Study On The Transformation Conditions And Microscopic Mechanism Of Rheological Properties Of High Concentration Coal Water Slurry

Slurry hydraulic pipeline transportation has been widely applied for the advantages of low cost and environment friendly.How to achieve maximum transport efficiency under small transport resistance to reduce operation cost in pipeline transportation has been focused.Studies of the rheological properties of two-phase flow under different condition can provide the basis for the design and optimize of pipeline system.Take paste and slurry as a whole,and measured rheological properties of coal water slurry under different particle sizes and concentrations were by rotary rheometer.The low field nuclear magnetic resonance(NMR)technology was used to explore different water statuses distributions in coal water slurries under different conditions,adsorption water,interstitial water and free water were distinguished and quantified.Then to make comprehensive analysis of slurry rheological properties changes and water statuses distribution to analyze the internal microscopic mechanism of viscosity changes of solid-liquid two phase flow.Determine the critical conditions when slurry changes into paste from the perspective of micro mechanism.The main works and conclusions are as follows:(1)The rheological properties change of coal-water slurry under different solid concentrations and particle sizes are measured.Coal-water slurry is Newtonian fluid,the shear stress increases linearly with the increase of shear rate under different condition,which conform to Bingham model with shear thinning effect.The viscosity increases with the increasing of concentration,and there is a critical concentration.The change rate of viscosity showed 30 times different when the concentration is lower or higher than the critical concentration.The reason is the change of separation distance of particles.Under a certain concentration,the viscosity decreases with the increase of particle size,for the change of surface physical and chemical effects and water content.(2)Based on NMR,it can be distinguished that there are three different water statuses mainly existed in coal-water slurry,which is adsorption water,interstitial water and free water,each can be quantified through T2 spectra.T2 spectra showed that Under a certain particle size,adsorption water has no connection with concentration,free water and interstitial water increases with the increase of concentration.Under the same concentration,adsorption water and interstitial water negatively correlated with particle size,and free water and particle size were positively correlated.The reason is the length of the particle spacing and the strength of the adsorption reunion.(3)Interaction relationship between micro water distribution in the slurry and macro rheological properties were analyzed,the critical concentration when slurry changes into paste was determined from the perspective of theory.The change of free water content is the root cause of the CWS rheological properties change.The parameter particle spacing ratio(L/d)was presented to consider separation distance,free water content,and particle size at the same time.0.05<L/d<0.10 is the critical condition when slurry changes into paste.Formula to calculate the critical concentration when slurry changes into paste was obtained by data fitting,which can provide basis for the determination of optimum transport condition.