Thermal Energy Utilization Efficiency Research Articles

Thermal energy resource utilization and sample image restoration technology based on Machine vision simulation in interior design

With the rise of sustainable building design, the traditional design methods are often unable to fully consider the optimal allocation and application of thermal energy resources. This study aims to explore the application of heat resource utilization and sample image restoration technology based on machine vision simulation technology in interior design, and provide practical solutions for optimizing indoor environment. In this paper, machine vision technology is used to monitor and model indoor space in real time, and heat energy flow and distribution under different design schemes are simulated. At the same time, the influence of different designs on thermal energy utilization efficiency is analyzed by using sample image restoration technology. In the study, a set of comprehensive evaluation indexes was established, which comprehensively considered the factors of heat efficiency, indoor comfort and energy consumption. The experimental results show that the simulation technology based on machine vision can accurately predict the indoor heat distribution and identify the best design scheme. At the same time, the sample image restoration technology significantly improves the evaluation accuracy of heat utilization efficiency. Through these methods, the optimized design scheme has higher thermal energy utilization than the traditional design, and significantly improves the indoor comfort. This study shows that the combination of machine vision simulation and sample image restoration technology can effectively improve the utilization efficiency of thermal energy resources in interior design, and provide new ideas and methods for sustainable building design.

Simulation of low energy building thermal energy cycle in IoT smart city planning based on environmental sensors and deep learning

With the intensification of global climate change, the reduction of building energy consumption has become an important goal of smart city development. By optimizing the thermal energy circulation system, low energy buildings can not only reduce energy consumption, but also improve living comfort. In recent years, with the help of environmental sensors and deep learning technology, the intelligent management of building heat energy cycle has become a research hotspot. The research constructs an intelligent thermal energy circulation system that integrates multiple environmental sensors for real-time monitoring of indoor and outdoor temperature, humidity and other key environmental parameters. A deep learning algorithm is used to analyze the collected data to optimize the control strategy of the thermal energy cycle. Through simulation, the energy efficiency performance of the scheme under different climatic conditions and building types was evaluated. The experimental results show that the control strategy based on environmental sensors and deep learning can significantly improve the thermal energy utilization efficiency of low-energy buildings, and the average energy consumption is greatly reduced compared with the traditional management mode. The system shows good adaptability and stability under different climate conditions. Therefore, the application of environmental sensors and deep learning technology in the thermal energy cycle of low-energy buildings can effectively promote the energy efficiency management of smart cities.

Enhancing the waste heat utilization of industrial park: A heat pump-centric network integration approach for multiple heat sources and users

The industrial sector, which is characterized by high energy consumption, primarily using fossil fuels, exhibits significant carbon emissions and severe pollution. Industrial parks generate abundant waste heat with varying flow rates and multiple grades, and also include industrial users with diverse heat demand profiles. Waste heat recovery is an effective method for reducing fossil fuel consumption. However, the current waste heat recovery methods focus on single-heat-source scenarios, making them unsuitable for use in industrial parks with multiple heat sources and heating loads. To achieve efficient matching between different sources and loads, this study developed a heat-pump-centric network system and establishes a two-stage optimization method for networked waste heat utilization. First, based on matrix algebra, a method for matching the generated waste heat with heat pump combinations and heat users was developed to obtain a networked heating path. Second, an optimization model for heat pump combinations was established, and linear integer programming algorithms were employed to obtain the optimal configuration and operational plan for the heating path. Finally, energy flow analysis was conducted to elucidate the optimal energy distribution. The results show that, compared to traditional heating modes, the proposed method achieved a 55 % reduction in energy consumption with a payback period of 4.6 years. The proposed system could enhance the matching between different grades of waste heat and heating demand, thereby improving the thermal energy utilization efficiency. The proposed method demonstrates significant energy saving with efficient utilization and economic benefits and can be applied to different scenarios with multiple sources and loads.

Low-pressure steam dropwise condensation on durable PFA-coated horizontal tube: Droplet dynamics in active region

The performance of low-pressure steam condensers is vital to the thermal energy utilization efficiency of the power cycle, refrigeration, heat pump, and seawater desalination systems. Dropwise condensation demonstrates better heat transfer performance than traditional filmwise condensation, and its performance is determined by the condensate droplet dynamic behaviors on hydrophobic surfaces. However, the droplet dynamics behavior on the horizontal tube has not been adequately investigated. In this study, a durable PFA-coated copper tube is achieved to sustain stable dropwise condensation at the vapor pressure ranging from 5 to 100 kPa. By optical observation of condensation on the horizontally oriented tube, the droplet dynamic characteristics and the influence of vapor pressure on the droplet dynamics are examined. We show that an ‘active droplet region’ (ADR), which is characterized by frequent droplet shedding and surface renewal promoting more active nucleation, growth, and departure of droplets, exists along the tube circumference. As a result of the varying droplet dynamics, a skew-normal distribution of sliding droplet numbers presents along the tube circumference. The droplets departing within ADR account for 80% of the total departure droplets. Then, the effect of steam pressure on the droplet dynamics behavior in ADR is studied systematically. The average sweeping frequency of droplets under steam pressure of 100 kPa increases by -122% more than that under steam pressure of 5 kPa. The growth rate of droplets and migration speed improve with steam pressure. Thus, the evolution rate of the transient size distribution becomes rapid as the vapor pressure increases. Taking vapor pressure and circumferential angle into consideration, a semi-empirical model for the prediction of condensate droplet departure radius on a horizontal tube is proposed, of which the standard deviation can be reduced to less than 15%. These findings and insights into droplet dynamic behaviors on PFA-coated hydrophobic horizontal tube are of great significance for the novel surface design strategy for the enhancement of dropwise condensation heat transfer.

Bayesian-optimized infrared grating for tailoring thermal emission to boost thermophotovoltaic performance

Thermophotovoltaic (TPV) devices, which can break the Shockley–Queisser limit (33.7%) and enhance the thermal energy utilization efficiency, have garnered increasing attention in recent decades. Structuring the emitter surface has been demonstrated to be powerful for tailoring thermal emission to enhance the power density and system efficiency of a TPV system. However, the design and optimization of the broad parameters of the surface nanostructures manually remain to be thorny issues. In this paper, the Bayesian algorithm under the framework of material informatics was coupled with a rigorous coupled wave analysis to optimize the geometry of the infrared grating nanostructure to achieve wavelength-selective emission to boost the TPV performance. It is demonstrated that only less than 0.173% of the total candidate structures were calculated to find out the optimal structure with high spectral emittance in the range of 0.3–1.708 μm, and the power density and system efficiency of the TPV system were enhanced to 4.20 W/cm2 and 35.37%, respectively. The present machine-learning-based optimization of a multi-parameter nanostructure can improve the performance of the TPV system significantly and can be extended to other physical fields in a feasible manner.

Experimental and numerical investigation on heat transfer enhancement of vertical triplex tube heat exchanger with fractal fins for latent thermal energy storage

Latent thermal energy storage (LTES) technology applied in the recovery of industrial waste heat, solar thermal applications, and energy conversation of buildings, etc. can solve the mismatches of thermal energy in supply and demand, space and time, and thus increasing the efficiency of thermal energy utilization. However, the heat transfer process in a latent heat exchanger(LHE) is limited due to the poor thermal conductivity of phase change material (PCM). Therefore, a vertical triple tube heat exchanger with fractal fins was applied to enhance the heat transfer process of the LTES system. The performance of the LHE with fractal fins was discussed and compared to that with traditional rectangular fins. The results manifest that fractal fins can effectively improve the heat transfer rate of the LHE by providing more heat flow channels and heat transfer areas. The total melting time of PCM in the LHE with fractal fins is reduced by 27.3% compared to that with rectangular fins during the heat charging process. Furthermore, the structure of fractal fin is optimized through a heat transfer model and numerical simulation. It was apparent from the simulation results that the PCM melting time of the LHE with optimized fractal fins is reduced by 35.6% compared with that of rectangular fins. It was also proved that the dual-channel structure is used to reasonably arrange the charging and discharging processes, which can make the LTES system achieve better results.

Benzaldehyde decorated octadecylamine for tailor-made molecular firefighting and efficient thermal energy management

• Benzaldehyde decorated octadecylamine for tailor-made thermal management. • Self-crosslinking of aromatic Schiff base for molecular firefighting. • Extensively reversible thermal transformation in a wide range of 30–100 °C. • Open a window for designing multifunctional phase change materials. More than 40% of the energy generated globally is consumed by residential and commercial buildings, so energy efficient materials for buildings are urgently needed at present. On-demand thermal energy storage/release using phase change materials (PCMs) can improve thermal energy utilization efficiency, however, they are facing low adaptability to temperature and easy flammability in the case of fulfilling high thermal management capacity. Herein, we report octadecylamine-based PCMs with tailor-made molecular firefighting and thermal energy management capability. These synthesized octadecylamine-based Schiff base-containing PCMs (SB-PCMs) may self-extinguish while encountering short-time fire and possess variable phase transition temperatures of 33, 42, 92, and 101 °C. Meanwhile, these SB-PCMs own high phase transition enthalpies of 161.4–183.4 J g −1 and excellent cyclic stability. When SB-PCMs as thermal energy management materials in wood plastic-based building materials, they show high adaptability to ambient temperature and excellent thermal management capability, achieving temperature regulation of 9.0 °C. Meanwhile, fire safety of the composite wood plastic materials is significantly improved. Detailed analysis confirms that the incorporated benzaldehyde with various positional substituted hydroxyl may induce noncovalent interactions (mainly hydrogen bond and π-π stacking) of SB-PCMs and further control their self-assembling processes, thus achieving multiple thermal responses of SB-PCMs; self-crosslinking charring of benzaldehyde-based Schiff base structure may retard fire spreading, therefore presenting molecular firefighting. Additional multistage thermochromic behaviors of SB-PCMs may extend their application in temperature-sensitive paint, intelligent fabric, etc. This work firstly represents a method for manipulating the multistage thermal and fire responses of PCM in the case of fulfilling high thermal energy management capacity and confirms its molecular-firefighting and energy efficient application in building materials.

Non-contact thermal transistor effects modulated by nanoscale mechanical deformation

Thermal management has become a promising field in recent years due to the limitation of energy resources and the global warming. An important topic in improving the efficiency of thermal energy utilization is how to control the flows of heat, and thermal rectifiers, such as the thermal transistor, have been proposed as units for modulating the flow of heat. In this work, a reconfigurable non-contact thermal transistor with two-dimensional grating is introduced. The thermal transistor consists of three parts: source, gate, and drain, with the gate working around the phase-transition temperature of vanadium dioxide, a type of phase-transition material. Results show that the unit has a clear transistor-like behavior. The surface phonon/plasmon polaritons supported by the insulating/metallic states that contribute to the radiative thermal transport can be modulated at a nanoscale separation. And the dynamic amplification factor varies from 12.8 to 26.7 when the stretchable polydimethylsiloxane is subjected to tension or compression. This work sheds light on studies about the controllable small-scale thermal transport due to mechanical deformations.

A comprehensive parametric, energy and exergy analysis of a novel physical energy storage system based on carbon dioxide Brayton cycle, low-temperature thermal storage, and cold energy storage

Low-temperature energy storage system is an important development direction of physical energy storage technology, which can avoid the technical difficulties caused by high-temperature conditions. In this paper, a novel physical energy storage system based on carbon dioxide Brayton cycle, low-temperature thermal storage, and cold energy storage was proposed. Water was chosen as the working medium for thermal storage, and ice slurry was chosen as the working medium for cold energy storage. The working processes of this low-temperature carbon dioxide energy storage system were introduced in detail and the corresponding thermodynamic model was established. In addition to the evaluation based on power efficiency and exergy efficiency, thermal energy utilization efficiency and cold energy utilization efficiency were defined to assess the feasibility of the independent operation of the system. Parametric analysis was carried out to analyze the effects of several important parameters on system performance. The results showed that, for the system under the basic working condition, power efficiency was 55.7%, exergy efficiency was 52.87%, thermal energy utilization efficiency was 83.3% and cold energy utilization efficiency was 89.5%. The total exergy destruction was 48.07 kW and the largest exergy destruction came from the compressor. According to the sensitivity analysis, in turbomachinery, turbine efficiency had the greatest influence on power efficiency as well as exergy efficiency, and when turbine efficiency increased by 1%, both power efficiency and exergy efficiency increased by 0.634%. There was an optimum for pressure ratio to get the maximum values of power efficiency and exergy efficiency, and the optimum was 6.5. The decrease of the pressure drop in heat exchangers could increase power efficiency and exergy efficiency whereas the decrease of minimum temperature difference in heat exchangers could increase the four efficiencies. Measured in terms of the degree of influence, heat exchanger3 had the greatest influence and should be paid more attention. As to the cooling medium, the increase of the inlet temperature of water could increase power efficiency and exergy efficiency. Besides, there was an optimum for the mass flow rate of water to maximize power efficiency and exergy efficiency. Finally, it should be noted that, to ensure that the storage of cold energy during the charge process could meet the demand of cold energy during the discharge process, all the parameters studied needed to be carefully set. Relevant research provided important guidance for understanding the thermodynamic performance of the low-temperature energy storage system with carbon dioxide as the working fluid.

Operation Optimization of Multi-District Integrated Energy System Considering Flexible Demand Response of Electric and Thermal Loads

Multi-district integrated energy system (IES) can make full use of the complementary characteristics of district power and thermal system, and loads in different districts. It can improve the flexibility and economy of system operation, which has a good development prospect. Firstly, based on the general energy transfer model of the district heating network (DHN), the DHN system is described by the basic equations of the heating network and nodes considering the characteristics of the transmission time delay and heat loss in pipelines. A coupling model of DHN and multi-district IES is established. Secondly, the flexible demand response (FDR) model of electric and thermal loads is established. The load characteristics of each district in IES are studied. A shiftable load model based on the electric quantity balance is constructed. Considering the flexibility of the heat demand, a thermal load adjustment model based on the comfort constraint is constructed to make the thermal load elastic and controllable in time and space. Finally, a mixed integer linear programming (MILP) model for operation optimization of multi-district IES with the DHN considering the FDR of electric and thermal loads is established based on the supply and demand sides. The result shows that the proposed model makes full use of the complementary characteristics of electric and thermal loads in different districts. It realizes the coordinated distribution of thermal energy among different districts and improves the efficiency of thermal energy utilization through the DHN. FDR effectively reduces the peak-valley difference of loads. It further reduces the total operating cost by the coordinated operation of the DHN and multi-district IES.

Facile assembly of cellulose-derived 3D-graphene/lithium hydroxide monohydrate nanocomposite for low-temperature chemical heat storage

Commonly used nanocarbon composite materials are routinely synthesized from petroleum-based resources. To avoid their bad impact on the environment, using cellulose-based materials as the promising resources is a better choice due to its easy acquisition and rich reserves. In this study, microcrystalline cellulose was selected as the carbon precursor to synthesize novel cellulose-derived 3D-graphene/LiOH·H2O nanomaterials for chemical heat storage to improve the efficiency of thermal energy utilization. The characterization and performance test results show that LiOH·H2O particles (5–20 nm) were highly dispersed on the 3D graphene carbon skeleton. These materials had excellent heat storage densities and thermal conductivities due to a completely new, hydrophilic, nano-reactive interface on 3D graphene. Among the materials, 3D-GF-VC-LiOH·H2O (Ascorbic acid-modified 3D-graphene/LiOH·H2O) exhibited the best heat storage and thermal conductivity properties. It achieved a thermal conductivity of 2.6 W/m K, which was 1.5 times that obtained with pure LiOH·H2O, and its heat storage density (2157 kJ/kg) was 3.3 times that of pure LiOH·H2O (661 kJ/kg). The activation energy could decrease to 27.5 kJ/mol. Moreover, the heat storage temperature range of LiOH·H2O was clearly expanded by introduction of 3D graphene. Hence, the addition of cellulose-derived 3D graphene is a very efficient means by which the design of chemical heat storage materials can be improved.

Integrated Aircraft Thermal Management System Modelling and Simulated Analysis

In order to improve the thermal energy utilization efficiency of aircraft, an integrated thermal management system model using endothermic fuel has been created in AMESIM. The system includes several thermal subsystems such as environment control system, the hydraulic equipment and power equipment cooling system, and anti-icing/de-icing system. The fuel oil was chosen for heat sink and it could cool the exothermic thermal system and transmit the energy to anti-icing/de-icing system in case of icing. Several simulation examples including three atmospheric conditions were accomplished. The results indicated that the present system had the ability to reuse the waste heat meanwhile all the thermal system worked normally. The anti-icing/de-icing didn’t need additional energy which realized less energy consumption. In addition, the model has the ability to facilitate the analysis and optimization of thermal systems on board.

Effect of foliar application of boron and tiba on crop phenology and solar energy utilization efficiency of spring sunflower under staggered sowing

Sunflower (Helianthus annuus L.) is a thermo-and photo-insensitive crop but environmental, nutritional and hormonal factors can cause variation in phasic development and energy utilization efficiency of crop. A study was conducted to investiagate crop phenology and thermal energy utilization efficiency of spring sunflower in relation to foliar application of boron and TIBA under staggered sowing (20 January, 10 February and 2 March). Early sown crop took significantly more number of days to attain all phenological stages. Foliar application of boron and TIBA increased the number of days to attain flowering and subsequent stages. The thermal units required to attain various phenological stages increased progressively due to delay in sowing but accumulated growing degree days for physiological maturity decreased with delay in sowing. Boron and TIBA treatments recorded markedly higher thermal units accumulation as compared to control for physiological maturity. Phenothermal index gradually increased from star bud to physiological maturity under all treatments. Late sown crop exhibited higher heat use efficiency at 30 DAS, but at 90 DAS and at harvest foliar application of boron and TIBA improved heat use efficiency of the crop.

A novel thermally driven pump and its test in a supercritical CO2loop system

SUMMARY In this paper, a novel thermally driven pump is introduced, and its test in a closed supercritical CO2 loop cycle system is studied. The thermally driven pump is a refrigerant-circulating pump composed of two expansion tanks, which has less electricity consumption and better reliability compared with conventional mechanical pumps. Experimental results showed that the system efficiency of the present thermally driven pump in the supercritical CO2 loop can be enhanced compared with that using the mechanical feed pump. In addition, it was found that the system efficiency with the thermally driven pump decreases with the outlet temperature of condenser. The thermal energy utilization efficiency of the loop system with the thermally driven pump can be increased when the condenser has higher efficiency. Copyright © 2012 John Wiley & Sons, Ltd.

Evaluation of biomass and thermal energy utilization efficiency of oilseed Brassica (Brassica juncea) under altered microenvironments

Abstract Changes in within-canopy microenvironments may significantly influence the physiological response pattern of the crop eventually influencing biomass, seed yield and their heat utilization behavior. Therefore, energy use efficiency in oilseed crop Brassica juncea was evaluated to have better understanding of impact of microenvironments on plant characteristics. Linear and non-linear regression analysis showed significant and positive response of Brassica towards time variable leaf area index (LAI), dry biomass accumulation and their heat utilization efficiencies. Linear and third order polynomial regression models indicated 81 and 94% variation in LAI and dry biomass production respectively as a function of time (t) while about 85–93% variation in thermal energy use efficiency (THUE) was observed which might be due to differential thermal heat accumulation at its various phenological stages. Its quantification was done with second order regression equations using accumulated thermal heat (TI) (R 2 = 0.93∗∗) and solar energy (PTI) (R 2 = 0.85∗∗). THUE was predicted as 0.1616 × LAI - 0.0294; R 2 = 0.74∗∗ using TI and 0.0179 × LAI - 0.0044; R 2 = 0.75∗∗ using PTI and 0.0378 + 0.0012 × (DM) -3E-07 × (DM) 2 ; R 2 = 0.97∗∗ using TI and 0.0042 + 0.0001 × (DM)−3E-08 × (DM) 2 ; R 2 = 0.96∗∗ using PTI. The significant changes in seed yield heat use efficiency of the order 80–87% were attributed to differential thermal energy utilization capacities. We conclude that the prediction models developed from this study could be used in predicting energy use efficiency in other related species of oilseed Brassica .

THE EFFECTS of GAS INJECTION ON the EFFICIENCY of THERMAL ENERGY UTILIZATION IN SPRAY DRYING1

ABSTRACTFactorial experimental designs were used to study the effects of gas injection on the efficiency of thermal energy utilization in evaporation by spray drying. Both the main effect and the interactions of this variable with feed pressure, feed concentration, nozzle size, and drying temperature were investigated. the use of gas injection led to a decrease in the thermal energy required for evaporation. the magnitude of this effect was larger at the lower levels of feed pressure, feed concentration, and drying temperature. However, this does not imply that spray drying is more energy efficient than such alternative modes of water removal as multi‐effect evaporation and reverse osmosis.