Experimental Fouling Investigation With Modified Surface Of Electroless Ni-P Coating

The formation of deposits on heat transfer surfaces is the least understood problem in the design of heat exchangers due to large number of influential parameters with poorly understood interaction. The present work aims at investigating of CaCO3fouling on the modified surface of electroless Ni-P coating and contributes to a better understanding of how the surface characteristics in terms of roughness and energy properties affect the mechanisms of precipitation fouling. A series of theoretical and experimental studies were carried out systematically in this work. The main results are as follow,First, the formation of calcium carbonate deposits on artificially roughened copper surfaces ranging from1.02μm to2.02μm was investigated. With the decrease of the roughness of copper surface the fouling deposits and the surface energy decreased first and then increased, reaches a minimum when Ra=1.29μm. In addition, experiments also have been conducted to investigate the performance of Ni-P coating subjected to calcium carbonate scale deposition. The experimental results demonstrate that there is an important impact of the material’s surface energy upon fouling formation and low surface energy of coat surface has advantage in anti-fouling effect. Compared with untreated copper surface, the Ni-P coating exhibits excellent anti-fouling behavior and could maintain the metastable polymorphs vaterite and aragonite kinetic stability.Second, tests have been undergone to achieve the fouling resistant curves and heat transfer performance curves of three types of tubes (copper tube, stainless steel tube and copper-based Ni-P coated tube) under convective heat transfer. The experimental results show that Ni-P coating significantly increase the duration of induction time as much as1.8-fold over that of the untreated copper tube, followed by a lower fouling rate and the asymptotic fouling resistance value is only28percent of untreated copper tube’s. For the Ni-P coated tube, the deposit layer is relatively thin, non-homogenous, adhered more loosely and could easily be washed away. In general, the Ni-P coated tube provides much better non-stick conditions than the other untreated tubes. The fouling behaviors of Ni-P coated tube were also examined under different parameters conditions such as fluid velocity, hardness and surface temperature.