What is Reversible expansion work?
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Asked in Graduate Degrees, IQ
Why does gas inside a cylinder cool when subjected to adiabatic expansion?
Asked in Chemistry
How the expanison of metals which is a reversible change put to good usesupport your answer by an example?
Is isothermal expansion reversible under ideal conditions?
No. All processes involving heat transfer are not reversible, since they result in an increase in entropy. Isothermal expansion implies heat transfer to maintain the system at a constant temperature. Normally an expanding gas would cool if there were no heat entering the system. Adiabatic processes involve no heat transfer and are reversible. The temperature can (and usually does) change during an adiabatic process.
What factors reduce the the efficiency of heat engine from its ideal value?
If we consider the "ideal value" to be a Carnot engine operating between the heat source and heat sink of the actual engine, there are several factors that reduce the efficiency of the actual engine - most of which are deviations from the Carnot cycle: Reversible isothermal expansion of the gas at the "hot" temperature, TH (isothermal heat addition). In reality, no expansion can be completely isothermal because heat transfer occurs at a finite rate, so an isothermal expansion would have to occur over infinite time. Also expansion in real heat engines is never reversible - some energy is lost to friction. Isentropic (reversible adiabatic) expansion of the gas (isentropic work output). This would require perfect insulation but perfect insulation does not exist. As in the previous step, the expansion cannot be reversible because of losses to friction. Reversible isothermal compression of the gas at the "cold" temperature, TC. (isothermal heat rejection) In reality, no compression can be completely isothermal because heat transfer occurs at a finite rate, so an isothermal compression would have to occur over infinite time. Also compression in real heat engines is never reversible - some energy is lost to friction. Isentropic compression of the gas (isentropic work input). This would require perfect insulation but perfect insulation does not exist. As in the previous step, the compression cannot be reversible because of losses to friction. Adding to this is the fact that most heat engines do something closer to isobaric expansions (across a valve) or isochoric (constant volume) heating and cooling, which are less efficient than the corresponding steps in the Carnot Cycle.