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Abstract
In this work, we present an exceptionally high heat transfer coefficient (HTC) and critical heat flux (CHF) achieved by graphene nanoplatelets (GNPs) and copper composite coatings with tunable surface properties. These coatings were created by a combination of powder metallurgy and manufacturing processes including ball milling, sintering, electrodeposition, and salt-patterning. We demonstrated correlations between various coating processes, resultant surface morphologies, properties, and improved boiling mechanism. Electrodeposition of GNP and copper particles led to formation of tall ridge-like structures and valleys to contain the boiling fluid in between. Higher CHF achieved for these coatings was attributed to the microlayer evaporation. It was observed that ball milling of GNP and copper particles prior to their sinter-coating enhanced their surface roughness that resulted in very high HTC, nearly 5.4 times higher than plain copper surfaces. Additional salt-patterning along with sinter-coating yielded interconnected porous networks with high nucleating activity that rendered record-breaking HTC of 1,314°kW/m2-°C. Combination of these coating processes can be adopted to tailor the surfaces and achieve better boiling performance. Novel techniques developed in this work can be applied to a variety of thermal engineering applications.
Highlights
IntroductionThe mechanisms underlying enhanced pool boiling heat transfer have been investigated in past few decades for efficient design of reboilers (Thome, 1988; Lavrikov et al, 2015), heat exchangers (Antonelli and O’Neill, 1981; Ohta et al, 2004), power electronics (Kercher et al, 2003; Wei et al, 2009; Sadaghiani et al, 2017; Sinha-Ray et al, 2017; Zhang et al, 2018; Chauhan and Kandlikar, 2019), and other high temperature engineering applications (Konishi and Mudawar, 2015; Mudawar, 2017)
The ball milling cycle included a short annealing cycle of 1 h after every 15 min of ball milling for cold welding of the copper and graphene nanoplatelets (GNPs) particles that promotes the draping of GNP around copper particles as seen on Figure 3B
We present various copper/graphene nanoplatelets (Cu/ GNP) based composite coatings for their applications in pool boiling heat transfer
Summary
The mechanisms underlying enhanced pool boiling heat transfer have been investigated in past few decades for efficient design of reboilers (Thome, 1988; Lavrikov et al, 2015), heat exchangers (Antonelli and O’Neill, 1981; Ohta et al, 2004), power electronics (Kercher et al, 2003; Wei et al, 2009; Sadaghiani et al, 2017; Sinha-Ray et al, 2017; Zhang et al, 2018; Chauhan and Kandlikar, 2019), and other high temperature engineering applications (Konishi and Mudawar, 2015; Mudawar, 2017) This is attributed to high heat transfer efficiencies or heat dissipation exhibited by pool boiling due to the absorption of large amount of latent heat which is accompanied by phase change from liquid to vapor (Kandlikar, 2019; Amalfi et al, 2020). Liquid jet impingement-based techniques have been implemented by other researchers as well to suppress nucleate boiling in unwanted regions and improve the resultant pool boiling performance (Jaikumar et al, 2017b; Yuan et al, 2019; Pi et al, 2020)
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