HOW DOES A HEAT PUMP EVAPORATOR WORK?
EVALED® evaporators take advantage of a natural phenomenon: evaporation.
It was born 45 years ago from a far-sighted intuition that demonstrated how accelerating this phenomenon, combined with the use of standard modular units, represents a cost-effective 'clean system' for separating water from pollutants with a higher boiling temperature than the water itself.
WHAT IS EVAPORATION?
Evaporation is the transition from the liquid to the gaseous state that only affects the surface of the liquid. If the boiling temperature (different for each liquid and related to pressure) is exceeded, the boiling process takes place, characterised by constant temperature and pressure parameters.
Both processes are referred to as vaporisation.
WHAT IS THE LATENT HEAT OF A LIQUID?
To reach this step, it is first necessary to supply heat (energy) to the liquid. The amount of heat required for the change of state to occur, called the latent heat of evaporation, depends on the type of liquid, its mass and its temperature.
For example, for a kilo of water at 373 K (100 °C), the latent heat is about 2300 kJ (550 kcal, 640 Wh) at atmospheric pressure (about 100 kPa).
The same amount of heat is released from water during the vapour stage, when the condensation phenomenon occurs.
WHAT IS THE BOILING POINT?
The boiling point corresponds to the temperature at which the vapour pressure equals the external pressure, so that vaporisation occurs tumultuously (boiling), so that it does not affect only the surface of the liquid but the entire mass.
The boiling point depends on the type of liquid and varies with pressure. That of water is at 373 K (100 °C) at an atmospheric pressure of about 100 kPa. At high altitudes, however, such as on mountain tops, where the pressure value is lower than at sea level, water boils at a lower temperature. Thus, when the pressure is very low (vacuum) and is about 4 kPa (40 mbar), the boiling temperature is reached at 302 K (29 °C).
Different liquids have different boiling points: ethyl alcohol, for example, has a boiling point of 351.4 K (78.4 °C) at 75 kPa (760 mbar).
WHAT IS BOILING POINT ELEVATION?
In the case of salt solutions, the boiling temperature at constant pressure changes depending on the presence of salts and their concentration. Boiling point elevation is therefore the difference between the boiling temperatures of water and that of a solution with a fixed concentration of salts. For example, the boiling temperature of a 35% w/w NaCl aqueous solution at atmospheric pressure will show an increase in boiling temperature of 10 K (at 37 °C).