Experimental study on surfactant drag reducer rheological property and turbulent drag reduction characteristic of pipe flow at high temperature conditions

Integration of drag reduction technology with medium-deep geothermal heating technology, operating at an average heat extraction temperature of 80 °C, demonstrates significant potential in reducing pump consumption and enhancing the energy efficiency of heating system. However, current surfactant drag reducers are primarily effective within medium to low temperature range (20–60 °C). To address the need for drag reducer suitable for high-temperature environment (≥80 °C), a thorough investigation was carried out. It includes the design and construction of devices for drag reducer in testing fluid rheological property and implementing experiments for evaluating turbulent heat transfer and drag reduction characteristics. This study specifically focuses on docosyltrimethylammonium chloride (BTAC) drag reducer. Results indicate that the maximum allowable temperature of BTAC drag reducer exceeds 80 °C. Moreover, its friction factor exhibits a nonlinear trend with Reynolds number (Re). It decreases firstly and then increases until the drag-reducing effect diminishes. Furthermore, the heat transfer reduction rate (HTR) and drag reduction rate (DR) increase with increasing solution concentration. Interestingly, within the valid temperature of 30–80 °C, the impacts of solution temperature on the two parameters are minimal. Notably, at 600 ppm concentration, 80 °C and Re = 60,400, the BTAC solution exhibits a peak drag reduction of 0.56 and a corresponding heat transfer reduction rate of 0.36.