Study On New Methods For Online Monitoring Of Two-Phase Flow In Mini/Micro-Channel

Two-phase flow in mini/micro-channel has broad application prospective in the field of chemical engineering,microelectronic,etc.To better study and apply two-phase flow in mini/micro-channel,it is necessary to realize the online monitoring of two-phase flow in mini/micro-channel.However,the existing monitoring methods are relatively limited.It is necessary to undertake more research works on the online monitoring of two-phase flow in mini/micro-channel.Conductance/impedance detection methods have the advantages of simple construction,good real-time performance,low-cost and are suitable for industrial environment.They have the potential to be applied on the online monitoring of two-phase flow in mini/micro-channel.However,most of the conventional conductance/impedance detection methods are contact detection methods.The electrodes of their sensors are in contact with the measured two-phase flow,which will lead to electrode polarization,the electrochemical erosion and electrode contamination.And they may disturb the flow of the fluid.The capacitively coupled contactless conductivity detection（C⁴D）technique provides an approach to develop a contactless conductance/impedance sensor and hence to realize online monitoring of two-phase flow in mini/micro-channel.However,up to date,few research works concerning the application of the C⁴D technique to online monitoring of two-phase flow in mini/micro-channel have been published.This dissertation aims to extend the application fileld of the C⁴D technique.A new C⁴D sensor,which can be used for online monitoring of two-phase flow in mini/micro-channel is developed to obtain the equivalent conductance information/impedance information of two-phase flow in mini/micro-channel.Meanwhile,by combing the new C⁴D sensor and information process technique,studies on online monitoring of two-phase flow in mini/micro-channel（especially of boliling in mini/micro-channel and droplet-based microfluidics）are carried out.The innovation and contributions are listed as follows:1.A C⁴D sensor based on series resonance principle is applied to online monitoring of statics boiling in mini-channel.With the C⁴D sensor and the perceptron algorithm,a new method for online monitoring of statics boiling in mini-channel is proposed.In this new method,the C⁴D sensor is used to obtain the equivalent conductance information of the fluid in mini-channel.With the features extracted from equivalent conductance information,the perceptron algorithm is used to realize the stage identification of bubble growth of statics boiling in mini-channel.Three prototypes with mini-channel of inner diameter of 1.6mm,2.0mm and 2.5mm were developed and online monitoring experiments were carried out to verify the effectiveness of the proposed method.Experimental results show that for all the developed prototypes,the identification accuracies for bubble growth stages of statics boiling in mini-channel are all greater than 90%.2.By the introduction of an LC circuit,a new C⁴D sensor that can be used for online monitoring of two-phase flow in micro-channel is developed.This new C⁴D sensor can obtain conductance/impedance information at a low excitation frequency and can overcome the unfavorable influence of coupling capacitance.To verify the effectiveness of the new C⁴D sensor and find out its input-output characteristics,conductivity and concetration measurement experiments were carried out in a microfluidic chip with a 500μm×50μm micro-channel at low excitation frequency.Experimental results indicate that the new C⁴D sensor can realize conductivity and concentration measurement at low excitation frequency（less than 50k Hz）.The LOD（limit of the detection）for conductivity measurement is 2.2μS/cm.The LODs for concentration measurement of Li Cl and K₂SO₄ are 19.0μmol/L and 8.2μmol/L,respectively.3.The new C⁴D sensor is applied to the online monitoring of flow boiling in micro-channel.With the new C⁴D sensor and Ho-Kashyapa algorithm（H-K algorithm）,a new method for online monitoring of flow boiling in micro-channel is developed.In this new method,the equivalent conductance information of the fluid in micro-channel is obtained by the new C⁴D sensor.With the features extracted from equivalent conductance information,the H-K algorithm is used to realize real-time flow pattern identification.With three results of real-time flow pattern identification,a comprehensive decision is used to determine the final monitoring result,i.e.to identify the flow pattern in a specific condition of flow boiling in micro-channel.Online monitoring experiments were carried out in a 5mm×0.5mm micro-channel to verify the effectiveness of the proposed method.The experimental results show that for all the four investigated flow patterns（single-phase flow,bubbly flow,slug flow and annular flow）,the accuracies of four flow patterns are all greater than 98%.4.The new C⁴D sensor is applied to the online monitoring of water-in-oil droplet in droplet-based microfluidics.A new method for online monitoring of water-in-oil gdroplet in droplet-based microfluidics is proposed.In the new method,the new C⁴D sensor is used to obtain the impedance information of the water-in-oil droplet in micro-channel.With the features extracted from impedance information and the developed measurement models,online measurement of droplet length and dispersed phase holdup are carried out to realize online monitoring of water-in-oil droplet.Online monitoring experiments were carried out in a microfluidic chip with a 500μm×500μm T-shaped micro-channel to verify the effectiveness of the proposed method.The experimental results show that the relative error for droplet length measurement is less than 10%and the maximum measurement error for dispersed phase holdup measurement is less than5%.The new method can realize online monitoring of water-in-oil droplet by the online measurement of droplet length and dispersed phase holdup.