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From this, the heat demand and steam load may be determined for full load and start-up. Whatever the application, when the heat transfer surface needs calculating, it is first necessary to evaluate the total mean heat transfer rate. These materials will act as a heat sink when immersed, and they need to be considered when sizing the heating surface area. The size of outflow heater will depend on the temperature of the bulk oil, the pumping temperature and the pumping rate.Īdding materials to open topped process tanks can also be regarded as a heat loss component which will increase thermal demand. Heat is therefore only demanded when oil is drawn off, and since the tank temperature is lowered, lagging can often be dispensed with. Heating elements are encased in a metal shroud protruding into the tank and designed such that only the oil in the immediate vicinity is drawn in and heated to the pumping temperature. Another method of heating can be employed, such as an outflow heater, as shown in Figure 2.6.4. Sometimes, with very large bulk oil storage tanks for example, it can make sense to maintain the holding temperature lower than the required pumping temperature, as this will reduce the heat losses from the tank surface area. The heating element, when sized on the sum of the mean values of both these components, should normally be able to satisfy the overall heat demand of the application. If the heating surface is sized only with consideration of the warm-up component, it is possible that not enough heat will be available for the process to reach its expected temperature. The total heat demand at any time is the sum of these two components. However, the heat loss component will increase as the product and vessel temperatures rise, and more heat is lost to the environment from the vessel or pipework. In any heating process, the warm-up component will decrease as the product temperature rises, and the differential temperature across the heating coil reduces. The manufacturer’s rating is an indication of the ideal capacity of an item and does not necessarily equate to the connected load. These ratings usually express the anticipated heat output in kW, but the steam consumption required in kg/h will depend on the recommended steam pressure.Ī change in any parameter which may alter the anticipated heat output, means that the thermal (design) rating and the connected load (actual steam consumption) will not be the same. The thermal rating (or design rating) is often displayed on the name-plate of an individual item of plant, as provided by the manufacturers. However, for a plant which is still at the design stage, or is not up and running, this method is of little use. This will provide relatively accurate data on the steam consumption for an existing plant. Steam consumption may be determined by direct measurement, using flowmetering equipment. The results acquired using this method are usually accurate enough for most purposes. Although heat transfer is not an exact science and there may be many unknown variables, it is possible to utilise previous experimental data from similar applications. The steam demand of the plant can be determined using a number of different methods:īy analysing the heat output on an item of plant using heat transfer equations, it may be possible to obtain an estimate for the steam consumption. This will enable pipe sizes to be calculated, while ancillaries such as control valves and steam traps can be sized to give the best possible results. The optimum design for a steam system will largely depend on whether the steam consumption rate has been accurately established. Including warm-up, heat losses and running loads. ![]() #Thermodynamics calculator as a function of time how to#How to calculate steam requirements for flow and non-flow applications. ![]()
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