| 1. |
- Moberg, Christina, et al.
(författare)
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De unga gör helt rätt när de stämmer staten
- 2022
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Ingår i: Aftonbladet. - 1103-9000.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 2. |
- Aacharya, Ananta, et al.
(författare)
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Development of a novel solar dryer with an incorporated heat exchanger
- 2024
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Ingår i: Solar Energy. - 0038-092X. ; 269
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Tidskriftsartikel (refereegranskat)abstract
- This study analyzes the thermal performance of an indirect-type solar dryer incorporated with a heat exchanger to recover heat from the exhaust. Data were recorded for 8 h from 9:00 to 17:00 from November to January to determine the drying rate for varying airflows from 2 l/s to 12 l/s under the weather conditions of Nepal and Bhutan. The air temperatures in multiple locations in the dryer were recorded and logged for 30-second intervals. The results indicated that incorporating a simple heat exchanger can achieve 78 % and 81 % effectiveness for the lowest tested airflow of 2.5 l/s and 2 l/s in Nepal and Bhutan. The heat transfer effectiveness increases with decreasing flow, resulting in a higher cold side outlet temperature of the heat exchanger for lower airflows. The solar air collector demonstrated efficient performance, achieving 80 % and 90 % efficiencies for the highest tested airflows of 12 l/s and 10 l/s in Nepal and Bhutan, respectively. Due to an increased heat transfer coefficient, the incoming air can effectively remove the accumulated heat from the absorber plate for higher airflows. The drying rates were observed to be the highest for 12 l/s, with a value of 85 g/(h × m2) for apples and 10 l/s, with a value of 56 g/(h × m2) for gingers in Nepal and Bhutan, respectively. From both cases, it can be concluded that the highest tested airflows provide higher air circulation for effective heat and mass transfer from the product to the surrounding air for drying.
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| 3. |
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| 4. |
- Atongka Tchoffor, Placid, et al.
(författare)
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Effects of Steam on the Release of Potassium, Chlorine, and Sulfur during Char Conversion, Investigated under Dual Fluidized Bed Gasification Conditions
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 28:11, s. 6953-6965
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Tidskriftsartikel (refereegranskat)abstract
- The corrosion and fouling of heat-transfer surfaces and the agglomeration of bed materials in fluidized beds are some of the ash-related problems caused by the transformation and release to the gas phase of ash-forming elements from biomass during thermochemical conversion processes. The magnitudes of these problems are largely dependent upon the release of potassium (K), chlorine (Cl), and sulfur (S) from the biomass. We investigated the effects of steam on the release of K, Cl, and S during char conversion, under conditions relevant for dual-fluidized-bed gasification (DFBG). The study was carried out with wheat straw in a laboratory-scale bubbling fluidized-bed reactor in the temperature range of 800-900 °C. The release of K, Cl, and S from wheat straw during devolatilization, char gasification, and char combustion was quantified with a mass balance that linked the masses of these elements in the wheat straw to the mass of the solid residue obtained at the end of each experiment. To facilitate analyses of the experimental results, leaching and the Brunauer-Emmett-Teller surface area measurement of the wheat straw and some of the solid residues were carried out. The results show that, during devolatilization, the release of volatile salts, e.g., KCl, is significantly limited by intraparticle diffusion resistance, owing to a compact char matrix (i.e., negligible porosity). However, during char gasification, steam renders the char less compact by expanding and/or creating new pores in the char. As a result, intraparticle diffusion resistance decreases, thereby facilitating the evaporation of volatile salts of K and S from the char matrix. The conversion of the char is also conducive to the release of char-bound K and S, especially at 900 °C. At temperatures of >800 °C, the relative proportions of the elements released and char gasified indicate that the release of K can somewhat be decoupled from the release of S and Cl by maximizing the extent of char conversion in the gasification chamber. The results also show that, during char combustion, the proportions of the char that can be combusted and the extent of the release of the elements are influenced by the extent to which the char is gasified in the gasification chamber.
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| 5. |
- Berggren, Björn, et al.
(författare)
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Innovative solution for heat recovery of ventilation air in older apartment buildings - with low intervention affecting the residents
- 2013
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Ingår i: ; , s. 428-438
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Konferensbidrag (refereegranskat)abstract
- Buildings today account for 40% of the world’s primary energy use and 24% of the greenhouse gas emissions. Reducing the energy use in buildings is an important measures to reduce energy dependency and greenhouse gas emissions. In Sweden, there are roughly 2 500 000 dwellings in multifamily houses and single family houses. There is a need to address the energy use within the existing dwellings; especially within multifamily buildings constructed 1960-1975, which accounts for almost one million dwellings or roughly 40 % of the dwelling stock in Sweden. There are good examples of energy renovations of buildings, reducing the energy use by more than 50 %. To reach the energy savings; balanced ventilation with heat recovery was a necessary measure in all projects. However, in all projects; loss of ceiling height in parts of the apartments is a consequence of the measure. Furthermore, it required the residents to temporary move during installment in the majority of the projects. The purpose of this study is to investigate the potential of using a heat exchanger, suitable for natural ventilation, exhaust air ventilation and hybrid ventilation, for installment in the existing building stock in Sweden. A qualitative and quantitative comparison is carried out; comparing mechanical exhaust air ventilation, balanced mechanical ventilation with heat recovery and the heat exchanger suitable for natural ventilation, exhaust air ventilation and hybrid ventilation. The qualitative analysis compares the advantages and disadvantages of the different ventilation system. The quantitative part investigates the potential energy savings and a potential quantity of dwellings where heat recovery may be installed. By installing heat recovery, energy used for space heating may be reduced by roughly 25%. Combining installment of heat recovery with improvement of the building envelope may reduce the energy demand for heating by roughly 75 %. Heat recovery should be able to install in roughly 80 % of the dwellings in the existing dwelling stock, built before 1980.
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| 6. |
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| 7. |
- Berggren, Björn, et al.
(författare)
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Normalisation of Measured Energy Use in Buildings — Need for a Review of the Swedish Regulations
- 2019
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Ingår i: Cold Climate HVAC 2018. CCC 2018. - Cham : Springer International Publishing. - 9783030006617 - 9783030006624 ; , s. 995-995
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Konferensbidrag (refereegranskat)abstract
- Normalisation of measured energy use in buildings is important in order to verify their performance in user phase. Two methods for normalisation have been presented in Sweden, static and dynamic normalisation. The static normalisation considers deviating hot water use, indoor temperature, internal loads and external climate. The dynamic normalisation is based on repeated simulation, meaning that the initial simulation, carried out during the design phase, is repeated with updated conditions regarding actual use of the building and exterior climate. The ratio between the first and second simulation is used as a factor for normalisation. A pre-study has been initiated in Sweden to enable further development of the two methods. This paper present the two methods, the initiated pre-study, and some early findings. The early findings show that there is need for further development of the methods presented.
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| 8. |
- Bernardo, Ricardo, et al.
(författare)
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Combined solar and membrane drying technologies for sustainable fruit preservation in low-income countries – prototype development, modelling, and testing
- 2021
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Ingår i: Solar Energy Advances. - : Elsevier BV. - 2667-1131. ; 1
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Tidskriftsartikel (refereegranskat)abstract
- This investigation consisted of developing and evaluating solar dryers together with semi-permeable membrane pouches for drying juicy fruits in low-income tropical countries. Two design iterations were carried out including prototype modelling and testing. The latest developed solar dryers were a passive and an active solar dryer. Modelling was initially carried out mathematically using an equation solver software followed by computational fluid dynamics. Preliminary measurements were carried out on a small-scale solar dryer. Thereafter, full-scale models were developed and tested, both in laboratory and in real conditions in Mozambique. Results from modelling were validated against measurements in laboratory in Sweden and field trials in Mozambique. Prototype building and testing in Mozambique was undertaken in collaboration with local farmers and a university. Measurement results show that the dryers help to prevent microbial growth through increased temperatures. The drying flux was increased by 50% for the passive, and by 100% for the active solar dryers compared to the ambient controls that did not use a solar dryer. The total drying time was below four days for all pouches in the dryers. The active solar dryer was shown to have the shortest drying time and the highest capacity (more pouches) but also the highest costs. Mould growth and juice fermentation were observed on control pouches drying in open air. These problems were solved with the use of solar dryer technology. However, some challenges with the membrane pouches require further development including degradation of the membrane when exposed to direct sunlight.
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| 9. |
- Bernardo, Ricardo, et al.
(författare)
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Measurements of the Electrical Incidence Angle Modifiers of an Asymmetrical Photovoltaic/Thermal Compound Parabolic Concentrating-Collector
- 2013
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Ingår i: Engineering. - : Scientific Research Publishing, Inc.. - 1947-3931 .- 1947-394X. ; 5, s. 37-43
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Tidskriftsartikel (refereegranskat)abstract
- Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmet-rical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maxi-mum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis.
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| 10. |
- Bernardo, Ricardo, et al.
(författare)
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Measurements of the Electrical Incidence Angle Modifiers of an Asymmetrical Photovoltaic/Thermal Compound Parabolic Concentrating-Collector
- 2013
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Ingår i: Engineering. - 1947-394X. ; 5:1B, s. 37-43
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Tidskriftsartikel (refereegranskat)abstract
- Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmetrical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maximum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis.
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