Experimental Investigation on the Effect of Size and Pitch of Hydrophobic Square Patterns on the Pool Boiling Heat Transfer Performance of Cylindrical Copper Surface

Abstract

Abstract:In this work, pool boiling heat transfer tests were conducted for investigating the effects of the size and pitch of the hydrophobic square patterns on a copper test piece with the following dimensions: 40 mm long, 25 mm outer diameter, and 18 mm inner diameter. The size of the square patterns and the pitch were varied with an increment of 0.5 mm from 1 mm to 3 mm and from 4.5 to 5.5 mm, respectively. Among the various square patterns of different size and pitch, the 2 mm size square pattern with 5 mm pitch (inter-distance 3 mm) was found to be the best because it gives the advantage of bubble coalescence behavior and also the rewetting phenomenon. The observed bubble departure diameter was 2.35 mm, and using this diameter, we predicted the maximum inter-distance between the patterns for producing inter coalescence of bubbles in the axial direction was 3.12 mm. Therefore, a side-by-side distance of 3 mm, which was closed to the estimated inter-distance graphically, can avoid the earlier inter coalescence of the bubbles between patterns on the surface in the axial direction. This results in better pool boiling heat transfer performance. Highlights: (1) Heterogeneous wettable structures were obtained on the copper surface using screen printing techniques; (2) The effect of the size and pitch of the hydrophobic patterns on the bubble dynamics was determined; (3) The wall superheats of all the heterogeneous wettable surfaces were less than the plain copper surface; (4) The highest heat transfer coefficient was obtained from the hydrophobic pattern with 2 mm size and 5 mm pitch.

A Meta-Analysis Review: Nanoparticles as a Gateway to Optimized Boiling Surfaces

“…Sujith Kumar et al [ 51 ] quantified the optimal size and pitch distance of hydrophobic islands created using polymethyl methacrylate resin and trichlorosilane as a hydrophobic agent. They designed square patterns on various cylindrical copper rods, with sizes varying from 1 mm to 3 mm and pitches from 4.5 mm to 5.5 mm, all in increments of 0.5 mm.…”

“…The inter-distance between hydrophobic spots should be sufficient to keep the replenishing liquid reaching heating surfaces and prevent early-stage bubble coalescence. In previous studies, Sujith Kumar et al [ 51 ] recommended values of around 3.2 mm for a particular set of experimental boundary conditions; however, generalisation to other applications should be further investigated. The pitch distances, sizes and shapes of hydrophobic areas on hydrophilic base surfaces are important and must be accurately determined and used to drive the design of biphilic surfaces.…”

Micro-Nano Scale Surface Coating for Nucleate Boiling Heat Transfer: A Critical Review

“…Recent studies showed that hydrophilic and hydrophobic surfaces have significant abilities for boiling heat transfer enhancements [124][125][126][127][128]. Modified surfaces with the ability to enhance HTC (Heat Transfer Coefficient) and CHF (Critical of Heat Flux) values show at least one of the following properties: (a) increase in the frequency of the bubbles, (b) increase in the nucleation sites, (c) reduction of bubble's contact area, (d) low onset superheat for nucleate boiling [129,130].…”