A two grade phase change material (PCM) based on CaCl 2 -water system has been investigated in a PCM-water heat exchanger. The crystallization of different hydrates of CaCl 2 extended the temperature range of heat storage and the storage stability was achieved by the application of wood chips as thickening agent. A short section of the heat exchanger tube (a few cm) can be characterized by a maximum curve of heat transfer coefficient in function of cooling time. Longer sections (a few meter) showed nearly constant heat transfer coefficient in the range of 115 +/-25 W/m 2 K. The heat storage system is to be applied to store solar energy and the stored heat is used to preheat the water input of domestic hot water supply system. Keywords heat storage · phase change material · solar energy · heat transfer coefficient
AcknowledgementThe authors are indebted to the Hungarian Research Fund (OTKA T-037496) for financial support.
Gábor BajnóczyDepartment of Chemical Technology, BME, H-1111, Budapest, Budafoki ut 8., Hungary e-mail: gbajnoczy@mail.bme.hu
Edit Gagyi Pálffy László Szolnoki Ernő PrépostffyDepartment of Chemical Technology, BME, H-1111, Budapest, Budafoki ut 8., Hungary
IntroductionThe temporal difference of energy source and energy needs made necessary the development of storage systems. The abundant amount of solar energy, which is collected during the summer, could be stored in such a big storage unit that does not come up to engineering and economic requirements. Systems which equalize the temporal difference in one or two days, can be economic. In summer the energy of the heat transfer fluid arriving from the solar collector at relatively high temperature (70˚C-90˚C) can be stored in insulated hot-water container.Except in summer, especially in winter, the temperature of the heat transfer fluid coming from the collector is relatively low (35-60 o C). In this period of time which means nine months a year, one way of storage is to use solid-liquid phase change materials. In comparatively small volume the phase change materials have great storage capacity in small temperature interval. Storage systems using these heat accumulator materials can store the energy from the solar collector at lower temperature level, too in winter. The stored energy can be used for pre-heating the cold incoming water, so in the households the unit which is actually produces hot-water (gas or electric boiler) is made up by the unit storing solar energy. So the traditional system integrated with solar energy storage might moderate the cost of energy consumption.
Sodium azide is being applied not only in air bag inflators but also in organic syntheses producing azide ions containing process waste waters, mostly in alkaline aqueous solutions. The elimination of azide ions was attained in these process waste waters with hydrogenation under pressure with skeletal type nickel catalyst. The azide instantaneously reacts with the hydrogen content of the Raney-nickel. In sufficient amount it can even completely deactivate the catalyst.
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