Improvement of thermal-hydraulic performance of plate heat exchanger by electroless nickel, copper and silver plating

Abstract

In this study, electroless plating of nickel, copper, and silver is applied to stainless steel 316 (SUS316) plate heat exchanger (PHE) to enhance thermal-hydraulic efficiency. The electroless plating experiment was first performed on small samples (30 × 30 × 1 mm) to determine optimum control parameters, i.e. solution concentration, current density, etching time prior to commercial PHE. The characteristics of the coating surfaces were indicated by static contact angle, thermal shock, roughness profile, Vickers hardness, SEM images, and EDS analysis. In order to research the effect of each electroless coating on PHE performance, a single-phase water flow heat transfer experiment was performed. The thermal-hydraulic efficiency was evaluated using the Overall Heat Transfer Coefficient (OHTC), Friction Factor, Number of Transfer Units (NTU), effectiveness and Performance of Evaluation Criterion (PEC). As a consequence, aqua regia solution with a volumetric ratio of 1HNO3: 2HCl: 75H2O, a current density of 0.1 A/cm2 and a 12-min etching were determined to be the optimum process parameters for optimizing surface area and minimizing mass loss. After electroless coating, the surface was completely changed from smooth to rough, resulting in a change from hydrophobicity to hydrophobicity, as well as a change in surface morphology. More significantly, all coated PHEs displayed a substantial increase in their performance, as shown by PEC ranging from 1.21 to 1.30 in the case of Silver-coated PHE, followed by 1.20–1.24 and 1.11–1.15 in the case of Copper and Nickel respectively.