Study on the Effect of Mechanical Action of A Front-Loading Washer on Washing Efficiency and Smoothness Appearance
Supervisor:wu xiong ying
In order to remove the stains,the clothes are lifted up by paddles on the inside wall of the drum and then drop.This action flexes the weave of the fabric and forces water and detergent through the clothes.The front-loading washer is the dominant design in Europe.In recent years,the domestic market share of front-loading washer has also increased.Recently,the researches on drum washing focus on the effect of traditional washing parameters,detergents and temperature on washing performance including washing efficiency and textile damage.However,agitation supplied by the back-and-forth rotation of the cylinder and gravity has been ignored.On the one hand,the drum washing process involves various complicated forces and the magnitude of the forces change over time.On the other hand,it is also difficult to characterize the mechanical action.However,it is of great importance to study the mechanism of the mechanical action,since it is the significant factor influencing washing performance.The textile motion trajectory tracking system was developed according to image process.The system can record the centroid of textile in real time.Based on this system,the effect of washing parameters,textile properties and geometry structure of inner drum on textile motion was studied.Secondly,dimensional analysis was used to study the interaction of these three types of parameters mentioned above.A dimensionless model of drum washer was established to study the effect of the dimensionless parameters and their interaction on washing efficiency.An advection-diffusion model was established to characterize the mass transfer along the thickness of fabric during the vertical falling process.Finally,the effect of mechanical action on wrinkling of cotton fabric was studied.The main research contents are as follows:(1)To develop a textile motion tracking system.This system can record the centroid of motion textile.Effective textile motion indexes were extracted,such as motion speed of centroid(speed of x direction,speed of y direction and total speed),acceleration,shear rate and residence time.Compared with the video of textile motion and the distributon of the centroid of the motion textile obtained from the system,it was proved that the system can be used to observe the movement of textile during washing.(2)The textile dynamics in a front-loading washer.Based on the textile motion tracking system,the fabric movement index system was established to study the effects of washing parameters,textile parameters and geometry structure of inner drum on textile motion.In general,textile motion can be classified into sliding,cascading and rotating.The distribution of Euler velocity was divided into two regions.A “passive region” which is located at the left bottom of the inner drum and an “active region” which is suited on the right top of the inner drum.The configuration of these two regions can influence the washing performance.A stagnant area on residence time distribution plot is coincident with the passive region occurring on the distribution of Euler velocity.Added mass can be used to explain the effect of water volume on the distribution of textile motion.The rotational speed of inner drum has a dramatic influence on textile motion due to centrifugal force.Textile properties and water volume can also affect the motion pattern.(3)The effect of mechanical action on washing efficiency.A dimensionless model of drum washer was established based on dimensional analysis to study how dimensionless parameters and their interaction influence washing efficiency.The results showed that the filling ratio,fabric surface friction coefficient,water ratio*Froude number,water ratio,viscosity of water and water ratio*friction coefficient are the significant factors affecting on washing efficiency.Besides,filling ratio,fabric surface friction coefficient and water ratio can also influence the distance between textile centroid and the center of the inner drum,thus affect the falling of textile.A convection-diffusion model along the thickness direction of fabric was built and the effect of gravity cannot be ignored.When the impact velocity of fabric is greater than 0.2 m/s,the transfer rate of water and detergent along the thickness direction of fabric increases.Temperature can also influence mass transfer rate.But there was no significant change between the mass transfer phenomenon at 35℃ and 60℃.(4)Tthe effect of mechanical action on smoothness appearance.Wash load,washing speed and spinning speed are the main factors affecting the formation of wrinkles during drum washing.The wrinkles formed in washing process are temporary and unstable.However,the compression stress acting on the cross section of the fiber in spinning process is about 0.17 MPa,which is about 10 times of the plastic deformation stress of cotton fiber with0.013 MPa to 0.019 MPa.In other words,wrinkles in washing process turn into folds in spinning process.The smoothness appearance of fabric decreased with the increase of wash load size because of decrease of free motion region.This is because that textiles tend to be trapped in the stagnant region in the inner drum and aggravate the wrinkles.The main innovation in this research are as follows:(1)The influence of washing parameters,fabric parameters and washer structure on textile motion was clarified by the research on the textile dynamics in a front-loading washer.The mechanism of the mechanical action was analyzed from the perspective of force analysis and fabric motion distribution.The results can be used to guide the subsequent researches.(2)For the first time,a detailed theoretical and experimental study on the water transfer along the thickness direction of the fabric has been implemented.The convective diffusion model of water and detergent along the thickness direction of the fabric was established.The influence of impact velocity and temperature on mass transfer was quantitatively discussed.The experimental data is in good agreement with the model calculation,enriching the theory of fabric washing.(3)The mechanism of cotton fabric wrinkling in the washing process is studied.The configuration of the passive movement area and the active movement area can affect the smoothness appearance of cotton fabric after washing.Wrinkles formed in washing process are temporary.These temporary wrinkles will transfer into permanent and fixed folds in spinning and drying process.The importance of the drop impact process on improving washing efficiency is explained from the perspective of fabric movement and mass transfer.The effect of textile motion on wrinkling of cotton fabric was also discussed.The results can be applied to the study of clothing care processes.In addition,the fabric trajectory tracking system is also suitable for tracking fabric movement during the drying phase.