The influence of collecting net on reverse osmosis membrane

In order to understand the transmission characteristics of the fabric, we must first understand the characteristics of the water flow when it flows on different interfaces. Generally, when water flows in a hydrophobic (lipophilic) pipe, slippage occurs. The result of slip is an increase in flow and a decrease in flow resistance [1]. Our light net is a kind of fabric used for collection, so it is required to have good water conductivity. Generally, the better the hydrophobicity, the better the water flow on its surface. Therefore, we take the hydrophobicity of the fabric as the first factor to be investigated.　　 Hydrophobicity refers to the physical property that a molecule (hydrophobe) and water repel each other [2]. This property can be judged by measuring the contact angle formed between the surface of the substrate and the water droplets on the surface of the substrate. The larger the angle, the better the hydrophobicity of the interface. In order to characterize the hydrophobicity of light nets with different structures, light net cloth samples with three weaving densities of A, B, and C are selected, and they respectively represent a sparse and dense weaving structure. Measure the contact angle of the surface. Measure the angle of the contact angle to determine the hydrophobicity of the three fabric samples. Three kinds of light net contact angle photos: 　　 From the above comparison chart, the hydrophobicity of A, B, and C are respectively A. It can be seen that tightly woven fabrics are more hydrophobic than loosely woven fabrics, and the water flow on the surface of the fabric should also be Faster. 2.2 The influence of different structures on the transmission rate. Make a table of the flow values u200bu200bobtained at each pressure test point, and compare the test data of two fabrics with different structures to get the following figure: Sample 1 has a loose structure with a wider flow channel; Sample 2 has a structure Tight, narrow runner. It can be seen from the above figure that the flow rates of the two samples are similar under the condition of 150 psi; above 150 psi, the flow rate of the tightly structured light net is higher than that of the loosely structured light net. It shows that under certain pressure conditions, the fabric structure has little effect on transmission and has basically the same transmission efficiency; but under high pressure conditions, due to the faster flow rate, the loosely structured fabric surface has poor hydrophobicity, and the interface transmission effect of the water flow is not good and easy Produce a greater resistance to hinder, thus affecting the water flow transmission. 2.3 The compression resistance of fabrics of different structures is to make a table of the flow values u200bu200bobtained at each pressure test point, and the following figure is obtained: The thickness of the reverse osmosis membrane membrane is much lower than the collection net, and under the high pressure water flow, the membrane and the collection net are attached The tightness will become larger and larger, which will easily cause compaction, and the diaphragm will sink deeply into the texture of the collection net. If compaction occurs, it will seriously affect the unobstructed flow of the water production channel, which will naturally reduce the water production efficiency and cause a significant drop in the water production of membrane elements. It can be seen from the collected data points that as the pressure increases, the transmission flow rate decreases. At the point close to the 1200psi pressure value, the transmission flow is only about half of the flow at the 200psi pressure value point. The traffic has dropped severely. This phenomenon can be explained from the structure of the light network. Light nets are made of warp-woven fabrics with or without coating. There are small gaps on the surface of the nets. The size of the gaps is affected by the fiber thickness of the woven fabric. The relationship between flow and pressure of reverse osmosis membrane is that with the increase of pressure, the flow also increases. The desalination screen is used as a collection in the membrane module, and the water produced by the membrane permeates through the surface of the desalination screen to flow, and finally reaches the porous central tube. There will be water flow in the horizontal and vertical directions of the light net. I personally think that the vertical seepage increases after the gap increases, thereby reducing the horizontal flow rate. This can also explain the decrease in transmission flow under high pressure. Under high pressure, the water permeability of the upper and lower diaphragms increases, and at the same time, the vertical direction of fresh net seepage is increased. This direction is the main direction of product water penetration, which cancels most of the power, and the horizontal water flow is greatly weakened. Another point of view is that the diaphragm is tightly attached to the desalination net under high pressure, and the diaphragm is pressed into the groove of the desalination net, which limits the water conduction efficiency and causes the water flux to attenuate.