Heat transfer characteristics of two-phase closed thermosyphons modified with inner surfaces of various wettabilities

Abstract

The heat transfer characteristics of two-phase closed thermosyphons (TPCTs) modified with inner surfaces of various wettabilities were experimentally studied. The wettability, which was quantified as the contact angle inside the thermosyphons, was varied by chemical etching and coating. For TPCT1-TPCT3 and TPCT8-TPCT10, introducing hydrophilic properties inside the evaporator sections increased the heat transfer coefficients of both evaporator and condenser at the same power. The evaporator and condenser heat transfer coefficients of TPCT8 and TPCT9 with combined hydrophilic and hydrophobic properties were higher than those of TPCT7 with smooth surface. The thermal resistances of TPCT1-TPCT3 with hydrophilic properties were lower than those of TPCT4-TPCT6 with hydrophobic properties at 40 W, 60 W and 80 W respectively. At the same power, as the contact angles on the evaporator sections of TCPT1 to TCPT6 increased gradually, the overall thermal resistances were elevated. The thermal resistance of TPCT7 with smooth surface was lower than those of TPCT4-TPCT6 with hydrophobic properties but higher than those of TPCT8 and TPCT9 at the same power. The thermal resistances of TPCT8 and TPCT9 may be lower than that of TPCT1 if the input power was further increased. In addition, as the contact angles of TPCT1-PTCT6 increased, the effective thermal conductivities gradually declined at all heat input powers. The effective thermal conductivities of TPCT1-TPCT3 with hydrophilic properties exceeded those of TPCT4-TPCT6 with hydrophobic properties and TPCT7 with smooth surface at different input powers. At the same input power, the effective thermal conductivities of TPCT8-TPCT10 were higher than those of TPCT4-TPCT6 modified with the hydrophobic properties, TPCT7 with smooth surface, TPCT11 and TPCT12 but lower than that of TPCT1.