Heat Recovery Performance Research Articles

Study on optimization of thermal injection parameters in fractured reservoirs of HDR

ABSTRACT To improve the heat recovery of hot dry rock (HDR) and realize the efficient and sustainable development of geothermal energy, it is necessary to analyse the factors affecting the heat recovery performance of HDR fractured reservoir. In this paper, a numerical model of heat recovery in fractured reservoirs with HDR is established. The effects of injection parameters on the heat recovery performance of the Enhanced Geothermal System (EGS) are compared and analysed by means of the average temperature, heat extraction rate, production temperature and heat recovery power of matrix rocks at different locations. The influence degree of injection flow rate and injection temperature on production temperature was analysed by grey correlation analysis method. The results showed that reducing the injection temperature is beneficial to fully extract the heat energy in the rock mass. The injection flow rate is positively correlated with the heat extraction rate and negatively correlated with the extraction temperature. In this simulation scheme, the optimal results are as follows: injection temperature is 298.15K, injection flow is 12 kg/s, and the influence of injection flow on production temperature is greater than that of injection temperature. This study provides a theoretical basis for the development and utilization of geothermal energy in HDR and provides a reference for the design of engineering operation parameters.

Self-assembled nanoflower-mediated interfacial polymerization through tunable intra- and inter-layer channels to boost total heat exchange performance

Total heat exchange membranes (THEMs) are vital for minimizing energy consumption and enhancing indoor air quality in energy recovery ventilation (ERV) systems. Manipulating the surface morphology of polyamide (PA) membranes via nanofiller-mediated interfacial polymerization is key to advancing total heat recovery performance. This study presented the fabrication of PA thin-film nanocomposite (TFN) membranes by integrating self-assembled poly(amic acid-imide) nanoflowers (P(AA-I)-NFs) with intertwined nanosheets into the organic phase. This facile approach effectively eliminated nonselective interphase voids and defects, owing to the superior polymer affinity of the organic nanoflowers. The finely tuned intra- and inter-layer channels within P(AA-I)-NFs significantly impacted monomer mass transfer, facilitated the shuttle effect, expanded the interfacial polymerization zone, and led to the formation of a rougher, thicker PA layer with enhanced surface area. The optimized P(AA-I)-NFs/PA TFN membranes exhibited outstanding performance, including CO₂ permeability of 0.51 GPU, water vapor permeability of 656.59 GPU, and an enthalpy exchange efficiency of 71.47 %, surpassing the trade-off limitations typically observed in commercial and other advanced THEMs. These findings underscored the potential of P(AA-I)-NFs-mediated TFN membranes as highly competitive candidates for next-generation ERV systems.

Mixed matrix membrane-based transport membrane condenser for improving the waste heat recovery performance in carbon capture process

Applying a transport membrane condenser (TMC) based on the hydrophilic ceramic membrane to recover the waste heat from the hot stripped gas could effectively reduce the heat consumption of CO2 regeneration in the carbon capture process. However, the high cost of ceramic membrane hindered the development of this technology. So in this study, a novel mixed matrix membrane (MMM) was proposed to replace the conventional ceramic membrane. MMMs were prepared by mixing carbon nanotube (CNT) into polyvinylidene fluoride (PVDF) casting solution through non-solvent phase separation method, and then were adopted for the waste heat recovery from the stripped gas featured with the molar ratio of CO2 to H2O(g) of 1:1∼1:2. Furthermore, the heat transfer resistance between the stripped gas and bypassed CO2-rich solvent when adopting MMMs was also analyzed through computational fluid dynamics (CFD). Results indicated that the addition of CNT or hydroxylated CNT (CNT-OH) effectively enhanced the heat recovery performance of MMMs. Moreover, MMMs prepared by mixing CNT-OH and hydroxylated boron nitride (BN–OH) further boosted the heat flux, achieving a maximum value of 23.72 MJ/(m2·h), representing an increase of up to 8.41 % compared to the original PVDF membrane without adding any additives. At the experimental conditions in this study, the gas-side individual thermal resistance dominated the overall thermal resistance and consequently the heat transfer performance. With an increase in the stripped gas flow rate, the ratio of individual heat transfer resistance of membrane to the overall resistance increased. Notably, the installation of baffles on the gas side of TMC reduced the gas-side thermal resistance. In this study, the optimum thermal conductivity of the organic membrane increased with the waste heat recovery scale from stripped gas. In addition, when the thermal conductivity of membrane exceeded 4 W/(m·°C), the increase in thermal conductivity on the waste heat recovery was not significant. This study confirmed the application potential of MMMs in the waste heat recovery.

Waste heat recovery in carbon capture process using a novel amphipathic inorganic membrane

To reduce the CO2 regeneration heat requirement in the CO2 chemical absorption process, a novel amphipathic ceramic membrane-based transport membrane condenser was developed in this study to act as a heat transfer medium in the rich solvent-split mechanism for enhancing the waste heat recovery performance from the stripped gas (i.e., mainly the gas mixture of CO2 and water vapor). Both hydrophobic and hydrophilic segments coexisted on one membrane surface of amphipathic ceramic membrane, while the other surface was totally hydrophilic. The surface characterization and waste heat recovery performance of the flat sheet amphipathic membrane were investigated, and the original hydrophilic ceramic membrane was adopted as the control. Results showed that the water contact angle with 108.9 ± 4° was screened for the hydrophobic surface of the ceramic membrane to achieve the best waste heat recovery performance. Additionally, the waste heat recovery performance of amphipathic membrane firstly increased and then dropped with an increase in the area ratio of hydrophobic surface to the total membrane surface. The maximum waste heat recovery of 13.39 MJ/(m2·h) was achieved at a hydrophobic area ratio of 37.5 % without segmenting by the hydrophilic surface, which was 5.6 % higher than that of the original hydrophilic ceramic membrane. Furthermore, the maximum water recovery of amphipathic membrane was 8.24 % higher than the original hydrophilic ceramic membrane. When the total area of hydrophobic surface was fixed, dividing the hydrophobic surface into two equally sized hydrophobic segments spaced by the hydrophilic segments could further improve the waste heat recovery performance of amphipathic membrane. This study might provide a new insight on improving the waste heat recovery performance of ceramic membrane.

A novel thermal management system for a cylindrical battery based on tubular thermoelectric generator

This study introduces an innovative thermal management system tailored for cylindrical Lithium-ion batteries. It integrates a tubular thermoelectric generator (TTEG) to handle both battery thermal management and the utilization of waste heat for power generation. The main focus lies in evaluating the waste heat recovery capabilities of the TTEG to enhance effective thermal management. The research investigates key geometric and operational parameters such as battery discharge rate (C-rate), thermocouple count (NTC), heat transfer coefficient (HTC), and thermoelectric leg height (HL) to comprehensively assess the overall system performance. The results highlight that integrating the TTEG improves thermal management and waste heat recovery in lithium-ion batteries. It demonstrates temperature reductions of up to 21 °C at a discharge rate of 3C compared to batteries without the TTEG thermal management system. Additionally, increasing the NTC leads to a rise in the maximum battery temperature, thereby enhancing waste heat recovery performance. For instance, increasing the number of thermocouples from 100 to 144 results in a substantial up to 70 % increase in TTEG voltage.Furthermore, enhancing HTC and HL positively impacts thermal performance, showing a significant decrease in the maximum battery temperature. Elevated HTC and HL also contribute to improving thermoelectric voltage, power, and conversion efficiency, highlighting their dual role in enhancing waste heat recovery. For instance, at peak conditions, there is a notable reduction of 2.66 °C in the maximum battery temperature with an HL of 12 mm compared to 4 mm. Additionally, increasing HTC from 10 to 20, particularly at maximum discharge, leads to a surge of 15.87 % in voltage and a substantial 34.28 % increase in output power.

Energy efficiency analysis of novel combined open absorption multifunctional heat pump and FlashME desalination system with a compressed air dryer

Energy intensive thermal desalination and compressed air-drying processes coupled with low grade heat recovery units can significantly contribute to carbon and energy footprint reduction. In this paper, a novel combined system based on an open absorption multifunctional heat pump and FlashME desalination system with a compressed air dryer is proposed to recover the latent heat from flue gas and efficiently utilize it to drive the desalination process for seawater treatment and supply the compressed dry air. The energy performance of the combined system is analyzed under the effect of various key operational parameters by simulating the validated process model. The results of energy analysis indicate that the novel system can recover the latent waste heat from flue gas with an efficiency of 83.02 % and supply the compressed dry air at low humidity of 1.41 g/kg by operating at a thermal COP of 1.95. Furthermore, the system can efficiently utilize the recovered low-grade heat to produce freshwater at a recovery rate of 23.14 %. The findings of the critical performance analysis show that the drying, and latent heat recovery performance of the coupled system is dependent mainly on the inlet parameters of the spray solution and the flue gas humidity. However, the water recovery of FlashME is totally dependent on heat capacity and the regeneration pressure such that the performance ratio increases from 1.51 to 4.03 by operating with hot seawater of 60–80 °C, when the regeneration pressure is raised up to 53.48 kPa. Moreover, the coupled system configured in parallel double stage can lower 11.43–37.78 % regeneration load along with 54.24 % improvement in distillate productivity when the operating pressure is raised up to 800 kPa and the rise in airflow rate in dryer can decrease the 10.41–52.45 % regeneration load on external heat source.

An empirical study on thermal efficiency and dusty moisture removal efficiency using enthalpy wheel in industrial waste incineration plant

In this work, an empirical study is conducted on the waste heat recovery and moisture removal performance of an enthalpy wheel installed in an industrial waste incineration plant. The enthalpy wheel made of a metal mesh is placed in parallel with the wet scrubber of the incineration plant to exchange heat with high-temperature exhaust at 200 °C. In the enthalpy wheel, exhaust gas and external air exchange heat in the form of a counter flow, and the condensation effect is maximized by installing a water-spray nozzle at the inlet of the enthalpy wheel. Empirical data were collected over 100 days spanning July to October. To evaluate the performance of the enthalpy wheel, thermal efficiency, moisture removal efficiency, and dust removal efficiency were tested under high-temperature humid conditions. In some results, the overall thermal efficiency reached peaked at 61.2 %. Regarding moisture removal performance, the average moisture removal rate was 493 kg/h, affording an efficiency of 49.2 %. In terms of dust removal performance, the average dust removal efficiency was 79.6 %.

Efficient and economic water and heat recovery from flue gas by novel hydrophilic polymeric membrane condenser

The membrane technology for water and heat recovery from flue gas possesses the advantages of a simple structure and high water quality. In this study, we propose a novel hydrophilic polymeric membrane condenser (HPMC) to efficiently recover water and heat from flue gas. Compared to current hydrophilic ceramic membrane condenser (HCMC), HPMC offers the benefits of cost-effectiveness and high packing density. An experimental investigation is conducted to explore the fluid flow characteristics as well as the water and heat recovery performance of HPMC. The maximum recovered water flux reaches 6.7 kg/(m2·h), while the maximum recovered heat flux amounts to 18.6 MJ/(m2·h). Enhancing gas/water flow rates or increasing heat transfer temperature difference can significantly improve both recovered water and heat fluxes. Notably, it is found that thermal resistance primarily stems from the polymeric membrane, emphasizing the importance of enhancing the membrane's thermal conductivity to improve HPMC performance. The overall heat transfer coefficient can be enhanced by increasing the gas/water flow rate, while the influence of gas/water temperature on the overall heat transfer coefficient is relatively insignificant. Furthermore, by fitting experimental data, a correlation formula for friction factor is obtained, which greatly enhances accuracy in pressure drop calculations under practical operating conditions. Based on the technical and economic analysis, the payback period for HPMC is merely 0.3 years, significantly shorter than that for HCMC, thereby indicating a substantial potential for commercial application of HPMC. This study demonstrates that the HPMC is an excellent candidate for recovering water and heat from flue gas, and the fundamental data provides valuable foundational insights for future enhancement of HPMC.

Design and performance analysis on a breathing-type instant heat recovery module for fresh air ventilation

The process of air exchange in buildings is essential for maintaining optimal indoor air quality. However, this process results in the loss of thermal energy in the form of sensible heat carried by the air, thereby increasing the energy demand of the buildings. In order to recover this thermal energy, the present study introduces a breathing-type instant heat recovery module for fresh air ventilation, inspired by the biological nasal breathing process. The performance of this module was thoroughly investigated through Fluent simulation and experimental tests. Based on the simulation results, the module exhibits the capability to decrease the outdoor air temperature by an average of 7.5 ℃ prior to its entry into the room. Consequently, this leads to a daily energy conservation of approximately 2.354 kW·h, accompanied by an energy recovery rate of 62.9 % under typical summer conditions. Notably, the heat recovery performance is more favorable during winter, resulting in daily energy savings of about 5.446 kW·h and an energy recovery rate of 62.2 %. The conducted experiments substantiate that the module is able to recuperate approximately 70 % of heat when the indoor temperature is set at 22 °C, while the outdoor temperature reaches its lowest point at 6 °C. The study describes an effective heat recovery technology for building air exchange using a breath-type instant heat recovery module. This could offer a new energy-saving solution for the renovation of fresh air systems.

The effects of fractures on porous flow and heat transfer in a reservoir of a U-shaped closed geothermal system

In geothermal reservoirs, fractures, serving as preferential channels for heat transfer fluid circulation, can cause complicated migration patterns and heat transfer characteristics of the fluids. However, the crucial issue of whether and how fractures within a hydrothermal reservoir of a closed geothermal system (CGS) affect reservoir heat transfer fluid migration and the system’s heat transfer is still poorly understood. In this study, we construct a thermo-hydraulic coupling finite-element model to investigate the effects of fractures on fluid flow and heat transfer enhanced by natural convection in a U-shaped closed geothermal system (UCGS) with a horizontal well. We systematically analyze the responses of fluid migration and heat extraction in the system to key factors, such as fracture aperture, fracture azimuth, fracture distribution, and reservoir permeability. The results show that, in a high permeability reservoir (such as 2 × 10−13 m2), the fracture with an aperture of a millimeter scale can greatly strengthen and control the natural convection induced by heat transfer around the horizontal well in a UCGS, achieving a heat recovery efficiency of six times higher than conduction alone within the reservoir. The fracture azimuth can control the heat production region by guiding the evolution of natural convection. Intersecting network-distributed fractures can effectively improve heat recovery area and performance (more than 15%) compared to a single fracture. Some specific fracture segments within a fracture network may exhibit synergy or inhibition in different heat extraction stages, while a fracture connecting in the deep reservoir and orienting to the horizontal well may lead to heat breakthrough. In addition, a low-permeability interlayer below the horizontal well can restrict the heat recovery (nearly 20% drop in our models), but a fracture penetrating the layer can compensate for this hindrance. The findings of this study can contribute to understanding the thermodynamic mechanisms of fluid flow and heat transfer in a fractured reservoir, and then utilizing them to maximize heat recovery rather than considering conduction only, thus providing scientific insights into engineering practices of the UCGS.

Comprehensive heat extraction performance and fractured reservoir cooling effect analysis of a novel mine enhanced geothermal system

Mining deep metal mines poses significant challenges due to the high-temperature conditions in such environments. However, the vast untapped geothermal energy within these mines holds great prospects for development and application. Herein, we proposed a novel technology for the deep mine cooling and enhanced geothermal system (DMC-EGS), which transforms the relationship between deep mining and geothermal resources from a source of heat harm to heat benefit, while also providing conditions for underground mining environment cooling. Understanding the fluid flow and heat transfer processes in the deep mine thermal reservoir is crucial for developing DMC-EGS. Based on the local thermal equilibrium theory, a three-dimensional thermal–hydraulic coupled model of the thermal reservoir in the Sanshan Island Mine containing multiple fractures was established. The impact of natural fractures and fracture number on the thermal recovery performance and cooling effect of the system was considered, and the optimization scheme of heat recovery wellbore was proposed for the deep thermal reservoir of Sanshan Island Mine. It can be found that fractures play a crucial role in fluid-rock heat exchange. Compared with scenarios without fractures, hydraulic fractures could significantly improve the heat transfer capacity and rock cooling effect, resulting in a 45.7% increase in the amplitude of rock matrix temperature decrease and more than a 1.76-fold increase in overall heat recovery efficiency. In addition, the number of fractures significantly impacted the temperature distribution within the rock formation, and an increased number of fractures was associated with more efficient heat recovery performance. When the number of fractures was 7, the cumulative thermal production could reach 6.767 × 109 J. Among the three thermal exploitation schemes compared, the DMC-EGS under the triple-well mode yielded the best heat recovery performance during the 40-year extraction period, superior to the conventional dual-well mode, while the one injection and two production mode demonstrated better heat recovery capacity and cooling effect.

An Experimental Study on Heat Recovery Performances of Three-Dimensional Heat Pipes in Air-Conditioning Systems

The applications of conventional heat pipes have been hindered by a few weaknesses, such as the low heat recovery effectiveness, the cross-pollution of fresh and exhaust air, and the difficult switch modes between winter and summer working conditions. In order to find solutions for those problems, a three-dimensional heat pipe exchanger was developed, and an experimental platform was built to test the heat recovery effectiveness of this heat pipe exchanger under different working conditions. Moreover, the operating performances of the three-dimensional heat pipe exchanger unit were monitored throughout one year in a hospital located in the hot summer and cold winter region of China. The field measurement results indicated that the heat recovery effectiveness could be effectively improved by reducing the air volume and the up-wind speed, increasing the cold air and hot air inlet temperature, and increasing the rows of pipes. According to optimizing the structure and operation parameters, the heat recovery efficiencies of the three-dimensional heat pipe exchanger increased by 65~85%. The recommended operation parameters of the three-dimensional heat pipe exchanger in winter and summer for indoor exhaust air temperature were 20 ± 2 °C and 22 ± 2 °C, respectively. The heat recovery effectiveness could reach up to 66% and 64.5% when the indoor and outdoor air temperature differences were higher than 11 °C and 5 °C in winter and summer, respectively. This study provides effective, reliable, and easily implementable methods for the application of three-dimensional heat pipe heat recovery devices in building HVAC systems. It offers guidance for the future design of heat pipe heat recovery devices.

Innovative arrangement of circular angled fins for maximizing the discharge performance of triple-tube heat storage systems

Abstract This study introduces a novel triple-tube latent heat storage system enhanced with circular angled fins to improve solidification and heat recovery performance. The fins are arranged in staggered pattern with alternating upward and downward orientations on both sides of the PCM shell. A validated numerical model was developed using the enthalpy method to simulate the intricate heat transfer and phase change physics. Effects of circular fins geometry and operating conditions were systematically quantified on discharge rates and temperature uniformity. Four fin dimension cases (thickness × length): (2 × 5), (1 × 10), (0.66 × 15), and (0.57 × 17.5) mm2 were analyzed. The results demonstrate that fins with greater length and reduced thickness exhibit superior performance due to enhanced heat transfer capabilities, resulting in quicker solidification and faster heat retrieval. The longest 17.5-mm fins, achieving full solidification in 1973 s with 44%, 19%, and 1.9% quicker than cases with 5-mm, 10-mm, and 15-mm long fins, respectively. Incorporating an additional fin upward further reduces the solidification time by 4.5% while improving heat recovery by 3.6%. The 17.5-mm long fins increase heat discharge by 48% and outlet heat-transfer fluid temperatures by 39% versus straight fin baselines. Lower inlet heat-transfer fluid temperatures (10°C vs 20°C) reduce PCM solidification times by 31% (1755s vs 2554s) while increasing heat recovery rates by 57% (56.3 W vs 35.8 W). Overall, the integrated angled fins create a customizable latent heat storage system with greatly intensified heat transfer and thermal performance compared to conventional shell-and-tube arrangements.

Influence of syngas components and ash particles on the radiative heat transfer in a radiant syngas cooler

Radiant syngas cooler (RSC) is widely used as a waste heat recovery equipment in industrial gasification. In this work, an RSC with radiation screens is established and the impact of gaseous radiative property models, gas components, and ash particles on heat transfer is investigated by numerical simulation method. Considering the syngas components and the pressure environment of the RSC, a modified weighted-sum-of-gray-gases model was developed. The modified model shows high accuracy in validation. In computational fluid dynamics simulation, the calculated steam production is only 0.63% in error with the industrial data. Compared with Smith’s model, the temperature decay along the axial direction calculated by the modified model is faster. Syngas components are of great significance to heat recovery capacity, especially when the absorbing gas fraction is less than 10%. After considering the influence of particles, the outlet temperature and the proportion of radiative heat transfer are less affected, but the difference in steam output reaches 2.7 t·h–1. The particle deposition on the wall greatly reduces the heat recovery performance of an RSC.

Performance analysis of a novel combined open absorption heat pump and FlashME seawater desalination system for flue gas heat and water recovery

Thermal desalination processes generally consume a huge amount of thermal energy and industries release a large amount of latent waste heat in flue gas exhausts into the environment. In order to efficiently utilize this waste heat and to improve the energy efficiency of desalination process, this paper presents a novel combined system based on the open cycle absorption heat pump and low-grade thermal energy driven FlashME desalination. The proposed combined system is designed to recover the latent waste heat from flue gas exhausts in a parallel double stage open absorption heat pump which is driven by multiple energy sources and efficiently utilizes the recovered low temperature heat in FlashME for freshwater production. The validated process model of the combined system is developed in Aspen Plus and a parametric assessment is carried out to analyze its energy performance with the impact of various independent operational parameters by using HCOOK-H2O as an absorbent solution. The simulation results of the parametric study show that the combined system is capable of recovering the waste heat with an efficiency of 89.42 % by operating at a thermal performance coefficient of 2.21 and utilizes this heat in the form of hot seawater at 70 °C to drive FlashME desalination process for freshwater production at the performance ratio of 3.05. The critical analysis of the results highlights that the heat recovery performance of the absorption cycle is strongly dependent on the inlet parameters of flue gas and spray solution. In contrast, the water recovery performance of FlashME is dependent on regeneration pressure such that the water recovery rate varies from 9.19 % to 37.17 % with a pressure variation between 23.23 and 51.39 kPa which raises the seawater temperature 60–79 °C before the flashing stage. Furthermore, the system is flexible enough to operate with two heat sources of different temperature levels by adjusting the regeneration load in separate regenerators.

Numerical simulation study of enhanced geothermal system modification and heat mining performance under cyclic injection

Enhanced geothermal systems (EGS) involve complex thermal–hydraulic-mechanical (THM) coupling. The reservoir's permeability evolution and heat extraction characteristics under cyclic variable pressure injection conditions are unknown. In this paper, a THM model that considered the dynamic changes of rock matrix and fluid properties was developed based on the theory of local heat balance. The THM coupling model investigated the effects of the number of fractures, initial permeability of fractures (kf), maximum injection pressure (P), frequency (td), and working fluid on the heat recovery performance of the EGS under cyclic injection for 20 years. Finally, the sensitivity of each parameter was discussed. When the number of fractures increased from 100 to 200, the temperature of the reservoir decreased by 68.5 K, and the cumulative heat energy extracted increased by 6.6 × 1014 J. With the increase of the initial permeability of the fractures, the irregularities in the temperature and permeability fields of the reservoir were significantly enhanced. When the maximum injection pressure increased from 34 MPa to 40 MPa, the permeability ratio of the reservoir increased by about 13.45 %, and the cumulative extracted thermal energy increased by 3.5 × 1014 J. The frequency of cyclic injection increased from 5 d to 45 d, the production temperature decreased by 26.78 K, and the permeability ratio of the reservoir and the cumulative extracted thermal energy increased. The low-temperature range of CO2-EGS is significantly larger than that of H2O-EGS, and the reservoir temperature decreases faster. The permeability of CO2-EGS increases by 29.32 %, and the cumulative thermal energy extraction increases by 17.5 × 1014 J compared with H2O-EGS. Parameter sensitivities were found for cyclic injection. Factors affecting production temperature and reservoir permeability in that order: P > td > kf. Injection frequency had a slightly greater impression on cumulative extracted thermal energy than injection pressure.

Performance enhancement of compound parabolic concentrating vaporized desalination system by spraying and steam heat recovery

This paper employs the compound parabolic concentrator to heat the thermal conduction oil as working fluid to a higher temperature. The feed water is sprayed and obtains heat from the working fluid in evaporation chamber. The spraying of feed water enhances heat and mass transfer and increases the vaporization intensity. The latent heat of steam is recovered to preheat the feed water which improves energy utilization. Multivariate orthogonal experiments were conducted to obtain the optimized nozzle arrangement in the evaporation chamber. Numerical simulations were performed to evaluate the effect of nozzle parameters on liquid film thickness and water production performance. In system performance experiments, the heat loss, heat recovery performance, fresh water production and gain output ratio in sunny weather were achieved. The daily fresh water production of the system was 15.1 kg with a maximum rate of 4.32 kg/h. The nozzle group arrangement optimization increases the fresh water production by 28.12 % and the maximum rate was 8.48 %. The heat recovery unit increases fresh water production by 13.18 %, with an average heat recovery efficiency of 0.85.

Enhanced radiation heat transfer performance of Alumina-Spinel composite sphere with hollow structure for rapidly ultra-high temperature thermal storage/release process

Heat storage technologies for high temperatures have recently been gaining increasing attention. For heat storage applications at high temperatures, such as industrial regenerative burner systems, the impact of radiant heat transfer on the efficiency of rapid heat storage and release cannot be ignored. Hence, the development of heat storage materials with high infrared radiation absorption is of great significance for energy saving and CO2 emission reduction. Consequently, this study innovatively proposes an advanced composite heat storage material, composited by alumina and a Fe-Co-Mn-Al spinel, with the aim of improving absorptivity. A medium-entropy approach is employed to improve IR absorptivity of alumina. Through the strategic adding of various transition metal oxides, the radiative absorptivity of the alumina material in the 600–1200 °C range increased from an initial 0.2 to an impressive 0.8, provided that doping additives remain below 10 wt%. The high-temperature heat storage material balances cost, heat recovery efficiency and thermal stability. In addition, the heat storage material is prepared as a hollow sphere to further enhance the heat storage density of rapid heat storage/release and reduce cost. Multi-scale numerical simulations are carried out to reveal the heat transfer enhancement mechanisms of modified materials and hollowing. radiative modification can significantly increase the heat storage and release capacity, especially at ultra-high temperatures above 1000 °C. Experimental evaluations using an actual regenerative burner further confirmed the heat recovery performance of this novel heat storage sphere. Comparing with conventional regenerative burner system, heating power remarkably increased by 24.6 %, and the heat storage density of packed bed improved by 16.7 %. This study promises to significantly improve the efficiency of rapid heat recovery at high temperature.

Maximizing the heat-recovery potential of nano-modified phase-change materials through gradual degradation of nanoparticle concentration

Efficient energy storage is a crucial aspect of renewable-energy production, particularly for addressing the time gap between energy generation and use. Nano-modified phase-change materials (nano-PCMs) have emerged as promising solutions for heat storage, enabling improved energy utilization. This study introduces a novel approach to enhancing the heat-recovery capabilities of nano-PCM composites by grading the nanoparticle concentration along the heat flow direction. This method addresses limitations of traditional uniform-concentration nano-PCMs that exhibit decreasing heat communication farther from the heat transfer surface. Computational fluid dynamics simulations examined solidification in a hexahedron enclosure and cylindrical shell-and-tube configuration using water and RT55 as base PCMs. Three nanoparticle concentration arrangements were tested: no-degrading concentration, three-concentration grading, and five-concentration grading, maintaining an overall 0.10 volume fraction. Results demonstrate that degraded concentrations accelerate solidification versus uniform concentration, improving heat recovery rate up to 12 % and 27 % for the hexahedron and cylindrical cases, respectively. Graded concentrations promote uniform temperature distribution and diffusion by improving nanoparticle-PCM communication compared to traditional nano-PCMs. The study provides novel insights into maximizing heat recovery performance of nano-PCM composites, with significant implications for energy storage and thermal management applications.

Thermo-Economic Performance of Organic Rankine Cycle-Based Waste Heat Recovery for Power Generation at a Wide Range of Operating Conditions

This study assesses the performance of organic Rankine cycle-based waste heat recovery systems under different working fluids and operating conditions. The basic ORC (BORC) and ORC with recuperator (RORC) are investigated for power generation and economy using toluene and benzene. Thermodynamic and economic indicators are studied at various expander inlet temperatures, expander inlet pressure, evaporation temperature, and condensation temperature. RORC achieves higher ηth by reducing heat source in the evaporator whereas BORC recovers more waste heat and improves Pnet. With toluene, BORC improves Pnet when increasing the expander inlet temperature and pressure. The lowest LCOE of 0.0532 US$/kWh is from BORC operated with toluene at a Pnet of 349 kW and decreases with an increase in expander inlet temperature. The addition of a recuperator adds to the costs of initial investment and LCOE and slightly improves the performance of the ORCs for waste heat recovery.