Surfactant 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.
07/30/2009-2/29/2012 PI: Jacques Zakin (Zakin.1@osu.edu), Co-PI: Srinivasa Raghavan The Department of Chemical and Biomolecular Engineering The Ohio State University April 24, 2012 Some specially formulated solutions reduce pressure drop of water in certain flow rate ranges. This interesting characteristic, called drag reduction (DR), makes such solutions promising working fluids in recirculating systems, such as district heating or cooling systems, to reduce the pumping energy requirements. Pumping energy in district heating or cooling systems takes up about 15% of the total energy requirements. By using DR solutions, it is possible to reduce by 50% or more the pumping energy costs. However, such DR solutions also suffer from reduced heat transfer capability. Therefore, it is of practical importance to temporarily enhance the heat transfer ability in heat exchangers while maintaining the DR capability of such solutions in the rest of the recirculation system. While various mechanical devices at the entrance of heat exchangers have been employed to temporarily enhance the heat transfer capability of drag reducing surfactant solutions by disturbing the flow, all of these in-flow mechanical devices result in additional pressure drop across the heat exchanger and so are not practical. To avoid the additional pressure loss, this project studied the use of external light irradiation instead of in-flow mechanical devices. The ideal fluid should be drag reducing in its normal state. At the entrance of a heat exchanger, the fluid is irradiated by light, loses its DR capabilities and has enhanced heat transfer capability in the heat exchanger. At the exit of the heat exchanger, the fluid is irradiated by a different wavelength of light to restore its DR capability. Thus this method combines the benefits of reduced pumping energy costs and good heat transfer. This project explored light-responsive aqueous solutions that can be used in district heating and cooling systems. Early in the study, a light-responsive solution was formulated with DR capability before light irradiation and enhanced heat transfer capability after light irradiation. But the effect of light irradiation on this solution is not reversible. As a result, the DR capability can not be restored. A paper was published in the journal, Langmuir, based on this light-responsive DR solution. Later we developed a light-responsive DR solution with reversible responses to light irradiations. This solution is a promising candidate for use in district heating and cooling systems, where its drag reduction and high heat transfer can be switched on and off repeatedly by external light irradiation. We have drafted a paper on this smart DR solution, and will submit it to a highly respected journal.
