The addition of nanoparticles into liquid,even at low concentrations,leads to an increase in both,dynamic viscosity and thermal conductivity.Furthermore,the increase in temperature causes an increase in thermal conduc...The addition of nanoparticles into liquid,even at low concentrations,leads to an increase in both,dynamic viscosity and thermal conductivity.Furthermore,the increase in temperature causes an increase in thermal conductivity and a decrease in the nanofluid viscosity.In this context,a numerical investigation of the competition between viscosity and thermal conductivity about their effects on heat transfer by Al_(2)O_(3)-water nanofluid was conducted.A numerical study of heat transfer in a square cavity,filled with Al_(2)O_(3)-water nanofluid and heated from the left side,was presented in this paper.Continuity,momentum,and thermal energy equations are solved by the finite volume method.Regarding the pressure-velocity coupling,the SIMPLER algorithm was used.The working conditions,allowing the increase of heat transfer,are established.In addition,two correlations for viscosity and thermal conductivity of Al_(2)O_(3)-water nanofluid as functions of the concentration and diameter size based on experimental measurement are proposed.These correlations were more precisely compared to those given by the theoretical models.Moreover,other models for viscosity and conductivity depending on temperature are used and discussed.The results reveal that heat transfer by Al_(2)O_(3)-water nanofluid is enhanced only when the temperature exceeds 40℃ and the diameter size does not exceed a certain limit of the order of 45-50 nm depending on temperature.展开更多
The addition of nanoparticles into liquid,even at low concentrations,leads to an increase in both,dynamic viscosity and thermal conductivity.Furthermore,the increase in temperature causes an increase in thermal conduc...The addition of nanoparticles into liquid,even at low concentrations,leads to an increase in both,dynamic viscosity and thermal conductivity.Furthermore,the increase in temperature causes an increase in thermal conductivity and a decrease in the nanofluid viscosity.In this context,a numerical investigation of the competition between viscosity and thermal conductivity about their effects on heat transfer by Al_(2)O_(3)-water nanofluid was conducted.A numerical study of heat transfer in a square cavity,filled with Al_(2)O_(3)-water nanofluid and heated from the left side,was presented in this paper.Continuity,momentum,and thermal energy equations are solved by the finite volume method.Regarding the pressure-velocity coupling,the SIMPLER algorithm was used.The working conditions,allowing the increase of heat transfer,are established.In addition,two correlations for viscosity and thermal conductivity of Al_(2)O_(3)-water nanofluid as functions of the concentration and diameter size based on experimental measurement are proposed.These correlations were more precisely compared to those given by the theoretical models.Moreover,other models for viscosity and conductivity depending on temperature are used and discussed.The results reveal that heat transfer by Al_(2)O_(3)-water nanofluid is enhanced only when the temperature exceeds 40℃ and the diameter size does not exceed a certain limit of the order of 45-50 nm depending on temperature.展开更多
We report carbon stock in biomass, litter and soil estimated for six locations in natural Quercus ilex L. stands of the Middle and High Moroccan Atlas. Twenty trees at each location were selected according to their di...We report carbon stock in biomass, litter and soil estimated for six locations in natural Quercus ilex L. stands of the Middle and High Moroccan Atlas. Twenty trees at each location were selected according to their diameter classes and felled to measure the biomass of trunk, branches, twigs and leaves and determine allometric relationships. Soil was sampled in five depths (0 - 15, 15 - 30, 30 - 50, 50 - 70 and 70 - 100 cm) and litterfall production measured in all tree stands. The total carbon stock in above-ground biomass ranged between 17 Mg·haǃ in Aït Aamar stand (High Atlas) and 91 Mg·haǃ in Ksiba stand (Middle Atlas). Perennial organs (trunk, branches and twigs) stored over 95% of the tree carbon stock. Soil organic carbon concentrations ranged from 0.01% (in 70 - 100 cm in all stands) to 8.1% (in 0 - 15 cm in the Ajdir stand in Middle Atlas). The total organic carbon stock in the soil ranged between 141.4 t·haǃ in Ajdir and 24.6 t·haǃ in Asloul. The litter contained 0.2 Mg C haǃ in the clearing (C2) stand of High Atlas and 14.3 Mg C haǃ in (Ajdir) of carbon. The best fitted model for predicting carbon stock in tree biomass was obtained by applying the allometric equation Y = aXb for each biomass fraction and stand, where Y is the aboveground biomass (dry weight) and X is the DBH (Mean diameter at breast height, 1.30 m). These previous data obtained in the present study confirm the important function of these natural forests as longterm C sinks, in forest biomass, litter and soil. The potential long term C storage of these systems is moderately high, especially in less-intensively managed forests that include large trees. The established relationship between DBH and carbon stock in different tree organs can be used for forest carbon accounting, and also synthesize available information on oak forest as a sink for atmospheric CO2, and identify the management options that may enhance the capacity for C capture/ storage in forest soils.展开更多
文摘The addition of nanoparticles into liquid,even at low concentrations,leads to an increase in both,dynamic viscosity and thermal conductivity.Furthermore,the increase in temperature causes an increase in thermal conductivity and a decrease in the nanofluid viscosity.In this context,a numerical investigation of the competition between viscosity and thermal conductivity about their effects on heat transfer by Al_(2)O_(3)-water nanofluid was conducted.A numerical study of heat transfer in a square cavity,filled with Al_(2)O_(3)-water nanofluid and heated from the left side,was presented in this paper.Continuity,momentum,and thermal energy equations are solved by the finite volume method.Regarding the pressure-velocity coupling,the SIMPLER algorithm was used.The working conditions,allowing the increase of heat transfer,are established.In addition,two correlations for viscosity and thermal conductivity of Al_(2)O_(3)-water nanofluid as functions of the concentration and diameter size based on experimental measurement are proposed.These correlations were more precisely compared to those given by the theoretical models.Moreover,other models for viscosity and conductivity depending on temperature are used and discussed.The results reveal that heat transfer by Al_(2)O_(3)-water nanofluid is enhanced only when the temperature exceeds 40℃ and the diameter size does not exceed a certain limit of the order of 45-50 nm depending on temperature.
文摘The addition of nanoparticles into liquid,even at low concentrations,leads to an increase in both,dynamic viscosity and thermal conductivity.Furthermore,the increase in temperature causes an increase in thermal conductivity and a decrease in the nanofluid viscosity.In this context,a numerical investigation of the competition between viscosity and thermal conductivity about their effects on heat transfer by Al_(2)O_(3)-water nanofluid was conducted.A numerical study of heat transfer in a square cavity,filled with Al_(2)O_(3)-water nanofluid and heated from the left side,was presented in this paper.Continuity,momentum,and thermal energy equations are solved by the finite volume method.Regarding the pressure-velocity coupling,the SIMPLER algorithm was used.The working conditions,allowing the increase of heat transfer,are established.In addition,two correlations for viscosity and thermal conductivity of Al_(2)O_(3)-water nanofluid as functions of the concentration and diameter size based on experimental measurement are proposed.These correlations were more precisely compared to those given by the theoretical models.Moreover,other models for viscosity and conductivity depending on temperature are used and discussed.The results reveal that heat transfer by Al_(2)O_(3)-water nanofluid is enhanced only when the temperature exceeds 40℃ and the diameter size does not exceed a certain limit of the order of 45-50 nm depending on temperature.
文摘We report carbon stock in biomass, litter and soil estimated for six locations in natural Quercus ilex L. stands of the Middle and High Moroccan Atlas. Twenty trees at each location were selected according to their diameter classes and felled to measure the biomass of trunk, branches, twigs and leaves and determine allometric relationships. Soil was sampled in five depths (0 - 15, 15 - 30, 30 - 50, 50 - 70 and 70 - 100 cm) and litterfall production measured in all tree stands. The total carbon stock in above-ground biomass ranged between 17 Mg·haǃ in Aït Aamar stand (High Atlas) and 91 Mg·haǃ in Ksiba stand (Middle Atlas). Perennial organs (trunk, branches and twigs) stored over 95% of the tree carbon stock. Soil organic carbon concentrations ranged from 0.01% (in 70 - 100 cm in all stands) to 8.1% (in 0 - 15 cm in the Ajdir stand in Middle Atlas). The total organic carbon stock in the soil ranged between 141.4 t·haǃ in Ajdir and 24.6 t·haǃ in Asloul. The litter contained 0.2 Mg C haǃ in the clearing (C2) stand of High Atlas and 14.3 Mg C haǃ in (Ajdir) of carbon. The best fitted model for predicting carbon stock in tree biomass was obtained by applying the allometric equation Y = aXb for each biomass fraction and stand, where Y is the aboveground biomass (dry weight) and X is the DBH (Mean diameter at breast height, 1.30 m). These previous data obtained in the present study confirm the important function of these natural forests as longterm C sinks, in forest biomass, litter and soil. The potential long term C storage of these systems is moderately high, especially in less-intensively managed forests that include large trees. The established relationship between DBH and carbon stock in different tree organs can be used for forest carbon accounting, and also synthesize available information on oak forest as a sink for atmospheric CO2, and identify the management options that may enhance the capacity for C capture/ storage in forest soils.
