Key Concepts
Evaporation causes cooling because it requires heat energy from the surrounding environment to change a liquid into a gas. As liquid particles gain energy to overcome the force of attraction between them, the surrounding environment loses heat energy, which cools the original surface.
Here are some examples of evaporation causing cooling.
- Sprinkling water on the ground: During hot summer evenings, people in villages often sprinkle water on the ground in front of their homes to use the high latent heat of evaporation to cool the ground and surrounding air.
- Sweating: The body uses evaporation when sweating to cool down. Sweat is 90% water, and as it evaporates, it converts from a liquid to a gas and thus removes heat from the body. It is common to refer to this process as evaporative cooling.
- Water from trees: Water that evaporates from tree leaves also cools the surrounding air.
Evaporation causes cooling because the process of turning liquid into gas requires heat energy from the liquid’s surroundings. As the heat evaporates, the remaining liquid cools. This is how it works.
- Liquid surface particles absorb energy from their surroundings and convert it into vapor.
- Evaporating molecules take their kinetic energy with them, lowering the average kinetic energy of the remaining liquid, which cools.
- Heat transfers as energy removed from the vaporized liquid reduces the liquid’s temperature along with the temperature of the chamber that holds the vaporized liquid.
CleanCold’s use of a metal vacuum chamber exploits metal’s excellent conductivity, which enhances the transfer of cooling to the external circulating water circuit.
The Cooling Science Behind Vacuum Driven Water Evaporation
CleanCold Technologies has developed a vacuum-driven water evaporation method that applies to various cooling applications. These include refrigeration, air conditioning, cold rooms, cold transport, and medical applications. Our innovative technology uses water that is a safe and natural refrigerant with zero GWP. It replaces the current HFC/HC/CO2/ ammonia/HFOs refrigerants used in existing systems, providing benefits for the cooling and refrigeration industries and the environment.
We all have experienced the cooling properties of vaporizing water. A typical scenario is when we come out of the pool after swimming; we feel a cooling sensation as the water evaporates from our skin. This cooling becomes more noticeable if the wind is blowing when we exit the water because the rapid evaporation drops the skin temperature faster. Our system relies on this evaporation process, as highlighted in Figure 1.
As shown in Figure 1 and the image below, as the pressure drops below atmospheric levels, the temperature of water evaporation decreases from 100°C. When the pressure reaches 7 mbar, the vaporization temperature is 2°C (typical refrigeration temperature). At 2 mbar, the vaporization occurs at typical freezer temperatures of -18°C.
- Temperature oF/oC Pressure (mbar/atm)
- 70°F/21°C 25 mbar/0.024 atm
- 65°F/18.3°C 20.5 mbar/0.020 atm
- 60°F/15.6°C 17.4 mbar/0.017 atm
- 50°F/10°C 12.5 mbar/0.012 atm
- 41°F/5°C 8.7 mbar/0.0086 atm
- 32°F/0°C 5.7 mbar/0.0056 atm
- 14°F/-10°C 2.6 mbar/0.00257 atm
- -4°F/-20°C 1.0 mbar / 0.00099 atm
Flash Evaporation Temperature of Water as Function of Pressure
CleanCold’s first commercial development will be a closed-loop refrigeration system developed to serve a cold-storage volume.
Hydrofluorocarbons and hydrocarbons in refrigeration account for around 20% of the global warming footprint. Common refrigerants in the U.S. and other countries have high GWP values, which is the main reason behind the push by the Environmental Protection Agency (EPA) to phase out their use. Despite this regulatory effort, the existence of many older systems that require significant upgrades before the switch to CO2 or ammonia is hampering enforcement.
For CO2, many existing systems cannot support the higher gas pressure required for carbon dioxide. The requirements of retrofitting are time-consuming and expensive. Retrofitting ammonia to use in existing systems is problematic, as it can escape from older systems. Additionally, there is a concern about using this gas because of its toxicity. Not surprisingly, retrofitting using CleanCold’s water-based system will provide significant cost and toxicity exposure benefits.
CleanCold Technologies System
External Enclosure
Exploded View
Internal Layout
CleanCold Technologies System
External Enclosure
Exploded View
Internal Layout