Evaporation of liquids at low temperatures

Abstract

Ukrainian enterprises annually generate millions cubic meters of mineralized water, which is discharged into surface reservoirs, and millions cubic meters of highly concentrated solutions and suspensions, which are accumulated and stored in special sludge storages. This waste water causes irreparable damage to the environment. A new method for the evaporation of industrial concentrates by fibrous materials with capillary properties was proposed not so long ago. The use of such materials allows an effective, autonomous, cheap, and extremely simple system to be created for the evaporation for various liquids and concentrates. The research methodology was as follows. Two graduated cylinders of the same diameter were used in our research. One cylinder was filled with the liquid phase to a certain level and used to control evaporation from the surface of the aqueous medium. In the other, experimental cylinder, a vertical cotton strip was additionally placed (from 1 to 21 layers of fabric). The width of the strip was 5 cm. The length of the strip was 50 cm. The density of cotton was 100 g/m2. The research method was to determine the height of liquid phase capillary rise along the strip of fabric and to evaluate reduction in the volume of liquid that evaporates in both cylinders at set temperatures. It was found that in the absence of wind and the distance between the vertically placed strips of 7–15 mm were sufficient to ensure the maximum evaporation intensity. Our long-term experiments in natural conditions confirmed the high efficiency of the proposed method. At an average daily air temperature of 2.3 °C, there was a significant evaporation from the surface of the fabric during the day. In this case, evaporation from the water surface was not observed. It should be noted that the intensity of evaporation under natural conditions depends on a significant number of factors (temperature, wind speed, luminosity, humidity, etc.), so it is difficult to detect a direct relationship between some of them. With increase only in the liquid phase temperature, the evaporation efficiency decreased. At a temperature of 20 °C, the laboratory installation (15 layers of cotton strip) increased the evaporation intensity by more than 2 times, at 46 °C by more than 5 times, at 57 °C by almost 3 times, but at 75 °C only by about 67 %. It is obvious that heating of the liquid phase alone less influences the evaporation process from the surface of the fabric strip, which was cooled rapidly in the atmosphere at a much lower temperature. Therefore, to increase the evaporation intensity, it is necessary to increase temperature for all components of the liquid–fabric system. A fabric with suitable properties, stretched between two metal racks and immersed into the liquid phase with the lower end, can be used as a simple evaporator. Our research has shown that the use of materials with capillary properties in the treatment of liquid solutions allows simple, cheap, and efficient devices to be created for evaporating water and converting liquid waste into a solid phase.