Experimental research on the effect of acid and ash deposition on heat transfer characteristics of PTFE-coated 3-D finned tube

Abstract

With characteristics of strong flow disturbance and high heat transfer coefficient, 3-D finned tubes have significant advantages in recovering flue gas waste heat. However, fly ash particles and sulfuric acid vapor in power plant flue gases can foul and corrode 3-D finned tubes when deposited on their wall surfaces, resulting in a reduction in the efficiency of the heat exchanger. To protect the heat exchanger from corrosion, corrosion resistance coatings are the most economical solution. However, acid and ash deposition and their effects on heat transfer performance of the 3-D finned tube coated with corrosion resistance coating have not been clear. In this work, firstly, uncoated, ceramic-coated, Teflon lacquer-coated and PTFE-coated 3-D finned tubes were immersed in sulfuric acid solution and the PTFE coating with better corrosion resistance was screened by corrosion weight loss method and SEM characterization. Then, the heat transfer performance of PTFE-coated 3-D finned tubes under acid-ash coupling conditions was investigated using the simulated flue gas method. Impacts of fin structure parameters (fin height, fin width and axial fin spacing) and experimental working conditions (cooling water inlet temperature, fly ash concentration and sulfuric acid volume fraction) on Nu number were investigated. Results demonstrate that PTFE-coated 3-D finned tube have a lower Nu at the initial moment than uncoated tubes. That is because PTFE coating increases the thermal resistance. However, as the experiment progressed to a steady state, Nu were higher and ash deposition weight was smaller in the PTFE-coated 3-D finned tube. In addition, the effects of fin structural parameters and experimental conditions on heat transfer characteristics of PTFE-coated 3-D finned tube were investigated. In the acid-ash coupled condition, the Nu value increases with an increase of fin height or a decrease of fin width and axial fin spacing. Also, decreasing the cooling water inlet temperature, the fly ash concentration, or the sulfuric acid vapor volume fraction increases the Nu value.