• Energy Research

In this paper a survey of solar-based driven thermoelectric technologies and their applications is presented. Initially, a brief analysis of the environmental problems related to the use of conventional technologies and energy sources is presented and the benefits offered by thermoelectric technologies and renewable energy systems are outlined. The development history of solar-based thermoelectric technologies is introduced together with the discussion of the existing drawbacks of current systems. Typical applications of the solar-driven thermoelectric refrigeration and the solar-driven thermoelectric power generation are presented in order to show to the reader the extent of their applicability. The application areas described in this paper show that solar-driven thermoelectric technologies could be used in a wide variety of fields. They are attractive technologies that not only can serve the needs for refrigeration, air-conditioning applications and power generation, but also can meet demand for energy conservation and environment protection.

Fluid flow maldistribution is considered as one of the main causes of performance deterioration in various energy and process systems, especially when parallel micro-or mini-channel fluidic networks are involved. For a specific purpose, the optimal flow distribution is not necessarily uniform. However, specific non-uniform distributions are somewhat more difficult to achieve than uniform ones. The insertion of a geometrically optimized baffle has been numerically confirmed as an effective solution to this issue, but experimental validation is still lacking which is indispensable for bridging the gap between theory and practice. This paper presents a numerical and experimental investigation on the realization of target flow distribution among parallel mini-channels, using the optimized baffle insertion method. A 15-channel fluidic network integrated with the distributor and the collector is fabricated and tested. Various perforated baffles are optimized and fabricated corresponding to different target distributions (uniform, ascending and descending). PIV technique is used for the flow distribution measurement while CFD simulations are also performed for comparison. CFD results and PIV data show that different target distributions could be successfully achieved by the optimized baffle insertion method. The robustness of the optimized baffle for uniform distribution is also evaluated and discussed to provide some guidelines for future applications.

AbstractThe heat storage by absorption process that is studied in the paper is devoted to building heating. A prototype has been built and tested in static and dynamic operating conditions that are compatible with domestic solar thermal collectors. The charging process has been proved successful. Absorption during the discharging phase is also verified. However, some problems related to the heat exchanger design have not allowed to observe the heat release as expected.

In the past decade, long-term sorption and thermochemical heat storage has generated lot of interest. This paper presents the state of the art in this field of research, materials used in these systems and technological difficulties that researchers are set against. An emphasis is put on recent demonstrative projects including absorption and adsorption for long-term solar energy storage. It emerges that considerable breakthrough have been made. Even though there is no mature long-term sorption or thermochemical energy storage yet, primarily due to the high cost of materials, the suitability of this technology to long-term storage remains its main power of attracting.

In this paper, a review of the research state of art of the solar sorption (absorption and adsorption) refrigeration technologies is presented. After an introduction of basic principles, the development history and recent progress in solar sorption refrigeration technologies are reported. The application areas of these technologies are categorized by cooling temperature demand. It shows that solar-powered sorption refrigeration technologies are attractive alternatives that not only can serve the needs for air-conditioning, refrigeration, ice making and congelation purposes, but also can meet demand for energy conservation and environment protection. However, a lot of research work still needs to be done for large-scale applications in industry and for the replacement of conventional refrigeration machines.

Abstract This paper examines experimentally the effects of constructal distributors or collectors, built on a binary pattern of pores, on flow equidistribution in a multi-channel heat exchanger. Thermal performance and pressure drop have been determined with different assembly configurations of constructal distributors, conventional pyramid distributors and a mini crossflow heat exchanger (MCHE). Experimental results show that the integration of constructal distributors/collectors could homogenize the fluid flow distribution and consequently lead to a better thermal performance of the MCHE, but it also results in higher pressure drops. Among all tested assembly configurations, the configuration where the inlet is equipped with a conventional pyramid distributor, and the outlet is equipped with a constructal collector (Apec) shows a relatively better thermal performance as well as low pressure drops under experimental conditions considered.

In this paper, the idea of coupling constructal distributors/collectors with a mini crossflow heat exchanger (MCHE) to solve the problem of flow maldistribution is presented. After a brief description of the design and scaling laws of the constructal distributor, experimental and simulation results have been discussed to investigate relations among flow distribution, heat transfer and pressure drop. It is shown that the introduction of constructal distributors and/or collectors could improve the quality of fluid distribution and consequently lead to heat transfer intensification of the MCHE, but it also results in higher pressure drops. Different assembly configurations involving distributor, heat exchanger and collector have also been compared. The configuration where the inlet is equipped with a conventional pyramid distributor and the outlet is equipped with a constructal collector (Apec) shows a relatively higher thermal performance as well as low pressure drops in our cases considered.