## 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

## EXAIR Siphon Fed Air Atomizing Liquid Spray Nozzles

Amongst EXAIR’s continuously growing product offering, some of the newest are a family of Air Atomizing Liquid Spray Nozzles that does not require a pressurized liquid source. These are known as the Siphon Fed Air Atomizing Nozzles. These nozzles can be easily implemented where a tank can be installed and lower the cost of the installation by not requiring a liquid pump, just point of use compressed air.

This action is done by the unique design of the air cap.  As the velocity of the air passes through the air cap, low pressure is created by a venturi.  The Siphon Fed Atomizing Nozzles can draw liquid from a suction height of 36” (91 cm), or gravity fed. They are manufactured from 303 stainless steel for durability and corrosion resistance. The Siphon Fed models can spray viscous fluids up to 200 centipoises and are used in many applications like rinsing, coating, cooling, quenching, humidification, or dust control. The images below showcases how simple the setup can be for the siphon and gravity fed installations.

EXAIR carries three different body sizes, 1/8” NPT, ¼” NPT, and ½” NPT ports; so, you can create a light mist or a heavy spray of liquid.  The maximum liquid flow rate is controlled by the air cap and liquid cap combination.  A unique feature of the EXAIR Atomizing Nozzle is that the caps are easily interchangeable for each body size to modify the spray patterns, control the amount of fluid, and reduce any downtime if cleaning is required.  The video below shows just how easily the changeover is done.

In addition to the three different inlet/body sizes, we also offer the Siphon Fed in both a round spray pattern or a flat fan spray pattern. These are also controlled by the air and liquid cap combination. This means it is easy to convert a round pattern that may be needed for a job, over to a flat fan pattern for the next setup. Each pattern is also available in several flow rates of liquid and air to dial in the performance required by the application.

Additionally, if you would like to positively shut the liquid flow off from the nozzle in order to prevent drips, over use of liquid, or to shut off the gravity fed liquid when not needed, the No-Drip versions of these nozzles is also available. This is easily controlled by simply reducing the compressed air operating pressure to below the designated cracking pressure of the patented No-Drip valve.

If you would like to discuss which spray nozzle is best suited for your application, please reach out to an Application Engineer.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

## FullStream Liquid Atomizing Nozzles

At EXAIR, we know compressed air, and we’ve been helping customers around the world get the most out of their compressed air systems since 1983. It was only logical that, about ten years ago, we got into using compressed air for liquid atomization.  If you’re looking to spray a liquid in a fine mist with a controllable pattern & flow rate, there are many advantages to using compressed air to atomize it:

• Maximum dispersion
• Optimal, efficient consumption
• Small droplet size

Since their introduction, EXAIR has come to offer 142 distinct models of Air Atomizing Spray Nozzles, and, along the way, we leveraged our engineering, machining, and manufacturing prowess to gain position as an industry leader in liquid spraying.  So much so, that, earlier this year, we introduced a spraying product line that doesn’t require compressed air:  the FullStream Cone Liquid Atomizing Nozzles.  Instead of using the energy of compressed air to effect atomization, these use the energy of the liquid’s pressure and flow to change the continuous stream of liquid flow entering the nozzle into a conical spray as it exits to atmospheric pressure.  Here’s how it works:

While Air Atomizing Spray Nozzles maintain their advantage of a smaller droplet size (ours consistently make droplets under 100 microns in size,) there are clear benefits in certain applications to the FullStream Cone Liquid Atomizing Nozzles:

• Higher liquid flow rates
• Increased liquid coverage
• More compact design

These are all important in applications like quenching, cooling, foam breaking, lubricating, degreasing, and sanitizing.  All stainless steel construction means they’ll stand up to a variety of chemicals…both in what’s being sprayed, and in the environment in which they’re installed.

If you have a liquid that needs sprayed, EXAIR has an engineered solution.  Call an EXAIR Application Engineer today to find out more.

Russ Bowman
Application Engineer
EXAIR Corporation
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## Atomization: What is it?

Atomization is a word that can be seen throughout the industry in rinsing, coating, painting, lubricating, and cooling applications. The act of atomization is simple, we often refer to it when looking at liquids and it means to break up the liquid stream and form fine droplets.  This is essentially a transfer of energy. There are two mainstream methods to atomize liquids for an application, both with their own advantages.

The first is air atomizing. This action is done by combining a stream of compressed air with either a pressurized fluid or a siphon/gravity fed liquid.  The air stream can be combined with the liquid internally to the nozzle, hence Internal Mix Atomizing Nozzles. It can also combine outside of the nozzle, like the External Mix Atomizing Nozzles. We have blogged before on where to use each of these as the reason to select between Internal Mix or External Mix is its own topic.

Benefits to air atomization are, smaller droplet/particulate size is achievable.  The compressed air atomization gives the ability to break up more viscous fluids to get better coverage or thinner layers of spray.  Air atomization also gives the ability to use smaller amounts of liquid because the air takes up a portion of the total flow exiting any nozzle.

The second type of atomizing nozzles are hydraulic atomization. This uses the energy from the liquid being pressurized to break up the liquid stream.  Sometimes there are physical impacts within the nozzle that cause the atomization, other times it is just the liquid leaving an orifice that causes the atomization. This gives the ability to still spray a liquid into droplets of various shapes, dimensions, and flow rates. The lack of compressed air often results in larger droplet sizes as well as higher liquid flow rates. Because the liquid has to be pressurized to certain levels it also becomes difficult to spray higher viscosity fluids through hydraulically atomized nozzles.

Benefits to hydraulically atomized spray nozzles range from stronger spray force for rinsing, ease of installation from not needing to plumb compressed air, ability to flow slurries, or other liquids that may clog or dry due to the design of air atomized spray nozzles.

If you would like to discuss the correct nozzle for your spray application, feel free to contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF