AUT Journal of Mechanical Engineering
Year:2023 | Volume:7 | Issue:4|Papers Count:6

This paper presents a numerical analysis of the solid-liquid phase change within a vertical double-tube heat exchanger containing a phase change material, considering intermittent boundary conditions with the application of the enthalpy-porosity technique. To enhance the rate of heat transfer, copper fins are integrated into the inner wall of the heat exchanger in both uniform and non-uniform arrangements. While the uniform placement of fins at equal intervals accelerates the melting process, it leads to a portion of the phase change material remaining solid at the bottom of the heat exchanger due to weakened natural convection. Conversely, positioning a greater number of fins with a non-uniform distribution at the bottom of the heat exchanger expedites the overall melting process. It is observed that compared to a finless heat exchanger and under constant boundary temperature, the complete melting time is reduced by 53%, 69%, and 75% for uniform fin distribution, and fin distribution with geometric progression q=2 and q=3, respectively. Furthermore, the findings showed that natural convection leads to a greater increase in liquid fraction during melting compared to the assumption of pure conduction. Specifically, liquid fraction increases by about 40% with natural convection and around 15% with pure conduction during the first melting period. While the decrease in liquid fraction is almost equivalent for both conditions during freezing.

In the present study, a new and efficient design of a double-pass solar air heater with converged air ducts is proposed and simulated numerically. In the designed solar collector, the inclined position of the absorber plate regarding the glass cover and bottom plate provides converged shapes for the upper and lower air ducts, in which the accelerated flows and extra turbulence generation cause an increased rate of convection heat transfer. This concept is evaluated by numerical solution of the governing equations for air turbulent flow consisting of the conservations of mass, momentum, and energy by the finite element method using the COMSOL Multi-physics. Besides, the conduction equation is solved to compute the temperature distributions inside all solid parts. Numerical findings reveal that the increased velocity of airflow inside the converged duct causes significant convection enhancement, especially in the downstream side of airflow with a thick thermal boundary layer. This behavior leads to a considerable decrease in the absorber temperature due to a higher convection coefficient. The air outlet temperature for the studied test case with the inclined angle of   is found 3.5  more than that obtained for the base model and the percentage of efficiency increase is calculated about 10% due to using a converged duct.

This abstract serves as a concise yet comprehensive overview of this research's contributions, highlighting its significance in advancing Adaptive Cruise Control technology and autonomous vehicles. The provided paper introduces an innovative approach to Adaptive Cruise Control systems, emphasizing safety, comfort, and efficiency. Also, the proposed Adaptive Cruise Control model surpasses traditional longitudinal velocity control by integrating lateral motion and surface condition considerations. The proposed control strategy uses a new tail-following approach with the implementation of a new throttle valve controller which results in a smoother deceleration with an average of 40 percent decrease in maximum deceleration value while following other vehicles. Also, the implementation of brakes is minimized to lower the overall energy waste in vehicle motion. The proposed Adaptive Cruise Control can regulate braking force and tail-following distance based on road surface material and circumstances. This action enhances safety while driving on various roads and weather conditions. One of the innovative sections in this study is the integration of lateral motion with Adaptive Cruise Control. This approach helps the vehicle to stay laterally stable by limiting the lateral acceleration of the vehicle. The research signifies a notable advancement in Adaptive Cruise Control technology, establishing a connection between vehicle dynamics and adaptive control algorithms.

One of the factors that can cause a reduction in the efficiency and performance of axial compressors is the tip leakage flow of the compressor blade. In the first, the compressor's performance curve is compared with experimental results obtained under the condition of no air injection, and a statistically significant agreement is observed. The present study investigates the impact of various parameters, including flow rate, diameter, angle, and injection location, on the compressor's performance curve and flow structure, taking into account the injection of air into a passage. The results indicate that the compressor's stall margin and stable range extension are at their maximum values at a specific scale of each of the aforementioned parameters. Any deviation from this scale, either by reducing or increasing the injection parameters, leads to a reduction in the above characteristics. Although the presence of injection leads to an increase in the total pressure ratio in all injection states compared to the state without injection, the adiabatic efficiency at similar mass flow rates exhibits no significant change. The results also indicate that flow injection in the most suitable state increases the stall margin amount by 27% and the stable range extension of the compressor by 192.

Ammonia (NH3) stands out as a leading option for large-scale renewable energy storage and long-distance transportation. By incorporating landfill gas and raising initial reactant temperatures, NH3 reactivity is effectively enhanced in gas turbines and boilers. This study focuses on exploring the laminar flame propagation of NH3/landfill mixtures under elevated conditions. Accurate predictions for laminar burning velocity were achieved through numerical simulations employing Ansys Chemkin-Pro, along with the San Diego, Okafor, and GRI-Mech 3.0 mechanisms. Elevating pressure from 1 to 10 bar resulted in a reduction in laminar burning velocity from 16.1 to 6 cm/s, ultimately leading to an increase in adiabatic flame temperature from 2102 to 2143 attributable to changes in combustion equilibrium. Also, the results underscored the significant influence of ammonia concentration on augmenting laminar burning velocities. In cases with higher laminar burning velocity, the proportion of NH3 added tends towards zero, while in cases with lower laminar burning velocity, the addition ratio of NH3 tends towards one. The addition of ammonia leads to a reduction in the pool of radicals. Put simply, because ammonia has a lower laminar burning velocity, the overall Laminar burning velocity of the mixture is reduced as the concentration of ammonia in the fuel mixture increases.

This research aims to find suitable measurements to detect the occurrence of turbine erosion in Micro Gas Turbine engines. For this purpose, the off-design operation of this engine under the turbine's normal and eroded conditions has been modeled and the behavior of different parameters of the gas path has been analyzed. Turbine erosion is one of the most popular issues in gas turbine performance degradation. Accordingly, to have proportional health condition monitoring and diagnostics, it is necessary to know the effects of turbine erosion. Characteristic curves of an eroded turbine is utilized by the proposed off-design model to find the best parameters to detect turbine erosion. In the course of this research, two operation scenarios, one with maintaining the output power and the other with maintaining turbine inlet temperature, are examined. In both scenarios, the running line shifts to a new location with higher airflow and lower pressure ratio. When turbine inlet temperature is maintained, fuel flow, pressure ratio, and output power fall dramatically (9.8%, 11.1%, and 14.3% respectively) while in the other scenario temperature in the combustion chamber inlet and the turbine exhaust with 7% and 7.6% rise and pressure ratio with 4.4% reduction show most deviations from the healthy condition. So depending on the control scenario, the proper parameters can be selected from these sensitive parameters to detect turbine erosion in the Micro Gas Turbine.