- #1
Rasmus10
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Hi
Im trying to understand the justification for flow work for a control volumen considering the 1. law of thermodynamics.
<br /> \[\begin{array}{l}<br /> \frac{d}{{dt}}(me) + \sum {{{(e\dot m)}_{out}}} - \sum {{{(e\dot m)}_{in}} = \dot Q + \dot W} + {{\dot W}_{fw}}\\<br /> {{\dot W}_{fw}} = \sum {{{(p \cdot v \cdot \dot m)}_{in}}} - \sum {{{(p \cdot v \cdot \dot m)}_{out}}} \\<br /> e = mass\,specific\,energy\\<br /> v = mass\,specific\,volumen\\<br /> {W_{fw}} = flow\,work<br /> \end{array}\]<br />
Re-arranging the equation is used to introduce enthaply. However, what i don't understand is, why do i have to include the term flowwork? Let's say that the pressure inside the CV is equal to the pressure outside, and no energy is lost due to friction, then there would be introduced no energy to the controlvolumen? No work is done on the gas entering the CV, hence no extra increase in energy?
This is essential the understanding of the definition of enthalpy, why i really need to understand it in depth.
A bonus question: Anyone that has an intuitive microscopic understanding of why adding heat at a high temperature increase the entropy less than adding it at a lower temperature?
Regards,
Rasmus
Im trying to understand the justification for flow work for a control volumen considering the 1. law of thermodynamics.
<br /> \[\begin{array}{l}<br /> \frac{d}{{dt}}(me) + \sum {{{(e\dot m)}_{out}}} - \sum {{{(e\dot m)}_{in}} = \dot Q + \dot W} + {{\dot W}_{fw}}\\<br /> {{\dot W}_{fw}} = \sum {{{(p \cdot v \cdot \dot m)}_{in}}} - \sum {{{(p \cdot v \cdot \dot m)}_{out}}} \\<br /> e = mass\,specific\,energy\\<br /> v = mass\,specific\,volumen\\<br /> {W_{fw}} = flow\,work<br /> \end{array}\]<br />
Re-arranging the equation is used to introduce enthaply. However, what i don't understand is, why do i have to include the term flowwork? Let's say that the pressure inside the CV is equal to the pressure outside, and no energy is lost due to friction, then there would be introduced no energy to the controlvolumen? No work is done on the gas entering the CV, hence no extra increase in energy?
This is essential the understanding of the definition of enthalpy, why i really need to understand it in depth.
A bonus question: Anyone that has an intuitive microscopic understanding of why adding heat at a high temperature increase the entropy less than adding it at a lower temperature?
Regards,
Rasmus