Rheological Properties of Heat Transfer Liquids for Solar Thermal Systems

Abstract

This article discusses the rheological properties of heat transfer fluids used in all year round solar systems. Four commercially known media were measured. Two of them were glycols based media and two of them alternative heat transfer fluids based on glycerol. Parameters of viscosity and density were measured in a wide range of temperature. Measured dependencies were mathematically approximated by Vogel-Fulcher-Tammanovou equation that very accurately describes their shape. The temperature coefficient of volumetric expansion β is another parameter of heat-transfer fluids described in this article. β plays a very important role in the construction of the solar system. The last parameter determining the year round operation is the freezing point. Freezing point was measured by the cryoscopic methods.