As part of modernizing the office building of the district heating operator in Ostro & lstrok;& eogon;ka, Poland, a new hybrid substation was built. The system is designed to both heat and cool the office building and is powered by the district heating network. It incorporates an adsorption chiller, three phase change material storages, a photovoltaic system and a smart management system. This paper focuses on the design and experimental determination of the exact characteristics of the phase change material storage, which is intended to support the chiller on the power supply side. The PCM used is RT62HC, with a peak phase change temperature of 63 degrees C and narrow phase transition characteristics. The design, presented briefly, highlights the experimental setup, the characterization of the phase-change material, and the thermal-hydraulic properties of the finned-tube heat exchanger. The laboratory tests included both the charging and discharging processes of the storage. During the tests, a ramp-type thermal forcing was used at rates of 0.5 K/h, 1 K/h, 2 K/h, and 3 K/h. Based on the tests, the dynamic characteristics of the storage were determined in the form of an effective enthalpy function. The results of this analysis were also used to determine the storage density of the system, which was found to be 49 kWh/m3 in the temperature range of 57 degrees C-67 degrees C. In this temperature range, the PCM storage has up to 4.5 times greater thermal capacity than a storage with water.

Non-invasive real-time measurements of phase content in the reservoir fluid are highly advantageous in the oil and gas industry and remain a current research topic. The paper presents an innovative, self-designed multi-electrode capacitance meter intended for detecting multiphase flow patterns in a low-permittivity medium, such as the reservoir fluid. The ca-pacitance sensor is built with delta-sigma charge modulators capacitance-to-digital converters. Machine learning is applied to convert the capacitance measurements into a tomographic image of the flow pattern. At present, the meter is built with eight electrodes. It is shown that the measurements are repeatable and have a good signal-to-noise ratio. The implemented neural network is capable of correctly reconstructing the tomographic images for a test tube filled with reservoir fluid and placed in various locations inside the test section.

The paper draws attention to the problems of evaluating stored heat capacity in a latent heat thermal energy storage (LHTES) that operates with unsteady inlet temperature conditions. These problems are studied for custom-built LHTES designed to be charged/discharged at varying heat transfer rates in a chilled water system. The LHTES incorporates a typical fin and tube heat exchanger and commercially available ATP 20 phase change material (PCM). For the designed storage construction, the ratio of heat transfer area to PCM volume is 354 m 2 / m 3 , and the ratio of PCM volume to the total volume (compactness factor) is 0.87. The LHTES thermal characteristics were investigated on a test stand using inlet temperature inputs changing linearly at 1, 2 or 3 K/h. During each test, a complete phase transition in the PCM was ensured. Based on LHTES inlet and outlet temperature profiles, enthalpy distributions versus outlet temperature were evaluated. The experiments proved that these distributions are not a material property as they depend on the geometric characteristics of the LHTES and charging/discharging rates. However, they can describe the thermal behaviour of the PCM filling the LHTES and include the influence of a non -uniform temperature distribution inside the LHTES on the PCM hysteresis and temperature range of the complete melting/solidification. These effects can be modelled by the proposed function of effective enthalpy. The effective enthalpy allows for relatively simple monitoring of phase transition progression in the LHTES based solely on the parameters measurable outside the storage.

The low thermal conductivity of organic phase change materials (PCMs) limits the heat transfer rate and increases the charging/discharging time of the latent heat thermal energy storage (LHTES). Among the efforts to improve the thermal response of LHTES is to directly increase the thermal conductivity of PCMs by adding highly conductive nanoparticles. The paper presents experimental investigation on improving the thermal conductivity of low-temperature PCM sold as RT22 HC, which can be used in passive or active cooling and heating systems in buildings. For this purpose, admixtures of graphene (GNP) and titanium dioxide (TiO 2 ) nanoparticles at different mass fractions (in range of 1-5 %) were tested. The results of the research for the nano-enhanced PCMs (NEPCMs) indicate that the addition of GNP or TiO 2 nanoparticles increases, respectively, the thermal conductivity by 0.35-0.51 W/m center dot K or 0.23-0.31 W/m center dot K in the solid state, and by 0.11-0.18 W/m center dot K or 0.10-0.12 W/ m center dot K in liquid. The highest thermal conductivity value of 0.67 W/m center dot K was measured in the solid state for RT22 HC with admixture of 5 % GNP and with SDBS (surfactant). The addition of GNP with SDBS reduces the heat capacity of the base PCM (RT22 HC) by 6-27 %, and the addition of TiO 2 nanoparticles with SDBS by 15-25 %, depending on the mass fraction of the nanoadditives. The novelty of this study are tests of the NEPCM thermal conductivity using the pipe Poensgen apparatus method for liquid and solid states and determination of the optimal mass fraction of nanoadditives in the NEPCM in terms of thermal conductivity and heat storage capacity characteristics. Application of this research results may contribute to a better thermal response of LHTES and reduce the use of fossil fuels in building heating and cooling systems.

After certain time of operation, the cross-section of cooling channels in injection molds may decrease due to fouling, i.e. the formation and growth of a layer of sediment on the walls of the channels. This phenomenon can decrease heat transfer or ultimately completely block the flow of coolant in the channel. The build-up of the sediment layer increases the temperature of the mold, which may consequently reduce the quality of the plastic products. In the paper, the pressure drop in a typical cooling channel of an injection mold is investigated, as well as the effect of the sediment layer on the coolant flow in an example channel with a diameter of 10 mm. A novelty is the developed analytical model that allows determining the pressure drop in the case when two perpendicular channels do not intersect centrally due to manufacturing inaccuracies that often happen when drilling long channels in hard materials. The proposed hydraulic model allows for calculation of the coolant pressure drop in real injection molds and can be an alternative to time-consuming CFD simulations. The presented results of measurements and the hydraulic model calculations show that the thickness of the sediment layer in the tested channel of the actual injection mold can be up to 1.7 mm. The hydraulic model proposed in this work allows for the estimation of the thickness of the sediment layer and the identification of places of local increase in the coolant velocity, where self-cleaning of the channels in injection molds may take place.

The construction sector accounts for 40% of total energy consumption and is increasing. To reduce energy consumption of heating and cooling systems during peak demand while maintaining thermal comfort, phase change materials (PCMs) are used more and more. Appropriate application of PCM and design of latent heat thermal energy storage (LHTES) requires in practice an in-depth knowledge of the thermal properties of PCMs. The aim of the paper is to present the results of experimental determination of the properties of two commer-cially available, organic PCMs - RT22HC and RT28 HC, using T-history method and pipe Poensgen apparatus. Results of experimental tests showed that these low-temperature PCMs could effectivity store heat and cold in a narrow temperature range of approx. 7 K for RT22 HC and about 3-4 K for RT28 HC. The average measured latent heat values are 190 kJ/kg for RT22 HC and 244 kJ/kg for RT28 HC. The distribution of energy stored in RT22 HC shows the peak in the temperature range of 21-23 degrees C (with 20-50 kJ/kgK for heating, 22-71 kJ/kgK for cooling). For RT28 HC this range is 27-28 degrees C (75-130 kJ/kgK for heating, 40-125 kJ/kgK for cooling). The diagrams of enthalpy present small hysteresis (0.5-1 K) in these materials. Thermal conductivity measurements using pipe Poensgen apparatus demonstrated that these PCMs have a low conductivity of 0.12-0.33 W/mK. The presented experimental research is intended to provide the data necessary for the correct design of LHTES with RT22 HC or RT28 HC intended to use in heating and cooling systems and to maintain thermal comfort in buildings.

The paper presents a theoretical analysis of thermal energy storage filled with phase change material (PCM) that is aimed at optimization of an adsorption chiller performance in an air-conditioning system.The equations describing a lumped parameter model were used to analyze internal heat transfer in the cooling installation.Those equations result from the energy balances of the chiller, PCM thermal storage unit and heat load.The influence of the control of the heat transfer fluid flow rate and heat capacity of the system components on the whole system operation was investigated.The model was used to validate the selection of Rubitherm RT62HC as a PCM for thermal storage.It also allowed us to assess the temperature levels that are likely to appear during the operation of the system before it will be constructed.

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.

The paper presents an analysis of heat and mass transfer in the mixing chamber (MC) of steam-water injectors. It is aimed at determination of two-phase flow parameters at the MC outlet. The steam condensation in MC is described by OD two-fluid model that assumes mechanical and thermodynamic nonequilibrium between vapor and liquid phases. To close the model equations, empirical correlation for condensate mass fraction at the MC outlet is proposed. It is based on pressure and temperature measurements on MC walls in four laboratory-scale injectors. The injectors differed primarily by motive steam expansion ratio that resulted in a change of steam pressure, temperature and velocity at the MC inlet. The proposed correlation predicts the condensate mass fraction with accuracy of 20% for the investigated injectors. Average heat transfer coefficient (HTC) in MC of the four injectors is also calculated using experimental data and then compared with the predictions of the proposed model. It is found that HTC values are in the range of 200-700 kW/m 2 K, depending predominantly on vapor-liquid temperature difference at the MC inlet. (C) 2020 Elsevier Ltd. All rights reserved.

This paper concerns analytical considerations on a complex phenomenon which is diffusive-inertial droplet separation from the twophase vapour-liquid flow which occurs in many devices in the power industry (e.g.heat pumps, steam turbines, organic Rankine cycles, etc.).The new mathematical model is mostly devoted to the analysis of the mechanisms of diffusion and inertia influencing the distance at which a droplet separates from the two-phase flow and falls on a channel wall.The analytical model was validated based on experimental data.The results obtained through the analytical computations stay in a satisfactory agreement with available literature data.

Due to dependence of energy generation from renewable sources on weather conditions, such systems require cooperation with energy storage facilities. Thermal energy storage with phase change materials (PCM) is often used in systems working with solar collectors, photovoltaic panels, heat pumps, air conditioning systems, waste heat recovery systems and other. However, the appropriate application of PCMs requires a good knowledge of the thermo-physical properties of the materials and practical knowledge of the actual stored energy which depends on the PCM heating/cooling rate. The paper presents measurements of the latent heat for PCMs that are used in low-temperature thermal energy storage. The measurement method used was differential scanning calorimetry (DSC). In the experiments, two commercially available materials RT15 and RT22 HC were investigated. The tests were performed at different heating/cooling rates ranging from 0.5 to 10 K/min for samples of a mass 6-11 mg. On the basis of the test results and the proposed calculation method, the total values of energy stored during the phase transition, the temperature of phase change and the heat capacity distributions were determined as a function of temperature. Attention has been paid to the effect of temperature change rate on the measured latent heat capacity that is an important issue in practical applications of PCM. The heat capacity (energy stored) versus temperature distributions for RT15 and RT22 HC materials resulting from the tests can be used in design of latent heat thermal energy storage (LHTES) systems co-working with renewable energy systems. The presented methodology can also be used for investigation of other PCMs. (c) 2021 Elsevier Ltd. All rights reserved.

Unlike the typical steam-water injector, the device investigated here operates with relatively low pressure motive steam which is expanded in convergent nozzle to critical (sonic) velocity only. Experimental test were conducted with motive steam pressure in the range of 62-130 kPa (abs), superheated up to 30 K. Distributions of pressure and temperature along the injector's mixing chamber and diffuser were recorded for selected inlet steam and water flow rates and outlet backpressures. The pressure was measured not only along the flow channel walls but also at the centerline near the steam nozzle outlet plane. Maximum backpressure for which the injector works stably was also determined for various inlet flow parameters. In theoretical part of the paper, control volume model was applied to predict the flow parameters in key cross-sections of the injector working with maximum discharge pressure. The proposed model results were compared with the measurements and good prediction of the outlet pressure and temperature was achieved. (C) 2019 Elsevier Ltd. All rights reserved.

In recent years, the use of storages filled with phase-change material (PCM) is increasingly considered. Such design is characterized by a higher density of thermal energy accumulation in comparison with water storages. However, the optimal use of the PCM storages requires a recognition of its dynamic characteristics during the loading and unloading process. This paper presents research aimed at understanding and dynamic description of the heat transfer process in a shell-and-tube thermal energy storage. The experimental test stand and the measurement and control system are described. The investigated storage had a form of a cylindrical tank of 40 dm3 volume in which a coil made of pipes with an external diameter of 3.35 mm was immersed in the PCM. The total heat transfer area was 9.4 m2. A lumped parameter model was used to describe mathematically the storage thermal dynamics. The PCM used was commercially available RT15 material with the heat capacity of 150 kJ/kg in the temperature range of 10–17°C. In the investigations, aperiodic (ramp) temperature inputs were used. The storage tests were carried out for low (12 h) and high (6 h) speeds of charging and discharging. The amplitude of the input signal and the liquid temperature at the storage inlet were set to include the phase transition interval of the PCM used. The obtained test results allowed to determine the enthalpy as a function of temperature for the whole storage. The experimental results were also used to validate 0D mathematical model of the heat storage.

The aim of the paper is to clarify the way by which pathogens in human body may be detected and destroyed during a flow of high frequency pulsating direct current (PDC), positively polarized, under the condition of electric resonance. The method was discovered by Dr. H. Clark. However she did not clarify the physical basis of the phenomenon. The authors consider the resonant method using principles of thermodynamics and electric current laws. The phenomena of inductance and capacitance are discussed. A measure of total resistance to PDC is represented by electric impedance (Z), which depends on the Ohm resistance (R), specific inductance (L), and capacitance (C). The analytical formula for resonance frequency f(r) as a function of conductance L and capacitance C is found. At the resonance the impedance goes to minimum and therefore the current intensity increases rapidly to its maximum value. Due to Joule-Lenz law the heat generation is proportional to the squared electric current intensity. This is manifested by sharp increase of a pathogen temperature. The temperature increase destroys pathogens. The second destructive action for pathogen comes from polarization forces which prevent a pathogen entrance to a body cell. The third positive thermodynamic aspect, with respect to pathogen destruction, comes from oscillatory heat generation which induces the oscillatory movements, local pressure fluctuation and leads to the mechanical destruction. It is worth to know that the method discussed above is valid for specific pathogen either alive or dead. It may be also used for detection of toxin, that is, inanimate matter. This was confirmed by Dr. Clark research.

The paper presents results of experimental investigation of microchannel boiling flow which was controlled by dielectrophoretic (DEP) restrictor. The DEP restrictor was connected to the microchannel liquid supply tube. Operation of DEP restrictor influenced the flow rate at the microchannel inlet. Resulting changes in flow structures and vapour content along the microchannel were observed and analysed with a high-speed video camera. Video recordings were synchronised with measurements of differential pressure between the channel inlet and outlet. It was found that it is possible to change average void fraction in the microchannel by switching on and off the voltage applied to the restrictor electrodes. However, to achieve significant variation of the void fraction, applied voltage should be of the order of 2000 Vpp. The voltage switching also generates oscillations of the differential pressure. The amplitude of these oscillations is proportional to the voltage magnitude, reaching 35 Pa for 2400 Vpp.

The paper presents theoretical analysis of flow dynamics in a heated microchannel in which flow rate may be controlled by dielectrophoretic (DEP) forces. Proposed model equations were derived in terms of lumped parameters characterising the system comprising of DEP controller and the microchannel. In result, an equation for liquid height of rise in the controller was obtained from momentum balances in the two elements of the considered system. In the model, the boiling process in the heated section of microchannel is taken into account through a pressure drop, which is a function of flow rate and uniform heat flux. Presented calculation results show that the DEP forces influence mainly the flow rate in the microchannel. In this way, by proper modulation of voltage applied to the DEP controller, it is possible to lower the frequency of Ledinegg instabilities.

A simple method of pressure drop calculation for two-phase flows of different fluids during convective boiling in channels is presented. It is based on experimental data of pressure drop multiplier R and void fraction φ obtained by Martinelli and Nelson for boiling of water in vertical tubes. The data cover the whole two-phase domain from ambient to critical pressure. Unfortunately, they have been presented in graphical forms. The first step in the procedure proposed in the paper was a transformation of the graphical data into analytical formulas which contain such dimensionless quantities as steam quality x, Martinelli parameter X, multiplier Φl2 and dimensionless coefficients D, m, E and k. In the second step, simple analytical formulas were determined to express the dimensionless coefficients as a function of physical property parameter K. In this way two simple analytical expressions for the multiplier R and void fraction φ were obtained. They are in analytical dimensionless form so they may be used directly for different fluids, not only for water. This is the main advantage of the proposed method.

The theoretical basis for the indirect measurement approach of mean heat transfer coefficient for the packed bed based on the modified single blow technique was presented and discussed in the paper. The methodology of this measurement approach dedicated to the matrix of the rotating regenerative gas heater was discussed in detail. The testing stand consisted of a dedicated experimental tunnel with auxiliary equipment and a measurement system are presented. Selected experimental results are presented and discussed for selected types of matrices of regenerative air preheaters for the wide range of Reynolds number of gas. The agreement between the theoretically predicted and measured temperature profiles was demonstrated. The exemplary dimensionless relationships between Colburn heat transfer factor, Darcy flow resistance factor and Reynolds number were presented for the investigated matrices of the regenerative gas heater.

The paper presents the results of experimental investigation of supercritical two-phase flow in steam-water injector. In the region of condensation shock wave, flow structures were captured with highspeed video camera simultaneously with recordings of pressure and temperature distributions. Visualisation of condensation terminus showed formation and evolution of vapour clouds. Their disappearance was accompanied by pressure pulses, which were recorded on the channel wall. In addition, dynamics of flow instability caused by excessive backpressure at the injector outlet was examined. (C) 2015 Elsevier Ltd. All rights reserved.

Two-phase vapour–liquid injectors may be applied as a feeding pump device or as a condensing device in many applications. In these injectors vapour is a motive fluid which enthalpy is used to compress and heat a liquid – the secondary fluid. The model of the cycle operation of the ejection system equipped with two-phase vapour liquid injector as a feeding pump was proposed. Two-fluid model for the two-phase flow in such injector was proposed in the paper. The model equations were formulated for one-dimensional steady flow. The analysis of the operation if this cycle was presented for isobutane as the working fluid.