As a clean and efficient energy source, natural gas has gradually increased in the proportion of global primary energy consumption. Since the gas source is always far from the consumer market, in order to facilitate storage and transportation, the natural gas needs to be liquefied. Spiral wound heat exchanges (SWHE) have been widely used as the main cryogenic heat exchanger in large-scale liquid natural gas (LNG) plants due to its advantages of multi-stream capability, high compactness, efficient heat transfers, sufficient flexibility and good robustness. However, the zeotropic hydrocarbon mixtures condensation flow in the tube side of SWHE, as a typical phase-change two-phase flow, its heat transfer mechanisms are still insufficient to understand, which limits the design and optimization of LNG SWHE. Thus, in this paper, the studie on zeotropic hydrocarbon mixtures condensation heat transfer in a helical pipe is proposed. Firstly, based on two-fluid model and thermal phase change model, a numerical method coupling with empirical correlations is established to predict condensation heat transfer for zeotropic mixtures, in which the mixed effects are taken into account. Meanwhile, the rationality of the above methods is verified based on the existing experimental results. Then, The effects of refrigerant components and operating parameters on flow patterns, heat transfer coefficients and heat and mass transfer resistance are discussed as the ranges of mass flux, saturation pressure and vapor quality are 200-800kg/(m^2^·s), 2-4MPa and 0.15-0.90, respectively. It can be found that the predicted results coincide with the experimental ones, with deviations within ±15%. For different zeotropic hydrocarbon mixtures, as the vapor quality increases, the stratified flow, half-annular flow and annular flow appears in turn. The mixed heat transfer coefficients are always smaller than film heat transfer coefficients owing to the existence of heat and mass transfer resistance in vapor core. Besides, both film and mixed heat transfer coefficients increase with the increase of vapor quality and mass flux, while decrease with the rise in saturation pressure. Further, heat and mass transfer resistances increase as the vapor quality and saturation pressure increase and the mass flux decreases. In addition, compared to methane/ethane/propane/nitrogen (65/25/5/5, mole%) mixture, the averaged heat transfer performance for methane/ethane (90/10, mole%) mixture improves 19.55%, whereas, the average heat and mass transfer resistance decreases 53.51%. This study is helpful for understanding the zeotropic mixtures condensation in tubes and gives some suggestions for the choice of refrigerant components used in LNG SWHE, to design more effective SWHE.


The Condensation Heat Transfer Characteristics of Zeotropic Hydrocarbon Mixtures in a Helical Pipe

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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