Flow boiling heat transfer of R1234yf on a microparticle coated copper surface

Abstract

This article investigates the flow boiling heat transfer of the low global warming potential refrigerant R1234yf on a microparticle coated surface obtained via high-pressure cold spray, a simple and nonexpensive technique. The sample was obtained by depositing pure copper particles with average size of 20 μm obtaining a 0.1 mm thick coating on a smooth copper plate 10 mm wide and 200 mm long. The experimental measurements were carried out at constant saturation temperature of 30°C, by varying the heat flux from 50 to 100 kW m⁻², the refrigerant mass flux from 30 to 200 kg m⁻² s⁻¹, and the vapor quality from 0.2 to 0.99. The coating was found to be hydrophilic, leading to hysteresis on the heat transfer behavior, which is discussed in detail. Furthermore, the experimental results are compared against similar measurements obtained during R1234yf flow boiling over a plain copper surface.

Nomenclature

cp	=	specific heat at constant pressure (J kg−1 K−1)
G	=	mass velocity (kg m−2 s−1)
h	=	specific enthalpy (J kg−1)
HF	=	heat flux (W m−2)
HTC	=	heat transfer coefficient (W m−2 K−1)
I	=	electric current (A)
m	=	mass flow rate (kg s−1)
p	=	pressure (bar)
P	=	power (W)
q	=	heat flow rate (W)
Sa	=	surface roughness (μm)
t	=	temperature (°C)
x	=	vapor quality (–)

Greek symbols

ΔV

=

electric potential difference (V)

Subscripts

base	=	base
Coated	=	referred to the coated surface
cr	=	critical
EL	=	electrical
i	=	ith element
in	=	inlet
L	=	saturated liquid
loss	=	losses
mean	=	mean
out	=	outlet
pc	=	precondenser
Plain	=	referred to the uncoated surface
ref	=	refrigerant
sat	=	saturation
TS	=	test section
V	=	saturated vapor
vs	=	superheated vapor
w	=	water
wall	=	at the wall