Study on the multi-factors interaction of annular pulsating heat pipe based on response surface method and temperature curve analysis

Pulsating heat pipe enable rapid heat transfer over long distances and is suited for solar collector applications. However, there is no pulsating heat pipe specially designed for evacuated solar collector, which leads to a large contact thermal resistance between the heat pipe and the evacuated pipe. In this paper, a new structure of annular pulsating heat pipe (APHP) was designed. In order to efficiently optimize the operation parameters and understand the interaction of factors, the three-factors three-levels Box-Behnken Design (BBD) model of response surface method (RSM) was used to establish the optimization program, and the accuracy was tested by analysis of variance. The significance and interaction of factors (heat transfer distance, cooling water temperature and cooling water flow rate) on the heat transfer performance were analyzed according to the temperature oscillation curve. The results show that heat transfer distance has a much more significant effect on the heat transfer capacity than the cooling water temperature and cooling water flow rate. Furthermore, over long heat transfer distance, adjusting the cooling water temperature has a greater impact on the heat transfer performance. While over short heat transfer distance, adjusting the cooling water flow rate has a greater impact. The optimal working condition predicted by RSM model is 375 mm heat transfer distance, 15 degrees C cooling water temperature and 1.0 L/ min cooling water flow rate. The actual average heat flow obtained from experiment was 99.47 W, with an error of only 2.04% from the predicted value. This paper illustrates the feasibility and efficiency of the response surface method for studying the heat transfer performance of PHP. The significance and interaction analysis of factors can provide guidance for the practical application.