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Abstract Effect of inclination angle to the thermal performance of a heat pipe photovoltaic/thermal system (HP-PV/T) system was rarely reported. In the present study, a HP-PV/T system was firstly constructed in an Enthalpy Difference Laboratory, where inclination angle was experimentally managed as the only variable. Meanwhile, a comprehensive numerical model for the HP-PV/T system was developed to validate the experiments. Particularly, a 3D model for the inclined heat pipe was also firstly involved. The simulation results show that liquid film thickness within the condenser or the evaporator stabilizes at a constant value at inclining condition. The relative filmwise thermal resistance of the condenser decreases first and then increases with inclination angle; while the evaporator shows an opposite trend to the condenser. The overall thermal resistance of solar heat pipe is mainly determined by the evaporator while the evaporator is mainly determined by the effective height of the liquid pool. The experimental and simulation results both indicate that the optimum inclination angle is 40°. The proposed model agrees well with the experimental results at big inclination angles (≥20°), it is practicable to reveal the influence of inclination angle to the thermal performance of a HP-PV/T system.

Abstract This contribution experimentally evaluates and compares the performance of an ORC (organic Rankine cycle) system for stationary bottoming WHR (waste heat recovery) application operating with two different working fluids, SES36 and R245fa. The test rig is a regenerative cycle equipped with a single screw expander modified from a standard compressor characterized by a nominal shaft power of 11 kW. A total of 36 and 43 steady-state points are collected for SES36 and R245fa respectively, over a wide range of operating conditions by changing the expander rotational speed, the pump frequency and the cooling condenser flow rate. The performances of the ORC components are individually evaluated. A maximum expander isentropic efficiency of 60% is reached using SES36 at 3000 rpm, and a value of 52% is reached with R245fa at 3000 rpm. However, for a given pressure ratio the expander output power is higher with R245fa than with SES36. The overall performance of the ORC unit are investigated in terms of first and second law efficiencies and net output power for the two fluids. The results experimentally demonstrate the correlation between the working fluid critical temperature and the ORC unit working characteristics for low temperature waste heat recovery applications. Open experimental data are provided for both fluids.

Abstract Adsorption technology offers a potential in vital applications like energy storage, cooling and heating, and water desalination which can be driven by low-grade or renewable heat sources leading to significant reduction in CO2 emissions. The adsorbent material is a key element in adsorption heat pump systems determining the performance, size and cost of such technology. Metal-organic frameworks (MOFs) are class of adsorbents with superior water uptake, high pore volume and surface area. This study describes the experimental testing of adsorption heat pumps using aluminium fumarate, CPO-27(Ni) and MIL-100(Fe) for various adsorption applications. Results showed that energy storage density of 1200 W h kg−1 was achieved using MIL-100(Fe) regenerated at 95°C, and cycle time of 90 min. For cooling applications, MIL-100(Fe) showed high specific cooling power of 226 W kg−1 at 95°C while aluminium fumarate produced 136 W kg−1 specific cooling power (SCP) at 90°C. Regarding water desalination, MIL-100(Fe) showed high water production rate specific daily water production (SDWP) of 19 m3 ton−1 day−1. For power generation, including a turbine in the adsorption system can increase the effective coefficient of performance (COP) of the adsorption cooling system by 22%. Integrating the adsorption cooling system with Organic Rankine Cycle (ORC) can produce an effective COP of 0.8.

Abstract While the limitation of the entrainment ratio in supersonic ejectors is a well-known phenomenon, there is still a need to gain insight on the choking phenomena at play in on-design operation. In state-of-the-art simplified models of supersonic ejectors, the secondary stream is assumed to reach sonic velocity in a hypothetical throat (Fabri-choking). However, an alternative explanation of the entrainment limitation known as the compound-choking theory states that a nozzle flow with two streams at different stagnation pressures may be choked with a subsonic stream if the other one is supersonic. In this paper, the compound-choking is highlighted in a supersonic ejector through a thorough analysis of numerical simulations validated against experimental data. In addition, comprehensive experimental data of supersonic ejectors are used to assess the performance of the compound-choking theory to predict the entrainment ratio in the on-design regime in various configurations. Most predictions are in the ± 10 % range when compared to the experimental data. Compared to state-of-the-art 1D models relying on the Fabri-choking assumption, the compound-choking theory is shown to generally perform better regarding the prediction of the on-design entrainment ratio. This study suggests that the compound-choking theory is well suited to model the choking process in supersonic ejectors.

Abstract The Organic Rankine Cycle can be applied to convert low temperature heat to electrical power using organic working fluids. Recently, a new generation of working fluids has been introduced with almost no Ozone Depletion Potential and significantly smaller Global Warming Potential, compared to currently used refrigerants. R1233zd-E is a promising low-GWP (global warming potential) alternative to R245fa, a widely used fluid in ORC (Organic Rankine Cycle) systems. This paper analyzes the applicability of the new fluid as drop-in replacement for R245fa in existing systems and compares system parameters such as cycle efficiency and power output. To this end, the influence of the process parameters mass-flow rate, condensation temperature and expander rotational speed is investigated experimentally for both fluids. The test rig used has an electrical heater as a heat source and a scroll compressor as an expander. As a conclusion, R1233zd-E can be used as a substitute for R245fa in existing ORC systems. In addition to the advantage of having a much smaller GWP, the use of R1233zd-E may lead to higher thermal efficiencies. Comparing the highest achieved thermal efficiency, R1233zd-E performs 6.92% better than R245fa. However, comparing the maximal gross power output, R245fa performs 12.17% better than R1233zd-E.

Abstract The objective of this work is to investigate the impact of a wave farm on the nearshore wave climate quantifying, for the first time, the interaction of the WECs (Wave Energy Converters) with the waves using ad hoc laboratory tests. To accomplish this objective, a procedure consisting of three main steps is implemented and illustrated with a case study: a wave farm of WaveCats (a lateral overtopping WEC) proposed for the Death Coast (NW Spain). First, the wave climate in the wave farm area is characterised and reference wave conditions are established. Second, wave-WEC interaction and, more specifically, wave energy transmission is determined by means of 3D physical model tests. Third, on the basis of the results of the laboratory tests, the impact of different layouts of the wave farm (single-row and two-row arrays) on the nearshore wave climate is computed using a high-resolution spectral wave model. The results indicate that the difference between the two layouts is negligible at a distance of 5000 m or greater past the farm. Although the case study concerns a specific WEC and area of deployment, the procedure is entirely general in that it can be applied to other WECs and areas of interest.

Abstract Herein a novel path is analysed for its economic viability to synergize the production of biomethane and dimethyl ether from biogas. We conduct a profitability analysis based on the discounted cash flow method. The results revealed an unprofitable process with high cost/revenues ratios. Profitable scenarios would be reached by setting prohibitive DME prices (1983–5566 €/t) or very high feed-in tariffs subsidies (95.22 €/MWh in the best case scenario). From the cost reduction side, the analysis revealed the need of reducing investment costs. For this purpose, we propose a percentage of investment as incentive scheme. Although the size increase benefits cost/revenues ratio, only the 1000 m3/h biogas plant size will reach profitability if 90% of the investment is subsidized. A sensitivity analysis to check the influence of some important economical parameters is also included. Overall this study evidences the big challenge that our society faces in the way towards a circular economy.

Abstract This paper presents a new numerical model designed to simulate energy mining in naturally fractured-faulted geothermal reservoirs. The model fully couples thermo-hydraulic (TH) processes with triple porosity-permeability properties in a unified geothermal reservoir simulation. This approach enables the investigation of multiphysical phenomena in fractured-faulted formations characterised by multiple pore media. Detailed investigations on the effects of these media on coupled transient fluid and heat flow capture basic features related to energy mining in deep geological formations. Case studies demonstrate that the model can provide a long-term assessment of deep geothermal reservoirs in naturally fractured and faulted porous media. The work provides fundamental insight into the heat transport and fluid flow through multiple pore media and the fracture-fault interface in deep geothermal reservoirs under various conditions and thus, provides a foundation for future research in the field of the enhanced energy recovery from geothermal reservoirs.

Abstract The effects of plasma-assisted ignition and combustion on the ignition-delay time (Tid) and intermediates in methanol combustion were simulated numerically through a chemical-kinetics mechanism of methanol oxidation. Plasma-assisted ignition can considerably shorten the Tid. Plasma-assisted ignition is more conducive to a low temperature and the lean combustion of a methanol-air mixture. According to the shortest Tid, the active particle order is: O