Browsing by Subject "HEAT-TRANSFER"

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  • Atashi, Nahid; Rahimi, Dariush; Sinclair, Victoria A.; Zaidan, Martha A.; Rusanen, Anton; Vuollekoski, Henri; Kulmala, Markku; Vesala, Timo; Hussein, Tareq (2021)
    Dew is a non-conventional source of water that has been gaining interest over the last two decades, especially in arid and semi-arid regions. In this study, we performed a long-term (1979-2018) energy balance model simulation to estimate dew formation potential in Iran aiming to identify dew formation zones and to investigate the impacts of long-term variation in meteorological parameters on dew formation. The annual average of dew occurrence in Iran was similar to 102 d, with the lowest number of dewy days in summer (similar to 7 d) and the highest in winter (similar to 45 d). The average daily dew yield was in the range of 0.03-0.14 Lm(-2) and the maximum was in the range of 0.29-0.52 Lm(-2). Six dew formation zones were identified based on cluster analysis of the time series of the simulated dew yield. The distribution of dew formation zones in Iran was closely aligned with topography and sources of moisture. Therefore, the coastal zones in the north and south of Iran (i.e., Caspian Sea and Oman Sea), showed the highest dew formation potential, with 53 and 34 Lm(-2) yr(-2), whereas the dry interior regions (i.e., central Iran and the Lut Desert), with the average of 12-18 Lm(-2) yr(-2), had the lowest potential for dew formation. Dew yield estimation is very sensitive to the choice of the heat transfer coefficient. The uncertainty analysis of the heat transfer coefficient using eight different parameterizations revealed that the parameterization used in this study the Richards (2004) formulation - gives estimates that are similar to the average of all methods and are neither much lower nor much higher than the majority of other parameterizations and the largest differences occur for the very low values of daily dew yield. Trend analysis results revealed a significant (p < 0:05) negative trend in the yearly dew yield in most parts of Iran during the last 4 decades (1979-2018). Such a negative trend in dew formation is likely due to an increase in air temperature and a decrease in relative humidity and cloudiness over the 40 years.
  • Vuollekoski, H.; Vogt, M.; Sinclair, V. A.; Duplissy, J.; Jarvinen, H.; Kyro, E. -M.; Makkonen, R.; Petaja, T.; Prisle, N. L.; Räisänen, P.; Sipila, M.; Ylhaisi, J.; Kulmala, M. (2015)
  • Kakaei Lafdani, Elham; Saarela, Taija; Laurén, Ari; Pumpanen, Jukka; Palviainen, Marjo (2020)
    Biochar can be an effective sorbent material for removal of nutrients from water due to its high specific surface area, porous structure, and high cation and anion exchange capacity. The aim of this study was to test a biochar reactor and to evaluate its efficiency in runoff water purification and consecutive nutrient recycling in clear-cut peatland forests. The goodness of the method was tested in a meso-scale (water volume thousands of liters) reactor experiment by circulating runoff water through wood biochar-filled columns and by determining water nutrient concentrations in the column inlet and outlet. The pseudo-first and second order kinetic models were fitted to the experimental data and the adsorption rate (K-dd) and maximum adsorption capacity (Q(max)) of the biochar reactor were quantified. The concentration of total nitrogen (TN) decreased by 58% during the 8-week experiment; the majority of TN adsorption occurred within the first 3 days. In addition, NO3-N and NH4-N concentrations decreased below the detection limit in 5 days after the beginning of the experiment. The maximum adsorption capacity of the biochar reactor varied between 0.03-0.04 mg g(-1) biochar for NH4-N, and was equal to 0.02 mg g(-1) biochar for TN. The results demonstrated that the biochar reactor was not able to adsorb TN when the water TN concentration was below 0.4 mg L-1. These results suggest that a biochar reactor can be a useful and effective method for runoff water purification in clear-cut forests and further development and testing is warranted. Unlike traditional water protection methods in peatland forestry, the biochar reactor can effectively remove NO3-N from water. This makes the biochar reactor a promising water protection tool to be tested in sites where there is the risk of a high rate of nutrient export after forest harvesting or drainage.