Ghalebsater
Mechanical
- Jul 2, 2013
- 1
Hello Colleagues,
In my problem I have a piston cylinder device that accepts heat from heat source and then Isobaric expansion occurs when pressure inside the cylinder is equivalent to the pressure caused by the mass of the piston. Here, we know that there is a heat input and a work output and hence the energy balance equation turns out to be: Qin = deltaU + Wout. Now if we invert(upside down) the piston cylinder device and we start cooling the cylinder to a point were the pressure is reduced to cause isobaric contraction (piston is being lifted while its mass is pulling downward). Please correct me if I am wrong here: although the volume is reducing I believe the system is still doing the work on the mass thus we should consider this as work output. Then Qout = -deltaU - Wout and Wout put should be considered as a positive quantity (Wout = -P*(V2-V1)for V2<V1). I would appreciate if you can share your thoughts which could confirm my logic or clear things for me.
Thank you in advance,
Note: The general form of energy equation I am using: Qin-Qout + Win-Wout = deltaU.
Gleb
In my problem I have a piston cylinder device that accepts heat from heat source and then Isobaric expansion occurs when pressure inside the cylinder is equivalent to the pressure caused by the mass of the piston. Here, we know that there is a heat input and a work output and hence the energy balance equation turns out to be: Qin = deltaU + Wout. Now if we invert(upside down) the piston cylinder device and we start cooling the cylinder to a point were the pressure is reduced to cause isobaric contraction (piston is being lifted while its mass is pulling downward). Please correct me if I am wrong here: although the volume is reducing I believe the system is still doing the work on the mass thus we should consider this as work output. Then Qout = -deltaU - Wout and Wout put should be considered as a positive quantity (Wout = -P*(V2-V1)for V2<V1). I would appreciate if you can share your thoughts which could confirm my logic or clear things for me.
Thank you in advance,
Note: The general form of energy equation I am using: Qin-Qout + Win-Wout = deltaU.
Gleb
