Structural optimization of axially grooved flat miniature heat pipes

Optimization of flat miniature heat pipes was carried out based on the exis ting and newly obtained experimental results and the quasi-Newton algorithm s employing the BFGS (Broyden, Flether, Golfarb, Shanno) method. The heat p ipe contains capillary axial grooves that were cut using the method of elec tric-discharge-machining (EDM). The general multivariable optimization meth ods were used to search for the optimum structure of the heat pipe. Based o n the optimization results, a miniature copper-water heat pipe with externa l overall dimensions of 7 x 3 x 120 mm was fabricated and tested. Maximum h eat transfer rates of 50 watts in the horizontal orientation and 70 watts i n the vertical orientation at a working temperature of 100 degreesC were ac hieved. The corresponding heat fluxes were 25 and 35 W/cm(2), respectively, based on the external heating surface area. These two values are increased to 40 and 56W/cm(2) if the calculation is based on the dimensions of the v apor space. The heat transport capacity of the optimized heat pipe was incr eased by 66% to 100% at the working temperature of 100 degreesC, compared t o the non-optimized heat pipes. The effective thermal conductance of the he at pipe was 60 to 110 times that of a copper bar having the same overall di mensions.