Experimental study on the thermal-hydraulic performance of modified chevron plate heat exchanger by electrochemical etching method

摘要

In this research, an improvement of thermal-hydraulic performance on the plate heat exchanger is obtained by modifying stainless steel 304 (SUS304) surfaces through electrochemical etching method. The result was obtained through experimental data regarding the overall heat transfer coefficient, friction factor, Number of Transfer Units (NTU), effectiveness and the thermal performance factor of water flow inside a plate heat exchanger. A series of etching cases was conducted in order to find the optimal conditions for an application on a commercial SUS304 corrugated plates with a symmetrical chevron angle of 30°. Originally, the as-received surface had a roughness (Ra) value of 0.22 μm and a static contact angle of 81.5°, after using aqua Regia solution of the volumetric ratio of Nitric acid = 1: Hydrochloric acid = 3: water = 175 (HNO_3: HCl: H_2O, respectively) with an applied voltage of 5 Ⅴ for etching time of 8 min, they increased to 0.88 μm and 147° with a mass loss of 5.1 wt.%. Under a test matrix of various Reynold number ranging from 3000 to 12,500, 60 °C to 90 °C for the hot side temperature and 10 °C to 40 °C for cold side temperature, for bare and modified plate heat exchanger (PHE), the overall heat transfer coefficient improved to 10.5-17.7%, 7.2-16.5% for effectiveness and 1.05 to 1.194 for Performance of Evaluation Criterion (PEC), while an unavoidable increase of friction factor by at least 21.3%.