Page 25 - Climate Control News July 2019

(iCVD), in which the coating material is vapor- ized and grafts onto the surface to be treated, such as a metal pipe, to form a thin coating. This process was developed at MIT by Gleason and is now widely used.
The authors optimized the iCVD process by tuning the grafting of coating molecules onto the surface, in order to minimize the pinning of condensing droplets and facilitate their easy shedding. The process could be carried out on lo- cation in industrial-scale equipment, and could be retrofitted into existing installations to pro- vide a boost in efficiency.
The process is “materials agnostic,” Khalil said, and can be applied on either flat surfaces or tubing made of stainless steel, titanium, or other metals commonly used in condensation heat- transfer processes that involve these low-sur- face-tension fluids. “Whatever materials are used in your facility’s heat exchanger, it tends to be scalable with this process,” he added.
The net result is that on these surfaces, con- densing fluids like the hydrocarbons pentane or liquid methane, or alcohols like ethanol, will readily form small droplets that quickly fall off the surface, making room for more to form, and in the process shedding heat from the metal to the droplets that fall away.
One area where such coatings could play a
useful role, Varanasi said, is in organic Rankine cycle systems, which are widely used for generat- ing power from waste heat in a variety of indus- trial processes. “These are inherently inefficient systems,” he says, “but this could make them more efficient.”
“This new approach to condensation is signifi- cant because it promotes drop formation (rather than film formation) even for low-surface-ten- sion fluids, which significantly improves the heat transfer efficiency,” says Jonathan Boreyko, an as- sistant professor of mechanical engineering at Virginia Tech, who was not connected to this re- search. While the iCVD process itself is not new, he said, “showing here that it can be used even for the condensation of low-surface-tension fluids is of significant practical importance, as many real- life phase-change systems do not use water.”
Saying the work is “of very high quality,” Bo- reyko adds that “simply showing for the first time that a thin, durable, and dry coating can promote the dropwise condensation of low-sur- face-tension fluids is very important for a wide variety of practical condenser systems.”
The research was supported by the Shell-MIT Energy Initiative partnership. The team included former MIT graduate students Taylor Farn- ham and Adam Paxson, and former postdocs Dan Soto and Asli Ugur Katmis. ✺
Heat Exchangers
LEFT: Researchers have made significant progress in promoting droplet formation and improving the efficiency of condensation systems.
BELOW: The main building of the Massachusetts Institute of Technology
CLIMATE CONTROL NEWS JULY 2019
CE
ENGINEERING
Quality Service Reliability
Save up to 50%
on all brands of compressors
Australia wide service
Remanufactured Products:
• Semi hermetic • Screw
Compressors • Centrifugal
• Ammonia • Hermetic • Onsite
remanufacturing • Insurance
Reports
Brisbane Rewinding Services:
• Stator rewinds
• Motor overhaul • Fan overhaul
• Pump overhaul • Laser alignment
Other Services:
We also buy and sell quality Hvac, refrigeration chillers and equipment.
More information:
Call us on
07 3345 6559
Email:
accounts@ceceng.com.au
Or visit our website:
www.ceceng.com.au
25
CE
ENGINEERING
Quality Service Reliability