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Abstract The combined production of electricity, heat and cold by a polygeneration system connected to a district heating and cooling network can provide high energy utilization efficiency. The inherent complexity of simultaneous production of different services and the high variability in the energy demand make combined cooling and heating systems performance highly dependent on the operational strategy. In this paper, an operational optimization method based on the moving average of real-time measurements of energy demands and ambient conditions is proposed. Real energy demand data from a district heating and cooling network close to Barcelona, Spain, are used to test the method. A complex polygeneration system is considered, consisting of an internal combustion engine, a double-effect absorption chiller, an electric chiller, a boiler and a cooling tower. A detailed modelling of the system is provided, considering partial load behavior of the components and ambient conditions effects. Results of the real-time optimal management are discussed and compared to traditional operational strategies and to the ideal optimal management achievable with perfectly accurate forecast of energy demands. Moreover, the optimal width of the window adopted for the moving average of real-time data is identified.

Abstract The general objective of the investigation described in this article is the experimental testing of solar assisted dryers reported earlier. The tests show good technical results with a conventional energy consumption decrease of 27–80% and an average solar system efficiency of approx. 40%. From the experimental results, it can also be concluded that, with controlled removal of the moist air, improved product quality, significant reduction in drying time and mass losses, etc. result. The introduction of solar dryers seems to be a promising way for drying various agricultural products.

Abstract Volumetric machines are the most suitable candidates to be used as expander in power units based on the Organic Rankine Cycle (ORC) thermodynamic concept, for waste heat recovery of Internal Combustion Engine in the on-the-road transportation sector. In particular, the technology of the Sliding Rotary Vane Expander (SRVE) shows intrinsic advantages thanks to their lower cost, shaping features, easier manufacturing and reliability and, generally speaking, very suitable operative conditions. Nevertheless, they show some disadvantages which are typical of volumetric machines, such as low capacity, limited expansion ratio and power lost by friction. Among the different technologies available to reduce the effects of these aspects (revolution speed increase, elliptical stators or with more complex geometries, tip blade optimization, rolling stators, etc.), the Dual-Intake Port (DIP) was assessed as a promising solution to enhance SVREs performance and operability. However, dual-intake port was still not conceived as design option. In this paper, a novel Sliding Vane Rotary Expander design concept involving a Dual Intake Port expander (DIP) option was developed and compared to the conventional Single Intake Port (SIP) one, under the same operating conditions. Thus, after an experimental comparison between SIP and DIP expanders, under the same conditions of mass flowrate, a theoretical expander model of the latter was validated on a set of experimental results. The model allows to outline the advantages of considering the dual port as a design option: for a specific flow rate and revolution speed, this option allows to reduce the friction losses, which represent a weak point of this volumetric machine. For a given mass flow rate of the working fluid, an additional feature is that it allows a sensible downsizing with respect to the SIP, with an axial dimension reduction up to 50%, ensuring additional weight and space saving. Despite the reduction of the dimensions, DIP produces a comparable mechanical power with respect to SIP, limiting the reduction to 8–10% of the SIP one with a 50% lower mechanical power loss due to friction. For the same flow rate, the added intake port determines a decrease of the intake pressure which is completely beneficial in terms of operating conditions of the overall recovery unit.

Abstract Aiming at designing biogas-to-electricity advanced systems, Solid Oxide Fuel Cells are promising candidates. They benefit from scalability on plant sizes that suit anaerobic digesters potentialities. For biogas-Solid Oxide Fuel Cells applications, the implementation of an external pre-reformer is usually considered. However, the possibility to perform direct fuel feeding to the Solid Oxide Fuel Cell offers new opportunities towards the realization of lean systems, which are competitive especially on small-scale installations (i.e. on-farm biogas-to-electricity conversion). In this frame, scientific literature is rather poor and, to cover this gap, system simulations are called for two reasons: first, to demonstrate the potential efficiency gain of new concepts; second, to provide a meaningful support for long-term experimental investigation on Solid Oxide Fuel Cells operated upon direct feeding of unreformed biogas. For that, the current study compares two system designs for biogas utilization into Solid Oxide Fuel Cells. The conventional one realizes biogas steam reforming prior the fuel cell, while the novel concept is based on direct feeding of partially upgraded biogas by means of carbon dioxide-separation membranes. As main outcome of the study, the system equipped with carbon dioxide-separation membranes achieves better performances than its conventional competitor does, scoring 51.1% energy efficiency and 52.3% exergy efficiency (compared to 37.2% and 38.6% respectively exhibited by the reformer-based system). Because of the lack a high endothermic process steps, the membrane-based system is also convenient whether heat recovery is required, producing a combined heat-and-power efficiency of 74.8% versus 47.0% obtained in the other system. Moreover, the results of a sensitivity analysis of the impact of membrane and reforming operating parameters on the overall system performances justify the convenience of adopting the solution of biogas direct feeding. Even in the hypothesis of a poorly performing membrane and an optimized reformer, the membrane-based system exhibits a gain in the system energy and combined heat-and-power efficiency of 25.2% and 34.9% respectively, with regard to the reforming-based concept. The forcefulness of this result is reinforced by a preliminary evaluation of capital expenditures, which represents a further economic advantage beside the economic revenue coming from a higher energy conversion efficiency.

Abstract In this work the use of a desiccant wheel for air humidification is investigated through a numerical and experimental approach. In the proposed humidification system, water vapour is adsorbed from outdoor environment and it is released directly to the air stream supplied to the building. Such a system can be an interesting alternative to steam humidifiers in hospitals or, more generally, in applications where air contamination is a critical issue and therefore adiabatic humidifiers are not allowed. Performance of the proposed system is deeply investigated and optimal values of desiccant wheel configuration parameters are discussed. It is shown that in the investigated conditions, which are representative of Southern Europe winter climate, the system can properly match the latent load of the building. Finally, power consumption referred to the primary source of the proposed humidification system is compared to the one of steam humidifiers. The present analysis is carried out through experimental tests of a desiccant wheel in winter humidification conditions and through a phenomenological model of the device, based on heat and mass transfer equations.

Abstract The effect of air temperature and air flow rate on the drying kinetics of Gelidium sesquipedale was investigated in convective solar drying. Drying was conducted at 40, 50 and 60 °C. The relative humidity was varied from 50% to 57%, and the drying air flow rate was varied from 0.0277 to 0.0833 m 3 /s. The expression for the drying rate equation is determined empirically from the characteristic drying curve. Thirteen mathematical models of thin layer drying are selected in order to estimate the suitable model for describing the drying curves. The two term model gives the best prediction of the drying curves and satisfactorily describes the drying characteristics of G. sesquipedale with a correlation coefficient R of 0.9999 and chi-square ( χ 2 ) of 3.381 × 10 −6 .