thermodynamics `specific heat problems

[haley5p]

Question 1

Pressure vessel contains helium (10kg ) at 50 °C and 550 Kpa The Tank is agitated by a fan rated at 500 watts for 3 hours

• calculate the work done on the system by the fan over the three hours (5400KJ)
• the temperature rise in the tank (173°C)
• The final pressure of the system (844 KPa)

Given the C_v of the helium is constant at 3.1156 kJ/kg/°C

Question 2

A gas manometer tank 10 m³ of nitrogen pressure 60 psi 350 K is heated by a resistance heater at 12 amps and 240 volts for 150 seconds the gas expands to maintain a constant pressure in the system. Assume on heat losses

• calculate the final temperature of the gas (560K)
• The work done by the system on the surroundings (2.478 MJ)
• The change in the internal energy of the system(22.2MJ)
• Cp= 2.06 KJ/Kg/ºK

Question1

 

More tricky question

Air at 1bar and 25°C is compressed to 5 bar and 25 °C by two different processes

• A) cooling at constant pressure followed by heating at constant volume
• B) heating at constant volume followed by cooling at constant pressure

Calculate the heat and work requirements plus changes in internal energy and enthalpy of the air for each path

 

Given the temperature changes are small the c_p and c_v can be considered constant

 

• CV= 20.78 and Cp= 29.10Jmol^-1K^-1
• at 25°C and 1 bar the molar volume of air is 0.02479m³mol^-1

 

 

 

 

 

 

 

^{please help me to solve these problems I would aprecciated so much}

^{i am so strugging with these problems!helpppppppppppppppp meeeeeee!}

[CaptainPanic]

!

Moderator Note

haley5p,

 

Please note that this is obviously homework. You will not get any answers, unless you show what you have so far done to solve these problems. Posting only the questions is not sufficient. You are obviously doing some engineering course, not a management course, so asking other people to do your work is not going to teach you the necessary skills to pass the class.

 

Everybody,

Please do not answer any questions until our OP has shown any efforts into solving these problems.

[haley5p]

2)

 

a)

 

to find out the final temperatura of gas we appy Gay-Lussac law :

p1v1/t1=p2v2/t2

 

V1=10m^3 v2=

p1=60psi I= 12 A

t1=350 k V=250 V

p2=0 I know I = v/r ohms law how to continue?

 

time=150 s

 

how to convert 60 psi to atm?How much is 1 psi in atm?

 

 

b)to find the work done by the system on the surroundings:

 

Work= integral of Pdv

 

knowing that P2v2^n=p1v1^n=constant

 

so work done by system on the surrounding is :

 

work=(R(t1-t2)/n-1))

 

c)change in internal energy

E=E2-E1 how to get E1 and E2?