghardaïa from 8:00 am to 6:00 pm. Theoretical analysis was also developed relying on the energy and exergy balance equations for the system components. An economic analysis is also performed by the life cycle cost analysis to evaluate the feasibility, annual performance, and payback period of the proposed solar system compared with that of the conventional system. Results showed that the proposed photovoltaic thermal generates an average daily production of 2.02 kWh, which is 55.1 % more than the conventional system. The energy and exergy efficiency of the proposed system are higher than the conventional system by 8.61 and 8.98 %, respectively. The levelized costs of energy associated with the proposed system (0.17 $/kWh) is lower than that of the conventional system by 11.76 %. The payback period of the proposed system (6.21 years) is lower than that of the conventional solar systems by 34.7 %. This means that the additional power generation obtained by the proposed system with skeleton-shaped fins was sufficient to offset the total life cycle costs.

Energy storage, thermal-hydraulic, and thermodynamic characteristics of a latent thermal energy storage system with 180-degree bifurcated fractal fins

The low thermal conductivity of organic phase change materials limits the performance of latent thermal energy storage (TES) systems. Inspired by fractal theory, this study proposes an innovative 180° fractal fin for enhancing the thermal performance of latent TES systems. The effects of length ratios (l) and fractal levels (N) are numerically investigated employing the enthalpy-porosity method. Compared with traditional rectangular fins, the results indicate that the 180° fractal fins reduce the integral average value of the maximum velocity by 2.24%–48.51%, which indicates the suppression of natural convection by the latter. Increasing l and N result in a general increase in melting time. Compared to the TES systems without fins and with rectangular fins, the 180° fractal fins can respectively reduce melting time by up to 88.79% and 28.00%, increase integral average Nusselt number by up to 7.30 times and 34.21%, and enhance energy storage power by a maximum of 8.55 times and 38.71%. Moreover, flow viscous entropy generation can be neglected compared to thermal entropy generation. In contrast to rectangular fins, the employment of fractal fins leads to a maximum reduction of 90.06% and 99.10% in total frictional entropy generation and thermal entropy generation, respectively.

Heat and mass transfer analysis of conducting non-Newtonian nanofluid flows over an elongating sheet with a non-uniform heat source

Nanofluids help in many fields to improve the performance of thermal systems by augmenting heat transfer rates through their thermophysical properties. The performance of the nanofluids with various base fluids may be different. Therefore, the study and comparison of behaviors of various nanofluids are useful in several applications such as fuel as a coolant in automobiles, and in medical and electronic equipment to reduce the thermal resistance. This research proposed a novel model to investigate the flow behavior of three different nanofluids over an elongating surface in the presence of a non-uniform heat source and thermal radiation effects. This investigation describes how the considered nanofluids behave in the presence of a transverse magnetic field, and other effects. The proposed governing boundary layer partial differential equations (PDEs) are reformed into a system of nonlinear ordinary differential equations (ODEs) by introducing the proper similarity transformation. The finalized equations are solved numerically with the help of the ND solve package in Mathematica software. We intended how the fluid flow and heat transfer are affected by non-dimensional controlling factors with the help of graphics. Further, the calculations and discussions are accompanied by the numerical values of the skin friction coefficient and heat and mass transfer rates. According to the current findings, the Maxwell nanofluid exhibits superior performance in velocity, and the Oldroyd-B nanofluid shows more concentration and less temperature. As a special case, the results of this investigation are compared with the existing results, and found a good agreement between the results.

Correlation study of thermal charging, discharging, and efficiency of graphene oxide-reinforced paraffin wax for thermal energy storage system

Nanocomposites, produced through mechanical blending, serve to enhance thermal performance of heat exchangers, solar collectors, and photovoltaic-thermal systems. This work employs an experimental methodology to assess the thermal charging (TC) and thermal discharging (TDC) of a composite generated by mixing graphene oxide (GO) and paraffin wax. TC and TDC of the GO-reinforced paraffin wax-based phase change material (PCM) have been examined across different flow rates (0.375, 0.75, and 1.5 L/min) and concentrations of GO (ranging from 0.25 to 1.00 vol%). The results exhibit a direct correlation between TC, TDC and efficiency, and reaction parameters (flow rate and volume concentration of GO). The experimental and predicted values of TCs, TDCs, and efficiencies fell ±15% (for TC and TDC), and ±9% for thermal efficiency, demonstrating a satisfactory level of agreement. This holds a practical application and valuable predictive tool for estimating TC, TDC, and thermal efficiency on known flow rates and concentrations of GO in wax-based PCMs.

A novel biogas-driven CCHP system based on chemical reinjection

In the process of vaporizing water within the biogas-driven CCHP system based on chemical recuperation, a significant temperature disparity in heat transfer exists, leading to increased irreversible loss, and the methane conversion rate is low because the gas turbine exhaust gas is difficult to drive efficient methane conversion. This paper proposed a novel biogas-driven CCHP system based on chemical reinjection. Through the reinjection of a portion of the exhaust gas into the reactor, a self-thermal reforming reaction process is engineered, leading to a substantial enhancement in methane conversion rate. The heat matching of the heat exchange unit is optimized by the reheat air, and the power generation and cooling capacity of the system are improved. Notably, the electricity and cooling generation of the new system increased by 55.52 kW (6.20 %) and 542.49 kW (101.49 %), respectively, while the exergy efficiency increased by 8.31 %. The study delves into the influence of key parameters on the system thermal performance. During the reforming process, the exhaust gas split ratio has a significant impact on carbon deposition and methane conversion. When the methane is nearly completely converted, there is no significant change in electricity generation of the system. Excessive turbine inlet temperature is found to be unfavorable for improving the exergy efficiency of the new system from a holistic system perspective. Finally, a comprehensive comparison of the thermal performance between the new system and the reference system is conducted under various ambient temperatures. This study offer a new design scheme for the efficient utilization of biogas.

Numerical-experimental study of the thermal behavior of a green facade in a warm climate in Mexico

Demographic growth entails an increase in the construction of buildings and streets, whose materials significantly absorb heat and, upon release, create discomfort for the inhabitants of large urban areas. Vegetation emerges as a crucial element to enhance both the indoor environment of buildings and the outdoor surroundings. Green facades present themselves as a highly efficient alternative to integrate vegetation in densely urbanized areas. This study focuses on evaluating the thermal performance of an indirect-type green facade system in a warm climate in Mexico. The research encompasses experimental measurements and numerical simulations of the thermal effect of the green facade and also a parametric study of the vertical leaf area index (LAIV) and air gap size. In the experimental test, temperatures were recorded in two identical test cells, one of which was equipped with a green facade with Pyrostegia Venusta plants on one of its surfaces. The numerical study validated the results obtained through experimental tests, using simulations of Computational Fluid Dynamics (CFD) considering a typical day for each season throughout the year. Validation results revealed Mean Percentage Errors (MPE) of −2.86 % and 0.25 %, Mean Bias Errors (MBE) of −0.49 °C and 0.08 °C, and Root Mean Square Errors (RMSE) of 1.34 °C and 1.29 °C for the bare facade and the green facade, respectively. In the numerical analysis, it was observed that the green facade succeeded in reducing the indoor air temperature in a range of 4.57 to 5.64 °C, while decreasing the heat flux in an interval of 7.84 to 16.79 W/m2. Moreover, a parametric study revealed that the LAIV ceases to be a significant parameter beyond 2.5, while the air gap size proves to be a considerably less influential factor compared to the LAIV. These results confirm the relevance of using vegetation in buildings to mitigate the effects of heat and improve the thermal comfort of inhabitants.

Performance of Photovoltaic Thermal and Biomass Gasification for Efficient Renewable Energy Generation: A Review

AbstractThis review presents the technical and operational performances of solar and biomass energy technologies viz photovoltaic thermal (PVT) and biomass gasification systems. This work aims to offer a reference and guidelines to the renewable energy‐related players, especially for those at the operational level and investors. This paper highlights the technical advantage of hybrid PVT with phase change material in terms of electrical and thermal efficiencies. While the operational performance of biomass gasification is thoroughly discussed via sensitivity analysis, the potential integration between solar and biomass gasification technologies is explored to complement and bolster the capabilities of both renewable systems within the power energy mix portfolio. Finally, few directions and significant takeaways considering the technical criteria are addressed for identifying efficient renewable energy generation.

Constraint-based analysis of heat transport and irreversibility in magnetic nanofluidic thermal systems

Purpose This paper aims to investigate the thermal performance of equivalent square and circular thermal systems and compare the heat transport and irreversibility of magnetohydrodynamic (MHD) nanofluid flow within these systems. Design/methodology/approach The research uses a constraint-based approach to analyze the impact of geometric shapes on heat transfer and irreversibility. Two equivalent systems, a square cavity and a circular cavity, are examined, considering identical heating/cooling lengths and fluid flow volume. The analysis includes parameters such as magnetic field strength, nanoparticle concentration and accompanying irreversibility. Findings This study reveals that circular geometry outperforms square geometry in terms of heat flow, fluid flow and heat transfer. The equivalent circular thermal system is more efficient, with heat transfer enhancements of approximately 17.7%. The corresponding irreversibility production rate is also higher, which is up to 17.6%. The total irreversibility production increases with Ra and decreases with a rise in Ha. However, the effect of magnetic field orientation (γ) on total EG is minor. Research limitations/implications Further research can explore additional geometric shapes, orientations and boundary conditions to expand the understanding of thermal performance in different configurations. Experimental validation can also complement the numerical analysis presented in this study. Originality/value This research introduces a constraint-based approach for evaluating heat transport and irreversibility in MHD nanofluid flow within square and circular thermal systems. The comparison of equivalent geometries and the consideration of constraint-based analysis contribute to the originality and value of this work. The findings provide insights for designing optimal thermal systems and advancing MHD nanofluid flow control mechanisms, offering potential for improved efficiency in various applications. Graphical Abstract

An optimization of efficient combined cycle power generation system for fusion power reactor

Fusion power plants can meet the energy demands of the world. The high thermal performance of a power generation system is still a challenge and one of the developing trends with a fusion reactor due to the high outlet temperature. A combined cycle system has been optimized to work at high outlet temperature and pressure of fusion power reactor with thermal power of 2500 MWth and its input parameter has been optimized along with impact of partial load to achieve high thermal performance very first time. The combined cycle based on the concept of two stages of expansion in the closed-Brayton-cycle and two reheaters in the Rankine cycle named Schematic-IV with the higher thermal performance of 58.19% as compared to Schematic-I, II and III has been proposed for a fusion power reactor. The increase in more than one expansion stage and reheat stage is not economical because it increased the thermal performance by about half of performance as compared to one. The effect of isentropic efficiency of compressor and heat rate have been investigated to validate the thermodynamic model and calculations. The optimized thermal performance of the combined cycle is 58.19% at a feed water mass flow rate of 592 kgs−1 and steam outlet temperature of 277 °C in the combined cycle. The heat rate decreased and thermal performance increased with the mass flow rate verifying that the thermodynamic model is correct. The thermodynamic analysis of the combined cycle-based nuclear reactor provides insights for better system thermal performance and reveals the effect of key parameters on the system performance.

A green hydrogen production system based on solar-assisted biogas steam reforming

In the context of a carbon–neutral world, biogas reforming technology has potential to realize the production of green hydrogen with distributed production. Traditional green hydrogen production system based on biogas reforming dependent on high temperature condition during the reforming process; besides, biogas is always identified as a free energy resource in existing studies. This study develops a new way for green hydrogen production based on solar-assisted biogas steam reforming. The heat demand in the digester is considered in the newly proposed system; thus, more reasonable conclusion in regard to system thermal performance could be draw compared with existing studies. An advanced biogas reforming process with high steam-to-carbon molar ratio by introducing a parabolic trough solar collector is designed. At the same time, coupled with the carbon capture scheme proposed by previous study, it has great potential to realize hydrogen production with negative carbon emissions. Combined with the carbon deposition analysis, system integrated thermal performances are compared within the margin of safety. High steam-to-carbon molar ratio in the new system obviously improves the hydrogen production rate, with a maximum increase of hydrogen yield reaching 24.21 kg/h. In addition, the heat supply capacity is also significantly enhanced, which can meet the heat load of the digester when the ambient temperature is 4.03 °C (the reference system is only 20.19 °C). In terms of the integrated thermal performance, the hydrogen production efficiency of the new system is 33.60 percentage points higher than that of the reference system. This study provides a new idea for green hydrogen production from the perspectives of low temperature condition and negative carbon emissions.

A virtual test rig for performance and efficiency assessment of heat pump thermal management system for battery electric vehicles

In a Battery Electric Vehicle (BEV), the optimization of its thermal state plays a crucial role in the achievement of relevant vehicle targets such as range, passenger comfort, and recharging times, as well as varying external ambient conditions. Therefore, selecting the most proper solution between the many possible architectures to manage the different thermal loads of a BEV needs the support of a robust simulation platform. In such a framework, a comprehensive numerical twin of an electric city car was developed in the GT-Suite environment and validated against experimental data. Through that, the promising performance of a Heat Pump (HP) based thermal layout has been demonstrated, against a standard Air Conditioning system integrated with a PTC heater, on a wide range of external ambient temperatures (reaching up to +20 % driving range improvement in cold conditions). The present layout proposed a sustainable alternative to the most common R134a as working fluid (i.e., propane) and the integration of multiple heat sources. In addition, different battery preconditioning strategies have been tested, tailored to the selected real-world mission profiles, obtaining a remarkable gain in terms of driving range for the HP system in cold conditions (up to 6 % at −10 °C and 4 % at −20 °C).

Preparation of Highly Thermally Conductive Hexagonal Boron Nitride‐Polyvinyl Alcohol/Polydimethylsiloxane Composite Using Combined Freeze‐Drying and Spatial Confining Forced Network Assembly Method

With the rapid advancement of electronic products, an increasing number of electronic components are being integrated onto chips, leading to a higher power consumption per unit area. Consequently, effective heat dissipation has become increasingly important. To address this heat dissipation challenge, this article introduces and prepares a highly thermally conductive polymer composite based on freeze‐drying, coupled with the spatial confining forced network assembly (SCFNA) method. The freeze‐drying process is used to create a three‐dimensional thermal conductive network. This network provides a well‐defined heat path. The SCFNA method enhances the regularity of the thermal conductive network within the matrix. Ultimately, this results in the significant thermal conductivity enhancement of the polymer composite. After freeze‐drying, when the mass ratio of hexagonal boron nitride to polyvinyl alcohol is 4:1, the sample prepared by SCFNA presents 72.6% higher thermal conductivity than the one obtained through direct infiltration. This achievement holds significant value for the advancement of polymer composites with high‐thermal conductivity and excellent mechanical properties. It can improve the low‐dissipation performance of polymer thermal conductive composite systems, meet the needs of high‐performance and low‐dissipation use of thermal management materials, and reduce the working temperature of electronic chips.

Entropy generation and heat transfer analysis of Eyring-Powell nanofluid flow through inclined microchannel subjected to magnetohydrodynamics and heat generation

The current study is inspired to investigate the influences of essential flow dynamics including magnetic field, variable dynamic viscosity, Joule heating, viscous dissipation, porous medium dissipation, heat source, thermal radiation, and convective heating on the mixed convection flow of Eyring-Powell Cu − water nanofluid trough an inclined microchannel in the presence of Darcy-Forchheimer porous medium. The governing mathematical model equations are formulated, converted into dimensionless and thereafter solved numerically in the MATLAB software via Bvp4c-package. The influences of the embedded dimensionless parameters on heat transfer behaviours and entropy generations are displayed trough graphs as well as their physical interpretations are discussed in detail. Consequently, it is revealed that the performance of microchannel thermal system is improved by factors such as injection/suction of fluids, Eyring-Powell fluid, magnetic field, non-Darcy porous medium, Cu − nanoparticles, thermal radiation and convective heating. The drag coefficient and Nusselt number augment with viscous dissipation, variable dynamic viscosity, Darcy porous medium, angle of inclination, Prandtl number and heat source. Moreover, the Nusselt number at around the left and right walls vicinity shows an opposite behaviour with escalating values of the Biot number and thus convective transfer of heat around the microchannel walls is remarkably important. Furthermore, the minimization of net entropy generation rate is achieved with Eyring-Powell fluid, magnetic field, Cu − nanoparticles, thermal radiation and convective heating but it escalates with variable dynamic viscosity, viscous dissipation, angle of inclination, heat source and Prandtl number. Indeed, the irreversibility due to the robust influence of porous medium shows dual behaviours on the net entropy generation rate. Finally, the numerical results are also validated by comparing with the results of already existing literatures and hence, a sounding agreement is attained.

Numerical investigation of heat transfer in wire and tube-based phase change material heat exchanger

The utilization of latent heat storage units with their high energy density and isothermal heat transfer behavior can enhance the performance of thermal energy systems. This study aims to investigate the effect of fin placement on the melting time of a wire and tube-based Phase Change Material (PCM) heat exchanger using numerical simulations. The study introduces a new complex geometry for the heat exchanger, and numerical analysis of heat transfer was conducted in Ansys Fluent software using an established solidification and melting model. The numerical results were validated against experimental data, and it was found that the position of the tubes and fins had a significant impact on heat transfer within the PCM. The model was able to predict temperature data with a maximum discrepancy of 3%.

The Effect of Uneven Metal Foam Distribution on Solar Compound Parabolic Trough Collector Receiver Thermal Performance

Solar energy is a key player among other renewable energies that reduce greenhouse gases and replace conventional fuel, i.e., to solve global warming and fossil fuel descending issues. However, the thermal solar systems’ performance should be enhanced to cope with intermittent solar radiation. Metal foam can be used as an enhancer in solar collectors’ receivers. However, metal foams are associated with pressure drop. To benefit from the metal foam as a thermal enhancer and overcome the pressure drop issue, the present study numerically and experimentally investigates a novel Compound Parabolic Solar Collector (CPC) receiver with innovative uneven metal foam inserts of varying thickness. Two pores per inch (PPI) Cu-foam inserts, PPI10 and PPI20, were tested. These inserts were strategically placed at three different positions along the receiver, with thicknesses of 3 cm, 2 cm, and 1 cm starting from the inlet side. In the experimental part, three tubular receivers were tested, empty, i.e., without metal foam, inserted with Cu-foam of PPI10, and inserted with Cu-foam of PPI20. The experiments were conducted from 09:00 AM to 04:00 PM. The investigation involved water volume flow rates from 0.2 to 0.6 l/min. The numerical part included solving the governing equations, i.e., mass, momentum, and energy conservation, simulating conditions similar to the experiments. The Brinckman model described the fluid flow through the metal foam. The thermal performance of the CPC system was evaluated using the Nusselt number (Nu), thermal efficiency, water bulk temperature, and water outlet-inlet temperature difference. Inserting Cu-foam of PPI20 resulted in the hourly maximum Nu and thermal efficiency compared to the empty and PPI10 cases. Experimentally, the hourly maximum Nu was 8.9, 8.4, and 7.9 for PPI20, PPI10, and empty receivers, respectively, at 0.6 l/min. The average thermal efficiency was 88.3, 85, and 81.9 for PPI20, PPI10, and empty receivers, respectively, at 0.6 l/min. As for the outlet-inlet water temperature difference, the highest values were at 0.2 l/min. Again, PPI20 recorded the best results, i.e., 23.3 K, 21.5 K, and 20.2 K for PPI20, PPI10, and empty cases, respectively.

Cooling performance and optimization of a thermal management system based on CO2 heat pump for electric vehicles

Efficient integrated thermal management scheme is crucial for improving the driving range, thermal comfort, and safety of electric vehicles. Compared with the synthetic refrigerant heat pump indirect cooling/heating on the vehicle electrical system, the natural refrigerant CO2 heat pump direct thermal controlling integrated into the thermal management system has advantages in the thermal cycle performance and environmental friendliness. The present study proposed a thermal management system based on CO2 heat hump with multiple working modes for enhancing vehicle energy utilization coefficient. The system thermal performance under the World Light Vehicle Test Cycle was investigated via energy and exergy analyses. The operational control strategies of the thermal management system were optimized for the thermal controls of the cabin, battery and motor. The results show that the minimum exergy destruction of the thermal system occurs at the optimal discharge pressure corresponding to the highest coefficient of performance. Ensuring two-phase latent heat transfer for battery cooling is the most effective measure to maintain battery temperature uniformity via dynamic collaborative regulation of expansion valves’ openings and compressor speed. Compared with constant expansion valve’s opening, the coefficient of performance of the system can be improved by a maximum of 10% with the saturated CO2 vapor at the outlet of battery cooling plate. Due to the low thermal capacitance and minimal thermal inertia of driving motor, its cooling performance is significantly influenced by the heat generation rate and refrigerant flow. Optimal motor cooling efficiency is achieved when controlling the refrigerant quality to 0.85 at the cooling passage outlet. Under the World Light Vehicle Test Cycle, the thermal management system effectively regulated the temperatures across different operating modes while operating at optimal discharge pressures.

Radiative Impact on Jeffery Trihybrid Convective Nanoflow over an Extensible Riga Plate: Multiple Linear Regression Analysis

Solar thermal systems utilize solar energy to generate heat, and the incorporation of nanoparticles such as Al2O3-Cu-Ni with a water base can elevate their efficiency. These nanofluids, composed of aluminum oxide, copper, and nickel nanoparticles dispersed in water, enhance heat absorption and transfer within the system. This improvement contributes to heightened overall performance and effectiveness of solar thermal systems. Cupronickel alloy helps in the process of desalination. Hence, this study examines the heat exchange properties in the context of a boundary layer flow of a trihybrid over a variable-thickness Riga plate stretched and heated by convective heat with non-Newtonian fluid (Jeffery) in the presence of thermal radiation. The governing equations of the boundary layer are transformed into a system of ordinary differential equations through appropriate similarity transformations, and those equations are resolved utilizing a boundary value problem program. The engineering parameters are analyzed through the application of multiple linear regression. The key finding of the investigation is that the Prandtl number, and thickness index number all have a positive impact on the Nusselt number. The presence of radiation and a uniform heat source improves the Nusselt number, physically this energy transfer improvement assists in higher solar collector efficacy; and converts that energy to usable heat. The rationale behind selecting trihybrid nanoparticles Al2O3, Cu, and Ni lies in the balance and inertness of Al2O3, with metals Cu, and Ni, both possessing more thermal conductivity.

Improvement of the performance of thermal energy storage systems with conical annular enclosure using magnetic field

This study numerically investigates the integration of passive and active heat transfer enhancement techniques to develop a highly efficient thermal storage system for quick charging rates. A conical design for the shell of latent heat thermal energy storage systems is combined with a diametrically magnetized cylindrical magnet to improve its performance. Numerical simulations explore the effect of the non-uniform magnetic field on latent heat thermal energy storage systems with conical enclosures at different tilting angles. The obtained results indicate that increasing the tilting angle of the enclosure of the nanoparticle enhanced phase change material reduces charging time by promoting more effective natural convection. Besides, the magnetic field enhances convective heat transfer between the heat transfer fluid and the nanoparticle enhanced phase change material, resulting in faster melting and the combined effects of magnetic and buoyancy forces reduce the overall melting time. The higher magnetic field intensities lead to a larger portion of the volume melting of nanoparticle enhanced phase change material and accelerated melting front advancement. Furthermore, the effect of the tilting angle on the process of melting is nearly eliminated for higher intensities of the applied magnetic field. This innovative combination holds significant potential for enhancing the performance of latent heat thermal energy storage systems, enabling efficient thermal storage and achieving rapid charging rates.

Study on thermal storage performance of a novel conical spiral tube heat storage system

Due to the structural advantage of the conical spiral tube, which is narrow at the top and wide at the bottom, it helps to improve the thermal response rate of the heat storage system. Therefore, this study proposes a novel conical spiral tube heat storage system. The software Fluent is used to conduct three-dimensional unsteady state calculations and investigate the effects of the conical ratio, taper, and length-to-diameter ratio on the phase change material (PCM) thermal storage performance. The results indicate that when the conical ratio is increased from 1.0 to 3.0, the PCM heat storage capacity is reduced by 1.05%, the melting time is shortened by 17.60%, the average heat storage rate is increased by 20.10%, and the heat storage efficiency is reduced by 0.10%. Continuing to increase the conical ratio, the optimization of the performance is not obvious. Subsequently, a conical ratio of 3.0 heat storage tank is used as the reference unit. When the tank taper is increased from 0 to 0.22 and the length-to-diameter ratio is increased from 1.44 to 1.85, the melting time is shortened by 7.59% and 32.62 %, the heat storage capacity is reduced by 3.45% and 9.24%, the average heat storage rate is increased by 4.47% and 34.69%, and the heat storage efficiency is reduced by 0.02% and increased by 7.99%, respectively. Continuing to increase the taper from 0.22 to 0.32 does not result in an effective improvement of the performance. This study is a good guide for the optimization of the thermal storage performance of spiral tube heat storage systems and the efficient use of solar energy.

Thermal performance of a novel underground energy migration system for greenhouse

The progression of Chinese solar greenhouse is shifting from an integrated insulation and heat storage system to a separated configuration. Retaining a significant amount of surplus air thermal energy during the day, it can be stored and released at night to meet heating demands. To effectively utilize the surplus air thermal energy, an underground energy migration system is proposed for storing it. The thermal environment of the greenhouse is analyzed in experiments after applying the system, and the required thermal performance for the system’s heating is calculated using the greenhouse’s thermal balance. A computational fluid dynamics method is employed to optimize the system while also determining the system’s impairing effect on the greenhouse’s thermal environment. The findings suggest that the insulation of heat storage units must be externally maintained to prevent soil interference with the system’s thermal performance. The optimal airflow rate for heat storage was 2 ∼ 2.5 m/s, and 2.5 ∼ 3 m/s for heat release. The average air temperature of greenhouse decreases 1.80 °C in daytime and increases 2.14 °C in nighttime by the underground energy migration system. Meanwhile, the heating coefficient of performance reaches 5.14. The system provides new ideas and methods for the recycling of clean energy in greenhouses.