Osmotic concentration of salt solutions in a countercurrent multiplier system

Analysing the principles of performance of the human kidney, in about 1940, Kuhn and co-workers established the theoretical and physical model of concentrating solutions without the use of substantial differences of pressure (the so-called loop of Henle). p]Continuing this idea, a system of double channel asymmetrical capillaries made of cellulose 2$\text{1}\text{2}$ acetate was constructed and sodium and potassium chloride solutions were concentrated. The degree of concentration increased for higher feed concentrations. In experiments with one metre loop longitudinal apparatus 20 gl^-1 NaCl feed solution, the final concentration was 25 gl^-1 NaCl. To obtain 1 m³day concentrated solution with 10% recovery, about 1m² of membrane area was required.