Capillary phenomena penetration

Another phenomenon is so called two-side filling of one-side closed conical capillaries with liquid [5]. On the one hand the more penetrant is trapped by the defect the wider indication will appear. Contrariwise it is almost impossible to extract a penetrant from the completely filled surface defects by dry developer [6]. In this study we propose the theory of the phenomenon. Besides experimental results of the investigation of two-side filling with various penetrants of conical capillaries are presented. Practical recommendations to optimize liquid penetrant testing process are proposed. 

Let us consider one more physical phenomenon, which can influence upon PT sensitivity and efficiency. There is a process of liquid s penetration inside a capillary, physical nature of that is not obvious up to present time. Let us consider one-side-closed conical capillary immersed in a liquid. If a liquid wets capillary wall, it flows towards cannel s top due to capillary pressure pc. This process is very fast and capillary imbibition stage is going on until the liquid fills the channel up to the depth l , which corresponds the equality pcm = (Pc + Pa), where pa - atmospheric pressure and pcm - the pressure of compressed air blocked in the channel. 

One more experimental result, which is important for PT is as follows. Only polar liquids fill conical capillaries from both sides. We used various penetrants to fill conical defects Pion , LZh-6A , LZhT , LUM-9 etc. It was established that only the penetrants containing polar liquid as the basic liquid component (various alcohols, water and others) manifest two-side filling phenomenon. This result gives one more confirmation of the physical mechanism of the phenomenon, based on liquid film flow, because the disjoining pressure strongly depends just on the polarity of a liquid. 

For some types of wetting more than just the contact angle is involved in the basic mechanism of the action. This is true in the laying of dust and the wetting of a fabric since in these situations the liquid is required to penetrate between dust particles or between the fibers of the fabric. TTie phenomenon is related to that of capillary rise, where the driving force is the pressure difference across the curved surface of the meniscus. The relevant equation is then Eq. X-36,... 

We shall not discuss the various consequences of penetration by limited amounts of liquid, but refer to the literature. The practical relevance is to discover how far ink from a pen or jet printer penetrates into the paper. When the added drops are very small this can lead to retention in the capillaries. In practice, this phenomenon can be troublesome sometimes it is referred to as the Jamin effect ). In order to displace it, one has to apply a pressure to overcome the difference between the advancing (at the front side of the drop) and receding (at the rear side) cmgles. This pressure difference across the drop amounts to... 

Soluble macromolecules of both natural and synthetic origins have been used as drug carriers. When compared with the particulate carriers, soluble macromolecules (i) encounter fewer barriers to their movement around the body and can enter into many organs by transport across capillary endothehum or in the liver by passage through the fenestration connecting the sinusoidal lumen to the space of Disse (ii) penetrate the cells by pinocytosis, which is a phenomenon universal to aU cells and which, unlike phagocytosis, does not require an external stimulus and (Hi) can be found in the blood many hours after their introduction (particulate carriers, in contrast, are rapidly cleared from the blood by the RES). The fate of soluble macromolecules in animals and humans, with special reference to the transfer of polymers from one body compartment to another, has been reviewed by Drobnik and Rypacek (67). 

The penetration of a liquid within a porous medium can be compared to a first approximation to the phenomenon of capillary rise. We shall derive what is commonly known as Washburn s equation. Consider a capillary tube touching a liquid surface with its axis vertical and internal radius tq. 

The ingress of oil into chocolate is seen to be a complex phenomenon. The dominant mechanism is a slow diffiision. The diliusion rate varies greatly with the type of oil, the phase the oil takes, and the preparation of the chocolate. Chir measurements also demonstrate a much faster, albeit more limited, penetration indicative of capillary flow... 

In Section 9.1, Figure 9.1, we have seen that adjacent to a charged surface there is an excess of counterions and a deficit of co-ions. Both contribute to the neutralization of the surface charge. Let us now focus on the expulsion of the co-ions. The expulsion of co-ions implies a reduced volume available for electrolyte, or, in other words, there is an excluded volume with respect to the presence of electrolyte. This is known as the Donnan effect. For the same reason salt (= electrolyte) cannot penetrate in narrow capillaries and pores having charged walls. Based on this phenomenon, porous membranes that are permeable for water but not for salt may be used in reversed osmosis (also called ultrafiltration). Practical applications of reversed osmosis are found in, for example, the production of potable water from seawater, in hemodialysis using artificial kidneys, and in the concentration of solutions such as fruit juices. 

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