<p>Like many streams, in recent years Spring Creek in South Dakota, a popular fishing location,&nbsp;has&nbsp;been experiencing higher&nbsp;surface water temperatures which negatively impact cold-water trout species.&nbsp;These higher temperatures significantly hinder the growth of trout which dames the value and reputation of the fishery. In the worst-case, the high temperatures cause die-off which, additionally, results in an increased financial burden to restock the stream.&nbsp;One way to potentially increase growth and survival rates is by providing localized refugia of colder water produced via active cooling systems. This would provide locations to which the trout can retreat during peak daily temperatures. The present work focuses on the design of the heat exchanger, for such a cooling system, that will be placed in the stream. Various prototypes of the heat exchanger subassembly were tested in a 1/10<sup>th</sup>-scaled model of a section of the creek. A staggered, triple-pass, tube-bundle heat exchanger was used. The prototypes consisted of just the heat exchanger placed directly in the scaled-stream model and of the heat exchanger placed inside an enclosure. The enclosure enclosed the heat exchanger on all sides except for a downstream-facing aperture. In the full-scale system, the aperture would allow fish to enter the cooled region of the enclosure. Four different enclosure designs were tested which varied the length of the enclosure and the size of the aperture. The temperature of the water was measured with thermistors at five locations near the heat exchanger while the freestream temperature was measured at an upstream location unaffected by the heat exchanger. The temperature of the cooling water flowing through the heat exchanger was measured at the heat exchanger inlet and outlet. The rate of heat transfer for the heat exchanger was determined from these inlet and outlet temperature measurements and from the measured flow rate through the heat exchanger. The key metrics used to evaluate the performance of the heat exchanger were the difference in temperature between the water near the heat exchanger and the freestream water temperature, the standard deviation of those individual temperature differences, and the amount of heat transfer needed to create the measured temperature change. The results show that, for all configurations of the enclosure, the enclosure significantly increases the average temperature difference while reducing the required amount of heat transfer. Without the enclosure, the average temperature difference is 0.64 °C, with a corresponding heat transfer requirement of 2.57&nbsp;kW/°C of cooling. However, with an enclosure twice the length of the heat exchanger, the average temperature difference is 1.95 °C, which required 0.59 kW/°C of cooling. The different configurations of the enclosures impact the three metrics. Increasing the length of the enclosure or decreasing the size of the aperture, decreases the average temperature difference but also decreases the standard deviation of the average temperature difference. Thus, the cooling effect is more evenly spread throughout the water in the enclosure. This indicates that the size of the heat exchanger relative to the size of the enclosure and the aperture can be used to balance the requirements of obtaining a relatively large temperature difference with a relatively low spatial variation in that temperature difference. These results will be used to guide to design of the large-scale heat exchanger.</p>

Investigations of Lab-Scale, Heat Exchanger Prototypes Designed to Provide Refugia for Trout

Paper Proceedings: https://asmedigitalcollection.asme.org/ES/ES2021/volume/84881

ASME 2021 Energy Sustainability (ES2021)

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