| 1. |
- Cao, Jing, et al.
(författare)
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Demonstration of Spectral Phase O-CDMA Encoding and Decoding in Monolithically Integrated Arrayed-Waveguide-Grating-Based Encoder
- 2006
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 18:21-24, s. 2602-2604
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Tidskriftsartikel (refereegranskat)abstract
- We report on successful spectral phase encoding and decoding operation in a pair of monolithically integrated InP encoder chips, each consisting of an arrayed waveguide grating (AWG) pair and an eight-channel electrooptic phase shifter array. The monolithic fabrication process includes anisotropic reactive ion etching and planarizing hydride-vapor-phase-epitaxy lateral regrowth to realize buried hetero-waveguide structures in AWGs and phase shifters. Electrooptical modulation in the phase shifter arrays in the encoder chip achieved Walsh-code-based optical code-division multiple access (O-CDMA) encoding and decoding. The matched-code encoding-decoding operation resulted in error-free performance in the presence of an interferer, indicating good potential for O-CDMA network applications.
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| 2. |
- Cao, Zhen, et al.
(författare)
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Electrophoretic deposition surfaces to enhance HFE-7200 pool boiling heat transfer and critical heat flux
- 2019
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Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 146
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Tidskriftsartikel (refereegranskat)abstract
- Modulated nanoparticle-coating surfaces were fabricated by an improved electrophoretic deposition technique in this study. Pool boiling experiments were studied for HFE-7200 on the modulated nanoparticle-coating surfaces, with a smooth surface and uniform coating surfaces as comparison. It was found that the present modulated coating surfaces can enhance the heat transfer coefficient and the critical heat flux by 60% and 20%–40%, respectively, in comparison to the smooth surface, while the uniform coating surface can improve heat transfer coefficients by maximum 100%, but cannot enhance critical heat fluxes. Heat transfer on the modulated nanoparticle-coating surfaces was theoretically analyzed by a mechanistic model which considered free convection, transient conduction and microlayer evaporation. The heat transfer can be predicted by the model, especially at low-to-moderate heat fluxes. Additionally, referring to the bubble visualization at critical heat fluxes, possible mechanisms to trigger critical heat fluxes were discussed. Afterwards, a critical heat flux model originating from the Zuber hydrodynamic instability model, was employed to predict the experimental results, showing a good prediction ability.
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| 3. |
- Cao, Zhen, et al.
(författare)
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Enhancement of HFE-7200 pool boiling heat transfer on copper surfaces with nanoparticle coatings
- 2018
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Ingår i: Proceeding: International Heat Transfer Conference 16. - 2377-424X. ; , s. 1341-1347
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Konferensbidrag (refereegranskat)abstract
- Saturated pool boiling heat transfer of HFE-7200 is investigated experimentally on copper surfaces with nanoparticle coatings at atmospheric pressure. The coatings are generated by an electrophoretic deposition method. Two modified surfaces are prepared with Cu-Zinc nanoparticles of 0.3 mg and 0.6 mg, respectively. During the deposition, ethanol works as the solvent while the electrical potential and deposition time are controlled as 9.5 V and 30 min, respectively. The experimental results show heat transfer is considerably enhanced by the nanoparticle coatings. The surface with 0.6 mg nanoparticles (EDS-2) performs better than the surface with 0.3 mg nanoparticles (EDS-1), and a maximum 140% heat transfer enhancement is achieved on the surface EDS-2 compared with the SS. However, the critical heat flux is not enhanced by the coatings but even slightly decreased. A high speed visualization is employed to capture bubble behavior. It is found that bubbles on EDS-1 and EDS-2 have smaller sizes and higher departure frequency than those on the SS before reaching the critical heat flux. However, at critical heat fluxes, a vapor blanket appears on all surfaces.
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| 4. |
- Cao, Zhen, et al.
(författare)
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Enhancement of HFE-7200 pool boiling heat transfer on copper surfaces with nanoparticle coatings
- 2018
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Ingår i: International Heat Transfer Conference 16. - Connecticut : Begell House. - 9781567004748 - 9781567004731 ; , s. -1347
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Konferensbidrag (refereegranskat)abstract
- Saturated pool boiling heat transfer of HFE-7200 is investigated experimentally on copper surfaces with nanoparticle coatings at atmospheric pressure. The coatings are generated by an electrophoretic deposition method. Two modified surfaces are prepared with Cu-Zinc nanoparticles of 0.3 mg and 0.6 mg, respectively. During the deposition, ethanol works as the solvent while the electrical potential and deposition time are controlled as 9.5 V and 30 min, respectively. The experimental results show heat transfer is considerably enhanced by the nanoparticle coatings. The surface with 0.6 mg nanoparticles (EDS-2) performs better than the surface with 0.3 mg nanoparticles (EDS-1), and a maximum 140% heat transfer enhancement is achieved on the surface EDS-2 compared with the SS. However, the critical heat flux is not enhanced by the coatings but even slightly decreased. A high speed visualization is employed to capture bubble behavior. It is found that bubbles on EDS-1 and EDS-2 have smaller sizes and higher departure frequency than those on the SS before reaching the critical heat flux. However, at critical heat fluxes, a vapor blanket appears on all surfaces.
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| 5. |
- Cao, Zhen, et al.
(författare)
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Nucleate pool boiling heat transfer of acetone and HFE7200 on copper surfaces with nanoparticle coatings
- 2019
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 158, s. 5872-5879
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Tidskriftsartikel (refereegranskat)abstract
- Nucleate pool boiling performance of two well-wetting liquids, i.e., acetone and HFE7200, on three nanoparticle-coatedsurfaces were experimentally studied and compared with that of the smoothsurface. Electrophoretic deposition was used to fabricate nano-porous surfaces.Surface roughness, static and advancing contact angles, capillarity of the smoothand coated surfaces were characterized. Compared to the smooth surface, thenanoparticle-coated surfaces decreased the wall superheat by more than 50% foracetone and 65% for HFE7200 at the same heat flux level, and accordinglyenhanced the heat transfer coefficient by up to 85% for acetone and up to 200%for HFE7200. Bubble departure diameters were measured and correlated with theadvancing contact angle, the capillary length and the Jacob number. A newmechanistic heat transfer model was proposed based on the heat flux partitionmethod. The advancing contact angle was suggested to be used for calculation ofthe active nucleation site density. Based on the mechanistic model, transientheat conduction on and around nucleation sites over the whole bubble cyclecontributes the most (>70%) to the total heat flux, while microlayerevaporation contributes around 10-30% to the total heat flux, with negligiblenatural convection. The critical heat flux was not enhanced for the twowell-wetting liquids.
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| 6. |
- Cao, Zhen, et al.
(författare)
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Pool boiling heat transfer enhancement of water by gold nanoparticles with an electrophoretic deposition method
- 2019
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Ingår i: Proceedings of the Asme International Mechanical Engineering Congress and Exposition, 2018, vol 8b. - : Amer Soc Mechanical Engineers. - 9780791852125
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Saturated pool boiling heat transfer of water is investigated experimentally on copper surfaces with nanoparticle coatings at atmospheric pressure. The coatings are generated by an electrophoretic deposition method (EPD). Three modified surfaces are prepared with gold nanoparticles of 0.20 mg, 0.25 mg and 0.30 mg, respectively. During the deposition, ethanol works as the solvent while the electrical potential and deposition time are controlled as 9.5 V and 30 min, respectively. The experimental results show that heat transfer coefficients (HTC) and critical heat fluxes (CHF) are enhanced on the modified surfaces. HTC increases with decreasing thickness of the coating, while CHF increases with increasing thickness of the coating. CHFs of EPD-0.20 mg, EPD-0.25 mg and EPD-0.30 mg are 93 W/cm2, 123 W/cm2 and 142 W/cm2, respectively, which are increased by 7%, 41% and 63% compared with the smooth surface. EPD-0.20 mg performs the best on heat transfer, with a maximum enhancement of around 60%. At the end, a brief review about mechanistic models of heat transfer at low and moderate heat fluxes is provided, based on which, the reasons why heat transfer is enhanced are discussed.
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| 7. |
- Cao, Zhen, et al.
(författare)
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Pool boiling of HFE-7200 on nanoparticle-coating surfaces: Experiments and heat transfer analysis
- 2018
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 133, s. 548-560
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, an electrophoretic deposition method was employed to modify copper surfaces withCu-Zn (100 nm) nanoparticles. Pool boiling heat transfer of HFE-7200 on the modified surfaces was experimentally studied. The results showed that the heat transfer coefficient on the modified surfaces was significantly enhanced compared with that on a smooth surface, e.g., a maximum 100% enhancement,while the maximum superheat on the modified surfaces was around 20 K lower than that on the smooth surface. However, the critical heat flux (CHF) was not improved considerably, and supplementary tests indicated that the wickability of HFE-7200 was almost the same on the modified surfaces and the smooth surface. The departure diameters of bubbles were recorded by a high speed camera, which were compared with several models in literature. Active nucleation site sizes were evaluated by the Hsu nucleation theory and active nucleation site densities were estimated by appropriate correlations.In addition, a heat transfer model, considering natural convection, re-formation of thermal boundary layer and microlayer evaporation, was formulated to predict the heat transfer on the modified surfaces and the smooth surface. A relatively good prediction was achieved.
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| 8. |
- Liu, Bin, et al.
(författare)
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Pool boiling heat transfer of N-pentane on micro/nanostructured surfaces
- 2018
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Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 130, s. 386-394
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, one type of uniformly nanostructured surface (NPDS) was modified by electrophoretic deposition. Two kinds of micro/nanostructured surfaces (FLS1 and FLS2) were fabricated on copper surfaces by femtosecond laser processing. The micro/nanostructured surfaces were further modified by electrophoretic deposition. Afterwards, composite micro/nanostructured surfaces (CS1 and CS2) were developed. Saturated pool boiling heat transfer of the modified surfaces was investigated experimentally. An organic fluid, n-pentane was chosen as the working liquid. Heat transfer coefficient and critical heat flux (CHF) of smooth and micro/nanostructured surfaces were studied. The results showed that the heat transfer coefficient (HTC) of all structured surfaces increased obviously with a notable decrease of wall superheat at CHF compared to the smooth surface, which was attributed to increments in nucleation site density and heat transfer area. The CHF of femtosecond laser processed surfaces was also increased compared with the smooth surface due to a much higher liquid spreading ability, while a uniformly nanostructured surface has no augmentation in CHF. Composite micro/nanostructured surfaces show the best heat transfer performance among all tested surfaces, and the critical heat flux and heat transfer coefficient were increased by more than 60% and 300% over the smooth surface, respectively. The liquid spreading ability of n-pentane on the tested surfaces was measured. For the well wetting liquid, the liquid spreading ability of the heated surface, instead of the wettability, is the main factor for CHF enhancement. It is suggested that a surface with multiscale structures can be an efficient way for boiling heat transfer enhancement.
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| 9. |
- Stanaway, Jeffrey D., et al.
(författare)
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Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990-2017: A systematic analysis for the Global Burden of Disease Study 2017
- 2018
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Ingår i: The Lancet. - 1474-547X .- 0140-6736. ; 392:10159, s. 1923-1994
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Tidskriftsartikel (refereegranskat)abstract
- Background The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 comparative risk assessment (CRA) is a comprehensive approach to risk factor quantification that offers a useful tool for synthesising evidence on risks and risk-outcome associations. With each annual GBD study, we update the GBD CRA to incorporate improved methods, new risks and risk-outcome pairs, and new data on risk exposure levels and risk- outcome associations. Methods We used the CRA framework developed for previous iterations of GBD to estimate levels and trends in exposure, attributable deaths, and attributable disability-adjusted life-years (DALYs), by age group, sex, year, and location for 84 behavioural, environmental and occupational, and metabolic risks or groups of risks from 1990 to 2017. This study included 476 risk-outcome pairs that met the GBD study criteria for convincing or probable evidence of causation. We extracted relative risk and exposure estimates from 46 749 randomised controlled trials, cohort studies, household surveys, census data, satellite data, and other sources. We used statistical models to pool data, adjust for bias, and incorporate covariates. Using the counterfactual scenario of theoretical minimum risk exposure level (TMREL), we estimated the portion of deaths and DALYs that could be attributed to a given risk. We explored the relationship between development and risk exposure by modelling the relationship between the Socio-demographic Index (SDI) and risk-weighted exposure prevalence and estimated expected levels of exposure and risk-attributable burden by SDI. Finally, we explored temporal changes in risk-attributable DALYs by decomposing those changes into six main component drivers of change as follows: (1) population growth; (2) changes in population age structures; (3) changes in exposure to environmental and occupational risks; (4) changes in exposure to behavioural risks; (5) changes in exposure to metabolic risks; and (6) changes due to all other factors, approximated as the risk-deleted death and DALY rates, where the risk-deleted rate is the rate that would be observed had we reduced the exposure levels to the TMREL for all risk factors included in GBD 2017.
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| 10. |
- Wu, Zan, et al.
(författare)
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Pool boiling heat transfer of n -pentane and acetone on nanostructured surfaces by electrophoretic deposition
- 2019
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Ingår i: Proceedings of the Asme International Mechanical Engineering Congress and Exposition, 2018, vol 8b. - : Amer Soc Mechanical Engineers. - 9780791852125
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Konferensbidrag (refereegranskat)abstract
- This work aims to investigate pool boiling heat transfer enhancement by using nanostructured surfaces. Two types of nanostructured surfaces were employed, gold nanoparticlecoated surfaces and alumina nanoparticle-coated surfaces. The nanostructured surfaces were fabricated by an electrophoretic deposition technique, depositing nanoparticles in a nanofluid onto smooth copper surfaces under an electric field. N -pentane and acetone were tested as working fluids. Compared to the smooth surface, the pool boiling heat transfer coefficient has been increased by 80% for n -pentane and acetone. Possible mechanisms for the enhancement in heat transfer are qualitatively provided. The increase in active nucleation site density due to multiple micro/nanopores on nanoparticle-coated surfaces is likely the main contributor. The critical heat flux on nanostructured surfaces are approximately the same as that on the smooth surface because both smooth and modified surfaces show similar wickability for the two working fluids.
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