Recent content by kbka

Hi again, thank you both. I see now that I'm confusing myself with all the trig. Messing up the distances. eq1: -R_bx*(h-cos(alpha)*l)+F_g*(sin(alpha)*l*1/2)=0 / kbka

Hi, Thank you both for your replies First of all this isn't a homework problem. It's a simplified version of something I'm designing. long story. It was placed here in the homework section by an admin. I do, however, see that in my attempt to explain and simplify the problem, I made it...

anyone? My main concern is if the moment balance marked as eq.1 is even possible with the boundary conditions. /kbka

Hi PF I have a statics problem that i solve. BUT I’m insecure rather or not it is solved correctly. The mechanical system is shown in the link below http://peecee.dk/upload/view/340798 A weight less wire is supsended from the wall in point C and attached to a heavy bar at point A. The...

I see. your way of setting it up does seem a bit more straight forward. I'll try that.. Thank you... And yes, the former post was regarding the same issue :) Q_goest, you're the man! Regards, kbka

I have been thinking now that it's not the work done on the fluid, but by the fluid. So it is equal to that done on the gas, but opposite in sign. So that the equation for the CV is M_w*u_w-M_w0*u_w0=int(m_dot*h-P*dV, time=0..tau) dV still being mass flow rate into the system over the density...

Of course :) I have a vessel filled with air and water. There is a constant flow of water, m, into the vessel, compressing the gas. The amount of gas in the vessel is constant. So, I first have a mass balance over time from 0 to t. So I know exactly how much water is in the vessel, and...

I should specify here. The energy balance is the first law of thermodynamics for a control volume. There's only mass flow into the system, and thus a change in mass over time... d/dt*(M*u)=m*h And as i wrote earlier, only internal energy is the unknown. The internal energy is obviously too...

Hi guys! Thanks for your replies. Still haven't solved the problem but I did come to think of something that may have to do with the large temp. increase. The energy balance I wrote where I believe the problem lies doesn't account for water actually being compressible. I haven't accounted for...

Hi PF! I'm modeling a system using EES in which compression of water occurs from approximately 2 bar to 200 bar. During the compression, the temperature rises from 300K to 305K. There's no heat transfer and the pump works as an ideal machine. I remember my thermo professor saying that...

Q_goest, Thank you for your thorough reply! This project is a setup that would (if ever realized) cost many millions of dollars. It would be a high capacity centralized Energy storage system. Its a new concept (Which I unfortunately have to keep secret) where I'm estimating the round trip...

I've asked some pump manufacturers about this and I never got a reply. Any suggestions to a manufacturer making centrifugal pumps at this scale?

Is the solution to just use a pump that can deliver 287 m of head. And let it pump at that setting throughout the whole process?

I tried. With no succes. It seems that at this high flow rate and pressure, very few options exists. I've only been able to find performance curves etc. for smaller pumps. (Head and flow) And again i can't really seem to find anything regarding how the varying head effects efficiency of the pump?

Hi PF! I have a question regarding the use of centrifugal pumps. I have a system with a constant flowrate of water at 2m^3/s pumping water from a lower to a higher reservoir. The inlet condition is a head of 10m. The Height of the upper reservoir will vary from 83m in the beginning to 287m...