Graphite Foam Thermosyphon Evaporator Performance: Parametric Investigation of the Effects of Working Fluid, Liquid Level, and Chamber Pressure

Abstract

Graphite foams have recently been developed at ORNL and are beginning to be applied to thermal management of electronics. These foams consist of a network of interconnected graphite ligaments whose thermal conductivities are up to five times higher than copper. The thermal conductivity of the bulk graphite foam is similar to aluminum, but graphite foam has one-fifth the density of aluminum. This combination of high thermal conductivity and low density results in a thermal diffusivity about four times higher than that of aluminum, allowing heat to rapidly propagate into the foam. This heat is spread out over the very large surface area within the foam, enabling large amounts of energy to be transferred with relatively low temperature difference. The use of graphite foam as the evaporator of a thermosyphon is investigated due to its potential to transfer large amounts of energy without the need for external pumping. A preliminary optimization of the parameters governing evaporator performance is performed using 2-level factorial design. Performance of the system with both PF-5060 and PF-5050 were examined as well as the effects of liquid level and chamber pressure.

Thermal performance of a carbon fiber composite material heat sink in an FC-72 thermosyphon

“…Coursey et al [10] studied the effects of working fluid, liquid level and chamber pressure on a graphite foam thermosyphon with PF-5060 and PF-5050 as the working fluids. They determined that lower operating pressures resulted in higher heat fluxes (10-70 W/ m 2 K) and different working fluids and fill ratios did not affect thermosyphon performance.…”

“…Marinite insulation saturation saturation temperature of fluid Teflon measured at Teflon lip up power moving towards test section dielectrics [8][9][10][11]. The effects of flux levels, fill ratio and condenser operating temperature on the overall thermal performance, including thermal resistance and heat transfer coefficient are examined.…”

Pool Boiling Experiments on a Nano-Structured Surface

“…Mudawar and Anderson [4] performed saturated as well as subcooled pool-boiling experiments using multilevels of low profile surfaces (microfins, microgrooves, and microstuds) and reported that the critical heat flux ("CHF") of 159.3 W/cm could be achieved at wall super heat of 65 C and liquid subcooling of 35 C using FC-72 as a working fluid. Coursey et al [5] explored the applicability of graphite foams to thermal management of electronic devices. The foams are composed of graphite ligaments which are reported to have thermal conductivity values (up to five times higher than for copper).…”

“…The working fluid used in this experiment was PF-5060 (Manufacturer: 3M Co.). PF-5060 (which is 95% pure FC-72 [5]) was chosen as the working liquid as a cheaper substitute for FC-72. Both liquids have nearly identical boiling characteristics (e.g., latent heat of vaporization, saturation temperature, liquid and vapor densities as well as specific heats, etc.).…”

Ultra — Thin Film Evaporation (UTF) — Application to Emerging Technologies in Cooling of Microelectronics

“…They reported heat transfer rates up to 100 W/cm 2 g . The use of graphite foam as the evaporator in a thermosyphon was investigated by Coursey et al [33]. These foams consist of a network of interconnected graphite ligaments whose thermal conductivities are up to five times higher than copper.…”