Flow condensing heat transfer of R410A, R22, and R32 inside a micro-fin tube

ABSTRACT

An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focuses on the influence of heat transfer area upon the condensation heat transfer coefficients. The test sections were made of double tubes using the counter-flow type; the refrigerants condensation inside the test tube enabled heat to exchange with cooling water that flows from the annular side. The saturation temperature and pressure of the refrigerants were measured at the inlet and outlet of the test sections to defined state of refrigerants, and the surface temperatures of the tube were measured. A differential pressure transducer directly measured the pressure drops in the test section. The heat transfer coefficients and pressure drops were calculated using the experimental data. The condensation heat transfer coefficient was measured at the saturation temperature of 48°C with mass fluxes of 50–380 kg/(m²s) and heat fluxes of 3–12 kW/m². The values of experimental heat transfer coefficient results are compared with the predicted values from the existing correlations in the literature, and a new condensation heat transfer coefficient correlation is proposed.

KEYWORDS:

• R410A
• R32
• R22
• condensation heat transfer
• micro-fin tube
• correlation

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by Ministry of Education, Science, and Technology (NRF-2016R1D1A1A09919697).

Nomenclature

A	=	area, m2
Cp	=	specific heat, kJ/kgK
Dh	=	hydraulic diameter, m
EHT	=	enhanced heat transfer
h	=	heat transfer coefficient, kW/m2K
i	=	enthalpy, kJ
Ja	=	Jacob number, $Ja=C{p}_l\left(T_{sat}-T_{wall}\right)/h_{fg}$
k	=	thermal conductivity, kW/mK
$\dot{m}$	=	mass flow rate, kg/s
Pr	=	Prandtl number
Pr	=	reduction pressure
q	=	heat flux, kW/m2
$\dot{Q}$	=	heat flow rate, kW
Re	=	Reynolds number
T	=	temperature, °C
Sv	=	dimensionless specific volume, $Sv=\left(\frac{{\rho }_l}{{\rho }_v}-1\right)/\left(x\frac{{\rho }_l}{{\rho }_v}+\left(1-x\right)\right)$
x	=	vapor quality

Greek symbols

ν	=	specific volume, m3/kg
µ	=	viscosity, Pa.s

Subscripts

f	=	fluid
g	=	gas
i	=	inside
o	=	outside
in	=	inlet
l	=	liquid
p	=	preheater
r	=	refrigerant
sat	=	saturation
w	=	wall