Thermodynamics: adiabatic compression

In summary, the conversation discusses finding the final temperature of an adiabatic compression process by using the equations for expansivity and compressibility, as well as the general equation for change in entropy. The final equation used to find the temperature rise is ## (\frac{∂T}{∂P})_s = \frac{Tv \alpha}{C_p} ##, where v is the specific volume, α is the expansivity, and C_p is the specific heat capacity at constant pressure.
  • #1
Another
104
5

Homework Statement


121212.png


Question
If changed isothermal compression process to adiabatic compression process. find the final temperature of process.

Homework Equations


## \alpha = \frac{1}{v} (\frac{∂v}{∂T})_{P} ## expansivity
## \beta = -\frac{1}{v} (\frac{∂v}{∂P})_{T} ## compressibility
##P_1^{1-γ}T_1^{γ}=P_2^{1-γ}T_2^{γ}##

##P_1 = 0.1 Mpa##
##P_2 = 100 Mpa##
##T_1 =15+273.15 K##

##γ= \frac{C_p}{C_v}##

The Attempt at a Solution



I don't know γ . So I must find the γ value.
##Tds = \frac{\beta C_v}{\alpha} dP+\frac{C_p}{\alpha v} d##
In adiabatic process ds = 0 So.
## 0= \frac{\beta C_v}{\alpha} dP_s+\frac{C_p}{\alpha v} dv_s##
## -\frac{\beta C_v}{\alpha} dP_s = \frac{C_p}{\alpha v} dv_s##
## -\frac{\beta \alpha v}{\alpha} dP_s = \frac{C_p}{C_v} dv_s##
So
## γ dv_s =- \beta v dP_s ##
## γ =-\beta v (\frac{dP}{dv})_s ##
I don't have a idea to find γ value . Please help me to find final temperature in a Question.
 

Attachments

  • 121212.png
    121212.png
    25 KB · Views: 664
Physics news on Phys.org
  • #2
You are trying to do the adiabatic reversible compression, correct?

What is the general equation for dS in terms of dT and dP?
 
  • Like
Likes Another
  • #3
Chestermiller said:
You are trying to do the adiabatic reversible compression, correct?

Yes. sir

Chestermiller said:
What is the general equation for dS in terms of dT and dP?

let s = f(T,P)
##ds = (\frac{∂s}{∂T})_PdT + (\frac{∂s}{∂P})_TdP##
 
  • #4
Another said:
Yes. sir
let s = f(T,P)
##ds = (\frac{∂s}{∂T})_PdT + (\frac{∂s}{∂P})_TdP##
In terms of ##C_P##, what is ##\frac{∂s}{∂T})_P##?
In terms of ##\left(\frac{\partial V}{\partial T}\right)_P##, what is ##(\frac{∂s}{∂P})_T##?
 
  • Like
Likes Another
  • #5
Chestermiller said:
In terms of ##C_P##, what is ##\frac{∂s}{∂T})_P##?
In terms of ##\left(\frac{\partial V}{\partial T}\right)_P##, what is ##(\frac{∂s}{∂P})_T##?

let ##s = f(P,T)## , ## u = f(P,Y) ## and ## Tds = du + pdv ##

##ds = (\frac{∂s}{∂P})_T dP + (\frac{∂s}{∂T})_P dT##
##du = (\frac{∂u}{∂P})_T dP + (\frac{∂u}{∂T})_P dT##
## Tds = (\frac{∂u}{∂P})_T dP + (\frac{∂u}{∂T})_P dT + Pdv ##
##dp = 0##
## Tds = (\frac{∂u}{∂T})_P dT + Pdv ##
## T(\frac{∂s}{∂T})_P = (\frac{∂u}{∂T})_P + P (\frac{∂v}{∂T})_P ##
## (\frac{∂s}{∂T})_P = \frac{C_P}{T}##

In maxwell relation
##(\frac{∂s}{∂P})_T = - \left(\frac{\partial V}{\partial T}\right)_P##
 
  • #6
Another said:
let ##s = f(P,T)## , ## u = f(P,Y) ## and ## Tds = du + pdv ##

##ds = (\frac{∂s}{∂P})_T dP + (\frac{∂s}{∂T})_P dT##
##du = (\frac{∂u}{∂P})_T dP + (\frac{∂u}{∂T})_P dT##
## Tds = (\frac{∂u}{∂P})_T dP + (\frac{∂u}{∂T})_P dT + Pdv ##
##dp = 0##
## Tds = (\frac{∂u}{∂T})_P dT + Pdv ##
## T(\frac{∂s}{∂T})_P = (\frac{∂u}{∂T})_P + P (\frac{∂v}{∂T})_P ##
## (\frac{∂s}{∂T})_P = \frac{C_P}{T}##

In maxwell relation
##(\frac{∂s}{∂P})_T = - \left(\frac{\partial V}{\partial T}\right)_P##
Good. So, if ds=0, what is dT/dP?
 
  • Like
Likes Another
  • #7
Chestermiller said:
Good. So, if ds=0, what is dT/dP?
##ds = (\frac{∂s}{∂P})_T dP + (\frac{∂s}{∂T})_P dT##
##0 = (\frac{∂s}{∂P})_T dP + (\frac{∂s}{∂T})_P dT##
## - (\frac{∂s}{∂P})_T dP = (\frac{∂s}{∂T})_P dT##
## (\frac{∂v}{∂T})_P = (\frac{∂s}{∂T})_P (\frac{∂T}{∂P})_s## and ## (\frac{∂v}{∂T})_P = v \alpha ##
## (\frac{∂T}{∂P})_s = \frac{Tv \alpha}{C_p}##

I am not sure
 
  • #8
Another said:
##ds = (\frac{∂s}{∂P})_T dP + (\frac{∂s}{∂T})_P dT##
##0 = (\frac{∂s}{∂P})_T dP + (\frac{∂s}{∂T})_P dT##
## - (\frac{∂s}{∂P})_T dP = (\frac{∂s}{∂T})_P dT##
## (\frac{∂v}{∂T})_P = (\frac{∂s}{∂T})_P (\frac{∂T}{∂P})_s## and ## (\frac{∂v}{∂T})_P = v \alpha ##
## (\frac{∂T}{∂P})_s = \frac{Tv \alpha}{C_p}##

I am not sure
This is correct. So substitute the numbers in and let's see what you get for the temperature rise (don't forget to use absolute temperature).
 
  • Like
Likes Another
  • #9
Chestermiller said:
This is correct. So substitute the numbers in and let's see what you get for the temperature rise (don't forget to use absolute temperature).
I'm thankful for that.
 

1. What is adiabatic compression?

Adiabatic compression is a process in thermodynamics where a gas is compressed without any heat entering or leaving the system. This results in an increase in temperature and pressure of the gas.

2. How is adiabatic compression different from isothermal compression?

Adiabatic compression is different from isothermal compression in that it does not allow for any heat transfer, whereas isothermal compression occurs at a constant temperature. Adiabatic compression also results in a greater increase in temperature and pressure compared to isothermal compression.

3. What is the first law of thermodynamics in relation to adiabatic compression?

The first law of thermodynamics states that energy cannot be created or destroyed, but it can be transferred from one form to another. In adiabatic compression, the internal energy of the gas increases as a result of the work done on it by the surroundings.

4. What are some real-world applications of adiabatic compression?

Adiabatic compression is commonly used in the operation of internal combustion engines, such as those found in cars. It is also used in refrigeration systems and air compressors.

5. What factors affect the efficiency of adiabatic compression?

The efficiency of adiabatic compression is affected by factors such as the type of gas being compressed, the compression ratio, and the speed at which the compression is carried out. In addition, the temperature and pressure of the surroundings can also impact the efficiency of adiabatic compression.

Similar threads

  • Introductory Physics Homework Help
Replies
3
Views
114
  • Introductory Physics Homework Help
Replies
1
Views
826
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
1
Views
767
  • Introductory Physics Homework Help
Replies
4
Views
831
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
967
Replies
1
Views
634
  • Introductory Physics Homework Help
Replies
6
Views
989
  • Introductory Physics Homework Help
Replies
2
Views
2K
Back
Top