Drag coefficient of a rising bubble in a shear-thinning fluid using the power-law scheme coupled with a Cahn-Hilliard equation with a variable mobility: A lattice Boltzmann study and comparison with experiment

This study aims to investigate the behavior of multicomponent fluid flows consisting of Newtonian and non-Newtonian components, especially terminal velocity of a rising bubble in a power-law fluid. A recent lattice Boltzmann (LB) model is extended using power-law scheme to be able to simulate both Newtonian and non-Newtonian fluid flows at high density and viscosity ratios. Also, a variable mobility is introduced in this study to minimize the unphysical error around small bubbles in the domain. A three-component fluid flow system is examined using a constant and variable mobility. It is shown that each component has more stability using variable mobility while constant mobility causes interface dissipation, leading to mass loss gradually. In addition, two test cases including power-law fluid flows driven between two parallel plates are conducted to show the accuracy and capability of the model. To find a grid-independent computational domain, a grid independency test is carried out to show that a 200*400 domain size is suitable for our computations. Then, terminal velocity of a rising bubble is compared to an existing correlation in the literature, indicating that the results are in good agreement with existing study so that average relative error in six different cases is 5.66 %. Also, the simulated examples show good conformity to experimental results over a range of the Reynolds and Eotvos numbers

Experimental and Numerical Design and Optimization of a Counter-Flow Heat Exchanger

A new inexpensive counter-flow heat exchanger has been designed and optimized for a vapor-compression cooling system in this research. The main aim is to experimentally and numerically evaluate the effect of an internal heat exchanger (IHX) adaptation in an automotive air conditioning system. In this new design of IHX, the high-pressure liquid passes through the central channel and the low-pressure vapor flows in several parallel channels in the opposite direction. The experimental set-up has been made up of original components of the air conditioning system of a medium sedan car, specially designed and built to analyze vehicle A/C equipment under real operating conditions. The results show that this compact IHX may achieve up to 10% of the evaporator capacity while low pressure drop will be imposed on this refrigeration cycle. Also, they confirm considerable decrease of compressor power consumption (CPC), which is intensified at higher evaporator air flow. A significant improvement of the coefficient of performance (COP) is achieved with the IHX employment too. The influence of operating conditions has been also discussed in this paper. Finally, numerical analyses have been briefly presented, which bring more details of the flow behavior and heat transfer phenomena, and help to determine the optimal arrangement of channels

Experimental and Numerical Design and Optimization of a Counter-Flow Heat Exchanger

A new inexpensive counter-flow heat exchanger has been designed and optimized for a vapor-compression cooling system in this research. The main aim is to experimentally and numerically evaluate the effect of an internal heat exchanger (IHX) adaptation in an automotive air conditioning system. In this new design of IHX, the high-pressure liquid passes through the central channel and the low-pressure vapor flows in several parallel channels in the opposite direction. The experimental set-up has been made up of original components of the air conditioning system of a medium sedan car, specially designed and built to analyze vehicle A/C equipment under real operating conditions. The results show that this compact IHX may achieve up to 10% of the evaporator capacity while low pressure drop will be imposed on this refrigeration cycle. Also, they confirm considerable decrease of compressor power consumption (CPC), which is intensified at higher evaporator air flow. A significant improvement of the coefficient of performance (COP) is achieved with the IHX employment too. The influence of operating conditions has been also discussed in this paper. Finally, numerical analyses have been briefly presented, which bring more details of the flow behavior and heat transfer phenomena, and help to determine the optimal arrangement of channels

Competitive interaction between maize, Xanthium strumarium and Datura stramonium affecting some canopy characteristics

Abstract Field experiments were conducted in 2006 and 2007 to evaluate Xanthium strumarium and Datura stramonium single and multispecies interferences with maize. At different weed densities (4, 8, 12 and 16 plants m -2 ), X. strumarium and D. stramonium were planted in five proportions of 0:100, 25:75, 50:50, 75:25 and 0:100. Monoculture of maize at 6 plant m -2 and pure stands of X. strumarium and D. stramonium at two densities of 4 and 16 plants m -2 were also included. The results showed that X. strumarium is the most competitive weed in mixed plant community of maize, X. strumarium and D. stramonium. Maize, mainly due to its greater height at high density of weeds and because of its greater height and LAI at low density of weeds, was more successful in competition for light than the two weed species. At mixture of X. strumarium and D. stramonium under competition with maize, X. strumarium due to its greater LAI and height, showed greater ability in light interception than the other weed species. Therefore, stronger competitive ability of a weed in competition for light may be attributed to its canopy characteristics e.g. greater height and LAI expansion. In the mixed plant community, these characteristics enable the species to soon occupy the space and capture the common resources i.e. light. To control these weeds in maize, appropriate control measures have to be taken in early growth stages

Effects of Lateral Spacing in Tape Irrigation System on Salinity Distribution in Soil Profile under Wheat Cultivation

Introduction In arid and semi-arid regions, agricultural sustainability needs to improve the consumption of water and soil resources. Low rainfall, high evaporation, low water quality and less leaching of solutes in the soil due to limited water resources are the main problems in these areas. The quality of water and soil resources in the provinces of Fars, Khuzestan, Yazd, Golestan and Khorasan also shows that most of the wheat farming lands in these provinces are always facing salinity issues. According to the conducted studies, saline water can be successfully used in irrigation, but application of unconventional water by surface irrigation systems with low efficiency due to evaporation and high water salts leads to soil salinity. Micro-irrigation methods increase water use efficiency by reducing water consumption and increasing yield, so that drip irrigation efficiency of 91-80% and irrigation levels of 50-73% have been reported. In recent years, the use of drip irrigation system (such as tape on wheat fields) has been recommended to farmers as a water management solution. Micro-irrigation systems by reducing water consumption and increasing yields, improve water use efficiency. Drip tape irrigation system compared to other surface and sprinkler irrigation methods, due to short irrigation periods and reduction of evaporation losses and deep infiltration even for crops can be proposed as an alternative. Drip tape irrigation in wheat cultivation can increase water use efficiency up to 2 times. Also, in irrigation with salt water, while maintaining humidity in the environment, it reduces salinity stress and by consuming less water and reducing the amount of wetting, it introduces less solutes into the soil. This method has limitations in wheat fields due to costs and also the possibility of soil salinity problems, some of which can be overcome by increasing the distance between the laterals and reducing the consumption of drip irrigation (Tape) per unit area.Materials and Methods  In this study, during the 2020-2021 at the Salinity Research Center of Yazd Province (Iran), the effect of lateral distances on the surface and depth distribution of soil salinity was investigated. For this purpose, two irrigation water salinity treatments, including 3 and 8 dS / m and two flood (T1) and drip irrigation systems (Tape) with lateral distances of 60 (T2), 100 (T3) and 140 (T4) cm were considered. Irrigation management treatments included the use of the flooding method (as the dominant method in wheat fields) and the use of the Tape drip irrigation method (as the proposed method with very low water consumption). A distance of 60 cm was considered as the optimal distance with complete water overlap, a distance of 100 cm was considered as an economic distance with the possibility of deep moisture distribution and a distance of 140 cm was considered as a large lateral distance. To investigate the salinity distribution and the accumulation of salts in the soil, regular soil sampling of different treatments was the end of the season.Results and Discussion In all irrigation treatments (saline and non-saline), despite the constant volume of water consumption per unit area of all treatments, in T3 and T4 treatments, irrigation depth increased compared to T2 treatment and reduced soil salinity in the wetting area (irrigated area). By increasing the horizontal distance of each point of the field from the lateral, the irrigation depth and leaching fraction decrease and consequently, the soil salinity of these points can also increase. Under non-saline irrigation conditions (salinity of 3 dS/m), soil salinity at intervals of zero (below the lateral), 15 and 30 cm, between 5.5 and 6.1 dS/m has been observed. Values below the threshold of tolerance to salinity of wheat plant and, in this regard, does not pose a risk to the plant. At a distance of 45, 60 and 70 cm from the water pipe, the salinity of the soil is higher than the threshold and if there is a plant in this area of the field, it will face serious damage.Conclusion  The results showed that although the Tape method in saline conditions (8 dS/m) compared to non-saline conditions (3 dS/m) leads to higher accumulation of solutes in the soil and increases the possibility of plant damage, but according to the final results of this study, by increasing the distances of irrigation laterals and proportionally increasing the depth of irrigation and keeping the salts away from the planting bed, a more suitable environment for plant growth can be prepared and higher economic benefits of this measure can be obtained. Also, in terms of controlling soil salinity, the conditions have been such that treatment with lateral distance of 140 cm compared to treatments of 60 and 100 cm has led to lower amounts of soil salinity in the subsurface and has provided better conditions for the plant. Thus, by increasing the distances of laterals from 60 to 140 cm and, consequently, increasing the depth of irrigation, it was possible to transfer solutes to lower depths of the soil

Evaluation and Estimation of Water Balance Components in Arid Zone Catchments Using RS and GIS Case Study: Manshad Catchment, Yazd Province

Today, water scarcity is one of the main problems around the world, especially in arid and semi arid regions. Iran is a country that is now faced with water scarcity. One of the effective solutions for water management in arid catchments is determination and analysis of water balance components. So this study has focused on determination of water balance components in arid-mountainous catchment of Manshad in Yazd province, during 2006-2007 cropping season. To estimate actual daily evapotranspiration (ETa) of the region, time series of MODIS images were acquired and used via the surface energy balance algorithm for land (SEBAL)methodology. Annual ETa then was calculated in the form of a pixel by pixel basis map. Also annual precipitation (P) and runoff (R) were calculated using rain gauge and hydrometric station records, respectively. Inaddition soil water storage of the catchment was estimated using double ring installation and infiltration rate measures. After determination of annual P and R, the ET component was calculated as the residual of water balance equation. Then the calculated ET was compared with the estimated ET of SEBAL methodology. Comparisons show the adequacy of SEBAL in estimation of actual ET at the studied condition. Finally, the results of the study show that a large portion of catchment available water wastes through evapotranspiration, nearly540 mm. The runoff and soil storage amounts of the studied year are about 117 and125 mm, respectively