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[en] The potential market for thermophotovoltaic (TPV) applications has been studied for civilian and industrial sectors in Japan. Comparing the performance of gas engines or turbines, as well as the underdeveloped power generation technologies such as fuel cells or chemical batteries, we have discussed the feasible application field of TPV systems to compete with those power generators. From the point of view of applicability for TPV systems in Japan, portable generators, co-generation systems and solar power plants are selected for our system analysis. The cost and performance targets of TPV systems for co-generation are also discussed by assuming a typical daily profile of electricity and hot water demands in Japanese homes. A progress report on the recent TPV research activities is given as well as a feasibility study concerning such TPV systems in Japan. (Author)
[en] A novel power MEMS concept, a micro thermophotovoltaic (TPV) system, is first described in this work, which would use hydrogen as fuel and would be capable of delivering 3-10 W electrical power in a package less than 1 cubic centimeter in volume. A microcombustor is one of the most important components of a micro TPV system. A high and uniform temperature distribution along the wall of the microcombustor is required to get a high electrical power output. However, sustaining combustion in a MEMS size combustor will be largely affected by the increased heat losses due to the high surface to volume ratio, which tends to suppress ignition and quench the reaction. In order to test the feasibility of combustion in microdevices and determine the relevant factors affecting microcombustion, numerical and experimental work was performed. The results indicated that a high and uniform temperature could be achieved along the wall of the flame tube
[en] The optical properties of sputter deposited hafnium fluoride films and their use in fabricating a front surface, interference filter for thermophotovoltaic energy conversion (TPV) were investigated. In particular, HfF4 films were being considered for the low index component in a multilayer interference filter that will selectively transmit photons in the wavelength range of 1.0 micro m to 2.4 micro m, and strongly reflect all other wavelengths
[en] Evaporation and space-charge requirements are evaluated to understand the effect of device scaling and fuel preheating for a liquid fuel injector using a multiplexed electrospray (MES) configuration in compact combustion applications. This work reveals the influence of the droplet diameter, droplet velocity and droplet surface temperature as well as the surrounding gas temperature on the size and performance of microfabricated MES. Measurements from MES devices are used in the model to accurately account for the droplet diameter versus flow rate relationship, the minimum droplet diameter and the relevant droplet velocities. A maximum extractor electrode to ground electrode distance of 3.1 mm required to overcome space-charge forces is found to be independent of voltage or droplet velocity for large levels of multiplexing. This maximum distance also becomes the required evaporation length scale which imposes minimum fuel pre-heating requirements for large flow densities. Required fuel preheating is therefore evaluated for both ethanol and 1-butanol with combustor parameters relevant to fuel reformation, thermoelectric conversion, thermophotovoltaic conversion and thermionic conversion
[en] An energy analysis is presented for n -dodecane/air combustion in a heat recirculating Inconel microreactor under vacuum conditions. Microreactor channels are partially coated with platinum enabling operating with coupled heterogeneous and homogeneous reactions. The radiant efficiency, important for thermophotovoltaic energy conversion, was found to decrease from 57% to 52% over 5 different runs covering 377 min of operation. A similar decrease in combustion efficiency was observed with 6%-8% energy lost to incomplete combustion and 5%- 6% lost through sensible heat in the exhaust. The remaining thermal loss is from unusable radiation and conduction through inlet and outlet tubing. Changes in the Inconel microreactor geometry and emissivity properties were observed. (paper)
[en] The basic characteristics of thermophotovoltaic heterostructure p-InAsSbP/n-InAs converters have been simulated. The converters have been designed so that a contact to the irradiated p-InAsSbP layer has a limited area or, in the flip-chip design, radiation is introduced through a contact-free part of the n+-InAs substrate. It has been shown that the design features of the converter influence its efficiency and active region temperature.
[en] The performance of micro combustion-driven power systems is strongly influenced by the combustor structure. A novel modular thermophotovoltaic (TPV) power generator is presented, which is based on the sub-millimeter parallel plate combustor. It has the potential to achieve a high power density because of the high radiation energy per unit volume due to the high surface-to-volume ratio of the micro-combustor. The work experimentally investigated the ignition limitation for two micro-combustors. It also studied the effects of three major parameters on a sub-millimeter combustor, namely hydrogen to oxygen mixing ratio, hydrogen volumetric flow rate and nozzle geometry. The results show that the combustion efficiency decreases with the increase of the hydrogen flow rate, which is caused by reduced residence time. The average wall temperature with the rectangular nozzle is 25 K higher than that with the circle nozzle. The output electrical power and power density of the modular TPV power generator are projected to be 0.175 W and 0.0722 W cm−3 respectively. We experimentally achieve 0.166 W of electrical power, which is in good agreement with the model prediction
[en] Highlights: • Thermophotovoltaics (TPV) can use a selective emitter to efficiently convert heat to electricity. • Strong candidates for selective emitter materials include tungsten and molybdenum. • Both emitter materials may exceed the Shockley–Queisser limit under ideal circumstances. - Abstract: Thermophotovoltaics convert heat into electricity via thermal radiation. The efficiency of this process depends critically on the selective emitter, which can be controlled by both the choice of the material and the emitter design. We find that surveying the set of refractory and near-refractory metals yields four primary candidates: tungsten, chromium, tantalum, and molybdenum. We developed a simulation tool known as TPVtest to consider the performance of each of these candidates. Tungsten yields the highest efficiencies at 35.20% at a temperature of 1573 K. However, molybdenum comes very close to this performance at 35.12% at the same temperature. Additionally, it presents the highest efficiency of 26.15% at the same temperature for a bandgap of 1.1 eV, as found in crystalline silicon. Furthermore, it may be possible to achieve improvements beyond the efficiencies quoted here by employing composite materials and advanced photovoltaic design concepts
[en] Highlights: • Effect of porosity and lattice dynamic on thermodynamic properties in pSi PhCs. • Slight instability in thermodynamics was revealed by porosity in triangular lattice. • Square lattice predicted optimal thermodynamic properties at low porosity & high T. • pSi PhCs can act as an active layer in thermophotovoltaic energy conversion system. • Lattice type and increasing porosity ensued a decline in thermodynamic properties. The prediction of thermodynamic properties performance in porous silicon (pSi) photonic crystals (PhCs) was studied for enhancement of light conversion into different types of energy based thermophotovoltaic energy conversion system. The unit-cell for 2D square and triangular lattices of circular air holes were formulated and solved using plane wave expansion (PWE) method. This was used to investigate the thermodynamic properties and the effect of lattice dynamic on these properties at different porosities in silicon PhCs; which are regarded as isolated and non-interacting particles systems. This was achieved by connecting density of states (DOS) and thermodynamic quantities as described in statistical physics. It revealed that irrespective of lattice type, increasing porosity ensued a decline in thermodynamic properties. Novel insights and theoretical concepts that could be integrated in thermophotovoltaic system were revealed. Regarding the square lattice, the optimum value of these properties except the free energy was obtained at for 20% and 50% porosities, and at for 80% porosity. Regardless of the porosity, the optimum value for the triangular lattice was found at . These characteristics have attempted to provide contributions with regards to the selection of the appropriate design for PhC in order to achieve high efficiency conversion.