10 replies to this topic

[Biomass Process]

Can we consider power consumed by agitator to consider it for temp rise of slurry or liquid in which agitator is being used . If yest is any body is having reference or calculations or basis for this consideration.

 

I does not mean that it is " Yeast " , it was typo error sorry for inconvenience ; instead of Yes I wrongly type yeast . My querys is that if our reaction requires some temp ;  so can we consider the heat generated during mixing of liquid by agitator -which upcourse requires power while considering heating requirment .  Power required by agitator  can be considered (as temp will  rise in slurry/liquid due to agitation ) while considering heating requirement of that reactor . Suppose tank is having heating coil; so temp rise due  to agitation in slurry can be considered while calculating heating requiremen. 

Suppose heating requirement is X and heat genereated due to agitation is Y so while designing heating requirement i.e.

 

Net heating requirment  for designing coil = X-Y .

Edited by Biomass Process, 06 June 2026 - 01:08 PM.

[breizh]

Googling AI mode :

 

Agitator power consumption for yeast depends on the vessel size, impeller type, and fermentation stage. In commercial propagation or brewing, typical specific power ranges from 0.5 to 2.0 kW/m³ of broth. Exact power is calculated using the fluid's density, viscosity, and the impeller's dimensionless Power Number (\(N_{p}\)). [1, 2, 3, 4, 5]

Key Factors in Power Calculations

To determine the required motor size, engineers use fluid dynamics to model the resistance the yeast broth exerts on the agitator blades. [1, 2]

• Power Equation: \(P = N_p \times \rho \times N^3 \times D_a^5\)
  • P = Power in Watts
  • \(N_{p}\) = Power Number (depends on impeller type, e.g., Rushton turbine, pitched blade)
  • ρ = Fluid density (approx. 1000 - 1050 kg/m³ for yeast broth)
  • N = Rotational speed in revolutions per second (RPS)
  • \(D_{a}\) = Impeller diameter in meters [1, 2, 3]
• Reynolds Number (\(N_{Re}\)): \(N_{Re} = \frac{\rho \times N \times D_a^2}{\mu}\)
  • μ = Broth viscosity. Note that as yeast concentration and cell mass increase, viscosity spikes, shifting mixing regimes from turbulent to transitional. [1, 2, 3, 4]

Industry Benchmarks & Guidelines

Energy requirements are distinctly divided by operational stages: [1]

• Yeast Propagation: Requires gentle to moderate mixing (typically 150 - 200 RPM) to keep nutrients homogenous without damaging cells. Small-to-medium volume propagators (like a 100 hl / 10 m³ tank) often homogenize perfectly within 1 to 2 minutes utilizing a 2.2 kW motor. [1, 2]
• High-Viscosity Fermentation: Viscous broths require more starting torque and intense energy. For medium-viscosity applications, 3 to 5 kW motors operating around 100 RPM are commonly standardized. [1, 2]

Good luck

Breizh

[katmar]

What you are describing is precisely the experiment that Joule did to prove the equivalence of heat and work.  See for example 

https://www.youtube....h?v=U_6oY0KhxXk

 

 

Depending on whether you are propagating the yeast or using it to ferment sugar there will also be heat of reaction to remove.  So you will probably need to add cooling coils to your tank to remove the heat from the mixing and the heat of reaction.

[Biomass Process]

Hello Mr Breizh,

 

I does not mean that it is " Yeast " , it was typo error sorry for inconvenience ; instead of Yes I wrongly type yeast . My querys is that if our reaction requires some temp ;  so can we consider the heat generated during mixing of liquid by agitator -which upcourse requires power while considering heating requirment .  Power required by agitator  can be considered (as temp will  rise in slurry/liquid due to agitation ) while considering heating requirement of that reactor . Suppose tank is having heating coil; so temp rise due  to agitation in slurry can be considered while calculating heating requiremen. 

Suppose heating requirement is X and heat genereated due to agitation is Y so while designing heating requirement i.e.

 

Net heating requirment  for designing coil = X-Y .

Edited by Biomass Process, 06 June 2026 - 11:54 AM.

[breizh]

Hi,

Noted.

Mechanical energy is converted to Thermal energy through friction and turbulence. This is an input to your system. Is this significant? 

In my experience with stirred tanks for polymerization and chemical reactions, I used the coil to heat and cool the system. 

 

Breizh 

[latexman]

Biomass Process,

While what you say is true, I’ve never included the heat from an agitator’s work. I’m my experience, it is usually negligible. Why? Look at the work to heat conversion factor. 1 BTU of heat = 778 ft-lb of work. A lot of work is needed to make a little bit of heat. I think you will find out the work is a very small part of the heat balance. Please let us know.

[katmar]

Like Breizh and Latexman stated, I have also never bothered to include the heat from the agitator's work because there are other losses and inefficiencies and it is always good to keep a bit of safety margin up your sleeve.  One thing that I have found is worth considering, but is not often mentioned in the texts, is the losses to the steel structure if the tank is bolted to the structure.  This is particularly true of cryogenic tanks where a lot of attention is given to the tank insulation but a significant portion of the "coolth" is lost via the mounting lugs and the steel structure.  This is easily fixed with some rubber or plastic spacers.  If you are agitating a cryogenic tank then the heat from the agitator would be working against you and in that case it would probably be worth taking into account.

[Biomass Process]

Hi All,

Thanks for reply .

But can we take in to consideration while calculating the heating requirement .

 

Your opnion pl .

 

I have  asked any AI , AI says  transfer of  all heat generated by agitator to slurry  and provided the calculation also . But I do not believe too much.

 

Any body has done this previously ,if any reference , any literaturte to prove that this can be considered ?

 

As per Newtons 3rd law of motion " Energy is converted from one form to another " so heat generation will be there , how much and can quantify it  ,to consider is the question. 

Edited by Biomass Process, 07 June 2026 - 10:36 PM.

[breizh]

My answer is NO, based on my experience.

Share with us your figures and calculation sheet.

Do the math, it will be an iterative solution. 

 

Breizh 

[latexman]

"But can we take in to consideration while calculating the heating requirement."  Yes, of course.

 

"Any body has done this previously, if any reference , any literature to prove that this can be considered?"  I have done it, long ago.  In my case, it was negligible.  You have to figure out if it is negligible in your case.  So calculate, then you will know if you can ignore it in similar cases in the future.

[breizh]

The point is to shorten cycle time, the more energy you can bring to the system the better it is. Same for heat transfer area, the bigger the better.

Breizh