## Humidification Calculations Related To Atomizing Spray Nozzles

I had an application where a customer needed to have a room at 75% relative humidity (RH).  They produced a nylon backing for carpet, and they needed the high RH to reduce the “stickiness” in the gluing process.  Currently they were at 40% RH in a room that was measured at 40ft long by 20ft wide by 20ft high (12.2m long X 6.1m wide X 6.1m high).  They wondered if our Atomizing Nozzles could help him to increase the relative humidity in the room.  I decided to put on my engineering hat to calculate the amount of water that he would need to increase the humidity.

Relative humidity (RH) is the percentage of water vapor as compared to the saturation level at the same temperature.  So, at 100% RH, the ambient air is saturated and cannot hold any more water vapor. You can feel the difference in the Amazon versus Arizona at the same temperature.  With dryer conditions, water can be added to increase the relative humidity; like a humidifier.  With the EXAIR Atomizing Nozzles, we can break liquid water into very small droplets to help increase the humidification rate.  For the customer above, I will have to determine what size and how many Atomizing Nozzles are required.

Equation 1

H = V * ACH * (Wf – Wi) / (v * 7000)

Where:

H – mass flow rate of water, Lbs/hr

V – Volume of room, ft3

ACH – Air changes per hour

Wf – Final Water Content, Grains/lb of dry air

Wi – Initial Water Content, Grains/lb of dry air

v – Specific Volume of Air, ft3/lb

Conversion Constant – 7000 Grains/lb

The customer stated that the room was set to 68oF (20oC), and they used an air handling unit (AHU) that produced 1,600 cfm (44.5 M3/min) of air into the room.  From these factors, we can determine some of the variables above.  For the Air Changes per Hour (ACH), we can use Equation 2.

Equation 2

ACH = 60 * Q / V

Where:

ACH – Air changes per hour

Q – Volumetric flow rate, CFM

V – Volume of room, ft3

The volume of the room is V = 40ft X 20ft X 20ft = 16,000 ft3.  The volumetric flow rate by the AHU is 1,600 ft3/min.  From Equation 2,

ACH = 60 * (1600 ft3/min) / 16,000 ft3

ACH = 6/hr.

In determining the water content values, you can find a chart online to determine the amount of water vapor that is contained in the air at a specific temperature and RH.  At 68oF (20oC), I was able to find the following information:

Wi = 40.58 Grains/lb of dry air at 40% RH

Wf = 76.71 Grains/lb of dry air at 75% RH

v = 14.286 ft3/lb @ 68 deg. F, 1 atm

V = 16,000 ft3

If we plug in the numbers that we have into Equation 1, we can determine how much water that we will need to spray into the air to increase the RH from 40% to 75%.

H = V * ACH * (Wf – Wi) / (v * 7000)

H = 16,000 ft^3 * 6/hr * (76.71 – 40.58 Grains/lb) / (14.286 ft^3/lb * 7000 Grains/lb)

H = 34.68 lb/hr

With my prior line of work in room humidification, we know that there is a lead/lag time between measuring and humidifying.  This may seem complicated, but it is important to get a steady state condition for the Relative Humidity.  To help this customer, I recommend a cycle time of 15 second to turn on and wait 105 seconds to re-measure the RH.  This will help to not over-saturate the room.  As for the location of the Atomizing Nozzles, we want to be near the ceiling to get the most “air” time to vaporize.  We also have to be careful to not allow the water spray to hit any objects or each other as this will cause the water to condense.

To start, I suggested our model AT2010SS No Drip Internal Mix 360o Hollow Circular Pattern.  This type of nozzle helps to extend the settling time of the water droplets; the amount of time that the droplets are suspended in the air.  The orientation of the spray is outward in all direction to increase coverage.  With the No Drip option, it is controlled by the air pressure to open and close the liquid side for spraying.  When the compressed air is turned off, a valve will seal the liquid side to not allow any drips.  It also helps to eliminate the need for any liquid valves next to the Atomizing Nozzles.  When it comes to cycle spraying, the No Drip option works wonderful.

In taking into consideration the flow rate required during operation time, we can calculate the amount of liquid flow required for the Atomizing Nozzle in Equation 3.

Equation 3:

Flow rate: Q = H / (D * T * f)

Where:

Q – Liquid flow rate (gal/hr or GPH)

H – Mass Flow Rate (lbs/hr)

D – Density of Water (8.34 lbs/gal)

T – Span division (no scale)

f – Intermittent Factor (no scale)

To determine the number of Atomizing Nozzles, we want to look at the time determination with the controller and the intermittence of operation.  With the ACH = 6/hour, the air in the room will change over every 10 minutes.  We want to have a balance between the new air and the existing air.  So, with the time measurement of 15 seconds on and 105 seconds off (2 minutes), we will have 5 humidity checks over the 10 minutes.  We can divide the amount of water to be injected into the room by the span division, T, to cover the time span for check and atomization.  Thus, T = 5.  We will also have to adjust the amount for only running 15 second intervals.  So, the intermittent factor, f, will be 0.0042 (the 15 seconds portion of the hour).

With these values, we get:

Q = (34.68 lbs/hr) / (8.34 lbs/gal * 5 * 0.0042)

Q = 198 gal/hr (GPH)

In the catalog, the model AT2010SS will flow 14.7 GPH (55.7 LPH) of water at 60 PSIG (4.1 Bar) liquid pressure.  If we divide these out, it will tell us how many atomizing nozzles that is needed to humidify the room.

Number of Nozzles: 198 GPH/14.7 GPH = 13.5 or 14 Atomizing Nozzles.

With the above Atomizing Nozzles, the company was able to control the RH at a high level for his manufacturing process.  In turn, he was able to increase productivity and reduce downtime.  If you need to increase the level of humidity in your area, you can contact an Application Engineer at EXAIR for help.  We can make it feel like the Amazon.

John Ball
Application Engineer
Email: johnball@exair.com

## Benefits of Atomized Liquid Nozzles vs. Liquid Nozzles

There are a great many applications that require a spray (as opposed to a stream) of liquid. Certain droplet sizes, and flow rates, are beneficial for certain applications. For example, if you’re fighting a fire, you want as high of a flow rate as possible – the more water you douse the fire with, the quicker it goes out.  You also want a fairly large droplet size, since a mist would tend to evaporate instead of extinguishing the flames.

Pressure washers also benefit from higher (though not near as high as fire hose) flow rates, and droplet sizes.  You want an appreciable flow rate, because that means high velocity, and good sized droplets combine that velocity with their relative mass to “blast” away dirt and detritus from the surface.

Medicine delivery devices, like asthma inhalers, are designed to produce mid-sized droplets, but pretty low (and controlled) flows.  The droplets need to be small enough to efficiently spread the medicine through the breathing passages, but large enough to where they won’t evaporate before they ‘plant’ on the nasal & bronchial membranes to get absorbed.

These are examples of “liquid-only” nozzles…no other media or means of force are used to effect the spraying action.  Most of the time, the droplet sizes in these applications are measured in hundreds of microns, which “liquid-only” nozzles are ideally suited to generate.  Other applications, however, call for much smaller droplet sizes…such as those only attainable through atomization.

EXAIR Atomizing Spray Nozzles use compressed air to create a fine mist of liquid, with droplet sizes as low as 22 microns.

Small droplet size is key to cost effectiveness in many applications:

• Think about expensive coatings…the smaller the droplet size, the better and more even the coverage, and the less you have to spray (and pay) out.
• Or humidification…smaller droplet size means more stays airborne, for longer, and in a larger space.
• Petroleum based lubricants, by their nature, only require a thin layer for best results.  Smaller droplets make as even and thin of a layer as possible.
• Dust control is much more effective with smaller droplet sizes, since the longer the mist lingers in the air, the more dust particles the individual droplets will adhere to…and then drop with them to the surface.  This also prevents getting the surface of the material any wetter than it has to be.

If you’d like to discuss a liquid spraying application, I’d love to hear from you.  Call me.

Russ Bowman
Application Engineer
EXAIR Corporation
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## No Drip, External Mix, Atomizing Spray Nozzle Overview

EXAIR’s Atomizing Spray Nozzles are used to clean, coat, or cool parts and they also lend themselves very well to humidification and dust control.  They are constructed from rugged and durable 303 SS to provide corrosion resistance and they can operate in temperatures up to 400°F (204°C). All EXAIR Atomizing Spray Nozzles are also CE compliant.

Atomizing Nozzles are separated into 5 categories – Internal Mix, External Mix and Siphon Fed, Deflected Flat Fan, and Internal Mix 360° Hollow Circular Pattern.  They are available in 1/8″, 1/4″ & 1/2″ NPT to make it easy to provide the coverage and flow rate you need for nearly any application.  For today’s focus, we will discuss the No Drip External Mix Atomizing Nozzles.

External Mix Atomizing Nozzles have the highest flow rates and are ideally suited where precise liquid flow is required and both the air and liquid are pressurized.  Also the External Mix Atomizing Spray Nozzles can easily atomize liquids with a viscosity above 300 cP (Centipoise).

Centipoise is defined as a dynamic viscosity measurement unit. A Centipoise (cP) is a non-SI (non-System International) measurement unit of dynamic viscosity in the centimeter gram second (CGS) system of units.

Our patented No Drip feature positively stops the liquid flow when the supply air pressure drops below 20 PSIG for 1/8″ NPT Nozzles or 30″ PSIG for the 1/4″ or 1/2″ NPT. By incorporating this feature into the design, it eliminates the need for any additional valves or supply lines.  They are available in flow rates that range from less than 2 GPH (7.57 LPH) for our Model EF9010SS 1/8 NPT No Drip External Mix Narrow Angle Flat Fan Pattern and up to 303 GPH (1,147 LPH) for the Model EF6010SS 1/2 NPT No Drip External Mix Narrow Angle Flat Fan Pattern.

When making a selection, below are some points to consider:

1. Volume of liquid required?
2. What is the viscosity of the liquid?
3. What type of spray pattern fits the application?

If you would like to discuss External Mix No Drip Air Nozzles or any of EXAIR’s safe, quiet & efficient compressed air products, I would enjoy hearing from you…give us a call.

Steve Harrison
Application Engineer
Send me an email
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## Atomizing Spray Nozzles from EXAIR

Do you ever need to spray a liquid?  If so lets look at two of EXAIR’s Atomizing Spray Nozzles or ASN for short.  The first model we will discuss is the AD1010SS Internal Mix Deflected Flat Fan Pattern.

To begin with all EXAIR ASN’s are made from SS for durability and liquid compatibility.  As its name implies it creates a flat fan pattern that exit’s the nozzle perpendicular to the air & liquid inlets as shown above.  This unique design lends itself nicely to applications with space constraints.  The AD1010SS is the ideal choice for coating the inside of enclosures or ductwork.  It is compatible with liquids up to 300 centipoise and the air and liquid are mixed in the air cap.  The AD1010SS is designed for pressure fed applications not requiring independent air and liquid control.  What is meant by that statement is that if you vary either the air or liquid pressures you change the spray pattern and volume.  See the chart below for clarification on pressures, volumes and spray patterns.

Next we will look at EXAIR model AT1010SS internal mix 360° hollow circular pattern ASN.

The AT1010SS internal mix 360° nozzle is designed for applications where the spray pattern must be oriented away from the nozzle in all directions.  360° nozzles are ideal where a smooth, even coating is needed on the ID of a pipe or similar ductwork.  It is compatible with liquids up to 300 centipoise and the air and liquid are mixed in the air cap.  The AT1010SS is designed for pressure fed applications not requiring independent air and liquid control.  As above if you vary either the air or liquid pressures you change the spray pattern and volume.  See the chart below for clarification on pressures, volumes and spray patterns. They also work great for operations where a mist over a broad area is needed, such as dust suppression, humidification and cooling.  See the chart below for clarification on pressures, volumes and spray patterns.

If you would like to discuss EXAIR’s Atomizing Spray Nozzles or any EXAIR compressed air product, I would enjoy hearing from you…give me a call.

Steve Harrison
Application Engineer

Send me an email
Find us on the Web