This site will look much better in a browser that supports web standards. We strongly recommend you upgrade your browser.

Image of an area suffering from salination problems. Image of Shakespeare quote

Notes on Refrigeration and Power Requirements

A number of distillation systems have been proposed. Most use high temperature evaporation combined with refrigerated condensation and conservation of some of the heat of condensation to assist with evaporation. This seems eminently rational but is difficult to apply on a large scale, especially if renewable energy sources are favoured. It is this consideration which leads to the MAXWATER concept, a feature of which is that the large surface area required for the collection of solar and wind energy is provided by simply arranging distillation to occur during transport of the water to areas of need.

A difficulty frequently pointed out is that a great deal of energy is needed to move the water. This difficulty is increased by the fact that seawater tends to be at sea level whereas areas in need of pure water are generally above sea level. Mention has been made of the use of tidal flow where available and also the lower density of wet air, which can reduce the energy required to distribute distilled water. Much power will be needed however. For most of the arrangements described, seawater will need to be pumped up about 10m/Km or more.

The best energy source for this would seem to be either of two kinds of wind energy collection. Either wind could be collected by large wind farms and provided as electricity using systems already available, or the wind could be collected by small wind turbines such as the Darrieus type, distributed along the length of the system. These could operate pumps directly, without the complication and loss of efficiency associated with conversion to electricity and then back to mechanical power. It is important to recognise that the variable output of wind power systems is of no concern here. Calm conditions never last long enough to cause any difficulties when the requirement is a constant output per year rather than per hour.

As to refrigeration, a glance at Graph 1 shows that far more water can be obtained in allowing temperature to fall from, say 75C to 25C(0.22 l / m3 ) than in refrigerating the vapour say from 25C to 0C (0.02 l / m3 ). A more significant advantage to be gained by the addition of a refrigeration step may be in minimising the rise in temperature which occurs on condenser walls due to the liberation of the heat of condensation. Refrigeration would appear to be simple to incorporate in systems of this kind. If my calculation is correct, a pressure increase from 100 kPa to only 130 kPa is adequate if the compressed vapour is then allowed to cool in a thin walled duct before escaping through a restriction into the condensing chamber.

A very small wind turbine with an output of 500 W should be sufficient and these could be installed every 100m or 200m, again driving compressor fans directly, without the need for electric generators.