Multi-stack coupled energy management strategy of a PEMFC based-CCHP system applied to data centers

Aiming at the power fluctuation and mismatch of the combined cooling, heating, and power (CCHP) system based on proton exchange membrane fuel cells (PEMFCs) and adsorption chiller, this study proposes a multi-stack coupled power supply strategy. The PEMFC stacks are divided into types Ⅰ, Ⅱ, and Ⅲ to meet the electric load and cooling load of the data center, and the heat requirements of the system. Meanwhile, economic analysis is conducted on the single-stack energy supply strategy and the multi-stack coupled energy supply strategy. The results show that with the multi-stack coupling power supply strategy, the cooling power and electric power almost completely match the load of the data center, without power fluctuations and overshoot. By smoothing the PID control results of the current of the stacks-Ⅲ, the heating power fluctuation is significantly reduced, and the maximum overshoot does not exceed 0.5 kW. Therefore, the strategy is conducive to the stable operation of the PEMFC stack and improves the lifetime of the system. Considering investment costs, maintenance costs, hydrogen costs, and electricity benefits, the multi-stack coupled energy supply strategy can save about 6.1 × 10⁵ $ per year. In summary, the multi-stack coupled energy supply strategy has advantages in system lifetime, operational stability, and economy.     

Methodological reviews and analyses on the emerging research trends and progresses of thermoelectric generators

Thermoelectric generator is among the earliest initiated electricity‐harvesting methods. It is a very potential power harvester that can convert wasteful thermal energy into electricity. However, it often suffers from low energy conversion rate due to its inconsistent heat source, inefficient thermoelectric material (or thermoelement) performance, and incompetent structural issues. Progressively for the first time, detailed methodological surveys and analyses are made for bulk, thick, and thin films in this review. This is in order to accommodate better insights and comprehensions on the emerging trends and progresses of thermoelectric generators from 1989 to 2017. The research interests in thermoelectric generators have started back in 1989, and have continuously experienced emerging progresses in the number of studies over the last years. The methodological reviews and analyses of thermoelectric generator showed that almost 46.6% of bulk and 46.1% of thick and thin film research works, respectively, are actively progressed in 2014 to 2017. Nearly 86.2% of bulk and 44.1% of thick and thin film thermoelectric generators are realizing in between 0.001 and 4 μW cm^?2 K^?2, while 43.1% of thick and thin films are earning among 10^?6 to 0.001 μW cm^?2 K^?2. The highest achievement made until now is 2.5 W cm^?2 at a temperature difference of 140 K and thermoelectric efficiency factor of 127.55 μW cm^?2 K^?2. This achievement remarked positive elevation for the field and interest in thermoelectric power generation. Consecutively, the research trends of fundamental devices' structure, thermoelement, fabrication, substrate, and heat source characteristics are analyzed too, along with the desired improvement highlights for the applications of thermoelectric generators.     

Evaluation of the power-generation capacity of wearable thermoelectric power generator

Employing thermoelectric generators (TEGs) to gather heat dissipating from the human body through the skin surface is a promising way to supply electronic power to wearable and pocket electronics. The uniqueness of this method lies in its direct utilization of the temperature difference between the environment and the human body, and complete elimination of power maintenance problems. However, most of the previous investigations on thermal energy harvesters are confined to the TEG and electronic system themselves because of the low quality of human energy. We evaluate the energy generation capacity of a wearable TEG subject to various conditions based on biological heat transfer theory. Through numerical simulation and corresponding parametric studies, we find that the temperature distribution in the thermopiles affects the criterion of the voltage output, suggesting that the temperature difference in a single point can be adopted as the criterion for uniform temperature distribution. However, the criterion has to be shifted to the sum of temperature difference on each thermocouple when the temperature distribution is inconsistent. In addition, the performance of the thermal energy harvester can be easily influenced by environmental conditions, as well as the physiological state and physical characteristics of the human body. To further validate the calculation results for the wearable TEG, a series of conceptual experiments are performed on a number of typical cases. The numerical simulation provides a good overview of the electricity generation capability of the TEG, which may prove useful in the design of future thermal energy harvesters.     

Evaluation of the power-generation capacity of wearable thermoelectric power generator

Employing thermoelectric generators (TEGs) to gather heat dissipating from the human body through the skin surface is a promising way to supply electronic power to wearable and pocket electronics. The uniqueness of this method lies in its direct utilization of the temperature difference between the environment and the human body, and complete elimination of power maintenance problems. However, most of the previous investigations on thermal energy harvesters are confined to the TEG and electronic system themselves because of the low quality of human energy. We evaluate the energy generation capacity of a wearable TEG subject to various conditions based on biological heat transfer theory. Through numerical simulation and corresponding parametric studies, we find that the temperature distribution in the thermopiles affects the criterion of the voltage output, suggesting that the temperature difference in a single point can be adopted as the criterion for uniform temperature distribution. However, the criterion has to be shifted to the sum of temperature difference on each thermocouple when the temperature distribution is inconsistent. In addition, the performance of the thermal energy harvester can be easily influenced by environmental conditions, as well as the physiological state and physical characteristics of the human body. To further validate the calculation results for the wearable TEG, a series of conceptual experiments are performed on a number of typical cases. The numerical simulation provides a good overview of the electricity generation capability of the TEG, which may prove useful in the design of future thermal energy harvesters.     

A 500 W low-temperature thermoelectric generator: Design and experimental study

Most of the current thermal power-generation technologies must first convert thermal energy to mechanical work before producing electricity. In this study, a direct heat to electricity (DHE) technology using the thermoelectric effect, without the need to change through mechanical energy, was applied to harvest low-enthalpy thermal work. Such a power generation system has been designed and built using thermoelectric generator (TEG) modules. Experiments have been conducted to measure the output power at different conditions: different inlet temperature and temperature differences between hot and cold sides. TEG modules manufactured with different materials have also been tested. The power generator assembled with 96 TEG modules had an installed power of 500 W at a temperature difference of around 200 °C. An output power of over 160 W has been generated with a temperature difference of 80 °C. The power generated by the thermoelectric system is almost directly proportional to the temperature difference between the hot and the cold sides. The cost of the DHE power generator is lower than that of photovoltaics (PV) in terms of equivalent energy generated.     

抽凝机组耦合热电转换辅助调峰系统参数设计

  目的  为适应新能源电力并网需求,原有抽凝热电联产机组深度调峰供热改造已为重要途径之一。现有包括电热泵和电锅炉在内的热电转换装置为辅助火电机组调峰提供了潜在途径。  方法  以350 MW抽凝机组为例,建立了以热电转换装置辅助调峰参数优化模型,重点分析了热电转换设备参数对深度调峰性能的影响;其次,分别对比了电热泵和蓄热电锅炉两种典型热电转换系统在不同装置容量、不同放热速率下的调峰深度;最后,介绍了300 MW燃煤机组的煤耗率与污染物排放水平,指出本系统的节能效益,并给出热电转换装置的最优参数。  结果  结果显示:当电热泵的热功率为100 MW、放热速率与热功率相匹配也为100 MW时,机组的调峰深度达到最大值,为73 MW左右;当蓄热式电锅炉的电功率为45 MW、放热速率为100 MW时,机组的调峰深度达到最大值,为70.05 MW。蓄热式电锅炉的储热量在24 h中内略有增加,净储热量的数值为967.5 kWh。  结论  功率和放热速率是衡量热电转换装置辅助机组调峰能力的重要参数,且二者之间要有一定程度上的匹配性,针对不同情景灵活匹配热电转换装置的类型与参数可大幅提升机组的调峰深度。     

Optimization of a 30 kW SOFC combined heat and power system with different cycles and hydrocarbon fuels

Solid oxide fuel cells (SOFCs) could generate power cleanly and efficiently by using a wide range of fuels. Through the recovery and utilization of the energy in the SOFC tail gas, SOFC combined heat and power (CHP) systems achieve efficient cascade utilization of fuels. In this article, an efficient 30 kW SOFC CHP system with multiple cycles is designed based on a commercial kw-level SOFC device. The energy and substances could be recycled at multiple levels in this system, which makes the system do not need external water supply anymore during working. Meanwhile, the performance, fuel applicability, flexibility and reliability of the system are investigated. Finally, an optimized operating condition is confirmed, in which the electrical efficiency is 54.0%, and the thermoelectric efficiency could reach 88.8% by using methanol as fuel.     

Performance of high-temperature heat exchangers in biomass fuel powered externally fired gas turbine systems

Recently, there has been wide-ranging research on the idea of biomass fuel powered externally firing micro gas turbines; but only a small subset of these studies has used experimental work to evaluate the systems. These systems have not yet been employed in Malaysia for applications in thermal energy or power generation. The objective of this study is to determine the performance of a stainless steel high-temperature heat exchanger, which was built to transfer thermal power from a biomass gasifier-combustor to the pure air turbine working fluid. The study is based on experimental work using different air blower capacities as an air supply. The heat exchanger achieved 694 °C turbine inlet temperature with an average effectiveness of 62.5%.     

Increase of COP in the thermoelectric refrigeration by the optimization of heat dissipation

A device for the dissipation the heat from the hot side of Peltier pellets in thermoelectric refrigeration, based on the principle of a thermosyphon with phase change is presented. The device design was accomplished by analytic calculations on the base of a semi-empirical formulation and simulations with computational fluids dynamics. In the experimental optimization phase, a prototype of thermosyphon with a thermal resistance of 0.110 K/W has been development, dissipating the heat of a Peltier pellet with the size of 40 × 40 mm, what is an improvement of 36% in the thermal resistance, with regard to the commercial fin dissipater.With the construction of the two prototypes of thermoelectric domestic refrigerators, one of them with the device developed, and the other with a conventional fins dissipater, it could be experimentally proved that the use of thermosyphon with phase change increases the coefficient of performance up to 32%.     

Design and analysis of a solar tower power plant integrated with thermal energy storage system for cogeneration

In the current study, a solar tower–based energy system integrated with a thermal energy storage option is offered to supply both the electricity and freshwater through distillation and reverse osmosis technologies. A high‐temperature thermal energy storage subsystem using molten salt is considered for the effective and efficient operation of the integrated system. The molten salt is heated up to 565°C through passing the solar tower. The thermal energy storage tanks are designed to store heat up to 12 hours. The temperature variations in the storage tanks are studied and compared accordingly for evaluation. The effect of operating temperatures on the freshwater production and overall system efficiency is determined. About 24.46 MW electricity is generated in the steam turbine under sunny conditions. Furthermore, the storage subsystem stores heat during sunny hours to utilize later in cloudy hours and night time. The produced power decreases to 20.17 MW in discharging hours due to temperature decrease in the tank. The electricity generated by the system is then used to produce freshwater through the reverse osmosis units and also to supply electricity for the residential use. A total flowrate of 240.02 kg/s freshwater is obtained by distillation and reverse osmosis subsystems.     

A coupled 3D electrochemical and thermal numerical analysis of the hybrid fuel cell-thermoelectric device system

While the integration of the fuel cell (FC) and the semiconductor thermoelectric device (TED) to form a clean energy hybrid FC-TED system has been previously studied using 0-D mathematical equations, a 3-D finite element model that couples together the physics between the two devices is yet to be comprehensively studied. This paper introduces a 3-D finite element model developed in COMSOL Multiphysics that simulates both the FC and the TED subsystems where the FC electrochemical dynamics and the TED's thermoelectric effect and heat transfer physics take place between them. The studied FC stack is in direct contact with one side of the TED via the top of the gas channel structure and the other side is then convectively cooled by active air cooling. Results demonstrate that the proposed model can easily simulate the TED as both a thermoelectric generator (TEG) or as a Peltier device for cooling and heating. In the TEG mode, energy harvesting efficiency is observed at only 0.1% but expected to improve with better TED to FC relative sizing. The Peltier heating mode is also found to be advantageous in terms of quickly regulating the FC stack temperature, a valuable feature for startup processes.     

Thermal‐hydraulic design features of a micronuclear reactor power source applied for multipurpose

Microheat pipe cooled reactor power source (HRP) designed for space or underwater vehicles meets the future demands, such as safer structure, longer operating time, and fewer mechanical moving parts. In this paper, potassium heat pipe cooled reactor power source system which generates 50 kWe electricity is proposed. The reactor core using uranium nitride fuel is cooled by 37 potassium high‐temperature heat pipes. The shields are designed as tungsten and water, and reactor reactivity is controlled by control drums. The thermoelectric generator (TEG) consists of thermoelectric conversion units and seawater cooler. The thermoelectric conversion units convert thermal energy to electric energy through the high‐performance thermoelectric material. A code applied for designing and analyzing the reactor power system is developed. It consists of multichannel reactor core model, heat pipe model using thermal resistance network, thermoelectric conversion, and thermal conductivity model. Then, the sensitivity analysis is performed on two key parameters including the length of the heat pipe condensation section and the cold junction temperature of the TE cell. Meanwhile, the steady‐state calculations are conducted. Results show that the maximum fuel temperature is 938 K located in the center of reactor core and the outlet temperature of coolant reaches 316 K. Both of them are within the limitation. It is concluded that the preliminary design of HPR design is reasonable and reliable. The designed residual heat removal system has sufficient safety margin to release the decay heat of the reactor. This research provides valuable analysis for the application of micronuclear power source.     

Design,modeling, and analysis of a high performance piezoelectric energy harvester for intelligent tires

Basic parameters affecting vehicle safety and performance such as pressure, temperature, friction coefficient, and contact‐patch dimensions are measured in intelligent tires via sensors that require electric power for operation and wireless communication to be synchronized to the vehicle monitoring and control system. Piezoelectric energy harvesters (PEHs) can extract a fraction of energy that is wasted as a result of deflection during rolling of tires, and this extracted energy can be used to power up sensors embedded in intelligent tires. A new design of PEH inspired from Cymbal PEHs is introduced, and its performance is evaluated in this paper. Cymbal PEHs are proven to be useful in vibration energy harvesting, and in this paper, for the first time, the modified shape of Cymbal energy harvester is used as strain‐based energy harvester for the tire application. The shape of the harvester is adjusted in a way that it can be safely embedded on the inner surface of tires. In addition to the high performance, ease of manufacturing is another advantage of this new design. A multiphysics model is developed and validated to determine the output voltage, power, and energy of the designed PEH. The modeling results indicated that the maximum output voltage, the maximum electric power, and the accumulated harvested energy are about 3.5 V, 2.8 mW, and 24 mJ/rev, respectively, which are sufficient to power two sensors. In addition, the possibility is shown to supply power to five sensors by increase in piezoelectric material thickness. The effect of rolling tire temperature on the performance of the proposed PEH is also studied.     

Harvesting of PEM fuel cell heat energy for a thermal engine in an underwater glider

The heat generated by a proton exchange membrane fuel cell (PEMFC) is generally removed from the cell by a cooling system. Combining heat energy and electricity in a PEMFC is highly desirable to achieve higher fuel efficiency. This paper describes the design of a new power system that combines the heat energy and electricity in a miniature PEMFC to improve the overall power efficiency in an underwater glider. The system makes use of the available heat energy for navigational power of the underwater glider while the electricity generated by the miniature PEMFC is used for the glider's sensors and control system. Experimental results show that the performance of the thermal engine can be obviously improved due to the high quality heat from the PEMFC compared with the ocean environmental thermal energy. Moreover, the overall fuel efficiency can be increased from 17 to 25% at different electric power levels by harvesting the PEMFC heat energy for an integrated fuel cell and thermal engine system in the underwater glider.     

微燃机分布式供能系统在医院及办公楼能源中心的实践

微燃机分布式供能系统选择微型燃气轮机发电机组(简称微燃机)作为原动机,具有系统整洁美观、运行稳定智能、安装环境要求不高、占地面积小、噪音低等优点。通过其在医院和办公楼能源中心中的实践,不仅验证了上述优点,而且通过对系统性能数据的实测,得出系统电力和余热均能被充分利用,热电比和年一次能源利用率均较高等结论。总结系统实施的经验,成功和不足,望能与同行业同仁分享。     

Experimental investigation of a novel heat pipe thermoelectric generator for waste heat recovery and electricity generation

Waste heat recovery helps reduce energy consumption, decreases carbon emissions, and enhances sustainable energy development. In China, energy-intensive industries dominate the industrial sector and have significant potential for waste heat recovery. We propose a novel waste heat recovery system assisted by a heat pipe and thermoelectric generator (TEG) namely, heat pipe TEG (HPTEG)，to simultaneously recover waste heat and achieve electricity generation. Moreover, the HPTEG provides a good approach to bridging the mismatch between energy supply and demand. Based on the technical reserve on high-temperature heat pipe manufacturing and TEG device integration, a laboratory-scale HPTEG prototype was established to investigate the coupling performances of the heat pipes and TEGs. Static energy conversion and passive thermal transport were achieved with the assistance of skutterudite TEGs and potassium heat pipes. Based on the HPTEG prototype, the heat transfer and the thermoelectric conversion performances were investigated. Potassium heat pipes exhibited excellent heat transfer performance with 95% thermal efficiency. The isothermality of such a heat pipe was excellent, and the heat pipe temperature gradient was within 15°C. The TEG's thermoelectric conversion efficiency of 7.5% and HPTEG's prototype system thermoelectric conversion efficiency of 6.2% were achieved. When the TEG hot surface temperature reached 625°C, the maximum electrical output power of the TEG peaked at 183.2 W, and the open-circuit voltage reached 42.2 V. The high performances of the HPTEG prototype demonstrated the potential of the HPTEG for use in engineering applications.     

“NCB”新型专用供热机

对供热机节能增效途径进行论述,分析了目前供热机的优缺点,从而提出"NCB"新型供热机.通过与原300MW抽-凝供热机比较,证明"NCB"新型供热机在供热能力和节能效益两方面均有明显的优越性.     

An experimental investigation on the thermal efficiency of fractal tree-like microchannel nets

In this paper, a fractal tree-like microchannel net heat sink (20 mm × 20 mm × 1.4 mm) for cooling of electronic chips was fabricated on a silicon wafers by advanced MEMS technology. The length, width and height of the entrance microchannel were 10 mm, 800 μm and 25 μm, respectively. The fractal dimension D and the circulation number m of the fractal tree-like microchannel net were 2 and 4, respectively. It is confirmed experimentally that the thermal efficiency (defined as heat transfer rate per unit power required) of such a fractal tree-like microchannel heat sink is much higher than that of the traditional parallel microchannel heat sink for the same heat transfer rate, the same temperature difference and the same inlet velocity.     

Triple hybrid system coupling fuel cell with wind turbine and thermal solar system

One of the most challenging issues in the domain of renewable energy is the instability of produced power. To put it another way, renewable resources such as solar energy cannot provide continuous energy supply because they rely on natural phenomena that vary randomly. That said, to cover the potential lack of energy that may occur, hybrid renewable energy system can be adopted. In other terms, instead of using single renewable energy source, two different sources can be utilized in order to optimize the output power all over the year. Furthermore, complementary energy system is needed along with renewable sources, to store energy and insure the supply during shortage period. With this in mind, a Green-Green energy system can be constructed by using green storage system such as Fuel Cell to be coupled with the renewable sources. In the light of green-green energy concept, the present paper examines a triple wind-solar-fuel cell combination in the aim of overcoming the energy shortage that occurs during several months of the year. A case study on the region of Dahr Al-Baidar in Lebanon is conducted to present the advantage of the proposed system. Results show that combining wind energy system with thermal solar system allows overcoming the low power produced by solar thermal system especially in winter. For illustration 16 kW are produced by wind turbine during the month of January, by contrast the thermal solar system provides 2 kW during the same period. Nevertheless, in June thermal solar offers 17 kW and wind turbine produces 11 kW.     

Performance analysis for the part-load operation of a solid oxide fuel cell–micro gas turbine hybrid system

In this paper, the performance evaluation of a solid oxide fuel cell (SOFC)–micro gas turbine (MGT) hybrid power generation system under the part-load operation was studied numerically. The present analysis code includes distributed parameters model of the cell stack module. The conversions of chemical species for electrochemical process and fuel reformation process are considered. Besides the temperature distributions of the working fluids and each solid part of cell module by accounting heat generation and heat transfers, are taken into calculation. Including all of them, comprehensive energy balance in the cell stack module is calculated. The variable MGT rotational speed operation scheme is adopted for the part-load operation. It will be made evident that the power generation efficiency of the hybrid system decreases together with the power output. The major reason for the performance degradation is the operating temperature reduction in the SOFC module, which is caused by decreasing the fuel supply and the heat generation in the cells. This reduction is also connected to the air flow rate supplement. The variable MGT rotational speed control requires flexible air flow regulations to maintain the SOFC operating temperature. It will lead to high efficient operation of the hybrid system.