Design and Evaluation of Lab-Scale, Heat Exchanger Prototypes to Provide Thermal Refugia for Trout

Abstract

In recent years, some streams and fisheries have been experiencing higher surface water temperatures, which negatively impact cold-water trout species. One potential solution is to provide localized refugia of colder water produced via active cooling. The present work focuses on the design and testing of a small-scale prototype heat exchanger, for such a cooling system. An effectiveness-NTU approach was used to model the heat exchanger and guide initial development of the prototypes. Based on the model, a staggered, tube-bundle heat exchanger was used. Various prototypes of the heat exchanger were tested in a 1/10th scaled model of a section of the creek. The prototypes consisted of just the heat exchanger placed directly in the scaled-stream model and of the heat exchanger placed inside an enclosure with an aperture. The results show that, without the enclosure, the average temperature difference is 0.64 °C, with a corresponding heat transfer requirement of 1.63 kW/°C of cooling. However, with an enclosure, the average temperature difference is 1.95 °C, which required 0.59 kW/°C of cooling. Modifications to the enclosure impact the average temperature difference and the temperature distribution within the enclosure, e.g., decrease the standard deviation of the temperature difference. Thus, the results show the need for the use of the enclosure to reduce the power requirement for the refugia, and obtain a desired temperature difference with a relatively low spatial variation in that temperature difference.

Experimental Investigation of a Prototype Thermal Refuge for Trout

“…It must provide adequate cooling to reduce the temperature of the surrounding water while allowing fish to access the refugia and maintaining a minimal electric power draw. Previously, the authors conducted lab-scale experiments with heat exchanger prototypes [15,16]. The lab-scale heat exchanger configurations were tested in a 1/10-scale model of a section of Spring Creek, South Dakota.…”

“…To the authors' best knowledge, the thermal refugia developed and field-tested in this study is a first-of-its-kind prototype and study. The prototype uses a tube-bundle heat exchanger in an enclosure with a downstream aperture as analyzed in the lab-scale experiments [15,16]. Prototype design variables tested include the enclosure length relative to the heat exchanger size, aperture size, and cooling fluid flow rates through the heat exchanger.…”