2 replies to this topic

[Hasam ullah]

Hi everyone

 

                   kindly help me. I know how to calculate liquid/liquid and gas/gas mixture properties like density,viscosity. My question is if from a reactor butanol,diesel and water are coming out at 176 ⁰c where boiling points of these compounds are as follows:

 

butanol  117 ⁰c

diesel     250-350⁰c

water      100⁰c

 I have to use this stream in a heat exchanger to heat another stream. Here water and butanol are gases and diesel is still liquid. so it is a liquid gas mixture. for this mixture which relationships would be use to calculate above mentioned properties. please reply as soon as possible. I would be very grateful to you.

[MrShorty]

It is difficult to give a detailed response to your query, because there is not enough information given. In particular, there is no mention of pressure at which the heat exchanger will be operating.

 

You state:

Here water and butanol are gases and diesel is still liquid. so it is a liquid gas mixture.

with the boiling points (to be more precise the normal boiling points) of these fluids. Normal boiling point assumes a pressure of 1 atm, but you don't specify the pressure. We could assume that this means you are operating at 1 atm, but that is certainly not a necessary assumption. Since 176 C is well below the critical point of both water and butanol, I would probaby call these "condensible gases" (if I wanted to call them gases at all), recognizing that, if there is enough pressure, these can exist as liquids as well.

 

With that in mind, I would probably start with some basic VLE calculations. Bubble and Dew points, maybe, then determine if the operating pressure is outside or inside of the two phase region. If you determine from this that only one phase exists, then it should be as easy as applying the methods you already know. If you determine that there really are two phases, then you will want to perform a flash calculation to determine how much of each phase is present and the composition of each phase. From that, you can use your existing methods to determine the properties of each phase. Then apply additional methodolgy to find the "average" or "bulk" properties of the two phase stream. For something like density this should be straightforward. For a propertly like viscosity, I'm not sure what it even means to talk about viscosity of a two phase stream (perhaps someone much more advanced in fluid mechanics can talk about this).

[Hasam ullah]

Thank you so much for your help.