Open systems, combustion

The gas turbine cycle may be either closed or open. The more common cycle is the open one, in which atmospheric air is continuously drawn into the compressor, heat is added to the air by the combustion of fuel in the combustion chamber, and the working fluid expands through the turbine and exhausts to the atmosphere. A schematic diagram of an open Brayton cycle, which is assumed to operate steadily as an open system, is shown in Fig. 4.2. 

Take a source, a compressor, a combustion chamber (heater), a turbine, and a sink from the open-system inventory shop and connect the five devices to form the open actual Brayton cycle. 

Heat engines that use gases as the working fluid in an open system model are treated in this chapter. The modern gas turbine engine operates on the Brayton cycle. The basic Brayton cycle consists of an isentropic compression process, an isobaric combustion process, an isentropic... 

From these three sources of information the peak value of the rate of pressure increase due to deflagration of mixtures of oxidizers and flammable substances is given at the maximum heat of reaction, and a similarity is found between the open systems in the IMO combustion rate test and the partially enclosed systems in the TNO deflagration test. 

The simplest type of open system of interest in combustion is the continuous-flow well-stirred tank reactor or CSTR, which is an idealization of tank reactors used widely in industry. In essence, this is simply a tank into which reactants flow continuously at some known volumetric flow-rate and the reactant-intermediate-product mixture is efficiently stirred so that there are no spatial concentration or temperature gradients. In order to maintain a constant reaction volume, there is a matching volumetric outflow of the mixture from the CSTR so that molecules spend only a finite time in the reactor. This is known as the mean residence time t es and is determined by the volumetric flow-rates and the reactor volume. 

Figure 2.1 Flow (open) system defined for combustion.

Open systems use atmospheric air for drying. In cases where products pose a potential for dust explosion, plants are provided with pressure relief or suppression systems. For recycle systems, the drying system medium is recycled, and the evaporated solvent recovered as condensate. There are two alternative designs. In the self-inertizing mode, oxygen content is held below 5 percent by combustion control at the heater. This is recommended for products with serious dust... 

The theory of spontaneous ignition can easily be understood by examining how combustion starts in a closed system, while forced ignition is discussed in an open system.13... 

To illustrate further, the relative humidity of air at 320°F is about 1% and the absolute humidity of the air is about 0.027 lbs. of water per pound of dry air. This already includes moisture from the products of combustion of the natural gas used for heating in an open system. This is a long way from... 

Problem Students may understand the increase of mass in an open system during combustion of metals and the formation of solid metal oxides. They are not convinced that the same is true for alcohol, paper or candles from their everyday experiences. In order to show it practically, one can place a lit tea-light (candle) on the balance in addition, carbon dioxide and steam can be captured with sodium hydroxide or soda lime (a mixture of sodium hydroxide and calcium oxide). In the apparatus (see picture), the gases are absorbed after... 

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