Optical properties of four types paraffin

As a typical phase change material (PCM), paraffin has widely used in solar energy. Therefore, researching optical properties of paraffin is of great importance in solar energy applications. In the present work, a double-thickness transmission method for single-layer liquid medium is used for measuring the optical constants of paraffin with different melting point (9#, 18#, 28#and 32#) in the wavelength range from 190 nm to 900 nm. Furthermore, the effect of optical path (10–50 mm) and experimental temperature (45–65 ℃) are also considered. As the results, the wavelength between 400 nm and 800 nm is high transmittance region of samples, however, the transmittance begins decline in part of infrared (800–900 nm). The transmittance decreases with the increase of optical path but the influence of measured temperature is slightly. The refractive index n and absorption index κ of samples are 1.15–1.43 and 1.1 × 10−7-3.3 × 10−6, respectively. In addition, as a storage material paraffin has weakest capacity of solar energy absorbed, the highest solar weighted absorption fraction Am only 8.36% by 18# paraffin, thus the absorption of paraffin must be improved.