PHYSICOCHEMICAL PROBLEMS CONNECTED WITH PHASE CHANGE MATERIALS

The physicochemical problems and some results of the investigation of latent heat storage materials, first of all salt hydrates such as sodium sulphate decahydrate, calcium chloride hexahydrate disodium hydrogen phosphate dodecahydrate and sodium acetate trihydrate are briefly reviewed

THERMODYNAMIC BEHAVIOUR OF A HEATING SYSTEM BASED ON TWO PHASE-CHANGE MATERIALS

The combined application of phase-change materials having low and high phase change temperature makes possible to increase the heating performance of the built-in latent energystorage heatings and at the same time to conserve their self-stability. Materials suitable for this purpose are: calcium chloride-hexahydrate and stearic acid. These materials are placed in elements made from tubes. Segregation was inhibited by the special design of electric heating plates situated in the elements. With an alternating disposition of various elements the fin effect can be well exploited. In the article data are presented to illustrate operational strategy and performance of the systems

DOMESTIC HOT WATER PRE-HEATER UTILIZING SOLAR ENERGY

A two grade phase change material (PCM) based on CaCl2-water system has been investigated in a PCM stuffed copper tube-water heat exchanger. The heat output of the two grades has been measured in exhausting cycle. 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

Kétfokozatú hőtároló anyag termikus tulajdonságai fázisváltó anyag - víz hőcserélőben = Thermal properties of double grade heat storage material in PCM - water heat exchanger

A kutatás tárgya kálcium-klorid - víz alapú, kétfokozatú, szilárd - folyadék fázisátalakuláson alapuló hőtároló töltet viselkedésének vizsgálata volt hőtároló anyag - víz hőcserélőben. A kálcium-klorid különböző kristályhidrátjainak (CaCl2.6H2O és CaCl2.4H2O) fázisátalakulásakor felszabaduló illetve elnyelődő hő lehetőséget adott a hőtárolás hőmérséklet tartományának kiterjesztésére. A hőtároló rendszer hosszú idejű stabilitását fareszelék, mint vastagító anyag , illetve stroncium-hidroxid oktahidrát, mint gócképző adagolásával sikerült elérni. A hőátadási vizsgálatok során megállapítottuk, hogy néhány centiméteres szakaszon a hőátadási tényező minimumot mutat a hűtési idő függvényében. Hosszabb szakaszt figyenlembevéve (néhány méter) a hőátadási tényező közelítőleg állandósul a 115 +/- 25 W/m2K tartományban. A vizsgált hőcserélő rendszer alkalmasnak látszik, hogy az alacsony hőfok szinten tárolt napenergiát háztartási melegvíz ellátó rendszerekben előmelegítőként alkalmazzuk. | A two grade phase change material (PCM) based on CaCl2-water system has been investigated in a PCM?water heat exchanger. The crystallization of different hydrates of CaCl2 (CaCl2.6H2O és CaCl2.4H2O)extended the temperature range of heat storage and the storage stability was achieved by the application of wood chips as thickening agent and Sr(OH)2.8 H2O as seeding crystals. 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/m2K. 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

GREEN ELECTRICITY FROM WOOD BENEFITS AND LIMITS IN HUNGARY

Renewable resources provide approximately 3.6\% of Hungary´s energy consumption. Although 83\% comes from the utilization of biomass its level of utilization is relatively low compared to the available amounts. The accessibility of renewable sources is considerably limited in Hungary. The greatest opportunity for the progress in Hungary lies in the utilization of biomass (firewood and fuelplant). 1MW electrical output needs 20 km2 of a 100-year old forest (oa with continuous renewing afforestation. In this paper we observe whether that endangers the forestry of Hungary, which is only about 20\% of the total area. We also dicuss the possibility to increase our 3.6\% energy share in renewable energy based on forest. Minor plants based on woody chips and pellets with some MW output, might be well integrated into the rational lumbering. Large amounts of plant grown for energetic use can be realized in plant growing areas of the food industry that will be freed as a result of the EU accession

HEAT STORAGE BY TWO-GRADE PHASE CHANGE MATERIAL

A two-grade heat storage system (60 °C - 30° C and 30 °C - 20°C) based on calcium chloride hexahydrate and calcium chloride tetrahydrate was developed. The storage capacity changes during the cycles are given, and a possible use of a solar energy storage system for domestic hot water is discussed

Solar energy storage by a two grade phase change material

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/m2K. 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