Heat Exchangers for Enclosure Thermal Management
In industry, electrical and electronic equipment are typically housed in an enclosure to protect the equipment from the environment. The type of environment determines the NEMA Type or IP Rating for the enclosure, which protects the equipment from an indoor versus outdoor environment, corrosive environments, dust, rain, snow and ice formation, hose directed water and possibly hazardous gases which could ignite.
What is Enclosure Thermal Management and Why is it Important?
Since most electrical and electronic equipment is not 100% efficient, a portion of the electrical energy is converted into heat. This heat causes a rise in the enclosure temperature, which can impact the operation and lifespan of the internal equipment.
In such cases, a type of thermal management system is needed to remove this heat and maintain a safe operating temperature. As this thermal management system is typically mounted to the enclosure surface, it must be able to maintain the enclosures' environmental integrity while in operation.
What is a Closed-Loop Cooling System for Enclosures?
To prevent ambient environmental contaminants from entering the enclosure, a closed-loop thermal management system is typically required. This system creates a physical barrier between the internal enclosure air and the external ambient air, preventing contaminants from entering. Several types of closed-loop cooling systems are available.
When an enclosure is installed outdoors and the ambient temperature is a few degrees below the desired internal temperature, an air-to-air heat exchanger is commonly used. These heat exchangers utilize a method of transferring the generated heat inside the enclosure to the cooler air outside of the enclosure through a heat exchanger element. Fans are typically used to circulate the heated enclosure air and the cool ambient air to this heat transfer element. The fan’s increased airflow allows for the use of physically smaller elements versus airflow from natural convection.
Heat Pipe Coils vs. Convoluted Core Heat Exchangers: Key Differences
Two of the most common types of air-to-air heat exchanger elements used in the enclosure cooling industry are:
- Heat pipe coils
- Convoluted cores
Heat pipe coils are typically constructed of thermally conductive metal tubing (copper or aluminum) with attached fins to enhance heat transfer. These coils are partially filled with a working fluid, or refrigerant. This fluid is used to transfer heat from the heated side of the coil, exposed to the inside enclosure air stream, to the cooled side of the coil located in the outside cool air stream.
A convoluted core is constructed of a thermally conductive material that is formed to maximum surface area for heat transfer, minimize airflow restriction, and maintain a sealed barrier between the enclosure and ambient environments.
Both heat transfer elements can provide satisfactory results when properly selected and applied according to the manufacturer’s specifications and the enclosures application requirements. However, convoluted core offers several important advantages.
Why Convoluted Core Technology is a More Reliable Cooling Solution
The convoluted core does not employ a working fluid to transfer heat from the enclosure to the outside ambient. The working fluid places limitations on the temperature range that the heat exchanger can be used. Also, the heat pipe coils use temperature differences to drive the working fluid from one side of the heat pipe to the other. This temperature difference can cause variations in the rate of heat transfer. Whereas the convoluted core does not utilize a working fluid, the heat transfer remains more consistent based on-air temperature differentials across a wide range of temperatures, with small variations due to air density.
Heat pipe cores can also be position sensitive as the working fluid can depend on gravity to assist with the flow of the working fluid. Convoluted cores are typically not position sensitive regarding heat transfer capacity.
Long-Term Investment to Protect Your Equipment
Over time, the heat pipe coil’s fluid passages will leak to its’ surroundings. This change in fluid composition will degrade the heat transfer capability. Also, if the fluid is a CFC, HCFC, or an HFC, this may be an environmental contaminant due to its global warming potential and/or possible ozone depletion.
The finned-tube design of heat pipe coils creates greater airflow resistance compared to convoluted cores. This means more energy is required for airflow, decreasing the cooling systems' operating efficiency. Also, this restrictive airflow causes more rapid fouling of the heat pipe coils surface with airborne contaminants. This coil fouling acts as thermal insulation inhibiting heat transfer and decreasing the overall heat transfer capability. The increased fouling rate of the heat pipe coil also requires more frequent maintenance to ensure optimum heat transfer.
In summary, based on aforementioned functional and design characteristics, you can see that the convoluted core heat transfer is simple, direct, and efficient with zero GWP and zero ODP. The convoluted core also requires less frequent maintenance than the heat pipe coil and offers many advantages over the heat pipe coil.