Photoreversible micellar solution as a smart drag-reducing fluid for use in district heating/cooling systems

Area of Science:

• Materials Science
• Chemical Engineering
• Fluid Dynamics

Background:

• District heating/cooling systems (DHCs) require efficient working fluids for both transport and heat exchange.
• Current fluids often involve trade-offs between drag reduction and heat transfer efficiency.

Purpose of the Study:

• To develop a photoresponsive micellar solution as a smart working fluid for DHCs.
• To enable reversible switching between drag reduction (DR) and efficient heat transfer (EHT) modes using light.

Main Methods:

• Formulation of an aqueous solution of oleyl bis(2-hydroxyethyl)methyl ammonium chloride (OHAC) and sodium 4-phenylazo benzoic acid (ACA).
• Utilized UV and visible light irradiation to induce photoisomerization of ACA (trans to cis and back).
• Characterized fluid properties (viscoelasticity, drag reduction, heat transfer) and nanostructure (cryo-TEM, 1H NMR).

Main Results:

• The OHAC/ACA solution exhibits tunable properties, switching between DR and EHT modes upon light stimulus.
• Trans-ACA leads to threadlike micelles, providing up to 80% drag reduction.
• Cis-ACA results in shorter micelles, enabling heat transfer comparable to water.

Conclusions:

• Photoresponsive micellar solutions offer a novel approach for optimizing DHC system performance.
• The light-induced reversible changes in micellar nanostructure are key to the fluid's dual functionality.
• This smart fluid technology has the potential to enhance energy efficiency in thermal management systems.