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- Borgström, Karin Margaretha, 1956-
(author)
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Determination of the thermal conductivity of the insulation in district heating mains : Field measurements
- 1994
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Doctoral thesis (other academic/artistic)abstract
- This thesis concerns the development of a measurement method for determination in the field of the thermal conductivity of the insulation in buried district heating mains. The thermal conductivity of the insulation is calculated from the measured value of the radial heat flow through the heating main, the measured temperature difference across the insulation, and the dimensions of the heating main. The heat flow has been measured with a heat flux sensor which was fitted to the surface of the casing. The temperature has been measured with copper/constantan thermocouples. It is a necessary condition for the method used in the project for determination of the thermal conductivity of the heating main insulation that the heating main is uncovered and is not in contact with the surrounding soil over a distance of about 1.5 m and that the measurements are made directly on the heating main. In this way, no account need be taken of the material surrounding the heating main, nor of the effect of this material on the measurements. No interference is needed with the heating main which would affect the distribution of the district heating water, and the heating main can remain in operation during measurements. Shielding insulation consisting of preformed insulation sections which were placed over the casing of the heating main and covered the heat flux sensor and some of the casing. The function of this insulation was to shield the heat flux sensor from external thermal disturbances. In the field measurements, a copper guard plate of 0.5 mm thickness, the temperature of which could be adjusted, was also placed over the shielding insulation in order to maintain the temperature on the heat flux sensor as constant as possible. When temperature and heat flow are measured, the instruments used will be affected by conditions which prevail at the time of measurement. It is therefore very important to analyse the sources of error which may arise in the measuring situation at hand. The effect of these factors on the measured values has been studied by ' laboratory measurements ' theoretical calculations ' field measurements On the basis of the resulting values of heat flows and temperatures obtained in field measurements on plastic heating mains which were operating under normal conditions, the thermal conductivity of the insulation of the main has been estimated. The method has been tested on plastic heating mains with directly foamed insulation, since this is the most common type of heating main both in the existing district heating network and in new construction. The measuring method can also be used on other circular heating mains.
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| 3. |
- Gellerstedt, Sten
(author)
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Arbete och hälsa vid skogsarbete: En multivariat studie av huggare och maskinförare
- 1993
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Doctoral thesis (other academic/artistic)abstract
- This thesis deals with a model of the influence of work, of individual capacities and on how work affects the individual. The studies are connected to the "work science" tradition. Manual and mechanized forest work with their physical and mental loads are described and analysed. The particular problems that field studies involve are discussed. In conclusion a vision of a future forest work is presented.
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| 4. |
- Karlsson, Krister, 1961-
(author)
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Electronic Structure Calculations: Materials with Weak and Strong Correlations
- 1992
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Doctoral thesis (other academic/artistic)abstract
- This thesis is devoted to studies of various electronic properties which can be extracted from photoemission spectroscopy. Both weakly and strongly correlated systems are discussed, ranging from free electron metal surfaces to strongly correlated copper oxide compounds. In order to study such a variety of systems, different calculational schemes have to be employed. This work is mainly based on band structure calculations using the local density approximation. However, for strongly correlated systems the need for model Hamiltonians is crucial. Subjects discussed are: * inverse photoemission spectra from the Cd(0001) surface obtained by a multiple scattering formalism. The results are in good agreement with recent experimental data. Especially, the one-step model is used to demonstrate image states excitations by secondary beams. * artificial structures, such as semiconductor heterojunctions and short-period superlattices, which are of vital importance for modern electronic devices. A method for tuning the band offset at semiconductor interfaces is proposed; by varying (n,m) for the GaAs/(AlAs)n(GaAs)m interface, the magnitude of the valence band offset can be designed. The metallic superlattice Mo/V was also studied, with emphasis on the application of hydrogen storage. * Schottky barrier heights. Final state screening effects can influence the Schottky barrier height, as deduced from measured core level shifts. According to our calculations, such effects may be of the order 0.1-0.2 eV. * chemical shifts in Cu2O, CuO and NaCuO2, where the Cu atom is formally mono-, di- and trivalent. We find similar chemical shifts between Cu atoms in YBa2Cu3O6.5 as between the Cu atoms in the model compounds. This suggests that different Cu atoms in YBa2Cu3O6.5 are formally mono-, di- and trivalent. The Cu 2p core level spectra were calculated using the Anderson impurity model, with parameters obtained from ab initio calculations. The results are related to the formal valence of Cu, and can be explained by a charge counting argument.
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