| 1. |
- Abrahamsson, Maria, et al.
(författare)
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Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl ligands.
- 2008
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Ingår i: Inorganic Chemistry. - : ACS. - 0020-1669 .- 1520-510X. ; 47:9, s. 3540-3548
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Tidskriftsartikel (refereegranskat)abstract
- The structural effect on the metal-to-ligand charge transfer (MLCT) excited-state lifetime has been investigated in bis-tridentate Ru(II)-polypyridyl complexes based on the terpyridine-like ligands [6-(2,2'-bipyridyl)](2-pyridyl)methane (1) and 2-[6-(2,2'-bipyridyl)]-2-(2-pyridyl)propane (2). A homoleptic ([Ru(2)(2)](2+)) and a heteroleptic complex ([Ru(ttpy)(2)](2+)) based on the new ligand 2 have been prepared and their photophysical and structural properties studied experimentally and theoretically and compared to the results for the previously reported [Ru(1)(2)](2+). The excited-state lifetime of the homoleptic Ru-II complex with the isopropylene-bridged ligand 2 was found to be 50 times shorter than that of the corresponding homoleptic Ru-II complex of ligand 1, containing a methylene bridge. A comparison of the ground-state geometries of the two homoleptic complexes shows that steric interactions involving the isopropylene bridges make the coordination to the central Ru-II ion less octahedral in [Ru(2)(2)](2+) than in [Ru(1)(2))(2+). Calculations indicate that the structural differences in these complexes influence their ligand field splittings as well as the relative stabilities of the triplet metal-to-ligand charge transfer ((MLCT)-M-3) and metal-centered ((MC)-M-3) excited states. The large difference in measured excited-state lifetimes for the two homoleptic Ru-II complexes is attributed to a strong influence of steric interactions on the ligand field strength, which in turn affects the activation barriers for thermal conversion from (MLCT)-M-3 states to short-lived (MC)-M-3 states.
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| 2. |
- Cederström, Björn, et al.
(författare)
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Generalized prism-array lenses for hard X-rays
- 2005
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Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 12, s. 340-344
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Tidskriftsartikel (refereegranskat)abstract
- A Fresnel-like X-ray lens can be constructed by a triangular array of identical prisms whose base corresponds to the 2 pi-shift length. Each column of prisms is progressively shifted from the optical axis by an arbitrary fraction of the prism height. Similarly to the multi-prism lens, quasi-parabolic profiles are formed by a superposition of straight-line segments. The resulting projected lens profile is approximately linear with a Fresnel-lens pattern superimposed on it to provide the focusing. This geometry exhibits a significantly larger effective aperture than conventional parabolic refractive lenses. Prototype lenses were fabricated by deep reactive ion etching of silicon. These one-dimensionally focusing lenses were tested at a synchrotron beamline and provided focal line-widths down to 1.4 mu m FWHM and an intensity gain of 39 at a photon energy of 13.4 keV. Fabrication imperfections gave rise to unwanted interference effects resulting in several intensity maxima in the focal plane. The presented design allows the focal length to be shortened without decreasing the feature size of the lens. Furthermore, this feature size does not limit the resolution as for real Fresnel optics.
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| 3. |
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| 4. |
- Chen, Yang, et al.
(författare)
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A NOVEL GAS-WATER HEAT EXCHANGER WITH MINICHANNELS
- 2009
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Ingår i: HT2008. - NEW YORK : AMER SOC MECHANICAL ENGINEERS. - 9780791848487 ; , s. 157-164
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Konferensbidrag (refereegranskat)abstract
- In the current study, a novel gas water heat exchanger with minichannels is designed, built and tested. The heat exchanger is mainly composed of a number of concentric ring shaped plates, which are made tip of several heat exchanger tubes. The ring shaped plates are arranged in parallel and placed in a shell. The heat exchanger is designed as a counter current heat exchanger with laminar flow on the heat exchanger's shell-side (gas side) and therefore has a very low pressure drop on the shell side. The heat exchanger was tested with water and hot air on its tube-side and shell-side respectively. All the necessary parameters like inlet and outlet temperatures on tube-side and shell-side as well as the pressure drop, flow rate of fluids, etc. were measured. Different existing correlations were used to calculate the overall heat transfer coefficient and the results were compared with the measured value. The measured results show that the new designed heat exchanger can achieve a good heat transfer performance and also maintain a low pressure drop on shell-side (gas side).
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| 5. |
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| 6. |
- Enochsson, Ola, et al.
(författare)
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CFRP strengthened openings in two-way concrete slabs : an experimental and numerical study
- 2007
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 21:4, s. 810-826
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Tidskriftsartikel (refereegranskat)abstract
- Rehabilitation and strengthening of concrete structures with externally bonded fibre reinforced polymers (FRPs) has been a viable technique for at least a decade. An interesting and useful application is strengthening of slabs or walls where openings are introduced. In these situations, FRP sheets are very suitable; not only because of their strength, but also due to that they are easy to apply in comparison to traditional steel girders or other lintel systems. Even though many benefits have been shown by strengthening openings with FRPs not much research have been presented in the literature. In this paper, laboratory tests on 11 slabs with openings, loaded with a distributed load are presented together with analytical and numerical evaluations. Six slabs with openings have been strengthened with carbon fibre reinforced polymers (CFRPs) sheets. These slabs are compared with traditionally steel reinforced slabs, both with (four slabs) and without openings (one slab). The slabs are quadratic with a side length of 2.6 m and a thickness of 100 mm. Two different sizes of openings are used, 0.85 × 0.85 m and 1.2 × 1.2 m. The results from the tests show that slabs with openings can be strengthened with externally bonded CFRP sheets. The performance is even better than for traditionally steel reinforced slabs. The numerical and analytical evaluations show good agreement with the experimental results.
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| 7. |
- Fernando, W. Primal D., et al.
(författare)
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A Minichannel Aluminium Tube Heat Exchanger - Part 1 : Evaluation of Single-Phase Heat Transfer Coefficients by the Wilson Plot Method
- 2008
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 31:4, s. 669-680
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Tidskriftsartikel (refereegranskat)abstract
- A prototype liquid-to-refrigerant heat exchanger was developed with the aim of minimizing the refrigerant charge in small systems. To allow correct calculation of the refrigerant side heat transfer, the heat exchanger was first tested for liquid-to-liquid (water-to-water) operation in order to determine the single-phase heat transfer performance. These single-phase tests are reported in this paper. The heat exchanger was made from extruded multiport aluminium tubes and was designed similar to a shell-and-tube heat exchanger. The heat transfer areas of the shell-side and tube-side were approximately 0.82 m(2) and 0.78 m(2), respectively. There were six rectangular-shaped parallel channels in a tube. The hydraulic diameter of the tube-side was 1.42 mm and of the shell-side 3.62 mm. Tests were conducted with varying water flow rates, temperature levels and heat fluxes on both the tube and shell sides at Reynolds numbers of approximately 170-6000 on the tube-side and 1000-5000 on the shell-side, respectively. The Wilson plot method was employed to investigate the heat transfer on both the shell and tube sides. In the Reynolds number range of 2300-6000, it was found that the Nusselt numbers agreed with those predicted by the Gnielinski correlation within +/- 5% accuracy. In the Reynolds number range of 170-1200 the Nusselt numbers gradually increased from 2.1 to 3.7. None of the previously reported correlations for laminar flow predicted the Nusselt numbers well in this range. The shell-side Nusselt numbers were found to be considerably higher than those predicted by correlations from the literature.
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| 8. |
- Fernando, W. Primal D., et al.
(författare)
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A minichannel aluminium tube heat exchanger - Part II : Evaporator Performance with Propane
- 2008
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 31:4, s. 681-695
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents heat transfer data for a multiport minichannel heat exchanger vertically mounted as an evaporator in a test-rig simulating a small water-to-water heat pump. The multiport minichannel heat exchanger was designed similar to a shell-and-tube type heat exchanger, with a six-channel tube of 1.42 mm hydraulic diameter, a tube-side heat transfer area of 0.777 m(2) and a shell-side heat transfer area of 0.815 m(2). Refrigerant propane with a desired vapour quality flowed upward through the tubes and exited with a desired superheat of 1-4 K. A temperature-controlled glycol solution that flowed downward on the shell-side supplied the heat for the evaporation of the propane. The heat transfer rate between the glycol solution and propane was controlled by varying the evaporation temperature and propane mass flow rate while the glycol flow rate was fixed (18.50 l min(-1)). Tests were conducted for a range of evaporation temperatures from -15 to +10 degrees C, heat flux from 2000 to 9000 W m(-2) and mass flux from 13 to 66 kg m(-2) s(-1). The heat transfer coefficients were compared with 14 correlations found in the literature. The experimental heat transfer coefficients were higher than those predicted by many of the correlations. A correlation which was previously developed for a very large and long tube (21 mm diameter and 10 m long) was in good agreement with the experimental data (97% of the data within 30%). Several other correlations were able to predict the data within a reasonable deviation (within 30%) after some adjustments to the correlations.
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| 9. |
- Fernando, W. Primal D., et al.
(författare)
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A minichannel aluminium tube heat exchanger - Part III : Condenser Performance with Propane
- 2008
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 31:4, s. 696-708
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports heat transfer results obtained during condensation of refrigerant propane inside a minichannel aluminium heat exchanger vertically mounted in an experimental setup simulating a water-to-water heat pump. The condenser was constructed of multiport minichannel aluminium tubes assembled as a shell-and-tube heat exchanger. Propane vapour entered the condenser tubes via the top end and exited sub-cooled from the bottom. Coolant water flowed upward on the shell-side. The heat transfer areas of the tube-side and the shell-side of the condenser were 0.941 m(2) and 0.985 m(2), respectively. The heat transfer rate between the two fluids was controlled by varying the evaporation temperature while the condensation temperature was fixed. The applied heat transfer rate was within 3900-9500 W for all tests. Experiments were performed at constant condensing temperatures of 30 degrees C, 40 degrees C and 50 degrees C, respectively. The cooling water flow rate was maintained at 11.90 l min(-1) for all tests. De-superheating length, two-phase length, sub-cooling length, local heat transfer coefficients and average heat transfer coefficients of the condenser were calculated. The experimental heat transfer coefficients were compared with predictions from correlations found in the literature. The experimental heat transfer coefficients in the different regions were higher than those predicted by the available correlations.
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| 10. |
- Fernando, W. Primal D., et al.
(författare)
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Performance of a single-family heat pump at different working conditions using small quantity of propane as refrigerant
- 2007
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Ingår i: Experimental heat transfer. - : Informa UK Limited. - 0891-6152 .- 1521-0480. ; 20:1, s. 57-71
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a domestic heat pump that uses a low quantity of propane as refrigerant has been experimentally investigated. The heat pump consists of two minichannel aluminium heat exchangers, a scroll compressor, and an electronic expansion valve. It was charged with the minimum amount of refrigerant propane required for the stable operation of the heat pump without permitting refrigerant vapor into the expansion valve at incoming heat source fluid temperature to the evaporator of +10 degrees C The inlet temperature of the heat source fluid passing through the evaporator was varied from +10 degrees C to -10 degrees C while holding the condensing temperature constant at 35 degrees C, 40 degrees C, 50 degrees C, and 60 degrees C, respectively. The minimum refrigerant charges required at above-tested condensing temperatures were found to decrease when the condensing temperature increased and were recorded as 230 g, 224 g, 215 g, and 205 g, respectively. The results confirm that a heat pump with 5 kW capacity can be designed with less than 200 g charge of refrigerant propane in the system. Due to the high solubility of propane in compressor lubrication oil, the amount of refrigerant which may escape rapidly in case of accident or leakage is less than 150 g.
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