Comprehensive numerical investigations on the thermal performance of heat recirculating micro combustor with pin fins for micro-thermal voltaic system applications

Aiming at improving the relatively low energy output and energy conversion efficiency of the micro-thermal voltaic (MTPV) system, an innovative heat recirculating micro combustor with pin fins is designed. The effects of pin fins arrangement, hydrogen/air equivalent ratio on the energy output and performance of CHMC, HMCP and HMCI are compared and investigated. The result shows that when the V_in is 6 m/s and Φ is 1.0, the emitter power of CHMC is 72.76W, and that of HCMP and HCMI micro combustor are 75.99W and 76.35W. and the emitter efficiency of CHMC, HCMP and HCMI is 41.93%, 43.26% and 44.01%. HMCI has better energy output capability compared with CHMC and HMCP. Even though, HMCI brings a higher pressure drop, it is within the acceptable range. When the V_in is 6 m/s, the pressure drop from the pin fins only accounts for 26.4% of the total pressure drop for HMCI. Through the study of equivalent ratio, it is found that HMCI has good adaptability in different equivalent ratio range. This work provides new ideas for the development of MTPV system in the future.     

Enhancement of thermal performance by converging-diverging channel in a micro tube combustor fueled by premixed hydrogen/air

As the core component of the micro thermophotovoltaic (MTPV) system, the micro combustor with a high and uniform wall temperature distribution is beneficial to improve the energy conversion efficiency. In this paper, a micro tube combustor with converging-diverging channel is proposed and the thermal performance is numerically investigated, compared with that of the micro combustor with cylindrical channel. The effects of inlet velocity of H₂/air mixture, dimensionless position and diameter of throat, and solid material on the thermal performance are widely analyzed. Results show that the outer wall temperature and emitter efficiency of the micro combustor with converging-diverging channel are higher than that of the micro combustor with cylindrical channel, and the converging-diverging channel has more uniform temperature distribution. The converging-diverging micro combustor with dimensionless throat position l = 0.375 and dimensionless throat diameter β = 0.4 is more suitable for the application of MTPV system. When H₂/air inlet velocity is 11 m/s and H₂/air equivalence ratio is 1.0, the mean wall temperature is increased by 82.39 K and the emitter efficiency is increased by 6.59%, while the normalized temperature standard deviation is reduced by 65.85%. Additionally, the use of SiC as wall material can improve the thermal performance of the micro combustor. It is worth noting that this work will offer us significant guidelines for the optimized work of micro tube combustor.     

Microthermophotovoltaic power generator with high power density

A promising energy source for portable MEMS devices, microthermophotovoltaic (micro-TPV) power generator, is described in this paper. The system mainly consists of a micro SiC combustor, and a GaSb photovoltaic (PV) cell array and a simple nine-layer dielectric filter, with a volume of about 3.1 cm³. When the flow rate of H₂ is 4.2 g/h, and H₂/O₂ ratio is 0.7, the system is able to deliver 3.06 W electrical power, the open-circuit voltage and short-circuit current are 2.31 V and 1.74 A, respectively, the result is a power density of about 1.0 W/cm³ (1 MW/m³). The effect of all kinds of factors on the performance of the micro-TPV system is also discussed in this paper.     

Exergy analysis and NOx emission of the H2-fueled micro burner with slinky projection shape channel for micro-thermophotovoltaic system

In order to improve the energy output of the MTPV system and reducing the NO_x emission, a novel micro burner with a slinky projection shape channel for the MTPV system is proposed. To conduct the numerical simulation, 3-D models with detailed H₂/air reaction mechanisms and the extended Zeldovich mechanism of NO_x generation are employed. The influence of the slinky projection amplitude, slinky projection fins number, and the basic oscillating channel radius on the energy conversion characteristics and the NOx emission is investigated. The increase of the slinky projection amplitude and slinky projection fins number can improve the energy output and exergy efficiency, as well as reduce the NOx emission. When the slinky projection amplitude is 0.4 mm and the slinky projection fins number is 42, the exergy efficiency reaches the maximum value of 70.3%, while the energy output of MTPV reaches the maximum value of 4.99 W at 10 m/s. Meanwhile, the decrease of the basic oscillating channel radius can significantly decrease the NO mole fraction at the outlet. Generally, an efficient technique to increase energy output and reduce NOx emission for the MTPV system is to introduce a micro burner with a slinky projection shape channel.     

微热光电系统燃烧器辐射光谱分析及温度预测

通过实验,测量出SiC和Al2O3两种不同材质的微燃烧器在不同温度下的光谱辐射曲线。比较分析各影响因素不变时外壁面的辐射能谱。结果表明:GaSb电池高效接受光电子的波长范围内,Al2O3材质的微型燃烧器在其能够达到的温度范围对提高微型热光电系统的热电转化效率有更为明显的作用,而这个温度界限通过实验很难确定。根据自身"小样本,贫信息"的特点,采用灰色理论建立灰色预测模型并得出温度在1 418K内,Al2O3的Eλ0-1.7较SiC更高。     

Experimental analysis of cell output performance for a TPV system

The experimental U-I characteristics of a single GaSb cell, a single Si cell and their modules in a TPV system using a SiC radiator were investigated. The influence of the radiator temperature and the radiator-cell distance on the output performances of a single cell and its module was analyzed. The results demonstrate that increasing the radiator temperature or decreasing the radiator-cell distance both lead to the increasing the short-circuit current density and the output power density, but the open-circuit voltage decreases because of the rise of the cell temperature. The maximum output power densities of a single GaSb cell and the corresponding module are 0.26 and 0.28 W/cm², respectively, which are approximately 4.3 and 6.0 times that of a single Si cell and its module for a combustion power of 4.2 kW and a radiator-cell distance of 1.1 cm. Furthermore, a mathematical physical model was constructed to analyze the influence of the cell temperature on the output performance of the cells. For a given radiator temperature and radiator-cell distance, the theoretical results indicate that the output power density decreases with cell temperature because of attenuation of the open-circuit voltage.     

Micropower source based on piezoelectric polymers

Abstract

Abstract

Parasitic harvesting of energy from environment is being investigated as a possible solution for powering electronic devices. One possible solution is to harvest energy generated from human walking, by placing a piezoelectric elements inside footwear. As the amount of available energy is extremely low, conversion effectiveness is of prime importance. This paper deals with a micropower source, designed to harvest energy from walking, built in a form of a shoe insole containing a piezoelectric material (43?μm thick polyethylene foil). Laboratory investigation of the piezoelectric properties is presented first, followed by a measurement result of an actual generator with 0·6?μW output power. Finally, a modification of the generator, by adding springy elements, is presented, resulting in ninefold increase in power output (to 5·6?μW).     

Low carbon ultrasonic production of alternate fuel: Operational and mechanistic concerns of the sonochemical process of hydrogen generation under various scenarios

Sonochemistry is considered as one of the cleaner pathways for hydrogen production. The present paper investigates the potential of this technique based upon mass, mass to energy and energy conversion metrics, using modelling and experimental approaches. Four scenarios are examined assuming four saturating gases, namely O₂, air, N₂ and Ar, four acoustic frequencies, i.e., 20, 210, 326 and 488 kHz, and considering common acoustic intensities then common net electric power. The study revealed that Ar is the best fitting saturating gas for the sonochemical production of hydrogen. With a common acoustic intensity of 0.48 W/cm², an optimum ratio of H₂ molar yield to acoustic energy intensity is retrieved at 210 kHz, while with a common net electric power of 87 W, the highest ratio of hydrogen yield to electric energy was observed at 20 kHz. Results were interpreted based upon emitter surface, energy conversion and distinction of calorimetric and cavitational energies.     

A miniaturized power generation system cascade utilizing thermal energy of a micro-combustor: Design and modelling

Currently, combustion-based micro power devices encounter the problem of low conversion efficiency. A miniaturized power generation system cascade utilizing thermal energy of a micro-combustor is proposed, because thermophotovoltaic (TPV) cells and thermoelectric (TE) modules work at different temperature levels. The system consists of a planar micro-combustor with a bended extension at the exit, two GaSb TPV modules to convert high temperature thermal radiation and two Bi–Te based TE modules attached to the bended extension to harness medium temperature thermal energy. The mathematical modelling approach to quantify the power output and conversion efficiency is systematically presented. The modelling results show that the integration of the TE modules could significantly improve the system efficiency. When burning the H₂/air mixture, the overall system efficiency could reach 2.5% under the flow condition of U₀ = 3 m/s and Φ = 1.0. Finally, measures for better thermal management to further enhance the conversion efficiency are discussed.     

Radiant thermal conversion in 0.53 eV GaInAsSb thermophotovoltaic diode

Based on the developed analytical absorption model for 0.53 eV GaInAsSb alloy and the suggested material parameters, evaluating active layer controlled thermal conversion has been systematically done for both p-on-n and n-on-p configuration in its normal and inverted construction. A universal, spectrum-insensitive optimal doping, N_a(d) = 3 × 10¹⁷ cm⁻³, is observed in diode light-doped layer for all concerned configurations. By improving the doping in the light-doped layer, thickness compensation between emitter and base has been observed for normal structures and, for each considered structure, suboptimal structures can be employed by consuming less material to achieve comparable output as that for optimal one. Comparing to GaSb diode, 2–3 fold efficiency enhancement can be expected for low-temperature spectrum illumination, making the concerned device an efficient candidate for low-temperature TPV applications.     

Use of Anionic Micelles in Photogalvanic Cells for Solar Energy Conversion and Storage Dioctylsulfosuccinate-mannitol-safranine System

Abstract

The photogalvanic cell containing dioctylsulfosuccinate micellar species, mannitol as an electron donar and safranine as photosensitizer has been used for solar energy conversion and storage. The electrical output of the cell was 870.0 mV as photopotential 150.0 μA as photocurrent and 130.5 μW as power at power point of the cell. The current voltage characteristics of the cell have been studied, and observed conversion efficiency was 0.7603%; determine fill factor was 0.50. The performance of the cell in dark was 40.0 minutes.     

Performance of low bandgap thermophotovoltaic cells in a small cogeneration system

In recent years there has been significant progress in fabrication of low bandgap thermophotovoltaic (TPV) devices, such as InGaAsSb, InGaAs and GaSb cells. However, only limited data are available in the literature with respect to the performance of these TPV cells in combustion-driven radiant sources. In this study, power generation using InGaAsSb TPV cells has been investigated in a gas-fired home heating furnace. The radiant power density and radiant efficiency of a gas-heated radiator were determined at different degrees of exhaust heat recuperation. Heat recuperation is shown to have a certain effect on combustion operation and radiant power output. The electric output characteristics of the InGaAsSb TPV devices were investigated under various operating conditions. An electric power density of 5.4×10³ W m⁻² was produced at a radiator temperature of 1463 K for the small cogeneration system. The cell short circuit density was observed to be greater than 1×10⁴ A m⁻² at a radiator temperature of 1203 K. Furthermore, the design aspects of combustion-driven TPV systems have been discussed. It is shown that development of a special combustion device with high conversion level of fuel chemical energy to useful radiant energy is required, to improve further the system efficiency.     

Numerical simulation model by volume averaging for the dissolution process of GaSb into InSb in a sandwich system

ABSTRACT

The volume-averaging continuum technique has been utilized to obtain numerical predictions for the transport phenomena occurring during the dissolution process of GaSb into InSb melt in a sandwich system. Dissolution and subsequent growth in this system are achieved by the application of a temperature gradient. The developed model was first verified for two test cases [(i) fluid/solid conjugate heat transfer and (ii) the solidification process of the binary system]. The code was then utilized to simulate the dissolution process of GaSb into InSb in the GaSb/InSb/GaSb sandwich system. The present results show that the developed volume-averaging model provides accurate predictions.     

Fabrication and simulation of GaSb thermophotovoltaic cells

In this paper we report on the recent progress in fabrication and simulation of GaSb photovoltaic (PV) cells with a Zn diffused emitter. The form of Zn profiles in the emitter has an essential impact on the power output of a PV cell. Different types of Zn profiles were realized and used for simulation of PV device parameters. Calculations based on PV cell measurements show that efficiencies up to 30% can be achieved assuming a blackbody temperature of 1300–1500 K and a perfect band edge filter.     

Partial oxidation of methane in a reciprocal flow porous burner with an external heat source

A reciprocal flow porous burner with an external heat source in the middle section was studied numerically to access the reactor efficiency for synthesis gas generation. The temperature and species profiles were predicted using a two temperature model with a detailed chemical mechanism. The effect of the variation of the power of the external heat source on the hydrogen and carbon monoxide yields was studied. The energy conversion efficiencies of the system with various power levels of the external heat source were evaluated. It is found that H₂ and CO yields increase significantly with the addition of the external heat source due to the temperature increase in the middle section of the burner. The CO₂ emissions remain small. The methane conversion ratio increases with increase of the power of the external heat source reaching 97%. The H₂ and CO conversion ratios yields are nearly doubled as the power of the external heat source increases from 0 to 750 W. The cold gas energy conversion efficiency decreases as the power of the external heat source increases. At the same time, the syngas energy conversion efficiency increases from 41% to 70%, while hydrogen energy conversion efficiency increases from 28% to 46%.     

Comparative investigation of combustion and thermal characteristics of a conventional micro combustor and micro combustor with internal straight/spiral fins for thermophotovoltaic system

The energy output and energy conversion efficiency of MTPV system are relatively low due to the energy loss. In order to improve the energy output of micro-thermophotovoltaic (MTPV) system, the internal straight and spiral fins are introduced into the micro combustor. The impact of hydrogen mass flow rate, equivalence ratio, and materials on the thermal performance are investigated. The increase of hydrogen mass flow rate brings higher average outer wall temperature, but the temperature difference also increases and the temperature uniformity becomes worse. The equivalence ratio of 1 is suggested to obtain higher average outer wall temperature and better temperature uniformity. The materials with higher thermal conductivity can obtain better thermal performance. Meanwhile, the higher thermal conductivity can also reduce the impact of introduction of internal fins.     

Thermophotovoltaic power generation systems using natural gas-fired radiant burners

Thermophotovoltaic (TPV) power generation in gas-fired furnaces is attracting technical attention. Considerable work has been done in the area of low bandgap GaSb cell-based TPV systems as well as silicon solar cell-based TPV systems. Previous investigations have shown that a radiant burner with a high conversion level of fuel to radiation energy must be developed to realize an efficient TPV system. In our work, we investigated different natural gas-fired radiant burners in order to raise the conversion of fuel energy to thermal radiation. These burners were used as radiation sources to establish and test two TPV prototype systems. It was found that for a non-surface combustion radiant burner, the radiation output can be enhanced using a thermal radiator with a porous structure. Also, we developed a cascaded radiant burner that generates two streams of radiation output. One stream illuminates silicon concentrator solar cells while the other drives low bandgap GaSb cells. In this way, useful radiation output and thus TPV system efficiency are significantly increased due to the cascaded utilization of combustion heat and optimized thermal management.     

High Power Density Pyroelectric Energy Conversion in Nanometer-Thick BaTiO3 Films

Solid-state pyroelectric nanomaterials can be used for thermal-to-electrical energy conversion in the presence of temperature fluctuations. This article reports investigation of energy conversion in a 200 nm thick BaTiO₃ film using the pyroelectric Ericsson cycle at cycle frequencies up to 3 kHz. The high cycle frequencies were achieved due to the low thermal mass of the nanometer-scale film, unlike previous studies in which the electrical power output was limited by the rate of heat transfer through the pyroelectric material. A microfabricated platform that allowed precise thermal and electrical cycling enabled us to study the effect of electric field range, temperature oscillation amplitude, and cycle frequency on the electrical power output from pyroelectric Ericsson cycles. We measured a maximum power density of 30 W/cm³ for a temperature range 20–120°C and electric field range 100–125 kV/cm, which represents a significant improvement over past work on pyroelectric cycles. The approach presented in this article could lead to high-power waste heat harvesting in systems with high-frequency temperature oscillations.     

Performance effect on the TEG system for waste heat recovery in automobiles using ZnO and SiO2 nanofluid coolants

Enhancement in heat transfer of the cold side is vital to amplify the performance of a thermoelectric generator (TEG). With enriched thermophysical properties of nanofluids, significant improvement in heat transfer process can be obtained. The current study concerns the performance comparison of an automobile waste heat recovery system with EG‐water (EG‐W) mixture, ZnO, and SiO₂ nanofluid as coolants for the TEG system. The effects on performance parameters, that is, circuit voltage, conversion efficiency, and output power with exhaust inlet temperature, the total area of TEG, Reynolds number, and particle concentration of nanofluids for the TEG system have been investigated. A detailed performance analysis revealed an increase in voltage, power output, and conversion efficiency of the TEG system with SiO ₂ nanofluid, followed by ZnO and EG‐W coolants. The electric power and conversion efficiency for SiO ₂ nanofluid at an exhaust inlet temperature of 500K were enhanced by 11.80% and 11.39% respectively, in comparison with EG‐W coolants. Moreover, the model speculates that an optimal total area of TEGs exists for the maximum power output of the system. With SiO ₂ nanofluid as a coolant, the total area of TEGs can be diminished by up to 34% as compared with EG‐W, which brings significant convenience for the placement of TEGs and reduces the cost of the TEG system.     

整形激光掺杂制备PERC电池选择性发射极研究

研究整形激光掺杂制备选择性发射极(SE)对p型单晶硅钝化发射极局域背接触(PERC)太阳电池的表面金字塔形貌、掺杂分布及电池性能的影响。整形激光具有能量分布均匀、对硅片损伤小等优点。通过改变激光的功率以及激光划线速度在p型单晶硅PERC太阳电池制备了不同掺杂分布的发射极。结合3D激光显微镜、扫描电子显微镜、EDS能谱分析、四探针方阻测试仪、电化学电容法等测试分析方法表征了样品的表面形貌、方阻变化、掺杂浓度曲线和电学性能。本文结合光斑重叠率将不同激光功率和激光划线速度采用公式统一转化为激光能量密度,从而得出制备选择性发射极的最佳激光能量密度。研究结果表明,当激光能量密度为0.97 J/cm2时,电池效率可以稳定提升0.25%以上,体现了整形激光SE技术应用于PERC电池的应用潜力。