What Is Solar Distillation?

Solar distillation method is the energy from the sun's radiation during distillation. The process of using solar energy to directly evaporate brine is a direct solar distillation process.

Solar distillation method is the energy from the sun's radiation during distillation. The process of using solar energy to directly evaporate brine is a direct solar distillation process.

The solar distillation device does not consume conventional energy, and has a simple structure and easy operation. It is very suitable to be used in some remote coastal areas with sufficient sunlight but lacking power and electrical energy. ^[1]

1. Heat transfer process of solar distillation device

Part of the energy projected by the solar radiation onto the tilted glass ceiling is absorbed by the ceiling glass, and part of it is absorbed by the salt water. After the salt water absorbs solar energy, the water temperature rises, and at the same time, some of the energy is used for evaporation and passed to the ceiling through steam condensation. The rest Energy is transmitted to the ceiling by radiation and convection, and a small amount of energy leaks through the bottom of the basin and surrounding insulation.

2.Calculation formula for heat absorption of solar distillation device

Due to the temperature difference between the water surface and the ceiling glass, there is humid air in the space of the still and specific geometric conditions, which makes the natural convection very intense and can be considered as turbulence. The convection, evaporation, and radiant heat transfer between the water surface of the basin and the top of the still is similar to the heat transfer between two infinitely long plates. For convective heat transfer

Evaporative heat transfer

And radiant heat transfer

For calculation of, apply the following calculation formula:

Where

Salt water surface temperature (K);

Inner surface temperature of ceiling glass (K);

With temperature

Corresponding partial pressure of water vapor (Newton / meter2);

With temperature

Corresponding partial pressure of water vapor (Newtons / meter2).

The above three formulas can be obtained

The main factors affecting the thermal performance of the still are the heat loss and the thermal inertia of the device and the salt water.

From the perspective of reducing heat loss, some measures can be taken:

1. Strengthen the insulation of the rest of the roof, reduce heat leakage, and use non-metallic materials with low thermal conductivity as much as possible on the structure.

2. The distiller maintains a good seal. Poor sealing causes steam leakage and will greatly affect water production.

3. Practice has proved that wind speed seriously affects water production. In order to reduce heat loss, the distiller should be built in a sheltered place or other windproof measures should be taken.

4. The use of sensible heat from fresh water should be considered.

To reduce the influence of thermal inertia on the thermal performance of the distiller, the following should be taken:

1. The water basin should use a material with a small heat capacity, and the thickness of the material should be as thin as possible while ensuring the structural strength.

2. For the depth of the salt water layer, in view of reducing the thermal inertia, the shallower the water layer, the better. However, after the shallow water layer evaporates, the salt water concentration increases, and a reflective salt layer is formed on the water surface, which enhances the reflection of the incident large sunlight, so the efficiency decreases. To this end, a heat-absorbing partition can be installed in the middle of the water layer to absorb solar radiation and increase the temperature of the upper layer. The baffle plays a role in suppressing the convection of the salt water, making the temperature of the lower seawater lower and the total concentration of the salt water not increasing much, which improves the performance of the still. ^[2]