M.Ing. / Scaling problems in a heating or cooling system can be recognised by one or more of the following symptoms. Reduction in heat transfer rate, in which the formation of an insulating deposit on a heat transfer surface significantly reduces the cooling or heating efficiency of the equipment. Reduced water flow, which results from a partial or complete blockage of pipelines, condenser tubes, or other openings. Even a small build-up of scale on a heat exchange surface reduces water flow. Scale may continue to build up in boilers until heat transfer is so low that the metal overheats, permitting the tubes to rapture under the operating pressure. Scale is usually found in water-handling equipment in which water is heated, i.e. hot-water storage tanks, boilers, etc. The magnitude of this problem may be appreciated by considering that scaling can cause degradation, or complete failure in thermal and hydraulic performance which increases initial and operating costs (Chan and Ghassemi, 1991). A fairly low-pressure boiler, with only 0.6 mm of calcium sulphate scale on the tubes results in a 180°C temperature drop. The cost involved due to heat transfer inefficiency and the removal of scale, in Britain alone, is estimated at £1 billion per annum (Darvill, 1993). Poor conductivity of a 25 mm thick CaC03 scale layer can decrease the heat transfer by 95% (Glater eta/., 1980), whereas a Si02 scale layer 0.5 mm thick results in a 90% decrease in heat transfer (Grutsch and McClintock, 1984).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:1850 |
| Date | 06 December 2011 |
| Creators | Smith, Christo |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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