To reduce energy consumption and increase energy efficiency in the building sector, thermal energy storage with phase change materials (PCMs) is used. The knowledge of the thermophysical properties and the characteristics of PCMs (like their enthalpy changes and the distribution of stored energy over a specified temperature range) is essential for proper selection of the PCM and optimal design of the latent thermal energy store (LHTES). This paper presents experimental tests of the thermophysical properties of three medium-temperature PCMs: OM65, OM55, RT55, which can be used in domestic hot water installations and heating systems. Self-made test chambers with temperature control using Peltier cells were used to perform measurements according to the T-history method. In this way the temperature range of the phase transition, latent heat, specific heat capacity, enthalpy and the distributions of stored energy of the three PCMs were determined. The paper also presents measurements of the thermal conductivity of these PCMs in liquid and solid state using a self-made pipe Poensgen apparatus. The presented experimental tests results are in good agreement with the manufacturers’ data and the results of other researchers obtained with the use of specialized instruments. The presented research results are intended to help designers in the selection of the right PCM for the future LHTES co-working with renewable energy systems, waste heat recovery systems and building heating systems.
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IntroductionDistribution of power in power networks is performed with the use of overhead power lines as well as underground power cables. The investment cost of the underground power cable distribution systems is higher compared to the use of overhead lines but gives higher reliability of supply, especially reflected in improved SAIDI and SAIFI indicators [1,19,24].Power cables are usually buried in the ground, but in many cases, their ending sections are placed in air, to be connected with conductors of overhead lines, as it is presented in Fig. 1. Depending on the height of the pole, length of the power cables in air can be from a few to several meters. Given that the cable section in the air is connected in series with a section buried in the ground, the ampacity of the whole power cable line depends on the section for which thermal condition for heat transfer from the cables is the worst. The worst thermal condition is expected for the section in air, during sunny weather and without any wind.The problem of power cables heating and calculation of their ampacity are the subject of many papers and standards, especially [12-
The paper presents the results of the experimental and numerical analysis of a six-hole orifice flow meter. The experiments were performed on humid air in a 100 mm diameter duct. The aim of this research was to investigate the mass flow and pressure drop dependency in an orifice of a predetermined shape and to compare the results obtained with computational formulas recommended in the ISO 5167-2 standard for a single-hole orifice flow meter. The experiments and calculations were performed on several multi-hole orifice geometries with different contraction coefficient in a wide range of Reynolds numbers. The pressure was probed immediately upstream and downstream of the orifice. The flow coefficient determined for the six-hole orifice flow meter investigated was compared with the flow coefficient of conventional single-hole orifice with the same contraction coefficient. The results from computational formulas for single-hole orifice from ISO 5167 are also included in the paper. During some experiments, an obstacle has been introduced in the duct at variable distance upstream from the orifice. The effect of the thus generated velocity field disturbance on the measured pressure drop was then investigated. Numerical simulation of the flow with the presence of the obstacle was also performed and compared with experimental data.
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