What is the most effective cooling tower system?

Pressure difference

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In a water boiler, draft is the difference between atmospheric pressure and the pressure existing in the furnace or flue gas passage.[1] Draft can also be referred to as the difference in pressure in the combustion chamber area which results in the motion of the flue gases and the air flow.[2]

Types of draft

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Drafts are produced by the rising combustion gases in the stack, flue, or by mechanical means. For example, a boiler can be put into four categories: natural, induced, balanced, and forced.

• Natural draft: When air or flue gases flow due to the difference in density of the hot flue gases and cooler ambient gases. The difference in density creates a pressure differential that moves the hotter flue gases into the cooler surroundings.[2]
• Forced draft: When air or flue gases are maintained above atmospheric pressure. Normally it is done with the help of a forced draft fan.[2]
• Induced draft: When air or flue gases flow under the effect of a gradually decreasing pressure below atmospheric pressure. In this case, the system is said to operate under induced draft. The stacks (or chimneys) provide sufficient natural draft to meet the low draft loss needs. In order to meet higher pressure differentials, the stacks must simultaneously operate with draft fans.[2]
• Balanced draft: When the static pressure is equal to the atmospheric pressure, the system is referred to as balanced draft. Draft is said to be zero in this system.[2]

For the proper and the optimized heat transfer from the flue gases to the boiler tubes draft holds a relatively high amount of significance. The combustion rate of the flue gases and the amount of heat transfer to the boiler are both dependent on the movement and motion of the flue gases. A boiler equipped with a combustion chamber which has a strong current of air (draft) through the fuel bed will increase the rate of combustion (which is the efficient utilization of fuel with minimum waste of unused fuel). The stronger movement will also increase the heat transfer rate from the flue gases to the boiler (which improves efficiency and circulation).[3]

Drafting in steam locomotives

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Since the stack of a locomotive is too short to provide natural draft, during normal running forced draft is achieved by directing the exhaust steam from the cylinders through a cone (&#;blast pipe&#;) upwards and into a skirt at the bottom of the stack. When the locomotive is stationary or in a restricted space &#;live&#; steam from the boiler is directed through an annular ring surrounding the blast pipe to produce the same effect.

See also

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References

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1. ^McGraw, Hill (). Dictionary of Scientific and Tech Terms. USA: Mc Graw Hill Publications. ISBN .

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2. a b c d e

   Babcox & Wilcox (). Steam/ its generation and use (38 ed.). USA: The Babcock & Wilcox Company. p. 17-1.

3. ^Ray, Walter T (). The Significance of Drafts in Boiler Practice. Washington: Government Printing Office. pp. 6&#;8.

Industrial cooling towers might be one of the most crucial parts of any industrial or HVAC process. These tall open-topped, water-cooling structures are responsible for cooling equipment vital for industrial or HVAC comfort cooling processes. You may be surprised to learn that there is much more to these cooling towers than you ever knew.

An industrial cooling tower can perform its work in a number of ways, using a range of technologies to cool process water. Keep reading to better help you understand the differences between the types of cooling towers available today. 

Cooling Tower Types

• Natural Draft Cooling Towers

As their name implies, natural draft cooling towers rely on natural convection to circulate air throughout the tower, which then cools the water. Air movement occurs due to differences in density between the entering air and the internal air within the tower. Warm, moist air, which is denser than cool air, will naturally rise through the tower, while the dry, cool air from outside will fall, creating a constant cycle of airflow.

• Mechanical Draft Cooling Towers

Unlike natural draft cooling towers, mechanical draft cooling towers employ fans or other mechanics to circulate air through the tower. Common fans used in these towers include propeller fans and centrifugal fans. Mechanical draft towers are more effective than natural draft towers, and can even be located inside a building with the proper exhaust system. However, they consume more power than natural draft cooling towers and cost more to operate as a result.

Types of Mechanical Draft Cooling Towers

There are two types of mechanical draft cooling towers:

A. Crossflow Towers
In a crossflow tower, air flows horizontally through the cooling tower&#;s structure while hot water flows downward from distribution basins. Crossflow towers can be as tall as counterflow towers, but they&#;re also more prone to freezing and are less efficient.

B. Counterflow Cooling Towers
This type of cooling tower moves air upward through the tower while water flows downward to cool the air. These towers are often more compact in footprint than crossflow towers and can save energy in the long run.

Cooling Tower Build Type 

Cooling towers can differ by build as well as heat transfer and air generation methods. When it comes to cooling tower build, there is the: 

• Package type. These are small, compact, and pre-fabricated cooling towers used for smaller industries, such as hospitals or schools. These are factory-fabricated and shipped on trucks.
• Field erection type. These are large, specified units used for power plants and other larger industrial factories. These are fabricated on-site and are larger than a typical house. 

Selecting sizing for cooling towers is a heat-load calculation, based on your process, cooling needs, and your building&#;s HVAC.

Heat Transfer Technique

When it comes to heat transfer methods, there are several types of cooling towers as well:

• Wet cooling towers (open circuit). These tend to be one of the most popular styles because they are cost-effective and will achieve the most possible cooling. Heat transfer is measured by way of a decrease in the process temperature and the wet bulb temperature, and how cold the water temperature becomes.
• Dry cooling towers. These work by using an electric motor that transfers heat that separates the fluid from the air. These towers use no water in their operations. 
• Fluid coil cooling towers (closed circuit). In closed-circuit cooling systems, water is mixed with glycol to form a fluid that then moves through a coil that is exposed to air afterward. These require more horsepower to achieve temperatures close to the open-circuit.

Which Type of Cooling Tower is More Efficient

The cooling tower efficiency formula reads as: μ = (ti - to) 100 / (ti - twb), which may be tough to understand by just looking at it. Fundamentally, a cooling tower&#;s efficiency is measured in terms of approach and range. When the topic of efficiency is discussed, it usually has to do with the type of airflow used within the unit, not its heat transfer method or size. 

A cooling tower will either be configured as a crossflow or a counterflow system. Counterflow (induced draft) systems are considered the most efficient of the two. Crossflow (forced draft) towers distribute hot water perpendicularly to the airflow, while counterflow towers distribute hot water directly into the airflow. 

However, counterflow towers can be taller which impact sites with height restrictions. Counterflow towers also have the benefit of keeping the cooling media out of any sunlight, preventing potential bacterial issues (like Legionnaires' disease).

How Can I Make My Cooling Tower More Efficient

No matter what type of cooling tower you have, there are always ways to improve if you&#;re wondering how to increase cooling tower efficiency. Some things you can consider:

• Installing new water piping. Installing even one piece of new piping where it is needed can improve energy efficiency. 
• Ensure your system is recycling water properly. Your tower should be recycling upward of 98 percent of water. If it isn&#;t, it may be time for a service call. Recycling water can improve water and energy efficiency.
• Increase cooling cycles. Be aware of how many cooling cycles your tower uses. Adjusting from three to six can make a difference in efficiency and save water usage. 

Delta Is Standing by to Help

What are your thoughts on the different types of cooling towers? Delta, the technology-leading cooling tower supplier and cooling tower manufacturer in USA, rises above the standards of other manufacturers to provide a 20-year warranty, so you do not have to worry about periodic replacements. And, Delta&#;s high-quality cooling tower designs offer customers not only an extended lifecycle but also fewer moving parts and, therefore, less maintenance downtime. Have any questions or comments for us on maintaining successful cooling tower systems? Let us know. Or, click here to get your quote today!

If you want to learn more, please visit our website air cooling system advantages and disadvantages.