Thermal Conversion Efficiency Research Articles

Preparation of graphitized carbon-coated glass fiber cloth materials with high mechanical strength, corrosion resistance, and solar-driven water evaporation performance

Global warming has highlighted the urgency of implementing renewable energy technologies. Solar-driven water evaporation has attracted significant attention because solar radiation is a green (i.e., renewable) energy source that can be applied for seawater desalination purposes. Various materials have been developed to promote the transformation of solar energy to heat to enhance the efficiency of steam generation. However, developing materials that are suitable for long-term applications, i.e., with high mechanical strength and antifouling resistance, is challenging. This report describes the preparation of carbon-coated glass fiber cloth (C-GFC) using a polymer pyrolysis method. The C-GFC exhibited high mechanical strength (240 MPa), anti-corrosion properties in acidic and alkaline environments, light absorption over 95%, and good hydrophilicity. After integrating the C-GFC into a three-layer evaporation generator device, the evaporation rate exceeded 1.5 kg m−2 h−1 under one sun, with 88% thermal conversion efficiency. Moreover, the C-GFC materials maintained their initial evaporation rate even after long-term treatment in acidic, alkaline, and seawater environments. The developed carbon-coated glass fiber cloth materials therefore demonstrate promising potential for photothermal water conversion applications.

Oxidation behavior and decomposition kinetics of mixed-waste biomass material

In Taiwan, approximately 379,000 automobiles and 588,000 motorcycles were recycled in 2019. Rigid polyurethane foam is one of the principal components of auto shredder residue. The amount of rigid polyurethane foam from the recycling of waste vehicles is 8,000 to 10,000 tons/year. In this study, waste Cryptomeria wood was mixed with waste rigid polyurethane foam to form derived fuels. The oxidation behaviors of the wood mixed with waste rigid polyurethane foam-derived fuels were investigated. The characteristics of the derived fuel made from wood mixed with waste rigid polyurethane foam showed that the ash content was less than 2.5% and its calorific value reached 21.9 MJ/kg. According to the Friedman equation, the activation energies of the wood mixed with 5%, 15%, and 30% of waste rigid polyurethane foam pellets were 212, 220, and 188 kJ/mol, respectively. The thermal conversion efficiencies of the wood mixed with 5%, 15%, and 30% of waste rigid polyurethane foam pellets were 30.2% to 48.1% by a water boiling test. The results showed that waste Cryptomeria mixed with waste rigid polyurethane foam-derived fuels is suitable for use as an alternative renewable energy fuel.

Effect of Different Soft Segment Contents on the Energy Storage Capacity and Photo-Thermal Performance of Polyurethane-Based/Graphene Oxide Composite Solid-Solid Phase Change Materials.

A series of polyurethane/graphene oxide (PU/GO) solid-solid phase change materials (SSPCMs) were synthesized by using GO as a light-absorbing filler and polyethylene glycol (PEG) as a phase change matrix. The effects of PEG content on the energy storage capacity, thermal stability and photo-thermal conversion performance of PU were investigated. The results show that the form-stability of PU/GO decreases while the phase change enthalpy and photo-thermal conversion efficiency of PU/GO increases with the increasing PEG content. The introduction of a very low content of GO can maintain comparable energy storage density and greatly improve light absorption by reasonably modulating the soft segment contents. The PU/GO composite with 92 wt% PEG has a phase change enthalpy of 138.12 J/g and a high photo-thermal conversion efficiency (87.6%). The composite solid-solid PCMs have great potential for effective energy storage and solar energy utilization.

Thermally Driven Continuous Rolling of a Thick-Walled Cylindrical Rod.

Self-sustained motion can take advantage of direct energy extraction from a steady external environment to maintain its own motion, and has potential applications in energy harvesting, robotic motion, and transportation. Recent experiments have found that a thermally responsive rod can perform self-sustained rolling on a flat hot plate with an angular velocity determined by the competition between the thermal driving moment and the friction moment. A rod with a hollow cross section tends to greatly reduce the frictional resistance, while promising improvements in thermal conversion efficiency. In this paper, through deriving the equilibrium equations for steady-state self-sustained rolling of the thick-walled cylindrical rod, estimating the temperature field on the rod cross-section, and solving the analytical solution of the thermally induced driving moment, the dynamic behavior of the thermally driven self-sustained rolling of the thick-walled cylindrical rod is theoretically investigated. In addition, we investigate in detail the effects of radius ratio, heat transfer coefficient, heat flux, contact angle, thermal expansion coefficient, and sliding friction coefficient on the angular velocity of the self-sustained rolling of the thick-walled cylindrical rod to obtain the optimal ratio of internal and external radius. The results are instructive for the application of thick-walled cylindrical rods in the fields of waste heat harvesters and soft robotics.

Progress on TiO2-based materials for solar water interfacial evaporation

Solar water interfacial evaporation (SWIE) has attracted much attention for harvesting clean water. Over the last few decades, researchers have developed an innovative photo-thermal material for high-performance solar water interfacial evaporation. For higher evaporation performance, TiO2-based materials gain attention as a promising photo-thermal material due to their light absorption capacity. This study compared conceptual designs of TiO2-based materials for SWIE. Structural design and engineering strategies for improving evaporation rates and higher thermal conversion efficiency were reviewed. In addition, the material’s thermal stability and heat management were analyzed. This review provides an overview of the current advances in photo-thermal TiO2 materials to motivate research and translation efforts from the laboratory to large-scale solar water clean water production. Additional benefits of TiO2 materials on solar water interfacial evaporation should be investigated beyond containers to solve interconnected water, environmental, and energy progression.

Research on Co-Combustion Behaviors of Binary and Ternary Blends of Coal, Walnut Shell, and Biochar by TGA

In this paper, the co-combustion behavior of the walnut shell, biochar, and coal, and the respective binary and ternary blends were investigated by thermogravimetric analysis (TGA) in the oxy-fuel atmosphere (21% O2/79% CO2). The combustion reactivity of coal was similar to biochar but lower than that of the walnut shell. The presence of the walnut shell improved the combustion performance of coal and biochar. The interaction between only biochar and coal was inhibited in the binary blends. The presence of the walnut shell in the ternary blend covered up the inhibition between biochar and coal. The average activation energy of each sample was obtained using the Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) kinetic models. The results of this study provide a reference for the rational utilization of biomass and biochar and the practical improvement of the thermal conversion efficiency of coal.

Numerical analysis and experimental study on the thermoelectric characteristics of the Al–Si alloy used for building energy storage tile

This paper aims to explore the feasibility of the silicon aluminum (Al–Si) alloy for usage as a thermoelectric tile on building roofs. Through the simulation of the heat conduction characteristics and temperature field distribution of the step-shaped Al–Si alloy sample, the effects of the thickness, material, and shape of the Al–Si alloy sample on its thermal conversion efficiency and temperature field distribution characteristics of continuous solar irradiation were studied. The energy conversion characteristics of the Al–Si alloy sample combined with a thermoelectric generator (TEG) were investigated by numerical analysis and experiment. The results show that the Al–Si alloy sample with a thickness of 10 mm had a good heat storage efficiency. Also, the Al–Si alloy tile with a plane shaped solar irradiation surface and the back-sun surface with a certain number of bosses has a better heat transfer efficiency. Through experiment and calculation demonstrate that an Al–Si alloy tile with 500 mm × 500 mm area could generate 1.64 W electric power.

Modelling and control strategy of a distributed small‐scale low‐temperature geothermal power generation system

At present, commercial geothermal power stations are mainly high-temperature and medium-temperature geothermal energy, while the large number of low-temperature geothermal energy resources are rarely used for power generation applications. This paper proposes a new model for energy conversion in low-temperature geothermal power systems. The basic structure and working principle of this new model are analysed, in detail, a low-temperature geothermal model and a Stirling engine model for geothermal energy conversion are established, and the control strategies on the rotor and stator sides of the Stirling-driven doubly-fed generator are discussed. Finally, the simulation analysis is carried out, and its results show that the thermal conversion efficiency of Stirling’s engine can reach 38%, the output AC voltage of the power generation system reaches the set value 50Hz, 190V, and the DC bus voltage is constant at 300V, which verified the validity of the proposed power generation model and related control strategies. This system expands the range of available heat sources in geothermal power generation, makes geothermal power generation more flexible in terms of site selection, power generation capacity and control, and provides a new idea for geothermal power generation structure.

Performance comparison of coiled actuators made of PA6 single fiber and yarn

The application of twisted and coiled synthetic fibers for energy conversion is promising due to their flexibility, lightweight and wearability. Although there are significant efforts on improving the performance of twisted and coiled polymer fibers, new understanding is still required about possible effects of the fabrication parameters and the precursor fiber type on thermal actuation performance and energy conversion efficiency. Herein, two types of coiled actuators were fabricated by inserting certain numbers of twists to polyamide 6 (PA6) single fibers and yarns, and the effects of twisting numbers and precursors type on actuation responses, physical properties, and structural changes were investigated. It was demonstrated that fiber-based and yarn-based actuators had different actuation properties where the former one showed a greater actuation load and the latter one had a faster torsional actuation. Also, the yarn-based samples generated faster torsion actuations with the rotation speed up to 16,000 rpm/m, and presented higher thermal actuation sensitivity. Depending on the obtained characteristics, the prepared actuators were used in developing smart textiles for different applications such as fabricating small spring-like robot, smart curtains, and infrared-sensitive functional gloves. • The operating principle of the fiber actuator was discussed. • The actuation properties of coiled PA6 single fiber and yarn have been compared. • The impact of the twisting and coiling process on the internal arrangements of precursors is investigated. • The different applications in textile for twisted fiber-based actuator are realized.

Effect of microstructure of nanoparticles and surrounding alcohol groups on energy transfer efficiency

• The higher water content, the greater the thermal conductivity of alcohol solutions. • Thermal conductivity of alcohol nanofluids is obviously higher than the base fluids. • There is a non-escaping adsorption layer on the surface of the Cu nanoparticles. • Presence of nanoparticles results in the microstructure change of the system. • The solid-like microstructure results in an increase of thermal conductivity. The low solar thermal conversion efficiency is an obstacle to the development of a new generation of high-efficiency energy-saving technologies. An important measure to improve the conversion efficiency is to improve the thermal conductivity of the working fluid. Nanofluids have a higher thermal conductivity than conventional fluids, which provides a strategy idea toward solving this problem. In this paper, three kinds of traditional fluids, ethanol, ethylene glycol (EG) and 1,2-propylene glycol (PG), were used as base solutions, and Cu nanoparticles with different volume fractions were added to form their corresponding nanofluids. The thermal conductivity of the different alcohol solutions and their nanofluid systems were simulated using molecular dynamics and the thermal conductivity enhancement mechanisms of these nanofluids on a micro-level were simulated and analyzed. It was found that the thermal conductivity of the ethanol/EG/PG-water solution was positively correlated with the water content of the system. The addition of Cu nanoparticles improved the thermal conductivity of the three kinds of alcohol nanofluids. The existence of base solution molecular adsorption layer on the surface of nanoparticles was an important factor contributing to the improvement of the thermal conductivity of nanofluids. Through the radial distribution function of the nanofluid system, and the visualization of the molecules in the adsorption layer, it was found that the arrangement of base solution molecules in the adsorption layer was similar to the orderly arrangement of solids. This type of solid-like microstructure rendered better heat transfer performance of the nanofluid than the base solution. Within the scope of this study, the maximum increase in the rate of the thermal conductivity of the ethanol/EG/PG-water solutions was 14.2, 30.6 and 22.6 %, respectively. In the alcohol nanofluid system, the thickness of the adsorption layer on the surface of Cu nanoparticles was ∼0.45 nm, which increased or decreased slightly based on the type of base solution. The above findings provide an important reference for improving solar thermal conversion efficiency.

MXene incorporated nanofluids for energy conversion performance augmentation of a concentrated photovoltaic/thermal solar collector

This research work introduces emerging two-dimensional (2D) MXene (Ti3C2) and Therminol55 oil-based mono and hybrid nanofluids for concentrated photovoltaic/thermal (CPV/T) solar systems. This study focuses on the experimental formulation, characterization of properties, and performance evaluation of the nanofluid-based CPV/T system. Thermo-physical (conductivity, viscosity, and rheology), optical (UV-vis and FT-IR), and stability (Zeta potential and TGA) properties of the formulated nanofluids are characterized at 0.025 wt.% to 0.125 wt.% concentrations of dispersed particles using experimental analysis. By suspending the nanomaterials, photo-thermal energy conversion is improved considerably, up to 85.98%. The thermal conductivity of pure oil is increased by adding Ti3C2 and CuO nanomaterials. The highest enhancements of up to 84.55% and 80.03% are observed for the TH-55/Ti3C2 and TH-55/Ti3C2 + CuO nanofluids, respectively. Furthermore, dynamic viscosity decreased dramatically over the temperature range investigated (25°C-105°C), and the nanofluid exhibited dominant Newtonian flow behavior as viscosity remained nearly constant up to a shear rate of 100 s−1. Numerical simulations of the experimentally evaluated nanofluids are performed to evaluate the effect on a CPV/T collector using a three-dimensional transient model. The numerical analysis revealed significant improvements in thermal and electrical energy conversion performance, as well as cooling effects. At a concentrated solar irradiance of 5000 W/m2 and an optimal flow rate of 3 L/min, the highest thermal and electrical energy conversion efficiency enhancements are found to be 12.8% and 2%, respectively.

Heat-transfer analysis of interfacial solar evaporation and effect of surface wettability on water condensation and collection

The use of solar energy for interfacial water evaporation has become a promising roadmap with the global energy and fresh water crisis becoming serious concerns. A systematic study of thermal energy conversion efficiency in interfacial solar evaporation has great significance for improving evaporation efficiency. In this study, an interfacial solar water-evaporation device was proposed, and heat balance analysis were conducted to investigate dominant heat transfer modes for improving the evaporation rate. The results indicate that thermal conduction of the insulation layer accounts for 5% of the input solar energy, and an improvement in the evaporation rate should be focused on reducing the convective heat transfer and radiative loss of the photothermal-layer surface. In addition, a water-collection device was designed to investigate the effect of surface wettability on the water condensation and collection of steam generated by interfacial solar evaporation. It can be found that a hydrophilic wall surface is conducive to steam adhesion and the spread of condensed water droplets, water-film flow, and water discharge; this effectively improves the performance of water collection. The water-collection device which is comprised of hydrophilic side walls and a cover made of ultraclear glass coated with hydrophilic material, can obtain a water-evaporation rate of 8.32 kg·m−2 h−1, water-collection rate of 6.10 kg·m−2 h−1, and water-collection efficiency of 73.21% under ten-sun illumination. The performance of the water-collection device under outdoor conditions was studied and it can be concluded that the evaporation rate and water collection rate can be improved by increasing the irradiation flux on the photothermal layer of the interfacial solar evaporator, or by reducing the effect of outdoor airflow. This study can provide theoretical guidance for the design and performance improvement of solar-driven interfacial water evaporation and collection devices.

Constructions of synergistic photothermal therapy antibacterial hydrogel based on polydopamine, tea polyphenols and polyvinyl alcohol and effects on wound healing in mouse

Hydrogels with significant antibacterial efficacy have enormous potential in wound healing. This work reported a series of effective antibacterial and antioxidant hydrogels based on tea polyphenols (TP), polydopamine (PDA), and polyvinyl alcohol (PVA). PDA-TP molecular chains are formed from oxidized TP and PDA. These molecular chains, which were cross-linked with PVA by cyclic freeze-thaw (FT), formed the PVA/PDA-TP hydrogel (PPTP). The number of freezing-thawing cycles and the amount of TP would affect the mechanical properties and swelling properties of hydrogel. The PPTP hydrogel exhibited high photo thermal conversion efficiency, high antibacterial efficacy, antioxidant properties, good cellular compatibility and short wound closure time. The PPTP hydrogel leaded to wound closure in approximately 10 d in a full-thickness skin defect mouse model. The preparation method of hydrogel with non-chemical cross-linked and ability of rapid high temperature generation provided a new way to apply TP to wound healing and proved that synergistic chemical and photothermal therapy can effectively inhibit resistant bacteria and accelerate wound healing.

Insight into the Investigation of Diamond Nanoparticles Suspended Therminol®55 Nanofluids on Concentrated Photovoltaic/Thermal Solar Collector.

Nanofluids are identified as advanced working fluids in the solar energy conversion field with superior heat transfer characteristics. This research work introduces carbon-based diamond nanomaterial and Therminol®55 oil-based nanofluids for implementation in a concentrated photovoltaic/thermal (CPV/T) solar collector. This study focuses on the experimental formulation, characterization of properties, and performance evaluation of the nanofluid-based CPV/T system. Thermo-physical (thermal conductivity, viscosity, and rheology), optical (UV-vis and FT-IR), and stability (Zeta potential) properties of the formulated nanofluids are characterized at 0.001–0.1 wt.% concentrations of dispersed particles using experimental assessment. The maximum photo-thermal energy conversion efficiency of the base fluid is improved by 120.80% at 0.1 wt.%. The thermal conductivity of pure oil is increased by adding the nanomaterial. The highest enhancement of 73.39% is observed for the TH-55/DP nanofluid. Furthermore, dynamic viscosity decreased dramatically across the temperature range studied (20–100 °C), and the nanofluid exhibited dominant Newtonian flow behavior, with viscosity remaining nearly constant up to a shear rate of 100 s−1. Numerical simulations of the nanofluid-operated CPV/T collector have disclosed substantial improvements. At a concentrated solar irradiance of 5000 W/m2 and an optimal flow rate of 3 L/min, the highest thermal and electrical energy conversion efficiency enhancements are found to be 11 and 1.8%, respectively.

Historical overview of power generation in solar parabolic dish collector system.

Solar energy is a promising form of energy that has the potential to meet all of the world's energy needs. Only half of the sun's energy reaches the earth's surface, even though it is more enough for meeting the world's energy need. Though there is a great deal of solar energy utilization technologies available, solar parabolic dish collector system got researchers focus because of its higher thermal energy conversion efficiency and its unique advantages. Several researchers have been enlightening new and emerging technologies in several countries. Hence, the authors would like to emphasize the progress in this while exercising an extensive review of different solar concentrating techniques using solar parabolic dish collector in order to produce heat and electrical power using direct and indirect energy conversion devices with wide range of applications. Their design advancement and progress applications in recent years particularly in related field are discussed too.

Thermal environment evaluation of plastic greenhouses in southern China and optimization by phase change materials

Plastic greenhouses, broadly applied in southern China, have insufficient thermal insulation and thermal storage, resulting in a poor thermal environment at night. This paper chose a plastic greenhouse in Chengdu, Sichuan province, to measure the thermal environment variation in winter. An energy balance model of the plastic greenhouse was developed and then verified by the measurements. The influence of the ground thermal storage on the indoor thermal environment was studied. As a good thermal mass, the ground soil could regulate the indoor thermal environment at night, especially by increasing the near-ground temperature. At night, the ground surface had higher temperatures than the indoor air, with a temperature difference of 4–6 °C. Further, phase change materials (PCMs) were proposed to improve the ground thermal storage conversion efficiency. The ground surface temperature of the plastic greenhouse with PCMs was higher than that of the plastic greenhouse without PCMs by 1 °C, and the average ground thermal storage conversion rate could be increased by 7%.

A cooling design for photovoltaic panels – Water-based PV/T system

This paper proposes an innovative thermal collector for photovoltaic-thermal (PV/T) systems. The thermal behavior of the photovoltaic module and the designed cooling box flow are coupled to achieve the thermal and electrical conversion efficiencies of the water-based PV/T system. Different inlet mass flow rates and temperatures are simulated under normal operating cell temperature conditions (NOCT). The temperature distribution and average temperature of the photovoltaic module layers are investigated. The results show that when the mass flow rate is 0.014 kg/s, and the inlet flow temperature is 15 °C, the PV module reaches an electrical conversion efficiency of 17.79% with 76.13% of thermal efficiency. The designed cooling system exhibits better performance with a significant increase in thermal and electrical conversion efficiency compared to current solutions in the literature. The findings in this paper highlight the utility of PV/T systems and their massive potential to popularize the solar energy field and harvest thermal and electrical energy simultaneously.

Research on temperature distribution characteristics and energy saving potential of wall implanted with heat pipes in heating season

As an important component of building energy consumption, wall heat loss needs to be studied urgently. Wall implanted with heat pipes (WIHP) is one of the latest research hotspots in this field. Firstly, the internal temperature distribution characteristics of WIHP are studied by numerical simulation in this paper. Secondly, the thermal conversion efficiency is proposed to evaluate the utilization of solar energy by WIHP. Finally, the energy saving potential of WIHP in heating season is analyzed. The results show that: (1) WIHP has a significant anisotropic heat transfer characteristic compared with the conventional wall; the average time lag of the inside surface is reduced by 2.3 h, and the average decrement factor is increased by 0.008. (2) The time lag difference between the upper and lower parts of WIHP is 6 h, and the time lag of the WIHP structural layer is increased by 1 h compared with the conventional wall. (3) The heat transfer of heat pipe increases with the increase of solar radiation, but the thermal conversion efficiency decreases. (4) WIHP can decrease the heat loss of the wall by 56% on average, and the cumulative heat loss is reduced by 5.29 kWh/m2.

Subsurface waste heat recovery from the abandoned steam assisted gravity drainage (SAGD) operations

A considerable fraction of the energy injected during the thermal recovery of oil remains in the subsurface and wasted in the surrounding geological formations after the profitable life of oil wells is over. This work studied the concept of thermal energy extraction from the abandoned SAGD operations in oil sands reservoirs for generating electric power. The cold water is injected as a working fluid to extract heat after the oil production is ceased, and the produced hot water is fed to a surface binary cycle to generate electric power. The results show that an oil sands reservoir after SAGD operations could be regarded as an artificial geothermal system suitable for thermal energy extraction. It is demonstrated that a total net electric energy output of 57 GWh could be achieved based on a single SAGD well pair during a ten-year heat-extraction time, indicating the huge heat extraction potential at full field scale. The results show that the thermal energy conversion efficiency to electricity for the abandoned SAGD wells can reach as high as 12%. The demonstrated subsurface waste heat recovery from the abandoned SAGD sites revealed that between 15 and 36% reduction in CO2 emission could be achieved.

Selective absorber and emitter boost water evaporation and condensation toward water collection

Solar evaporation has attracted much attention for water collection. However, previous studies on the traditional interface evaporation pay little attention to the selective spectral properties of solar absorbers, leading to mid-infrared radiative heat loss. Besides, during the vapor condensation, the scatter and absorption of the droplets reduce the incident solar intensity on the evaporation interface below. In this work, a freshwater collection strategy combining solar selective absorber and daytime passive radiative cooling techniques is proposed. The solar selective absorber achieves a high solar thermal conversion efficiency (ηevap = 0.894 at 1 sun) to enhance solar evaporation. The passive daytime radiative cooling coating achieves a high solar reflectance R¯solar = 0.927 and thermal emittance ε¯LWIR = 0.929 in the atmospheric transmission window to cool the condensation surface and enhance vapor condensation. In addition, the contact angle is optimized to be 79° by manipulating the hydrophilicity of the condensation surface to ensure the droplet nucleation and shedding. Indoor experiments show that the water collection rate reaches 0.43 kg m−2 h−1. This work provides a promising water collection strategy through solar heating and radiative cooling.