Abstract
The article presents the results of preliminary research aimed at determining the possibility of using microencapsulated phase change material (mPCM) slurries as a working fluid in installations with a flat liquid solar collector. In the tests, the following were used as the working fluid: water (reference liquid) and 10% wt. and 20% wt. of an aqueous solution of the product under the trade name MICRONAL® 5428 X. As the product contained 43% mPCM, the mass fraction of mPCM in the working liquid was 4.3% and 8.6%, respectively. The research was carried out in laboratory conditions in the range of irradiance I = 250–950 W/m2. Each of the three working fluids flowed through the collector in the amount of 20 kg/h, 40 kg/h, and 80 kg/h. The working fluid was supplied to the collector with a constant temperature Tin = 20 ± 0.5 °C. It was found that the temperature of the working fluid at the collector outlet increases with the increase in the radiation intensity, but the temperature achieved depended on the type of working fluid. The greater the share of mPCM in the working liquid, the lower the temperature of the liquid leaving the solar collector. It was found that the type of working fluid does not influence the achieved thermal power of the collector. The negative influence of mPCM on the operation of the solar collector was not noticed; the positive aspect of using mPCM in the solar installation should be emphasized—the reduced temperature of the medium allows the reduction in heat losses to the environment from the installation, especially in a low-temperature environment.
Highlights
The interest in acquiring and storing solar energy was started by the energy crisis that took place in the 1940s
The analyses showed that the use of microencapsulated phase change material (mPCM) in the base fluid resulted in an approximate 7% increase in the annual efficiency of the collector regardless of the orientation and the tilt angle
In the tests, distilled and demineralized water and two aqueous mPCM slurries were used as the working liquid
Summary
The interest in acquiring and storing solar energy was started by the energy crisis that took place in the 1940s. Hottel’s pioneering works from 1942 constitute the basis for the construction of the most common devices for obtaining solar energy—flat, liquid solar collectors [1]. Simultaneous work has been carried out to improve the thermal efficiency of solar collectors and to find new solutions to store large amounts of thermal energy. The current solutions of liquid solar collectors are based on the use of water as the basic working medium. The theoretical working range of the collector is between 0 ◦ C and 100 ◦ C. This range can be extended by using water propylene glycol (T = −25–200 ◦ C)
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