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In this paper, the condensation heat transfer of hydrocarbon mixtures refrigerant (methane/propane) flowing in a helical tube with 10 mm hydraulic diameter was investigated by experiments and numerical simulations. The experiments were conducted at mass flux of 200–400 kg/(m 2 ·s), saturation pressure of 0–4Mpa and heat flux of 4.8–5 kW/m 2 . Also, the effects of mass flux, vapor quality, and saturation pressure on heat transfer coefficient were studied. It was observed that the heat transfer coefficients increased with the increase of mass flux and vapor quality, while the heat transfer coefficients generally decreased as the saturation pressure increased. Meanwhile, annular flow(half-annular flow, annular flow) and Non-annular flow patterns (slug flow, stratified flow, wavy flow, transition flow) were observed during the condensation of methane/propane mixtures refrigerant. And a new flow pattern transition line for hydrocarbon refrigerants condensation process was proposed. The condensation heat transfer coefficient data were compared with several existing correlations, and a modified heat transfer correlation for different flow patterns was proposed, which predicted the results well with a mean absolute error of 10.03%. [ABSTRACT FROM AUTHOR]

Helical tube has been widely used in liquefied natural gas (LNG) liquefying applications. However, studies on the heat transfer performance of hydrocarbon mixture refrigerant in a helical tube have rarely been conducted. In this paper, condensation heat transfer characteristics of hydrocarbon mixture refrigerant in a helical tube were investigated numerically. The tests were conducted at saturation pressure of 2–4 MPa, mass flux of 100–400 kg/(m 2 ·s) and vapor quality 0–1. The numerical model was well verified by experimental data. And the effects of different structural parameters (tube diameter, helix angle and curvature diameter) and operating parameters (mass flux, heat flux and saturation pressure) on the heat transfer of hydrocarbons refrigeration were considered. The results showed that the tube diameter and mass flux had significant effect on condensation heat transfer coefficient. Meanwhile, stratified flow, half-annular flow and annular flow were observed during the condensation of methane/propane mixtures refrigerant by simulations, and a new flow pattern transition line for hydrocarbon refrigerants condensation process was proposed. Finally, the simulation results were compared with several well-known condensation heat transfer correlations. The research results will provide some constructive instructions for more effective design of LNG heat exchanger. [ABSTRACT FROM AUTHOR]

• Ahrens model provides the best accuracy for void fraction. • The condensation pressure drop characteristics of hydrocarbon mixture were studied. • Pressure drop of mixture decreases as the propane mass fraction increased. • A comparison of pressure drop correction based on flow pattern was conducted. • An improved frictional pressure drop correlation was proposed. A study was conducted to investigate the void fraction and pressure drop characteristics of methane/propane under different mass flux, saturation pressure and heat flux in a helically coiled tube, and the effects of distribution ratio (methane/propane) 50/50, 66/34 and 80/20 mole% were also analyzed. The friction pressure drop increased with the mass flux increased. Similarly, with the decrease of saturation pressure, friction pressure drops decreased. For a different distribution ratio, the friction pressure loss increases as the propane component increased in the mixture. Meanwhile, existing correlation models of different forms were used to evaluate the void fraction, and the Ahrens model provided the best accuracy with a MARD (mean absolute relative deviation) of 2.85%. In addition, the existing pressure drop correlations were used to compare with simulated data. Friedel correlation gave a well prediction for non-annular data with a MARD of 16.1%, while Cavallini correlation can well predict annular flow data with a MARD of 16.6%. Finally, considering the influence of flow regime transition, a new frictional pressure drop correlative was proposed, which can predict the data well with MARD of 5.4%. [ABSTRACT FROM AUTHOR]

• Flow patterns for zeotropic hydrocarbon mixtures were observed. • A new flow pattern transition line between annular and non-annular flow pattern was proposed. • An improved heat transfer correlation was proposed. An experimental and simulation investigation of condensation flow pattern and heat transfer characteristics of zeotropic hydrocarbon mixtures methane/propane and ethane/propane in a helical tube was presented. Flow visualization was conducted to capture flow pattern during flow condensation. The flow mechanisms were categorized into six different flow patterns: slug flow, stratified flow, transition flow, wavy flow, half-annular flow and annular flow. In addition, several existing two-phase flow pattern maps in horizontal tube were compared with the flow pattern data. Then a new flow pattern transition line between annular and non-annular flow pattern was proposed. Based on the flow pattern transition line, the heat transfer data under different flow pattern were compared with the existing heat transfer corrections. Finally, an improved heat transfer correlation was proposed and well coincided with the data with a mean absolute relative deviation (MARD) of 13.8%. [ABSTRACT FROM AUTHOR]