How to Solve the 4th Thermodynamics Question on Heat Capacity?

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SUMMARY

The discussion centers on solving the fourth question of a thermodynamics homework assignment regarding heat capacity. Participants clarify that the specific heat capacity of liquid water is 4.18 kJ/kg°C and that for air, it is approximately 1.01 kJ/kg°C. The relationship between the heat lost by air and the heat absorbed by water is established as Pair = -Pwater. Confusion arises from the inability to find Cv/Cp values for water in reference tables, which is addressed by referencing basic physics knowledge.

PREREQUISITES
  • Understanding of thermodynamics principles, specifically heat transfer.
  • Familiarity with specific heat capacity concepts.
  • Knowledge of mass flow rates in thermodynamic systems.
  • Basic physics background, particularly regarding Cv and Cp values.
NEXT STEPS
  • Research the derivation and application of the first law of thermodynamics.
  • Study the differences between Cv and Cp for various substances.
  • Explore heat transfer equations in thermodynamic systems.
  • Learn about the specific heat capacities of other common fluids.
USEFUL FOR

Students studying thermodynamics, educators teaching heat transfer concepts, and professionals in engineering fields requiring knowledge of heat capacity and thermodynamic principles.

DrVirz
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Homework Statement


Hi all, please see uploaded pics. I can do the first 3 questions but can't get my head around the 4th. Any help is appreciated.

Capture_zpsiwkqpcld.jpg


DSC_0157_zpswmfhsrg7.jpg
 
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The rate at which heat is lost by the air P_{air}, equals to minus the rate P_{water}at which heat is absorbed by the water. So it will be P_{air}=-P_{water}.

P_{air}=C_{air}\dot{m}_{air}(47-167), P_{water}=C_{water}\dot{m}_{water}(40-35)
 
Hi Delta,

What have you denoted as C?
 
Its the specific heat capacity. For water is 4.17 and for air around 1.01 at the temperatures of this problem.
 
I thought it was the specific heat capacity but I can only find the Cv/Cp for water in any of the tables from my text which was confusing me a bit.

Cheers for the help!
 
DrVirz said:
I thought it was the specific heat capacity but I can only find the Cv/Cp for water in any of the tables from my text which was confusing me a bit.

Cheers for the help!
It's liquid water. What is the heat capacity of liquid water?

Chet
 
Chestermiller said:
It's liquid water. What is the heat capacity of liquid water?

Chet

Sorry in my previous post i meant to say CANT find the Cv/Cp value for water in any of my tables.
 
DrVirz said:
Sorry in my previous post i meant to say CANT find the Cv/Cp value for water in any of my tables.
The heat capacity of liquid water is 4.18 kJ/kg C. Did you not see Δ2's post # 4? Are you saying you never had this in freshman physics?

Chet
 
Chestermiller said:
The heat capacity of liquid water is 4.18 kJ/kg C. Did you not see Δ2's post # 4? Are you saying you never had this in freshman physics?

Chet

Yes I did see that in Delta's post. I am just saying, naturally, I refer to the tables for my data values and when I didn't come across a value for water it threw me off. I thought I had done something wrong. That's what happens when you have been studying all day I guess, time to take a rest.
 
  • #10
DrVirz said:
Yes I did see that in Delta's post. I am just saying, naturally, I refer to the tables for my data values and when I didn't come across a value for water it threw me off. I thought I had done something wrong. That's what happens when you have been studying all day I guess, time to take a rest.
All I did was Google "heat capacity of water."

Chet
 

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