Thermal Energy Conservation Research Articles

Numerical Investigation of Effect Partially Corrugated Heated Wall on Behaviour Natural Convection Heat Transfer in A Square Enclosure

For fluid flow and heat transfer with engineering industrial applications important methods called natural convection are used. The current numerical study focuses on the effect of changing the heating positions of the corrugated left wall on heat transfer by natural convection with laminar flow in a closed square two-dimensional cavity filled with air as a working fluid. The code of a commercial program (COMSOL Multiphysics 6.0) was used to solve the mathematical equations governing fluid flow represented by continuity, momentum, and conservation of thermal energy. The right wall is exposed to a cold temperature, the other walls are thermally insulated. The effect of partial heating of the left corrugated wall and the Rayleigh number on the process of heat transfer by free convection was studied. At different Rayleigh numbers, flow field patterns and temperature distribution lines appear. The average Nusselt number, the average air temperature, and the flow field are slightly affected by low Rayleigh numbers, while with high Rayleigh numbers, these parameters are significantly and noticeably affected and behave differently by changing the heating sites. Numerical results show negligible effects of wall heating sites at low Rayleigh numbers and significant effects at high Rayleigh numbers. Also, the Nusselt number increases progressively with increasing Rayleigh number, so the heat transfer process gets improved.

Random Walk Modeling of Conductive Heat Transport in Discontinuous Media

AbstractWe consider heat transport within a discontinuous domain by relying on the modeling approach proposed by Baioni et al. Such approach has been specifically designed to address diffusive processes in media with discontinuous physical properties and generalized boundary conditions at the discontinuities. Three algorithms are here applied to estimate the conductive heat transport in a bimaterial medium. The algorithms undergo testing using two test cases that share the same computational domain but differ in terms of their initial conditions. According to the numerical results all the algorithms ensure the conservation of thermal energy and preserve thermal equilibrium under steady state conditions. The Generalized Uffink Method (GUM) and Generalized HYMLA demonstrate sensitivity to the choice of the time step, whereas the Generalized Skew Brownian Motion appears to be unaffected by the value of $$\Delta t$$ Δ t . The GUM algorithm presents an optimal trade-off between accuracy and computational time.

Research and Application of Electromagnetic Heating Device for Digital Well Site Crude Oil Export

Abstract Most well sites have discontinued using the associated gas-fired furnaces in response to the current situation in the oil fields. Coal-fired heating furnaces are environmentally polluting and prohibited due to local environmental regulations. These two heating methods can cause high costs, poor heating efficiency, and environmental pollution, which cannot be achieved through remote digital monitoring. Research has been conducted on the digital electromagnetic heating device for crude oil in the well site, focusing on introducing its main components and functions, including the electromagnetic heating body, frequency conversion control cabinet, and digital remote monitoring terminal. This device provides one-way internal heating without a heat source, resulting in high thermal efficiency, safety, environmental friendliness, and energy conservation. It comprehensively addresses the drawbacks of traditional electric heating, characterized by low efficiency, susceptibility to damage, and difficult maintenance. In 2022, it was applied at three well sites in the Tongzhai operation area of the Third Oil Production Plant of Changqing Oilfield, replacing the existing gas-fired and coal-fired heating furnaces to heat crude oil, as well as heating the heating belt and various electric heating pipes. This device is highly efficient, safe, environmentally friendly, and energy-saving. Additionally, the temperature and pressure of electromagnetic heating crude oil can be digitally and remotely monitored.

Nanoencapsulation of phase change material with CuO nanoparticles: Development of thermal properties for energy storage

Today, the efficient use of energy resources has become essential due to the increasing need for energy. Therefore, thermal energy storage systems are used to minimize lost energy and more efficient energy consumption can be achieved by preventing energy losses. Phase change materials (PCMs) can be effectively used in thermal energy storage and are among the promising materials for a carbon–neutral future. In this study, the synthesis of nanoencapsulated phase change material (NEPCM) containing CuO NPs for use in thermal energy storage systems is included. In the production of phase change material, Copper oxide Nanoparticles were added into urea–formaldehyde resin as shell material, and an NEPCM, a eutectic mixture of capric acid-myristic acid, was prepared. Since the final product will be used in the structure, the phase change material was optimized for room temperature. In-situ polymerization, the synthesis process was carried out to obtain a better shell material to improve thermal properties and prevent leakage. Scanning Electron Microscopy and Fourier-transform infrared spectroscopy analysis were used to determine the morphology and chemical structure of the prepared NEPCM. Elemental analysis was performed to determine the presence of CuO NPs as shell material in urea–formaldehyde resin. Differential scanning calorimetry analyses were performed to determine the thermophysical properties. While the thermal degradation for CuO NPs-NEPCM occurred between 22.78–29.45 °C, the thermal degradation temperature shifted and the thermal degradation status in the first stage was less than that of normal NEPCM. It was observed that the thermal stability and strength of NEPCM increased with the addition of CuO NPs. NEPCM containing CuO NPs has thermal energy storage and energy conservation potential in buildings as a heat storage material. This study can provide an effective way to synthesize form-stable CuO-doped NEPCMs that are economically feasible for thermal applications and have the potential to contribute to future energy storage requirements.

Analysis of home thermal energy conservation and green environment design based on intelligent devices and optical image monitoring

Global climate change and energy crisis are becoming increasingly serious, and household energy consumption occupies a certain proportion in the overall energy consumption. The purpose of this study is to analyze thermal energy use in home environment through intelligent devices and optical image monitoring technology, so as to achieve effective energy conservation and environmental optimization design. In this paper, intelligent sensors and optical image monitoring equipment are used to monitor and collect the thermal energy consumption of different households in real time. At the same time, data analysis technology is used to deeply analyze the heat flow, heat loss and equipment use efficiency in the home. The study compares the effect of traditional energy-saving methods and intelligent monitoring technology. After implementing targeted optimization design through intelligent monitoring equipment, the overall thermal energy saving rate is higher, and the comfort level and green index of the home environment are significantly improved. The results show that intelligent equipment and optical image monitoring technology show a good application prospect in home thermal energy saving. Through accurate monitoring and data analysis, heat energy waste can be effectively identified, so as to take corresponding measures to achieve energy conservation and emission reduction, and promote the landing of green environmental design.

Optimizing thermal comfort and energy efficiency in hospitals with PCM-Enhanced wall systems

Currently, outpatient areas in hospital buildings daily accommodate a significant number of patients with various diseases, presenting a dual challenge of augmenting architectural energy efficiency while concurrently elevating levels of indoor comfort. This research introduces a novel approach to enhancing hospital optimal design: by incorporating Phase Change Materials (PCM) within the architectural walls and using automated machine learning to integrate multi-objective optimization for developing PCM wall system strategies under a comprehensive criteria framework. The findings demonstrate that the incorporation of PCM into the walls of buildings markedly improves indoor comfort while simultaneously reducing the demand for energy. However, these benefits come at the cost of certain financial efficiencies. Specifically, after achieving the targeted optimal thermal comfort, the extent of thermal comfort enhancement across various patient groups ranged from 37.0% to 43.5%. Concurrently, energy efficiency improvements were observed to range between 7.64% and 7.98%. The Life Cycle Cost (LCC) of these optimization strategies falls within a range of 44,950 to 83,894 CNY. In summary, these findings underscore the potential of using PCM within the building wall system to advance thermal comfort management and energy conservation design.

Selection of tropical plants for an extensive green roof with abilities of thermal performance, energy conservation, and greenhouse gas mitigation

The development of green roofs to mitigate urban heat island effect is critical for conserving energy and reducing carbon footprint. This study evaluated the thermal performance of an extensive green roof design compared with a conventional roof and assessed the suitability of thirty-two plants for low-maintenance green roofs in a tropical area. Experiments were carried out in four phases, covering the tropical climatic conditions from June 2016 to December 2017. The results indicate that a green roof temperature was significantly lower than that of a conventional roof by 12 °C. This led to an 84 % reduction in heat transfer through the building, potentially leading to a decrease in electricity consumption by 0.20 kWh/m2/8 h and saving electricity costs by 0.019 USD/m2/8 h, achieved through a reduction in the cooling load on air conditioners. The highest carbon dioxide removal achieved in this study was 3.01 kgCO2/m2, with an effective mitigation of greenhouse gases by 28.46 kgCO2eq/m2/year. The top three plant species recommended for a low-maintenance green roof are Dracaena cochinchinensis, Santisukia kerrii, and Dracaena kaweesakii. The plant characteristics for low-maintenance green roofs in tropical climates include drought and extreme weather tolerance, disease and insect resistance, short and spreading roots, succulent leaves with ability to store water, low water requirements, slow growth rate, easy availability locally and affordability, thriving in low-nutrient conditions, and a high evapotranspiration rate. In applicable contexts, green roofs designed with suitable tropical plants could potentially enhance urban environments and contribute to achieving low-carbon and environmental sustainability.

Thermal shock protection with scalable heat-absorbing aerogels

Improving thermal insulation is vital for addressing thermal protection and energy efficiency challenges. Though silica aerogel has a record-low thermal conductivity at ambient pressure, its high production cost, due to its nanoscale porous structure, has hindered its widespread use. In this study, we introduce a cost-effective and mild method that enhances insulation by incorporating phase change materials (PCMs) into a micron-porous framework. With a thermal conductivity at 0.041 W m−1K−1 on par with conventional insulation materials, this PCMs aerogel presents additional advantages for thermal protection from transient high-temperature loads by effectively delaying heat propagation through heat absorption. Moreover, the PCMs aerogel remains stable under cyclic deformation and heating up to 300 °C and is self-extinguishing in the presence of fire. Our approach offers a promising alternative for affordable insulation materials with potential wide applications in thermal protection and energy conservation areas.

Application of green building thermal energy conservation based on light imaging equipment in landscape optimization of waterfront space

As the global focus on sustainable development intensifies, green buildings have become an important way to reduce energy consumption and improve environmental quality. The purpose of this study is to explore the application of technology based on optical imaging equipment in the heat saving of green buildings, especially in the landscape optimization of waterfront space, and evaluate its effectiveness and feasibility. In this study, light imaging equipment was used to monitor the heat distribution of different green buildings in the waterfront space, and combined with environmental data and energy consumption, the influence of architectural design and landscape configuration on heat energy conservation was analyzed. Through case study and quantitative analysis, the optimization effect of different design schemes on thermal effect is evaluated. The study found that rational allocation of buildings and surrounding landscape can significantly reduce heat loss, reflecting the importance of heat management. Light imaging technology effectively reveals the thermal energy dynamics of buildings under different weather conditions, verifying the potential of green buildings to reduce energy consumption. Therefore, the research based on optical imaging equipment provides a new perspective and method for the energy saving of green buildings in the waterfront space, and demonstrates the important role of optimizing landscape design in improving building energy efficiency.

Multi-objectives occupant-centric control of thermostats and natural ventilation systems in cold climate conditions using real-time occupant-related information

Recently, Occupant-Centric Controls (OCCs) have attracted great attention. Many studies have applied OCCs to mechanical ventilation systems, while natural ventilation systems have gathered much less attention. The natural ventilation effect, driven by opening windows or vents, can be effective in improving indoor air quality, however, result in a leakage of interior heating energy in winter in cold climates. Therefore, the controls of thermostats and natural ventilation systems shall be designed well so that satisfying levels of thermal comfort, air quality and energy conservation can be simultaneously guaranteed. This study proposes an OCC and applies it to thermostats and natural ventilation systems for indoor thermal comfort, air quality and heating energy management. The strategy comprises three controllers: occupancy-based on-off controller, controller of setpoint of indoor air temperature and window openness controller. First, real-time profiles of heat gains from occupants and window openness were collected by employing vision-based detection. Second, a parametric building simulation study was conducted, and then simulation data were generated to develop predictive shallow artificial neural networks for forecasting the indoor conditions and energy performance of the investigated room. Third, the performance of the proposed strategy was examined. Compared to the baselines, the control could offer a decrease in building heating loads by between 43.4% and 63.8 % and an improvement of predicted mean vote levels by 0.36–0.37. The proposed OCC could also maintain indoor CO2 concentrations below 1000 ppm for about 91 % of the studied time, while 84.2 % of the time with several peaks over 3000 ppm in the baseline cases.

Thermal stability of magneto-hybridized silicon and aluminum oxides nanoparticle in C3H8O2-Williamson exothermic reactive fluid with thin radiation for perovskite solar power

The need to increase thermal power stability and energy conservation have spurred the interest in various renewable energies. A diverse range of fabrication techniques and architectures have been developed to meet the global energy demand. Perovskite solar power technologies are the next emerging generation of photovoltaic thermal power systems for an enhanced and stable power supply. Thus, this project examines the thin radiation thermal stability of combined magneto-hybrid silicon oxide (SiO2) and aluminum oxide (Al2O3) nanoparticles in exothermic propylene glycol (C3H8O2)-Williamson fluid for perovskite thermal cells improvement. Without particles agglomeration, the fluid flow is influenced by lower wall velocity, Joule heating and Williamson shear stress in a bounded domain. An invariant coupled differential model is obtained through the similarity transformation of the governing model. The solutions to the invariant model is provided using semi-discretized finite difference method. The outcomes revealed that nanoparticles thermal propagation for perovskite power generation is strengthened with rising Brinkman number, radiation, and Frank-Kamenetskii terms. Also, criticality is raised at the unstable thermal region but damped at the stable thermal regime.

A Bibliometric Analysis of the Outdoor Thermal Environment Based on CiteSpace

The outdoor thermal environment (OTE) is closely related to sustainable urban development and human living, and related research has attracted widespread attention. The research hotspots and research frontiers were obtained using CiteSpace to analyze 4473 relevant studies published in English from the Web of Science (WOS) core database from 1998 to 2023. The results show that (1) Hong Kong Polytechnic University, National University of Singapore, Chinese Academy of Sciences, Tsinghua University, and Harbin Institute of Technology are important in OTE research. China has the largest number of publications in the field of OTE, but the United States has the greatest centrality and significant influence. (2) The focus of OTE keyword clustering research is divided into four main categories: thermal environment perception, the thermal environment index, thermal environment quality, and thermal environment optimization. (3) The frontiers of OTE research have changed from focusing on environmental quality, thermal perception, numerical simulation, urban space, and thermal adaptation to thermal mitigation, energy conservation, energy consumption, and optimization strategies. Visualization research in the field of OTE helps to provide references for the direction of future research on improving climate change, human thermal comfort, urban planning, and pre-planning.

Coupled thermomechanical analysis using isoparametric curved shell elements

This study focuses on the coupled thermo-mechanical formulation in isoparametric shell elements and its implementation in curved laminar structures. The formulation is based on the direct isoparametric formulation, specifically designed for flat and curved shell elements, and relies on the theory of degenerated solids. The research provides a comprehensive description of the coupled thermo-mechanical analysis, including the mechanical equilibrium equations, the interrelations between stress, temperature, displacement, deformation, and the conservation of thermal energy. It adopts a simultaneous approach to addressing the impacts of temperature and mechanical loads. The paper elaborates on various numerical examples that substantiate the formulation. These examples include simulations that encompass linear scenarios, which are then compared to analytical solutions and results derived from other numerical software. The examples highlighted include one-dimensional temperature diffusion, radial diffusion, and the thermal behavior of a cylindrical cover and a pipe under a linear temperature gradient. These simulations demonstrate the formulation's capacity to accurately capture the interactions between temperature variations and structural displacements. They also confirm the alignment of the proposed model with existing analytical and numerical solutions. In conclusion, the research provides a good framework for coupled thermo-mechanical analysis. The flexibility of the formulation is evidenced across different configurations and scenarios, accommodating various types of boundary conditions such as constant and linear temperature fields, distributed loads, and constraints on displacements and rotations. It effectively manages temperature flows across one, two, and three dimensions, highlighting its extensive applicability in the realm of structural analysis. This versatility underscores its broad applicability in the field of structural analysis.

Study of hybrid nanofluid flow in a stationary cone-disk system with temperature-dependent fluid properties

Cone-disk systems find frequent use such as conical diffusers, medical devices, various rheometric, and viscosimetry applications. In this study, we investigate the three-dimensional flow of a water-based Ag-MgO hybrid nanofluid in a static cone-disk system while considering temperature-dependent fluid properties. How the variable fluid properties affect the dynamics and heat transfer features is studied by Reynolds’s linearized model for variable viscosity and Chiam’s model for variable thermal conductivity. The single-phase nanofluid model is utilized to describe convective heat transfer in hybrid nanofluids, incorporating the experimental data. This model is developed as a coupled system of convective-diffusion equations, encompassing the conservation of momentum and the conservation of thermal energy, in conjunction with an incompressibility condition. A self-similar model is developed by the Lie-group scaling transformations, and the subsequent self-similar equations are then solved numerically. The influence of variable fluid parameters on both swirling and non-swirling flow cases is analyzed. Additionally, the Nusselt number for the disk surface is calculated. It is found that an increase in the temperature-dependent viscosity parameter enhances heat transfer characteristics in the static cone-disk system, while the thermal conductivity parameter has the opposite effect.

Hydrophilicity regulation of carbon nanotubes as phase-change materials for thermal energy storage

Solid-liquid phase-change materials (PCMs) offer exciting prospects for thermal energy conservation, whose performance is greatly affected by the carrier materials. Using expanded vermiculite (EV) as frameworks, carbon nanotube arrays (CNTs) were grown between EV layers by chemical vapor deposition (CVD). Then, the paraffin (PA) was loaded on the EV@CNTs composite by vacuum impregnation to prepare composite PCMs (PA/EV@CNTs), where the PA is organic carrier and the EV@CNTs acts as porous supports with high structural strength. The loading capacity of PA is further regulated by the hydrotropism of CNTs which effectively prevents the leakage of molten PA. The in-situ grown CNTs significantly improves the thermal conductivity of PCMs, improving the efficiency of energy conversion. With maximum PA loading capacity of 95 wt%, the thermal conductivity of PA/EV@CNTs-95% reaching 0.7176 W/mK, which was 1.73 and 2.96 times higher than that of pristine EV and PA. The phase change latent heat of PA/EV@CNTs-95% was measured to be 168.54 J/g, which is 1.48 times higher than that of PA/EV. After 100 cycles, the PA/EV@CNTs still maintains excellent thermal stability, and the enthalpy retention rate is 98.73%. The incorporation of high thermal conductivity amphipathicity CNTs in these PCMs makes them promising candidate for various applications such as energy-efficient buildings, thermal management in electronic devices, and self-cleaning materials.

Ultrathin SiO2 aerogel papers with hierarchical scale enable high-temperature thermal insulation

Aerogel composites reinforced by fibers have found extensive applications in the field of thermal insulation and energy conservation. However, the composites are hindered by their high infrared radiation transmittance and weak interface adhesion in practical applications. Herein, we designed and prepared a novel thin composite called ‘fiber/whisker/aerogel paper’ (SWAP) with a thickness of less than 1 mm. The SWAP integrated SiC nanowhiskers (SiCnw) as opacifiers and ultrafine SiO2 fibers as reinforcement, fabricated through wet manufacturing and sol-gel process. The ‘fiber/aerogel paper’ (SAP) and SWAP exhibited low thermal conductivity at room temperature, measuring 0.025 W/(m·K) and 0.033 W/(m·K), respectively. Additionally, they exhibited low densities of 0.195 g/cm3 and 0.225 g/cm3, respectively. Notably, SWAP exhibited excellent high-temperature insulation performance, primarily due to its low infrared transmittance (50% at 3 μm). The incorporation of SiCnw and ultrafine SiO2 fibers collectively enhanced the interfacial adhesion with the aerogel matrix even amidst rigorous testing (weight loss less than 3%). SWAP also demonstrated flexibility, high thermal stability, hydrophobicity, and flame resistance. Furthermore, a comprehensive investigation into the performance variations and influencing g factors of the material was conducted under different heat treatment conditions. This research provides guidance for the application of such materials under high temperatures.

A Novel Multifunctional Photonic Film for Colored Passive Daytime Radiative Cooling and Energy Harvesting.

Passive daytime radiative cooling (PDRC) materials with sustainable energy harvesting capability is critical to concurrently reduce traditional cooling energy utilized for thermal comfort and transfer natural clean energies into electricity. Herein, a versatile photonic film (Ecoflex@BTO@UAFL) based on a novel fluorescent luminescence color passive radiative cooling with triboelectric and piezoelectric effect is developed by filling the dielectric BaTiO3 (BTO) nanoparticles and ultraviolet absorption fluorescent luminescence (UAFL) powder into the elastic Ecoflex matrix. Test results demonstrate that the Ecoflex@BTO@UAFL photonic film exhibits a maximum passive radiative cooling effect of ∽10.1 °C in the daytime. Meanwhile, its average temperature drop in the daytime is ~4.48 °C, which is 0.91 °C higher than that of the Ecoflex@BTO photonic film (3.56 °C) due to the addition of UAFL material. Owing to the high dielectric constant and piezoelectric effect of BTO nanoparticles, the maximum power density (0.53Wm-2, 1Hz @ 10 N) of the Ecoflex@BTO photonic film-based hybrid nanogenerator is promoted by 70.9% compared to the Ecoflex film-based TENG. This work provides an ingenious strategy for combining PDRC effects with triboelectric and piezoelectric properties, which can spontaneously achieve thermal comfort and energy conservation, offering a new insight into multifunctional energy saving.

Occupant-centric HVAC and window control: A reinforcement learning model for enhancing indoor thermal comfort and energy efficiency

Occupant behavior plays a crucial role in enhancing indoor thermal comfort and achieving energy efficiency by influencing the operational modes of Heating, Ventilation, and Air Conditioning (HVAC) systems as well as windows. However, accurately quantifying the impact of occupant behavior on the indoor environment presents significant challenges in practical applications. This study introduces an innovative approach by leveraging the ASHRAE Global Building Occupant Behavior Database and harnessing the power of XGBoost in conjunction with Deep Q Networks (DQN) to construct a reinforcement learning model. This model enables precise prediction of the impact of occupant behavior on the indoor environment at the next time step under varying indoor-outdoor conditions, simultaneously targeting the dual objectives of indoor thermal comfort and energy conservation. By applying the XGB-DQN model in sample rooms of four international cities with distinct features, the results demonstrate a significant increase in indoor thermal comfort duration by 24 %, accompanied by a 24.7 % decrease in air conditioning usage compared to baseline models and actual occupant data. This research represents a pioneering effort in applying reinforcement learning techniques to accurately predict occupant behavior's impact on indoor environments, offering valuable insights for intelligent building design and energy management.

Balancing thermal comfort and energy efficiency in high-rise public housing in Hong Kong: Insights and recommendations

As global warming intensifies, passive design for public housing in hot and humid climates has become a pressing issue. Achieving a balance between thermal comfort and energy conservation is particularly challenging in low-income public rental housing, where residents may endure extended periods of uncomfortable and unhealthy thermal conditions without resorting to air conditioning. In this study, EnergyPlus simulations are employed in combination with a novel thermal-comfort-based HVAC control approach to evaluate the performance of 14 Passive Cooling Strategies (PCS) in optimizing thermal comfort and energy conservation in high-rise public apartments of various sizes and orientations in Hong Kong, particularly under extreme summer conditions. The results reveal that, during extreme summer weather, the implementation of PCS primarily enhances thermal comfort conditions in May and September, while facing challenges in creating comfortable conditions during peak summer months. Most PCSs struggle to improve indoor comfort while simultaneously reducing energy consumption, with two exceptions: 1) Cross-ventilation-based designs enhance thermal comfort without increasing cooling energy consumption. 2) With energy-saving HVAC and opening control behavior, coupled with the use of fans for improving indoor thermal comfort, all PCSs can achieve a simultaneous improvement in thermal comfort and a reduction in cooling energy consumption. This results in a reduction in summer air-conditioning operation time of up to 50% and a decrease in air-conditioning cooling energy consumption of up to 30%. Regarding the impact of building size and orientation: 1) Small apartments show a heightened sensitivity to PCSs, particularly concerning indoor temperature, thermal comfort, and cooling energy consumption. 2) The influence of building orientation on cooling and comfort time in any PCS varies by less than 10% of its average and is even lower in PCSs with lower internal heat gain.

Multistage smart radiator with gradient emittance based on phase change materials VO2/GST/IST

In this Letter, we present a multistage smart radiator with a gradient emittance that gradually increases with increasing temperature in the spectral range of 2.5–15 μm. Such smart radiator is a relatively simple multilayered structure composed of three phase change materials (PCMs): VO2, GST, and IST. The smart radiator achieves multistage manipulation of emittance through phase transitions of PCMs, with the largest emittance tunability of ∼0.85. The underlying mechanism involves manipulating the Fabry–Pérot resonance and antireflection. Additionally, the emittance is found to be relatively insensitive to polarization and incident angles. The proposed multistage smart radiator exposes excellent potential for exploitation in thermal management and energy conservation.