There are much scientific researches devoted to the thermodynamic descriptions of constructions used in ancient civilizations. In “Thermodynamics of a shallow solar still” by Torchia-Núñez et al., scientists have approached the principle of solar distillation plants in the most detailed and complete way. In addition, they dedicated most of their work to the study of thermodynamic parameters that have a direct or indirect effect on the result. This report is intended to summarize Torchia-Núñez et al.’s article.
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Quite an extensive research work is divided into five blocks, the first and the last of which are devoted to introduction and conclusions. The most extensive section, the second one, is dedicated to describing the factors that affect the amount of moisture collected. The third section examines the mechanisms of heat transport inside and outside the unit. The fourth section is focused on the mathematical description of physical processes that take place during solar distillation.
Torchia-Núñez et al. begin the study with a historical explanation of the importance of the plants. The subject of the section is literary sources that described the phenomenon of distillation under the influence of solar radiation from the perspective of the science of the time. Thus, according to the authors, the views on the process are expressed by Aristotle. Nevertheless, the first most complete treatise was written only in 1589 by the author GB Della Porta — as a result, other, more rationalistic works followed it. However, the writers especially emphasize that each of the works they mentioned was not based on the mathematical description of processes but investigated only the mechanics of the distiller.
The authors cite an image that accurately demonstrates the principle of the device. They consciously chose the most general and simple mechanism of apparatus, which has a trapezoidal shape with a sloping glass lid. After that, the researchers begin the most significant part devoted to the factors that affect the performance of the solar unit. In particular, they describe in detail six parameters, the data on which are found in a systematic review of sources. It is essential to clarify that the article especially emphasizes that the influence of specific factors may be contradictory, given the lack of development of the topic. In general, the section deals with solar radiation, topological maps, thermal insulation, wind speed, wall temperature, and glass lid angle. At least half of the page is given to each of the parameters, but especially solar maps should be highlighted. The authors mention twice in the article the energy efficiency of such units in terms of treatment of salt or contaminated water, but they also pay attention to regions with low temperature and solar radiation. Torchia-Núñez et al. suggest that scarce solar radiation should not become a decisive factor when considering installing a distiller.
The next point concerns the internal and external thermal effects. Similar to what was discussed in the lectures, the researchers use coefficients such as the numbers of Nusselt, Prandtl, and Raleigh. In addition, the authors stress that the scientific sources are used to calculate different types of flow: laminar, transient, and turbulent. Six different methods of heat transfer inside the unit and three outside are shown. The researchers focus on the contribution that a particular type of heat transfer makes to overall energy efficiency. To solve the problems of eliminating undesirable losses, they propose several measures to strengthen the structure or placement in particular areas.
Subsequently, the article concentrates on mathematical equations to calculate the energy and exergy balance, although Torchia-Núñez et al. write that the use of the term “balance” concerning exergic activity is not justified. They specify that the exergy analysis of thermodynamic balance does not exclude the energetic one but supplements it. The authors cite several key equations, and especially emphasize their dependence on time. They conclude the central part of the study by pointing to the need for a complete analysis of the second law of thermodynamics for any solar technology.
Torchia-Núñez, J. C., Cervantes-de-Gortari, J., & Porta-Gándara, M. A. (2014). Thermodynamics of a shallow solar still. Energy and Power Engineering, 6(9), 246-265. Web.