Hydrodynamic effects on soiled surfaces : an experimental study and theoretical analysis

This thesis presents the findings of an investigation aimed at understanding the effects of hydrodynamic shear stress on soil removal from textile surfaces both inside the washing machine and in closely controlled laboratory conditions.The research has involved developing a technique for the indirect measurement of shear stress based on pressure recordings and small block probes that provide both an indication of shear stress magnitude and direction. The probes have been investigated and calibrated in a purpose-built, rectangular-section, water tunnel in which tests were also carried out on specially prepared soiled cotton textile samples. This has allowed the correlation between shear stress and soil removal efficiency for 15k ≤ Re ≤ 155k. A more general investigation involving the washing machine has also been carried out so as to quantify and compare the effects of detergency, water temperature, time, abrasion, warping and tangential shear force.The hydrodynamic conditions inside the washing machine were investigated providing insight into flow conditions both on the inside and outside of the wash load. This was achieved through the use of a wireless device in the form of a sphere with an on-board pressure-flow sensor and radio transmitter for remote monitoring via radio. This remote data acquisition system was designed, developed and patented by the author. A model of the wash load motion has also been developed and high speed filming techniques employed to qualify and quantify the wash load dynamics.The main outcome of the research may be summarised as follows:- Hydrodynamic shear stress up to 7.7Pa a circa (15k ≤ Re ≤ 155k) is inadequate to remove soil from the standard EMPA textile surfaces.- Only 10-15% of the soil removed in the washing machines can be attributed to abrasion, warping (due to churning) and hydrodynamic shear stress, the rest is attributed to detergency and heat transfer.- There are at least two different flow domains within a horizontal-axis washing machine, one on the inside of the wash load and one on the outside.- Flow conditions on both the inside and outside are turbulent and velocities up to several meters per second have been recorded

本论文阐述了针对理解水流剪切应力对纺织品表面土壤去除效应的研究发现，该研究涵盖了在洗衣机内部以及严格控制实验室条件下进行土壤去除效应的研究。研究过程中，研究者开发了一种基于压力记录及小型方块探头间接测量剪切应力的技术，该探头不仅能指示剪切应力的大小，还能确定其方向。探头在专门设计的矩形截面水道中进行过检测和校准，并在该水道中对特别制备的受污染棉纺织样品进行了测试，从而得出了剪切应力与土壤去除效率之间的相关性，范围在15k ≤ Re ≤ 155k之间。此外，还进行了一项更广泛的涉及洗衣机的调查，以量化并比较洗涤剂、水温、时间、磨损、扭曲和切向剪切力的影响。洗衣机内部的水动力学条件也得到了研究，从而揭示了洗涤负载内外部的流动状况。这一研究通过使用一种带有船上压力流量传感器和无线电发射机的无线设备，通过无线电远程监测，实现了对远程数据采集系统的设计、开发和专利申请。同时，还开发了一种洗涤负载运动的模型，并采用高速摄影技术对洗涤负载的动力学进行了定性和定量分析。研究的主要成果可概括如下：在15k ≤ Re ≤ 155k的范围内，7.7Pa的水动力剪切应力不足以从标准EMPA纺织品表面去除土壤；在洗衣机中去除的土壤中，仅有10-15%可归因于磨损、扭曲（由于搅拌引起的）和水动力剪切应力，其余部分归因于洗涤剂和热量传递；在水平轴洗衣机内部至少存在两个不同的流动域，一个位于洗涤负载内部，另一个位于外部；内部和外部均存在湍流流动，记录到的速度高达数米每秒。