Thermal conductivity and heat capacity measurements of paraffin embedded in a porous matrix

Paraffins such as octadecane are known as phase change materials (PCM). With their high enthalpy change of the phase transition they can store low grade thermal energy. Because of the ability to store more heat per unit mass at nearly constant temperature than sensible heat media, PCMs are advantageous in many respects. It is often necessary to improve the relative poor thermal conductivity of the PCM to achieve better heat-exchange rates in technical applications. To accomplish this, the PCMs are embedded into porous matrices. The porous material also provides a structure to support the PCM both in the liquid and solid state. A good knowledge of the thermal properties of the PCM is essential to predict the behavior of a latent heat thermal energy storage system. Therefore thermal conductivity and heat capacity measurements on several porous materials filled with paraffins are presented in this paper. The matrix materials are building materials such as clay brick and sand lime brick on the one hand and a highly heat conducting open porous aluminum foam with a mass density of about 1.3 g(.)cm(-3) on the other hand. A heat-flow-meter apparatus and a laser flash thermal diffusivity system combined with the measurement of the mass density and the specific heat capacity were used for the determination of the thermal conductivity.