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Title: Effect of Ball Milled and Sintered Graphene Nanoplatelets–Copper Composite Coatings on Bubble Dynamics and Pool Boiling Heat Transfer
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NSF-PAR ID:
10149696
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Advanced Engineering Materials
Volume:
22
Issue:
7
ISSN:
1438-1656
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    We demonstrate a novel technique to achieve highly surface active, functional, and tunable hierarchical porous coated surfaces with high wickability using a combination of ball milling, salt-templating, and sintering techniques. Specifically, using ball-milling to obtain graphene nanoplatelets (GNP) draped copper particles followed by salt templated sintering to induce the strength and cohesiveness to the particles. The salt-templating method was specifically used to promote porosity on the coatings. A systematic study was conducted by varying size of the copper particles, ratio of GNP to copper particles, and process parameters to generate a variety of microporous coatings possessing interconnected pores and tunnels that were observed using electron microscopy. Pool boiling tests exhibited a very high critical heat flux of 289 W/cm2at a wall superheat of just 2.2 °C for the salt templated 3 wt% GNP draped 20 µm diameter copper particles with exceedingly high wicking rates compared to non-salt-templated sintered coatings. The dramatic improvement in the pool boiling performance occurring at a very low surface temperature due to tunable surface properties is highly desirable in heat transfer and many other engineering applications.

     
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    This work presents the experimental characterization of pool boiling heat transfer enhancement on cylindrical tubes with circumferential micro-channels using saturated water at atmospheric pressure as the working fluid. Three engineered copper tubes with 300 μm, 600 μm and 900 μm fin width and a fixed 400 μm channel width with 410 μm channel depth were machined using CNC. To compare the boiling enhancement on engineered tubes, one plain copper tube was used as the reference heater. The active heating area on the cylindrical tubes had a dimension of 9.5 mm outer diameter and 10.5 mm length. A custom-built cylindrical heater was designed using a nichrome wire coil of 30 AWG with a resistance of 19.57 Ω/inch of coil to provide joule heating to the cylindrical tubes. The electrical wire was insulated from the copper heater using a thin layer of alumina paste. The saturated pool boiling tests up to critical heat flux (CHF) were conducted at atmospheric pressure. While an approximate CHF of ∼70 W/cm2 was achieved for the plain copper tube, the cylindrical tube with microchannel geometry showed a CHF range of 131–144 W/cm2 that corresponds to 87%–100% enhancement as compared to plain cylindrical tube.

     
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