Oscillating heat pipes offer elegant thermal management
In physics, heat is energy in motion — always moving between or through things. Pulling a blanket up at night traps the heat that naturally transfers from our bodies as we sleep; lighting a fire under a kettle transfers heat from the flames to our stovetop meal; and the sun transfers heat into the sand on a beach, making it impossible to walk without shoes.
Heat transfer has become an issue of increasing importance in the case of high performance electronics. Greater electrical demands are being required of electronic components and systems of shrinking size, and in turn, higher heat loads are being placed on ever smaller packages. Common cooling solutions, such as fan-blown air over heat sinks, are not sufficient for today’s advanced electronics, which in the absence of an improved thermal management solution, suffer reduced performance and lifetime.
As such, electronics cooling has become a “hot” research topic. Researchers around the world, including Hongbin “Bill” Ma at the University of Missouri, are looking for solutions to this pervasive and growing problem. Since 1999, Dr. Ma and his team in MU’s Mechanical Engineering Department have been advancing a nascent thermal management technology with great promise: oscillating heat pipes (OHPs).
“In electronic systems, when the temperature goes up the life span goes down. Oscillating heat pipes are a highly efficient heat transfer device that can solve this problem,” said Ma of his patented research focus.
Conventional heat pipes are liquid-filled tubes that connect at one end to an area that requires cooling — the evaporator — and at the other end to a place that will dissipate heat — the condenser. Rather than a single tube, an OHP consists of a series of connected tubes in a maze-like configuration in which liquid and vapor are sealed. When heated, the vapor and liquid begin a varied “pulsating” flow that transfers heat more efficiently due to the network of channels.
Ma has received funding from a number of high-profile companies and agencies to investigate the use of OHPs to cool a variety of electronic applications including Intel, Northrop Grumman, National Science Foundation, Defense Advanced Research Projects Agency, Air Force Research Lab and the Office of Naval Research. Currently, the researcher and others in the company he co-founded in Columbia, ThermAvant Technologies, are working with a number of leading defense contractors and military agencies to integrate the OHP technology into military and commercial systems.
“We are trying to make it less expensive,” said Ma, indicating they are experimenting with a variety of materials and liquids. “This research will have an especially significant impact on computers because the OHP heat spreader can result in more compact and more efficient computers.”
Additional applications of the technology may require flexible components. A collaboration with mechanical engineering alumnus Josh Arnone, founder and chief technology officer at Cardioptimus LLC and senior engineer at Kogent Surgical LLC, is a good example. The project seeks to develop a new way to stabilize patients on operating tables and prevent hypothermia during surgery. Ma said the patient positioning device embedded with heat pipes would take only one hour to recharge, compared to eight hours re-charge time with current technology.
In addition, Ma is working on a glove that would use heat pipes to warm the hands of those with chronically cold digits by harvesting heat from the person’s arm.
Ma also has used a similar concept to that of OHPs in collaborative cryopreservation research in which extreme rapid cooling is required. Current techniques use liquid nitrogen to achieve the necessary sub-zero temperature within 1.3 seconds. Using thin film evaporation, the process can be completed in 0.4 seconds, increasing the likelihood that frozen cells will remain viable.
In addition to breaking new ground in thermal management, Ma’s research program has blazed career paths for many of the 34 honors undergraduates, 20 master’s and 12 doctoral students who have conducted research in his lab.
“Scott Thompson worked with me for eight years from when he was an undergraduate until he earned his Ph.D.,” said Ma. “He is now teaching at Mississippi State as an assistant professor”
Ma said his students have gone on to work for Intel, Dell, Northrop Grumman, Aerospace Corporation, Honeywell, General Electric and ThermAvant. One of the Mechanical Engineering Department’s new faculty members, Matthew Maschmann, worked in Ma’s lab as both an undergraduate and graduate research assistant.
“Heat transfer is an important topic and one day it occurred to me that oscillating heat pipes would be very efficient in this process,” said Ma. “To date, I have written over 120 journal papers on OHP and phase change heat transfer.”
Ma’s continuing research and the growing number of engineers trained in his lab increase the odds that OHP technology may play a future role in an electronic device in your home or workplace.