[en] Straw is a non-hazardous by-product of crop plants processing. Currently, it represent one of the most important biomass resource. The huge quantities of straw annually produced generate big problems in what concerns their disposal. The traditional field burning is no longer accepted, so another disposal solutions must be found and recycling is the most attractive. The paper refers to such a solution consisting in the conversion of the straw energy potential into electricity in a power plant based on an air turbine. This power system it is in fact an external combustion engine, derived from a gas turbine engine and operating with air as working fluid instead of combustion gases. In order to make possible the use of straw as fuel, the conventional combustion chamber is substituted by a hot air generator. Schematic of this power system and the results of its energetic analysis are presented in the paper. There are analysed the main performance indicators, namely thermal efficiency, output power, fuel consumption and specific fuel consumption. The results of the study indicate the analysed power system as an interesting solution for straw recycling. (paper)

[en] Hybrid electric vehicles (HEV) are currently considered a viable solution for fossil fuel saving and pollutant emissions reduction in transportation sector. The typical HEV configuration contains a reciprocating internal combustion engine – gasoline or diesel. Aiming to increase performance and reduce pollution, a study on performance, size and mass of a HEV configuration with micro gas and steam turbine was developed. The proposed system generates 100 kW output power and operates with compressed natural gas (CNG hybrid technology), which is a fuel more environmentally friendly than gasoline or diesel. The study revealed that analysed system performs better than most advanced equivalent ICE engines while its size and mass fit into the bodywork of a car. A solution for arrangement of the system components in the case of a car is also presented. (paper)

[en] The global need for energy increases with mankind evolution and proliferation. The sharp decrease in fossil fuel sources and pollution increase, triggered research for renewable energy sources. The solar energy, available and sustainable, may be easily converted into both electricity and thermal energy. The photovoltaic paradox (need solar energy to function, but the electricity output decreases if temperature rises under the Sun’s heat) was controlled by using various cooling techniques for panels. A large number of papers published to date in literature on solar energy conversion applications are reviewed and classified. The emphasis is placed on methods employed to increase the solar-to-electricity energy conversion efficiency, i.e. thermal management of photovoltaic panels. The use of thermoelectric modules (in PV-T-TE devices, photovoltaic-thermal-thermoelectric) is highlighted. (paper)

[en] Water spraying into the cooling air flow is one of the most efficient methods for heat transfer enhancement. Consequently, it is currently used in several applications and is analysed as a solution for others, where compactness is very important. Considering two practical cases, an air cooled steam condenser and a compact automotive radiator, authors performed an experimental study applying this method for a fin-and-tube heat exchanger with inline tube arrangement. Experiments were carried out using a wind tunnel. Reynolds number varied in the range 2082… 4432, which includes entire transient flow range. Maximum specific sprayed water flow was 1.5⋅10⁻³ kg of water per kg of dry air. For this specific flow, an increase of 52 to 73% was achieved for the overall specific heat transfer coefficient. The cooling air pressure loss in heat exchanger almost doubled at maximum Reynolds number, compared to the case described by minimum Reynolds number. (paper)

[en] The functioning of a Vuilleumier heat pump with four variable-volume chambers and six heat exchangers was numerically simulated using a theoretical adiabatic physico-mathematical model. All four variable-volume chambers were assumed as adiabatic and the heat exchangers were considered as isothermal. The model uses the piston movement laws given by the mechanism and not simplified sinusoidal ones. The adiabatic functioning was described through thermodynamic diagrams showing pressure and temperatures cyclical variations inside the machine and inside each adiabatic chamber. The model allows to estimate the heat pump performances, highlighting the energy exchanged by the working agent inside heaters and coolers and the coefficient of performance. The adiabatic model is able to emphasize the energy transfer that appears between the branches of the machine, feature that simpler theoretical models do not have. This analysis of the functioning with the adiabatic model could be extended for a Vuilleumier heat pump that rejects heat at two different temperatures. (paper)

[en] The progress of solar energy conversion technologies during the last few decades triggered the development of various types of collectors, thermal, photovoltaic (PV), or hybrid. In this paper, authors present the basic elements of thermal (energy and exergy) analysis solar collectors and their efficiency. The review of thermal analyses covers basic types of collectors and is extended to some constructive variations, e.g. with supplemental thermal elements (TEG). Thermal radiation proves to be the most important energy loss factor, due to the large temperature difference between the collector surface and the sky. To determine the total efficiency of solar collector operation, as a more complex analysis method of solar collector systems is proposed, to include economic, environmental and life-cycle analysis elements. (paper)

[en] The anticipated depletion of conventional fuels (crude oil, coal) reserves as energy sources triggered extended researches for renewable energy sources. In the last few decades, technologies for energy conversion from solar to electric and thermal energy evolved rapidly. Some recent photovoltaic (PV) panel cooling methods involve thermoelectric (TE) elements. The authors proposed a trifold panel that employs both thermal (T) and TE cooling to lower the temperature of PV panel operation and extract energy from waste heat. Recently, an important number of publications tackled various aspects of PV-TE and PV-T-TE hybrid systems, especially for building integration applications. This paper attempts to cover important topics, with emphasis on aspects related to design and characterization of mobile applications. (paper)

[en] The concept design and construction of a one-stage heat-driven compressor is presented. A physico-mathematical model used for analyzing the heat-driven compressor stage is presented. The model is a theoretical one, that takes into account a perfect gas agent and no thermodynamic losses. Performances and output of the theoretical one-stage heat-driven compressor are calculated and analyzed. An exemplification by numerical simulation was performed in this regard. The device could use solar energy for heating. Multi-stage units could obtain larger compression ratios. (paper)

[en] Hybrid electric vehicles are currently considered a viable solution for fossil fuel saving and pollutant emissions reduction in transportation sector. The typical configuration of a hybrid electric propulsion system contains a reciprocating internal combustion engine – gasoline or diesel. Aiming to increase performance and to reduce pollution in road transport, a hybrid electric propulsion system based on a micro gas and steam turbine system operating with compressed natural gas is proposed in the paper. The micro gas turbine has a recuperative heat exchanger and the steam cycle has one pressure level. The study analysed the performance of the proposed system as a function of gas turbine engine pressure ratio and temperature difference of the gas turbine engine heat exchanger. Results indicate that, at equal power, the analysed system is more performant than internal combustion engines currently used in hybrid electric propulsion, so they could represent a viable solution in this field. (paper)

[en] The theoretical functioning of a kinematic one-stage beta-type Stirling motor-driven compressor was analyzed. This machine comprises a kinematic Stirling engine and a reciprocating compressor in one single block. A double acting cylinder houses a piston that plays both the roles of the power piston of the Stirling engine and of the compressor’s piston. The maximum performances of this machine are determined through numerical modelling. For a certain compression ratio of the compressor, a functioning regime for which the work produced by the Stirling engine is equal to the absolute value of the work consumed by the compressor can be found. (paper)