In boiler when water is heated, if the water is hard then would contain salts. So on heating the water the water particles are evaporated by the time and the saturated salts are left behind. Now its the part of the boiler, if the inner walls are made up of non stick material or such then the salts which is left as a precipitate will not stick on the same and hence make the water thicker and thicker as more and more water will evaporate which would result in a very thick liquid substance having a lot of salt rather than water, this is known as SLUDGE. On the other hand if the inner walls of the boiler is not made up of such non sticking material then the salts would stick on them resulting a formation of a thick layer of salts on the walls, this is known as SCALE.
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Natural circulationForce circulation1.In Natural circulation boiler the circulation is done by means of nature.In Forced circulation Boiler the circulation is done by the means of pumps.2.These type boilers are low capacity boilers.These type boilers are of high capacity boilers.3.The heating of boiler parts is not uniform, so, there are chances of differential expansion of parts and hence chances of cracks are maximum.The heating of boiler parts is uniform, so, there is no chance of differential expansion of parts and hence chances of cracks are minimum.4.These boilers take maximum time from cold start.These boilers take minimum time from cold start.5.There is a scale formation between the water tubes and hence blockage of pipes.There is no scale formation between the water tubes and hence no blockage of pipes.6.These boilers produce lesser steam and have low pressure steam.These boilers produce steam at 30 to 650 tons per hour, at the temp of temp. & 160 bar pressure.
The difference between a large-scale aid project and appropriate technology is that a large-scale aid is when a country receives a lot of aid, so it's basically given to the people, but an appropriate technology is developed by the people themselves without any aid.
A manufacturing plant basically manufactures a chemical on a mass scale however a pilot plant helps to develop the process on a small scale, before a manufacturing plant is built.
There may not be any science involved in engineering as it is a process of detailing based on available/validated science. engineering design is purely mathematical calculations and drawings as per scale after desdigning.
Horticulture deals with plant cultivation, that is, to prepare the land for raising crops,[on a smaller scale that Agriculture], and Agronomy deals with using plants for food, feed, fuel, fiber, and pharmaceutical crops.