45 research outputs found
A Novel Organic Rankine Cycle (ORC) for High Temperature Applications
Full text linkThe current experimental ORC setups for long-haul Heavy Duty Diesel Engines (HDDE) are not reaching the desired fuel savings within the expected costs. Pathways to improve ORC performance and cost-effectiveness remain a major challenge facing the automotive sector. This paper presents the conceptual overview and simulation results (using Aspen HYSYS) of a novel ORC especially tailored for high temperature heat sources (300-400°C) in truck applications. With a fundamental revision of the expansion and heat transfer characteristics, the advantage of the proposed novel ORC included an equivalent performance to the conventional ORC despite a 20% reduction in the total heat transfer area and a 40% reduction in the size of the expansion machine. This resulted in a 15% improvement in the Cost/kW value of the system, whilst offering 5.1% improvement in engine thermal efficiency at highway driving conditions
Waste heat recovery using fluid bottoming cycles for heavy duty diesel engines
Full text linkA typical long-haul heavy duty Diesel engine currently rejects up to 50% of the total fuel energy in the form of heat. Due to increasing CO2 emissions and fuel costs, there is a growing interest in techniques that can even partially utilise this wasted resource to improve the overall system efficiency. Fluid Bottoming Cycles (FBC) including Rankine and organic Rankine cycles offer one means towards converting waste heat into usable power. This thesis investigates the potential of FBCs to improve the net power of two computationally modelled (Ricardo WAVE V8.1) 10 litre engine platforms operating at Euro 6 emission levels. The heat to power conversion potential of a FBC largely depends on the selected working fluid, its associated cycle operating mode and the system architecture. Firstly, a detailed systematic methodology for the selection and evaluation of pure working fluids was developed and applied using an advanced chemical process modelling tool (Aspen HYSYS V7.3). Using cycle and fluid fundamentals, screening criteria, and ranking indices, the methodology identified ethyl iodide, methanol, R30, acetone, R152 and E152a as the most suitable fluids amongst the 1800 synthetic, organic and inorganic fluids. Secondly, by varying the expansion inlet parameters, simulations were conducted using 10 pure, dry, isentropic and wet working fluids. The aim was to reduce cycle irreversibilities, highlight the significant sensitivity and performance results, provide directions for practical implementation, and offer new opportunities in energy conversion. For the low, medium and high thermal boundary conditions respectively, liquid expansion (E152a), low pressure limited superheat expansion (methanol, R30, acetone) or dry supercritical expansion (R152), and high pressure limited superheat expansion (using the high temperature organic fluids) were identified as techno-economic optimum. These optimal ORC operating modes achieved efficiencies 65-77% of the theoretical cycle limits. Finally, 13 combinations of thermal and sub-system architectures were methodically analysed and classified in terms of their level of complexity, average system power and relative size. To provide tailored solutions, the pure working fluid methodology was additionally adapted to examine over 750 water blends and 700 organic blends. Aqueous blends of 3-Methyl-1-Butanol and 1-propanol were found to be best suited to the dual pressure and the dual cycle systems. Furthermore, the ethanol-toluene blend was preferred for the high temperature recuperated cycle. The dual cycle system (aqueous blend and E152a combination) showed the maximum potential and produced an average of 7.5% of additional engine crankshaft power
Organic Rankine cycle – review and research directions in engine applications
Full text linkWaste heat to power conversion using Organic Rankine Cycles (ORC) is expected to play an important role in CO2 reductions from diesel engines. Firstly, a review of automotive ORCs is presented focusing on the pure working fluids, thermal architectures and expanders. The discussion includes, but is not limited to: R245fa, ethanol and water as fluids; series, parallel and cascade as architectures; dry saturated, superheated and supercritical as expansion conditions; and scroll, radial turbine and piston as expansion machines. Secondly, research direction in versatile expander and holistic architecture (NOx + CO2) are proposed. Benefits of using the proposed unconventional approaches are quantified using Ricardo Wave and Aspen HYSYS for diesel engine and ORC modelling. Results indicate that, the implementation of versatile piston expander tolerant to two-phase and using cyclopentane can potentially increase the highway drive cycle power by 8%. Furthermore, holistic architecture offering complete utilisation of charge air and exhaust recirculation heat increased the performance noticeably to 5% of engine power at the design point condition
Organic Rankine cycle thermal architecture – From concept to demonstration
Full text linkWaste heat to power conversion is expected to play a key role in reducing CO2 emissions in the mid-to-large scale internal combustion engines. The realisation of cost-effective deployment of Organic Rankine Cycles (ORC) is shown to be hindered by several key factors, including, disconnect between parameters considered in simulation studies to those demonstrated experimentally, utilisation of low-grade ORC practice for high-grade applications, challenges in integrating multiple heat recovery sources etc. To address such challenges, a programme of ‘concept-to-demonstration’ is in progress at the University of Brighton, with the presented focus here being on the thermal architecture.This paper describes some of the important features of a new experimental ORC test-rig that may contribute towards increased overall conversion efficiencies. These features include, firstly, a variable heat source setup, allowing the potential to replicate a wide range of realistic gaseous sources. Secondly, the direct utilisation of the High-Temperature (HT) exhaust gases, which is expected to lower the specific evaporator exergy cost by 22%. Thirdly, deployment of HT water blends, this is estimated to increase the potential of overall conversion efficiency by 2.4 times. Fourthly, a flexible thermal platform, offering multiple and efficient heat utilisation, with a holistic approach to NOx reduction, downsizing and exhaust heat recovery. Finally, advanced process conditions (e.g. 29.3 bar, 270.9 °C), which corresponds to the near-optimal region, and offers the possibility of a 12.5% conversion rate of heat recovered to expansion power. The potential benefits are quantified using a combination of published literature, procurement findings, simulation results (Aspen HYSYS) and preliminary experimental measurements (NI LabVIEW). The paper concludes with the rational for the next intended research effort, i.e. high-pressure ratio and two-phase expansion machines
An innovative Organic Rankine Cycle system for integrated cooling and heat recovery
Full text linkConverting a portion of the waste heat into usable power by implementing Rankine and Organic Rankine Cycles (ORC) on long-haul trucks is seen as a potential way to improve the overall system efficiency. To identify techno-economical heat sources across the drive cycle of a Heavy Duty Diesel Engine (HDDE), an energy and exergy analysis was performed on all the available heat streams. As a result, to recover the combined exhaust gases and coolant heat, a reference cascade system was analysed. Owing to the nature of this application, a size vs. performance optimisation was performed for the cascade system utilising water and R245fa fluid combination. Despite a 1.8% Brake Thermal Efficiency (BTE) improvement, the key consideration in the research and development efforts for ORC systems was identified as the investigation of technical paths that may improve the practicality of such a heat-to-power conversion concept. For this, simple holistic solutions were considered vital to meet the impending CO2 regulations. To provide a potential solution, an innovative dual-pressure ORC system is therefore proposed to partially address the shortcomings of the cascade system. This innovative system is a function of new working fluids (i.e. water blends), its associated cycle operating mode and a novel architecture (i.e. direct engine block heat recovery). A screening and evaluation methodology applied to water–organic blends is presented. Simulations conducted in Aspen HYSYS V8 showed that, compared to the reference cascade system, the proposed dual-pressure system has the potential to deliver an average of 20% improvement in the system power, a 50% reduction in the total heat exchanger footprint, and a reduced system complexity. These advantages bode well for an integrated and relatively compact engine cooling and exhaust heat recovery solution for future automotive HDDEs. Implementation of the proposed system at mid-speed high-load engine operating condition increased the overall BTE from 41.4% to a maximum of 43.6%
An innovative organic Rankine cycle approach for high temperature applications
Full text linkOrganic Rankine Cycles (ORC) using toluene and hexamethyldisiloxane (MM) are put forward as a means of improving the efficiency of automotive heavy duty engines, and provide a reference for comparison in this study. Despite an efficiency improvement potential of 4–4.7%, the current ORC approach is not reaching the required fuel savings within the expected costs. As such, innovative pathways to improve the ORC performance and cost-effectiveness are of great importance to the research community. This paper presents a partial solution by means of a conceptual overview and simulation results for ORCs especially tailored for high-temperature applications. A fundamental revision of the heat transfer and expansion characteristics is presented, without increasing the system integration complexity. These characteristics are attributed to the use of formulated organic blends with toluene and MM as a significant blend component. The developed 22 criteria blend screening methodology is presented. Simulation results show that for an equivalent expansion volume flow ratio, and product of heat transfer coefficient and area, the blends offer a 22–24% improvement in the net power. This resulted in a 15–18% cost savings compared to the reference ORC. The simulations were conducted in Aspen HYSYS V8 using the Peng-Robinson and Wilson fluid property packages
A Novel Integrated Cooling and Heat Recovery System Using Organic Rankine Cycle for Diesel Engines
Full text linkDiesel engines offer at least two sources for heat recovery, namely, engine coolant and exhaust gases. The continued trend of cooler engine intake temperatures and engine downsizing now means that the charge air cooling has additionally become a noticeable load on the engine cooling module. There exists key challenges in integrating multiple heat sources, and hence, heat recovery has been typically suggested as an add-on solution using either high temperature heat (i.e. exhaust gases) or low temperature heat (i.e. engine coolant). This paper proposes a novel process integration, termed, the dual process system, to recover exhaust heat and also provide cooling for the charge air. This system is a function of innovative approaches in system architecture (non-isothermal cascade condenser, liquid expander), working fluids (water-organic zeotrope, environment friendly refrigerant) and cycle operation (trilateral flash cycle). The system is simulated using an advanced chemical process modelling tool, Aspen HYSYS. As a case study, steady-state heat recovery was considered at the rated condition from a 12.8 litre engine model. Simulation results showed that the use of the dual process system on new engine platforms can potentially offer 7.2% of additional engine crankshaft power. This corresponded to a 55% increase in power generation compared to the two conventional independent heat recovery cycles targeting the high temperature and the low temperature heat sources
A study of organic Rankine cycle systems with the expansion process performed by twin screw machines
No full textThe prediction of the performance of energy systems that recover power from low grade heat is one of the most important requirements for reducing their investment cost and optimising system efficiency. The aim of this work was to study, model and analyse an Organic Rankine cycle (ORC) system using a twin screw expander to generate the power output, with HFC-245fa, as the working fluid. A software package (Power Plant Performance Prediction Program), simulating ORC system performance was therefore prepared for this purpose. Major components were represented by proper units and relations between the system’s constituents defined. The preferred analytical procedure depends on both the system complexity and the requirements of the study. In this case, the whole cycle was simulated in order to obtain a good understanding of its behaviour with the aim of estimating its optimum operating conditions. The procedure adopted was to start from a basic case and then improve it, in a realistic way, in order to evaluate the system potential. Performance indicators, like thermal efficiency, specific net output, total UA and surface of the heat exchangers, as well as the relative cost of the system all need to be taken into account but it is impossible to optimise all of them simultaneously. The design value for these parameters is therefore a matter of choice, or compromise.
Efficiencies of ORC systems were calculated based on the assumption that the working fluid entered the expander as wet vapour. For the heat source and sink conditions chosen for this study, the overall cycle efficiency was estimated as approximately 6% using R245fa. This and the power output are highly dependent on the ambient air temperature when using air-cooled condensers. Allowing for a small degree of subcooling at the condenser exit, it is shown that the heat recovery should be maximised
A Novel Integrated Cooling and Heat Recovery System Using Organic Rankine Cycle for Diesel Engines
Full text linkDiesel engines offer at least two sources for heat recovery, namely, engine coolant and exhaust gases. The continued trend of cooler engine intake temperatures and engine downsizing now means that the charge air cooling has additionally become a noticeable load on the engine cooling module. There exists key challenges in integrating multiple heat sources, and hence, heat recovery has been typically suggested as an add-on solution using either high temperature heat (i.e. exhaust gases) or low temperature heat (i.e. engine coolant). This paper proposes a novel process integration, termed, the dual process system, to recover exhaust heat and also provide cooling for the charge air. This system is a function of innovative approaches in system architecture (non-isothermal cascade condenser, liquid expander), working fluids (water-organic zeotrope, environment friendly refrigerant) and cycle operation (trilateral flash cycle). The system is simulated using an advanced chemical process modelling tool, Aspen HYSYS. As a case study, steady-state heat recovery was considered at the rated condition from a 12.8 litre engine model. Simulation results showed that the use of the dual process system on new engine platforms can potentially offer 7.2% of additional engine crankshaft power. This corresponded to a 55% increase in power generation compared to the two conventional independent heat recovery cycles targeting the high temperature and the low temperature heat sources
Twenty-year review of author characteristics and academic articles published in a medical student journal
No full textAll issues of the NZMSJ published prior to 2024 were retrospectively reviewed. Academic article characteristics and author demographics were described using counts and proportions. Characteristics were compared between the first and second decades of NZMSJ publication. For Issue 26 to Issue 36, journal metrics were also obtained. There were 144 academic articles published in the NZMSJ between 2004 and 2023. First authors tended to be medical students (74%), in
their clinical years of medical school (56%), and from local universities (72%). There was a decline in the proportion of articles authored by preclinical students (from 25% to 6%) and with University of Otago affiliation (from (59% to 28%) when comparing the first and second decades of NZMSJ publication. Most articles had a single author (67%), were academic essays (38%), and were on a medical topic (58%). The median time between submission and acceptance was 3 months (IQR 2-6 months)
