Abstract
An experimental investigation is conducted on crystal growth formation of R134a with additives, as phase change materials (PCMs), for cooling applications. The experimental investigation focuses on the crystal growth time and the characteristics of the formed PCMs. The formation of refrigerant clathrates at different operating conditions is investigated due to their potential use in active and passive cooling applications in electronic and residential cooling. The PCMs are made using R134a clathrate and distilled water with different refrigerant proportions and five different additives. The additives are used to improve the clathrate formation time and the crystal growth propagation under direct contact heat transfer mode. PCMs are formed in glass tubes and their crystal growth of freezing onset and crystal growth formation time is recorded at different operating temperatures. Refrigerant R134a percentages of 25%, 30%, 35%, and 40% are used to form clathrate. For the additives, ethanol, sodium chloride, magnesium nitrate hexahydrate, copper, and aluminum are used. PCMs are formed using controllable constant temperature water bath. The low crystal growth formation time showed that the PCM requires low energy input to change its phase, whereas more time shows PCM takes more energy to transform. A comparative study is conducted to compare the crystal growth formation time for different PCMs. R134a refrigerant clathrate without any additive is used as the base PCM. The results showed that metal additives reduced the crystal growth formation time, ethanol and sodium chloride increased the crystal growth formation time. Magnesium nitrate hexahydrate maintains it the same as that of the base PCM. It is also found that the freezing time depended not only on the thermal properties of the used additives but also on their ability to mix homogeneously in the refrigerant clathrate. Furthermore, some additives are considered to be very useful in enhancing the crystal growth formation of the clathrate with a stabilized crystalline structure. PCM with high latent heats over narrow temperature ranges are desirable as they offer high energy density at uniform temperatures applicable for cooling applications.
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