Airflow Calculations Imparted from water spray nozzle 1

[Heaviside1925]

I have never posted on here before and I am frankly frustrated I cannot get traction on this design. The design I am working on is the use of a spray nozzle to induce flow for the movement of a hazardous vapor. I have attempted to find "like" applications from other industries such as venturi scrubbing, venturi metering, venturi injection, spray nozzle theory and design and have not come up with any suitable design guidelines to assist me in this. All the examples I have found seem to be focused on other variables specific to its application and many either use a constant mass air flow or negate it entirely. From I purely kinetic standpoint, I am adding energy to a closed system via the spray nozzle at a constant rate, so some of this energy from the fluid leaving the spray nozzle is being transferred to the vapor. Thats the theory anyways and I have a list of assumptions that can be made such as vapor and fluid temperature, vapor liquid saturation, pressures, dimensions, etc. but I have yet to find suitable design criteria to apply these. I have found experimental data that I can partially extrapolate from, but I am surprised I cannot find the exact application I am looking for, which is basically using a water spray to move air.

Any assistance in pointing me to an appropriate application or reference would be appreciated. I have attached a visual example as a reference, thank you in advanced.

 

[1503-44]

Basically looking at shear transfer, ie. viscosity.
Moving a gas by shear transfer from a liquid is horribly inefficient.
Viscosity of a gas is about 1/100 that of water.
A looser right out of the starting gate.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

What is going on here?

That diagram makes no sense to me. Can you explain further what you are trying to do in that tube?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Heaviside1925]

I apologize, when I included that screenshot, it was intuitive to me but now that I look at it with no context it does not make sense. Top left: saturated vapor (dark blue) flows from left to right into vertical venturi where it is entrained with a stream of lean absorbent liquid (yellow). Both travel downward through the venturi neck and exit the bottom of the venturi with the vapor flowing (light blue) left to right again and the rich absorbent liquid (orange) gravity draining to the left.

I know how to calculate the mass fractions /partial pressures / scrubbing efficiency and so on. Where I am getting hung up, is all these calculations are based on a certain mass flux. Since there is already a kinetic process occurring, i.e. shear transfer through viscosity, I would like to determine the mass flux already present and work backwards from there. There are additional variables, since it is a polar solvent, that I'd like to find as well. Even though shear transfer will likely be the main driver, there should additionally be other mechanisms that are time and dimensionally dependent such as some of the vapor being adsorbed then de-absorbed.

I just included that last paragraph for context. My area of focus for this post are the kinetics around the initial vapor / liquid interaction and my attempt to set up a steady state equation to determine flow rate prior to its entry into the venturi section with liquid flow rate, geometry, droplet size being the variables. The picture I had in my head is from the fire service. A common ventilation method the fire service employs is what they call positive pressure ventilation. This method involves setting up a pressure driver at one end of the structure and providing a flow path through the structure to a predetermined opening to control the spread of smoke and fire gases in the structure. The two commonly used pressure drivers are either a fan or fog nozzle, with the later having its divergent cone placed just inside the opening they are wanting to provide ventilation from. There are even published rules of thumb for this process with cone angle, flow rate and opening dimensions being the main variables. What I am unaware of are the variables being negated and since this process is orders of magnitude larger than the one I am looking at, I do not feel comfortable using these rules as a design basis.

I am fairly certain there are other industries that employ a similar mechanism of moving air/vapor using a liquid nozzle. Having someone point me in that direction is the main intent of my post.

 

[Compositepro]

Venturi design requires very specific geometry which depends on factors like delta P desired to be generated and flow rates of each stream.
An energy balance might give what is theoretically possible given an ideal geometry. But that won't help with designing the geometry.
Stokes law could be used for a spray into a straight pipe section.

 

[Heaviside1925]

Compositepro,
I have a long history of venturi's going back to my instrument engineer days, so I appreciate your comments concerning design and D/d ratios. That said, my concern is upstream of the venturi. When I look at applying Stokes, I am not comfortable with discounting advection inertial forces, which brings me back to Navier-Stokes, which I am trying to avoid. I have found some applications close to what I am needing concerning dust entrainment using spray nozzles in the mining industry, where spray nozzles are described in terms of spay power per airflow W/m^3/s but I have not been able to find the derivation of these equations. I will keep digging around in this application and hopefully I will come across what I am looking for. In the meantime, if anyone is aware of other similar applications, I'd appreciate your comments.

 

[georgeverghese]

Take a look at page 14-66 in the 7th edn of Perry Chem Engg Handbook in the discussion on 2 fluid (vapor-liquid) atomizers of various sorts (including venturi type atomizers) and studies done on them.

 

[Heaviside1925]

Chem-E's and their Perry's, I should've known Thank you georgeeverhese, that got me exactly where I needed to be.