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On this paper a test rig that focuses on the dynamic and transient behavior of an ORC system for waste heat recovery is presented. An experimental campaign is carried out in order to analyze the transient behavior of a single finned-tube evaporator under continuous and discrete fluctuations of the heat source. The experimental results show the dynamic response of a custom-made ORC evaporator to sinusoidal fluctuations and ramp changes of the heat source. Due to its large thermal inertia, the evaporator is able to dampen fluctuations of the heat source in the MHz range, in fact, effectively ���filtering out��� sinusoidal fluctuations with frequencies larger than at least 1.67 MHz. This large thermal inertia of the ORC evaporator is accomplished by means of a heat exchanger design where the fins have a significant mass. The study illustrates how the design of the evaporator can be an important aspect in ORC dynamic performance that is often taken for granted. This is critical for applications in which the variability of the heat source is inherent, such as waste heat recovery.

In this paper, packed bed thermal energy storage consisting of three phase change materials cascaded in series is investigated. Phase change materials are macro-encapsulated in capsules with diameter ranged from 50 mm to 100 mm and placed in thermal storage tank with internal diameter of 1 m. With such encapsulation size, void ratios between 0.45 and 0.51 are recorded, depending on the diameter ratio of the tank internal diameter to the encapsulation outer diameter. Such void space contributes to no energy storage and wastes the volume of thermal storage tank. For packing of particles with two different sizes in a cylindrical tank, void ratio of as low as 0.20 has been recorded experimentally. Such concept is tested in this paper in which sensible heat thermal storage material with much smaller size is used to fill the void space in a macro-encapsulated phase change material thermal storage system to reduce the void ratio. Parametric analyses are then carried out based on (1) encapsulation size of the phase change materials, (2) updated void ratio of system after filling with sensible heat material and (3) phase change material storage capacity. Compared to the baseline case, cyclic efficiency of a thermal storage system increases by ≈ 13.5% with thermal storage capacity increase from 10 to 30 kWh, increases by ≈ 9.6% with reduction of encapsulation size from 100 mm to 50 mm (diameter ratio increases from 10 to 20) and increases by ≈ 13.2% if void ratio is reduced with solid sensible heat material to 0.30 and subsequently filled with heat transfer fluid. For the best case simulated (optimized with all three parameters), cyclic efficiency increases by ≈ 21.9% compared to the baseline case. National Research Foundation (NRF) Accepted version This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Energy NIC grant (NRF Award No.: NRF-ENIC-SERTD-SMES- NTUJTCI3C-2016).

Secondary flow injection is proposed as a novel method to increase the efficiency of a mixed flow turbocharger turbine. This paper discusses and analyses the flow injection via a slot covering partially the shroud of the turbine using a steady state numerical analysis. The simulations we re performed at a rotational speed of 30,000 rev/min and a Genetic Algorithm was used to achieve an optimal flow injection geometry and conditions near the turbine peak condition. The optimisation resulted in a slot located 5.5mm from blade tip leading edge, 5mm wide, with an injection velocity of 116m/s oriented with a yaw angle of 80 degrees and a pitch angle of 60 degrees. Then, the same set of injection parameters was used across the entire speed line to assess the impacts of injection. The simulation results show an improvement in total -to- static isentropic efficiency throughout all the simulated operating points in the speed line, with an increase in efficiency of 2.6 percentage points at the optimise d peak efficiency point. Detailed flow analysis was conducted at three selected points: point 1 (lowest passage mass flow) , point 5 (peak efficiency), and point 8 (highest passage mas s flow). Visualisation of the flow features shows that the injected flow affects both the tip leakage flow as well as the hub suction- side separation vortex at all 3 selected points. The injected flow forces the flow to migrate flow towards the hub, creating a partial blockage and forces the passage flow to m ore closely follow the streamwise direction. This weakens the suction side hub separation vortex and thus reduces the losses induced. Additionally, the injection strengthens the tip leakage vortex, which improves blade loading near the tip but, in some cases, it consequently leads to greater loss generation near the tip region. Overall, with injection, the normalised pas sage entropy generation is reduced by 25.1%, 25.5% and 1 6.9% for point 1, point 5 and point 8 respectively. The results obtained are explained and discussed in detail in the paper., {"references":["BEHR, T., KALFAS, A. I. & ABHARI, R. S. 2008. Control of rotor tip leakage through cooling injection from the casing in a high-work turbine. Journal of Turbomachinery, 130, 031014.","BENTON, S. I., BONS, J. P. & SONDERGAARD, R. 2013. Secondary Flow Loss Reduction Through Blowing for a High- Lift Front-Loaded Low Pressure Turbine Cascade. Journal of Turbomachinery, 135, 021020.","BLOXHAM, M. J. & BONS, J. P. 2010. Leading-Edge Endwall Suction and Midspan Blowing to Reduce Turbomachinery Losses. Journal of Propulsion and Power, 26, 1268-1275.","DENTON, J. D. 1993. The 1993 igti scholar lecture: Loss mechanisms in turbomachines. Journal of Turbomachinery, 115, 621-656.","GAO, J., ZHENG, Q., DONG, P. & ZHA, X. 2014. Control of Tip Leakage Vortex Breakdown by Tip Injection in Unshrouded Turbines. Journal of Propulsion and Power, 30, 1510-1519.","HERWIG, H. & KOCK., F. 2007. Direct and indirect methods of calculating entropy generation rates in turbulent convective heat transfer problems. Heat and mass transfer 43, 207-215.","KIRTLEY, K. R., BEACH, T. A. & ROGO, C. 1993. Aeroloads and secondary flows in a transonic mixed- flow turbine stage. Journal of turbomachinery, 115, 590-600.","LIU, H., ROMAGNOLI, A., MARTINEZ-BOTAS, R., RAJOO, S. & PADZILLAH, M. H. Multi-Injection Turbine Housing: A Novel Concept for Tip-Leakage Improvement in Radial Turbines. ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition, 2017 Charlotte, NC, USA. American Society of Mechanical Engineers, V02CT44A022-V02CT44A022.","LÜDDECKE, B., FILSINGER, D. & EHRHARD, J. 2012. On Mixed Flow Turbines for Automotive Turbocharger Applications. International Journal of rotating machinery.","NEWTON, P., PALENSCHAT, T., MARTINEZ-BOTAS, R. & SEILER, M. Entropy generation rate in a mixed flow turbine passage. International Gas Turbine Congress 2015, 2015 Tokyo, Japan.","NIU, M. & ZANG, S. 2011. Experimental and numerical investigations of tip injection on tip clearance flow in an axial turbine cascade. Experimental Thermal and Fluid Science 35, 1214-1222.","PADZILLAH, M. H., RAJOO, S. & MARTINEZ-BOTAS, R. F. 2014. Influence of speed and frequency towards t he automotive turbocharger turbine performance under pulsating flow conditions. Energy Conversion and Management, 80.","PALFREYMAN, D. & MARTINEZ-BOTAS., R. F. Numerical study of the internal flow field characteristics in mixed flow turbines. Proceedings of the ASME Turbo Expo, Jun 3-6 2002 Amsterdam.","PRAISNER, T. J., GROVER, E. A., KNEZEVICI, D. C., POPOVIC, I., SJOLANDER, S. A., CLARK, J. P. & SONDERGAARD, R. 2013. Toward the Expansion of Low- Pressure-Turbine Airfoil Design Space. Journal of Turbomachinery, 135, 061007.","ROSIC, B. & DENTON, J. D. 2008. Control of shroud leakage loss by reducing circumferential mixing. Journal of Turbomachinery, 130, 021010.","SCHABOWSKI, Z. & HODSON, H. 2014. The reduction of over tip leakage loss in unshrouded axial turbines using winglets and squealers. Journal of Turbomachinery, 136, 041001.","WHITFIELD, A. & BAINES, N. C. 1990. Design of Radial Turbomachines, Longman Scientific & Technical. 10","YAMAMOTO, A. 1989. Endwall flow/loss mechanisms in a linear turbine cascade with blade tip clearance. Journal of Turbomachinery, 111, 264-275"]}

In this paper, packed bed regenerators using different phase change materials cascaded in series for cold energy storage are investigated with specific focus on charging behaviour. Indeed, when one phase change material has significantly different thermodynamic properties than the others, or when flow rate of heat transfer fluid which contains cold energy to be stored is low, there can be an undesired scenario of overcharging certain phase change materials. This scenario subsequently leads to wastage of cold energy, especially when the phase change material meant for high grade cold storage is overcharged. Two solutions are suggested such as changing the encapsulation size of the affected phase change materials or increasing the storage capacity of the phase change material, or combining both of them. It is found out that increasing the storage capacity alone can solve the overcharging problem, with an improvement on the storage capacity of the regenerator. However, this increase in storage capacity also increases overall charge time of the regenerator. When incorporating both increase in storage capacity and encapsulation size of the affected PCM, the increment in storage capacity is less, but it brings an advantage of slighter increase in the overall charge time of the regenerator. It is also proven that in any of the cases, the efficiency in recovering or storing the high grade cold energy, is improved compared to the baseline cases. NRF (Natl Research Foundation, S’pore) Accepted version

Le migrazioni internazionali rappresentano per l’Unione Europea un problema e una sfida tali da andare oltre il Partenariato Euro-Mediterraneo, fino a mettere in discussione la sua stessa esistenza. Le ragioni che hanno condotto ad una così critica situazione sono molteplici e hanno come origine il fatto che i migranti internazionali rappresentano una “risorsa” dimenticata del Partenariato economico-finanziario. La Dichiarazione di Barcellona non ha recepito né la natura economica del fenomeno, né il ruolo del Mediterraneo quale centro di un “sistema migratorio” intercontinentale in espansione. Ciò ha generato politiche migratorie Euro-Mediterranee oscillanti fra sicurezza delle frontiere e promozione dell’integrazione attraverso iniziative decentrate e unilaterali. Per superare la crisi occorre prendere coscienza del fenomeno (quindi della distinzione fra rifugiati, migranti internazionali e migranti interni), della sua incorporazione nei processi globalizzati di sviluppo e crescita delle economie e della necessità di gestirlo nell’ambito di un disegno strategico di tutti i paesi che coinvolge. Occorre andare oltre il “co-sviluppo”, verso una nuova forma di cooperazione economica fra paesi a differente livello di avanzamento che concepiscano il Mediterraneo come “progetto”.