Modeling And Experiment Research On Fabric Drying Mechanism In Printing And Dyeing Heat Setting

Heat setting is an important process during fabric printing and dyeing produce.Heat setting mainly focus on the problem like warp elongation,wept shrinkage,and wept skew after preprocessing of printing and dyeing.heat setting takes advantage of air flow of high temperature and large velocity to achieve drying the fabric,stabilize the dimension of the textile,and make the fabric flat.The mechanisms of heat setting similar the porous material drying,influenced by many factors simultaneously.The factors above-mentioned includes extern drying environment(air temperature,air velocity,relative humidity,etc.),material property(porosity,density,thermal conductivity coefficient,specific heat capacity,etc.).Extern drying environment is determined by the structure of the air duct in the heat setting machine(the whole dimension of the air duct,the baffle`s structure,the nozzle `s distribution)and operation parameter.There exists lack of theoretically instruction to the adjustment of heat setting`s operation parameter for different kind of textile.The adjustment of operation parament usually rely on people`s experience at present,which result in no assurance on the product`s quality,generate large amount of energy wasting.Numerical simulation is carried out to study how the factors influence porous fabric drying progress.Cotton fabric drying under single nozzle impingement is taken as a study target,to demonstrate how the operation parameter influence the drying progress.The mathematical model and numerical result `s reliability is verified by experiment.the content and conclusion is listed as following:Introduction about the general porous drying `s progress and characteristic is mentioned.Based on the characteristic of porous fabric`s structure and diffusion theory,the mathematical model describing porous fabric drying progress was constructed.Implementing above-mentioned mathematical model to calculate the cotton fabric drying under single nozzle jet impinging.The conservation variable including temperature and molar concentration of liquid water.The temperature calculated has the corresponding feature of preheating period,constant drying period,decreasing drying period,conform to the characteristic of general porous material drying.we use the mathematical model to calculate different operation parameter(jet temperature,jet velocity,the distance between fabric and nozzle)`s influence on fabric drying,and analysis the mechanism how the factors influence the fabric drying process.Increasing the airflow temperature or the air flow velocity both could boost evaporation,but in different way.Evaporation was boosted by increasing the convective heat transfer coefficient,when increasing airflow`s velocity.Evaporation was boosted by increasing the content concentration difference of vapor between fabric surface and airflow,when increasing airflow`s temperature.The distance between the nozzle and the fabric effects the fabric drying process by influencing the convective heat transfer coefficient `s distribution.The relative humidity becomes larger when increasing initial water content,which result in higher evaporation rates.But time needed for completing fabric drying is still determined by initial water content.The higher initial water content,the longer time needed for fabric drying.the experiment platform has also been set up,to study the temperature variation on time and temperature distribution during fabric drying,and analysis the drying characteristic under single nozzle impinging.The numerical result `s reliability is verified by corresponding input in experiment,and analysis the reason results in the difference between experiment result and numerical result.The numerical simulation on baffle`s structure and the distribution of nozzle was carried out,the results shows that fully-enclosed baffle will get a better velocity angle which is beneficial for drying process.The different form of baffle has little effect on the uniformity of flow rate and velocity angle between nozzle`s outlet.Staggered nozzle distribution effects the velocity angle and flow rate `s distribution by joint effect with the wall of air duct on airflow.