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.
The Great Hungarian Plain (GHP) served as a geographic funnel for population mobility throughout prehistory. Genomic and isotopic research demonstrates non-linear genetic turnover and technological shifts between the Copper and Iron Ages of the GHP, which influenced the dietary strategies of numerous cultures that intermixed and overlapped through time. Given the complexities of these prehistoric cultural and demographic processes, this study aims to identify and elucidate diachronic and culture-specific dietary signatures. We report on stable carbon and nitrogen isotope ratios from 74 individuals from nineteen sites in the GHP dating to a ~ 3000-year time span between the Early Bronze and Early Iron Ages. The samples broadly indicate a terrestrial C3 diet with nuanced differences amongst populations and through time, suggesting exogenous influences that manifested in subsistence strategies. Slightly elevated δ15N values for Bronze Age samples imply higher reliance on protein than in the Iron Age. Interestingly, the Füzesabony have carbon values typical of C4 vegetation indicating millet consumption, or that of a grain with comparable δ13C ratios, which corroborates evidence from outside the GHP for its early cultivation during the Middle Bronze Age. Finally, our results also suggest locally diverse subsistence economies for GHP Scythians.
The Great Hungarian Plain (GHP) served as a geographic funnel for population mobility throughout prehistory. Genomic and isotopic research demonstrates non-linear genetic turnover and technological shifts between the Copper and Iron Ages of the GHP, which influenced the dietary strategies of numerous cultures that intermixed and overlapped through time. Given the complexities of these prehistoric cultural and demographic processes, this study aims to improve our understanding of diachronic and culture-specific dietary signatures. Here we report on stable carbon and nitrogen isotope values from 75 individuals from twenty sites in the GHP dating to a ~ 3000-year time span between the Early Bronze and Early Iron Ages. The samples broadly indicate a terrestrial C3 diet with nuanced differences amongst cultures, suggesting exogenous influences that manifested in subsistence strategies. Compared to the Iron Age, the Bronze Age samples have slightly elevated δ15N values implying higher reliance on protein. Interestingly, carbon values typical of C4 vegetation indicate the consumption of millet, or a grain with comparable δ13C values during the Middle Bronze Age. Overall, our results suggest a gradual transition in dietary patterns from the Early Bronze to Early Iron Age, demonstrating a relationship between subsistence and time periods, congruent with the archaeological record.
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