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

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Discussion Overview

The discussion revolves around a homework problem related to heat capacity in thermodynamics, specifically focusing on the fourth question of a set involving heat transfer between air and water. Participants seek clarification on specific heat capacities and their application in solving the problem.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses difficulty in understanding the fourth question of the homework set and requests assistance.
  • Another participant suggests that the rate of heat lost by air equals the rate of heat absorbed by water, presenting equations for both rates involving specific heat capacities and mass flow rates.
  • There is a query about the notation used for specific heat capacity, with clarification provided that it refers to the specific heat capacity of air and water.
  • Participants discuss the specific heat capacity values for water (4.18 kJ/kg·C) and air (approximately 1.01 kJ/kg·C), with some confusion expressed regarding the availability of these values in reference tables.
  • One participant mentions that they could not find the Cv/Cp values for water in their tables, leading to confusion about the data needed for the problem.
  • Another participant acknowledges the confusion and suggests that they simply searched online for the heat capacity of water.

Areas of Agreement / Disagreement

Participants generally agree on the specific heat capacity values for water and air, but there is no consensus on the availability of these values in reference materials, leading to some confusion among participants.

Contextual Notes

Participants reference specific heat capacities and their application in calculations, but there is uncertainty regarding the sources of these values and their presentation in textbooks or tables.

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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