Performance Evaluation When Using Nanofluids in Loop Heat Pipe and Pulsating Heat Pipe 2007-01-3193

This paper presents an experimental investigation regarding the use of solid nanoparticles added to water as a working fluid, to form a so-called nanofluid. Tests were made with a miniature loop heat pipe (mLHP) and an open loop pulsating heat pipe (OLPHP). Results show that the addition of 3.5% (by mass) of nickel nanoparticles in water presented improvement on the mLHP thermal performance at heat loads around 10 W when compared with the operation with pure water. However, when operating at higher heat loads, the mLHP presented worse performance. When operating the mLHP and nanofluid with a concentration of 5% (by mass) of nickel nanoparticles, the device did not show reliable operation. The OLPHP was tested with water and copper nanoparticles at a concentration of 5% (by mass). When testing the OLPHP under several orientations and comparing to its operation with pure water, the nanofluid presented to initialize the more intensive pulsation behavior at lower heat loads when compared with operation with pure water, also presenting operation at lower evaporator temperatures. Such a characteristics could be directly related to the use of solid nanoparticles that increase the liquid thermal conductivity. The use of nanofluids presents to be more beneficial to the OLPHP than to the mLHP, as the first one does not present a wick structure.