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| 2. |
- Berntsson, Thore, 1947, et al.
(author)
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Heat transfer of nonazeotropic mixtures in a falling film evaporator
- 1985
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In: ASHRAE:s Annual Meeting, Honolulu, 23-27 June 1985: - ASHRAE Transactions. ; 91:1, s. 1337-1350
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Conference paper (other academic/artistic)abstract
- The evaporative heat transfer coefficient for nonazeotropicmixtures of R12 and R114 has been studied in a falling filmheat exchanger. The main aim with the project has been tostudy how the heat transfer coefficient is influenced bythe additional mass transfer resistance that is introducedwhen a mixture is used instead of a pure refrigerant.The test apparatus consisted of one tube, which was heatedfrom the outside and with the refrigerant forming a fallingfilm on the inside. The heating was done by a liquidflowing in an annular space countercurrently to the fallingfilm.From the results it can be concluded that the heat transfercoefficients for the mixtures at surface evaporation conditions are between the corresponding ones for the pure refrigerants at given Re numbers. This indicates that theadditional mass transfer resistance when a mixture is usedis small in a falling film at such conditions. This isprobably due to the small film thickness.The heat transfer coefficients versus the heat flux werealso measured. Again, the values for the mixtures at agiven'heat flux fall between the corresponding for thetwo pure refrigerants, both at surface evaporation andnucleate boiling conditions.
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| 4. |
- Holmberg, Per, 1957, et al.
(author)
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Technico-economic aspects on heat transformers
- 1990
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In: Paper to be presented at Workshop on Concepts for energysavings in Heat Pumps and Refigeration Systems August 31st 1990 at The Royal Inst. of techn.,Sthlm.
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Conference paper (peer-reviewed)
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| 5. |
- Latz, Gunnar, 1984, et al.
(author)
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Comparison of Working Fluids in Both Subcritical and Supercritical Rankine Cycles for Waste-Heat Recovery Systems in Heavy-Duty Vehicles
- 2012
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Journal article (peer-reviewed)abstract
- In a modern internal combustion engine, most of the fuel energy is dissipated as heat, mainly in the form of hot exhaust gas. A high temperature is required to allow conversion of the engine-out emissions in the catalytic system, but the temperature is usually still high downstream of the exhaust gas aftertreatment system. One way to recover some of this residual heat is to implement a Rankine cycle, which is connected to the exhaust system via a heat exchanger. The relatively low weight increase due to the additional components does not cause a significant fuel penalty, particularly for heavy-duty vehicles. The efficiency of a waste-heat recovery system such as a Rankine cycle depends on the efficiencies of the individual components and the choice of a suitable working fluid for the given boundary conditions. Commonly used pure working fluids have the drawback of an isothermal evaporation and condensation, which increases irreversibility, and consequently decreases the efficiency during the heat transfer. Previous work has suggested that one way to overcome this problem is to use zeotropic mixed working fluids. These have already been applied in several stationary systems and refrigerant cycles but not yet in waste-heat recovery systems for portable applications. This theoretical study compares different pure working fluids and zeotropic mixtures in both subcritical and supercritical Rankine cycles. The main objective was to analyze the respective energy and exergy efficiencies by modeling the Rankine cycles. The results suggested that the final fluid and cycle choice is limited by the exhaust-gas temperature range of a heavy-duty diesel engine and realistic condensation conditions for the fluid. Further, environmental and safety concerns over working fluids in portable applications are important challenges, which need to be taken into account in selecting an appropriate fluid. Copyright © 2012 SAE International.
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| 6. |
- Latz, Gunnar, 1984, et al.
(author)
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Performance Analysis of a Reciprocating Piston Expander and a Plate Type Exhaust Gas Recirculation Boiler in a Water-Based Rankine Cycle for Heat Recovery from a Heavy Duty Diesel Engine
- 2016
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In: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 9:7, s. 495-
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Journal article (peer-reviewed)abstract
- The exhaust gas in an internal combustion engine provides favorable conditions for a waste-heat recovery (WHR) system. The highest potential is achieved by the Rankine cycle as a heat recovery technology. There are only few experimental studies that investigate full-scale systems using water-based working fluids and their effects on the performance and operation of a Rankine cycle heat recovery system. This paper discusses experimental results and practical challenges with a WHR system when utilizing heat from the exhaust gas recirculation system of a truck engine. The results showed that the boiler’s pinch point necessitated trade-offs between maintaining adequate boiling pressure while achieving acceptable cooling of the EGR and superheating of the water. The expander used in the system had a geometric compression ratio of 21 together with a steam outlet timing that caused high re-compression. Inlet pressures of up to 30 bar were therefore required for a stable expander power output. Such high pressures increased the pump power, and reduced the EGR cooling in the boiler because of pinch-point effects. Simulations indicated that reducing the expander’s compression ratio from 21 to 13 would allow 30% lower steam supply pressures without adversely affecting the expander’s power output.
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| 7. |
- Latz, Gunnar, 1984, et al.
(author)
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Selecting an expansion machine for vehicle waste-heat recovery systems based on the Rankine cycle
- 2013
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2
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Conference paper (peer-reviewed)abstract
- An important objective in combustion engine research is to develop strategies for recovering waste heat and thereby increasing the efficiency of the propulsion system. Waste-heat recovery systems based on the Rankine cycle are the most efficient tools for recovering energy from the exhaust gas and the Exhaust Gas Recirculation (EGR) system. The properties of the working fluid and the expansion machine have significant effects on Rankine cycle efficiency. The expansion machine is particularly important because it is the interface at which recovered heat energy is ultimately converted into power. Parameters such as the pressure, temperature and mass-flow conditions in the cycle can be derived for a given waste-heat source and expressed as dimensionless numbers that can be used to determine whether displacement expanders or turbo expanders would be preferable under the circumstances considered. The goal of this theoretical study was to use this approach to analyze waste-heat recovery systems for a heavy-duty diesel engine and a light-duty gasoline engine. Given the different waste-heat rates of these two engines, the relationships between Rankine cycle performance and design aspects such as the expansion ratio and the locations of pinch points in the heat exchanger were evaluated. The calculated values of these parameters were used as inputs in a dimensionless analysis to identify an optimal expansion machine for each case. The impact of varying the working fluid used was investigated, since it had a large impact on the results obtained and provided insights into design dependencies in these systems.
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| 8. |
- Latz, Gunnar, 1984, et al.
(author)
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WATER-BASED RANKINE-CYCLE WASTE HEAT RECOVERY SYSTEMS FOR ENGINES: CHALLENGES AND OPPORTUNITIES
- 2015
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In: Proceedings of the 3rd International Seminar on ORC Power Systems.
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Conference paper (peer-reviewed)abstract
- Much of the fuel energy in an internal combustion engine is lost as heat, mainly through hot exhaust gas. The high energy losses, and high temperatures of the exhaust gas, provide favorable conditions for applying a waste-heat recovery system. Among the available options, systems based on the Rankine cycle show the highest potential in terms of reducing fuel consumption. Water or water-based mixtures have several advantages over organic fluids as working fluids for such applications of the Rankine cycle, in terms of cost, thermal stability, safety and complexity of the system. They also have several disadvantages, including possible freezing for pure water, high boiling temperature and high heat of vaporization. Hence, higher temperatures and amounts of waste heat are needed for reliable operation of the system. However, few experimental investigations have addressed the practical challenges associated with water and their effects on the performance and operation of a system in a driving cycle. This paper presents results of experiments with a full-scale system for recovering waste heat from the exhaust gas recirculation (EGR) of a 12.8 L heavy-duty Diesel engine on a test bench. The working fluid used in the experiments was deionized water and a 2-cylinder piston expander served as an expansion device. The engine was kept in standard configuration, except for minor modifications required to implement the heat-recovery system. The prototype EGR boiler was designed to fit in the space initially designated for the production EGR cooler. The assembly was operated in the operating points of the European Stationary Cycle (ESC). The results show that the trade-off between boiling pressure, sufficient superheating of the water and cooling of the EGR caused by the pinch-point in the boiler poses a major challenge when using water as a fluid. Low flow rates at low load points were challenging for boiler stability. During operation, the blow-by of working fluid into the lubrication system of the expander and vice versa was also problematic. Special steam-engine oil with high viscosity and good water separation capability was used to weaken this effect. The Rankine cycle-based test system attained a thermal efficiency of 10% with EGR as the only heat source. Results, major constraints and possible means to improve the system when using water as a working fluid are presented here. Simulation models developed for the EGR boiler and the piston expander supported this effort.
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| 9. |
- Munch, Karin, 1954, et al.
(author)
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A Comparison of Drop-In Diesel Fuel Blends Containing Heavy Alcohols Considering Both Engine Properties and Global Warming Potentials
- 2016
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2016-Octobeer
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Journal article (peer-reviewed)abstract
- Heavy alcohols can be mixed with fossil diesel to produce blended fuels that can be used in diesel engines. Alcohols can be obtained from fossil resources, but can also be produced more sustainably from renewable raw materials. The use of such biofuels can help to reduce greenhouse gas (GHG) emissions from the transport sector. This study examines four alcohol/diesel blends each containing one heavy alcohol: n-butanol, iso-butanol, 2-ethyl hexanol and n-octanol. All of the blends where prepared to function as drop-in fuels in existing engines with factory settings. To compensate for the alcohols′ low cetane numbers (CN), a third component with high CN was added to each blend, namely hydrotreated vegetable oil (HVO). The composition of each mixture was selected to give an overall CN equal to that of fossil diesel fuel. The four blends were compared in terms of sustainability, their performance in engine tests using a single-cylinder light duty engine, and their general physicochemical properties. Lifecycle analyses indicated that replacing fossil diesel with diesel-biofuel blends could reduce GHG emissions by between 22 and 58 %. The greatest reduction was predicted to occur with the isobutanol containing blend and the second greatest with the 2-ethylhexanol blend. Analysis of the blends' physical properties showed that the ones including octanol isomers resemble fossil diesel more closely than those containing butanol. Engine experiments indicated that the blends' combustion behavior and thermal efficiencies were very similar to those of conventional diesel fuel. However, on average, the blends produced approximately 50% less soot than diesel.
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