Experimental investigation of heat transfer characteristics in a miniature flat heat pipe with multi-channels

The heat transfer characteristics of a miniatured flat heat pipe (MFHP) with multi-channels, featuring a port diameter of 1.18 mm, is investigated experimentally. Various operating parameters are considered, including the working fluid volume (V_f = 1.5, 2.5, and 3.5 ml), length of the liquid reservoir (L_res = No reservoir, 5, and 10 mm), orientation such as axial face (α_a) or lateral side (α_l), inclination angles (α = −15 to 90^o), and cooling water flow rates (ṁ_i = 10, 15, and 20 LPH). Based on the experiments, the optimal values for the working fluid volume, reservoir length, and flow rate are determined as V_f = 2.5 ml, L_res = 5 mm, and ṁ_i = 20 LPH, respectively. Further analysis reveals that, the heat dissipation rate for the axial face is significantly higher than that of the lateral side, with an average percentage increase of 35.4 %. However, the lateral side outperforms the axial face in terms of stabilizing the evaporator wall temperature, reducing fluctuations by an average of 24.5 %. Moreover, the presence of multi-channels allows the MFHP in axial face orientation to dissipate a maximum heat load of 15 W against gravity at an inclination angle of α_a = −15^o. Finally, the variations in MFHP operation based on the orientation and its underlying physical mechanisms that contribute to enhancing heat transfer are discussed.