Active cooling is a heat-reducing mechanism that is typically implemented in electronic devices and indoor buildings to ensure proper heat transfer and circulation from within.

Unlike its counterpart passive cooling, active cooling is entirely dependent on energy consumption in order to operate. It uses various mechanical systems that consume energy to dissipate heat. It is commonly implemented in systems that are unable to maintain their temperature through passive means. Active cooling systems are usually powered through the use of electricity or thermal energy but it's possible for some systems to be powered by solar energy or even hydroelectric energy. They need to be well-maintained and sustainable in order for them to perform its necessary tasks or the possibility of damages within objects could occur. Various applications of commercial active cooling systems include indoor air conditioners, computer fans, and heat pumps.

Building usage

Many buildings require high demands in cooling and as many as 27 out of the 50 largest metropolitan areas around the world are located in areas of hot or tropical weather. With this, engineers have to establish the heat balance in order to ensure proper ventilation throughout the structure.

The heat balance equation is given as:

<math>p \cdot c_p\cdot V \cdot dT/dt = E_{int} + E_{Conv} + E_{Vent} + E_{AC}</math>

where <math>p</math> is the air density, <math>c_p</math> is the specific heat capacity of air at constant pressure, <math>dT/dt</math> is the rate of heat transfer, <math>E_{int}</math> is the internal heat gains, <math>E_{Conv}</math> is the heat transfer through the envelope, <math>E_{Vent}</math> is the heat gain/loss between indoor and outdoor air, and <math>E_{AC}</math> is the mechanical heat transfer.

There are two types of heat pumps:

Compression heat pumps

Being the more popular variant of the two, compression heat pumps operates through the use of the refrigerant cycle. The vapor refrigerant in the air gets compressed while increasing in temperature, creating a superheated vapor. The vapor then goes through a condenser and converts into a liquid form, dispelling more heat in the process. Traveling through the expansion valve, the liquid refrigerant forms a mixture of liquid and vapor. As it passes through the evaporator, vapor refrigerant forms and expels into the air, repeating the refrigerant cycle.

Absorption heat pumps

The process for the absorption heat pump works similarly to the compression variant with the main contrast being the usage of an absorber instead of a compressor. The absorber takes in the vapor refrigerant and creates a liquid form which then travels into the liquid pump to be turned into superheated vapor. The absorption heat pump utilizes both electric and heat for its functionality compared to compression heat pumps which only uses electricity.

It can be divided by:

Direct

This method evaporates the water which would then travel directly into the air stream, producing a small form of humidity. It usually requires a decent amount of water consumption in order to properly lower the temperature of the surrounding area.

Indirect

This method evaporates the water into a second air stream and then putting it through a heat exchanger, lowering the temperature of the main air stream without adding any humidity. Compared to direct evaporative coolers, it requires much less water consumption to operate and lowering temperature.

Near Immersion Active Cooling (NIAC)

Near Immersion Active Cooling, or NIAC, is a thermal management technique that has been recently researched in an effort to reduce the amount of heat accumulation generated by Wire + Arc Additive Manufacturing, or WAAM (a metal 3-D printing technology). NIAC utilizes a cooling liquid that surrounds the WAAM within a work tank and increases the water level when metal is being deposited. The direct contact with the liquid allows for quick withdrawal of heat from the WAAM, decreasing temperature by a significant amount.

In a 2020 experiment, researchers wanted to discover the feasibility of using the NIAC and to test its cooling capabilities. The experiment compared the effectiveness of mitigating temperature generated by the WAAM between natural cooling, passive cooling, and near immersion active cooling. Natural cooling used air, passive cooling used a cooling liquid that stays on a fixed level, and NIAC used a cooling liquid that rises based on the actions of the WAAM.

  • Mechanical properties: NIAC tends to equalize the mechanical properties, especially ductility, in contrast to both natural and passive cooling.

They concluded NIAC is viable and comparable to conventional cooling methods such as passive and natural cooling.