| 1. |
- Risberg, Daniel, et al.
(författare)
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CFD modelling of radiators in buildings with user defined wall functions
- 2016
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 64, s. 266-273
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Tidskriftsartikel (refereegranskat)abstract
- The most widely used turbulence model for indoor CFD simulations, the k-ε model, has exhibited problems with treating natural convective heat transfer, while other turbulence models have shown to be too computationally demanding. This paper studies how to deal with natural convective heat transfer for a radiator in order to simplify the simulations, reduce the numbers of cells and the simulation time. By adding user-defined wall functions the number of cells can be reduced considerably compared with the k-ω SST turbulence model. The user-defined wall function proposed can also be used with a correction factor for different radiator types without the need to resolve the radiator surface in detail. Compared to manufacturer data the error is less than 0.2% for the investigated radiator height and temperature.
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| 2. |
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| 3. |
- Risberg, Daniel, et al.
(författare)
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Investigation of thermal indoor climate for a passive house in a sub-Arctic region using computational fluid dynamics
- 2019
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Ingår i: Indoor + Built Environment. - : Sage Publications. - 1420-326X .- 1423-0070. ; 28:5, s. 677-692
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Tidskriftsartikel (refereegranskat)abstract
- There is currently an increasing trend in Europe to build passive houses. In order to reduce the cost of installation, an air-heating system may be an interesting alternative. Heat supplied through ventilation ducts located at the ceiling was studied with computational fluid dynamics technique. The purpose was to illustrate the thermal indoor climate of the building. To validate the performed simulations, measurements were carried out in several rooms of the building. Furthermore, this study investigated if a designed passive house located above the Arctic Circle could fulfil heat requirements for a Swedish passive house standard. Our results show a heat loss factor of 18.8 W/m2 floor area and an annual specific energy use of 67.9 kWh/m2 floor area, would fulfils the criteria. Validation of simulations through measurements shows good agreement with simulations if the thermal inertia of the building was considered. Calculation of heat losses from a building with a backward weighted moving average outdoor temperature produced correct prediction of the heat losses. To describe the indoor thermal climate correctly, the entire volume needs to be considered, not only one point, which normally is obtained with building simulation software. The supply airflow must carefully be considered to fulfil a good indoor climate.
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| 4. |
- Risberg, Daniel, et al.
(författare)
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The impact of snow and soil freezing for commonly used foundation types in a subarctic climate
- 2018
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Ingår i: Energy and Buildings. - : Elsevier. - 0378-7788 .- 1872-6178. ; 173, s. 268-280
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Tidskriftsartikel (refereegranskat)abstract
- Heat losses from a building foundation are affected by both the surrounding conditions and the surrounding soil properties. These include many factors that complicate the analysis of heat loss, such as thermal storage, snow and soil freezing. The effect of snow and soil freezing was studied with a 3D simulation model in a subarctic climate.The heat losses from the most commonly used foundation types in Sweden were studied. This paper shows that it is possible to achieve a good thermal estimation of the air temperatures in a crawl space, with an average difference of 0.4°C compared with the validation data over a year. Snow and soil freezing reduce the annual heat losses through the different foundation types by 7-10% and the maximum heat loss rate by 13-25%. In order to describe the heat transfer correctly, snow must be included in the calculations, while soil freezing has only a minor impact. The 3D model implemented in this study shows a significant impact on the soil temperatures when these parameters are included.For a subarctic climate, the commonly used calculation methods based on the European standard ISO 13370 are not thorough enough to calculate the heat transfer through a foundation accurately.
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| 5. |
- Risberg, Mikael, et al.
(författare)
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Numerical calculation of heat losses for crawl space foundation at different locations in Sweden
- 2020
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Ingår i: Results in Engineering. - : Elsevier. - 2590-1230. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Crawl space is one of the most common foundation types in Sweden, and over five hundred thousand family houses have this type of foundation. This study determines how the heat losses variate at six different locations in Sweden from the south to the north. The average heat for a year varied between 1.76 and 3.07 W/m2. The maximum heat flux was 4.43 W/m2 in Kiruna, while Falsterbo has a maximum heat flux of 3.18 W/m2. Minimum heat flux varied between 0.43 and 1.38 W/m2. A sensitivity study of the important parameter showed that the temperature is the most important parameter with a decrease in average heat flux of 0.15 W/m2 per degree increase in air temperature. Snow depth and snow days are less sensitive and give less than a 2.3% decrease for the average heat flux with a variation of ±50% and ±20 days, respectively.
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| 6. |
- Abubaker, Jamal, et al.
(författare)
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Biogas residues as fertilisers - Effects on wheat growth and soil microbial activities
- 2012
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 99, s. 126-134
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Tidskriftsartikel (refereegranskat)abstract
- Residues from the biogas process are a relatively new type of organic fertiliser with composition varying with origin of the raw material fed into the biogas process. The performance of four different biogas residues (BRs) was evaluated and compared with that of pig slurry (PS) and mineral fertiliser (NPK) in pots filled with sandy soil and fertilised at rates corresponding to 35,70 and 140 kg NH4+-N ha(-1). After sowing with spring wheat, the pots were incubated in a growth chamber. Total biomass yield and relative yields of ear, straw and root fractions were measured at harvest. Nitrogen mineralisation capacity (NMC) and potential ammonium oxidation rate (PAO) in soil were assessed. The fertilisation based on NH4+-N led to high addition of Tot C, Org N, Tot P, Tot K, Tot Mg and Zn at application of PS compared with BR. Biomass yields generally increased with increasing fertiliser rate but the response varied between the fertilisers. The BR yields compared well with NPK, but PS resulted in significantly higher yields. PS gave lower relative biomass of ears and higher relative biomass of roots compared with BR and NPK. The BR treatment yielding the lowest overall biomass also produced plants with the lowest relative root biomass, but partly compensated for this by increasing the relative ear biomass with increasing fertiliser rate. The NMC and PAO in soil had increased by the end of the experiment in almost all treatments. The high NMC in the PS treatment resulted in calculated mineralised N corresponding to 50-82 kg ha(-1) during the experimental period. In conclusion, fertilisation with biogas residues gave similar biomass yields but increased NMC and PAO in soil compared with NPK. Pig slurry gave the overall highest yields and NMC, but a PAO comparable to most BR. (C) 2012 Elsevier Ltd. All rights reserved.
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| 7. |
- Abubaker, Jamal, et al.
(författare)
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Short-Term Effects of Biogas Digestates and Pig Slurry Application on Soil Microbial Activity
- 2015
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Ingår i: Applied and Environmental Soil Science. - : Hindawi Limited. - 1687-7667 .- 1687-7675. ; 2015, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- The effect of four biogas digestates (BD-A, BD-B, BD-C, and BD-D) and pig slurry (PS) on soil microbial functions was assessed at application rates corresponding to 0–1120 kg-N ha−1. At dose corresponding to 140 kg-N ha−1, 30.9–32.5% of the carbon applied in BD-A, BD-C, and PS was utilized during 12 days, while for BD-B and BD-D corresponding utilization was 19.0 and 16.9%, respectively. All BDs resulted in net nitrogen assimilation at low rates (17.5–140 kg-N ha−1) but net mineralization dominated at higher rates. PS resulted in net mineralization at all application rates. All residues inhibited potential ammonium oxidation (PAO), with EC50-values ranging between 45 and 302 kg-N ha−1. Low rates of BDs appeared to weakly stimulate potential denitrification activity (PDA), while higher rates resulted in logarithmic decrease. The EC50-values for PDA were between 238 and 347 kg-N ha−1. No inhibition of PDA was observed after amendment with PS. In conclusion, biogas digestates inhibited ammonia oxidation and denitrification, which could be an early warning of potential hazardous substances in the digestates. However, this effect can also be regarded as positive, since it may reduce nitrogen losses.
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| 8. |
- Carlsson, Per, et al.
(författare)
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Spatially resolved measurements of gas composition in a pressurised black liquor gasifier
- 2009
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Ingår i: Environmental Progress & Sustainable Energy. - : Wiley. - 1944-7442 .- 1944-7450. ; 28:3, s. 316-323
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Tidskriftsartikel (refereegranskat)abstract
- Black liquor gasification is a new process for recovery of energy and chemicals in black liquor from the Kraft pulping process. The process can be combined with catalytic conversion of syngas into motor fuels. The potential for motor fuel production from black liquor in Sweden is to replace about 25% of the current consumption ofgasoline and diesel. For Finland the figure is even higher while for Canada it is about 14% and for the USA about 2%. © 2009 American Institute of Chemical Engineers Environ Prog, 28: 316-323, 2009.
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| 9. |
- Chen, Jingjing, et al.
(författare)
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A high efficient heat exchanger with twisted geometries for biogas process with manure slurry
- 2020
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Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- Heat-transfer enhancement in manure slurry is crucial for increasing the efficiency and production of biogas during anaerobic digestion in biogas plants. In this study, a novel heat exchanger with an optimal twisted geometry was developed based on the numerical screening of the twisted tubes with equilateral polygons, and experiments were conducted to validate the numerical results. It was observed that the SST k-ω model is more efficient than other turbulence models in representing the heat transfer performance of the twisted tubes, and the numerical model with a thermostatic wall can be used to reliably screen the twisted geometries. The twisted hexagonal tube has the optimal geometry, with enhancement capability of up to 1.4 times compared to that of the circular tube. The formation of high continuity regions with relatively strong heat-transfer rates along the heat-exchange wall is the main reason for the high performance during heat transfer. The external heating process was integrated in a full-scale biogas plant, and the model and algorithm were developed and validated with additional experiments to describe the overall performance of both conventional and screened optimal geometries under different conditions. It was observed that a profit equivalent to 39% of total production for a large-scale biogas plant can be achieved owing to energy conservation in external heating with the twisted hexagonal tubes.
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| 10. |
- Chen, Jingjing, et al.
(författare)
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Heat-transfer performance of twisted tubes for highly viscous food waste slurry from biogas plants
- 2022
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Ingår i: Biotechnology for Biofuels and Bioproducts. - : Springer Nature. - 2731-3654. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Background: The use of food waste as feedstock shows high production of biogas via anaerobic digestion, but requires efficient heat transfer in food waste slurry at heating and cooling processes. The lack of rheological properties hampered the research on the heat-transfer process for food waste slurry. Referentially, the twisted hexagonal and elliptical rubes have been proved as the optimal enhanced geometry for heat transfer of medium viscous slurries with non-Newtonian behavior and Newtonian fluids, respectively. It remains unknown whether improvements can be achieved by using twisted geometries in combination with food waste slurry in processes including heating and cooling.Results: Food waste slurry was observed to exhibit highly viscous, significant temperature-dependence, and strongly shear-thinning rheological characteristics. Experiments confirmed the heat-transfer enhancement of twisted hexagonal tubes for food waste slurry and validated the computational fluid dynamics-based simulations with an average deviation of 14.2%. Twisted hexagonal tubes were observed to be more effective at low-temperature differences and possess an enhancement factor of up to 2.75; while twisted elliptical tubes only exhibited limited heat-transfer enhancement at high Reynolds numbers. The heat-transfer enhancement achieved by twisted hexagonal tubes was attributed to the low dynamic viscosity in the boundary layer induced by the strong and continuous shear effect near the walls of the tube.Conclusions: This study determined the rheological properties of food waste slurry, confirmed the heat-transfer enhancement of the twisted hexagonal tubes experimentally and numerically, and revealed the mechanism of heat-transfer enhancement based on shear rate distributions.
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