# Search results for query: *

1. ### Heat exchanger - efficiency of the cycle

its not a homework problem, I was just curious while reading about the textbook chapter on power cycles, since it is desirable to have high temperature input, I was thinking maybe that temperature can be so high that the temperature of the fluid coming out of the turbine might able to reach...
2. ### Heat exchanger - efficiency of the cycle

Homework Statement Homework Equations The Attempt at a Solution Since we want the fluid to be in liquid state before entering a boiler, and super-heated water can only reach 374°C before entering super-critical state, suppose after the expansion, the temperature at point 3 is still higher...
3. ### Does the transfer function exist for an unforced system?

Thank you, I thought the plant transfer function G_p(s) = output(s) / input(s)? how it is independent? are you saying that it always exists but cannot be calculated without some type of inputs?
4. ### Does the transfer function exist for an unforced system?

Homework Statement c is the coefficient of damping, k is the spring constant, and m is the mass. if the cart is displaced from rest by distance X_0 and released at t=0 with initial velocity v_0=1. Homework Equations The Attempt at a Solution Ok this might be a stupid question because I...
5. ### Are theses approaches correct? (entropy change of water turning into steam)

oh wow , yeah, I can't believe I forgot about that..I was reading that part just two weeks ago, thank you!
6. ### Are theses approaches correct? (entropy change of water turning into steam)

is there an equation that shows this relationship?
7. ### Are theses approaches correct? (entropy change of water turning into steam)

Thank you, but how do you know its a constant temperature process from the fact that it's in liquid-vapor mixture state?

Thank you!
9. ### Are theses approaches correct? (entropy change of water turning into steam)

Homework Statement An insulated piston-cylinder device contains 5 L of saturated liquid water at a constant pressure of 150 kPa. An electric resistance heater inside the cylinder is now turned on, and 2200 kJ of energy is transferred to the steam. Determine the entropy change of the water...
10. ### Why does this solution assume it's a steady-flow system?

ohhh I see! so in another words, the internal energy in the inlet is the same as the internal energy inside the bottle? its 4 am here in New York, I might be brain dead, would this problem be different if the inlet is a cylindrical pipe? sorry if I am asking stupid questions
11. ### Why does this solution assume it's a steady-flow system?

Thank you very much for taking the time to read all that and answering my questions! I got it now. I am not sure how to find H and U2 without the tables, are you saying using ideal gas equation to find volume and then H=U2+PV? and ΔU= mass*specific heat of air*change in temperature? but we do...
12. ### Why does this solution assume it's a steady-flow system?

Homework Statement Homework Equations unreliable source of solution: The Attempt at a Solution [/B] I came across this problem while practicing for the final exam in thermodynamic,my attempt: i recall this type of problems are not steady-flow system. Since the change in kinetic and...
13. ### Do we assume the mixing chamber has an outlet?

it implies that the properties inside the chamber is constant, therefor there must be an exit for it to be a steady flow?
14. ### Do we assume the mixing chamber has an outlet?

Homework Statement Hot and cold streams of a fluid are mixed in a rigid mixing chamber. The hot fluid flows into the chamber at a mass flow rate of 5 kg/s with an energy in the amount of 150 kJ/kg. The cold fluid flows into the chamber with a mass flow rate of 15 kg/s and carries energy in the...
15. ### Why is the output in the middle of the block diagram?

(mentor note: not really a homework as the OP seeks understanding from an article) 1. Homework Statement I saw this on https://www.electronicshub.org/open-loop-system/, I thought the dry clothes should be the output, and heating the cloth should be the plant/process, I am so confused...
16. ### Support PF: Buy on Amazon.com from here

thats so cool, though I can see PF could lose some  because of it lol.

18. ### The Halpin Tsai relation to Voigt model

I think you are right, Thank you!
19. ### The Halpin Tsai relation to Voigt model

Homework Statement Homework Equations Halpin Tsai equation:[/B] Voigt model: P*=VfPf+VmPm Vf= volume of fiber/ volume of composite Vm= volume of matrix / volume of composite ζ= estimated parameter Pf, Pm= fiber and matrix properties V_v=1-Vf-Vm The Attempt at a Solution Since there is no...
20. ### Where did torsional shear stress in the x-y plane came from?

Homework Statement Homework Equations maximum torsional shear stress = (Torque*radius)/polar moment of inertia The Attempt at a Solution I am lost on equation(4-14), I looked through the textbook but didn't find a derivation.
21. ### Heat transfer boundary condition

wow, you are right, I got stuck on trying to write that term base on which temperature is higher and which is lower, thank you very much for the awesome explanation!
22. ### Heat transfer boundary condition

it's from here : isn't distal temperature same as ambient temperature in this case? so I guess if surface is cooling, then we have to take surface temperature minus ambient temperature, if the surface is being heated, then we have to take the ambient temperature minus surface temperature? but...
23. ### Heat transfer boundary condition

Homework Statement I am confused on how it's using the surrounding temperature minus the surface temperature as its the other way around in the Newton's law of cooling, Doing that would change the sign of convection right? I don't see the reason to do that, since if left side is hotter, then...
24. ### Derivative of x(t)?

thank you, I see, so it doesn't matter if x is a function of t, we just integrate it regularly?
25. ### Derivative of x(t)?

Homework Statement Homework Equations The Attempt at a Solution I am trying to repair my rusty calculus. I don't see how du = dx*dt/dt, I know its chain rule, but I got (du/dx)*(dx/dt) instead of dxdt/dt, if I recall correctly, you cannot treat dt or dx as a variable, so they don't...
26. ### Derivation process? (Heatsink Fin Heat Conduction Equations)

thank you, I got it now. the reason we differentiate θ(x) is because T_inf is treated as a constant right? therefore it is same as dT/dx.
27. ### Derivation process? (Heatsink Fin Heat Conduction Equations)

Homework Statement I don't understand the derivation of the right side of the last equation. Homework Equations The Attempt at a Solution I got to this point, I also don't understand why it did not include C_2 for the variation of temp. along the fin. I am guessing the right side is...
28. ### What happened to the negative sign?

silly me, thank you!
29. ### What happened to the negative sign?

Homework Statement Homework Equations The Attempt at a Solution I thought it would become d/dx(-kAc*dT/dx)+hp(T-T)=0 instead of where the equation in the red box? I don't see how are they equivalent [/B]
30. ### Which force creates the torque?

Homework Statement Homework Equations The Attempt at a Solution F12 is just an internal force caused by the joint 1 right? how can an internal force cause a torque?
31. ### Minimum number of teeth given the gear train ratio?

Homework Statement Homework Equations The Attempt at a Solution for this class, we were not taught with contact ratio equations, nor the pressure angle is given, so for this type of problems, do we just assume that minimum number of teeth on a pinion will be 12? 3 integer factors of 180 can...
32. ### Simple gear train, typo?

gear ratio can not be greater than 10 correct?
33. ### Simple gear train, typo?

thank you, i probably can't trust my professor's lecture notes anymore...
34. ### Simple gear train, typo?

the new exact d1 should be T1*Pc/pi, correct? but it has only Pc/T1
35. ### Simple gear train, typo?

Homework Statement Homework Equations The Attempt at a Solution if you do 38*25/pi , you would get 302.394 for the exact pitch circle diameter, similarly, exact d2 should be 907.183 mm, is it a typo? or did I miss something?
36. ### Heated piston & cylinder device with saturated water and vapor states

Thank you! really appreciated!
37. ### Pressure of a piston cylinder device after heated

is it clearly specified in the above two problems? the only difference I noticed is that the first problem is in a single phase ( super-heated), and the second problem is in two phase region. is that why we can assume the second problem's final pressure does not equal initial pressure?
38. ### Heated piston & cylinder device with saturated water and vapor states

oh right, 18 is the MW. Thank You!
39. ### Heated piston & cylinder device with saturated water and vapor states

what did I do wrong?
40. ### Pressure of a piston cylinder device after heated

Homework Statement I am confused on when will pressure of two states be the same for a piston cylinder device. Below are two problems where one's final pressure equals the initial pressure and one is not. Homework Equations The Attempt at a Solution Initially, I thought a...
41. ### Heated piston & cylinder device with saturated water and vapor states

ok, this time I got 18.46 which is very far from unity. but finding Z requires final conditions, and the question ask for final conditions...i feel like its too late to use Z to determine whether not i should use ideal gas equation, since I already have final conditions.
42. ### Heated piston & cylinder device with saturated water and vapor states

oops, I forgot to convert the temperature to Kelvin, so my Z should be about 0.458, which is far from unity.
43. ### What does sat. stands for in thermodynamic?

haha I just realized it...I thought that row is parallel with -20...
44. ### What does sat. stands for in thermodynamic?

Homework Statement The saturation temperature is given in the parentheses. then what is Sat. on the Temperature column? Homework Equations The Attempt at a Solution
45. ### Heated piston & cylinder device with saturated water and vapor states

My professor said that temperature and pressure are independent in super-heated region, I searched for independent definition, it says that if two properties are independent, i can vary one while holding one at constant . So its like saying I can increase or decrease pressure while holding...
46. ### Heated piston & cylinder device with saturated water and vapor states

Thanks a lot. so my initial pressure was correct (using h=u+Pv) ? I hope I am not asking too many questions...I am a bit confused on how temperature and pressure are independent in super-heated region, if you increase the temperature, the vapor pressure will increase since the molecules are...
47. ### Heated piston & cylinder device with saturated water and vapor states

but in this case, the piston is not connected to anything right? I got another question,for part b) i keep getting 370.697 for the final T and 21.223 MPa for the final pressure, a little off from the solution. I have a feeling that the solution did not simply interpolate on v, but I failed to...
48. ### Heated piston & cylinder device with saturated water and vapor states

ok, but why is the final pressure not equal to initial pressure in this problem?
49. ### Heated piston & cylinder device with saturated water and vapor states

thank you, because I assumed a piston-cylinder device has a constant pressure from state 1 to state 2, since the piston is free to move. I guess the pressure is not constant then? why is it not constant though? so in the case of exams where we are not given the T,S diagram, how do we know the...
50. ### Heated piston & cylinder device with saturated water and vapor states

[Mentor note: Thread title changed to describe actual problem being presented] 1. Homework Statement Homework Equations The Attempt at a Solution I understand you have to interpolate temperature and pressure of the saturated vapor from the table, since there is no matched final specific...