Enhanced Boiling of Saturated Water Over 2 × 3 AISI 304 Tube Bundles Coated With Diamond-Like Carbon for Two-Phase Heat Exchanger Applications

Abstract

This study aims to address the endeavor of the research community to improve the two-phase heat transfer (HT) characteristics of AISI-304 tubes with low thermal conductivity. This is achieved by applying diamond-like carbon (DLC) coating over the smooth tube using PVD techniques. This article specifically examines the pool and flow boiling HT phenomena of distilled water over a 2 × 3 tube bundle (TB) coated with DLC and is compared with respect to a conventional smooth TB. The experimental wall superheat and heat transfer coefficients (HTC) of both smooth and coated TB are analyzed for a range of mass flux [20–100 kg/(m2s)], heat fluxes [15–75 kW/m2], and pitch-to-diameter ratio (P/D) [1.25, 1.6, and 1.95]. The findings show that the DLC-coated TB results in higher HTC than the smooth TB. The DLC-coated tubes have higher wettability, which facilitates the flooding of the nano-and micropores, leading to enhanced HT performance of TB. In particular, the DLC-coated TB showed a 40% increase in HTC at the lowest P/D in pool boiling mode and a 34% increase in flow boiling mode at the highest P/D. This clearly shows a distinctive feature of DLC-coated TB where the enhanced HT performance in pool and flow boiling modes occurred in the reverse arrangement of P/D. The qualitative study behind the better HT ability of DLC-coated TB is done through high-speed image visualization. The study can help to implement DLC-coated TB in two-phase heat exchangers as its excellent corrosion resistance and antifouling properties are well established.