Research On Fluid Flow And Heat Transfer Characteristics Of Submerged Combustion Vaporizer

Submerged combustion vaporizer(SCV)is the key heat exchange equipments for LNG chain,the working principle of SCV mainly utilizes water bath as intermediate medium to achieve the heat exchange between the flue gas and trans-crtical LNG.Recently,the domestic running SCVs are mainly imported from the Japan and German,they have not been designed and manufactured by China,the main reasons lie in the inadequate research on the two-phase fluid sweeping tube bundle on the shell-side and trans-critical convective heat transfer of LNG in the serpentine tube,the quantitative design and calculation method has not yet formed.Therefore,the fluid flow and heat transfer characteristics of SCV were investigated by the experiments and numerical simulation in this paper,the main works and conclusions were as follows:(1)A set of SCV experimental apparatus was designed and built,the coupled heat transfer process between the shell-side two-phase fluid sweeping the tube bundle and the tube-side trans-critical fluid vaporization was studied.The phenomenon that shell-side two-phase fluid sweeping tube bundle could be observed during the operation of SCV,moreover,the parameters such as heat load,volume flow rate of flue gas,water height,tube-side fluid temperature and pressure,the water bath temperature and outer tube bundle wall temperature could be controlled and recorded.(2)The fluid flow and heat transfer characteristics of SCV tests were conducted,the influences of medium conditons on the coupled heat transfer performance were studied,the key parameters affected the efficient run of SCV were revealed.Experimental results showed that the severe disturbance of bubbles and the circulating water contributed to the heat transfer capacity of SCV.The optimized heat transfer performance of SCV could be adjusted by the matching relationship among the tube-side mass flux,superficial flue gas and static water height,ensuring the main shell-side heat transfer area was not frozen and tube-side fluid met the requirement of gasification.(3)On the basis of the experimental study,the mathematical model was established for coupled flow and heat transfer process among two-phase fluid,tube bundle wall and trans-crtical LNG,the model was verified by the experimental results.Through the numerical simulation,the trans-critical LNG convective heat transfer characteristic in the serpentine tube and two-phase fluid sweeping the tube bundle convective heat transfer characteristic were studied.Results showed that inside the serpentine tube,under the effect of drastic change of fluid thermos-physical properties,the local heat transfer coefficient increased firstly and then decreased,it reached the maximum value near the pseudo-critical tempereaure.Under the influence of Dean vortex shear,the local heat transfer coefficient in the bend sections was significantly increased.The condensation of vapor in the flue gas could strengthen fluid heat transfer capacity outside the tube bundle,and the heat transfer performance of fluid was better when the gas hold-up in the weir was 25%?45%.(4)Through the numerical simulation,based on this set of experimental apparatus,the coupled heat transfer characteristic of SCV was studied,the optimized operating conditions of heat transfer performance of SCV were given.Results showed that the ratio of shell-side mass flow rate of flue gas and tube-side mass flow rate of LNG should be controlled in the 0.2?0.3,meanwhile,the ratio of static water height and weir height should be controlled in the 0.6?0.9.The dimensionless correlations were proposed to predicte the tube-side and shell-side fluid heat transfer characteristics of SCV,the prediction deviations were within ±20%and±25%,which could provide the reference for the design of project SCV.