Thermal Conversion Efficiency Research Articles

Time-Controlling the Latent Heat Release of Fatty Acids using Static Electric Field

Latent heat released during freezing of phase change material (PCM), which occurs at a constant temperature, can be modified using an electric field, through a process called electrofreezing. To date, the effects of the electric field on the freezing of salt solutions or salt hydrates of inorganic PCM, such as reduction of the supercooling degree, increase of nucleation rate, and reduction of the induction time due to changes in the Gibbs free energy, have been the focus. In this paper, we describe the electrofreezing of stearic acid and lauric acid of fatty acid PCM. Because common organic PCM has relatively small or even zero supercooling, the effect of the DC electric field on the time of latent heat release at a constant temperature and crystallization time was more pronounced. A comparison was also done with inorganic CaCl2⋅6H2O PCM using previously published data. We propose that the two time parameters are closely related to the electrical and thermal conductivities. Different nucleation mechanisms for fatty acids and CaCl2⋅6H2O with interactions between the crystalline sample and electric field, as well as dissimilar Joule heating effects, have been proposed. Changes in the chemical structure and thermal stability due to electric field treatment are evaluated using the Fourier-transform infrared spectra, the decomposition and melting temperatures, and the calculation of the latent heat of fusion. We also discuss the potential applications of lauric and stearic acids as phase change composites in thermoresponsive devices for high electrical to thermal energy conversion efficiencies.

A conjugated polymer‐liposome complex: A contiguous water‐stable, electronic, and optical interface

AbstractThe electronic and optical properties of conjugated polymers and conjugated polyelectrolytes have attracted considerable research interest across a broad range of applications. Interfacing them with the lipid bilayer enables the engineering of interfaces with unique characteristics, facilitated by accessing the properties of each constituent material. Research done on these interfaces tap into a broad range of applications. Fundamental studies have been conducted to gain insight into the polymer interaction with a lipid membrane that mimics the biological cell. Bioimaging and biosensing devices have been developed, exploiting optical and superquenching properties of the polymer. Delivery systems based on these complexes were applied in photothermal therapy using the polymer high thermal conversion efficiency. This minireview presents a summary of this research, highlighting that while the field remains in its early development, conjugated polymer/polyelectrolyte interfaces hold huge potential for biomedical applications.

Low-cost and facile fabrication of a candle soot/adsorbent cotton 3D-interfacial solar steam generation for effective water evaporation

Solar-driven water evaporation is considered an environmental-friendly method for energy-efficient clean water production. However, directly using solar energy to generate steam is impractical due to its high cost, complex systems, and low efficiency. Herein, a candle soot (CS)/adsorbent cotton (AC) 3D-interfacial solar steam generation (3D-ISSG) with simple configuration and off-grid operation was reported by depositing low cost and conveniently fabrication candle soot nanoparticles on adsorbent cotton matrix via a simple home-made process. In this system, the 3D photothermal cone was introduced to separate the contact area between bulk water and the CS/AC membrane to minimize the heat loss, accordingly achieving an efficient interface heating to further improve the water evaporation rate. The synthesized CS/AC 3D-ISSG is easy to fabricate, thus achieving a lower cost for water evaporation. The fabricated CS/AC 3D-ISSG achieved water evaporation rates of 1.27 kg m−2 h−1 under 1 sun with a solar thermal conversion efficiency up to 80.70%. The results of this work provide a reference for further study of photothermal materials with low cost and excellent properties and their application in clean water production.

Comparative Biodrying Performance of Municipal Solid Waste in the Reactor under Greenhouse and Non-greenhouse Conditions

The high moisture content of municipal solid waste yields a lower energy content of solid fuel that affects the thermal conversion efficiency. Biodrying is an alternative drying method using bio-heat generated by microbial metabolism to reduce the moisture content of municipal solid waste. This research was conducted in three pilot-scale biodrying reactors, two under greenhouse conditions compared with one conventional non-greenhouse condition. Two bunkers with greenhouse cladding were connected with aerators, and airflow rates were set at 0.4 and 0.6 m3/(kgwaste·day), respectively. Meanwhile, a passive aeration method was applied to the non-greenhouse bunker. This study aims to investigate the effect of the greenhouse condition on the biodrying process and assess the performance of the drying process through different operating conditions. The result shows that the greenhouse mainly affects the air temperature rise in the reactor. The aeration rate is positively correlated with weight reduction (r = 0.93). At 0.6 m3/(kgwaste·day) airflow rate, the treatment can reach a moisture content less than 30% on average within ten days, while at 0.4 m3/(kgwaste·day) airflow rate, it takes 15 days to reduce the moisture content to less than 30%. Biodrying under the greenhouse condition with active aeration potentially achieves desirable moisture content reduction and heating value increase more efficiently than the common biodrying. However, the airflow rate is a crucial factor in determining the suitable drying time in biodrying under the greenhouse condition.

Corrosion performance of candidate boiler tube alloys under advanced pressurized oxy-fuel combustion conditions

Advanced pressurized oxy-fuel combustion technology has been developed for the significantly improved thermal energy conversion efficiency and reduced greenhouse gas emission. However, significant knowledge gap exists in terms of the selection of appropriate boiler tube materials, which has delayed the commercialization of this promising technology. In this study, the corrosion performance of the three candidate alloys (SS347, Alloy 800AT and Alloy 825) was investigated in the hot flue gas mixtures (60% H2O + 33% CO2 + 2–7% O2) at 600 °C and 15 MPa to simulate typical pressurized oxy-fuel natural gas combustion environments. On all the alloys, Cr2O3 was the main surface oxide and several alloying elements (including Si, and/or Al+Ti) accumulated at the interface of oxide layer/substrate. Among the gas species, O2 acted as the dominant oxidizing agent with a critical content of ∼2%, above which nodular oxidation was suppressed and corrosion rates of alloys were greatly reduced. H2O was likely to enhance the growth and evaporation of oxides, while CO2 did not trigger carburization during the testing period. From a corrosion perspective, three alloys exhibit promising potential for boiler tube constructions while Alloy 825 exhibited the best corrosion performance.

Bioinspired Fractal Design of Waste Biomass‐Derived Solar–Thermal Materials for Highly Efficient Solar Evaporation

AbstractSolar evaporation is considered a promising technology to address the issue of fresh water scarcity. Although many efforts have been directed towards increasing the solar–thermal conversion efficiency, there remain challenges to develop efficient and cost‐effective solar–thermal materials from readily available raw materials. Furthermore, further structural modification of the original biomass structure, particularly at multiple length scales, are seldom reported, which may further improve the solar–thermal performance of these material systems. Herein, a novel low‐cost system is developed based on a common bio‐waste, pomelo peels (PPs), through a bioinspired fractal structural design strategy, fractal carbonized pomelo peels (FCPP). This FCPP system shows an extremely high solar spectrum absorption of ≈98%, and marvelous evaporation rate of 1.95 kg m−2 h−1 with a solar–thermal efficiency of 92.4%. In addition, the mechanisms of the evaporation enhancement by fractal structural design are identified by numerical and experimental methods. Moreover, using FCPP in solar desalination shows great superiority in terms of cost and its potential in sewage treatment is also studied. The present work is an insightful attempt on providing a novel proposal to develop bio‐waste‐derived solar–thermal materials and construct biomimetic structures for efficient solar evaporation and applications.

Highly efficient solar water evaporation of TiO2@TiN hyperbranched nanowires-carbonized wood hierarchical photothermal conversion material

Solar water evaporation is a significant technique for water purification, desalination, and distillation. The approaches to obtain low-cost, low toxic and reusable material with high solar water evaporation efficiency are essential to solve the problem of drinking water shortage. Herein, we first synthesize TiO2@TiN hyperbranched nanowires on carbonized wood (CW) for solar water evaporation with a high solar water evaporation rate of 1.5252 kg m−2 h−1 and a solar thermal conversion efficiency about 94.01% under 1 kW m−2 simulated solar irradiation. The outstanding solar water evaporation performance can be contributed to the unique design of combining TiO2@TiN hyperbranched nanowires with CW. TiO2@TiN hyperbranched nanowires have better solar light absorption and higher specific area to evaporate water than TiN nanoparticles and nanotubes. At the same time, the evaporation enthalpy of water in the hyperbranched nanowires deceases obviously compared with that of normal bulk water. Besides, the hierarchical material possesses good stability and high solar evaporation efficiency both in seawater and in deionized water.

Prediction of Carbon Content in Fly Ash in Ultra Supercritical Generation Unit with Long Short-term Memory Neural Network

The accurate measurement of carbon content in fly ash is the basis of improving the thermal conversion efficiency of boiler and reducing the coal consumption of power generation. Based on the operation data of 1000MW Ultra-supercritical Unit in a thermal power plant, the input parameters of the model were selected by correlation analysis. The Long Short-Term Memory neural network (LSTM) was used to establish a prediction model with the boiler operation parameters as the input and the carbon content of the boiler fly ash as the output. According to the actual operation data of the unit, the prediction performance of the model was trained and tested. The simulation results show that the average prediction error of the LSTM model is 2.8136%, and 86% of the total samples are data with error less than 4.5%, which means it has high accuracy and strong generalization ability.

Flame-retardant and solid-solid phase change composites based on dopamine-decorated BP nanosheets/Polyurethane for efficient solar-to-thermal energy storage

For utilisation of solar energy, the development of form-stable phase change material (PCM) composites with excellent flame retardancy and superior solar–thermal conversion performance is critical. Here, by incorporating dopamine-decorated black phosphorus nanosheets (PDA@BP) into polyethylene glycol-based polyurethane (PEG-PU), novel form-stable PCM composites (PBPCMs) having superior solar–thermal conversion performance and excellent flame retardancy were fabricated. PDA@BP, covalently bonded to PEG-PU, acted as an efficient photothermal filler to capture solar energy and convert it to thermal energy, while PEG-PU absorbed and stored the thermal energy via phase transition. A light irradiation experiment and thermal conductivity test demonstrated that introducing PDA@BP effectively improved the solar–thermal conversion efficiency (up to 88.5%) and thermal conductivity (69.4% increase) of PCM composites. Moreover, by introducing PDA@BP into PBPCMs, the total heat release and heat release rate decreased considerably, while the limiting oxygen index value and char yield increased, demonstrating the considerably enhanced flame retardancy of PCM composites. PBPCMs with superior solar–thermal conversion performance and excellent flame retardancy show considerable potential in the solar–thermal conversion and storage field.

Free-standing reduced graphene oxide (rGO) membrane for salt-rejecting solar desalination via size effect

Abstract Interfacial solar vapor generation has revived the solar-thermal-based desalination due to its high conversion efficiency of solar energy. However, most solar evaporators reported so far suffer from severe salt-clogging problems during solar desalination, leading to performance degradation and structural instability. Here, we demonstrate a free-standing salt-rejecting reduced graphene oxide (rGO) membrane serving as an efficient, stable, and antisalt-fouling solar evaporator. The evaporation rate of the membrane reaches up to 1.27 kg m−2 h−1 (solar–thermal conversion efficiency ∼79%) under one sun, out of 3.5 wt% brine. More strikingly, due to the tailored narrow interlayer spacing, the rGO membrane can effectively reject ions, preventing salt accumulation even for high salinity brine (∼8 wt% concentration). With enabled salt-antifouling capability, flexibility, as well as stability, our rGO membrane serves as a promising solar evaporator for high salinity brine treatment.

Chinese ink enabled wood evaporator for continuous water desalination

Solar-driven water desalination is considered as an efficient and sustainable approach to produce clean water. In this work, a bilayered evaporator composed of black Chinese ink layer and wood sheet substrate for continuous desalination is rationally designed. Millimeter-sized hole arrays were drilled within the wood substrate. The ink coating on the wood surface offers strong and broad light absorption. The hierarchical channels in the wood itself functions as thermal insulator and promotes water transport. In addition, the drilled hole arrays provide salt-rejection pathways and enable the wood evaporator with antifouling property. The wood evaporator (H-C-Wood) shows a stable solar thermal conversion efficiency of 74% and an evaporation rate of 1.6 kg m−2 h−1 under simulated 1 sun irradiation. Such ink deposited solar steam generation device is low cost and has a self-regenerating ability.

Porous Graphene/Polyimide Membrane with a Three-Dimensional Architecture for Rapid and Efficient Solar Desalination via Interfacial Evaporation

The solar desalination via interfacial evaporation has shown great potential to address the freshwater scarcity issue. However, the evaporation rate and solar thermal conversion efficiency of the c...

Shape-stabilized Phase Change Materials Based on Carbon Matrix for Thermal Performance Enhancement: A Review

With the growingly serious energy crisis and the dramatically increasing greenhouse gas emission worldwide, thermal energy storage has been attracting extensive attention for its application in re-regeneration energy, which provides a perfect solution to coordinate the mismatch between energy supply and demand. Organic phase change materials are the most widely used materials for thermal energy storage, but the inherent disadvantages drastically impede their further application, such as low thermal conductivity and leakage. Previous research shows that carbon-based scaffold can effectively prevent the leakage during phase transition attributing to the capillary force and the surface tension between the phase change material and the micro-channel surface. The porous structure provides abundant heat transfer areas, and the scaffold itself is perfect heat transfer media. It makes the heat transfer greatly enhanced by combining with carbon-based matrix. This composite shows huge potential for promoting the efficiency of thermal management and energy conversion. This paper gives a state-to-art review about the development of shape-stabilized composite phase change material with carbon-based matrix as the supporting material for organic phase change material including the fabrication and thermal property of the composite phase change material, and the newest application of the composite.

Flexible and Efficient Solar Thermal Generators Based on Polypyrrole Coated Natural Latex Foam for Multimedia Purification

Solar evaporation has emerged as a facile and attractive technology for clean water production, desalination, and organic solvent purification by virtue of abundant solar energy. However, developing a high-performance, environment friendly, and scalable solar evaporator remains a significant challenge. Herein, a one-step, low-cost, and easy-to-manufacture synthesis of a three-dimensional macroporous solar steam generator is reported based on polypyrrole coated natural latex (PPy-NL) foam, offering a sustainable solution to the ever-growing issues of the energy and water crises. The as-prepared foam exhibits good wettability, acid and alkali resistance, high mechanical strength, low thermal conductivity (0.2257 W m–¹ K–¹) and excellent light absorption of ∼95% owing to the introduction of PPy coating. Among polymer photothermal materials, PPy-NL foam gives a vapor generation rate of 1.76 kg m–² h–¹ with a superb solar thermal conversion efficiency of 98% under 1 sun illumination. Furthermore, PPy-NL foam can be directly used to purify various types of wastewater and organic solvent with a high rejection of ions (nearly 100%), oil, and dye. This simple fabrication process with renewable polymer resources and photothermal materials provides a fundamental guidance and practical application value toward developing high-performance solar evaporation technologies for remote areas and individuals.

High Efficiency Solar Membranes Structurally Designed with 3D Core-2D Shell SiO2@Amino-Carbon Hybrid Advanced Composite for Facile Steam Generation.

Steam generation through efficient utilization of solar energy is a promising technology in addressing the challenge of global freshwater shortage and water pollution. One of the biggest hurdles for traditional photothermal membranes to function continuously in a high temperature, high salt, and corrosive environment has been attributed to their rapid decline of mechanical properties. In this work, a highly efficient solar-driven interfacial water evaporation system has been developed via a polydopamine/carbon/silicon (PCS) composite membrane supported by a floating insulation foam substrate. A 3.1 fold increase in the water vaporization rate was recorded compared with the pure water system. The 2D-carbon nanolayer on the surface was successfully prepared by carbonizing low-cost linear polyethylene with a glass fiber (GF) membrane as the substrate, and then the carbon membrane was modified with dopamine to control water transport on the carbon coating and within the glass fiber. The PCS membrane has a high efficiency for solar steam generation owing to high optical absorption and has excellent solar thermal conversion capability. The evaporation rate and solar thermal conversion efficiency of the PCS membrane under simulated sunlight irradiation with 1 sun (1 kW·m-2) are 1.39 kg·m-2·h-1 and 80.4% respectively, which are significantly higher compared to GF membrane, carbon/silicon (CS) membrane, and pure water without a photothermal membrane. The water evaporation system retained high efficiency after 20 cycles under simulated sunlight irradiation of 1 sun. This study provides critical insight on the design and fabrication of a highly efficient and durable evaporation system.

Enhancement of Photo-Thermal Conversion Performance of the Nanofluids Through Spectral Complementarity between Silver and Cesium Tungstate Oxide Nanoparticles

Nanofluids with full-spectrum absorption properties are highly desirable for direct solar thermal energy conversion applications. In this work, Ag and CsWO3 nanofluids, which exhibit absorption both in the visible and near-infrared (NIR) region, are integrated to obtain two-component hybrid nanofluids. The hybrid nanofluids show broad band absorption with a solar weighted absorption fraction of 99.6%, compared to 18% and 54% for the base liquid (ethylene glycol) and CsWO3 nanofluids, respectively. The highest photo-thermal conversion performance for the hybrid nanofluids is obtained with Ag/CsWO3 weight ratio of 3/7. The solar thermal conversion efficiency of the optimum hybrid nanofluids is 67%, 10% and 15% higher than single Ag and CsWO3 nanofluids. The two-component hybrid nanofluid provides an alternative for making the best use of solar energy.

Energy, exergy and exergoeconomic analysis of a combined cooling, desalination and power system

Ocean thermal energy has attracted much attention for its unique advantages. Multi-generation systems are emerging as an effective solution to further improve energy efficiency and economy of ocean thermal energy conversion (OTEC) system. In this paper, a novel hybrid OTEC system combing cooling, desalination and power (CCDP) is proposed facing the actual demands of remote islands at low latitudes. The cogeneration of cooling capacity, fresh water and power are achieved by the subsystems of ejector refrigeration cycle (ERC), multi-effect distillation (MED) desalination and organic Rankine cycle (ORC). A detailed mathematical model for the proposed system is developed based on the thermodynamics and exergoeconomics. The effects of key operating parameters on the system performances are investigated from the perspectives of energy, exergy and exergoeconomic. The results indicate that the highest primary energy saving ratio (PESR) and exergy efficiency of the proposed system are up to 33.72% and 29.33%, respectively. The main sources of exergy destruction are the MED unit, generator and ejector, accounting for about 80% of the total exergy destruction. The improvement of both thermodynamic and exergoeconomic performances can be achieved at a higher generation pressure and a larger distillate production. The rise of condensing pressure is conducive to cutting down the unit costs of products, but will result in lower exergy efficiency and PESR.

Building Polyoxometalate "Nano-Walls" on 3D Porous Carbon Paper: A Solar Steam Generation System for Water Purification.

As promising fresh-water purification devices, solar steam generation systems have attracted significant attention recently. However, in practice, the approach often suffers from a poor solar energy conversion efficiency and a low water production rate due to poor material selection and inefficient microscopic structure design. Here, we fabricate an efficient solar steam generation system by "building" polyoxometalate "nano-walls" on rice paper-derived three-dimensional porous carbon paper. In this solar steam generation system, the height of the vertically aligned CoP4 Mo6 "nano-walls" range from 100 to 150 nm with thicknesses about 15 to 25 nm. Under 1 sun irradiation (1 sun = 1 kW m-2 ), the surface temperature increases from 29 to 50 °C in a short time with a solar thermal conversion efficiency achieving 92.8 %. The stability and durability of this solar steam generation system, which withstands fifteen cycle continuous tests, also offer good prospects. Its attractive solar energy conversion performance originates from the intense sunlight absorption and high conversion ability of the CoP4 Mo6 "nano-walls", as well as extremely promising heat localization and water transportation properties of the three-dimensional porous carbon paper. This solar steam generation system, which has produced some inspiring results, is employed for seawater desalination and for purification of water polluted with organic dyes.

Performance and profit analysis of thermoelectric power generators mounted on channels with different cross-sectional shapes

In order to generate electric power by thermoelectricity, thermoelectric modules are mounted on peripheral surface of a channel and hot fluid moves along the inside of the channel. Despite the importance of cross-section shape on the performance of power generator, no comprehensive study has been previously performed to clarify the thermal/hydraulic characteristics of different cross-sections on thermoelectric generators. Hence, in this paper, three-dimensional numerical simulations are carried out to investigate the performance of thermoelectric generators mounted on channels with five different cross-sectional shapes. The effect of Re number, hot air inlet temperature, thermoelectric cold side temperature, and load ratio on the maximum output power, pumping power, net power and thermal conversion efficiency are studied. Results revealed that the thermoelectric generator device with a rectangular-shape channel provides the highest output power and thermal conversion efficiency. With the increase of Re number, the amount of output power and pumping power increase. However, the net power and thermal conversion efficiency improves up to a specific Re number and then diminishes. Besides, increment of hot side inlet temperature intensifies the net power and thermal conversion efficiency of all channels while the increment of cold side temperature has a minor effect on the thermal conversion efficiency of thermoelectric.

Thermoelectric power generations from vehicle exhaust gas with TiO2 nanofluid cooling

Vehicle engine efficiency is considered low by approximately 30% only. More than half of the fuel energy from the engine is lost in exhaust piping and dissipated through cooling systems. One alternative approach to increase engine efficiency is by utilizing the waste heat recovery system that emphasizes on the conversion from heat to electrical energy. This is possible with the use of a thermoelectric generator (TEG). The challenges of using a TEG in the heat exchanger application is due to its low thermal conversion efficiency and low power output. To increase the efficiency of TEG, the nanofluid cooling, specifically titanium oxide (TiO2), was introduced into the system. Nanofluids have been tested in the past in many heat exchanger applications and have shown heat transfer improvements. This study had conducted testing using a TEG set-up that connected to a vehicle exhaust system. The TiO2-water nanofluid functioned as a cooling medium to remove the heat from the TEG cold surface. Engine speed in idling conditions varied during the testing between 700 and 1500 RPMs. This project aimed to investigate and conduct an experiment on TEG power generation using waste heat from vehicle exhaust gas with TiO2-water cooling. The experiment objective was to assess the effectiveness of TiO2-water nanofluids cooling, and its effect on the TEG power output and efficiency. TiO2 has positively enhanced TEG thermal conversion and electrical power output when compared to water cooling, through various engine speeds.