Thermal Energy Conversion Efficiency Research Articles

A facile method to prepare transparent and stretchable epidermal thin film heaters

A stretchable and semi-transparent epidermal thin film heater (TFH) has been fabricated by using silver nanowire (Ag NW) networks as a Joule heat generator and polydimethylsiloxane (PDMS) as a stretchable and transparent matrix. The device is a conductive layer of interconnected Ag NWs sandwiched with two layers of PDMS. The output power and transparency of the device were rationally tuned by adjusting the Ag NW amount. Our results show that the device transparency at 600 nm decreases from 70% to 46% when we tuned the sheet resistance of Ag NW layer from 30.0 Ω/□ to 5.4 Ω/□. The TFH shows a favorable stretchability, and it can almost completely recover when we applied a strain up to 200% or after a fatigue test of 1000 cycles, 50% in strain. The ultimate temperature in air reached up to 81 °C when we applied an electric field of 1.0 V/cm. Its epidermal heating performance was simulated by warming a piece of pork, and it can make the subcutaneous temperature increase 12 °C. A model to evaluate the heating performance of TFHs with thermal capacity per-unit area, device resistance and energy conversion efficiency was also proposed, which will fatally determine their heating rate and ultimate temperature.

Fabrication and Investigation of Photovoltaic Converters Based on Polycrystalline Silicon Grown on Borosilicate Glass

The microcrystalline Si layers with grain sizes of up to several tens of micrometers were grown. The physical vapor deposition (PVD), amorphous–liquid–crystalline (ALC) transition technique and a steady-state liquid phase epitaxy (SSLPE) are used for the fabrication of three different samples. The first sample under consideration was prepared first by deposition of a-Si onto glass substrates by PVD at room temperature, followed by heating from the front side to ~300°C and deposition of an indium metallic solvent. At the preparation of the second sample, an additional silicon layer with the thickness of 400 nm was deposited. A sample, when after that a c-Si was grown on the seed layer by SSLPE from indium solution is referred as a third sample. The resulting samples have a strong absorption edge in the mid-infrared region around 1960 cm−1. Six well-resolved oscillations with an average period of δB = 0.1214 T are revealed on the third sample’s magnetoresistance curve at gradually increasing of the magnetic field from zero up to 1.6 T. It is assumed that either Aharonov–Bohm effect or kinetic phenomena taking place in the grains boundaries at lateral current flow are responsible for those oscillations. Quantitative evaluations show that due to the strong absorption in mid-infrared region, enlargement of the photoresponse spectrum will occur and the efficiency of solar and other thermal energy conversion should be around ~10–15% higher than that of traditional PV cells based on silicon on glass structures.

The Experimental Study of Rankine Cycle in Ocean Thermal Energy Conversion

For the purpose of studying the influence of evaporation temperature on system efficiency and turbine efficiency of ocean thermal energy conversion (OTEC) Rankine cycle in different temperature differences. The 15kW OTEC experiment system has been designed and built. By maintaining hot seawater and turbine parameters, OTEC Rankine cycle has been experimentally studied. The results showed that the system efficiency and turbine efficiency increase with the increase of seawater temperature difference, and when the temperature difference is 19.7°C, matching the design conditions: turbine efficiency is 73%, output power is 15kW. The system efficiency and turbine efficiency show a tendency of rising first and then decreasing with the increase of evaporating temperature at given temperature difference.

On the Flow Stability in a Circular Cylinder based Open Volumetric Air Receiver for Solar Convective Furnace

The arid desert regions are considered for installing the concentrated solar thermal based systems owing to the available direct normal irradiance. For process heat applications, like the solar convective furnace that requires an air temperature of 750 K the open volumetric air receiver is preferred. Such innovative concepts are envisaged for achieving high thermal energy conversion efficiency. For the prolonged operation of the solar convective furnace system the stable flow is necessary. On the other hand, the thermally induced flow instability is reported in the open volumetric air receivers at a high temperature. This may limit the operating temperature range of a receiver. In this paper the flow stability analysis in a circular cylinder based open volumetric air receiver with the straight pores is presented. The findings allow expecting a stable flow regime in such an absorber pore at a high flux concentration and temperature.

Optical absorption of carbon-gold core-shell nanoparticles

In order to enhance the solar thermal energy conversion efficiency, we propose to use carbon-gold core-shell nanoparticles dispersed in liquid water. This work demonstrates theoretically that an absorbing carbon (C) core enclosed in a plasmonic gold (Au) nanoshell can enhance the absorption peak while broadening the absorption band; giving rise to a much higher solar absorption than most previously studied core-shell combinations. The exact Mie solution is used to evaluate the absorption efficiency factor of spherical nanoparticles in the wavelength region from 300 nm to 1100 nm as well as the electric field and power dissipation profiles inside the nanoparticles at specified wavelengths (mostly at the localized surface plasmon resonance wavelength). The field enhancement by the localized plasmons at the gold surfaces boosts the absorption of the carbon particle, resulting in a redshift of the absorption peak with increased peak height and bandwidth. In addition to spherical nanoparticles, we use the finite-difference time-domain method to calculate the absorption of cubic core-shell nanoparticles. Even stronger enhancement can be achieved with cubic C-Au core-shell structures due to the localized plasmonic resonances at the sharp edges of the Au shell. The solar absorption efficiency factor can exceed 1.5 in the spherical case and reach 2.3 in the cubic case with a shell thickness of 10 nm. Such broadband absorption enhancement is in great demand for solar thermal applications including steam generation.

Preliminary design and performance analysis of a radial inflow turbine for ocean thermal energy conversion

Ocean thermal energy conversion is an organic Rankine cycle for generating power using the temperature difference between surface seawater and deep seawater. The potential of ocean thermal energy is significant, and it is an environmentally friendly power system. However, its thermal efficiency is very low due to the low temperature difference between surface seawater and deep seawater. Hence, it is essential to develop a high efficiency turbine in order to improve the thermal efficiency of ocean thermal energy conversion. The precise preliminary design for the high efficiency radial inflow turbine requires selection of the appropriate flow and loading coefficients for the target efficiency. A new approach for the appropriate choice of flow and loading coefficients is proposed in this study. The meanline analysis and three-dimensional viscous simulations for the designed turbine are conducted in order to verify the proposed approach in design and off-design conditions. The results demonstrate that the optimum radial inflow turbine for the design conditions can be designed through applying the proposed model.

Build and Test Research of a Coaxial Hybrid-power Gas Engine Heat Pump System Based on LiFePO4 Battery

Power batteries of hybrid-power gas engine heat pump (HPGHP) often encounter frequent charge and discharge operations, which have an adverse effect on nature gas conversion efficiency of system. In order to improve the dynamic efficiency and economic performance of HPGHP, this paper raises a coaxial HPGHP facility, which takes the LiFePO4 battery as the auxiliary power source to drive the compressor. Logic threshold control strategy is put forward to distribute power between the gas engine and battery pack. Test research was operated to verify the advantageous performance of LiFePO4 battery HPGHP. The results show that LiFePO4 battery HPGHP can achieve an obvious energy saving effect, especially in low-load condition and high-load condition. When compressor speed increases from700rpm to 2500rpm, COP decreases from 4.76 to 3.25, heating capacity increases from 14.52 to 33.13kW. The maximum difference of LiFePO4 battery HPGHP and lead-acid battery HPGHP is respectively 13.2%, 11.28% and 10.2% separately for engine thermal efficiency, gas-consumed rate, and energy conversion efficiency under the same load. In addition, reclaimed heat is tested and the result shows that LiFePO4 battery HPGHP is 11.82% lower than conventional nature gas heat pump (GHP).

Experimental research and performance study of a coaxial hybrid-power gas engine heat pump system based on LiFePO4 battery

Power batteries of hybrid-power gas engine heat pump (HPGHP) often encounter instantaneous power demand. Due to working modes switching caused by the frequent variation of external load, the batteries tend to perform frequent charge and discharge operations, which has an adverse effect on energy conversion efficiency of system. In order to improve the dynamic efficiency and economical performance of HPGHP, this paper raises a novel HPGHP system, which takes the LiFePO4 battery as the auxiliary power source to drive the compressor. Logic threshold control strategy is put forward to distribute power between the gas engine and battery pack. Test research on COP, heating capacity, engine thermal efficiency, fuel-consumed rate, energy conversion efficiency and reclaimed heat have been operated to verify the advantageous performance of LiFePO4 battery HPGHP. The results show that LiFePO4 battery HPGHP can achieve an obvious energy saving effect, especially in low-load condition and high-load condition. When compressor speed increases from700rpm to 2500rpm, COP decreases from 4.76 to 3.25, heating capacity increases from 14.52 to 33.13kW. Compared with lead-acid battery HPGHP under the same load, LiFePO4 battery HPGHP shows better performance. Engine thermal efficiency and energy conversion efficiency of LiFePO4 battery HPGHP are higher than those of lead-acid battery HPGHP, and fuel-consumed rate is lower. The maximum differences of engine thermal efficiency, energy conversion efficiency, fuel-consumed rate are 13.2%, 10.2% and 11.28%, respectively. In addition, reclaimed heat is also tested and the result shows that LiFePO4 battery HPGHP is 11.82% lower than conventional GHP.

Integrating Domestic Air Conditioner with Solar Water Heater of the Development of an Energy-Saving Heating System

The current thesis proposed the integration of air conditioners that exhaust heat with solar energy to enhance the overall efficiency of thermal energy conversion. The analysis of thermal storage tanks of different volumes revealed that a two-ton air conditioner operating for an hour produced double energy than normal sunshine for a day. With thermal storage tanks of fixed volume, the integration of air conditioners of different tons with solar energy indicated that air conditioners of less tons produced faster and more efficient energy conversion. Therefore, the current thesis proposed that the modification of condenser in domestic air conditioner into water-cooled condenser not only enhanced the energy efficiency of air conditioners but also increased hot water supplies since hot water from air conditioners could be integrated into solar water heaters. By doing so, energy conservation and carbon reduction could be achieved.

The efficiency of thermal energy conversion into electricity by means of the thermovoltaic effect

The efficiency of thermal energy conversion into electricity based on the thermovoltaic effect has been studied. Experiments were performed on samarium sulfide (SmS) samples containing a region doped with excess samarium up to Sm1.04S. The conversion efficiency increases with time from 17 to 36% due to a decrease in the amount of absorbed thermal energy at unchanged power of the generated electric energy.

Study of relationship between temperature and thermal energy, operating conditions as well as environmental factors in large-scale lithium-ion batteries

SUMMARY We have developed a thermal model for a large-scale lithium-ion cell and have simulated its thermal behaviors during charge, discharge, and charge–discharge cycles with different current rates by using the software of COMSOL Multiphysics 3.5a. In this work, thermal energy and its distribution were firstly calculated based on experimental data under different operating conditions. A new parameter, called thermal energy conversion efficiency, was proposed to describe relative value of thermal energy in the cell. The thermal energy conversion efficiency and the temperature were plotted in a figure to show their relativity. The temperature variation was also studied systemically when the cell underwent discharge–charge cycles. A low rate charge is validated to be a favorable factor in protecting the cell from overheating during charge–discharge cycles. A connection resistance is proved to be a main factor that accelerates the rise of temperature in the spot near a terminal column, which should be eliminated as much as possible to protect the cell from local overheating. Copyright © 2014 John Wiley & Sons, Ltd.

Efficiency comparison of subcritical OTEC power cycle using various working fluids

This paper presents an investigation into the thermal efficiency and main component size of the subcritical ocean thermal energy conversion (OTEC) power cycle using various working fluids under different operation conditions. The analysis procedure was performed with a simulation program written in Engineering Equation Solver. With the given analysis conditions, efficiencies of three types of working fluids were evaluated and compared. It was found that the thermal efficiencies of the subcritical OTEC power cycle depend strongly on the evaporating and condensing temperature, and turbine efficiency, while not roughly depending on superheating degrees and pump efficiencies. With a thorough grasp of these results, an efficient OTEC power cycle can be designed. R717 and R404A yielded the highest and lowest thermal efficiencies among the wet fluids, and R22 showed the largest efficiency among the dry fluids. For the iso-entropic fluids, R245fa provided the highest thermal efficiency. In comparison of main component sizes, R404A and R744 had the largest and smallest condenser size, respectively. Also, R744 exhibited the smallest evaporator size, and R404A and R227ea show the largest size. And R744 and R245fa gave the largest and smallest pump size, respectively. From the results of thermal efficiency and main components for various working fluids in the OTEC power cycle, R717 in the subcritical OTEC power cycle is the preferred working fluid, except for its toxicity and flammability.

Thermal Load based Adaptive Tracking for Flat Plate Solar Collectors

The energy output of solar-thermal systems using flat plate collectors can be improved by tracking. Tracking is well known as a path for increasing the amount of solar radiation received by the collector; additionally the paper proposes a new concept that considers the inverse tracking as a viable option for protecting the collectors against overheating. An analysis of the thermal energy output and conversion efficiency is done considering forward tracking in three different days with different radiation profile (cloudy, sunny and mixed days), followed by an analysis of the inverse tracking concept. The in-field data show that there is a limiting angle below which inverse tracking is not effective and this value is estimated at 40° as compared with the optimal orientation. A logical scheme is proposed based on four different programs for forward tracking, inverse tracking, maximum inverse tracking or fixing the collector; this decisional scheme covers a broad range of functional situations having as central concept the production of thermal energy only when needed, for satisfying the demand, decreasing the energy consumption for forced circulation and supporting the systems reliability and safety.

Novel Mo–Si3N4 based selective coating for high temperature concentrating solar power applications

A novel selective coating material based on Mo–Si3N4 has been investigated for the first time. Accurate combination of the individual component layers based on optical simulations and precise control of layers thickness and composition leads to high solar absorptivity (αSol=0.926) and low thermal emissivity (ε25°C=0.017) on a silver film, resulting in a high solar thermal energy conversion efficiency. The tandem absorber is stable in moderate vacuum at temperatures above 600°C showing low emissivity (estimated value at 600°C is ε600°C=0.109) evidencing its relevance for high temperature solar selective applications. A full optical and thermal analysis of a parabolic trough concentrator (PTC) system confirmed the potential of the novel coating material to be used for CSP technology.

온배수를 이용한 혼합냉매용 해양온도차 발전 사이클의 성능 특성

In this paper, the performance analysis for evaporation capacity, total work and efficiency of the ocean thermal energy conversion(OTEC) power system using mixed refrigerant(R32,R152a) is conducted to find the effect of hot wasted water on OTEC power system. The system in this study is applied with two stage turbine, regenerator, cooler and separator on Organic Rankine Cycle. The commercial program HYSYS is used for the performance analysis. The main results were summarized as follows : The efficiency of the OTEC power cycle has a largely effect on the evaporation capacity and total work. As increasing temperature of heat source water, evaporator's capacity is decreased but total work increase. Otherwise, using hot wasted water bring effects not only increasing system efficiency but also declining evaporator's capacity. Thus With a thorough grasp of these effect, it is necessary to find way to use hot wasted water emitted by power plant and so on.

Diffusion Combustion Characteristics of H<sub>2</sub>/Air in the Micro Porous Media Combustor

In order to improve thermal to-electric energy conversion efficiency of the micro gas turbine power generation system, a novel micro porous media combustor is designed and experimental investigation on the H2/air diffusion combustion is performed to obtain its combustion characteristics. High efficiency diffusion combustion of H2/air can be stabilized in the very wide operating range, especially at higher excess air ratio. Exhaust gas temperature is markedly improved and meanwhile heat loss ratio is evidently decreased. Moreover, in the certain operating ranges, the greater the combustion thermal power and excess air ratio, the smaller heat loss of the micro combustor will be. The micro porous media combustor should be a preferred micro combustor for developing the micro gas turbine power generation system.

폐쇄형 해양온도차발전 사이클 효율 향상 방안

본 연구에서는 폐쇄형 해양온도차발전 효율 향상 방안으로 재열기, 재생기 및 다단 터빈을 적용하여 각 사이클 성능을 비교·분석하였다. 기화기 증발 열원으로 26℃의 해양표층수를 이용하고 응축기 냉각 열원으로 5℃의 해양심층수를 이용하는 것으로 가정하였고, 작동유체로는 암모니아를 적용하였다. 3가지 효율 향상 방안에 대한 사이클 효율, 응축기 및 증발기 용량 등 사이클 성능을 비교·분석하였다. 기본 폐쇄형 해양온도차발전 사이클에 재생기를 적용하기 위해서 사이클 시뮬레이션을 수행한 결과, 재생기부착을 위한 열교환 라인은 터빈 출구 작동유체와 펌프 출구의 작동유체를 열교환하는 것이 사이클 효율향상에 기여하는 것으로 나타났다. 또한, 기본 사이클에 유용도 0.9의 재열기를 적용한 결과, 터빈 2기를 적용시 사이클 효율이 3.14%로 증가하였고, 동일 총 출력에 대해서 응축기 및 증발기에 필요한 해양표층수 및 해양심층수량이 감소하였다. 사이클 성능 향상 방안으로 기본적인 폐쇄형 해양온도차발전 사이클에 재생기, 재열기 및 터빈 2기를 적용한 결과 기본 폐쇄형 해양온도차발전 사이클에 비해 효율은 약 6.5% 향상되었다.

The DOE advanced gas reactor fuel development and qualification program

The high outlet temperatures and high thermal-energy conversion efficiency of modular high-temperature gas-cooled reactors (HTGRs) enable an efficient and cost-effective integration of the reactor system with non-electricity-generation applications, such as process heat and/or hydrogen production, for the many petrochemical and other industrial processes that require temperatures between 300°C and 900°C. The U.S. Department of Energy (DOE) has selected the HTGR concept for the Next Generation Nuclear Plant (NGNP) Project as a transformative application of nuclear energy that will demonstrate emissions-free nuclear-assisted electricity, process heat, and hydrogen production, thereby reducing greenhouse-gas emissions and enhancing energy security. The objective of the DOE Advanced Gas Reactor (AGR) Fuel Development and Qualification program is to qualify tristructural isotropic (TRISO)-coated particle fuel for use in HTGRs. An overview of the program and recent progress is presented.

Design and operation of integrated pilot-scale dimethyl ether synthesis system via pyrolysis/gasification of corncob

The integrated pilot-scale dimethyl ether (DME) synthesis system from corncob was demonstrated for modernizing utilization of biomass residues. The raw bio-syngas was obtained by the pyrolyzer/gasifier at the yield rate of 40–45 Nm 3/h. The content of tar in the raw bio-syngas was decreased to less than 20 mg/Nm 3 by high temperature gasification of the pyrolysates under O 2-rich air. More than 70% CO 2 in the raw bio-syngas was removed by pressure-swing adsorption unit (PSA). The bio-syngas (H 2/CO ≈ 1) was catalytically converted to DME in the fixed-bed tubular reactor directly over Cu/Zn/Al/HZSM-5 catalysts. CO conversion and space–time yield of DME were in the range of 82.0–73.6% and 124.3–203.8 kg/m cat 3/h, respectively, with a similar DME selectivity when gas hourly space velocity (GHSV, volumetric flow rate of syngas at STP divided by the volume of catalyst) increased from 650 h −1 to 1500 h −1 at 260 °C and 4.3 MPa. And the selectivity to methanol and C 2 + products was less than 0.65% under typical synthesis condition. The thermal energy conversion efficiency was ca. 32.0% and about 16.4% carbon in dried corncob was essentially converted to DME with the production cost of ca. ¥ 3737/ton DME. Cu (1 1 1) was assumed to be the active phase for DME synthesis, confirmed by X-ray diffraction (XRD) characterization.

Future Zero Emission Carbon Technology—Valuation and Policy Issues

Today, coal-fired power plants produce about 51 percent of the total 3,883 billion kWh of the annual electrical energy output in the U.S. Demand for electricity is expected to grow in the future. Coal can and will continue to play a substantial role in the future global energy supply, despite its high emission of CO 2 and low thermal energy conversion efficiency of about 37 percent. This is due to the fact that it is inexpensive and global reserves are abundant. Furthermore, cost-competitive and environmentally acceptable energy alternatives are lacking. New technologies could also make coal-fired power plants more efficient and environmentally benign. One such technology is the zero emission coal (ZEC) power plant. How much will such a technology cost? How competitive will it be in the electric energy market when used as a technology for mitigating CO 2 emissions? If there were regulatory mechanisms such as a carbon tax to regulate CO 2 emission, what would the minimum carbon tax be that should be imposed? This article introduces an economic model that can be used to analyze and assess the economic viability of the ZEC technology vis-a-vis other competing energy generating technologies, e.g. conventional coal-fired, combined-cycle gas turbine, and nuclear power plants, using valuation techniques employed in the electric energy industry such as revenue requirement (e.g. cost-of-service).