Abstract:In this present study, numerical and theoretical analysis were both used to investigate the effect of the variable baffle spacing on the thermal characteristics of a small shell and tube heat exchanger. The numerical study was performed by using a three dimensional computational fluid dynamics (CFD) method and the computations were performed under steady-state conditions. We employed five different cases where the first had equal baffle spacing and the others had variable ones considering different configurations for balancing the pressure drop on the shell side. Theoretical calculations were run using the Bell-Delaware and Kern methods which are the most commonly used methods in the available literature. We show that the thermal performance of a shell and tube heat exchanger can be improved by evaluating together the results of the CFD and Bell-Delaware methods. From the numerical results, we can say that variable spacing with centered baffle spacing scheme can be proposed as an alternative shell side construction layout compared to an equal baffle spacing scheme. The numerical results were in good agreement with the theoretical data in the available literature.

In this study, the aerodynamic performance of seven different airfoils named CLARK Y, CLARK YH, Curtis C-72, FX 66-S-196 V1, NACA4412, NACA4415, and NACA4418 was numerically investigated under seven different angles of attack ranging from 0° to 30° in increments of 5°. 2D (two-dimensional) CFD (Computational Fluid Dynamics) models of airfoils were created and performed under steady-state conditions. When the changes of the lift coefficient and drag coefficient with the angles of attack were examined, it was observed that the drag coefficient increased with the increasing angle of attack. On the other hand, the lift coefficient firstly increased and then decreased a little and remained constant. For all airfoils, this value is calculated to be the highest around 10 to 15°. The obtained results from the numerical simulations were also analyzed by using the GRA (Grey Relation Analysis) method. While determining the best aerodynamic performance with this method, “higher is the better” and “lower is the better” normalization processes were used for lift coefficient and drag coefficient, respectively. As a result of the GRA analysis made with the numerical results, it was seen that the best and the worst performances were presented by Curtis C-72 and Clark Y airfoil profiles at 10° angle of attack condition, respectively. On the other hand, at 15° and higher angle of attack conditions, the best and the worst performances were presented by NACA4418 and Clark YH airfoil profiles, respectively. The performance of the best model was also seen in the velocity distribution compared to other models.

In this paper, a detailed combined 1D model of Heating, Ventilation and Air Conditioning systems of a vehicle were developed by using the LMS Imagine Lab Amesim software package. The numerical simulations were considered for soaking and cool down analysis under different environmental conditions. The thermal performance of different refrigerants as R-134a and R-1234yf were evaluated in terms of thermal performance and energy consumption. According to the soaking simulation results, the cabin air temperature values ranged from 49°C to 57°C in general. The maximum increase in cabin air temperature value was about 22°C obtained for 1000 15 W/m 2 solar load. The total time until reaching the steady-state conditions for a target temperature value (23.5°C) was different for all simulations. The total time was calculated as 910 seconds for 1000 W/m 2 solar load by using R134a refrigerant loop. The results also showed that although the thermal performance of R-134a was slightly better, R-1234yf can be used due to its environmental properties with acceptable performance. The calculated COP values during cooldown analysis were ranged from 1.71 to 4.52 in general. The minimum value was obtained for the cases which had a maximum solar load and higher cabin interior temperature values. The calculated temperature data for soaking and cool down analysis were in good agreement with the reference data presented in this study. These numerical results are very important for reducing the thermal load of the vehicle cabin considering energy consumption of the HVAC system for different thermal conditions.

Incremental sheet forming (ISF) is developed in order to meet the increasing demand for sheet metal forming and because it is a more economical method. First of all, this method gains attention become it is a die-less method. Furthermore, process flexibility and higher formability are other advantages of this method. In this study, AA2024-T3 sheets with a determined geometry and parameters were formed using the ISF method. Among the forming process parameters, tool path, step size and lubrication parameters were changed. The tool diameter, feed rate, spindle speed, angle of the wall and the tool coating parameters were kept constant. The thickness distributions and geometrical accuracy of the processed samples with the three-dimensional laser scanning method were examined accurately. It is clear from the results that the tool path that spirals and always keeps in touch is more successful than the tool path that makes it an incremental process. ISF is preferable to die production for limited production runs because it is more economic and the processing time is short.