Computational Fluid Dynamics (CFD)
Atie Farrokh; Miralam Mahdi
Abstract
Chillers are among the most widely used air-conditioning systems, and improving their thermal performance can significantly reduce energy consumption. In the present study, the effects of Al₂O₃/water and Al₂O₃–TiO₂/water nanofluids on the performance characteristics of a shell-and-tube ...
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Chillers are among the most widely used air-conditioning systems, and improving their thermal performance can significantly reduce energy consumption. In the present study, the effects of Al₂O₃/water and Al₂O₃–TiO₂/water nanofluids on the performance characteristics of a shell-and-tube chiller evaporator were numerically investigated using an Eulerian-Lagrangian Discrete Phase Model (DPM). The influences of nanoparticle volume fraction, inlet fluid temperature, evaporator temperature, mass flow rate, and number of baffles were examined. Three evaporator configurations with 3, 5, and 7 baffles were considered.The results showed that increasing the number of baffles from 5 to 7 enhanced the overall heat transfer coefficient by 6.94%. The addition of Al₂O₃ nanoparticles increased the overall heat transfer coefficient by 5.8%, while the use of Al₂O₃–TiO₂ hybrid nanoparticles resulted in an enhancement of up to 8.8%. Analysis of the performance evaluation criterion (PEC) indicated that nanoparticle volume fractions up to 0.03 provide favorable thermal performance, with an optimum value around 0.02. The results also demonstrated a significant difference between the DPM and conventional single-phase predictions, with a relative discrepancy of approximately 68% in the estimated heat transfer enhancement under the investigated conditions. The findings confirm the potential of nanofluids, particularly hybrid nanofluids, for enhancing the thermal performance of shell-and-tube chiller evaporators.
Fluid Mechanics
M. Mahdi; M. Shariatnia; M. Rahimi
Abstract
Microbubbles are used in ultrasound imaging, targeted drug delivery, destruction of cancerous tissues, etc. On the other hand, the demographic behaviors of small bubbles under the influence of Ultrasound have not been fully detected or studied. This study investigates the effect of the radial distribution ...
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Microbubbles are used in ultrasound imaging, targeted drug delivery, destruction of cancerous tissues, etc. On the other hand, the demographic behaviors of small bubbles under the influence of Ultrasound have not been fully detected or studied. This study investigates the effect of the radial distribution of Sonazoid microbubbles on frequency response. It is shown that the optimal subharmonic response is possible by controlling the size distribution. For this reason, the numerical simulation of the dynamic behavior of a coated microbubble is performed using MATLAB coding and the modified Rayleigh-Plesset equation. The Gaussian distribution is then applied, and the frequency response is investigated. It was shown that at a constant excitation pressure of 0.4 MPa and a standard deviation of 0.2, with increasing mean radius, the fundamental response increases. The subharmonic response increases reaches a peak value and decreases. This peak value occurs for frequencies of 4,6, and 8 MHz in the mean radius of 0.8, 1 and 1.6 μm. By increasing the frequency of excitation, it is transferred to a smaller mean radius. It is also observed that the fundamental and subharmonic responses are amplified by increasing the excitation pressure. Studies show that the optimal subharmonic response can be achieved for various applications by controlling the size distribution of microbubbles.
Computational Fluid Dynamics (CFD)
M. S. Sharifi; M. Mahdi; K. Maghsoudi
Abstract
The shape of the air flow in the interior is heavily influenced by the air distribution system and the way air enters and exits. By numerically simulating flow by computational fluid dynamics, one can determine the flow pattern and temperature distribution and, with the help of the results, provide an ...
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The shape of the air flow in the interior is heavily influenced by the air distribution system and the way air enters and exits. By numerically simulating flow by computational fluid dynamics, one can determine the flow pattern and temperature distribution and, with the help of the results, provide an optimal design of the air conditioning system. In this study, a chamber was first constructed and the temperature distribution inside it was measured. There was a fan installed at the back of the chamber for drainage. At the chamber entrance, three inlet for entering the flow were considered. The air from the middle inlet was heated by a heater. To prevent heat loss, the body of the enclosure was insulated. Several temperature sensors were installed at certain positions of the chamber for temperature measurement. Using Fluent software, the model of a full-sized chamber was created. Meshing is a hybrid and was used as a boundary layer Mesh. The inlet and outlet temperature of the chamber and the air output rates as boundary conditions were used in the simulation. Numerical analysis for K-ε and K-ω turbulence models was performed and different wall conditions were investigated. The numerical simulation results were in good agreement with the measurement results. Using the K-ε turbulence model with a scalable wall function had a better accuracy than other models. Changes in velocity and temperature were presented in graphs and contours at different positions of the compartment.
