Experimental and analytical investigations on heat transfer performance of naphthalene heat pipe heat exchanger

Abstract

The heat transfer performance of a naphthalene heat pipe (HP) heat exchanger (HE) was theoretically analyzed and experimentally confirmed. The tested HE comprised a staggered 9 × 17 array of copper tubes with 144 U-bends, forming a closed loop. The working fluid was naphthalene with a filling ratio of 45 %. The operating temperature range was 80–300 °C, and the airflow rate was 100, 150, 200, or 400 m3/h. The maximum heat transfer rate was discovered to be 3.86 kW, and the HP thermal resistance was approximately 0.00553 K/W for an air flow rate of 100 m3/h and at an operating temperature of 300 °C; the maximum thermal conductivity was 7155.43 W/m·K. The experimental data were compared with the predictions of empirically derived equations; the best predictions were obtained when the Jouhara and Robinson correlation for condensation was combined with the Kutateladze correlation for evaporation. The mean deviations of the predictions were 36.05 % for the overall thermal resistance and 17.34 % for the average temperature difference between the evaporation and the air side. Although the thermal conductivity of the naphthalene HP was much lower than that of a water HP, it improved as the temperature increased; hence, naphthalene HPs are effective for high-temperature heat recovery.