Humidity and Cooling

Nozzles for Humidifying

Increasing the humidity levels can be important in a variety of environments.  The key to successful humidifying sprays is the controlled spraying of finely atomised sprays.  If too much liquid is put into the system then condensation or precipitation may occur.  If too little is put in then the desired levels of humidity will not be maintained.

General Principle of Humidifying Systems

Humidifying systems generally only require very moderate levels of spray. The amount of water needed to raise the humidity of a given environment will depend upon:

1- The ambient humidity level i.e. the starting point
2- The rate at which the air in the area is exchanged with the wider atmosphere. This will depend upon ventilation and air movements.
3- The temperature of the room. This will affect evaporation rates as well as the overall carrying capacity of the air

In order achieve swift humidification from a spray nozzle one needs to keep the droplet size a small as possible and to distribute the water over a wide area. This will help the small droplets evaporate into the air a quickly as possible raising the humidity level.

The rate at which water will evaporate from any system depends upon heat, wind, surface area and ambient humidity.  As humidity increases the rate of evaporation also increases as there is more water held in the air for heat to act upon.  It is this fact that humidifying systems exploit.  By increasing the level of moisture in the air one can increase the rate of removal and thus maintain a steady higher level of moisture through continual or regular spraying.  Of course, there is a limit to how “loaded” air can be with water and once a certain level is reached condensation or precipitation will occur.

Key Engineering Considerations

Droplet size
When selecting nozzles for such systems one generally needs to look at low flow rate variants.  It is important to achieve very fine atomisation so that the natural evaporative forces can act swiftly on the spray. With a very fine spray it is possible to ensure complete evaporation before there is any chance of wetting occurring, conversely if the wrong nozzle is selected and the droplet size is to large then the water may come into contact with surfaces prior to evaporation.

Reach
To give the water the best chance to evaporate quickly it is best to distribute it as widely as possible within the area. This is particularly true in areas with poor ventilation and little natural air movement.

Nozzles

Air atomisers

Air atomising nozzles deliver very fine droplets at low flow rates making them ideal for humidifying systems. In addition to that the air used in the nozzle helps project the fine spray from the nozzle so that it can spread out into a large room quickly and efficiently.

These nozzles require both an air and water supply to work. If both are available they are the ideal choice for humidification system.

Hydraulic nozzles
If a suitable air supply is not available then standard misting nozzles can be suitable for humidification systems. These nozzles will require higher fluid pressures to achieve a droplet size small enough to facilitate rapid evaporation, typically pressures of at least 7 bar will be needed.

Further details on nozzle selection for humidifying systems can be found in the the “key engineering considerations” sub sections of this page. These can be accessed by the blue menu to the right hand side of this page.  Information on the different designs of spray nozzle that might be suitable for humidifying applications can be accessed by the grey menu, also to the right.

The information contained in the “engineering considerations pages” and the “nozzle designs” pages is summarized in the “Humidification Nozzle Selection Table” which can be accessed by clicking on the orange button, also to the right hand side of this page.

GAS COOLING NOZZLES

The cooling of gas flows by injecting water or other coolants is a very common application for our spray nozzles. Correct nozzle selection is of critical importance in many spray cooling applications as the properties of the spray will determine how quickly heat is absorbed and where the spray will reach within a given gas flow.

Nozzle selection

When spraying into a hot gas flow above the boiling point of the coolant most of the cooling is caused by taking heat from the gas to evaporate the fluid. The rate of evaporation will depend on the average droplet size of the spray. Sprays consisting of smaller droplets will evaporate far more rapidly that sprays containing larger droplets. In fast moving gas flows this can be very important as often cooling needs to be achieved before the gas reaches another point in the process. Correct nozzle selection can thus reduce the need for long quench chambers.

Not just droplet size

Whilst sprays consisting of very small droplets will absorb heat faster they will also become entrained within gas flows more easily. This means that if a spray is too fine it may only cool a channel within a gas flow rather than the whole gas volume. So there is often a balancing act to be performed between getting sufficiently small droplets to achieve rapid heat transfer and have enough larger droplets to carry the spray into a gas stream and distribute it evenly.

Variable gas flows

In many applications the amount of gas that needs to be cooled can vary depending on operating conditions. For example the pre-quenching of hot flue gasses before they enter a scrubber may vary dramatically depending on what is happening further up the process line to produce the gases. Variable cooling loads present problems for spray cooling because lowering the amount of coolant spray will typically mean lowering fluid pressure which will increase the droplet size and thus increase evaporation time. This means that in lower gas flow scenarios cooling may not be achieved in time, or may necessitate a deliberately larger quench chamber.

There are a number of ways in which good nozzle selection can help overcome variable gas flow cooling problems. The use of spillback nozzle systems means that droplet size can be kept relatively stead even if the pressure and flow rate are reduced. Alternatively air atomising systems with variable air and fluid pressures can be used to maintain smaller droplets at reduced flows. Finally multi nozzles arrays can be deployed to given variable flows at stable droplet sizes.

Spray nozzles

Gas cooling nozzle selection will vary greatly depending on the application. For many cooling applications our spiral TF nozzles produce an excellent combination of small droplets mixed with some larger droplets to give penetration into rapidly moving gasses. For variable gas flows our spillback lances can provide optimum cooling even under highly changeable process loads. Our Spriral Air (SA) nozzles give a robust air atomising system suitable for use in hot gas flows that require finely atomised sprays for rapid quenching.

As gas cooling is a wide and highly varied application other nozzle types may well be recommended depending on the situation.

HUMIDIFICATION

Humidify air in ducts, drying kilns, curing rooms, greenhouses, and other open areas; area Misting

Humidification by Spray Nozzle Process:

In many industrial processes, commercial processes, and agricultural settings it is necessary or advantageous to increase the water content of the air in a duct, chamber, or room. Spray nozzles which make very small droplets are effective at increasing the amount of water that is present in the air. For reducing the temperature of a hot gas by evaporating water into it, please see Gas Cooling.

Humidity is a measure of how much water vapor is present in air. The volume of water vapor that can be held in air varies strongly with temperature; warm air can hold more water vapor than cold air. Simply speaking, relative humidity is the ratio of the amount of water vapor in the air to the amount of water vapor that could be held by the air at that temperature. Technically, relative humidity is the ratio of partial pressure due to water vapor to the saturation vapor pressure, multiplied by 100%.

Nozzles used as humidifiers work by creating very small water droplets and projecting them into the air. The very small droplet size allows it to evaporate quickly even at normal ambient temperatures. This evaporated water increases the humidity level of the air. Typically a relatively small amount of water is evaporated to increase the relative humidity and this small amount of water does not appreciably affect the temperature of the air. When changing the humidity level considerably, the temperature may change by several degrees. Our engineers can help you through the psychrometric calculations to achieve your process needs.

Humidification Nozzle Recommendations:

For normal ambient temperatures and slow moving air, such as humidification of a room, one of the best nozzles to select is the XAAD which uses compressed air to atomize the water into very fine drops. Typical pressures for the XAAD are 10-60 psi water and 10-100 psi air. If compressed air is not available or desired, using a MicroWhirl or PJ at high pressure (100 to 1000 psi) is also effective. If humidifying a large amount of air or if the air is at elevated temperatures, higher flow direct pressure nozzles like the L or TF may be suitable.

When humidifying a room or area Misting, spacing nozzles evenly is important. To humidify a gas stream, mounting nozzle heads 5-6 inches apart is normally recommended. When humidifying a room, a review of the air flow through the room can help to decide where to place the nozzles.

For most applications, Stainless Steel nozzles work best. An advantage of the XA series Air Atomizing nozzle is that is can be supplied with a built-in pneumatic shutoff. Combining this shutoff with a humidistat, a solenoid valve, and some tubing, a simple humidity control system can easily be created.

Our experienced engineers can determine which nozzle is best for your application.

Humidification Nozzle Common Uses/Installations:

Humidification nozzles are used to moisten air in ducts, keep an even humidity in drying kilns, achieve a high relative humidity in curing rooms and greenhouses, keep the humidity constant in baking operations, and any other application where humidity is critical to the process.

Typical operating conditions for this application are listed for each nozzle

COOLING DELUGE NOZZLES

Process cooling for food, chemical, and industrial processes

Cooling a solid object quickly is typically accomplished by deluging it with a coolant, most often water. The rate at which the object can be cooled with a water deluge depends on the shape of the object, initial temperature, final desired temperature, the heat capacity of the object, and the convection coefficient between the object and the water. Shape takes into account the surface area, volume, and indirectly the thermal conductivity of the object. It is also important to take into account that the object’s ability to transfer heat may not be uniform, as it may be made of several substances.

The basic idea is to distribute a high volume of water completely over the object, allowing the greatest contact and therefore heat transfer from the object to the water. Nozzle spray is advantageous because it can provide full coverage of virtually any object shape. Cooling takes time; the major advantage of spraying the coolant is the ability to speed up the process as compared to simple submersion. As the object cools down, the water in contact heats up. In order to continue cooling, the warmed water should be flushed away to make space for more cool water. This flushing action is an inherent characteristic of the flood of liquid produced by a nozzle.

The rate of heat transfer is usually complicated both theoretically and computationally, involving difficult calculations. BETE can help your company determine which nozzles will be most effective at deluge cooling for your process.

Selecting a Cooling Deluge Nozzle:

The nozzles listed below have a Full Cone spray and a wide range of spray angles. Full cone designs are ideal for a cooling deluge because they provide the most uniform coverage over a given area. These nozzles also have a wide range of spray angles to allow flexibility in laying out the cooling system. In situations where significant heat is present, 316 Stainless Steel is often prefered.

BETE’s clog-resistant MaxiPass has the largest free passage available, making it resistant to clogging and applicable when recycling the cooling water. The MaxiPass’ unique design makes it very efficient and reliable, even in harsh conditions. If temperatures are relatively low and free passage is not a concern, plastic NC nozzles are very reliable and come in a wide range of flow rates, including very high flow. WL nozzles offer uniform coverage at lower flows than the MaxiPass or NC. Standard manufacturing materials for the MaxiPass and WL are Brass, Stainless Steel, PVC, polypropylene, and PTFE. Standard materials for the NC are PVC, polypropylene, and PTFE.

Our experienced engineers can determine which nozzle is best for your application

Typical operating conditions for this application are listed for each nozzle

EVAPORATIVE GAS COOLING

Cool hot flue gases prior to entering a baghouse or temperature-sensitive equipment

Evaporative Gas Cooling Process:
In many processes a gas is raised to temperatures that could easily damage downstream equipment. This can either be by direct combustion, as in the case of flue gas, or by secondary heating. The quickest and most effective way to cool a hot gas is through the evaporation of an injected liquid. Changing the phase of the liquid to gas consumes enormous amounts of energy compared to sensible cooling. As an example, heating water from 32 °F to 212 °F (0 °C to 100 °C) requires about 180 BTU/lbm (418 kJ/kg). Converting that same water from liquid at 212 °F (100 °C) to steam at 212 °F (100 °C) requires about 1000 BTU/lbm (2320 kJ/kg), or more than 5 times the energy. The energy used to vaporize the gas is taken from the hot gas, thus lowering its temperature.

In evaporative gas cooling, a mist of water is sprayed into the hot gas. In many cases this is flue gas from a combustion process. The water then evaporates, cooling the system rapidly as the energy is used to change the water from liquid to gas. When a volume of water is atomized into smaller droplets, more surface area is exposed, allowing the evaporation rate to increase.

Selecting an Evaporative Cooling Nozzle: 

The rate of evaporation is often critical as the gas must reach its final temperature before a fixed point downstream. The evaporation rate is dependent on the droplet size, temperature differential, and partial pressure among other variables. It is important to note that since spray nozzles produce a droplet size spectrum rather than a single droplet size, expertise is needed to correctly choose between different types of nozzles.

Our applications engineers can confidently assess which nozzle to recommend with the information acquired through the BETE Gas Cooling/Quenching Application Data Sheet (PDF – 229 KB). This data will also allow the engineer to calculate the amount of water, pressure, and drop size that is necessary for your application.

Typical operating conditions for this application are listed for each nozzle

PART AND PRODUCT COOLING NOZZLES

Cool hot parts on conveyors from pre-treatment ovens

BETE provides a range of high-quality nozzles that are useful for reducing the temperature of various components and parts using a deluge spray. Many production processes require the product to be hot during work and then cooled back to ambient temperature. In metal processing industries, castings, extrusions, and hot-worked products fall into this category, as do any components that have been heat treated. In the food industry, many products are packaged hot and must be cooled before storage and shipment. Regardless of whether you are cooling steel or soup, BETE can provide the right nozzle for your application.

Contact us today to speak with our engineers about finding the best nozzles to fit your needs. Our engineers are available to review your product cooling application to help verify quantity and type of nozzles required based on the cooling fluid flow requirements and specific material and shape of your products.

Common Product Cooling Nozzle Uses:

• Conveyor Cooling (Recommended Nozzles: BJ, NF, NFD, FF): BETE’s Flat Fan nozzles provide the even spray coverage needed to cover parts as they travel on conveyors.
• Stationary Cooling (Recommended Nozzles: TF, WL, CW, MPL, MaxiPass): Our Full Cone nozzles can cover a wide area with water and are useful for thoroughly cooling parts that are sitting still.
• Extrusion Cooling (Recommended Nozzles: BJ, NF, WL, CW, MPL, MaxiPass): Our fan and Full Cone nozzles provide the even coverage required to cool extruded products as they travel through a dedicated cooling zone.
• Complex Casting Cooling (Recommended Nozzles: XA): Some complex castings have varying wall thickness and require adjustable nozzles to cool the part evenly. Our air-atomizing XA series of nozzles can be tailored to handle these castings.

Common Designs and Specifications:

• Common Nozzle Types: Flat Fan, Full Cone, Air Atomizing
• Common Spray Patterns: Flat Fan, Full Cone, Misting
• Common Materials: Stainless Steel

Selecting Product Cooling Nozzles:

• Preferred BETE models: BJ, NF, NFD, FF, TF, WL, CW, MaxiPass, MPL, XA
• Important factors to consider: product material, product shape and thickness, product speed, temperatures, flow rates, operating pressures
• Our experienced engineers can help determine which nozzle is best for your application.

Typical operating conditions for this application are listed for each nozzle

COOL HOT PARTS ON CONVEYORS FROM PRE-TREATMENT OVENS

BETE provides a range of high-quality nozzles that are useful for reducing the temperature of various components and parts using a deluge spray. Many production processes require the product to be hot during work and then cooled back to ambient temperature. In metal processing industries, castings, extrusions, and hot-worked products fall into this category, as do any components that have been heat treated. In the food industry, many products are packaged hot and must be cooled before storage and shipment. Regardless of whether you are cooling steel or soup, BETE can provide the right nozzle for your application.

Contact us today to speak with our engineers about finding the best nozzles to fit your needs. Our engineers are available to review your product cooling application to help verify quantity and type of nozzles required based on the cooling fluid flow requirements and specific material and shape of your products.

Common Product Cooling Nozzle Uses:

• Conveyor Cooling (Recommended Nozzles: BJ, NF, NFD, FF): BETE’s Flat Fan nozzles provide the even spray coverage needed to cover parts as they travel on conveyors.
• Stationary Cooling (Recommended Nozzles: TF, WL, CW, MPL, MaxiPass): Our Full Cone nozzles can cover a wide area with water and are useful for thoroughly cooling parts that are sitting still.
• Extrusion Cooling (Recommended Nozzles: BJ, NF, WL, CW, MPL, MaxiPass): Our fan and Full Cone nozzles provide the even coverage required to cool extruded products as they travel through a dedicated cooling zone.
• Complex Casting Cooling (Recommended Nozzles: XA): Some complex castings have varying wall thickness and require adjustable nozzles to cool the part evenly. Our air-atomizing XA series of nozzles can be tailored to handle these castings.

Common Designs and Specifications:

• Common Nozzle Types: Flat Fan, Full Cone, Air Atomizing
• Common Spray Patterns: Flat Fan, Full Cone, Misting
• Common Materials: Stainless Steel

Selecting Product Cooling Nozzles:

• Preferred BETE models: BJ, NF, NFD, FF, TF, WL, CW, MaxiPass, MPL, XA
• Important factors to consider: product material, product shape and thickness, product speed, temperatures, flow rates, operating pressures
• Our experienced engineers can help determine which nozzle is best for your application.

Typical operating conditions for this application are listed for each nozzle