[Open Source Design Project] - Falling Film Evaporator



Are you using oil, steam or water to heat the evaporator and what about adding vacuum or is your calculation of 40-45kw with vacuum ?


I’d personally go with steam, but natural gas is cheap where I live.

Vacuum levels don’t really change the thermodynamics much. Most of the energy input is the phase changes, not the temperature changes.

Those numbers assume a 50 degree Celsius delta between the input and the evaporation temp. Making it 100 degrees only adds an extra ~5kW or so.


Wakawakalj, if adding vacuum does not change the amount of energy needed to make the phase change. Would we not want to run evaporation at normal atmospheric pressure to increase the temperature of the condensate. This would be the most efficient way to run our chiller and chilling being the most expensive thing to run and initial cost. Let me know if my line of thinking is correct or am I off base here.


Well, there is a small effect on the phase change energy required, though I think it’s minimal, and I’m not sure which direction it goes actually. A good chemist or can probably chime in here as I’m starting to get outside my realm of experience.

The evaporation temperature depression by using vacuum is primarily to minimize potential degradation of the active ingredients. A standard commercial chiller unit should be happy to run all day long at about 4 Celsius, give or take. If you’ve pulled light vacuum so you evaporate at 50 instead of ~78, you’re protecting your cannabinoids, and you’ve still got a more than sufficient delta between the vapour and condensing coils.


@wakawakalj as a biologist I’m probably further from my field, but I’d say you’ve got it spot on :wink:


You’ll want:
Gear Pumps 25k
Vacuum system and Regulator 10k
Enthalpy Booster(Solution Preheater) 5k

18kw (50-75L/hr) 30k
36kw (100-150L/hr) +20k

So basically:
18kw (50-75L/hr) would be around $135K before tax
36kw (100-150L/hr) would be around $155k before tax


Version 2

@710st sell us some gear pumps?


lookin good!


those low profile vessels are a nice touch.


What’s the lead time/price for this? Also what type of throughput are you seeing?


60-100k depending on options.

1-2gpm+ depending on heating/cooling choices on v1, this is v2 and should be 2gpm+ since it solved the vapor lock issue v1 had.

Lead time is variable, you will need to contact them directly


How much evaporation surface area does your v2 have?

Looks so sexy!



55 tubes
.5" OD
.37" ID
.065" Wall Thickness
46.76" Length

54.35"² Tube Inner Surface Area
73.45"² Tube Outer Surface Area

x 55

2988.7"² T ID SA
4039.75"² T OD SA


14 tubes
.5" OD
.37" ID
.065" Wall Thickness
24.76" Length

28.78"² Tube Inner Surface Area
38.89"² Tube Outer Surface Area

x 14

402.92 ”² T ID SA
544.46"² T OD SA

3391.62"² Total Combined ID SA
4584.21"² Total Combined OD SA


Pretty sure I’ve seen some math floating around in here that could get me close to telling you the max amt of ethanol that could be evaporated with this surface area…


Hey future,

I think your math is off by a factor of 2.

.37in x 3.14 x 46.76in x 55 = 2988 sq in Total ID SA

I appreciate you sharing your design with us.


Based on some back of the envelope scaling from the known throughput of the BZB unit (maybe 180-200L/hr maximum with adequate cooling), and the heat transfer areas (33.79 sqft for BZB, 20.75 sqft for Future’s), one could guess that about 120L/hr is a reasonable estimation.

But then after I run those numbers, I look above and see that Future says that he’s getting 2+ gpm (450+ L/hr), which is way more than that. I don’t really feel like busting out my thermo textbooks to go back to first principles and figure out why. Maybe the 1/8" tubes on the BZB (if they’re still using that ID) are too small and saturate too fast?

If it’s really $60-100k (without heat/cooling sources of course) for 2+gpm of ethanol recovery that is by far the best value proposition on the market right now. And making me seriously consider scrapping my own design.


Yup, entered diameter in place of radius :sweat:


Couple variables and observations

-Solution was at 40-45c in the pre preheater barrel.

-The faster I ran the water flow, the faster she went all around.

(Remember I had it plumbed 10c well water at 7lpm, then into the 200k BTU propane heater, out at 80c and from there to the evaporator, from there to the preheater)

Obviously surface area is eventually the limiting factor all other things considered, but I’d love to see some math behind all of this. My initial observations we’re limited by a design flaw in v1.


No matter how you look at it, it is a simple thermal energy equation. Yes, the surface area will help the rate of vaporization, but it is limited to the extent of energy capable of conducting via the surface pathway. Recirculation over the same pathway will yield similar results to more surface area so long as you have adequate heat energy to back it up.

At 200k btu (58kw), that thing should rip. You have enough heat energy for over 60gph of vaporization, the problem is re-condensating that massive heat load. Tap water will be hard pressed to keep up even at optimal flow rates and ground temps. Calcification of the HE and other issues come up too.

The math is pretty straight forward as the specific heat equation you can find here

You can find the isobaric heat capacity of ethanol based upon temperature here


Once you have your mass balance you can factor by the thermal conductivity capacity of 304 or 316 (whatever you are using). That info is here


You will have a theoretical maximum vaporization rate from the above info. I say theoretical because that math assumes you are operating with no energy losses. That also needs to be factored.

Our unit is 22kw on the front end, 22kw on the back end. We hit 100lph+ (25gph+). We also added tablet remote PLC control and are going to add some sensors to optimize. Come check it out at the Vegas show. Here is a teaser link.

Hope to see you there also Dustin.


Here’s a calculator that can be used to determine approximate energy requirements for specific amounts of ethanol recovery. This is the ideal/perfect situation setup, actual heat recovery rates will be lower so long as you’re obeying the laws of thermodynamics… which everyone should do.