Thermal Performance Research Articles

Thermal performance and energy efficacy of membrane-assisted radiant cooling outdoors

Membrane-assisted radiant cooling systems offer a promising solution for directly cooling human bodies in outdoor settings. In this study a prototype system is experimentally assessed, which comprised of two wall-mounted panels and one ceiling-mounted panel with the cooling provided by a water chiller system. Three different radiant panel surface temperatures (Tsur =14.3°C, 17.8°C, 21.9°C) were tested to observe possible condensation and to measure the heat flux, and a thermal comfort survey was conducted in combination to analyze the system energy efficacy. The results indicate that selecting appropriate panel surface temperatures under different ambient universal thermal climate index (UTCI) conditions can not only effectively avoid energy surplus but also improve thermal comfort for people. When the ambient UTCI is 38.1°C, the panel surface temperature needs to be lowered to 14.3°C to achieve neutral thermal sensation while 333.7 W of cooling energy is required; but when the ambient UTCI is 29.9°C, a panel surface temperature of 21.9°C would suffice with a much lower energy demand. It is also concluded that the surface condensation may occur but can be controlled. This experimental study provides solid data for the further development of radiant cooling technology for open-space applications.

Thermal management of counter terminal lithium-ion battery using Bio-based PCM

Research interest in applying Phase Change Materials (PCMs) for thermal management has been evident across various applications. In several studies, researchers have also suggested the use of PCMs for thermal management in lithium-ion batteries. The current study focuses on thermal management of lithium-ion batteries with terminal configurations positioned in a counter layout, comparing scenarios with and without the implementation of Bio-based PCM. Analysis has been conducted at various discharge rates (1C, 5C, and 10C) using the MSMD model in ANSYS Fluent software for transient analysis. Thermal performance has been numerically evaluated by analyzing temperature, voltage, and PCM’s liquid fraction. The results show that counter terminal lithium-ion batteries exhibit more uniform heat distribution compared to those with terminals in parallel configuration. At a 1C discharge rate, the maximum temperature peaks at 326.15 K, demonstrating a notable 6.23 % reduction with PCM integration. Similarly, at 5C and 10C discharge rates, the maximum temperatures peaks at 346.54 K and 372.99 K, respectively, witness reductions of 10.16 % and 12.44 % due to PCM utilization. Furthermore, the application of PCM facilitates a uniform drop in voltage during discharge, enhancing overall battery performance and longevity.

Dual regulation of thermal conductivity and mechanical performance of nano cellulose-based composite via mimicking plant cell wall structure

Combining thermal conductive fillers and flexible polymers is an agile approach to fabricating composites with heat-conducting performance. However, the thermal conductivity of the composites is hard to reach an equal level to the functional fillers. The mainspring is that the thermally conductive pathways within the composite could not be well-constructed due to the air-induced interface thermal resistance. Herein, inspired by the plant cell wall structure, polyvinyl alcohol (PVA) with abundant hydroxyl groups was adopted as a binder for boosting the thermally conductive pathways construction between cellulose nanofiber (CNF) and alkalized hexagonal boron nitride (BN-OH), also for strengthening the mechanical performance of the composite. The results showed that the tensile strength and through-plane thermal conductivity of the composite were high up to 91.0 MPa and 2.2 W m−1 K−1 at 40 wt% PVA content, exhibiting 121 % and 450 % enhancements compared to pure CNF film (41.2 MPa and 0.4 W m−1 K−1). Moreover, the composite also presented high thermal stability (decomposition temperature of onset was 218 °C) and good hydrophobicity properties. Overall, this study innovatively proposes an idea for enhancing the thermal conductivity and improving the mechanical properties of the composite, which is indispensable for developing thermal management materials for next-generation electronics.

Thermal energy storage using phase change material for solar thermal technologies: A sustainable and efficient approach

Over-exploitation of fossil-based energy sources is majorly responsible for greenhouse gas emissions which causes global warming and climate change. To mitigate these challenges renewable energy sources, especially solar thermal technologies, can play a decisive role. United Nations also proposes steps to attenuate the adverse effects of fossil-based energy and climate change through Sustainable Development Goals (SDG7 and SDG8). Solar thermal technologies have seen a huge capacity expansion around the globe in previous decades because of their inherent advantages. However, solar energy faces crucial limitations of fluctuating intensity and time-dependent availability. This decreases solar thermal system performance and makes solar thermal technologies time-dependent. To overcome these challenges, integrating phase change material (PCM) in solar thermal technologies makes a sustainable approach to enhance the efficacy, productivity, and utilization rate of solar thermal technologies. In this manuscript, the sustainable approach of integrating PCM in solar thermal technologies was reviewed. This includes literature on PCMs which covers classification, properties, importance, and limitation. Comprehensive data on the integration of PCM with solar thermal technologies such as solar water heating, solar desalination, solar cooking, solar dryers, solar PV/T, solar ponds, solar chimneys, and solar power plants were reported explicitly in terms of the type of PCM, efficiency and their productivity. In addition, the effect of PCMs integration in solar thermal technologies was analyzed in terms of mitigation of CO2 emissions and economic analysis at different locations around the World.

Machine learning accelerated the performance analysis on PCM-liquid coupled battery thermal management system

With the increasing prominence of thermal management issues in lithium-ion batteries, the performance of active-passive hybrid battery thermal management systems attracts extensive attention. In this study, a novel phase change material-liquid cooling coupled battery thermal management system was designed. The effects of battery arrangement structure, liquid flow direction, mass flow rate, startup temperature, phase change material melting point, and liquid cooling power consumption on the thermal management performance of the battery module during high-rate discharge were numerically investigated. The results show that the phase change material-liquid cooling system can effectively regulates battery temperature within safe limits under optimal operational conditions. Compared to the module without liquid cooling with an initial temperature of 40 °C, the maximum temperature is reduced by 15.18 °C and 27.5 °C during 3C and 5C discharge, respectively. Lower liquid cooling startup temperature and higher liquid flow rate contribute further to reducing the maximum module temperature, albeit with increased energy consumption. Compared to continuously operating liquid cooling at 0.01 kg/s, adjusting liquid cooling operating point with minimized power usage can drastically reduce energy consumption by up to 94.71 % during 5C discharge and ambient temperature conditions. Additionally, machine learning with three multi-objective regression prediction models were utilized to predict the temperature and energy consumption of the proposed coupled system. The error between the Random Forest model's predicted values and the simulation results was determined to be <5 %.

Experimental investigation on the thermal enhancement of spherical macro-encapsulated phase change material assisted soil heat accumulators

Reserved cavities during construction have the potential to serve as the space to efficiently harness shallow geothermal energy resources in light of the underground spaces' rapid expansion. Earth-air heat exchanger technology is an effective way among all the technologies. However, as the heat storage capacity of the surrounding soil gradually diminishes due to the long-term operation of the system, it is recommended to incorporate phase change materials (PCMs) with a stabilized heat storage capacity to improve the overall thermal performance of the system. This research specifically recommends back-filling macro-encapsulated PCMs measuring 15–25 mm in order to prevent backfill contamination caused by PCM leakage. The shells and cores of the PCMs are polypropylene spheres and n-heptadecane. Different volume proportions of macro-encapsulated PCMs are used in the design of modified soil accumulators. 27 groups of orthogonal array experimental tables were made using the Taguchi method to test the improved heat accumulator's performance with different heating sources. According to the results, adding PCMs causes the peak temperature to change and increases overall energy storage by 7.2 %. The most significant factor is the soil moisture content, which accounts for 62.47 % of the overall impact of the PCM's heat storage ratio and total heat storage capacity. With a contribution of 20.41 %, the PCM ratio is ranked second. Furthermore, optimization options for the primary parameters that impact the total heat storage and heat storage ratio of the PCM are offered. This paper offers references for the potential use of the PCM-assisted EAHE system design in real-world engineering applications.

Numerical and experimental investigations on thermal performance of Li-ion battery during explosion

Electric vehicles (EVs) are eco-friendly alternative to internal combustion (IC) engine based vehicles to combat with global warming. Lithium-ion batteries (LIBs) are adopted in EVs and their performance and longevity depends on thermal environment. Inadequate thermal management results in suboptimal performance, thermal runaway and consequent explosion in extreme cases. The present study delves into the experimental investigation on catastrophic failure of a Lithium ion cell under abusive conditions. The temperature variations leading up to the point of explosion were meticulously monitored, revealing a critical temperature of 440 K just before the explosion. The pressure waves during the explosion gives the sound pressure levels from 46.2 dB to 83.85 dB within a 34 ms time window and the predominant portion of sound generated during the explosion lies in the range of 129 to 3488 Hz. The battery pack discharge experiments show a temperature rises above the critical limit of 313.15 K and sudden voltage drops to the cut of value of 20 V at t = 850 s during 1C discharge condition, which shows the warning of explosion. Numerical model was developed to simulate the complex conjugate heat transfer in the cell and simulation results are validated. To underscore the practical implications, a case study of fire accident during battery cooling experiment was presented. From the insights gained by explosion of single-cell and fire accident of battery, several recommendations are provided, which includes the orientation of cells within the EVs aiming at the safety of battery design and operation.

Optimizing thermal energy storage in rectangular unit: Exploring the impact of moving fin with phase change material

This research presents an innovative moving fin design for a latent heat storage unit, with the objective of improving thermal performance. The methodology integrates numerical simulation, a machine learning approach, and a multi-objective genetic optimization algorithm (NSGA-II). The study optimizes fin parameters, such as fin velocity (Vf), fin thickness (tf), fin length (Lf) and initial fin position (yf). The optimization process aims to maximize both power (P) and stored energy per mass (Em), assigning equal importance to both criteria. The outcomes reveal a considerable rise in power with minor compromises in stored energy per mass. The incorporation of moving fins in rectangular enclosure with PCM leads to a significant power boost while preserving stored latent energy with minimal compromise. In comparison to the no-fin condition, fixed 1-fin and fixed 3-fin configurations lead to stored energy losses of 4.16 % and 11.73 %, respectively, accompanied by power increases of 20.48 % and 51.17 %, respectively. Conversely, the optimized condition for maximum power with moving fins incurs a mere 2.73 % stored energy loss but achieves a remarkable 173.92 % increase in power. The optimized design parameters for maximizing power (P) include Vf = 22.5 × 10−3 mm/s, yf = 60 mm, tf = 2 mm, and Lf = 40 mm.

Experimental investigation on the thermal performance of high temperature two-phase loop thermosyphon

High-temperature two-phase loop thermosyphons (TPLTs) have the potential to be applied in high-temperature thermochemical conversions, concentrated solar energy, and nuclear energy. However, there has been limited investigation on the thermal performance of TPLTs so far. This work experimentally examines the thermal performance of TPLTs using alkali metals (NaK alloy and pure Na) as working fluids, aiming for internal energy recovery of a double-riser reactor. The effects of filling ratios (FRs), heating temperature, and altitude difference between the evaporator and condenser are investigated regarding start-up characteristics and steady-state performance. The experimental results show that the TPLT with NaK as the working fluid can successfully complete the start-up when the heating temperature is set to above 650 °C under the test conditions. However, the TPLT using pure Na as the working fluid can't successfully complete the start-up from a frozen state without a preheating operation. According to the variations in thermal resistance, an FR of 38% in the TPLT allows for the best heat-transfer performance under steady state when compared to the conditions that FRs are equal to 25% and 50%. Additionally, placing the condenser slightly higher than the evaporator is beneficial for improving the steady-state performance. However, if the condenser is lower than the evaporator, its steady-state performance is remarkably degraded.

Nutrient availability influences the thermal response of marine diatoms

AbstractUnderstanding how phytoplankton growth responds to temperature is critical for forecasting marine productivity in a warming ocean. While previous laboratory studies have shown that phytoplankton thermal traits such as optimal temperature (Topt) can be affected by nutrient availability, it is unclear whether this can be extrapolated to natural communities. To address this, we tested the impacts of nutrient availability on the thermal responses of two cosmopolitan diatom genera, Pseudo‐nitzschia and Leptocylindrus, through a series of in situ manipulation experiments on natural phytoplankton communities. Analysis of the thermal performance curves revealed that nutrient limitation during summer not only limited the growth of these two genera but also reduced their Topt and the maximum growth rates (μmax). Topt was close to or lower than in situ temperature under ambient nutrient conditions, suggesting that further warming may have a detrimental effect on their growth. However, increasing nutrient supply could counteract this by enhancing Topt and μmax. To further confirm the interactive effects of nutrients and temperature on diatoms, we analyzed a 20‐yr monitoring dataset on Pseudo‐nitzschia, Leptocylindrus, and the whole diatom assembly in Hong Kong coastal waters. We found that the abundances of marine diatoms were significantly higher at high temperatures under nutrient‐rich environments while relatively low under low nutrient concentrations. Findings on natural diatom cell density align with the growth performance derived from in situ manipulation experiments, suggesting that abundant nutrients bolster marine diatoms in coping with warming. Our results highlight the importance of considering the influence of nutrient availability on thermal response of phytoplankton growth, which sheds light on how marine primary production may change under climate warming.

Enhancing thermal efficiency in flat plate solar collectors through internal barrier optimization

This study investigates the impact of introducing horizontal barriers within the internal cavity of flat plate solar collectors on their thermal efficiency. The primary objective is to enhance thermal performance by reducing convective heat loss. An experimental test bench was constructed to evaluate five solar collectors under controlled conditions. One collector was unmodified as a reference, while the other four had 1 to 4 horizontal barriers inserted between the absorber plate and glass cover. Each collector’s efficiency was assessed by measuring inlet and outlet water temperatures, incident solar radiation, ambient temperature, and water flow rate. Efficiency versus heat loss parameter curves were generated, and correction factors were applied to account for material and sensor differences. The collector with four barriers demonstrated the highest overall thermal efficiency, achieving an efficiency improvement of up to 12 % compared to the reference collector. Specifically, the efficiency of the reference collector was around 70 %, while the collector with four barriers reached an efficiency of approximately 82 %. Introducing two barriers resulted in a 9 % increase in efficiency, bringing it to about 79 %. Conversely, the collector with three barriers showed a slight decrease in efficiency to 68 %. The barriers effectively reduced internal convective heat loss, enhancing the collector’s ability to harness incident solar radiation. Inserting horizontal barriers within the internal cavity of flat plate solar collectors significantly improves thermal efficiency by reducing convective heat loss. The optimal configuration, based on this study, involves using four barriers. This method presents a straightforward yet effective approach to enhancing solar collector performance. Future research should focus on refining barrier design and placement for different collector sizes and geometries, potentially supporting broader adoption of solar thermal energy systems and contributing to sustainable energy solutions.

Microstructure and corrosion resistance of novel rare-earth-zirconia doped Y2O3 plasma-sprayed coating

Y2O3 coatings are widely applied in semiconductor etching machines to protect the inner walls of aluminum alloys. This study reports the preparation of yttria-based coatings on aluminum alloy substrates using atmospheric laminar plasma spraying (ALPS) methods. In this study, four yttria-based coatings were designed and tested for their thermal performance, plasma etching resistance, and resistance to laser ablation. The rare-earth-zirconia (RE-ZrO2) doped Y2O3 coating exhibited the best thermal insulation performance, with a thermal conductivity of approximately 0.6 W m−1 k−1 at 600 °C. Plasma etching experiments demonstrated that more rare-earth fluorides were generated on the surface of the RE-ZrO2 doped Y2O3 coating, which weakened the plasma energy. Finally, the lowest etching rate was achieved. Laser ablation experiments demonstrated that the depth of the ablation pit on the surface of the RE-ZrO2 doped Y2O3 coating was shallow, indicating good laser ablation resistance. These results indicate that rare-earth-doped yttria-based coatings provide excellent corrosion protection against plasma etching and laser ablation.

Double envelope vacuum insulation panel to contribute to the long-term thermal insulation performance

Vacuum insulation panels (VIPs) have a potential to be used for retrofitting thermal insulation to existing buildings from the viewpoint of low thermal conductivity, small thickness, and light weight. However, in order to realize vacuum insulation panels applicable to building thermal insulation, it is necessary to overcome the challenge of maintaining the low pressure at which high thermal insulation performance can be achieved for several decades. The authors propose double envelope VIPs to maintain this long-term high thermal insulation performance. The double envelope VIP is fabricated by creating a single envelope VIP, wrapping the VIP with core materials, and then inserting it into the envelope for vacuum sealing. By applying the double envelope VIPs, the pressure difference and the permeation of gas in the inner VIP can be drastically reduced, resulting in a longer VIP lifetime. In this paper, the gas permeabilities of the gas barrier envelopes are experimentally estimated. Then, the pressure ageing in the double envelope VIP is calculated. The inner pressure of double envelope VIP after 50 years is 5.4 Pa for the envelope of aluminium composite film, indicating that low pressure can be maintained long-term. Next, the authors carry out accelerated test, in which the double envelope VIPs are placed in a chamber at 80oC and removed every two weeks to measure the effective thermal conductivity. Even after 141 weeks, one sample with a getter agent on the inside and a desiccant agent on the outside indicates only 10.5 % decrease in the thermal resistance. From this result, the long-term high thermal insulation performance can be obtained by fabricating double envelope VIPs.

A computational analysis of the impact of nanofluids (Al2O3)on the PCM melting process in a rectangular container

The effect of nanofluids on the melting process of PCMs (RT58 paraffin wax) in a rectangle container is a topic of interest for many researchers. The use of nanofluids in PCMs can lead to faster and more efficient melting, resulting in improved energy storage and cooling performance. This paper has studied four cases with varying percentages of nanofluids. The percentage of nanofluid in PCM can affect the material's thermal conductivity and heat transfer performance. By varying the percentage of nanofluids, researchers aim to optimize the use of these in PCMs to achieve the best melting performance. Findings have shown that increasing the percentage of nanofluids in PCM can lead to improved thermal conductivity and heat transfer performance. However, at high concentrations (30% percent), the viscosity of the nanofluid can increase, leading to a decrease in heat transfer performance. Results show that at 30 min, PCM with 30% nanofluid melts 13.79% more than PCM without. Using 20% nanofluid in the PCM results in a melting percentage of 7.41%, decreasing to 3.85% at 10%.The specific application and the type of nanofluid used determine the optimal concentration of nanofluid in PCMs. This study is important for the use of phase-change materials in the cooling of large electronic devices.

Electromagnetic and thermal performance study on a canted stack of REBCO tapes

Abstract Due to the critical current limitation of a single REBCO tape, stacking methods are generally employed to increase the current carrying capacity in practical high-temperature superconducting (HTS) applications. However, the overall critical current is strongly dependent on the self-magnetic field, which is influenced by the geometrical arrangement of conductors in the stack. Due to the brittle ceramic property, REBCO tapes are conventionally bent along the thickness side of the tape. However, the difference in bending radii of the outer and inner tape surfaces in the stack may lead to fracture deformation, thereby limiting the stacking number of REBCO tapes. To balance the stacking number with the bending issue, canted stack is proposed as a variant of normal stack for REBCO tapes. As a potential HTS intermediate component, it is imperative to conduct a comprehensive study on electromagnetic and thermal performance of canted stack. The unique geometrical arrangement of canted stack introduces new factors that affect critical current and transport AC loss. This paper concludes the special influencing factors of canted stack, including canted angle, stacking number, tape width, and spatial structure. The metal interleaving method is introduced for spatial distribution changing and thermal stability. Furthermore, orthogonal analysis is performed to elucidate the comprehensive correlation among these multiple factors. This study provides insights into the overall critical current and transport AC loss for different combinations of canted stack and establishes a predicting function for critical current to support the structural design of canted stack. Based on the specific case study, the improvement effect of canted stack is confirmed by both experiments and simulations.

Thermal and cyclic performance of aluminum alloy composite phase change microcapsules for high-temperature thermal energy storage

Al alloys are suitable for high-temperature applications such as solar thermal power generation and industrial heat utilization. However, addressing the challenges of high-temperature corrosion and material failure in Al alloys is of paramount importance. In practical industrial applications, there is a need to develop encapsulation techniques applicable to a wider range of Al alloy types and phase change temperature ranges, exploring the universality of the technology and the diversity of application scenarios. In this study, a dual encapsulation was conducted on binary and ternary Al alloys (including Al-Ni, Al-Mg, Al-Si-Mg, and Al-Mg-Zn). Aiming at thermal energy storage, four composite phase change microcapsules (CPCM) were successfully prepared and subjected to material characterization, thermal performance analysis, and thermal cyclic tests in air environments. After 2000 thermal cycles, no cracks were observed on the surface of the four CPCMs, and the microstructure remained intact. The components of the CPCMs maintained good chemical compatibility. Among the four types of CPCMs, the Al-Si-Mg CPCMs exhibited the best thermal cyclic stability, with a latent heat reduction rate of 19.5 % after 2000 cycles. The experimental results indicated that the dual encapsulation strategy was effective for various types of Al alloy PCMs, thereby expanding the application of Al alloys in high-temperature thermal storage. Furthermore, Al alloys with more regular morphology and lower active metal content exhibited better thermal performance and cyclic capability, making them more suitable candidates for high-temperature thermal storage applications.

Mesoscopic Study on Effective Thermal Conductivity of Aerogel Based on a Modified LBM

ABSTRACT Aerogel with nano-aerogel structure is regarded as advanced thermal insulation material. Therefore, the impacts of their microstructure and physical features on thermal conductivity are vital for optimizing their fabrication. An improved random growth approach was proposed in this paper to theoretically derive the effective thermal conductivity (ETC) of nano-aerogel. This model can accurately depict the random distribution versus the real microstructure. The Lattice-Boltzmann Method (LBM) was introduced into the model to investigate the nano-scale heat transmission in nano-aerogel with porous structure. The developed model provided significant advantages beyond previous approaches for nano-aerogel by altering the particle’s parameters (e.g. particle’s diameter, specific surface area, and morphological structure) to investigate their effects on thermal performance. Comparison with existing literature was made to validate the accuracy. It indicated good agreement among the modeling results, experimental data, and reference values, implying the accuracy of the modified model. It was demonstrated that the optimal model with 150 kg·m−3 in density gained the lowest effective thermal conductivity and the ideal core distribution probability (while C d = 0.01). An inner vacuum of less than 1.0 Pa was recommended for hunting for optimal adiabatic performance. Moreover, it proved that ETC decreased by increasing the specific surface area of aerogel grain at an optimal density of about 150 kg·m−3.

Multifunctional electrochromic yarns for variable optical and thermal regulation

In this study, tungsten oxide and polyaniline hybrid films were deposited on the surface of stainless steel yarns by electrochemical deposition, and the electrochromic yarns with double electrochromic layer structure were formed. WO3 acts as a protective layer and binder to connect PANI nanorods, thereby improving electrochemical stability and electrochromic performance. The electrochromic yarns present five color changes in the voltage range of −0.4 V-1.1 V, the optical modulation of 59.98 %, the response time of 0.75 s, the coloration efficiency of 74.89 cm2/C, good electrochemical cycling stability (100 cycles without significant degeneration) and washing durability. At the same time, stable electrochromic behavior is still maintained in the bending state. The device based electrochromic yarns also has reversible multi-color variation, fast reaction time, and long-term stability. What's more, the device can be embroidered or woven into the fabric and designed into patterns of different colors. More color combinations can be achieved by adjusting the voltage. Finally, the fabric based on multifunction electrochromic yarns are used to study the thermal shielding performance. It can effectively block thermal radiation. These results indicate that the electrochromic yarn has promising potential for high-performance optical and thermal regulation applications. This research provides a prospective strategy for constructing multifunctional electronic devices in wearable application.

Facile preparation of graphene aerogel as a thermal insulation material

A simple low temperature and cost-effective hydrothermal method via reduction self-assembly and freeze-drying was fabricated to prepare graphene aerogel (rGO). After the reduction process, most of the oxygen-containing groups in graphene oxide have been removed by ascorbic acid. The surface C/O atomic ratio detected in rGO is about 7.26. The aerogel presents a nanoporous structure. This porous structure could act as a barrier to heat conduction. By heating the graphene aerogel and using infrared thermal imager to detect the temperature, the temperature difference between the top and the bottom of the aerogel reached 80 °C, which showed excellent thermal insulation performance. In addition, by testing the thermal imaging image of graphene aerogel placed on the skin surface, it exhibited an infrared stealth effect. This carbon aerogel may offer potential for the fabrication and application for thermal insulation and infrared stealth material systems.

Enhancing Digital Camera Image Quality and Thermal Efficiency Analysis

Digital camera technology has made significant advances in recent years, enabling the capture of high-resolution images. However, along with the pursuit of image quality, the thermal performance of digital cameras remains a critical consideration, especially in long-term use scenarios or adverse environmental conditions. This is essential in various fields like surveillance, smart cities, etc. This paper explores the application of image overlay algorithms, specifically high dynamic range (HDR) imaging techniques, and examines the impact of thermal efficiency on image quality in digital cameras. Through controlled experiments and analysis, this study aims to improve digital imaging capabilities.