Electric Field and Surfactant Enhanced Boiling

Technology #16766

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(a) Pool boiling of a solution of 2.6 mM SDS (negatively charged) in DI water at a constant heater power of 60 W with potential applied between the silver foil boiling surface and an immersed titanium counter electrode. A (b) −0.1 to −2.0 V switch decreased bubble nucleation within 600 ms due to electrostatic desorption of SDS from boiling surface. A (c) −2.0 to −0.1 V switch increased nucleation within 300 ms due to adsorption of SDSPlain DI water (black), −0.1 V (red) and −2.0 V (blue) boiling curves for 2.6 mM (a) NaBr, (b) MEGA-10, (c) SDS and (d) DTAB. Time averaged data points from an individual boiling experiment with error bars (2 standard deviations in data spread from time averaging) and moving averages (lines) are shown. Boiling was not affected by voltage for (a) NaBr and (b) MEGA-10. For (c) negatively charged SDS, the boiling curve at −2.0 V was right-shifted with higher CHF compared with −0.1 V. For (d) positively charged DTAB, the boiling curve at −2.0 V was left-shifted with lower CHF compared with −0.1 V. The maximum change in HTC (tunability) at constant q′′ (horizontal arrows) and constant superheat (vertical arrows) are shown for SDS and DTAB.A solution of 2.6 mM DTAB (positively charged) in DI water was pool boiled in an experimental set-up (a) where eight separate gold electrodes were switched between −2.0 V (yellow) and −0.1 V (grey) to turn on/off bubble nucleation. Images taken at different times with a high-speed camera show (b) no nucleation of bubbles when no electrodes were activated, and (c–j) bubble nucleation only on the particular electrode that was activated
Categories
Inventors
Professor Evelyn Wang
Department of Mechanical Engineering, MIT
External Link (drl.mit.edu)
Jeremy Cho
Department of Mechanical Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Tunable Nucleate Boiling using Electric Fields and Ionic Surfactants

US Patent Pending 2015-0167959
Publications
Turning bubbles on and off during boiling using charged surfactants
Nature Communications, Oct. 21, 2015 Article number: 8599

Applications

This technology enhances boiling heat transfer, which can be used for steam generation, distillation, heat dissipation, or any other application where a controlled heat transfer rate is desired. Fields of use range from domestic cooking to power plants.

Problem Addressed

A heat transfer coefficient (HTC) is defined between a hot surface and boiling fluid. To increase boiling efficiency the HTC should be increased; however, as the superheat increases a critical heat flux (CHF) is reached, where coalescence of bubbles at the surface causes a vapor film to form that impedes the heat transfer. Typically, the CHF is maximized by increasing surface roughness and wettability; however, highly wetting behavior suppresses nucleation. Thus superheats are larger for a highly wetting surface, which is non-ideal from an HTC and energy efficiency standpoint. This technology increases the HTC and energy efficiency by adding surfactants to the fluid and applying an electric field to the system.

Technology

The system consists of a boiling surface, a fluid, a charged surfactant in the fluid, and a counter-electrode. The surfactant increase the HTC and decreases the wettability through solid-liquid adsorption, rendering the surface less wettable and promoting nucleation. In order to maximize capacitance (adsorption of the surfactant) at the boiling surface, the counter-electrode should have a much higher surface area than the boiling surface area. It was observed that the HTC increased with an applied electric field. For negatively charged surfactants a negative field and for positively charged surfactants a positive field increased the HTC. The tunability of the HTC was ±10%. This means that by adding surfactants and applying an appropriate electric field the efficiency of boiling is increased which can decrease the operation cost.  

Advantages

  • Increases HTC during boiling
  • Increases energy efficiency of boiling