Investigating the Use of Light-Responsive Surfactant Fluids in Turbulent Drag Reduction

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0933295ZakinSurfactant fluids that form wormlike micelles (WLMs) are used as drag reducing (DR) agents in district heating/ cooling systems (DHCs). DHCs are an efficient way to heat and cool homes and buildings and are becoming increasingly popular around the world. DR agents reduce the friction losses in turbulent flow and thereby help to conserve up to 50% of the pumping energy costs in DHCs. However, a key problem with WLM-based fluids in DHCs is that they also reduce the rates for heat transfer (HT) in heat exchangers. This cancels the beneficial effects of drag reduction. In this project, the investigators seek to overcome the above problem by using a class of light responsive or photorheological (PR) surfactant fluids. The concept is to switch off the WLMs (convert them into spherical micelles) using UV light just before the fluid enters the heat exchanger, and thereafter switch the WLMs back on once the fluid exits the heat exchanger. This way, the investigators hope to obtain a combination of efficient HT rates as well as efficient DR in pipe flow. The PI on this project is an expert on drag reduction, especially with surfactant fluids. The co-PI has recently devised a new class of PR fluids using simple, inexpensive surfactants and counterions. Together, the PIs bring a fresh, potentially transformative, approach to an old problem. Intellectual Merit: The concept of using PR fluids in DR applications is a high risk, high reward exploratory approach that could translate into a substantial breakthrough if it can be shown to work. The present project is a pilot study over one year to demonstrate proof of principle. When the PR fluid contains WLMs, it is expected to give excellent drag reduction; when the microstructure is switched to much smaller spherical micelles, it should give efficient, water like heat transfer rates. We are aware of the challenges involved in this project, in particular, the need to rapidly switch the structure in a short time window. The solutions to these challenges are to utilize a combination of engineering principles as well as physical/organic chemistry. The investigators will modify the formulation of the PR fluids so that the photoisomerization of the constituent organic counterions is accomplished rapidly. Broader Impact: The potential total energy savings with the use of PR fluids would make them very attractive for use in DHC systems. If this project is successful, we will bring this work to the attention of the DHC field, e.g., by presentations at meetings of the International District Heating and Cooling Association where DHC engineers from around the world meet to exchange new technical ideas. The PI has a long history of working with this field and has organized meetings and workshops with NSF support. This project will also contribute to the education of graduate and undergraduate students. Both the PI and co PI have a strong track record of involving undergraduate students in their research, including those from under represented minority groups.