December 4, 2013
Dr. Doba Jackson
Thermodynamics within a Heat Engine
Physical chemistry can be considered anything that undergoes a physical or chemical change using the underlying concepts of mathematics and physics. According to chemist Gilbert Newton Lewis, “Physical chemistry is everything that is interesting” (ACS). When you think about it, physical chemistry is all around us in the world we live in today. Some aspects of physical chemistry can even range anywhere from tropical storms to turbines, or steam engines and just about everything in between. So it’s pretty much, in some form or fashion, involved in all that we do. A major piece of physical chemistry is thermodynamics. Thermodynamics is the study of the effects of heat, work, and energy on a system (NASA). The three laws of thermodynamics really give off a better understanding of what thermodynamics really is and how it can apply to everything around us. One example of something we are constantly around that also plays a role in thermodynamics is a heat engine. Within a heat engine, lie the simplest and most true examples of what thermodynamics is really all about. The first law of thermodynamics, also known as the conservation of energy, states that energy can neither be created nor destroyed. Which is pretty much saying that power generating processes and energy sources can convert energy from one form to another; therefore the internal energy must be a constant (engineering). For a heat engine, thermal energy is converted to mechanical work by the system. One commonly used heat engine is a basic gas powered cyclic engine such as a gas turbine. For a heat engine, such as the gas turbine, the energy or heat is converted when the combustion of the working substance, such as gas, is ignited. The heat source that ignites the combustion is done by an electric spark, known as a spark-ignition (turbivo). This causes the combustion to create a high temperature flow. In other words, the energy is applied in the form of heat to change the state of a working fluid and then extracted in the form of mechanical work to return the working fluid to its initial state (mpoweruk). This step of the process is carried out by the expansion and contraction of the pistons when the working substance goes from a condensed liquid to an expanded gas state within the closed system of each individual piston. The movement of the pistons however, is only the beginning of the process of the engine. Now that the working substance has reached a high temperature state, the system must be cooled. Cooling and releasing are the next big steps of the heat engine process and are able to occur at the same time. These two important factors are where the second law steps in. The second law of thermodynamics states the constraints on the direction of the heat transfer and the efficiencies of the closed system. In other words, heat flows naturally from regions of higher temperature to regions of lower temperature, but that it will not flow naturally the other way. Heat can be made to flow from a colder region to a hotter region, but heat only does this when it is forced. On the other hand, heat flows from hot to cold spontaneously (physics). This law pertains to heat engines because this is when the heat is transferred to the cold reservoir until it reaches a lower temperature flow. This causes the temperature of the system to decrease, initially cooling it off. The final step of this process is the releasing of the excess heat. We know the releasing of the heat or energy as exhaustion, such as what comes out in the black clouds from chemical plants or even the exhaust pipes on our vehicles. The consequence of the thermal energy loss from the heat engine is that there will be less availability for the energy to do useful work (mpoweruk). This statement is what places limitations of the maximum possible efficiencies of a closed system, and is therefore what...
Cited: http://portal.acs.org/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_ARTICLEMAIN&node_id=1188&content_id=CTP_003398&use_sec=true&sec_url_var=region1&__uuid=8017a086-56bb-4132-85af-bfe3737b5bf0. ACS scientific journal. Physical Chemists.
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