Experimental investigation on flow boiling heat transfer characteristics of R1234ze(E)/R152a in 6-mm ID horizontal smooth tube

ABSTRACT

The near-azeotropic refrigerant mixture R1234ze(E)/R152a (40/60 by mass%) was an excellent alternative refrigerant with outstanding environmental protection and thermophysical properties as well as good cycle performance. The flow boiling heat transfer characteristics of R1234ze(E)/R152a (40/60 by mass%) in horizontal smooth copper tube with inner diameter (ID) of 6 mm were investigated experimentally. The effects of mass flux (100–200 kg·m⁻²·s⁻¹), saturation temperature (285.15–291.15 K), heat flux (5–20 kW·m⁻²), and vapor quality (0.02–0.98) on the boiling heat transfer coefficient (HTC) and critical vapor quality were analyzed. It was found that the boiling HTCs increased with increasing heat flux or saturation temperature, and decreased at first but then increased with rising mass flux. The boiling HTCs almost kept constant firstly but then decreased with increasing vapor quality. Besides, the critical vapor quality decreased with increasing heat flux or decreasing mass flux. Finally, the experimental results were compared with several correlations which predict boiling heat transfer characteristics, it could be concluded that the correlations proposed by Jung et al. and Choi et al., respectively, had high prediction accuracy.

KEYWORDS:

• Experimental investigation
• R1234ze(E)/R152a
• boiling
• flow
• heat transfer

Nomenclature

Variables

A area, m2	=
$d_i$inside diameter of inner tube, m	=
$d_o$ outside diameter of inner tube, m	=
$E_{preh}$ heating power of preheated section,W	=
$G$ mass flux, kg·m−2·s−1	=
$h$boiling heat transfer coefficient, W·m−2·K−1	=
$H_l$ enthalpy of saturation liquid phase under the inlet pressure of preheated section, J·kg−1	=
$H_V$ enthalpy of saturation vapor phase under the inlet pressure of preheated section, J·kg−1	=
$H_{sub}$ enthalpy of subcooled state under the inlet pressure of preheated section, J·kg−1	=
$L$ the effective length of test section, m	=
m mass flow, kg·h−1	=
N data points	=
$q$ heat flux,W·m−2	=
$Q$heat flow rate, W	=
T – refrigerant temperature, K	=
t wall temperature, K	=
$t_{wo}$ average temperature on the outside wall of inner tube, K	=
V volume flow, m3·h−1	=
$x$ vapor quality	=

Subscripts

ac – acceleration	=
exp experimental value	=
in inlet of test section	=
out outlet of test section	=
p pressure, Mpa	=
pred prediction value	=
preh preheated section	=
ref – refrigerant	=
sat saturation state	=
w constant temperature heating water	=
w1–w4 point on the outside wall of inner tube respectively	=

Greek symbols

${\rho }_v$regrigerant density of vapor phase, kg·m−3	=
${\rho }_l$ regrigerant density of liquid phase, kg·m−3	=
$C_p$ specific heat capacity, J·kg−1·K−1	=
$\mathrm{\Delta }$ change in variable,-	=
$\rho$ density, 998 kg·m−3	=
$\lambda$ thermal conductivity of copper, 407 W·m−1·K−1	=
δ – wall thickness, m	=

Acknowledgments

This investigation was supported by the National Natural Science Foundation of China (51766010). The authors also would like to gratefully acknowledge the support of the Institute of Refrigeration of Huazhong University of Science and Technology.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51766010].