Radiation-Temperature Dependence of Water and Aqueous Solution

The dependence of the thermal radiation power of fresh water and an aqueous solution of sodium chloride on temperature was experimentally studied. The measurements were carried out in the open air in the range of liquid temperatures of (7–70) °C and an ambient air temperature of about 0°C. To measure the thermal radiation power of the liquid surface, a setup with a set of highly sensitive chromel-copel thermocouples as an electromagnetic radiation receiver was used. An immersion thermometer was used to measure the liquid temperature. The dependences of the thermal radiation power of fresh water and a saline solution on the temperature of the liquids were measured. It was found that the thermal radiation power of an aqueous solution in the studied temperature range can have local minima. The spectral regions, in which the thermal radiation power of an aqueous solution can decrease with an increase in thermodynamic temperature, were determined. The temperature regions of possible minima of the thermal radiation power of water and a saline solution were found. Measurements have shown that the extreme points of thermal radiation power for fresh water and saline solution can be located at 29 °C for fresh water and at 41°C for salt water. It is suggested that the occurrence of local minima may be associated with the structural rearrangement of water clusters of the surface temperature film. A discrepancy between the experimental results and the theory is noted. The reason for this discrepancy is explained. Estimates are made of the ratios of the thicknesses of the surface temperature film and the skin layer for the maximum spectral density of the radiant exitance of liquids. It is shown that the magnitude of the thermal radiation power should be largely determined by the temperature of the surface film, which can differ significantly from the temperature in the volume. A comparison is made with the known results of studies of fresh water radiation emission in the microwave range.