Thermal System Research Articles

Performance of a CO2-based mixture cycled transcritical pumped thermal energy storage system

Performance of a CO2-based mixture cycled transcritical pumped thermal energy storage system

Enhancing and mapping thermal boundary conductance across bonded Si-SiC interface

SiC is a promising substrate for Si-on-insulator (SOI) wafers for efficient thermal management owing to its high thermal conductivity and large bandgap. However, fabricating a Si device layer on a SiC substrate with a high and uniform thermal-boundary conductance (TBC) at the wafer scale is challenging. In this study, a 4-inch Si-on-SiC wafer was fabricated using a room-temperature surface-activated bonding method, and the TBC was measured using the time-domain thermoreflectance (TDTR) method. The obtained TBC was 109 MW/m2K in the as-bonded sample, improving to 293 MW/m2K after annealing at 750 °C, representing a 78 % increase compared to previously reported values for a Si–SiC interface formed by bonding methods. Such enhancement is attributed to the absence of an oxide layer at the interface. Furthermore, we assessed the actual spatial distribution of the TBC in the SOI system by combining the TDTR mapping with a mathematical model to remove the influence of random errors in the experiment. The spatial distributions before and after annealing were 7 % and 17 %, respectively. Such variation highlights the need to consider the TBC distribution when designing thermal management systems.

Fuel constrained sustainable water-gas-heat-power generation expansion planning of isolated microgrid

On account of slowly reducing of fossil-fuel, profitable utilization of available fossil-fuel to produce electric power is a major concern for electric power producers. Here, short-period fuel constrained power, heat, natural gas and clean water augmentation planning (FCPHGWAP) of isolated microgrid considering carbon capture is presented. FCPHGWAP finds out the most economical and consistent augmentation plan to meet the prophesied power, heat, natural gas and clean water demand over a short-term time horizon whilst satisfying several technical as well as societal constraints. An archetypical system having extant diesel generators (DGs), PVT panel, wind turbine generator (WG), micro-cogeneration unit (MCU), battery energy storage system (BESS), plug-in electric vehicles (PEVs), thermal energy storage system, natural gas storage unit, carbon capture unit (CCU), electrolyzer, hydrogen storage unit and aspirant PVT panel, WGs, MCUs and PEVs is taken into consideration. Self-organizing hierarchical particle swarm optimizer with time-varying acceleration coefficients and grey wolf optimization are used to solve this FCPHGWAP problem. It is observed that net present value having fuel constraints is less than that of without fuel constraints.

Thermal analysis of packed bed thermal energy storage system with dimpled spherical capsules

The thermal storage potential of a packed bed filled with paraffin wax capsules was examined. Heat transfer fluid (HTF) at 70 °C inlet temperature for dimpled and plain stainless-steel capsules was compared for three different flow rates, 1 L/min, 3 L/min and 5 L/min. In general, dimpled spherical capsules sustain more heat than plain spherical capsules at the same flow rate, according to instantaneous and cumulative heat stored. Spherical capsules with dimples exhibited a 30 % improvement in charging rate compared to smooth spheres, particularly at elevated flow rates. Specifically, at a flow rate of 5 L/min, dimpled capsules achieved faster charging and sustained higher temperature compared to plain capsules. Higher flow rates (3 and 5 L/min) result in steeper temperature increases and an earlier peak temperature phase compared to the lower flow rate (1 L/min). Key dimensionless heat transfer numbers were examined. The Stefan number was found to be 0.1966 for an HTF inlet temperature of 70 °C and a latent heat of fusion (Lm) of 213 kJ/kg. Heat transfer increases when Reynolds numbers increased from laminar (123.8 at 1 L/min) to turbulent (619.1 at 5 L/min). Rayleigh number decreased over time but increased for dimpled capsules, indicating improved convection. Dimpled capsules had higher Nusselt numbers and increases with flow rate, indicating better convective heat transfer. Dimpled capsules absorbed heat faster and stored more energy, giving them a viable and efficient Packed Bed Latent Thermal Energy Storage system design.

Effect of hypergravity on CHF for water flow boiling in a rectangular channel

Abstract Hypergravity during the maneuver of aircraft can obviously increase the intensity of disturbance in flow boiling. The critical heat flux (CHF) is a critical parameter to prevent the aircraft thermal management system from drying out. On a rotating platform with distilled water as the working fluid, an experimental investigation into the water flow boiling CHF characteristics in a rectangular channel under hypergravity was carried out. In this study, the influence of hypergravity, entry temperature, mass velocity with heating direction on flow boiling CHF have been investigated and discussed. The results show that hypergravity has a clear effect on the CHF by improving two-phase mixing and bubble separation. CHF increases as the hypergravity and mass velocity increase but decreases as the inlet temperature rises. The orientation of the heating has a clear impact on CHF. A new fitting correlation was discovered as a result of the current study.

Bioconvection flow of Carreau nanomaterial invoking Soret and Dufour impacts

Background and objectiveThermal transport enhancement through nanomaterial flow has gained much attention of the investigators recently. Such attention is for applications in engineering, petroleum industries, geothermal engineering and pharmaceutical developments such as X-ray imaging, welding process, semiconductor material production, thermal storage system, electric cooling devices, drug delivery, magma solidification etc. In view of such interest here we analyze the bioconvective stretched flow of Carreau nanoliquid. Thermal, microorganism and mass convective constraints are considered. Gyrotactic microorganisms within presence of chemical reaction is considered. Variable thermal conductivity is considered. Dufour and Soret features are under consideration. Thermophoresis diffusion and random movement features are considered. Energy relation comprises heat generation and radiation. MethodologyNonlinear dimensionless expressions are developed by employing suitable transformations. Numerical computations are obtained by implementation of Newton built in-shooting technique. ResultsPerformance of liquid flow, concentration, microorganism field, and thermal field is studied. Numerical values of quantities of engineering performance via influential parameters are explored. Larger Weissenberg number yield velocity increase. Reduction in velocity through bioconvection Rayleigh number is witnessed. Concentration and thermal field through solutal thermal Biot numbers have similar effect. An increment in thermal distribution and Nusselt number for Dufour number is detected. Increasing values of Soret number and chemical reaction correspond to decay in concentration. An augmentation in thermal transfer rate and temperature through radiation is noticed. An increment in density number against Peclet and bioconvection Lewis numbers is noticed.

Optimal capacity allocation and scheduling strategy for CSP+PV hybrid standalone power plants

Solar photovoltaic (PV) power generation, as an important clean technology, has been widely adopted globally, especially in remote island areas where access to the main power grid is unavailable. PV power can serve as the primary energy source for standalone island grids. However, due to its dependence on sunlight, PV power output fluctuates, particularly during nighttime and under poor lighting conditions, necessitating the integration of energy storage technology or alternative power generation methods to ensure continuous power supply. Concentrating solar power (CSP) generation, as an emerging technology, can provide efficient power output when solar radiation is abundant and ensure continuous power supply through thermal energy storage systems during adverse weather conditions or nighttime. Although CSP offers advantages such as dispatchability, its high construction and maintenance costs may pose challenges in commercial deployment. Hybrid solar power plants combining both PV and CSP technologies leverage the strengths of both, ensuring more stable and economically viable power output. This study establishes a model for hybrid solar power plants, considering the impact of PV and CSP component capacities and proportions on performance and costs, i.e., capacity allocation. To maximize the overall benefits of standalone microgrids while ensuring the stability of the power station, a capacity allocation method guided by economic dispatch is proposed. Through iterative analysis, the optimal configuration is determined to minimize the system's equivalent annual costs. Simulation experiments validate the financial feasibility of hybrid solar power plants and the reliability of the proposed configuration method.

Machine learning analysis for heat transfer enhancement in nano-encapsulated phase change materials within L-shaped enclosure with heated blocks

Phase change materials(PCMs) are crucial to energy storage systems due to their enhanced thermal properties. They significantly boost energy efficiency and promote sustainability. Nevertheless, the low thermal conductivity of PCMs presents a significant challenge, which is addressed by utilizing nano-encapsulation to enhance energy efficiency in energy storage systems. Motivated by this, the current study conducts a theoretical investigation to explore the heat transfer characteristics in a buoyancy-driven Nano-Encapsulated Phase Change Materials(NEPCM) nanofluid within an L-shaped porous enclosure with the impacts of a heated block and magnetic field. Furthermore, the fusion temperature plays a crucial role in initiating phase change in NEPCM, thereby impacting the heat transfer process. Hence, identifying the optimal fusion temperature is essential. To accomplish this, a machine learning approach was employed to identify the ideal fusion temperature. A dataset of 160 data points across four different fusion temperature values was used in this analysis. Additionally, the machine learning model analyzed how variations in fusion temperatures impact physical parameters. An in-house Matlab code is utilized to solve the dimensionless fluid transport equations employing the finite difference method. The results indicate that increasing the nanoparticle volume fraction significantly enhances the heat transfer rate across all physical parameters. Specifically, under higher thermal buoyancy force, increasing the volume fraction from 1% to 5% results in a 90.04% increase in the heat transfer rate. The numerical analysis demonstrates that heat transfer rates improve significantly when the fusion temperature is adjusted to 0.5, a result further validated by machine learning techniques. At this temperature, thermal buoyancy force increases by 0.98% and 2.68% compared to values of 0.1 and 0.9, respectively, while the Stefan number shows increases of 159.42% and 87.48% under these conditions; thereby, the heat transfer rate increases at this value. This computational study provides important insights into the significance of fusion temperature, emphasizing the need to determine its optimal value for improving heat transfer. Identifying this optimal value can enhance the efficiency of thermal energy storage systems and improve cooling performance in electronic devices.

Investigation of the Arrangement of Aluminum Fins on the Thermal Behavior of Lauric Acid as a Phase Change Material in a Two-pipe Heat Exchanger by CFD Simulation

BackgroundPhase change material (PCM) thermal storage systems store more thermal energy per unit volume than sensible heat storage systems. PCMs offer a potential solution to reduce energy consumption in various thermal engineering applications. This study aimed to examine how fin arrangement affected the thermal efficiency and melting time of PCMs. MethodsA two-dimensional numerical analysis of the melting process of lauric acid in a heat exchanger featuring two pipelines and fins was conducted using CFD simulation. In most previous investigations, the heat transfer fluid was a single-phase liquid. An enthalpy-porosity technique was used to model the solid and liquid phases of PCM. The governing equations were solved using the commercial software ANSYS Fluent 2021, and the pressure and velocity equations were coupled using the SIMPLE algorithm. Significant FindingsThe best model among the 13 tested was Model 5, which featured 6 fins and a consistent angle of 60 degrees. For Model 5, the melting time was 1818.3 seconds. Due to sensible heating, the fin's temperature (Temp) rose gradually from 300 K to 318 K. Temp then gradually increased as the PCM melted in the phase transition zone between 316.5 K and 321.2 K. Once the phase transition was complete, the PCM's Temp steadily rose from 324 K to 340 K. In Model 5, the inner wall Temp and the maximum Temp of the PCM were closest, at 327.34 K and 333.55 K, respectively. The thermal shock between the PCM and the ambient Temp caused a peak heat flux at the beginning of the PCM loading process.

Synthetic thermal image generation and processing for close proximity operations

The new scenarios foreseen in forthcoming space missions have increased interest towards optical-based relative navigation techniques, which have demonstrated efficacy in a variety of operational conditions. Although object detection methods have predominantly been used within the visible spectrum, optical payloads struggle in weak lighting conditions and are susceptible to overexposure. Consequently, thermal imaging systems are being investigated as a potential solution, as their integration into the current systems would greatly extend future mission capabilities. This study seeks to fill the gap in literature by assessing the performance of state-of-the-art object detection algorithms with images captured in the thermal spectrum. Given the scarcity of readily available thermal infrared (TIR) images captured in orbit, a novel rendering pipeline is implemented to generate physically accurate thermal images relevant to close-proximity scenarios. These synthetic representations feature a simplified target spacecraft against Earth and deep space backgrounds, including variations in illumination conditions, material properties, relative state, and scale. To ensure realistic outputs, the radiative field of the Earth is modelled based on satellite measurements collected in the cloud and Earth radiant energy system (CERES) database. To enrich the fidelity of the outputs, a thermal sensor model and the corresponding noise levels are introduced in the pipeline. The generated images are then used to test the performance of traditional object detection algorithms in discerning the region of interest (ROI) under different orbital scenarios. The results demonstrate the effectiveness of the selected methodologies in mitigating the influence of the Earth in the ROI extraction process, while also revealing a performance degradation due to the presence of multi-material targets.

A novel hybrid battery thermal management system using TPMS structure and delayed cooling scheme

Phase change material (PCM) cooling plays an important role in battery thermal management systems (BTMS). However, PCM has been suffering from low thermal conductivity and inefficient latent heat recovery. Based on this, this study designs a hybrid BTMS combining triply periodic minimal surface (TPMS), PCM, and liquid cooling, and proposes a cooling scheme that determines the operating time of the coolant based on the battery temperature. The system aims to improve the utilization of PCM in two different ways: structural design and cooling scheme. Numerical analysis was used to compare the effects of different structures on the melting rate of PCM and to study the thermal performance of the battery module under various cooling schemes. The results show that the effective thermal conductivity of PCM/TPMS composites reaches 21 W/(m·K), which can effectively enhance the heat absorption rate of PCM. In particular, the I-graph-and-wrapped-package (IWP) structure combined with PCM is the most effective. Under the continuous cooling scheme, when the coolant flow rate is 0.04 m/s, the temperature of the battery at a 3C discharge rate can be controlled at 308.28 K, but the PCM utilization rate is only 0.25. After adopting the delayed cooling scheme, the performance of the BTMS cooling remains excellent, with the battery temperature at only 309.88 K and the liquid phase rate of PCM reaching 0.97. For the first time, the heat absorbed by passive cooling is comparable to that of active cooling in the BTMS heat absorption energy distribution, with a 73 % reduction in pumping energy consumption. Furthermore, under cycling conditions, the delayed cooling scheme still performs well, recovering all the latent heat from PCM and keeping the battery temperature below 313.15 K. In addition, it should be noted that the flow rate of the coolant should be determined by the charging rate. Additionally, the BTMS is capable of addressing the heat dissipation challenges in different ambient temperatures. This study can guide for the design of PCM in hybrid BTMS.

Unveiling Potential: Hybrid Nanofluid-Driven Strategies for Maximizing Electrical Efficiency in Photovoltaic Thermal Systems with Trapezoidal Flow Channel for Coolant Purposes

In this article, a photovoltaic thermal (PV/T) system is optimized using hybrid nanofluids composed of copper and aluminum oxide, with water as the base fluid for cooling applications. The PV/T system features a simple configuration, with mono-crystalline silicon above the flow channel, copper functioning as the absorber, and a trapezoidal-shaped flow channel. The inlet height of the flow channel is fixed, while the outlet height is variable, defining an aspect ratio that ranges from 0.4 to 1. Numerical modeling is carried out using COMSOL Multiphysics 6.0 through the finite element method, applying the two-dimensional incompressible Navier-Stokes and energy equations. The study focuses on analyzing cell temperature and electrical efficiency using both qualitative and quantitative approaches by varying the Reynolds number, aspect ratio, inlet temperature, and volume fraction of the hybrid nanofluids.Key findings: The results demonstrated a significant 37% reduction in cell temperature as the Reynolds number increased from 100 to 400, and a 1.8% reduction when the aspect ratio was minimized to 0.4. Additionally, cell efficiency improved by 8.4% and 2.1% as the Reynolds number increased from 100 to 1000 and the volume fraction from 0.01 to 0.1, respectively. These findings provide effective strategies for enhancing the electrical efficiency of PV/T systems. "The study suggests optimizing the cell efficiency of PV/T systems through a new configuration of the flow channel, focusing on adjusting the outlet height and the concentration of nanoparticles in the base fluid.

Copper based high temperature heat storage macrocapsules with optimized inner cavity

The development of practical high temperature metallic phase change macrocapsules still faces difficulties, because metallic phase change materials undergo volume expansion during phase transformations, which can lead to outer shell rupture. When a core made of stacked metal powders is used, a cavity is eventually formed inside the capsule that acts as a cushion for volume expansion, thus reducing the risk of capsule rupture. However, the cavity will weaken the thermal storage capacity of the capsule, and in order to obtain a capsule with good thermal storage capacity and long-time cycling stability, it is necessary to find a suitable cavity volume of the capsule. In this paper, Cu powders are used as the core raw material, which are spherelized into millimeter level spheres, and the Cu powder spheres are isostatically pressed using an isostatic presser under different pressures to achieve the optimization of the cavity volume by reducing the gap between the powders. The high strength α-Al2O3 is selected as the shell, and sintering additives MgO and SiO2 are doped into the raw material, and the Cu@MgO-SiO2/Al2O3 capsules are prepared after two-step sintering treatment. The material properties and thermal storage properties of the capsules are investigated in detail, which have strong thermal storage properties, for example, in the temperature interval of 1000-1100 ℃, capsules with a core-shell structure (named as 9@1.5-100MPa, prepared with initial diameter of Cu core of 9mm, shell thickness of 1.5mm, and isostatic pressing under 100MPa to the core precursor) exhibit a high heat storage density of 222J/g and 841 MJ/m³. In addition, we conduct melting-solidification cycle tests, which confirms the excellent durability of the capsules. The comprehensive results show that the Cu@MgO-SiO2/Al2O3 macrocapsules possess strong thermal storage capacity and can be used as effective thermal storage materials, especially in advanced high temperature thermal storage systems.

Order Degree and Centrality Analysis of Advanced Fighter Environmental Control System and Thermal Management System

As fighter aircraft become more advanced, traditional air cycle systems have fallen short of meeting the complex environmental control requirements. Advanced fighters such as the F-22 Raptor have responded to these challenges by adopting integrated thermal management systems. These systems feature complex thermodynamic processes and intricate information transmission pathways among various components, creating a sophisticated network structure. To unravel the complexity of such systems, this paper employs a blend of thermodynamics and information theory. We conduct multi-level analysis using structure entropy method and centrality algorithms to explore the information transmission characteristics within these thermodynamic systems. At the system level, we find that variation in environmental parameters have only a 1% impact on order degree, whereas the influence from the system's own structure is more pronounced. At the component level, within the whole system, the varies components in AFT PAO and fuel loops emerge as critical hubs for information transmission. Among these components, the PAO/Fuel stands out as the most important, with closeness and betweenness centrality exceeding that of all other components by at least 11.5% and 29.1%. This study offers a theoretical foundation for the optimization of thermodynamic system structure and layout, viewed through the lens of information theory.

Thermal uniformity analysis of a hybrid battery pack using integrated phase change material, metal foam, and counterflow minichannels

This study investigates the thermal performance and temperature uniformity of a hybrid battery thermal management system (BTMS) that integrates phase change material (PCM), metal foam, and minichannels. Computational fluid dynamics is used to model the PCM melting process and heat transfer between all components. The primary goal of the work is to investigate BTMS architectures which can enhance thermal uniformity and prevent critical temperature rise in a high-voltage battery pack under fast discharging and real-world driving cycle. Four BTMS designs are compared. The design that integrates PCM, metal foam, and counterflow minichannels is shown to have the best performance. At low pumping power (coolant Reynolds number Re = 10), this design reduces the peak battery temperature by 11.5 K compared to a design employing pure PCM only. This configuration also ensures a temperature difference of less than 5 K among individual battery cells, addressing thermal safety considerations and extending battery lifespan. Further analysis revealed that the inclusion of metal foam delays PCM melting, enhances both system and battery thermal uniformity, and offers a higher performance-to-weight ratio compared to designs without metal foam. Although wavy-shaped minichannels offer minimal temperature improvement (0.3 K) over straight minichannels, their higher cost and increased pumping power requirements do not justify their practicality. Under both fast discharging and real driving conditions, the first design with pure PCM provides uniform heat distribution within batteries but fails to maintain the maximum battery temperature within the optimal range. Overall, this study highlights the effectiveness of the proposed hybrid BTMS design in providing uniform temperature distribution and maintaining the maximum battery temperature within the optimal range under harsh environmental conditions, fast discharging, and the Urban Dynamometer Driving Schedule (UDDS) drive cycle.

Performance Enhancement in Air Gap Membrane Distillation Using Heat Recovery Configurations

Experimental investigations were conducted on an air gap membrane distillation (AGMD) unit to evaluate the impact of heat recovery on system performance. The study utilized a steady-state heat source in conjunction with a spiral air gap membrane module for water desalination. The process was implemented using two configurations aimed to minimize heat loss enhancing productivity, gain output ratio (GOR), and thermal efficiency. The experiments involved feedwater with salt concentrations ranging from 10,000 to 30,000 ppm. The measurements were recorded for inlet and outlet temperatures of the heat source, water productivity, and thermal efficiency at various coolant and water feed flow rates. These configurations effectively addressed critical technical challenges in thermal AGMD systems by optimizing heat recovery. The incorporation of heat recovery resulted in a significant increase in water productivity by 37.07% compared to systems without heat recovery while maintaining the same initial heat input. The heat recovery in series (HRSS) and parallel (HRPS) configurations resulted in power consumption reductions of approximately 29.7% and 23.1%, respectively compared to the conventional configuration (CC) at a flow rate of 12 L/min. The levelized cost of water (LCOW) for the AGMD system was comprehensively evaluated and found to be $ 7.71 per cubic meter. This figure reflected the total cost of water production over the system's operational lifespan including capital expenditures, operating and maintenance costs, and energy consumption. The calculated LCOW provides a clear indicator of the system's economic viability, demonstrating the cost required to produce each cubic meter of water through the AGMD.

An experimental study to evaluate the performance of variable-width channel cold plates for cooling rectangular Li-ion batteries

The limited cooling capacity of cold plates employing conventional channel designs represents a key obstacle in thermal management systems. The persistent growth of the thermal boundary layer and the uneven distribution of flow across the channels are the principal challenges encountered in this context. To overcome these challenges, this study aims to analyse a modified cold plate of obstructed variable-width channels that can improve the hydrothermal performance and temperature uniformity. Different shapes of pin fins and grooves with variable sizes that match the width of the variable-width channels are proposed. Specifically, four types of pin fins–grooves were used: ellipse, drop, rhombus and trapezoid. The traditional cold plate served as a basis for evaluating the performance of new designs of cold plates. In addition to the traditional cold plate, the four proposed designs of cold plates were manufactured from copper. Experiments were conducted with water as a working fluid under a laminar flow for a flow rate range of 0.004–0.04 kg/s and a discharge C-rate range of 1C–2C. Results indicated that the use of variable-width channels with all shapes of fins–grooves effectively contributed to improving the heat dissipation of the cold plate, accompanied with an increase in hydraulic pumping power. At the highest flow rate, the best improvement percentage in the Nusselt number of 82.5% was achieved when trapezoidal pin fins–grooves were used; by contrast, the lowest pumping power increasing percentage of 33.2% was obtained when elliptical pin fins–grooves were adopted. The best hydraulic/thermal performance was achieved when trapezoidal pin fins were utilised, with the highest figure of merit of 1.685.

Optimization of a cold thermal energy storage system with micro heat pipe arrays by statistical approach: Taguchi method and response surface method

Optimization of a cold thermal energy storage system with micro heat pipe arrays by statistical approach: Taguchi method and response surface method

Expanded graphite encapsulation of nitrates for enhanced thermal transport: Mechanism insight and component screening

The efficient improvement of the heat transfer capability of high-temperature molten salts and the accurate measurement within the operating temperature range is vital for improving the efficiency of concentrating solar power devices. Through theoretical investigation, this paper explores different thermal properties including thermal conductivity, phase transition properties and interfacial interactions using a range of expanded graphite/nitrates (EG/nitrates). Molecular dynamics simulations reveal that the EG/eutectic salt (ES) exhibits optimal comprehensive properties. Experimentally prepared EG/ES composite phase change materials (PCMs), coupled with theoretical predictions, demonstrate exceptional thermal conductivity (2.2 W m−1 K−1) and a significant latent heat of phase change (>80 J g−1). The calculation results of the interaction energy between the host-guest indicate that the strong interaction of the EG to ES restricts the molecule movement, leading to a weak temperature dependence of the thermal conductivity of the EG/ES composite PCM. This contrasts with the conventional understanding of PCM thermal conductivity, which typically exhibits a sharp change during the phase transition from solid state to liquid state. Additionally, the thermal response of 15 wt% EG/ES is increased by 27.2 % compared to pure ES, which effectively helps alleviate local overheating in practical applications. The progress made so far sheds light on the mechanism behind the improved heat transfer and storage performance of nitrate from a microscopic view, offering valuable theoretical insight for developing high-efficient nitrate PCMs in solar thermal power generation systems.

Experimental investigation of a low-temperature packed-bed thermal storage system with graphite-based composite phase change material

Experimental investigation of a low-temperature packed-bed thermal storage system with graphite-based composite phase change material