ClassX Video Lessons Youtube Channel The Engineering Mindset Absorption Chiller, How it works – working principle hvac
Welcome to an exploration of absorption chillers, a fascinating component of HVAC systems. Unlike traditional chillers, absorption chillers do not rely on compressors. Instead, they use heat to produce cooling, which might sound a bit perplexing at first. However, by the end of this article, you’ll have a solid grasp of how these systems function.
Absorption chillers stand out because they use water as a refrigerant, combined with either ammonia or lithium bromide. Lithium bromide is more commonly used due to its safety and non-toxic nature. This article will focus on water-lithium bromide chillers, which are prevalent in the industry.
To understand absorption chillers, it’s essential to grasp three fundamental concepts:
Water’s boiling point changes with pressure. At standard atmospheric pressure, water boils at 100 degrees Celsius (212 degrees Fahrenheit). However, at lower pressures, such as those found at high altitudes, the boiling point decreases. In absorption chillers, the evaporator and absorber operate under very low pressures, almost like a vacuum. For example, at 0.84 kPa (0.12 psia), water boils at approximately 4.5 degrees Celsius (40 degrees Fahrenheit).
Lithium bromide is a liquid salt that naturally attracts moisture from the air. When it comes into contact with water vapor, the two substances are drawn together, facilitating the absorption process.
When water and lithium bromide are mixed, they can be separated by applying heat. Heating the mixture causes the lithium bromide to become denser and settle, while the water vapor rises.
An absorption chiller consists of several key components:
The cycle begins with a mixture of approximately 60% lithium bromide and 40% water, known as the weak solution. This mixture is pumped from the absorber through the heat exchanger to the generator tank. Heat, often from waste sources, is added to the generator, causing water to boil off as steam and fill the condenser, while lithium bromide settles at the bottom.
The hot lithium bromide then flows through the heat exchanger, transferring heat to the weak solution line. Once cooled, it moves to the absorber, where it mixes with water and is pumped back to the generator, continuing the cycle.
In the condenser, hot water vapor is cooled and condensed back into liquid form. This is achieved by circulating water through a sealed pipe, which is then sent to a cooling tower to release the collected heat. The cooled water condenses the vapor, which collects in a tray below.
This liquid water flows to the evaporator, where it is sprayed into the chamber. Operating at low pressure, the evaporator causes the water to flash and cool to about 4 degrees Celsius (40 degrees Fahrenheit). The chilled water loop absorbs unwanted heat from the building, entering at around 12 degrees Celsius (54 degrees Fahrenheit) and exiting at approximately 7 degrees Celsius (45 degrees Fahrenheit).
Any water that doesn’t evaporate is recirculated and sprayed again until fully evaporated. The evaporating water vapor is drawn to the strong lithium bromide solution in the absorber, creating a vacuum. The cooling tower water loop removes the heat generated from this mixing process, condensing any residual vapor or lithium bromide particles back into liquid form.
Finally, the lithium bromide and water mixture is collected at the bottom of the absorber, ready to be pumped back to the generator, repeating the cycle.
And there you have it—a comprehensive overview of how absorption chillers work. This innovative technology offers an efficient way to provide cooling using heat, making it a valuable component in modern HVAC systems.
Create a detailed diagram of an absorption chiller system. Use software like Lucidchart or draw.io to illustrate the main components and the flow of the absorption chiller cycle. Label each part and describe its function. Share your diagram with classmates for feedback and discussion.
Conduct a simple experiment to observe how pressure affects the boiling point of water. Use a vacuum pump to reduce the pressure in a sealed container and measure the boiling point of water. Relate your findings to the operation of the evaporator in absorption chillers.
Research a real-world application of absorption chillers in a commercial building or industrial setting. Analyze the benefits and challenges faced in the implementation. Present your findings in a report, highlighting how the principles discussed in the article are applied in practice.
Engage in a group discussion about the environmental impact of absorption chillers compared to traditional chillers. Consider factors such as energy sources, efficiency, and emissions. Prepare a short presentation summarizing your group’s conclusions and suggestions for improvement.
Use simulation software like MATLAB or Simulink to model the absorption chiller cycle. Input different variables such as heat source temperature and ambient conditions to observe their effects on system performance. Share your simulation results and insights with the class.
Sure! Here’s a sanitized version of the YouTube transcript:
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Hello everyone, Paul here from TheEngineeringMindset.com. In this video, we will explore the basics of absorption chillers and how they operate.
An absorption chiller differs from other chillers because it does not use a compressor. Instead, it utilizes heat to generate cooling. This concept may seem a bit confusing at first, but by the end of this video, you will have a clear understanding of how it works.
One interesting aspect of absorption chillers is that they do not use conventional refrigerants like R134A or R22. Instead, they use water as a refrigerant, which is mixed with either ammonia or lithium bromide. Lithium bromide is the more common choice due to its safety and non-toxic properties. In this video, we will focus on how water-lithium bromide chillers operate, as they are quite similar.
Before we dive into the inner workings of an absorption chiller, it’s important to understand three key concepts that are fundamental to their operation.
First, when we boil water, it changes from a liquid to a vapor. The boiling point of water varies with pressure; increasing pressure raises the boiling point, while decreasing pressure lowers it. For instance, at atmospheric pressure, water boils at around 100 degrees Celsius (212 degrees Fahrenheit). However, at higher altitudes, such as the top of Mount Everest, where the atmospheric pressure is lower, water boils at about 70 degrees Celsius (158 degrees Fahrenheit).
In an absorption chiller, the evaporator and absorber operate at very low pressures, almost near vacuum conditions. At a pressure of approximately 0.84 kPa (0.12 psia), water boils at around 4.5 degrees Celsius (40 degrees Fahrenheit). When steam passes over a pipe containing cold water, it transfers thermal energy to the water, causing it to condense back into liquid form.
The second concept to understand is that lithium bromide is a salt in liquid form, which attracts moisture from the air. When lithium bromide is sprayed onto water vapor, the two are drawn together.
The third point is that when water and lithium bromide are mixed, they can be separated by applying heat. Heating the mixture causes the lithium bromide to become denser and settle at the bottom, while the water vapor rises.
Now that we have covered these basics, let’s look at the main components of an absorption chiller. The top chamber contains the condenser and generator, while the lower half houses the evaporator and absorber. Additionally, there is a heat exchanger located near the bottom to enhance system efficiency.
A mixture of approximately 60% lithium bromide and 40% water is pumped from the absorber through the heat exchanger and into the generator tank at the top. This mixture is referred to as the weak solution. The generator fills with this mixture, creating a reservoir. Heat is then added to the reservoir, typically from waste heat, which initiates the separation process. The heat causes water particles to boil off and fill the condenser with steam, while the heavier lithium bromide settles at the bottom.
The hot liquid lithium bromide flows to the heat exchanger, where it transfers heat to the weak solution line. Once cooled, it moves to the absorber, where it mixes with water before being pumped back to the generator to repeat the cycle.
Next, we need to condense the hot water vapor in the condenser to return it to liquid form. Water circulates through a sealed pipe in the condenser and is sent to the cooling tower, where it releases the collected heat. The cooling tower water is cool enough to condense the hot water vapor into liquid, which then collects in a tray below.
This liquid water flows down to the evaporator, where it is sprayed into the chamber. The evaporator operates at very low pressure, causing the incoming water to flash and drop in temperature to around 4 degrees Celsius (40 degrees Fahrenheit). The chilled water loop then runs into the evaporator, absorbing unwanted heat from the building.
As the chilled water enters at around 12 degrees Celsius (54 degrees Fahrenheit), it transfers its thermal energy through the tube wall into the thin film of cold water sprayed across the outside of the chilled water tubes. The two water streams remain separate, and as heat transfers into the outer water, it evaporates into steam due to the low pressure in the chamber, carrying away unwanted heat.
By the time the water exits the chiller, it should be around 7 degrees Celsius (approximately 45 degrees Fahrenheit), ready to be pumped around the building to collect more heat.
Any water that does not evaporate is recirculated back to the top of the evaporator and sprayed again until it fully evaporates. The evaporating water vapor is attracted to the strong lithium bromide solution in the absorber, creating a vacuum in the chamber. The attraction between the water and lithium bromide particles is strong enough to pull the water vapor into the absorber.
The heat generated from the mixing of the two fluids needs to be removed, which is why the cooling tower water loop also passes through the absorber to take away unwanted heat. The cooling tower water condenses any residual water vapor or lithium bromide particles back into liquid form.
Once this process is complete, the mixture of lithium bromide and water is collected at the bottom of the absorber and is ready to be pumped back to the generator to repeat the cycle.
So there you have it—the basics of how an absorption chiller works. Thank you for watching! I hope this video has been helpful. Please don’t forget to like, subscribe, and share. If you have any comments, feel free to leave them below. Also, check out our website, TheEngineeringMindset.com. Thanks again for watching!
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This version maintains the informative content while removing any informal language and ensuring clarity.
Absorption – The process by which one substance takes in or absorbs another substance, often used in the context of heat or energy transfer in engineering systems. – In absorption refrigeration systems, the refrigerant is absorbed by a liquid, which is then heated to release the refrigerant vapor.
Chillers – Devices used to remove heat from a liquid via a vapor-compression or absorption refrigeration cycle, commonly used in industrial and commercial cooling applications. – The university’s new laboratory building is equipped with high-efficiency chillers to maintain optimal temperatures for sensitive experiments.
Lithium – A chemical element often used in batteries and as a component in absorption refrigeration systems, where it acts as a desiccant. – Lithium bromide is commonly used in absorption chillers due to its ability to absorb water vapor effectively.
Bromide – A compound of bromine with another element, often used in absorption refrigeration systems as a refrigerant or absorbent. – The lithium bromide solution in the absorption chiller helps in the efficient transfer of heat by absorbing water vapor.
Water – A universal solvent and essential component in many engineering systems, often used as a coolant or heat transfer medium. – In the cooling tower, water is used to dissipate heat from the condenser, maintaining the efficiency of the refrigeration cycle.
Pressure – The force exerted per unit area, crucial in understanding fluid dynamics and thermodynamics in engineering systems. – Engineers must carefully monitor the pressure levels in a steam turbine to ensure safe and efficient operation.
Heat – A form of energy transfer between systems or bodies due to a temperature difference, fundamental in thermodynamics and energy systems. – The heat generated by the combustion process is converted into mechanical energy in an internal combustion engine.
Cooling – The process of removing heat from a system or substance, often to maintain a desired temperature or to improve efficiency. – Effective cooling of electronic components is essential to prevent overheating and ensure reliable performance.
Condenser – A device used to condense a gaseous substance into a liquid by removing heat, commonly found in refrigeration and air conditioning systems. – The condenser in the air conditioning unit releases heat to the outside environment, allowing the refrigerant to cycle back to the evaporator.
Evaporator – A component in refrigeration systems where the refrigerant absorbs heat and evaporates, thus cooling the surrounding environment. – In the refrigeration cycle, the evaporator absorbs heat from the interior of the refrigerator, keeping the contents cool.
