Convective condensation heat transfer of R134a in tubes at different inclination angles

Abstract

An experimental study of convective condensation heat transfer of R134a was conducted in an inclined smooth copper tube of inner diameter of 8.38 mm. The mean vapor quality ranged between 0.1 and 0.9, mass flux between 200 and 400 kg/m²s, inclination angle between −90^o (vertical downward) and +90^o (vertical upward) at a saturation temperature of 50^oC. The results show that the inclination angle and mean vapor quality strongly influence the coefficient of heat transfer. The developed correlation gave an average and mean deviations of 3.44% and 9.22%, respectively, for horizontal flow and, 5.25% and 19.41%, respectively, for vertical downward flow.

Keywords:

• Condensation
• correlation
• heat transfer coefficient
• inclination angle
• smooth tube

Funding

The funding obtained from the NRF, TESP, University of Stellenbosch/ University of Pretoria, SANERI/SANEDI, CSIR, EEDSM Hub, and NAC is acknowledged and duly appreciated.

Nomenclature

A	=	area (m2)
	=	specific heat capacity (kJ/kg.K)
d	=	diameter (m)
EB	=	energy balance
	=	Froude dimensionless number
g	=	gravitational acceleration (m2s)
G	=	mass flux (kg/m2s)
h	=	enthalpy (J/kg)
HMFR	=	heat and mass flux ratio
hfg	=	heat of condensation (kJ/kg)
k	=	thermal conductivity (W/mK)
L	=	length of test section (m)
	=	mass flow rate (kg/s)
Nu	=	Nusselt number
Pr	=	Prandtl number
Q	=	heat transfer rate (W)
R	=	thermal resistance (K/W)
Re	=	Reynolds number
T	=	temperature (°C)
x	=	vapor quality
z	=	axial direction

Greek symbols

	=	heat transfer coefficient (W/m2K)
	=	inclination angle (radian)
	=	Martinelli parameter
	=	viscosity (Pa.s)
	=	density (kg/m3)

Subscripts

Cu	=	copper
H2O	=	water
i	=	inner
in	=	inlet
j	=	measurement location
l	=	saturation liquid
in	=	inner
out	=	outer
pre	=	pre-condenser
ref	=	refrigerant
sat	=	saturation
test	=	test-condenser
TP	=	two-phase
v	=	saturated vapor
w	=	wall

Additional information

Funding

The funding obtained from the NRF, TESP, University of Stellenbosch/ University of Pretoria, SANERI/SANEDI, CSIR, EEDSM Hub, and NAC is acknowledged and duly appreciated.