Solar Heating and Cooling systems are a virtuous alternative to conventional air conditioning plants, as a renewable energy source (solar energy) is exploited. In this paper the coupling of low temperature solar devices with an innovative desiccant-based air handling unit, which meets the sensible and latent loads of a simulated lecture room, is analyzed through TRNSYS dynamic simulation software. The components have been characterized by means of experimental tests carried out at the test facility of Università degli Studi del Sannio. The desiccant-based air handling unit current set-up allows summer operation only. However, heating operation is also simulated, as comfort conditions can be maintained in the conditioned space exploiting solar thermal energy also in winter, with some modifications to the air handling unit. A parametric analysis is performed to compare different technical solutions (collector types, surface, tilt angle) and to identify the optimal one, taking into account energy, economic and environmental performance with respect to a reference system. The best case in terms of energy and environmental performance is represented by evacuated collectors, achieving a primary energy saving of 64% and a CO 2 emissions reduction of 61%; flat-plate collectors are instead the best solution in terms of pay-back period (6 years).

Reducing carbon dioxide (CO 2 ) emissions from power plants utilizing fossil fuels is expected to become substantially more important in the near- to medium-term due to increasing costs associated to national and international greenhouse gas regulations, such as the Kyoto protocol and the European Union Emission Trading Scheme. However, since net efficiency penalties caused by capturing CO 2 emissions from power plants are significant, measures to reduce or recover efficiency losses are of substantial interest. For a state-of-the-art 400 MW natural gas-fueled combined cycle (NGCC) power plant, post-combustion CO 2 removal based on chemical solvents like amines is expected to reduce the net plant efficiency in the order of 9–12 percentage points at 90% overall CO 2 capture. A first step that has been proposed earlier to improve the capture efficiency and reduce capture equipment costs for NGCC is exhaust gas recirculation (EGR). An alternative or complementary approach to increase the overall plant efficiency could be the recovery of available low temperature heat from the solvent-based CO 2 removal systems and related process equipment. Low temperature heat is available in substantial quantities in flue gas coolers that are required upstream of the CO 2 capture unit, and that are used for exhaust gas recirculation, if applied. Typical temperature levels are in the order of 80°C or up to 100 °C on the hot end. Additional low-grade heat sources are the amine condenser which operates at around 100–130 °C and the amine reboiler water cooling that could reach temperatures of up to 130–140°C. The thermal energy of these various sources could be utilized in a variety of low-temperature heat recovery systems. This paper evaluates heat recovery by means of an Organic Rankine Cycle (ORC) that — in contrast to traditional steam Rankine cycles — is able to convert heat into electricity efficiently even at comparably low temperatures. By producing additional electrical power in the heat recovery system, the global performance of the power plant can be further improved. This study indicates a theoretical entitlement of up to additional 1–1.5 percentage points in efficiency that could be gained by integrating ORC technology with a post-combustion capture system for natural gas combined cycles. The analysis is based on fundamental thermodynamic analyses and does not include an engineering- or component-level design and feasibility analysis. Different ORC configurations have been considered for thermal energy recovery at varying temperature levels from the above-mentioned sources. The study focuses on simultaneous low-grade heat recovery in a single ORC loop. Heat recovery options that are discussed include in series, in parallel or cascaded arrangements of heat exchangers. Different organic operating fluids, including carbon dioxide, R245fa, and N-butane were considered for the analysis. The ORC performance was evaluated for the most promising organic working fluid by a parametric study. Optimum cycle operating temperatures and pressures were identified in order to evaluate the most efficient approach for low temperature heat recovery.

The Stirling engine, as an external combustion engine, can be powered using a variety of heat sources including the continuous combustion process thus achieving significantly reduced emissions. Energy systems powered by a Stirling engines meet the needs of various applications not only in the domestic and industrial sections but in military and space gadgets as well. Stirling engines can also be used as cryocoolers in medical applications where they are called to achieve very low temperatures. Each energy system using Stirling Engine optimizes its performance in specific operating conditions. The system capacity depends on the geometric and structural characteristics, the design of the unit, the environment in which the engine is allowed to it works as well as the size of the load. In order to study the function and the efficiency of Stirling energy systems a CHP SOLO 161V -ALPHA TYPE STIRLING ENGINE was installed in the Laboratory of Applied Thermodynamics of NTUA. A thermodynamic analysis has been conducted using appropriate computing codes. The effect of each independent variable on the system performance was investigated. The study was divided into distinct levels of detail, bringing out each variable. Initially, the performance of the heat engine was examined assuming an ideal regenerator. Then, the effectiveness of the regenerator was evaluated as well as its effect on the engine performance, while the effect of the pressure drop and the energy dissipation on the engine efficiency was also investigated. Measurements were conducted using different operational conditions concerning the heating load of the engine. The effect of the geometrical characteristics of the regenerator on power output and engine performance was examined based on the results of a simulation analysis. Moreover, the power output and the efficiency of the machine in relation to the thermal load of the unit and the average pressure of the working medium were investigated. Major performance input characters affecting geometrical and operational parameters of the unit were identified leading to unit optimization with specific combinations leading to increased system performance. Simulation results were validated by comparison to corresponding values obtained by relative experiments conducted with the SOLO unit. Finally, a sensitivity analysis was performed in order to investigate the effect of the operating conditions on the performance of an alpha type Stirling Engine.

This paper presents the influence of commanding parameters as load and relative sliding speed, on the surface characteristics. Tests were done on a roller-roller tribotester. There were studied the influence of load, relative sliding speed and lubricant on the skewness and the kurtosis of the surface profile, but also on common parameters such as Ra and Rz. Such a study may be used for selecting a suitable lubricant (especially grease), after testing it under severe conditions, close to the actual ones. Profilograms indicate that treated steel has a better tribological behavior, under the above-mentioned testing conditions, for a roller-roller system. When running at low temperatures, there were noticed gripping traces, pointed out in shape and size by profilograms recorded on the roller generatrix. For all testing conditions, the more viscous grease (UM185Li2 EP – multifunctional grease) had a better behavior as concerning the profile parameters of the roller surfaces, and it provides a probably almost continuous film between rollers thus, a good protection of the metallic surfaces, process also underlined by low values for the recorded friction moment. A comparative study of the surface topography, obtained under the same testing conditions, may do at least a qualitative hierarchy of the grease grades, which could give recommendations for selecting lubricants and durability improvement of actual tribosystems.

Low operating temperature SOFCs permit a larger range of choices for materials, higher durability, and less volume and mass of a SOFC system. However, the low operating temperature poses a difficulty for the reforming of the hydrocarbon fuel: external reforming and internal reforming (IR). In this work, we develop a numerical model for simulating an indirect internal reforming section to introduce effects of the electrochemical promotion and coupling between selective anode catalysts and selective cathode catalysts in the catalyst pack in a planar solid oxide fuel cell operating at an intermediate temperature. The model employs a simplified geometrical model of an indirect internal reforming section in the anode chamber of the planar solid oxide fuel cell. However, the model includes very complicated combination of conventional reforming processes, electrochemical promotion and coupling. The model is simulated by using an in-house computer code. The results predict that the electrochemical promotion and coupling in a microscopic scale can enable a significant reforming and production of hydrogen at a relatively low temperature (500°C) with different conditions.

The mechanical properties of magma around the glass transition temperature have not been characterized yet, though this subject is considered to be important in dynamics of volcanic eruptions. In this paper, we present an experimental investigation of stress-strain relation of synthetic magma at various temperatures and strain rates. The material behaves as an elastic solid at low temperature and/or high strain rate, and as a viscous fluid at high temperature and/or low strain rate. In the transition, it reveals work-hardening response. Although the work-hardening nature has not been reported for noncrystalline magma, it is important in constructing a mathematical model to represent the flow-to-fracture transition of magma, namely the transition of eruptions from effusive to explosive styles.

Concerns about the effect of CO 2 emissions on climate change and rising energy costs have renewed the interest in efficiency improvement in fossil fuel use as well as the utilization of locally available low or moderate temperature heat sources, such as geothermal or solar. This paper summarizes twenty years of Ormat’s very significant achievements in developing cycles, configurations and equipment for electricity generation from low grade waste heat and water dominated geothermal resources. As of the end of 2007 some 30 plants ranging from 200 kW to 130 MW totaling about 1000 MW are in operation.

The Homogeneous Charge Compression Ignition (HCCI) combustion has potential to radically reduce emissions, especially NOx, but is inherently difficult to achieve and control, especially when natural gas is used as fuel. Hydrogen addition, particularly from fuel reforming was successfully used as an aid. Methane reforming with exhaust gas and air in a monolith catalytic reactor is presented here as a source of hydrogen. An open-loop fuel exhaust gas reforming system has been developed and tested; experimental results are compared with two different models of basic thermodynamic equilibria calculations. The experimental results have shown that for low temperature of engine exhaust gas, typical for HCCI conditions, additional air is needed to produce the quantities of H2 required to enhance the feasibility and range of HCCI combustion. At the low reactor inlet temperatures needed for the HCCI application the simplified three-reaction thermodynamic model is in broad agreement with experimental results, while the high hydrogen yields predicted from the multi-component equilibrium model for medium temperature reforming are difficult to achieve in a practical reformer.

A thermoelectric generator (TEG) produces electric power directly out of a heat flux across a certain temperature difference. This thermoelectric effect is based on interlinking effects of thermodynamic forces and fluxes (Seebeck and Peltier effect). Within the present work, a prototype unit using Bi 2 Te 3 semiconductor elements is installed at the biomass combined heat and power (CHP) plant in Gu¨ssing, Austria. Different operation points are examined according to a specific test program in order to find operating figures and describe the technical and economical potential of the TEG. A model of the TEG is implemented in the simulation software IPSEpro and verified with results from the experiments. Based on the model, the test plant is extrapolated to the size of possible demonstration plants for which electric output and energetic efficiency are calculated. For the entire CHP plant, the costs for retrofitting standard heat exchangers to TEGs are calculated and compared to the expected revenues from feeding the additional electricity into the grid. It can be concluded that the TEG gives way for new concepts and ideas but the expenses, especially with respect to the high material costs of the semiconductor, do not support a technically efficient and economically lucrative application of the TEG combined with decentralized heat and power production at present time.

The preparation and physico-chemical characterization of mesoporous and microporous carbons, obtained via a casting procedure, from a SBA-15 silica and a commercial Na-Y zeolite, is reported. XRD spectra showed that ordered carbon replicas occur in all cases. Micro-Raman spectra showed that rather homogeneous powders are obtained, exhibiting the presence of a graphitized carbon phase of small imperfect graphene sheets, typical of sp 2 C, along with an amorphous one, notwithstanding the relatively low temperature adopted during the carbonization processes (1173 K). N 2 adsorption isotherms at 77 K allowed the determination of BET surface areas and pore volumes: on account of the high porosity and the low specific weight, with respect to zeolites, for example, these carbon materials could be promising media for hydrogen storage. They could be used as such, or after convenient functionalization or metal doping.

The new surface hardening methods for hard alloys are developed: (1) high-temperature process for producing multicomponent carbide coatings by thermochemical heat treatment of hard alloys at 1050 °C and (2) low-temperature process for producing thin-film coatings by chemical treatment of hard alloys in specially prepared aqueous suspensions of nanosized hard refractory compounds and subsequent tempering (minimal temperature is 130°C). The structure and properties of the obtained coatings are examined. The coatings permit improving substantially the service life of cutting tools.