I was starting with using the DWSIM process simulator for some days agoes, and in that case I found out that the software is missing unit operations for a condenser and falling film evaporator. ( Condensing of steam on the outside of the tubes with product inside the tubes.) So far im trying to import an excel document i have made including vba codes for simulating the falling film evaporator. In that case I found out that I cant import .xlsm files to DWSIM??
Any suggestions how I should simulating the falling film evaporator and condenser?
I want to simulating evaporating of milk, and in that case I need to make a milk components. The most easy way must be to build it as water + solids. But wouldnt it give problems when we are going to evaporates it? So far I can read DWSIM has problems with Steam (water) + liquid (water) + solids ( Fat, Protein, Lactose). And suggestions how to build the component?
thanks in advance
Rasmus Nielsen
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Hi,
I think i can help you as i am doing similar simulations quite successfull - but not with milk.
To answer your questions:
The appropriate unit operation for your thin film evaporator would be the heat exchanger. This UO will calculate heating and cooling/condensation as you require. As this is not a standard tube and shell heat exchanger you have to select the appropriate calculation mode where you specify heat exchange area and heat transfer coefficient.
As far as i understand you don't need to simulate a second liquid phase (oil/fat?), only liquid, solid and vapour phases? If yes, you need to select the VLSE flash algorithm (=Vapour/Liquid/Solid-Equilibrium). This will do the job. But this algorithm is not capable to calculate a second liquid phase (oil/water) which would require a VLLE flash (no solids possible) instead. If you need that you may define this flash procedure for the unit operation where this is needed.
You require a milk-component. The most simple way would be to find a component with similar properties which may be used as a surrogate for milk. If this is not possible you need to create a new user component. To define that you will need to add all required properties manually. Do you have any data on that? I think i would have to assist you on that to get a reasonable representation of your process. This can be a very tricky procedure as "milk" is no well defined chemical substance.
The most important properties for your new "milk"-component (=without water) for you would be:
x "solubility" in water
x Density of water/milk mixtures at different temperatures
x heat capacity of water/milk mixtures at different temperatures
x heat capacity and solid density of pure milk
x does milk have a vapour pressure? I guess not.
Gregor
Last edit: Gregor Reichert 2016-11-15
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Good morning
1. So far I has built a model in where I use heat exchangers, with calculation type: outlet temperatures (UA), in where the overall heat transfer coefficient and heat exchanger area is defined. The vapour/liquid is then separates and the vapour part is recompressed and supplied to the heat exchanger as hot steam though the recycle block. The liquid part forwarded to the next pass by a pump (new heat exchanger).
(simulating a falling film evaporator with multi pass. The vapor from the milk at the bottom of the evaporator is separated and recompressed by Mechanical vapor recompression fan. “ adiabatic compressor” and supplied as hot steam.)
Thanks, I will check the VLSE flash algorithm. (we don’t need to simulating the second liquid phase.
We have some milk properties, and I will return to you with the data later today.
Again, thanks for your reply.
Rasmus
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Im not sure what is the most easy way to simulating our milk product. So far I think it maybe will be most easy if we consider milk as a mixture of insoluble solids and water.
Milk exist in many different types, as skim milk, whole milk , all depending on the water content/solids content and compositon of the solids. The solids consist mostly of Protein, fat, lactose, citric acid and ash.
if we consider whole milk, we can assume that the density of the solids is constant at 1300 kg/m3
The Cp of the solids can be assumed to be constant at 1.675 kJ/kgK at all temperatures.
Regarding the vapour pressure, the boiling point elevation (BPE) has to be considered since it is a function of the content of solids in the mixture. BPE= BPE_0 *( C/C_0)
For Whole milk: BPE_0 = 1 oC, C_0 = 0.5 kg solids/ kg water.
C = kg solids/kg water in the mixture.
So at 0 % solids in the mixture, the vapor pressure will follow the vapor pressure for water.
Any informations you need or we has to consinder ?
Thanks in advance.
Rasmus
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Hi Rasmus,
i created a milk component with your data. This component has an extremely low vapour pressure and nearly is not evaporating. Use NRTL/Uniquac property package and Nested Loops VLE flash.
In this simulation milk always will be a liquid, no solid. This should be sufficient for you. Calculations with solids sometimes may become problematic. Therefore you should stick to this flash type as long as there are no special requirements.
You may create several mixtures at different temperatures to check all required properties like density, boiling point, ...
You need to create a new user component database where you save this component into it. Then you tell DWSIM to use this new database (general setup) and restart DWSIM new. Now you will find milk in your component list.
Thanks for your help, so far it works and the simulation gives a good approximation of our data through excel modelling. I will return if I have any questions.
Have a nice day :)
Rasmus
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hi all.
I was starting with using the DWSIM process simulator for some days agoes, and in that case I found out that the software is missing unit operations for a condenser and falling film evaporator. ( Condensing of steam on the outside of the tubes with product inside the tubes.) So far im trying to import an excel document i have made including vba codes for simulating the falling film evaporator. In that case I found out that I cant import .xlsm files to DWSIM??
Any suggestions how I should simulating the falling film evaporator and condenser?
thanks in advance
Rasmus Nielsen
Hi,
I think i can help you as i am doing similar simulations quite successfull - but not with milk.
To answer your questions:
The appropriate unit operation for your thin film evaporator would be the heat exchanger. This UO will calculate heating and cooling/condensation as you require. As this is not a standard tube and shell heat exchanger you have to select the appropriate calculation mode where you specify heat exchange area and heat transfer coefficient.
As far as i understand you don't need to simulate a second liquid phase (oil/fat?), only liquid, solid and vapour phases? If yes, you need to select the VLSE flash algorithm (=Vapour/Liquid/Solid-Equilibrium). This will do the job. But this algorithm is not capable to calculate a second liquid phase (oil/water) which would require a VLLE flash (no solids possible) instead. If you need that you may define this flash procedure for the unit operation where this is needed.
You require a milk-component. The most simple way would be to find a component with similar properties which may be used as a surrogate for milk. If this is not possible you need to create a new user component. To define that you will need to add all required properties manually. Do you have any data on that? I think i would have to assist you on that to get a reasonable representation of your process. This can be a very tricky procedure as "milk" is no well defined chemical substance.
The most important properties for your new "milk"-component (=without water) for you would be:
x "solubility" in water
x Density of water/milk mixtures at different temperatures
x heat capacity of water/milk mixtures at different temperatures
x heat capacity and solid density of pure milk
x does milk have a vapour pressure? I guess not.
Gregor
Last edit: Gregor Reichert 2016-11-15
Good morning
1. So far I has built a model in where I use heat exchangers, with calculation type: outlet temperatures (UA), in where the overall heat transfer coefficient and heat exchanger area is defined. The vapour/liquid is then separates and the vapour part is recompressed and supplied to the heat exchanger as hot steam though the recycle block. The liquid part forwarded to the next pass by a pump (new heat exchanger).
(simulating a falling film evaporator with multi pass. The vapor from the milk at the bottom of the evaporator is separated and recompressed by Mechanical vapor recompression fan. “ adiabatic compressor” and supplied as hot steam.)
Again, thanks for your reply.
Rasmus
Hello Gregor
Im not sure what is the most easy way to simulating our milk product. So far I think it maybe will be most easy if we consider milk as a mixture of insoluble solids and water.
Milk exist in many different types, as skim milk, whole milk , all depending on the water content/solids content and compositon of the solids. The solids consist mostly of Protein, fat, lactose, citric acid and ash.
if we consider whole milk, we can assume that the density of the solids is constant at 1300 kg/m3
The Cp of the solids can be assumed to be constant at 1.675 kJ/kgK at all temperatures.
Regarding the vapour pressure, the boiling point elevation (BPE) has to be considered since it is a function of the content of solids in the mixture. BPE= BPE_0 *( C/C_0)
For Whole milk: BPE_0 = 1 oC, C_0 = 0.5 kg solids/ kg water.
C = kg solids/kg water in the mixture.
So at 0 % solids in the mixture, the vapor pressure will follow the vapor pressure for water.
Any informations you need or we has to consinder ?
Thanks in advance.
Rasmus
Hi Rasmus,
i created a milk component with your data. This component has an extremely low vapour pressure and nearly is not evaporating. Use NRTL/Uniquac property package and Nested Loops VLE flash.
In this simulation milk always will be a liquid, no solid. This should be sufficient for you. Calculations with solids sometimes may become problematic. Therefore you should stick to this flash type as long as there are no special requirements.
You may create several mixtures at different temperatures to check all required properties like density, boiling point, ...
You need to create a new user component database where you save this component into it. Then you tell DWSIM to use this new database (general setup) and restart DWSIM new. Now you will find milk in your component list.
Please check if this is sufficient for you.
Gregor
Hello Gregor
Thanks for your help, so far it works and the simulation gives a good approximation of our data through excel modelling. I will return if I have any questions.
Have a nice day :)
Rasmus
Hello,
I am very interested in the simulation of falling film evaporator for milk, is it possible for you to share it with me Rasmus ?
Thanks in advance
Deniz