Thermal Conversion Efficiency Research Articles

Conceptual design for combined ocean thermal energy conversion using computational fluid dynamics and heat balance analysis

To overcome the limited efficiency of ocean thermal energy conversion (OTEC), particularly in the mid-latitudes, combined OTEC (C-OTEC) could use power extracted from the latent heat of a power plant condenser. Past research in South Korea has demonstrated the feasibility of a 10 kW C-OTEC system using R134a as a working fluid. As the next phase, a 200 kW C-OTEC demonstration facility with a thermal efficiency of greater than 3% is proposed. This paper presents the engineering design process for kW-scale C-OTEC within a 100 MW-scale thermal power plant. The design process is divided into two stages. First, to predict patterns in steam flow to a connected external evaporator with a porous medium, computational fluid dynamics are calculated. The results show a conservative margin suitable for the conceptual design. Second, an iterative heat balance simulation method simultaneously evaluates the heat balance analysis of the C-OTEC design and the thermal impact of the existing power plant. The design stages are then integrated in terms of heat transference capacity.

Enhancing the figure of merit in thermoelectric materials by adding silicate aerogel

To achieve practical applications of thermoelectric materials in large scale, materials with high thermal conversion efficiency, low cost, and operating at a proper temperature range are required. Owing to the inversely relationship between electrical conductivity (σ) and Seebeck coefficient (S), it is a great challenge to improve high power factor (PF = σS2) of a thermoelectric material. Here, we show that by adding a small amount of silicate aerogel to existing promising materials, including Bi0.5Sb1.5Te3 (p-type), Cu0.01Bi2Te2.7Se0.3 (n-type), and p-type MgAgSb, significantly improves the figure of merit (zT) of the materials. For the BiTe-based materials, the primary gain in zT comes from a significant reduced thermal conductivity, while preserving high PF for the aerogel mixed composites. On the other hand, the enhancement of zT in aerogel-added p-type MgAg0.97Sb0.99 material is not due to the reduction in thermal conductivity but rather an enhancement in PF, which is important for practical applications. Furthermore, the materials we present in this work are bulk polycrystalline samples, which are relatively easy to produce without complicated synthesis processes.

Donor–Acceptor Charge Migration System of Superhydrophilic Covalent Triazine Framework and Carbon Nanotube toward High Performance Solar Thermal Conversion

The intrinsic hydrophobicity, deficient light absorption of solar energy, and the energy loss from the radiation relaxation of charges that decreases the solar–thermal conversion efficiency, have severely hindered the application of conjugated polymers in solar steam generation. Here, the construction of a donor–acceptor system constituted by a superhydrophilic covalent triazine framework (CTF) and carbon nanotube (CNT), which can enhance the water extraction and supply, was reported to effectively suppress the energy loss via controllable charge migration. The resulting donor–acceptor charge migration system could not only extend light harvesting but also increase energy conversion efficiency by decreasing undesired radiation relaxation, and hence it delivers a high performance in solar steam generation with a rate of 1.59 kg m–2 h–1 and a solar thermal conversion efficiency of 93.2% under 1 sun irradiation. This work provides a convenient strategy and new mechanism to improve the solar thermal conversion of the porous organic semiconductors.

Dual promoter strategy enhances co-expression of α-L-rhamnosidase and enhanced fluorescent protein for whole-cell catalysis and bioresource valorization

Developing circular economy is the only way to improve the efficiency of resource utilization. Whole-cell catalysis is an effective method to recycle enzymes, improve catalytic efficiency, and reduce production costs. The enzyme, α-L-rhamnosidase has considerable application prospects in the field of biocatalysis as it can hydrolyze a variety of α-L rhamnoses. In the present study, the genes for α-L-rhamnosidase (rhaB1) and enhanced fluorescent protein (EGFP) were co-expressed using a bi-promoter expression vector pRSFDuet1 and their enzymatic properties were evaluated. To our knowledge, this study has established an effective rhamnosidase-fluorescent indicator and whole-cell catalytic system for the first time. Moreover, we analyzed the change in the activity of the crude rhaB1-EGFP as well as its whole-cell during the biocatalysis process using fluorescence intensity. Recombinant rhaB1-EGFP as a product which contains rhaB1 and EGFP showed higher thermal stability, pH stability, and conversion efficiency than rhaB1, and its optimum temperature for rutin catalysis was ideal for industrial applications. Moreover, under the optimal conditions of a rutin concentration of 0.05 g/L, pH of 6.0, temperature of 40 °C, a yield of 92.5% was obtained. Furthermore, we demonstrated the relationship between the fluorescence intensity and enzyme activity. This study established a highly efficient whole-cell catalytic system whose activity can be evaluated by fluorescence intensity, providing a reference for enzyme recycling.

Efficient 3D-interfacial solar steam generation enabled by photothermal nanodiamonds paint-coat with optimized heat management

Photothermal materials are crucial for maximizing the solar energy in solar steam generation. The conventional photothermal materials have limited absorption broadband, complicated manufacture, expensive cost and difficulty in scaling up. To remedy this dilemma, we herein propose a novel cost-effective nanodiamonds(NDs) paint-coat using filter papers (FPs) as a supporting scaffold. The phy-chemical characterizations of samples like morphology, structure and optical properties indicate that the NDs paint-coat has bandwidth absorption, porous network structure, and high absorption ability. For the sake of evaluating their practical applications, NDs paint-coat and 3D conical structures were further designed to constitute a 3D-interfacial solar steam generation (3D-ISSG). Owing to the rationally 3D structure, the heat loss and optical loss have been effectively restrained through optimized heat management within the 3D-ISSG. The experimental results show that the solar thermal conversion efficiency of 3D-ISSG was achieved up to 82.97% for evaporation under one sun illumination (1 kW/m2), which is about 4.16 times as high as the pure water. Moreover, the 3D-ISSG performs reliable reusability after 15 cycling experiments under 1 kW/m2 solar illumination, indicating its broad application prospect for new energy devices, seawater desalination and water treatment.

Study on the Synthesis and Photothermal Conversion Property of Polyaniline

A series of polyaniline (PANI) with different HCl/aniline and DBSA/aniline molar ratio was synthesized in this paper. The structure of PANI was characterized using IR spectroscopy. The effect of pH, thermal stability and photothermal conversion properties of PANI were investigated. The results showed that the IR spectrum presented typical absorption peaks of PANI-ES. The pH had a big influence on the optical property of PANI. The PANI had high thermal stability in all HCl/aniline molar ratio. The molar ration of DBSA/aniline can influence the photothermal conversion of PANI, whereas the doped PANI showed better photo thermal conversion efficiency than that of dedoped PANI.

Enhanced thermal stability of the TiB2–ZrB2 composite ceramic based high temperature spectrally selective absorber coatings: Optical properties, failure analysis and chromaticity investigation

The long-term thermal instability and low solar-thermal conversion efficiency are challenging issues to be addressed for the solar selective absorbing coatings (SSAC). Herein, we describe a novel design for a high-performance SSAC based on TiB2–ZrB2 composite ceramic. The TiB2–ZrB2/Al2O3 coatings which deposited on stainless steel (SS) substrates exhibit a high solar-thermal conversion efficiency (η600°C = 82.6%) at 600 °C black body radiation. After annealing at 600 and 700 °C for 100 h in vacuum, the coatings exhibit a higher solar-thermal conversion efficiency of η600°C = 84.3%. Unfortunately, the η600°C decreases to 67.5% when the coating is annealed at the 800 °C for 100 h in vacuum, which is put down to oxidation of the absorbing layer, as evidenced by scanning electron microscope (SEM) and Raman spectra. In addition, the color of the coating is changed from dark blue to bright yellow during the thermal stability experiments.

Graphene Oxide-Grafted Magnetic Nanorings Mediated Magnetothermodynamic Therapy Favoring Reactive Oxygen Species-Related Immune Response for Enhanced Antitumor Efficacy.

In this study, a magnetothermodynamic (MTD) therapy is introduced as an efficient systemic cancer treatment, by combining the magnetothermal effect and the reactive oxygen species (ROS)-related immunologic effect, in order to overcome the obstacle of limited therapeutic efficacy in current magnetothermal therapy (MTT). This approach was achieved by the development of an elaborate ferrimagnetic vortex-domain iron oxide nanoring and graphene oxide (FVIOs-GO) hybrid nanoparticle as the efficient MTD agent. Such a FVIOs-GO nanoplatform was shown to have high thermal conversion efficiency, and it was further proved to generate a significantly amplified ROS level under an alternating magnetic field (AMF). Both in vitro and in vivo results revealed that amplified ROS generation was the dominant factor in provoking a strong immune response at a physiological tolerable temperature below 40 °C in a hypoxic tumor microenvironment. This was supported by the exposure of calreticulin (CRT) on 83% of the 4T1 breast cancer cell surface, direct promotion of macrophage polarization to pro-inflammatory M1 phenotypes, and further elevation of tumor-infiltrating T lymphocytes. As a result of the dual action of magnetothermal effect and ROS-related immunologic effect, impressive in vivo systemic therapeutic efficacy was attained at a low dosage of 3 mg Fe/kg with two AMF treatments, as compared to that of MTT (high dosage of 6-18 mg/kg under four to eight AMF treatments). The MTD therapy reported here has highlighted the inadequacy of conventional MTT that solely relies on the heating effect of the MNPs. Thus, by employing a ROS-mediated immunologic effect, future cancer magnetotherapies can be designed with greatly improved antitumor capabilities.

Modeling and Optimization for Gas Distribution Patterns on Biomass Gasification Performance of a Bubbling Spout Fluidized Bed

Gas distribution patterns exert a great impact on the gas–solid flow, heat and mass transfer, and reaction characteristics and thus affect significantly the thermal conversion efficiency inside the...

High energy storage efficiency and thermal stability of A‐site‐deficient and 110‐textured BaTiO3–BiScO3 thin films

AbstractThe development of thin film dielectrics having both high energy density and energy conversion efficiency, as well as good thermal stability, is necessary for practical application in high‐temperature power electronics. In addition, there is a demand for the development of new Pb‐free high‐energy density dielectric materials due to environmental concerns. In this regard, thin films of weakly coupled relaxors based on solid solutions of BaTiO3–BiMeO3 have shown good promise, because they exhibit a remarkably large polarization over a wide temperature range. Nevertheless, the performance of Pb‐free thin films has lagged behind that of their Pb‐based counterparts in terms of thermal stability and energy conversion efficiency. Toward this end, most recent studies on BaTiO3–BiMeO3 systems have focused on the optimization of material composition, while relatively less attention has been paid to other aspects such as defect chemistry and crystallographic texture. In this study, we examine the effects of A‐site vacancy and crystallographic texture on the energy storage performance of BaTiO3–BiScO3 thin films synthesized using pulsed laser deposition (PLD). It is shown that a high energy storage density (Wr) of ~28.8 J/cm3 and a high efficiency of η >90% are achieved through a combination of moderate A‐site vacancy concentration and (110) crystallographic texture. Furthermore, Wr remains nearly temperature independent while a high efficiency of η >80% is maintained for temperatures up to 200°C, which constitutes one of the best performances for Pb‐free ferroelectric films for high‐temperature capacitor applications.

Photo-Thermal Conversion Efficiency of Spectrally Selective Cr <sub>2</sub>O <sub>3</sub>/Cr/Cr <sub>2</sub>O <sub>3</sub> Multilayered Solar Absorber

Renewable energy is the alternative resource to deal with environmental problems and to satisfy the ever-increasing energy demand. Concentrating Solar Power (CSP) systems are valuable candidates to harness solar energy. CSP systems first convert solar radiation into thermal energy which is much easier and economical than storing electricity. The solar absorbing surface is the critical part of CSP systems, as it directly affects the efficiency of the solar thermal energy conversion into electricity. To achieve high conversion efficiency of incident light into heat, the solar absorber should be spectrally selective. To obtain this spectral selectivity, various designs such as absorbing semiconductor-metal tandems, composite films and multilayer interference stacks with multiple dielectric and metallic thin films have been used such as Cr2O3, Al2O3, HfO2, Ni, Cr, and Zr. However, their optical properties determine the efficiency of the energy conversion from the concentrated solar irradiation to the thermal energy recovered by the heat transfer fluid or nanofluid. This paper experimentally investigates on the photo-thermal conversion efficiency of Cr2O3/Cr/Cr2O3 multilayered selective solar absorber (SSA) deposited onto stainless steel substrates by using an electron beam physical vapor deposition technique. Interestingly, the fabricated Cr2O3/Cr/Cr2O3 SSA showed good photo-thermal conversion efficiency with a peak temperature exceeding 180 °C after an irradiation time of 2500 s; this obtained value is comparable to the performance of state-of-the-art SSA surfaces.

Energy and economic analysis of thermoelectric generator on wood fuel

The advantages of thermoelectric generator (TEG) are the absence of moving parts, reliability, long service life, the possibility of fully automatic operation without maintenance. At the same time, TEGs also have disadvantages - low efficiency and high cost. In this regard, it is advisable to use them in autonomous installations of small power, as well as in devices intended mainly for heat supply, when the low efficiency of thermal energy conversion into electrical energy does not play a role. It is the latter case that is realized in furnaces that burn biomass. In this paper, we consider the main physical effects due to which the direct conversion of thermal energy into electrical energy occurs in semiconductor thermoelements. The conjugate problem of heat and electric charge transfer with temperature-dependent properties of a semiconductor is reduced to a problem with constant properties. Based on the literature data, the boundary conditions for the TEG were selected, its sizes were optimized, current-voltage characteristics were constructed, and the maximum power and efficiency were determined. Estimates of the cost and economic efficiency of using TEG are made.

Theoretical and Experimental Evaluation of a Thermoelectric Generator Using Concentration and Thermal Energy Storage

To improve the thermoelectric conversion efficiency of solar thermoelectric power, a concentration solar thermoelectric generator (CTEG) unit based on concentrating and storing energy is designed. A Fresnel lens is used to concentrate thermal energy, and a phase change material (PCM) is used to store thermal energy to increase the temperature difference between the hot and cold ends of thermoelectric (TE) sheets. The heat stored in the PCM container will help to generate continuous solar energy at night and improve the thermal power conversion efficiency of the TEGs. The energy conversion equilibrium equation is established for the CTEG unit. By numerical calculation, we conclude that the absorption rate of the coating surface is reduced by 0.1 and the maximum thermoelectric conversion efficiency is reduced by approximately 0.4%. By selecting different heights of the heat exchanger, the unit supplies 1.025 v, 0.4204 v and 0.299 v open circuit voltages on average for approximately 30, 44 and 53 minutes, respectively. Therefore, the height of the heat exchanger affects the rate of heat energy absorption and release. The reversible operation of the CTEG-PCM unit is conducive to the day and night operation of solar power generation and is more suitable to solving the self-supplying power problem for wireless temperature sensors in forests.

Comprehensive understanding of magnetic hyperthermia for improving antitumor therapeutic efficacy.

Magnetic hyperthermia (MH) has been introduced clinically as an alternative approach for the focal treatment of tumors. MH utilizes the heat generated by the magnetic nanoparticles (MNPs) when subjected to an alternating magnetic field (AMF). It has become an important topic in the nanomedical field due to their multitudes of advantages towards effective antitumor therapy such as high biosafety, deep tissue penetration, and targeted selective tumor killing. However, in order for MH to progress and to realize its paramount potential as an alternative choice for cancer treatment, tremendous challenges have to be overcome. Thus, the efficiency of MH therapy needs enhancement. In its recent 60-year of history, the field of MH has focused primarily on heating using MNPs for therapeutic applications. Increasing the thermal conversion efficiency of MNPs is the fundamental strategy for improving therapeutic efficacy. Recently, emerging experimental evidence indicates that MNPs-MH produces nano-scale heat effects without macroscopic temperature rise. A deep understanding of the effect of this localized induction heat for the destruction of subcellular/cellular structures further supports the efficacy of MH in improving therapeutic therapy. In this review, the currently available strategies for improving the antitumor therapeutic efficacy of MNPs-MH will be discussed. Firstly, the recent advancements in engineering MNP size, composition, shape, and surface to significantly improve their energy dissipation rates will be explored. Secondly, the latest studies depicting the effect of local induction heat for selectively disrupting cells/intracellular structures will be examined. Thirdly, strategies to enhance the therapeutics by combining MH therapy with chemotherapy, radiotherapy, immunotherapy, photothermal/photodynamic therapy (PDT), and gene therapy will be reviewed. Lastly, the prospect and significant challenges in MH-based antitumor therapy will be discussed. This review is to provide a comprehensive understanding of MH for improving antitumor therapeutic efficacy, which would be of utmost benefit towards guiding the users and for the future development of MNPs-MH towards successful application in medicine.

Ultralight and highly compressible coal oxide-modified graphene aerogels for organic solvent absorption and light-to-heat conversion

Ultralight, hydrophobic, highly compressible and low-cost coal oxide-modified graphene aerogels exhibit high absorption capacity and high solar thermal conversion efficiency.

Modeling a novel combined solid oxide electrolysis cell (SOEC) - Biomass gasification renewable methanol production system

Chemical energy storage in the form of hydrogen is playing an important role in the synthesis of alternative energy carriers such as Synthetic Natural Gas (SNG), Methanol and Dimethyl ether (DME) supplementing with a carbon source. The only renewable carbon source is biomass, which is a limited resource. However, the addition of hydrogen could potentially extend the existing biomass resources. This paper describes the modeling of a novel combined Solid Oxide Electrolysis Cell (SOEC) and oxygen blown biomass gasification system using Aspen Plus. One of the advantages of using such a combined system is the use of oxygen for gasification and reforming. The comparison of reforming technologies showed that an autothermal reformer (ATR) could be an advantage since oxygen is already available from the electrolysis stack and the ATR produced syngas has a higher CO/CO2 ratio, which increases the methanol synthesis’s reaction rate. ATR requires much less energy ∼13 MW for almost complete methane conversion compared to ∼35 MW for Steam Reforming (SR). The advantage of using inter-cooled compression upstream or downstream for such a combined process has been explained. A methanol thermal conversion efficiency of 72.08% can be achieved for gasification and SOEC combined system compared to 55.7% for an only gasifier system.

Enhanced thermal stability of solar selective absorber based on nano-multilayered AlCrSiO films

Solar selective absorbers are excellent candidates to improve the solar thermal conversion efficiency. However, the absorbers with thermal stability at high working temperatures are still lacking. Here, we reported a solar selective absorber based on nano-multilayered AlCrSiO films synthesized by a cathodic arc ion plating system. The absorber, consisted of a TiN IR reflective layer, two nano-multilayered AlCrSiO films, and a top amorphous oxide AlCrSiO layer, had high absorptance of 0.923–0.927 and low emittance of 0.160–0.193. To study the high temperature thermal stability, the absorber was annealed at 600–700 °C in air for 200 h. The variations in the optical performances and microstructures of the annealed absorber were characterized by UV–Vis-near IR spectrophotometer, FTIR, TEM, SEM, EDS, XRD, and Raman. The results indicated that the absorber had a thermal stability with a selectivity of 0.923/0.161 up to 650 °C in air for 200 h. The nano-multilayered structure of AlCrSiO films was highly stable when annealed at 650 °C. The amorphous AlCrSiO layer could form a dense oxide layer capping on the absorber surface, effectively limiting the oxygen diffusion into the inter absorber. Therefore, the AlCrSiO-based solar selective absorber with excellent thermal stability could be possibly applied to high temperature solar thermal conversion.

Combined Modality Therapy Based on Hybrid Gold Nanostars Coated with Temperature Sensitive Liposomes to Overcome Paclitaxel-Resistance in Hepatic Carcinoma.

In this study, we prepared gold nanostar (GNS) composite nanoparticles containing siRNA of cyclooxygenase-2(siCOX-2) that were modified by tumor targeting ligand 2-deoxyglucose (DG) and transmembrane peptide 9-poly-D-arginine (9R) to form siCOX-2(9R/DG-GNS). Paclitaxel loaded temperature sensitive liposomes (PTX-TSL) were surface-modified to produce PTX-TSL-siCOX-2(9R/DG-GNS) displaying homogeneous star-shaped structures of suitable size (293.93 nm ± 3.21) and zeta potentials (2.47 mV ± 0.22). PTX-TSL-siCOX-2(9R/DG-GNS) had a high thermal conversion efficiency under 808 nm laser radiation and a superior transfection efficiency, which may be related to the targeting effects of DG and increased heat induced membrane permeability. COX-2 expression in HepG2/PTX cells was significantly suppressed by PTX-TSL-siCOX-2(9R/DG-GNS) in high temperatures. The co-delivery system inhibited drug-resistant cell growth rates by ≥77% and increased the cell apoptosis rate about 47% at elevated temperatures. PTX-TSL and siCOX-2 loaded gold nanostar particles, therefore, show promise for overcoming tumor resistance.

Evaluation of photothermal properties for absorption of solar energy by Co3O4 nanofluids synthesized using endophytic fungus Aspergillus nidulans

An attempt has been made to compare the optical properties of cobalt oxide (Co3O4) nanoparticles using experimental values and theoretical predictions. Optical transmittance of the nanoparticles obtained was higher than 65% in 550–850 nm containing visible spectrum and the experimental results were in accordance with the predictive datum. The absorption coefficient peak observed is close to the predictive value and is present in the visible region of the light. In addition, there was an excellent agreement between theoretical and experimental results in extinction coefficient and refractive index. Besides, this work proposes and validates a novel idea of using Co3O4 nanofluids to enhance solar thermal conversion efficiency. Co3O4 nanofluids synthesized using endophytic fungus Aspergillus nidulans isolated from a medicinal plant, Nothapodytes foetida has been used to illustrate the energy storage capacity of nanofluids. Experimental results reveal that Co3O4 nanofluids have good specific absorption rate (SAR) and better photo-thermal conversion efficiency than water. Nanofluid exhibited a greater temperature gradient than pure water, which is desired. Thus the good absorption ability of Co3O4 nanofluids for solar energy indicated that it is suitable for direct absorption solar thermal energy systems.

Photovoltaic-thermal (PVT) technology: Review and case study

Nowadays, solar technology converts solar energy into electricity and heat separately. For electricity generation, the main obstacle is the fact that the photovoltaic cells produce less energy as the temperature increases. To overcome this, cooling techniques can be used to raise the efficiency of solar cells, in order to obtain greater power generation. The photovoltaic-thermal hybrid solar collector (or PVT) is an equipment that integrates a photovoltaic (PV) module, for the conversion of solar energy into electrical energy, and a module with high thermal conversion efficiency (T), which employs a thermal fluid. This optimization of solar conversion technology has the main objective of cooling the photovoltaic cells, for increased generation of electricity, while also resulting in useful thermal energy from the working fluid, therefore constituting a cogeneration equipment. The present work reviews the development and global panorama of PVT technology. Afterwards, a case study of a PVT system is presented, together with a theoretical and experimental study. A thermography analysis performed in this PVT system is also examined, which allows for a real-time study of its operating regimes in different conditions, mainly of its thermal behaviour, and for the diagnosis of hot spots that signal potential defects in the cells.