Thermodynamics: adiabatic compression

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Homework Help Overview

The discussion revolves around an adiabatic compression process in thermodynamics, where the original poster seeks to determine the final temperature after changing from an isothermal to an adiabatic process. The problem involves various thermodynamic equations and parameters, including expansivity, compressibility, and the specific heat ratio.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the need to find the specific heat ratio (γ) and explore the general equations for entropy change (dS) in relation to temperature and pressure. There are inquiries about the relationships between different thermodynamic properties and how they apply to the adiabatic process.

Discussion Status

The conversation is active, with participants engaging in mathematical reasoning and clarifying concepts related to the adiabatic process. Some guidance has been provided regarding the equations and relationships involved, but there is no explicit consensus on the final temperature or a complete solution yet.

Contextual Notes

Participants are working under the constraints of a homework assignment, which may limit the information available and the methods they can employ. The original poster expresses uncertainty about certain values needed for calculations, particularly the specific heat ratio.

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Homework Statement


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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.
 

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You are trying to do the adiabatic reversible compression, correct?

What is the general equation for dS in terms of dT and dP?
 
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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##
 
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##?
 
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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##
 
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?
 
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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
 
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).
 
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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.
 

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