| 1. |
- Gustafsson, Ola, et al.
(författare)
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Flat tube heat exchangers - Direct and indirect noise levels in heat pump applications
- 2014
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 66:1-2, s. 104-112
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Tidskriftsartikel (refereegranskat)abstract
- In the outdoor unit of an air-source heat pump the fan is a major noise source. The noise level from the fan is dependent on its state of operation: high air-flow and high pressure drop often result in higher noise levels. In addition, an evaporator that obstructs an air flow is a noise source in itself, something that may contribute to the total noise level. To be able to reduce the noise level, heat exchanger designs other than the common finned round tubes were investigated in this study. Three types of heat exchanger were evaluated to detect differences in noise level and air-side heat transfer performance at varying air flow. The measured sound power level from all the heat exchangers was low in comparison to the fan sound power level (direct effect). However, the heat exchanger design was shown to have an important influence on the sound power level from the fan (indirect effect). One of the heat exchangers with flat tubes was found to have the lowest sound power level, both direct and indirect, and also the highest heat transfer rate. This type of flat tube heat exchanger has the potential to reduce the overall noise level of a heat pump while maintaining heat transfer efficiency.
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| 2. |
- Gustafsson, Ola, et al.
(författare)
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NOISE LEVEL IN RELATION TO ENERGY PERFORMANCE OF AIR-TO-AIR HEAT PUMPS
- 2011
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Ingår i: 10th international heat pump conference.
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Konferensbidrag (refereegranskat)abstract
- With increased use of air source heat pumps, a possible barrier for further market growth and customer acceptance is their noise level. The disturbance is both an issue for the owner of the heat pump and the neighbors since both the indoor and the outdoor units radiate sound. The purpose of this study is to create an understanding of the noise generation of air-to-air heat pumps and relate this to their energy performance. This knowledge is then to be used in continued work when describing the total disturbance of a heat pump.Two heat pumps, both of inverter type and with different noise performance were selected for measurements. Energy performance, in the form of Coefficient of Performance (COP), was evaluated at different operating conditions. Measurements of the sound power level were performed on both the outdoor and the indoor units. Results show that the sound level from the indoor units is independent of the outdoor conditions. The noise from the outdoor units varies with different climates and the variation is particularly large at part load conditions.
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| 3. |
- Larsson, Monica, 1979, et al.
(författare)
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An Experimental Investigation of Fischer-Tropsch Fuels in a Light-Duty Diesel Engine
- 2007
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Konferensbidrag (refereegranskat)abstract
- Experiments were performed using a Light-Duty, single-cylinder, research engine in which the emissions, fuel consumption and combustion characteristics of two Fischer-Tropsch (F-T) Diesel fuels derived from natural gas and two conventional Diesel fuels (Swedish low sulfur Diesel and European EN 590 Diesel) were compared. Due to their low aromatic contents combustion with the F-T Diesel fuels resulted in lower soot emissions than combustion with the conventional Diesel fuels. The hydrocarbon emissions were also significantly lower with F-T fuel combustion. Moreover the F-T fuels tended to yield lower CO emissions than the conventional Diesel fuels. The low emissions from the F-T Diesel fuels, and the potential for producing such fuels from biomass, are powerful reason for future interest and research in this field.
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| 4. |
- Larsson, Monica, 1979
(författare)
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An Experimental Study of Fischer-Tropsch Fuels in a Diesel Engine
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alternative fuels for Diesel engines include ester-based fuels (derived from sources such as rapeseed, soybeans and palm oil), dimethyl ether, and various synthetic fuels. Use of these fuels could contribute to a cleaner environment, reduce global warming and improve the human health by reducing levels of harmful emissions. One such fuel is Fischer-Tropsch (F-T) fuel, a synthetic fuel that can be produced from coal, natural gas or biomass, the properties of which heavily depend on the catalyst used in its production.Various published studies have shown that use of F-T fuels could reduce emissions of soot, NOx, HC and CO, to varying degrees, since they have a number of desirable properties, including low sulfur and aromatic contents, high cetane numbers and low density. To further explore the performance of F-T fuels, and the emissions generated when they are used, engine tests were performed at Chalmers in both HCCI and conventional Diesel combustion modes. The engine used in the investigations was a single cylinder, 0.5 liter, research engine, and the performance of two F-T Diesel fuels derived from natural gas, produced by Statoil in Trondheim, was compared with that of two conventional Diesel fuels (Swedish low sulfur Diesel and European EN 590 Diesel). In HCCI combustion mode the soot emissions were too low for meaningful comparison between the fuels. However, HC and NOx emissions were lower when using the F-T fuels. There were no significant between-fuel differences in emissions of CO and CO2, or fuel consumption. In HCCI combustion mode, the combustion was phased by using exhaust gas recirculation (EGR), thus there were no between-fuel differences in ignition delay, despite the early injection (which is a key feature of HCCI combustion). However, higher levels of EGR were needed for the F-T fuels than for the standard Diesel fuels, which reduced the thermal efficiency of the engine.In conventional Diesel combustion mode the soot emissions were markedly lower (by up to 30 percent) when using the F-T fuels than when using the already clean Swedish low-sulfur Diesel. Reductions were also found in HC and CO emissions, while CO2 and fuel consumption values obtained with the different fuels were similar. The high cetane number of the F-T fuels resulted in shorter ignition delays for the pilot injections. A challenge that had to be met before widespread use of F-T fuels could be economically viable was to minimize their production costs. However, these costs have fallen sharply, through a combination of intense research efforts and the construction of F-T plants with high production capacities, and they are now competitive with oil from fossil sources, so long as the price of the latter is higher than $25/barrel. The possibilities of producing Fischer-Tropsch fuels from several feed-stocks and using existing engines without modifications are major advantages with F-T fuels. Moreover, F-T fuels can be blended in any proportions with petroleum-based Diesel, and existing refueling and maintenance infrastructure can be used for vehicles running on them. All these advantages, and the cleanliness of their exhaust gases, make F-T fuels attractive alternative Diesel fuels.
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| 5. |
- Larsson, Monica, 1979, et al.
(författare)
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Combustion of Fischer-Tropsch, RME and Conventional Fuels in a Heavy-Duty Diesel Engine
- 2007
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Konferensbidrag (refereegranskat)abstract
- This investigation includes a comparison of two Fischer-Tropsch (FT) fuels derived from natural gas and a Rapeseed Methyl Ester (RME) fuel with Swedish low sulfur Diesel in terms of emissions levels, fuel consumption and combustion parameters. The engine used in the study was an AVL single cylinder heavy-duty engine, equipped with a cylinder head of a Volvo D12 engine. Two loads (25% and 100%) were investigated at a constant engine speed of 1200 rpm. The engine was calibrated to operate in different levels of EGR and with variable injections timings. A design of experiments was constructed to investigate the effects of these variables, and to identify optimal settings. The results showed that the soot emissions yielded by FT and RME fuels are up to 40 and 80 percent lower than those yielded by the Swedish Diesel. In addition the FT fuel gave slightly lower, and the RME significant higher NOx emissions than the Swedish Diesel. Due to the low heating value of the RME fuel, the fuel consumption was increased by 10% compared with the Swedish Diesel. The fuel consumption with the FT fuel, which has a similar heating value to conventional fuels, was not significantly different from that obtained with the Diesel.
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| 6. |
- Larsson, Monica, 1979, et al.
(författare)
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Comparison of Conventional Diesel and Fischer-Tropsch Diesel Fuels for HCCI Combustion
- 2006
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Ingår i: JSAE Annual Spring Congresse 2006.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Engine tests were performed with Swedish low sulfur Diesel, European EN 590 Diesel and two natural gas-derived Fischer-Tropsch Diesel fuels in a light-duty single-cylinder engine to compare their emission, fuel consumption, and combustion characteristics. The engine was operated in HCCI combustion mode with multiple injections and different injection timings. The combustion was phased to a constant CA50 for all operating points by adjusting the amount of EGR. Low soot emissions are expected with HCCI, and no significant differences between the various fuels were detected in this respect. However, NOx emissions were lower for the F-T fuels than the other fuels, due to their high cetane number and higher EGR requirements.
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| 7. |
- Lima Ochoterena, Raul, 1978, et al.
(författare)
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Optical studies of spray development and combustion characterization of oxygenated and Fischer-Tropsch fuels
- 2008
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Ingår i: 2008 World Congress; Detroit, MI; United States; 14 April 2008 through 17 April 2008. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Konferensbidrag (refereegranskat)abstract
- Optical studies of combusting diesel sprays were doneon three different alternative liquid fuels and compared toSwedish environmental class 1 diesel fuel (MK1). Thealternative fuels were Rapeseed Oil Methyl Ester (RME),Palm Oil Methyl Ester (PME) and Fischer-Tropsch (FT)fuel.The studies were carried out in the Chalmers HighPressure High Temperature spray rig under conditionssimilar to those prevailing in a direct-injected dieselengine prior to injection. High speed shadowgraphs wereacquired to measure the penetration of the continuousliquid phase, droplets and ligaments, and vaporpenetration. Flame temperatures and relative sootconcentrations were measured by emission based, lineof-sight, optical methods. A comparison betweenprevious engine tests and spray rig experiments wasconducted in order to provide a deeper explanation of thecombustion phenomena in the engine tests.Results pertaining to spray behavior show that highviscosity fuels have wider spray cone angles, smallerdischarge coefficients (Cd) and shorter vapor penetrationthan low viscosity fuels. Continuous liquid phasepenetration is related to differences in surface tension,viscosity and density; while the penetration of dropletsand ligaments is related to volatility, their penetration isshort for highly volatile fuels and long for low-volatilityfuels.Engine tests show that particle matter (PM) emissionsare generally lower when these alternative fuels areused, but the use of RME leads to increased NOxemissions correlating with elevated flame temperatures.
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| 8. |
- Salihovic, Samira, 1985-, et al.
(författare)
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Changes in markers of liver function in relation to changes in perfluoroalkyl substances : A longitudinal study
- 2018
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Ingår i: Environment International. - : Elsevier. - 0160-4120 .- 1873-6750. ; 117, s. 196-203
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Tidskriftsartikel (refereegranskat)abstract
- Background: While it is known that perfluoroalkyl substances (PFASs) induce liver toxicity in experimental studies, the evidence of an association in humans is inconsistent.Objective: The main aim of the present study was to examine the association of PFAS concentrations and markers of liver function using panel data.Methods: We investigated 1002 individuals from Sweden (50% women) at ages 70, 75 and 80 in 2001-2014. Eight PFASs were measured in plasma using isotope dilution ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS). Bilirubin and hepatic enzymes alanine aminotransferase (ALT), alkaline phosphatase (ALP), and gamma-glutamyltransferase (GGT) were determined in serum using an immunoassay methodology. Mixed-effects linear regression models were used to examine the relationship between the changes in markers of liver function and changes in PFAS levels.Results: The changes in majority of PFAS concentrations were positively associated with the changes in activity of ALT, ALP, and GGT and inversely associated with the changes in circulating bilirubin after adjustment for gender and the time-updated covariates LDL- and HDL-cholesterol, serum triglycerides, BMI, statin use, smoking, fasting glucose levels and correction for multiple testing. For example, changes in perfluorononanoic acid (PFNA) were associated with the changes liver function markers beta(BILIRUBIN) = -1.56, 95% confidence interval (CI) -1.93 to -1.19, beta(ALT)= 0.04, 95% CI 0.03-0.06, and beta(ALP)= 0.11, 95% CI 0.06-0.15.Conclusion: Our longitudinal assessment established associations between changes in markers of liver function and changes in plasma PFAS concentrations. These findings suggest a relationship between low-dose background PFAS exposure and altered liver function in the general population.
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