Thermal Potential of Flat Evaporator Miniature Loop Heat Pipes for Notebook Cooling

Thermal management of laptops is an increasingly challenging task because of the high-heat flux associated with the microprocessors and the limited space available for the thermal control system inside the cabinet. In this paper, results are discussed from an investigation of two different designs of miniature loop heat pipes (mLHPs) for thermal control of compact electronic devices including notebooks. Two prototypes of mLHP, one with a disk-shaped evaporator, 30 mm diameter and 10 mm thick, and the other with a rectangular-shaped evaporator, 47 x 37 mm(2) plan area and 5 mm thick, were designed to handle heat fluxes up to 50 W/cm(2). In the disk-shaped evaporator, the compensation chamber was incorporated into the overall thickness of the evaporator, whereas for the rectangular-shaped evaporator a new design approach was used in which the compensation chamber was positioned on the sides of the wick structure such that it was coplanar with the evaporator section. The new design approach helped to decrease the thickness of the rectangular evaporator by 50% and therefore improved the ability to integrate miniature loop heat pipe technology into compact electronics enclosures. All of the thermal tests on mLHP prototypes were conducted in horizontal configurations. Total thermal resistance of the designed mLHPs was between 1 and 5 degrees C/W. A comparative study of the mLHPs with conventional heat pipe and microchannel-based active liquid cooling systems has shown the superior heat transfer capability of the passively operating loop scheme for high-heat flux applications, and helped to classify mLHPs as candidates for laptop thermal management.