Thermodynamics - Using steam tables to find unknowns

In summary, to determine the temperature, quality, and internal energy of 5 kg of pure water in a rigid container of volume 1 m3 at a pressure of 2 bar, you will need to use the ideal gas equation and steam tables. Your calculations for temperature seem to be correct, and to find the internal energy and quality, you will need to use the specific enthalpy and saturation temperature and pressure values from the steam tables. It may also be helpful to review the concepts of enthalpy and quality in thermodynamics for a better understanding of these calculations.
  • #1
mandangalo
3
0

Homework Statement


Determine the temperature, quality, and internal energy of 5 kg of (pure) water in a rigid container of volume 1 m3 at a pressure of 2 bar.


Homework Equations


PV = nRT (maybe?)
quality = nv/(nl + nv) where l = number of moles in liquid phase and v = number of moles in vapor phase

The Attempt at a Solution


So far I have been able to determine that since P = 2 bars, it is also equal to 200 kPa.
V is also equal to 1000L.
5kg H2O*(1000g/1kg)*(1 mol H2O/18.01g H2O)=277.53 moles H2O.
Plugging this into the ideal gas equation, and rearranging to solve for T, I got this:
T = (200 kPa)(1000L)/(277.53 moles)(8.314 J*mol-1*K-1) = 86.68K = -186.47oC

First off, are my calculations correct? If not, where did I go wrong?
Secondly, once temperature is correctly solved for, how do I use that information with steam tables to find out the internal energy and composition of water in the liquid and vapor phases? My textbook does not give any examples of how to calculate those.
 
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  • #2


Your calculations for temperature seem to be correct. However, for the internal energy and quality, you will need to use the steam tables. These tables provide the thermodynamic properties of water at different temperatures and pressures. You can find these tables online or in a thermodynamics textbook.

To find the internal energy, you will need to use the specific enthalpy values from the steam tables. The specific enthalpy is the total energy of a substance per unit mass. For water, there will be different specific enthalpy values for the liquid and vapor phases at a given temperature and pressure. You can use the specific enthalpy values to calculate the internal energy of the water in the container.

To find the quality, you will need to use the saturation temperature and pressure values from the steam tables. The saturation temperature is the temperature at which water changes from liquid to vapor at a given pressure. The saturation pressure is the pressure at which water changes from liquid to vapor at a given temperature. Using these values, you can calculate the quality of the water using the equation you provided in the post.

Overall, to find the internal energy and quality of the water in the container, you will need to use the steam tables and the information you have already calculated for temperature and pressure. It may also be helpful to review the concepts of enthalpy and quality in thermodynamics to better understand these calculations.
 

1. What is thermodynamics?

Thermodynamics is a branch of physics that studies the relationship between heat, energy, and work.

2. How do steam tables work?

Steam tables are a set of tables that provide information about the physical properties of water and steam at different temperatures and pressures. They can be used to find unknown values, such as specific enthalpy or entropy, by interpolating between known values in the tables.

3. What are the units used in steam tables?

The units used in steam tables depend on the specific table being used, but they typically include temperature in degrees Celsius or Kelvin, pressure in bar or kilopascal, and specific enthalpy and entropy in kilojoules per kilogram.

4. How can steam tables be used to find unknowns?

To use steam tables to find unknown values, you must first determine the known values, such as temperature and pressure, and then locate those values in the tables. From there, you can interpolate to find the corresponding unknown values.

5. What are some common applications of using steam tables?

Steam tables are commonly used in the fields of thermodynamics, engineering, and energy production to calculate and analyze the properties of water and steam. They are also useful for designing and operating steam turbines, boilers, and other steam-based systems.

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