Dear Vasco Oliveira,

As a first approximation, I think you could assume the specific volume average. It is also valuable to remind that if you are doing indirect measurements of the specific volume, i.e. taking pressure and temperature at each location, it is recommended to perform the uncertainty propagation to verify if it meets your accuracy requirement. Another point is, unless you are working with micro or mini-channel evaporator, should you not expect to have a constant pressure throughout the evaporator? I hope more experienced colleagues could help us with this issue.

Regards

Thank you for your answer Mr. Rocha,

Answering the question, yes, it is expected to have a constant pressure.

Kind regards

I think the theoretical simulation could be conducted at first to verify your idea, if there is special simulation packages for your evaporator, like CoilDesign or other software (e.g. Aspen Exchanger Design & Rating), or you could model the heat exchanger and simulate the heat exchanger by yourself.

I would also like to proposal a method based on heat changer surface temperature profile along the refrigerant flow direction, and hope it could work and is suitable for you:

1. Several temperature sensors, e.g. thermocouples that do not affect the heat exchanger operation significantly, could be installed on the heat exchanger surface along the refrigerant flow direction.

2. The sensor's data could be regarded as the refrigerant temperature since the metal wall's thermal resistance is usually very small.

3. All the sensor's data along the flow direction, is actually the temperature profile of refrigerant, and based on this and evaporation pressure (assuming the pressure drop is small enough), we could estimate the refrigerant states (two-phase flow or single phase) at various locations, and the respective lengthes of gas-phase, liquid-phase and two-phase regions could be obtained (namely phase boundaries).

4. Of, course, the sensor number should be high enough, to obtain the accurate Boundary of each phase.

5. It is usually simple to calculate single phase refrigerant mass, based on refrigerant temperature and pressure (namely the density of single phase), the phase's length and heat exchanrge's geometry (e.g. inner diameter of the tube where refrigerant flows).

6. But for 2-phase, for simplicification, a linear vapor mass fraction profile along flow direction could be assumed, then the two-phase density profile along flow direction could also be obtained based on vapor fraction and evaporation pressure, then we could calculate this section mass. For your problem, the inlet vapor mass fraction should be known according to your problem statement.

7. Then, sum each phase's charge, the total charge could be obtained.