Multi-layer walls

The main fluids of interest with plastics are oxygen and water vapour (for packaging applications) and CO2 (for carbonated drinks applications). Fig. 1.13 and Fig. 1.14 illustrate the type of behaviour exhibited by a range of plastics. In some cases it is necessary to use multiple layers of plastics because no single plastic offers the combination of price, permeation resistance, printability, etc. required for the application. When multi-layers are used, an overall permeation constant for the composite wall may be obtained from... 

Jasper, McL, T. and Scudder, C. M. (1941) Trans. Am. Inst. Chem. Eng. 37, 885. Multi-layer constmction of thick wall pressure vessels. 

The vent area ratio for a single layer structure is the vent area divided by the total area of the wall. The vent area ratio for a multi-layer structure is... 

Many ammonia synthesis converters operate at 150 to 200 bar and around 515°C. Under these conditions, nitriding and hydrogen embrittlement can occur. The pressure shell is a multi-layer or multi-wall carbon steel vessel. The internal catalyst baskets, contained in the shell, are made of SS 321 material88. 

Beneath the epicuticular wax layer is the cuticle which bounds the epidermal cells and lines the sub-stomatal cavities. Structurally, it is noncellular and often multi-layered, comprising an inner region which merges with cellulose fibrils of the epidermal cell wall (cuticular layer, fibrillar in organization) (2). The chemical component of the cuticle proper is an... 

The analogy to electrical circuits is also used to extend the relationships derived in section 1.2.1 for overall heat transfer, to walls with several layers. Walls with two or more layers are often used in technical practice. A good example of these multi-layer walls is the addition of an insulating layer made from a material with low thermal conductivity Ais. Fig. 1.13 shows a temperature profile for a wall that consists of a number of layers. The resistance to heat transfer for each layer in series is added together and this gives the overall heat transfer resistance for the wall as... 

Protective radiation shields are used to reduce the radiative exchange between walls at different temperatures thin foils or sheets made of good reflecting materials are placed between the walls, Fig. 5.66. The spaces between the protective shields are normally evacuated so that heat transfer by convection is prevented. This multi-layer arrangement is used predominantly in cryogenic applications for the insulation of containers for very cold liquified gases. 

Combining the results of the TEM+ED and XPS analysis we may conclude that at the low deposition temperatures, i.e. below 400°C the films consist mainly of Ni3C type crystalline phase. Films grown at or above 400°C have a cubic (fee) Ni or NiCx structure constituting the crystalline part of the structure [19, 23], The access carbon, which is not incorporated into the NixC carbide, constitutes the multi-layered graphitic walls separating the Ni-NixC crystalline grains. 

The situation becomes even more unpredictable since crystallisation of even pure salt solutions does not occur at a given point of relative humidity. Also the behaviour of the solvent, in this case water, within the porous system of the multi-layered plaster and paint layer system is different to, and much more complicated than, in vitro experiments. Therefore, we have to accept that the prediction of crystallisation and hydration cycles of salt mixtures within the porous wall painting system is one of the most difficult tasks one can imagine. 

FEM analysis will establish the approximate thickness of carbon-fibre panelling required to meet overall stress requirements (expressed in g/m ). It will also establish the quality of carbon fibres required (expressed typically in terms of HT(A/S), UM, etc.) as well as their orientation (e.g. single-or multi-directional layer). Further analysis will identify in which areas the carbon-fibre thickness can be reduced to 50% if required, with local reinforcements applied to meet stress levels. This analysis can also help establish where carbon-fibre composites can be replaced by basalt-fibre composite components. As an example, FEM analysis would reveal that, based on the chosen wall design concept, a 4 x 400 g/m multi-layer carbon HT-fibre would achieve the required strength. It would also highlight those areas which would need... 

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