Solar Engineering Of Thermal Processes

The increasing installed area of solar technologies around the world gives us an idea about the unlimited potential available in solar energy. This combined with the rising fossil fuel prices and frequent power outages, favor decentralized power generation among domestic consumers and small industries. However, the low energy of the solar PV module, the low exergy of the solar flat plate thermal collector and limited usable shadow-free space on building roof-tops could be overcome by the high overall (electrical and thermal) efficiency of a solar Photovoltaic Thermal (PV/T) system, which combines the electrical and thermal components in a single unit area. This paper gives a brief overview of the different solar flat plate PV/T technologies, their efficiencies, applications, advantages, limitations and research opportunities available.

Flat plate solar photovoltaic–thermal (PV/T) systems : A reference guide

Combined solar photovoltaic-thermal systems (PVT) facilitate conversion of solar radiations into electricity and heat simultaneously. A significant amount of work has been carried out on these systems since 1970. Different PVT systems have been invented in the last thirty years. Several theoretical, mathematical, numerical and experimental models are introduced by many investigators across the world. The present article gives a broad classification and review of published research work on these systems. The article mostly covers the experimental work carried out on the different types of PVT systems in the last decade. The latest technology of liquid spectrum filters for PVT systems are also explored in depth.

Photovoltaic -Thermal systems (PVT): Technology review and future trends

Throughout history, distillation has been the most widespread separation method. However, despite its simplicity and flexibility, distillation still remains very energy inefficient. Novel distillation concepts based on process intensification, can deliver major benefits, not just in terms of significantly lower energy use, but also in reducing capital investment and improving eco-efficiency. While very likely to remain the separation technology of choice for the next decades, there is no doubt that distillation technology needs to make radical changes in order to meet the demands of the energy-conscious modern society. This article aims to show that in spite of its long age, distillation technology is still young and full of breakthrough opportunities. Moreover, it provides a broad overview of the recent developments in distillation based on process intensification principles, for example heat pump assisted distillation (e.g. vapor compression or compression–resorption), heat-integrated distillation column, membrane distillation, HiGee distillation, cyclic distillation, thermally coupled distillation systems (Petlyuk), dividing-wall column, and reactive distillation. These developments as well as the future perspectives of distillation are discussed in the context of changes towards a more energy efficient and sustainable chemical process industry. Several key examples are also included to illustrate the astonishing potential of these new distillation concepts to significantly reduce the capital and operating cost at industrial scale. © 2013 Society of Chemical Industry

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Distillation technology - still young and full of breakthrough opportunities

One of the most widely known solar thermal applications is solar water heating. In terms of installation expenditures and energy cost over the total life of the system, solar water heating technology has proven to be cost efficient for several domestic and industrial applications. Technological practicability of these systems has long been recognized and is presently employed in commercial sectors of many countries. This paper presents an overview of various types of solar assisted water heating systems and their market potential. Residential solar water heating is a promising age old technology, which has been evolved and developed both in the range and quality as a successful packaged market–product. The first part of this paper analyzes the performances along with how unique they are of different types of solar water heating systems and the later part of the paper covers its economic aspects.

Solar water heating systems and their market trends

An acoustic field spontaneously induced in a thermoacoustic prime mover consisting of a looped tube and resonator is determined through simultaneously measurements of pressure P and velocity U. A thermal efficiency of the thermoacoustic prime mover of this type has been reported to reach 30%. The measurements of the acoustic field in the present system revealed that a phase lead of U relative to P takes a negative value of about −20° in the regenerator where the output power of the prime mover is generated. It was concluded that the possession of a negative phase lead at this position is taken as a clue in a significant increase in the output power. Moreover, the analysis in the thermoacoustic mechanism shows that a precise position for the location of a second regenerator acting as a heat pump exists in the looped tube. Indeed, by locating the second regenerator at the position, a thermoacoustic cooler was constructed. The thermoacoustic cooler could generate a low temperature of −25 °C without involving any moving parts.

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Experimental studies of a thermoacoustic Stirling prime mover and its application to a cooler

A gas in a tube spontaneously oscillates when the temperature gradient applied along the wall of the tube is higher than the critical value. This spontaneous gas oscillation is caused by the thermal interaction between the gas and the tube wall. The stability limit of the thermally induced gas oscillation is numerically investigated by using the linear stability theory and a transfer matrix method. It is well known that an acoustic wave excited by the spontaneous gas oscillation occurring in a looped tube is different from that in a straight tube with two ends; a traveling acoustic wave is induced in a looped tube, whereas a standing acoustic wave is caused in a straight tube. The conditions for the stability limits in both tube types were calculated. The calculated and measured conditions were compared and were found to be in good agreement. Calculations performed by varying the value of the Prandtl number of the gas were used to determine the reasons for the existence of the stability limits of the looped and straight tubes.

Stability analysis of thermally induced spontaneous gas oscillations in straight and looped tubes

Two-sensor method proposed by Fusco et al. [“Two-sensor power measurements in lossy ducts,” J. Acoust. Soc. Am. 91, 2229–2235 (1992)] is a novel technique that determines acoustic intensity of a gas column in a wide duct from measurements of pressure based on the boundary layer approximation. For further development of this method, its validity is experimentally tested through comparison with the direct method measuring the pressure and the velocity simultaneously, and its formulation is modified to include the narrow duct range where the duct radius is smaller than the viscous boundary layer thickness of the gas. It is shown that the modified two-sensor method enables quick and accurate evaluation of the acoustic intensity seamlessly from narrow to wide duct ranges.

https://aue.repo.nii.ac.jp/?action=repository_action_common_download&item_id=4846&item_no=1&attribute_id=15&file_no=1

Experimental verification of a two-sensor acoustic intensity measurement in lossy ducts.

This paper reports on the acoustic streaming in a looped-tube thermoacoustic prime mover equipped with an asymmetric constriction called a jet pump. The time-averaged mass flow velocity was determined using visualization methods and using acoustic field measurements. It was demonstrated that the magnitude and the direction of the velocity were dependent on the orientation of the jet pump. From the observed velocities, we estimated the heat carried away from the hot heat exchanger by the mass flow. It was shown that the heat loss was decreased from 30 W to 6.5 W by reversing the orientation of the jet pump, when the input heat power supplied to the prime mover was 100 W. The influence of the acoustic streaming was also studied from the cooling temperature of the looped-tube cooler.

Measurements of acoustic streaming in a looped-tube thermoacoustic engine with a jet pump

S. Backhaus and G. W. Swift [Nature 399, 335(1999)] have built a prototype thermoacoustic Stirling engine based on traveling wave energy conversions, and demonstrated that its efficiency reached above 40% of the Carnot efficiency. We experimentally investigate an acoustic field in the engine through simultaneous measurements of velocity U and pressure P. By focusing on the phase lead Φ of U relative to P in its regenerator, we find that the engine can achieve such a high efficiency by the negative Φ about −20° rather than a traveling wave phase (Φ=0).

Yuki Ueda

Papers

Experimental studies of a thermoacoustic Stirling prime mover and its application to a cooler

Stability analysis of thermally induced spontaneous gas oscillations in straight and looped tubes

Experimental verification of a two-sensor acoustic intensity measurement in lossy ducts.

Measurements of acoustic streaming in a looped-tube thermoacoustic engine with a jet pump

Acoustic field in a thermoacoustic Stirling engine having a looped tube and resonator