Energy
Farhaad Nasiri Khamesloo; Davood Domiri Ganji
Articles in Press, Accepted Manuscript, Available Online from 20 March 2024
Abstract
The dissipation of heat generated in electronic and industrial chips is essential for the health of these components. For this purpose, one of the best choices is a microchannel heatsink, which offers a lower pressure drop compared to other channels while maintaining a high heat transfer rate. In this ...
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The dissipation of heat generated in electronic and industrial chips is essential for the health of these components. For this purpose, one of the best choices is a microchannel heatsink, which offers a lower pressure drop compared to other channels while maintaining a high heat transfer rate. In this study, a fractal microchannel heatsink, introduced in recent years, has been numerically investigated. To enhance the performance of the microchannel, two types of fins have been added to the microchannel walls, resulting in the creation of two new geometries. In the first new geometry, fins are placed at the bottom of the microchannel, while in the second one, fins are placed on the sidewalls of the microchannel. It is worth mentioning that the volume of fins used is consistent across both geometries. Thermal and hydraulic parameters have been examined, revealing that both new geometries increase the Nusselt number, with the highest increase observed in the microchannel with fins on the sidewalls, amounting to 28%. Additionally, both geometries increase the pumping power, with the highest increase observed in the microchannel with fins at the bottom, reaching 120%. Finally, by evaluating the performance coefficient, it was determined that the microchannel with fins on the sidewalls increases the overall performance by 3 to 6% across different flow rates, whereas the microchannel with fins at the bottom reduces the system's performance by 7%. Therefore, for efficient dissipation of the generated heat, it is preferable to use a microchannel heatsink with fins on the sidewalls.
Energy
A. Bagheri; S. Karimian Aliabadi; F. Ommi; K. Ghaemi Osgouie
Abstract
Herein, a non-boiling two-phase flow containing air and water through a downward flow in a vertical tube with helical corrugations has been investigated. In this simulation, various flow rates for air and water are considered, and three corrugation pitches 1, 1.5, and 2 cm are included. It can be seen ...
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Herein, a non-boiling two-phase flow containing air and water through a downward flow in a vertical tube with helical corrugations has been investigated. In this simulation, various flow rates for air and water are considered, and three corrugation pitches 1, 1.5, and 2 cm are included. It can be seen in the results that the pressure drop values decrease with an increase in volume fraction. It should be noted that the reduction of pressure drop values with the reduction of volume fraction (VF) is based on the reduction of the water flow rate, which is visible. By comparing the pressure drop values for each corrugation pitch, it can be seen that as the pitch decreases, the pressure drop values increase significantly. The results for Nusselt number show that Nusselt number decreased with an increase in the volume fraction. By reducing the water flow rate, the intensity of the main flow is reduced the intensity of turbulence is also reduced and the heat transfer coefficient is reduced. Ultimately, the cost-benefit ratio has been utilized to show real results for each studied case.
Energy
A. Mohammadi; M. Hakimizadeh
Abstract
Gas hydrate formation is a new technology to uptake carbon dioxide. In the present work, the kinetics of changes in the volume of unreacted water, the formed carbon dioxide hydrate, and also the unreacted gas inside the reactor were investigated with the passage of time. Experiments were performed in ...
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Gas hydrate formation is a new technology to uptake carbon dioxide. In the present work, the kinetics of changes in the volume of unreacted water, the formed carbon dioxide hydrate, and also the unreacted gas inside the reactor were investigated with the passage of time. Experiments were performed in a stagnant 169 cm3 double-walled reactor at a temperature of 275.15 K and a pressure of 3 MPa. The tests were done by using the isochoric-isothermal method. The results of the experiments showed that the volume of unreacted water decreased with respect to time and the volume of hydrate formed increased. Taking into account the different molar volumes of hydrate formed and the molar volume of reacted water in the test conditions, the changes in gas volume inside the reactor were calculated with the passage of time. The gas volume inside the reactor decreased from 144 cm3 at the beginning of the process to 141.62 cm3 at the end of the reaction. By decreasing the pressure during carbon dioxide hydrate formation process, the amount of hydration number increased from 6.047 mol/mol to 6.109 mol/mol.
Energy
A. Amini; N. M. Nouri; S. Niazi; A. Abedi
Abstract
Surface-piercing propellers (SPP) are known as one of the most efficient propellers in marine sciences and maritime industries. In this study, different types of simulations were performed on an SPP in various rotational speeds in open water conditions, and a numerical study was also carried out on a ...
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Surface-piercing propellers (SPP) are known as one of the most efficient propellers in marine sciences and maritime industries. In this study, different types of simulations were performed on an SPP in various rotational speeds in open water conditions, and a numerical study was also carried out on a particular type of such propellers. In fact the main purpose of this paper is comparing the simulation results with the experimental results from past in order to derive a trustable soultion for future works. For this purpose, the surface-piercing propeller was simulated by OpenFoam software (an open source software with high range of capabilities) in order to analyze the results. The performance curve was then plotted and compared with the ones from open water tests. In this case the turbulance model of K-Epsilon RNG was used which is capable of increasing Y+ to 300 which is monitored at the end of the simulation with the maximum amount of 315 and the average of 80. Results showed that the curves followed the same pattern and trends in the numerical study, and the report pointed to similar findings. In conclusion, it was proved that the sliding mesh method was a proper way for simulating propellers, particularly SPPs. The curves for thrust and torque coefficients of the SPP were also compared with the literature and the efficiency curve was plotted.
Energy
A. Yousefi; R. Shafaghat; M. Beykani; A. Aghajani Afghan; S. T. Seyyed Mostafa
Abstract
Surface piercing propellers are special supercavitation propellers operating at free surface. These propellers are designed to have the best performance at the highest speed. The geometric parameters of the number of blades and the pitch ratio will significantly impact the critical advance coefficient ...
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Surface piercing propellers are special supercavitation propellers operating at free surface. These propellers are designed to have the best performance at the highest speed. The geometric parameters of the number of blades and the pitch ratio will significantly impact the critical advance coefficient range, ventilation and consequently the hydrodynamic performance of the propeller. Therefore, in this paper, the effect of two crucial parameters of pitch ratio and number of blades were experimentally studied in free surface water tunnel. After calibration and evaluation of uncertainty, two 5-bladed propellers with same section profile and pitch ratio of 1.5 and 1.4 used to investigate effect of pitch ratio. The results of two 5-blade and 6-blade propellers with same section profile and pitch ratio of 1.4 were compared. The immersion ratio was 40%, and the shaft inclination angle was zero. Results showed that increasing the pitch ratio increased the thrust and torque coefficients by 30%; while increasing the critical advance coefficient. Consequently that has led to the development of a full ventilation range and improved hydrodynamic performance of the propeller. In addition, by increasing the number of blades, at values greater than the critical advance coefficient, the thrust and torque coefficients were increased by 10%. However, the critical advanced coefficient changes were negligible. Comparing the results in the three-dimensional contours showed that with the change in the number of blades, by increasing the pitch ratio, the critical advance coefficient increased; which led to a further increase in efficiency.
Energy
A. Amini; N. M. Nouri
Abstract
The Surface-Piercing propeller blades move in and out of the water with each rotation to reduce the immersion depth from the free surface to the shaft axis . The main challenge facing surface piercing propellers, however, is their lower efficiency at lower advance velocity, compared to other propulsion ...
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The Surface-Piercing propeller blades move in and out of the water with each rotation to reduce the immersion depth from the free surface to the shaft axis . The main challenge facing surface piercing propellers, however, is their lower efficiency at lower advance velocity, compared to other propulsion systems. To improve the performance of the propeller, an aeration mechanism was used at low advance velocities so that air was blown to the surface behind the propeller. Experimental studies were carried out on a propeller model in the Hydrotech laboratory of the Iran University of Science and Technology, and the effect of the injected air velocity ratio was evaluated at different immersion ratios. Based on the results obtained, it was concluded that an increase in the injected air velocity ratio could only promote thrust enhancement under specific conditions. For immersion ratios of 0.85 and more, as well as advance coefficients of 0.6 and more, a change in the velocity ratio of the injected air could not lead to an improvement in thrust. The best performance was identified with an immersion ratio of 0.4 and an advance coefficient of 0.4, while thrust performance at below or above of this condition declined .
Energy
S. A. Shourehdeli; K. Mobini; A. Asakereh
Abstract
A number of isentropic coefficients are used in the one-dimensional models which predict ejector performance at critical mode. Some of these coefficients have considerable effects on accuracy of the model. These coefficients depend on geometry, working fluid and operating conditions; but, they are usually ...
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A number of isentropic coefficients are used in the one-dimensional models which predict ejector performance at critical mode. Some of these coefficients have considerable effects on accuracy of the model. These coefficients depend on geometry, working fluid and operating conditions; but, they are usually taken constants or are presented as functions of geometry and working condition based on a specific experiment. In this work, the idea of using the flow parameters to determine these coefficients is introduced and has been analyzed. For this purpose, four models with different formulations are employed. The fluid has been considered as a real gas; hence, the models which are based on the ideal gas assumption are modified. The experimental data related to some ejectors with different geometries, working fluids and working conditions have been used. Using the empirical data, correlations between some of the isentropic coefficients and the flow parameters are developed for some models. Using these correlations, entrainment ratios are calculated with the maximum relative error of 35%, while in most cases the maximum relative error is about 10%. However, errors are acceptable since the empirical data are extracted from a vast range of different geometrical and operational conditions.
Energy
N. Tayari; M. Nikpour
Abstract
One of the crucial issues in early stages of designing process of a building is a lack of architects’ knowledge about the energy consumption in different forms of building with different proportions, especially in central courtyard forms. The purpose of this research is to investigate the effectiveness ...
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One of the crucial issues in early stages of designing process of a building is a lack of architects’ knowledge about the energy consumption in different forms of building with different proportions, especially in central courtyard forms. The purpose of this research is to investigate the effectiveness of the ratio of perimeter to the height of the courtyard (R1) and the ratio of width to length of the courtyard (R2) on energy consumption. In the first step of this research, different proportions of central courtyard with different R1 and R2 were simulated in design builder software. Then, multi linear regression was used to find out the effect of different proportions (R1 and R2) on energy consumption through SPSS software. Finally, the effect of R1 and R 2 ratio on energy consumption was validated through investigating six existing central courtyard forms. The result demonstrated that the effective coefficient of the R1 and R2 ratio on energy consumption were -25.41 and 62.69 respectively. Findings of this research help architects to achieve relative acknowledge about the energy consumption of different proportions of the courtyard forms for creating more energy efficient forms.
