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The paper analyzes energy consumption as a performance indicator for micro-manufacturing. A comparative analysis between micro-EDM and ultrashort pulse laser drilling is performed on the basis of similar process outputs like drilled thickness of 350 μm, hole diameter of 180 ± 3 μm, drilling time, micro-hole shape and inner surface quality. Experimental data revealed that ultrashort pulse laser drilling enabled root mean squared surface roughness of about 100 nm in a drilling time of 2.5 s, whereas using a conventional micro-EDM drilling operation with a 10 s duration yielded surface roughness of 380 nm. For ultrashort pulse laser ablation the specific energy consumption is increased, as the drilling time is decreased due to an increase of the adopted pulse energy up to 50 μJ but the surface roughness and the capability of obtaining very sharp edges remain unchanged. With a calculated energy intensity in the order of 10 10 J/kg and a process rate in the order of 10 −6 kg/h, ultrashort pulse laser drilling can be considered as a valid alternative from both technology point of view and specific energy consumption to similar drilling process, like micro-EDM which is characterized by a lower process rate and a higher energy intensity. [ABSTRACT FROM AUTHOR]

The paper analyzes the perspective of a solution for the mutual interaction of a Photovoltaic (PV) generator and a Ground Source Heat Pump (GSHP) in the context of a residential building. The idea is to analyze the operating performance of a system that permits the maximum self-consumption of the energy generated by a small-size PV system installed on the same building: this kind of systems could be useful for further penetration of renewable energy in a complex energy context. The problem is analyzed basing on the data of an experimental analysis of a real case, in the town of Pisa, Italy. A typical house equipped with a GSHP and a PV plant of similar size (about 3.7 kW of peak power) is monitored during a year of operation in order to test the feasibility of the technical solution for a more general application. The data concerns both the operation of the two systems and the interaction with the electric grid. The possible utilization of this solution in the perspective of promotion of self-consumption policies and of Nearly Zero Energy Buildings (NZEB) is discussed and analyzed showing that the level of interaction with the electrical grid is quite high. [ABSTRACT FROM AUTHOR]

The use of the two-phase closed thermosyphons (TPCTs) is increasing for many heat transfer applications. This paper reviews the most recent published experimental and theoretical studies on the TPCT. After a description of the TPCT operating principle and the performance characteristics, the heat transfer analysis in condenser and evaporator sections that depends on the complex two-phase process are described. The influence of the affecting parameters on the performance of TPCTs such as the geometry (diameter, shape and length), the inclination angle, the filling ratio (FR), the working fluid, the operating temperature and pressure analyzed by various researchers is discussed. The various operating limits occurring in a thermosyphon includes viscous, sonic, dryout, boiling and flooding are also analyzed. Considering the application of TPCTs, the paper presents a review of experimental tests and applications. This paper can be used as the starting point for the researcher interested in the TPCTs and their renewable energy applications. [ABSTRACT FROM AUTHOR]

Abstract: A methodological approach for analytical modelling of deep penetration laser beam welding (LBW) of stainless steels and its experimental verification is provided. After an analysis of the problem in general terms and a review of the modelling activity, a particular double source model is proposed and discussed. The model allows the derivation of penetration and width of melting zone caused by moving laser beam. Dependences of penetration length, width of the melting zone and aspect ratio of the zone were derived as a function of welding speed and laser power. The theoretical results obtained using the particular model are discussed and analyzed in comparison with experimental data obtained on a typical test case. Optimal conditions for obtaining a preliminary optimization of the process parameters were derived based on experimental results. The case study in the present paper, referred to the assembly of fuel injectors for automotive industry, demonstrates that when laser welding is performed at high speeds on thin wall components the energy released by the laser per unit of surface (energy density, ED) can be used to describe the heat transfer to the material and to shorten the experimental phase avoiding the dependencies on each single process parameter. [Copyright &y& Elsevier]

This paper analyzes the optimal sizing of a particular solution for renewable energy residential building integration. The solution combines a photovoltaic (PV) plant with a heat pump (HP). The idea is to develop a system that permits the maximum level of self-consumption of renewable energy generated by using a small-scale solar array installed on the same building. The problem is analyzed using data obtained from an experimental system installed in a building in Pisa, Italy. The residential house was equipped with a PV plant (about 3.7 kW of peak power), assisting a HP of similar electrical power (3.8 kW). The system was monitored for eight years of continuous operation. With reference to the data acquired from the long-term experimental analysis and considering a more general perspective, we discuss criteria and guidelines for the design of such a system. We focus on the possibility of exporting energy to the electrical grid, from the perspective of obtaining self-consumption schemes. Considering that one of the problems with small-scale PV plants is represented by the bidirectional energy flows from and to the grid, possible alternative solutions for the design are outlined, with both a size reduction in the plant and utilization of a storage system considered. Different design objectives are considered in the analysis. [ABSTRACT FROM AUTHOR]

This paper deals with the experimental analysis and numerical simulation of a two-phase closed thermosyphon (TPCT) in the aim to predict its transient performances. A concern in the design and operation of the TPCT is evaluating working fluid loading charge to maximize performance while avoiding dryout in the evaporator section and geyser boiling phenomena. The model includes the heat transfer through the wall, the vapor core, the liquid pool and the falling condensate film. The complete two-dimensional conservation equations for mass, momentum, and energy are solved using a finite volume scheme for the vapor flow and the pipe wall. The liquid film is modeled by using one-dimensional quasi-steady Nusselt type solution. An experimental facility has been also designed and operated to determine the operating condition and measure the maximum heat transfer rate and the overall thermal resistance of the TPCT. The total length and the diameter of pipe are 500 mm and 35 mm, respectively. The experiments have been performed in the heat transfer range of 30–700 W and filling ratios of 16, 35 and 135%. The numerical predictions for the maximum heat transport rate due to the transient local dryout are shown to be in close agreement with the experimental results under normal operation. However, for obtained liquid film dryout a discrepancy is observed. The geyser boiling is also evaluated under certain operating condition. [ABSTRACT FROM AUTHOR]

The perspectives of utilization of a screen mesh heat pipe (HP) for low to medium operating temperature applications are studied in this study. A two-dimensional mathematical model for heat and mass transfer of HPs is presented to define its performances under steady state operations. The model couples heat conduction in the wall with both liquid flow in the wick and vapor flow in the core. Experimental analysis is developed to evaluate the influence of operating parameters (the orientation and the cooling temperature) as well as the evaporator section length on the performance of the HP. Furthermore, a modeling approach to optimize the HP performance from a thermal point of view is presented. Using the heat transfer capability and total thermal resistance as the objective function and the structure parameters as the decision variable, the optimization design for the HP is performed using the Non-Dominated Sorting in Genetic Algorithms-II (NSGA-II). The results show that the optimal wick thickness and wick permeability to be a strong function of the heat flux. It is concluded that to have lower thermal resistance at lower heat fluxes for a screen mesh wick HP may have a large effective thermal conductivity, but have a small permeability. While at high heat transfer rate a small effective thermal conductivity, but a large permeability is recommended. The designer must always make trade-offs between these competing factors to obtain an optimal wick design. The investigations are aimed to determine working limits and thermal performance of HPs for low to medium operating temperature applications. [ABSTRACT FROM AUTHOR]