Characterization of graphene-filled fluoropolymer coatings for condensing heat exchangers.

Mitchell Cierpisz,Youliang He,Joselyne Mcphedran,Afsaneh Edrisy

doi:10.1177/00219983211037053

Mitchell Cierpisz, Youliang He + Show 2 more

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https://doi.org/10.1177/00219983211037053

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Abstract

Condensing heat exchangers are thermal devices subjected to extremely corrosive environments due to the formation of acidic condensates on the heat-exchange elements during service. To protect the heat exchangers from chemical attack, perfluoroalkoxy (PFA) coating has been applied as a barrier layer onto the surfaces of the heat-exchange elements to prevent corrosion. However, PFA has intrinsically poor thermal conductivity, and low wear resistance; thus, it is not naturally a good material for heat exchanger application. In this study, graphene nanoplatelets (GNPs) are incorporated into PFA powder as coating materials to improve the thermal properties of the fluoropolymer, for condensing heat exchangers application. Two grades of GNPs (8 nm and 60 nm layer thickness) are tested to evaluate the effect of graphene addition on the thermal, adhesion, electrical, and wear properties of the composites, which are compared to those mixed with multi-walled carbon nanotubes (MWCNTs). The results showed that both grades of GNPs significantly increased the thermal conductivity, i.e., ∼8× that of the virgin PFA. The composites incorporated with both grades of GNPs also demonstrated good coating adhesion strength and wear resistance, as well as excellent corrosion resistance. The composite filled with MWCNTs exhibited poor surface finish and minimal improvement in thermal performance.

Highlights

Waste heat recovery is a key technology for the processing industry to reduce energy waste by recycling the waste heat contained in hot exhaust streams, consisting of up to 70% of the total energy from the input fuel.[1]
This paper investigates the effect of graphene and multi-walled carbon nanotubes (MWCNTs), as potential fillers, on the thermal, adhesion and tribological performance of PFA-based composite coatings
When the filler content reached 20 wt%, both grades of graphene nanoplatelets (GNPs) fillers form well-established networks within the PFA matrix, whereas the MWCNT-filled sample does not form a network between filler particles

Summary

Introduction

Waste heat recovery is a key technology for the processing industry to reduce energy waste by recycling the waste heat contained in hot exhaust streams, consisting of up to 70% of the total energy from the input fuel.[1] Low-temperature waste heat, i.e. temperatures below $230C, accounts for $60% of all unrecovered waste heat,[1] since low-grade waste heat is not economically viable to recover using conventional heat recovery techniques. To maximize the recoverable energy, it is necessary to recover both the latent and sensible heats, which requires the exhaust streams to be cooled below their dew points At these temperatures, corrosive acids condense on the heat-exchange element surfaces, causing severe corrosion and premature failure of the heat recovery equipment.[1,2] Traditional heat exchangers made of low-cost metals (e.g. aluminum, stainless steel, copper, etc.) are not suitable for the condensing environment due to the catastrophic chemical attack on the heat-exchange elements. Exotic metals such as titanium, tantalum, niobium, etc., may withstand the corrosive conditions, but they are not economically viable for low-grade waste heat recovery

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