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This paper presents a comprehensive review of significant studies that are relevant to thermal energy storage technologies using phase change materials (PCMs). The review focuses on the techniques applied to enhance the performance of thermal storage systems and the methods used to analyse the heat transfer problems in PCMs. In addition, this paper reviews the published results and discussions on the heat transfer intensification methods including application of fins, filling materials, nano-fluids, nano-particles, microencapsulation and the thermal conductivity enhancement method. Furthermore, the experimental and mathematical methods to enhance the thermal conductivity of PCMs are summarised, and the methods used to determine the nanofluid dynamic viscosity in recent investigations are also listed and discussed. The focus of this review is to provide a solid basis for the identification of the optimal design for the various heat transfer applications using PCM. [ABSTRACT FROM AUTHOR]

This paper analyzes the state of the art in R & D on integration of phase change materials into building structures for their passive thermal control. Such perspective phase change materials as paraffins, fatty acids and their blends, as well as fatty acid esters, are considered for passive thermal control of buildings. Gypsum wallboards, concretes, porous and other materials used for building structures forming are discussed. Various technologies of the PCM integration into building structures are described. The characteristics of three laboratory small models of buildings, which were subject of investigations, are presented in this paper. The results of comparative tests on fifteen full size buildings containing elements with PCMs are summarized. Experiments conducted by a number of researchers on passive solar buildings demonstrated that the application of phase change heat storage materials decreases the variation in the air temperature in the rooms; shifts the peak of energy consumption for heating and cooling of lightweight buildings by several hours and decreases energy consumption for maintaining the comfort temperature levels in buildings. Recommendations for further research activities in this field are proposed at the end of this review article. [ABSTRACT FROM AUTHOR]

Thermal energy storage is considered as one the most perspective technologies for increasing the efficiency of energy conversion processes and effective utilization of available sources of heat. Advantages and technical attractiveness of the thermal energy storing have resulted in continuously increasing numbers of research activities, especially in the last four decades. Among various applications of thermal energy storage, the heat or cold accumulation in the temperature range from −50 °C to 120 °C has a greater market potential and this can be carried out using a wide range of phase change latent heat materials. Among these materials the salt hydrates deserve a special attention and currently a large number of phase change compositions based on salt hydrates are produced commercially and available on the market. However, reliable data on thermophysical properties as well as their thermal stability over their lifetime is required to build effective storage systems. Currently this data is insufficient and is scattered across numerous sources that are often difficult to access for potential consumers. This paper summarises practically all available original experimental data on the phase change diagram of salt–water systems, melting temperatures, heat of fusion, specific heat, density, thermal conductivity, and thermal diffusivity in solid and liquid states and viscosity in the liquid state for 18 salt hydrates. The above information is provided for major market products on the basis of the salt hydrates for latent heat storage. The wholesale prices for pure salt, salt hydrates, and salt hydrate heat storage compositions are also additionally discussed. [ABSTRACT FROM AUTHOR]

An innovative small dynamic water desalination plant was developed and tested under laboratory conditions. The system is a combination of a heat pipe evacuated tube solar collector, conventional condenser and novel fluid piston converter. Saline water is boiled and turned into vapour in the manifold of the solar collector. A small fraction of the solar energy supplied to the plant is used to drive the fluid piston converter. Oscillations of the fluid piston periodically change the volume and pressure in the plant. For the duration of approximately half of the periodic cycle the pressure in the plant drops below the atmospheric level causing flash boiling of saline water in the manifold of the solar collector. Generated vapour is turned into fresh water in the condenser which is surrounded by a cooling jacket with saline water. The flash boiling effect improves the fresh water production capacity of the plant. Additionally, the fluid piston converter drives a pump which provides lifting of saline water from a well and pumps this through the cooling jacket of the condenser to a saline water storage tank. This tank replenishes saline water in the manifold of the solar collector. Experimental investigations demonstrated the saline water self-circulation capability of the plant and increase in the fresh water production compared to the static mode of operation. Experimental data was also used to calibrate the mathematical model of the plant. Comparison of theoretical and experimental information demonstrates that the model accurately predicts the performance of the plant. The proposed novel system with greater fresh water production capacity has a simple design and is easy to manufacture using low cost materials and therefore can be mass deployed for small scale saline water pumping and desalination across different regions with the relatively high solar radiation and shortage in the drinking water supply. [ABSTRACT FROM AUTHOR]

Abstract: The performance of a spark ignition internal combustion engine (SI ICE) fueled with biomass gas (woodgas) is evaluated using an analytical mathematical model. For the evaluation, the model was based on the fuel-air thermodynamic cycle for spark ignition engines, taking into account the composition of woodgas used as fuel, the thermodynamic properties of the fuel supplied, the cylinder geometric characteristics, the engine operational conditions, the effects of heat losses in the cycle through the walls of the cylinders and due to the loss as gas “blow-by”, the influence of dissociation processes during the combustion and the residual gases remaining in the cylinders at the beginning of the compression stroke. The model can predict of the internal temperatures profiles, heat flow, as well as the work and pressure in relation to crank angle. It was used also to evaluate the influence of the rotation speed, the air ratio and the ignition timing on the engine indicated power. It was found that when feeding the engine with woodgas, a power output between 59 and 65% can be obtained, in comparison it's powered by gasoline. Additionally, the analysis shown the engine performance when feeding it with pure methane (100%), to give an idea about what would happen if the same engine is fueled with natural gas under the same conditions (the main component of natural gas is methane and the presence of this in composition generally varies between 70 and 95%). [Copyright &y& Elsevier]

Abstract: Biomass downdraft reactors, coupled with reciprocating internal combustion engines (RICEs), are a viable technology for small scale heat and power generation. This paper contains information gathered from a review of published papers on the effects of the particle size and the moisture content of biomass feedstock and the air/fuel equivalence ratio used in the gasification process with regard to the quality of the producer gas. Additionally, data on the parameters of producer gas, such as its energy density, flame speed, knock tendency, auto-ignition delay period and the typical spark ignition timing, are systematised. Finally, information on the typical performance of various diesel and spark ignition RICEs fuelled with producer gas is presented. [Copyright &y& Elsevier]

Abstract: A mathematical model which was developed to predict steady state performance of a biomass downdraft gasifier/spark ignition engine power system is described. A mathematical model of the integrated system consists of two parts: the fixed bed downdraft gasifier and spark ignition internal combustion engine models. For calculations the gasifier is split into three zones, namely drying – pyrolysis, oxidation and reduction sections. The gasifier’s mathematical model consists of three separate sub-models, each describing the processes in the corresponding zone. The process taking place in the reduction zone has been described using chemical kinetic principles in order to avoid introduction of assumptions related to achievement of the thermo-chemical equilibrium state during gasifier’s operation. The model is capable to accurately predict molar concentrations of different species in syngas (CO2, CO, H2O, H2, CH4 and N2) and the temperature profile in the gasifier along its height. This information then can be used for sizing the reactor and material selection. The engine’s model is based on the fuel–air thermodynamic cycle for spark ignition engines and such model takes into account the composition of syngas used as fuel. The engine’s model also takes into account effects of heat losses in the cycle through the walls of the cylinders and due to the gas blow by. Finally, the influence of dissociation processes during the combustion and the residual gases remaining in the cylinders at the beginning of the compression stroke is accounted for computations of the engine’s performance. The numerical results obtained using the proposed model are in a good agreement with data produced with the use of other theoretical models and experimental data published in open literature and with experimental data obtained in these investigations. The proposed model is applicable for modelling integrated downdraft gasifier/engine biomass energy systems and can be used for more accurate adjustment of design parameters of the gasifier and the engine in order to provide the higher overall efficiency of the system. [Copyright &y& Elsevier]

[Display omitted] • A novel cooling system with a simple design was developed. • The system is based on fluid piston machines and solar collector. • The system was tested on a solar radiation simulation test rig. • The experimental performance results of the system are analysed. • The prototype's performance is comparable to that of main existing technologies. The development of novel and improvement of existing technologies for utilising solar thermal energy for cooling purposes traditionally attracts increased attention in both industry and academia. This work presents the development of a novel cooling system with a simple design and direct utilisation of solar thermal energy. The cooling system combines a liquid piston engine and cooling machine and is driven by an evacuated tube solar collector. A prototype of such the system was designed, built and tested in laboratory conditions using a solar radiation simulator. Variations in pressures, temperatures, and the fluid piston oscillation amplitudes in the system during its operation were recorded, and the indicated power of the engine and cooling capacity of the system were determined for a range of operation and design parameters. For the heat input range of 700–900 W and the constant temperature of the cooling water equal to 26.0 °C, the engine indicated power and cooling capacity of the system varied in the range of 70.0–88.0 and 51.0–61.0 W. The corresponding indicated efficiency of the engine and cooling system were in the range of 10.0–9.7 and 7.2–6.7%. The temperature in the cooling chamber was registered in the range of 20.0–18.2 °C at an ambient temperature of 24.0 °C. The COP of the cooling machine decreased from 0.71 to 0.69. The system performance improved in tests with a constant heat input (700 W) and reducing cooling water temperature. For cooling water temperature reduction from 26.0 to 18.0 °C, the engine indicated power and cooling capacity of the system varied in the range of 70.0–111.9 and 51.0–72.0 W. The corresponding indicated efficiency of the engine and cooling system were in the range of 10.0–16.0 and 7.2–10.3%. The COP of the cooling machine decreased from 0.71 to 0.64. The temperature in the cooling chamber was registered in the range of 20.0–14.4 °C at an ambient temperature of 24.0 °C. Experimental results obtained using the system's initial design demonstrate that the engine has efficiency comparable to low-temperature steam and Organic Rankine Cycle turbines. The Coefficient of Performance of the system is similar to that of single-stage absorption chillers. [ABSTRACT FROM AUTHOR]

Abstract: The continuous increase in the level of greenhouse gas emissions and the climb in fuel prices are the main driving forces behind efforts to more effectively utilise various sources of renewable energy. In many parts of the world, direct solar radiation is considered to be one of the most prospective sources of energy. However, the large-scale utilisation of this form of energy is possible only if the effective technology for its storage can be developed with acceptable capital and running costs. One of prospective techniques of storing solar energy is the application of phase change materials (PCMs). Unfortunately, prior to the large-scale practical application of this technology, it is necessary to resolve numerous problems at the research and development stage. This paper looks at the current state of research in this particular field, with the main focus being on the assessment of the thermal properties of various PCMs, methods of heat transfer enhancement and design configurations of heat storage facilities to be used as a part of solar passive and active space heating systems, greenhouses and solar cooking. [Copyright &y& Elsevier]

• Solar energy and PCM are used to augment the indoor steam curing process. • Mathematical model of the curing process is developed. • Comparison with experiments confirms the accuracy of the mathematical modelling. • Benefits of the proposed technology are quantitively demonstrated. Steam is used to provide heating and moisture in the curing process for the production of precast concrete (PC) construction elements. The generation of steam requires large amounts of fossil fuels. This study considers the incorporation of solar thermal energy into the steam curing of PC construction elements for reducing the need for fossil fuels and associated CO 2 emissions. For this purpose, the board made of composite phase change material covers the inner surface of the main sun-facing wall in the heating & curing building. The PCM board is heated by sun rays and accumulates thermal energy during the PCM's phase transition, and this energy then is released to the indoor environment of the building, reducing the amount of steam required to maintain a certain level of temperature during the curing process. The energy consumption simulation software, EnergyPlus, and two physical models (built on the scale of 1:3) were used to study the effects of two different PCMs on the thermal performance of such new type of heating & curing buildings. Composite PCMs considered were GH-33 and GH-37 with 33 and 37 °C melting temperatures developed by the research team. The theoretical and experimental results are in good agreement and demonstrate that, compared to the GH-33, GH-37 PCM increases the temperature of the inner surface of the main sun-facing wall and the upper surface temperature of the PC construction element by 3.4 and 1.4 °C, respectively. The heat accumulation and discharge rates also were greater by 62%. For the investigated design of the building and given location in China, the deployment of studied PCM wall panels results in a reduction in the annual energy consumption and CO2 emissions by 58.6 GJ and 5 tons, respectively. The method developed for applying solar energy and selecting PCMs for augmenting steam curing of PC construction elements can be deployed in different geographical regions. [ABSTRACT FROM AUTHOR]

• The laboratory and full-scale prototypes of the novel solar air collector were tested. • Fuel economy achieved in tests varies from 11% to 81% depending on weather conditions. • The increased concentration ratio of about 1.4 was obtained without a sun-tracking device. • The mathematical model of the collector was validated against experimental results. • The model was used to define the rational design parameters of the full-scale prototype. The application of greenhouse technologies is rapidly expanding in China and other regions of the world with the continental climate. Such technologies are characterized by a considerable consumption of fossil fuels, especially in winter periods. Various renewable energy technologies are used to reduce the energy demand in greenhouses, including solar heating. Simpler designs of water or air solar collectors are preferred without sun-tracking devices and reduced dimensions and weight. In this work, a novel solar multi-surface air collector with double-receiver tubes, which does not require a sun-tracking device is proposed and has increased concentration ratio and sun rays convergence and reduced thermal losses. The laboratory and full-scale prototypes of the proposed novel collector were manufactured and tested in laboratory conditions during the December-January period as a part of the greenhouse with the active-passive ventilation wall and latent thermal storage, located in the Beijing Region. Results of experiments demonstrate that the solar collector increases the average temperatures of the greenhouse north wall inner surface by 7.5 °C, indoor air during the night-time by 1.8 °C and indoor soil by 1.5 °C. The novel collector provided active heat gains of 11.831 GJ during the December-January period and satisfied from 11% to 81% of the heat load. A lumped parameter mathematical model of the proposed collector was developed, and the comparison of simulation results and experimental data demonstrate its high accuracy in prediction of the collector performance. The model was used to study the influences of outdoor meteorological parameters, air velocity in the receiver tubes and their length on the performance of the collector. This data was used to determine the rational design parameters and air velocity of the full-scale collector. The model was also used to rationalize the variation of air velocity in the receiver tube during the day. [ABSTRACT FROM AUTHOR]

Prefabricated concrete (PC) components require curing at the specific environment after being cast for the concrete to harden to the required levels over a certain period of time. Currently, steam curing is used as the major technique in concrete production. However, this method is highly energy consuming and requires large amounts of fossil fuels. Analysis of thermal process parameters in PC curing and thermal properties of phase change materials (PCMs), developed by the research team at Beijing University of Technology for the greenhouse applications, resulted in the development of the conceptual design of passive solar PC steam curing buildings with on-wall PCM heat storage. The process of selection of the PCM for installation on the inner surface of the main sun-facing wall of solar passive curing buildings is described. The selection is the result of the evaluation of suitable PCMs using the simultaneous process of transient energy consumption simulation with the deployment of EnergyPlus software and one-dimensional unsteady heat transfer modelling across the thickness of the thermal storage. The EnergyPlus simulations were calibrated against experimental data obtained in the curing building in Hebei Province, China. Theoretical simulations for such the building demonstrate that a GH-37 PCM panel with a thickness of 50 mm is suitable for such the application. The temperature range of phase transition for the GH-37 PCM is between 37.4 and 43.5 °C with latent heat equal to 227.5 kJ/kg. Compared to the same case but without PCM, the monthly and nocturnal average temperature of the inner surface of the main sun-facing wall increases by 1.3 °C and 2.7 °C, respectively. The heating load is reduced by 6.4, 5.8, 3.4 and 2.9 GJ in spring, autumn, summer and winter periods, respectively. The amount of annual steam consumption is reduced by 4.7%. • The design concept of solar-assisted PC curing room with PCM was proposed. • Mathematical model of the PC solar-assisted curing room with PCM was carried out. • The selection of a suitable PCM and its optimal thickness was carried out. • The proposed design solution provides annual energy saving of 4.7%. [ABSTRACT FROM AUTHOR]

• Rapid calculation of physical dimensions of passive solar greenhouses was derived. • The correctness of the proposed analytical method was experimentally confirmed. • The rapid calculation method is valid for a wide range of geographical latitudes. Space formation of passive solar greenhouses plays a dominant role in the creation of required lighing and thermal conditions and in increasing the efficiency of solar energy utilisation. In this study, the energy balance equation analysis was implemented in EnergyPlus software to numerically model the thermal performance of a passive solar greenhouse, located in the Beijing Region. Comparison of numerical and experimental data indicated a high prediction accuracy of the numerical model, which then was used to conduct a parametric analysis of the effect of main physical dimensions on the energy performance of such greenhouses. As a result, a range of rational values of physical dimensions was proposed for this type of greenhouses. The originality of the research approach is using parametric analysis data, obtained from the calibrated numerical model of greenhouses, to derive novel analytical correlations for rapid calculation of the main physical dimensions of passive solar greenhouses. The correctness of the proposed novel analytical method for calculation of main physical dimensions of passive solar greenhouses was experimentally confirmed in a series of comparative physical tests on various greenhouse models. The advantage of the proposed analytical correlations is that these are valid for a wide range of geographical latitudes in China and other regions, where a similar type of greenhouses can be exploited. [ABSTRACT FROM AUTHOR]