Aftercooler/Heat Exchanger
An important but little-known fact about pneumatic conveying is that the temperature of air rises due to the adiabatic process as the air is compressed (see below to learn more). Any good designer will understand where the heat is in the system and mitigate it if needed.
If the material conveyed is reactive to the heat we may need to mitigate the heat before the material is exposed to it.
One way to mitigate the heat is with an aftercooler/heat exchanger.
How does it work?
A standard aftercooler unit is composed of tubing (containing water or air) and fins that help it achieve cooling. When in operation, ambient air is pulled into the aftercooler to help remove moisture from the compressed air by condensation while reducing process temperatures to satisfactory levels. Compressed air aftercoolers are manufactured as either water or air-cooled variants.
For air-cooled compressed air aftercoolers, ambient air is directed over tubes containing hot compressed air to remove generated heat in a heat exchange process. In a water-cooled version (also called an air-to-water cooler), water is channeled through tubes running alongside compressed air pipes to achieve cooling.
US Systems proudly manufactures air-cooled heat exchangers.
To order: please specify the inlet and outlet type and sizes and the required airflow.
What is Adiabatic Compression?
Adiabatic compression is a process where a gas is compressed without any heat exchange with its surroundings. This causes the gas temperature to increase as it is compressed.
How Rotary Lobe PD Blowers Achieve Adiabatic Compression
Rotary lobe positive displacement (PD) blowers achieve adiabatic compression by trapping a fixed volume of air and compressing it as the lobes rotate. Here’s the process:
- Air Intake: The lobes rotate, drawing air into the chamber.
- Compression: The air is compressed within the chamber as the lobes continue to rotate.
- Discharge: The compressed air is released through the outlet at a higher pressure.
An Example:
If ambient air temperature is 80°F, a pressure increase to 10 PSI will yield conveying air that is ~176°F.
- Reduce moisture: By decreasing the temperature of the compressed air, the aftercooler minimizes the amount of condensation that forms, preventing moisture buildup and subsequent issues in the system.
- Improve system efficiency: Aftercoolers enable the use of smaller dryers or dryers with lower energy consumption, as the cooled air reduces the load on the dryer.
- Enhance product quality: By maintaining a consistent air temperature, the aftercooler ensures that the conveyed materials are not exposed to excessive heat, which can affect their properties or quality.
Key Design Considerations
- System configuration: The aftercooler’s placement in the pneumatic conveying system is critical. It should be situated close to the blower to maximize cooling efficiency.
- Coolant selection: The choice of coolant (air or liquid) depends on the specific application, ambient conditions, and desired level of cooling.
- Heat exchanger design: The aftercooler’s heat exchanger design should be optimized for efficient heat transfer, taking into account factors like airflow rates, pressure drops, and material compatibility.
Benefits of Aftercoolers in Pneumatic Conveying
- Improved system reliability: By reducing moisture and heat buildup, aftercoolers minimize the risk of corrosion, scaling, and other issues that can affect system performance.
- Enhanced product quality: By maintaining a consistent air temperature and reducing moisture, aftercoolers help ensure the quality and consistency of conveyed materials.
