| 1. |
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| 2. |
- Baskakov, A.P., et al.
(author)
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Complex Heat Transfer in Furnaces with a Circulating Fluidized Bed
- 2001
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In: Heat Transfer Research. - 1064-2285. ; 37:7-8, s. 343-348
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Journal article (peer-reviewed)abstract
- Intensity of heat transfer to screen surfaces in the furnaces with a circulating fluidized bed (CFB) is determined by both radiation and convection of particles. Due to the formation of a thermal boundary layer near the screens the role of radiation decreases and that of convection increases with an increase in concentration of particles in the furnace. Generalization of the data obtained in pilot-full-scale and industrial furnaces with a CFB allowed one to obtain a simple empirical dependence of the furnace-mean coefficient of heat transfer α (W/(m2·K) on the volumetric-mean concentration of particles c (kg/m3): α = 85·c0.3.
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| 3. |
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| 4. |
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| 5. |
- Breitholtz, Claes, 1967, et al.
(author)
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Heat balance over the fluid-dynamic boundary layer of a circulating fluidized bed furnace
- 1998
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In: International Journal of Heat and Mass Transfer. - 0017-9310. ; 41:8-9, s. 1013-1024
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Journal article (peer-reviewed)abstract
- A heat balance over the fluid-dynamic boundary layer of a circulating fluidized bed furnace hasbeen formullated in order to calculate the heat transfer to the walls. The convective heat transfer is relatedto a horizontal particle flow from the core to the wall region, and an additive radiative heat transferconstituent is calculated for the particulate medium. An empirical description of the vertical distributionof solids and the transversal temperature profile are needed for the evaluation. The calculated heat transfercoefficients were compared with measurements in three commercial boilers and the deviation was less than40%, which is in the same order as the uncertainty of the experimental data.
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| 6. |
- Breitholtz, Claes, 1967, et al.
(author)
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Heat transfer in circulating fluidized bed boilers - do we know sufficiently?
- 1997
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In: Trends in heat mass and momentum transfer. - 0973-2446. ; 3, s. 85-104
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Journal article (peer-reviewed)abstract
- A considerable amount of work, mostly measurements, has been dedicated to heat transfer in circulating fluidized bed combustors. The results show that the radiative constituent of heat transfer varies between limits depending on the optical thickness of a particle boundary layer, and that the convective constituent can be related to the average cross-sectional suspension density. Based on this information reasonable estimates of heat transfer coefficients can be made. Experimental data from boiler conditions and ambient conditions are compared introducing a compensation for thermal radiation and changes in the properties of the gas with temperature. A good agreement is achieved between the two sets of data, except for cross-sectional average suspension densities below about 5 kg/m3. Locally there is a variation in heat transfer across the membrane-tube wall, and the heat transfer to the tube crest can be twice that to the adjacent fin. Heat transfer models are reviewed and applied to a hot (boiler) case and a cold (laboratory) case. The deviation of computed heat transfer coefficients from the measured ones was larger than the scatter in the measured data. The differences in the results from the models are primarily explained by uncertainties in the fluid-dynamic model parameters. For refined estimates and optimisation, knowledge of the detailed behaviour of the fluid-dynamics of the combustor is necessary. In this field the thickness of the a gas-gap between wall and particle suspension, the cover factor of the time-resolved fluctuating particle concentration, and the in-flow of particles towards the wall are insufficiently known and further work is necessary. In addition, further work is needed concerning the local heat transfer to membrane-tube walls
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| 7. |
- Breitholtz, Claes, 1967, et al.
(author)
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Translation of Heat Transfer Measurements from Laboratory CFBs to the Conditions of CFB-Boilers
- 2003
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In: Heat Transfer Research. - 1064-2285. ; 34:3-4, s. 252-269
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Journal article (peer-reviewed)abstract
- The aim of this work is to find a method for translation of heat transfer data from cold laboratory units to boiler conditions. From a compilation of existing data on heat transfer to walls in hot and cold circulating fluidized beds it is concluded that the results can be translated approximately by compensating for changes in the thermal conductivity of the gas and thermal radiation. A more general methodology is developed by deriving the criteria for thermal similarity. The only criterion that was added to those for fluid-dynamic similarity was the ratio of heat capacity of gas and particles. The thermal scaling is tested by comparing heat transfer measurements in a boiler with measurements in a scaled laboratory model. The results show that the Nusselt numbers were not the same in the boiler and the scaled model, which can be a result of the characteristic length-scale chosen, a too low heat capacity of the scaled particles or a failure to scale the local fluid-dynamics at the wall.
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| 8. |
- Breitholtz, Claes, 1967, et al.
(author)
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Translation of heat transfer measurements from laboratory CFBs to the conditions of CFB-boilers
- 2000
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In: IV Minsk Int Heat and Mass Transfer Forum,. / V.A. Borodulya, Teplitsky, J.C., Vinogradov, L.M., Palchonok, G.I.. - 9856456126 ; 6, s. 12-23
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Book chapter (other academic/artistic)
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| 9. |
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| 10. |
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| 11. |
- Breitholtz, Marcus, 1974, et al.
(author)
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Overlayer resonance and quantum well state of Cs/Cu(111) studied with angle-resolved photoemission, LEED, and first-principles calculations
- 2007
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In: Physical Review B. - 1098-0121. ; 75:15, s. 9-
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Journal article (peer-reviewed)abstract
- Angle-resolved photoemission spectroscopy and low-energy electron diffraction are used to study submonolayer coverages of Cs on Cu(111) at room temperature (RT) and 170 K. At RT, the Cs saturation coverage is approximately 90% of the full monolayer coverage. The full monolayer is characterized by a quantum well state (QWS) band having an energy of 25 meV below the Fermi level (E-F) in the (Gamma) over bar point and a resonance band extending to energies below the Cu band gap. This is supported by our first-principles calculations. Low-energy electron diffraction shows that the Cs overalyer forms a (2x2) structure over a wide coverage range, in which the QWS has energies from 50 meV above to 25 meV below E-F. The continued energy shift of the QWS after saturation of the diffraction angles is interpreted in terms of vacancies in the overlayer.
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| 12. |
- Castro, Mafalda, et al.
(author)
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Bioaccumulation Potential of CPs in Aquatic Organisms : Uptake and Depuration in Daphnia magna
- 2019
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 53:16, s. 9533-9541
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Journal article (peer-reviewed)abstract
- Chlorinated paraffins (CPs) are industrial chemicals, subdivided into three categories: short chain (SCCPs), medium chain (MCCPs), and long chain (LCCPs) chlorinated paraffins. SCCPs are currently restricted in Europe and North America. MC and LCCPs are being used as substitution products, but there is a knowledge gap concerning their bioaccumulation potential in aquatic organisms. In this work, we performed laboratory bioconcentration (passive uptake) and bioaccumulation (including dietary uptake) experiments with Daphnia magna using five different CP technical substances. All tested CP technical substances were bioaccumulative in D. magna, with log BCF and log BAF values ranging between 6.7-7.0 and 6.5-7.0 (L kg lipid(-1)), respectively. An increase in carbon chain length and an increase in chlorine content (% w/w) of the CP technical substances had significant positive effects on the log BCF and log BAF values. For the different CP technical substances, 50% depuration was achieved after 2 to 10 h when D. magna were transferred to clean media. Our results show that SC, MC, and LCCPs are (very)bioaccumulative in aquatic organisms. We believe these data can aid the ongoing policy discussion concerning the environmental risk posed by CPs.
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| 13. |
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| 14. |
- Castro, Mafalda, et al.
(author)
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Partitioning of Chlorinated Paraffins (CPs) to Daphnia magna Overlaps between Restricted and in-Use Categories
- 2018
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 52:17, s. 9713-9721
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Journal article (peer-reviewed)abstract
- Chlorinated paraffins (CPs) are high-production volume industrial chemicals consisting of n-alkanes (with 10 to 30 carbon atoms in the chain) with chlorine content from 30 to 70% of weight. In Europe, the use of short chain chlorinated paraffins (SCCPs) has been restricted by the Stockholm Convention on POPs due to their PBT (persistent, bioaccumulative and toxic) properties. Medium (MCCPs) and long chain (LCCPs) chlorinated paraffins are used as substitution products. In this work we studied the partitioning behavior of five different CP technical mixtures from the established categories (2 SCCPs, 1 MCCP, 1 LCCP and 1 CP technical mixture covering all categories) using passive dosing, by determining the partitioning coefficient of CP technical mixtures between silicone and water (Ksilicone-water) as well as between organic matter and water (Koc-water). We show that both silicone-water and organic carbon water partition coefficients overlap between different categories of CP technical mixtures. These results indicate that in-use MCCPs and LCCPs may be equally or more bioaccumulative than restricted SCCPs. For the tested mixtures, both chlorine content and carbon chain length showed a significant correlation with both Ksilicone-water and Koc-water.
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| 15. |
- Dahlquist, Fanny, et al.
(author)
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2.8 kV, forward drop JBS diode with low leakage
- 2000
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In: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 338-342, s. 1179-1182
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Journal article (peer-reviewed)abstract
- High voltage Schottky-, Junction Barrier Schottky (JBS)- and PiN-diodes with an implanted JTE termination have been fabricated on the same 4H-SiC wafer. Blocking voltages of 2.5-2.8 kV were reached for JBS and PiN diodes while the Schottky diodes reach about 2.0 kV. It is shown that the JBS design increases the blocking voltage effectively compared to the Schottky device with less than 10% increase in on-state static losses. Also, a comparison of static losses to a PiN diode gives a decrease of 40% for the JBS. The leakage current is also lowered by two decades compared to the Schottky device at its blocking voltage. Temperature measurements show that the low leakage current is maintained up to at least 225 °C.
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| 16. |
- Danielsson, Erik, et al.
(author)
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Simulation Study of on-state Losses as Function of Carrier Life-time for a GaN/SiC High Power HBT Design
- 1999
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In: Physica scripta. T. - 0281-1847. ; 79, s. 290-293
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Journal article (peer-reviewed)abstract
- SiC has several properties that makes it more suitable than silicon for high power devices. One problem with SiC bipolar devices is the short carrier life times, and this problem becomes more severe when designing devices for high voltage applications since the dimensions are larger. This work investigates how the Shockley-Read-Hall lifetime influences the on-state characteristics of a HBT or BJT switch in 4H-SiC. The on-state characteristics were simulated with varying SRH lifetimes in the base and drift region. Comparisons were made at 100 A/cm2 collector current density, Jc, and at the base current density, JB, where the total on-state power loss of the design is at minimum. The SRH lifetime in the drift region is the dominant parameter for on-state performance, whereas the SRH lifetime in the base is of much less importance. The simulations showed that to reach an acceptable JC/JB-ratio of 100 at power minimum a SRH lifetime of at least 100 ÎŒs in the drift region was needed for the HBT design. This lifetime is far from the experimental values reported for 4H-SiC. The advantages of the heterojunction in comparison to ordinary BJTs decreases with shorter SRH lifetimes, but an improvement could always be seen.
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| 17. |
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| 18. |
- Domeij, Martin, et al.
(author)
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Avalanche injection in high voltage Si PiN diodes
- 1997
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In: Physica scripta. T. - 0281-1847. ; T69, s. 134-137
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Journal article (peer-reviewed)abstract
- An experimental technique using optical excitation by a YAG laser pulse for studying avalanche injection in power devices is demonstrated This technique enables the creation of high uniform excess carrier concentrations in an optically defined device volume, involving very little heating. A method for determining the onset of avalanche multiplication, by studying the time integral of the reverse recovery current, is proposed. A PiN diode is observed to turn off from avalanching at a dissipated power density of more than 200 kW/cm(2).
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| 19. |
- Domeij, Martin, et al.
(author)
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Dynamic avalanche and trapped charge in 4H-SiC diodes
- 2000
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In: SILICON CARBIDE AND RELATED MATERIALS. ; , s. 1327-1330, s. 1327-1330
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Book chapter (other academic/artistic)abstract
- A dynamically reduced breakdown voltage from more than 2 kV under static conditions to 300 V during reverse recovery was measured for 4H-SiC p(+)nn(+) diodes. Device simulation indicates that deep hole-trapping donors in the n-base, close the pn junction, could explain the dynamically reduced breakdown voltage. Hole traps situated 0.66 eV above the valence band were found in the diode n-base by DLTS measurements.
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| 20. |
- Domeij, Martin, et al.
(author)
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Dynamic avalanche in 3.3-kV Si power diodes
- 1999
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In: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 46:4, s. 781-786
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Journal article (peer-reviewed)abstract
- Measurements of the safe reverse recovery limit were performed for 3.3-kV Si power diodes using a novel optical experimental technique. In this experiment, influence of the junction termination is effectively eliminated by optical generation of a laterally-localized carrier plasma. The turn-off failures observed in measurements at two temperatures showed no temperature dependence and could not be reproduced in ordinary one-dimensional (1-D) or two-dimensional (2-D) device simulations. To simulate the stability of the current density toward current filamentation, two 1-D diodes with an area ratio 1:19 and a 10% difference in initial carrier plasma level, were simulated in parallel. This resulted in a strongly inhomogeneous current distribution, and a rapid reverse voltage fall resembling the measured turn-off failures. Inhomogeneous current distribution in these simulations appears as the current decay ceases due to impact ionization, in qualitative agreement with a current instability condition proposed by Wachutka [1].
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| 21. |
- Domeij, Martin, et al.
(author)
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Dynamic avalanche in Si power diodes and impact ionization at the nn(+) junction
- 2000
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In: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 44:3, s. 477-485
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Journal article (peer-reviewed)abstract
- The reverse recovery failure limit was measured with an optical technique for power diodes which sustain high levels of dynamic avalanche. Measurements and simulations indicate that these diodes withstand dynamic avalanche at the pn-junction and eventually fail as a result of a strongly inhomogeneous current distribution caused by the onset of impact ionisation at the diode nn(+) junction - a mechanism similar to the reverse bias second breakdown of bipolar transistors.
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| 22. |
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| 23. |
- Domeij, Martin, et al.
(author)
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Stable dynamic avalanche in Si power diodes
- 1999
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 74:21, s. 3170-3172
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Journal article (peer-reviewed)abstract
- A stable dynamic avalanche at a maximum power density of about 2.4 MW/cm(2) was measured in small areas of 3.3 kV Si power diodes, using an optical measurement technique, and very good dynamic ruggedness was verified in a conventional turn-off measurement. Device simulations of a diode with a shallow n(+) emitter indicate that impact ionization at the nn(+) junction can result in negative differential resistance (NDR) and current filamentation, whereas a deep n(+) emitter in the experimentally studied diode suppresses NDR. It is, therefore, proposed that the deep n(+) emitter is important for the stable dynamic avalanche.
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| 24. |
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| 25. |
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| 26. |
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| 27. |
- Palchonok, Gennadij, 1950, et al.
(author)
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Heat transfer in the boundary layer of a circulating fluidized bed boiler
- 1996
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In: Proc of the 8th Engineering Foundation Conference on Fluidization. - 0939204541 ; 8, s. 291-309
-
Conference paper (peer-reviewed)abstract
- The heat transfer coefficient was measured with dark (steel) and light (silver) spherical probes, 5-15 mm in diameter, in a circulating fluidized bed boiler under various operating conditions. The probes were located ar different axial and radial positions in the wall region of the furnace, where fluid dynamic and thermal boundary layers are formed. A model is proposed to connect the measured heat transfer coefficient and its constituents with the local bed characteristics.
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| 28. |
- Palchonok, G.I., et al.
(author)
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Intensification of heat transfer in the freeboard of a circulating fluidized bed: influence of turbulence (In Russian)
- 2000
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In: IV Minsk Int Heat and Mass Transfer Forum, / Borodulya, V.A., Teplitsky, J.C., Vinogradov, L.M., Palchonok, G.I.. - 9856456126 ; 6
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Book chapter (other academic/artistic)
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| 29. |
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| 30. |
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