Experimental comparison and numerical study of flow and heat transfer characteristics of the pipe rows in heat pipe heat exchanger

Lube oil cooling is a very important heat transfer process on board, and the use of liquid-liquid heat pipe heat exchangers (HPHE) is easier to maintain and save energy, and does not have the risk of leakage. In this work, the heat transfer and flow in the heat pipe row of liquid-liquid HPHE is analyzed. The numerical model of HPHE based on the thermal resistance network of heat pipe is constructed and verified with the actual experimental data, and its maximum deviation is 8.1%. Results show that increasing the working fluid temperature in the evaporative section improved the operating performance of the heat pipe inside the HPHE, with the maximum equivalent thermal conductivity reaching 7112 W·m−1·K−1 at 70 °C. Furthermore, increasing the hot fluid flow rate improved the heat transfer rate of the HPHE more than increasing the cold fluid inlet flow rate. The convective heat transfer performance equations were fitted to the HPHE, with reliable accuracy within 5% obtained for both the forced convection correlations in the condensing and evaporating sections. The pipe row effect was observed to have some variability, with the periodic variation of the heat transfer coefficient per pipe row being more pronounced. The heat transfer coefficient of the pipe row at the outlet decreased by 15.5%, and the heat transfer coefficient of the pipe row at the baffle gap was also about 15% lower than that of the middle pipe row.