Simple way of draining is to create the least resistant path for the water to

Simple way of draining is to create the least

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Simple way of draining is to create the least resistant path for the water to flow. That is, provide a sump just below the autoclave heat exchanger and then pump back the water to the cooling water sump. This also reduces water wastage and prevents hot water/steam entering the cooling tower. The modern autoclaves employ seamless stainless steel (SS) tubes with extruded fins on the tube, which minimize pressure losses. These SS tubes have high heat-transfer area per unit volume of space they occupy. 6. Pressurization System The system must ensure that the required pressurization rates in the autoclave are met. The average pressurization rate in modern autoclaves is 2 bar/min. Nowadays, many autoclaves use nitrogen as the pressurization medium instead of air. This is because the autoclave cure consumables are highly inflammable in the air medium due to the presence of oxygen. There have been several reports of autoclave fire resulting invariably in the loss of the component. Though the nitrogen medium ensures fire-free autoclave cure cycles, care must be taken to avoid danger to personnel (possibility of asphyxiation) in nitrogen environments due to the lower oxygen levels. The nitrogen gas pressurization system consists of a primary compressor, nitrogen plant, booster compressor, storage tanks, and associated piping circuitry as shown in Figure 7 . The primary compressor takes in the air from the atmosphere and pressurizes it to 7 bar(g). The nitrogen plant receives the air at 7 bar(g) and by a process known as Pressure Swing Adsorption (PSA) isolates nitrogen from the atmospheric air. The PSA has emerged as one of the popular methods of producing nitrogen. The nitrogen purity produced by this method is of the order of 99%, which is adequate for curing of aerospace polymeric composites in autoclaves. The nitrogen, thus, isolated is further pressurized using a booster compressor to higher pressures, typically 17– 22 bar. Higher pressure is required to create su cient pres- sure di ff erential in order to meet the required pressurization rate. The nitrogen storage tanks are sized in such a way that the free-air delivery (FAD) of these storage tanks is 2.5 times the FAD of the autoclave. For example, the FAD of a 200-cubic-meter autoclave operating at 7 bar(g) would be 1400 cubic meters and consequently, the FAD of the nitrogen storage tanks would Autoclave Heat exchanger C t Sump for H.E drain water Main sump Pumps C Blower motor Fan Pumps Cooling tower Control valve Figure 6: Schematic of cooling system. Nitrogen generation plant Nitrogen filter Exhaust silencer Nitrogen reservoirs Autoclave shell Seal pressurization tank instrumentation Pressurization tank To pneumatically operated instruments Pneumatic loading bridge To atmosphere Figure 7: Schematic of pressurization system.
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