تجزیه و تحلیل عملکرد سیستم دماهای فرآیندی خورشیدی

This paper describes the results of a simulation study, validated by experimental results of a solar process heat system and represents the unsteady performance analysis of the system. The study focuses on the effect that the collector flow rates, temperature distribution and stratification have on the overall thermal and exergetic performance of the particular systems. The simulation is performed for the process heat system established in İzmir, Turkey. The analysis considers the unsteady-state thermal and exergetic analysis of the collector and the storage tank individually. The variation of the storage tank temperature is evaluated along the height of the storage tank at every hour during a day. The values obtained from the measurements at the İzmir Organize Sanayi Bölgesi-Industrial Process Heat System are compared with the predicted simulation results. The effects of the mass flow rates and temperature distribution of the load and collector on the performance of the system are discussed. The simulation results indicate that the exergetic efficiency is highly dependent on the ratio of mass flow rates and the use of an auxiliary heater in the system.

Solar thermal technologies are capable of providing heat across a wide range of temperatures, making them potentially attractive for meeting end use energy requirements in industrial process heat (IPH) applications, commercial heating and commercial cooling. Cylindrical parabolic collector systems look very promising for delivering IPH for applications in 95°C to 350°C (200 F to 660 F) delivery temperature range. The unsteady exergy analysis of solar systems is particularly useful in their design. The exergy analysis provides the basis for choosing the operating range of the solar collectors. The requirements for greater conversion efficiency and the introduction of new devices have led to the need for improved methods of predicting design parameters. The performance analysis of the solar heat system through exergy analysis has led the designer to improve the design parameters. In the solar engineering literature many papers have dealt with the performance of solar hot water systems [1], [2], [3], [4], [5], [6] and [7]. In these studies the performance analysis is based on the energetic study of the collector array and storage tanks and the stratification in storage tanks increases the system performance in a noticeable degree. These systems, however, considered a flat plate collector array and all of them were designed for systems which produced water temperatures around 60°C for domestic use. If the energy intercepted from the sun can be used immediately (i.e. if the load is equal to the total solar energy harvested by the collector during the same period), then storing the energy is not a good way of using the solar energy due to the entropy generation process associated with the heat transfer between the storage tank and the ambient. However, there is usually a difference between the user demand and the solar energy supply. It is in this case that the thermodynamically optimised system is the subject of this study. The objective of this article is to illustrate quantitatively the exergy delivery of a solar process heat system and to show how this potential can be maximised by design. Because of the high exergy content of solar thermal radiation, one of the engineering tasks is to find ways to maximize the collection and delivery of exergy through the solar energy systems. This leads researchers to find ways to avoid the irreversible destruction of exergy in the process of collection and delivery to the user. Considering the solar process heat system shown in Fig. 1, the test results were obtained from the IOSB–IPH system. The effects of mass flow rates and temperature distribution on the performances of the system have been analyzed through the first and second laws of thermodynamics. Full-size image (11 K) Fig. 1. Schematic view of the solar process heat system.

For operation of solar process heat plants, control of the temperature and mass flow rates have to be used to match the temperature requirements. This can be achieved by the integration of simulation model knowledge into a suitable exergy structure. In this study, by evaluating the exergy loss associated with the mismatch between a time varying supply of raw solar energy and a rigid or varying energy demand placed by a certain user, the effect on system performance has been discussed. The performance of a collector user system, plaqued by this mismatch can then be compared with the second law performance systems which have storage. The developed simulation program can be used for modelling and design of solar process heat systems. Because of the controlled operation, the calculated results are, however, more sensitive to model deviations. Overall the main conclusion of this study is that the daily regime of operation of a solar collection storage installation can be selected by design to maximize the delivery of solar exergy to the user.