Numerical Simulation of Liquified Natural Gas Boiling Heat Transfer Characteristics in Helically Coiled Tube-in-Tube Heat Exchangers

Helically coiled tube-in-tube (HCTT) heat exchangers are widely applied to the process technology because of their compactness and higher heat transfer efficiency. HCTT heat exchangers play an important role in liquified natural gas (LNG) use and cold energy recovery. The heat transfer characteristics, pressure distribution, and degree of vaporization of LNG in HCTT heat exchangers are numerically investigated. By comparing the simulation results of the computational model with existing experimental results, the effectiveness of the computational model is verified. The numerical simulation results show the vapor volume fraction of the HCTT heat exchanger is related to the inlet Reynolds number, inner tube diameters, and helix diameter. The vapor volume fraction increases rapidly from the fourth to the seventh equal division points of the helix tube length. On condition that the inlet Reynolds number is greater than 33500, the pressure drop rate gradually increases. When the magnitude of the vapor volume fraction is below 0.2, the heat transfer coefficient increase rate is greater than that when the vapor volume fraction is above 0.2. The heat exchange efficiency of HCTT heat exchangers increases with the decrease of the ratio of helix diameter to inner tube diameter.