How to calculate amount of vapor given q(t) and p(t)?

AI Thread Summary
To calculate the mass flow of water vapor as a function of time, initial conditions such as mass of liquid water, temperature, and pressure must be established. The heat added over time and the pressure function are critical inputs for modeling. The discussion emphasizes the need for constraints on temperature and pressure, with specific ranges provided. The system is defined as an open container filled with air, with no heat losses and without considering thermal inertia. A clear understanding of these parameters is essential for accurately determining the mass flow of water vapor.
Stefan2015
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Hi everybody,

I am trying to build a small model which basically should be able output "mass flow of water vapor as a function of time" given following inputs:
- initial mass liquid water m_l_0 [kg]
- initial temperature of liquid water T_l_0 [°C]
- initial pressure p_0 [Pa]
- heat added as a function of time q(t) [J/s]
- pressure as a function of time p(t) [Pa]

So for example a vessel with m_l_0 = 100 kg and T_l_0 = 80 °C is given.
The heat added function q(t) = q1 for time t>=0 & t<t1 and q(t) = q2 for t>=t1.
The pressure p(t) is given as a linear function with p(t) = p_0 - C x T, with C being some constant [Pa/°C].

Given this example, what will the mass flow of water vapor m_vap(t) be?

I started by calculating the system given enthalpy H_sys = m x T x cp and comparing it to the maximum enthalpy of the system at boiling point H_max = m x T_boil(p) x cp (which is pressure dependent). Once H_sys >H_max vapor will be released...

I would like to know how what you think will be the best approach for to do so?

Thank you!


Stefan
 
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You haven't constrained your problem adequately. Please give it another try.
 
Bystander said:
You haven't constrained your problem adequately. Please give it another try.

You mean temperature and pressure constraints?

Ranges of temperature I am looking into:
0-150°C

Pressure range:
60 000 - 140 000 Pa (0.06-0.14 MPa)
 
Is this in an open container or a closed container? Is there air present, or is the entire pressure comprised of water vapor pressure? Is the system insulated, aside from the heat added? Does the container have thermal inertia?

Chet
 
Hi Chet,

Answers to your question:
- Open container
- Container is filled with air
- No heat loses
- Thermal inertia is not considered

Thank you and a happy new year!

Stefan
 
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