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rppearso
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I have been working on a series of questions dealing with gas expansion and temperature change for my PE exam.
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rppearso said:I have been working on a series of questions dealing with gas expansion and temperature change for my PE exam.
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rppearso said:I am kinda working the thermal expansion of methanol in tandum with joule thompson expansion. I am studying for my PE right now (along with doing that thermal expansion of methanol at work) and I am having the same set of problems dealing with air, I attempted to use joule thompson to model rapid expansion of gas (the calcs under methanol expansion actually apply more to joule thompson rather than liquid expansion). If you view the work I did attached to thermal expansion of methanol (and I will also attach the mathcad and updated hand calcs) you will see that you get temperature trends opposite of what is expected and after going through the first law derivation and a bernoulli differential equation its pretty frustrating because it should be correct for the rapid expansion of a gas, I was doing this in order to develop an equation for T2 in terms of pressure change using a vander walls equation of state.
All that being said I need to progress with my PE study so I have just been using the air tables at the back of the PE book but I am not sure what Vr actually is. In an otto cycle in the constant volume expansion V is constant from D to A but Vr is not what exactly is Vr, we never used air tables in college and while I can crank out the PE problems using the methods in the book I would really like to know what it is I am doing.
This has been a very good site and I am glad I found it, it keeps me doing things that are useful and more away from political sites which just waste your time.
I have the updated joule thompson calcs worked out using the bernoulli differential equation (the roots of the methodology of solving first order non seperable differential equations will have to wait another day in a different section, but what is up with the integrating factor and why can you assume the constant of integration goes away, among other questions) and I will post them as soon as I can consolidate my work and scan everything in.
stewartcs said:Vr generally stands for Reduced Volume (i.e. The ratio of the specific volume of a substance to its critical volume). Not sure without seeing the book you are reading though.
CS
The relationship between gas expansion and temperature change is described by Charles's Law, which states that the volume of a gas is directly proportional to its Kelvin temperature, assuming constant pressure and amount of gas. This means that as the temperature of a gas increases, its volume also increases, and vice versa.
The ideal gas law, PV = nRT, can be used to calculate temperature change in the PE Exam by rearranging the equation to solve for temperature (T). This allows you to calculate the temperature of a gas given its pressure (P), volume (V), and number of moles (n). It is important to note that this equation only applies to ideal gases, which do not exist in real life but are used as a simplified model for calculations.
Adiabatic gas expansion is a process where the gas expands without gaining or losing heat, meaning the temperature of the gas remains constant. In contrast, isothermal gas expansion is a process where the gas expands while maintaining a constant temperature. Adiabatic expansion is typically a rapid process, while isothermal expansion is slower and requires a heat source or sink to maintain the constant temperature.
According to the ideal gas law, as the temperature of a gas increases, its pressure also increases, assuming constant volume and amount of gas. This is because as the gas particles gain kinetic energy with higher temperature, they collide more frequently with the walls of the container, resulting in an increase in pressure. Conversely, if the temperature decreases, the pressure of the gas will also decrease.
No, according to Charles's Law, the volume of a gas is directly proportional to its temperature, assuming constant pressure and amount of gas. This means that if the temperature of a gas changes, its volume will also change. However, if the volume of a gas is kept constant, then its temperature cannot change according to this relationship. This is known as isochoric (constant volume) gas expansion.