CFD Simulation on the Effect of Adding Dimple Balls Stagger Position on Base Plate on the Performance of V-Corrugated Air Heating Solar Collector

The ever-increasing increase in energy consumption requires great attention. Therefore, efforts need to be made to find new energy sources, such as solar energy. The absorber plate absorbs solar energy in the form of radiation, and heat is transferred by convection to the working fluid through the solar collector. Increasing the thermal efficiency of the solar air collector by modifying the absorption area using a v-corrugated absorber and also increasing the convection heat transfer coefficient by creating turbulence in the heat transfer area. Flow turbulence can be achieved by providing a disturbance in the form of a dimple in the working fluid channel above the base plate. This research was conducted utilizing numerical simulations and experiments. CFD simulation aims to obtain the most optimum ratio of ΔT/ΔP values of diameter and dimple distance using ANSYS Fluent software with a diameter variation of 6mm, 8mm, 10mm, and 45mm spacing; 50mm, and 5mm. Based on the results of CFD simulations that have been carried out on each variation of the distance and diameter of the dimple, it can be concluded that the closer the distance between the dimples, the smaller the resulting pressure drop, and the larger the diameter of the dimple, the greater the resulting temperature value. The use of a larger dimple diameter results in an increase in the heat transfer area and further increases the outlet temperature. The expected ratio is the value of the largest temperature increase and the smallest pressure drop. In the calculation of the total ratio, the dimple diameter of 10 mm with a distance of 45 mm has the highest ΔT/ΔP ratio value.


Introduction
Based on projection data [1] published by the Agency for the Assessment and Application of Technology (BPPT), the industrial sector's energy demand is projected to continue to increase with an average growth of 3.9% per year.The increase in energy consumption that occurs requires great attention.Therefore, efforts need to be made to find new or alternative energy sources to support the country's energy needs.One of the alternative energy sources is radiation energy from sunlight.The proper utilization of solar energy is to be used in two ways: solar panels and collectors.Solar panels are devices that can convert light energy into electrical energy.In contrast, solar collectors are devices that utilize solar radiation and produce high-temperature working fluids used in households, hotels, hospitals, industrial sectors, and others [2].The air heater solar collector consists of an absorber plate that absorbs solar radiation, a channel through which the air flows, and a transparent cover [3].The solar collector above still has a low convection heat transfer coefficient between the absorber plate and the air flowing below it.To increase the heat transfer coefficient, modifications were made to the absorber plate, which was formed into a vcorrugated.This gave higher efficiency than the flat plate absorber [4].Another efficient effort to increase heat transfer on the v-corrugated absorber plate is the addition of vertically bent obstacle plates [3].
Research on solar collectors to increase the heat transfer coefficient has been carried out by previous researchers with various modifications and has been shown to improve performance.The performance of the solar collector can be reviewed based on several parameters,ely thermal and large pressure drop [5].It can be analyzed to characterize its thermal performance and pressure drop using the Computational Fluid Dynamic (CFD) simulation method.From this basis, research on the use of solar energy is needed to support the use of new and renewable energy (EBT) [6].
Dimensional absorber plate assemblies for plates with and without dimple balls prove that surface geometry enhancement, such as having dimple balls, can increase heat transfer to the absorber tube, mainly due to an increase in the area for diffusion heat transfer [7].In this study, the solar collector was given the addition of dimple balls, which would be applied to the base plate with the stagger position in several size variations that were adjusted to the dimensions of the base plate.The research was conducted using a Computational Fluid Dynamics (CFD) simulation and aims to determine the effect of adding dimple balls to the base plate on changes in temperature (delta) and pressure on the inlet and outlet sides.

Problem Statement
Numerical research was carried out using the Computational Fluid Dynamics (CFD) program with the ANSYS FLUENT application, which focused on adding dimple balls to the solar collector base plate.A 3D model consisting of a solar air collector involving an air inlet, a V-corrugated absorber plate, and an air outlet was modeled by ANSYS Workbench.The results were obtained in the simulation using ANSYS FLUENT software, and the absorbent plate has dimensions of 900 mm long, 30 mm wide, and 1 mm thick.

Ansys Numerical Simulation
Computational Fluid Dynamics (CFD) is an analytical system that uses numerical methods and algorithms to cover phenomena such as fluid flow, heat transfer, and chemical reactions in computerbased simulations.This technology is compelling and covers various industrial and non-industrial applications.Some examples are: a. Aerodynamics of aircraft and vehicles: lift and drag b.Ship hydrodynamics c.Power generation: combustion in IC engines and gas turbines d.Turbomachinery: flows in rotating passages, diffusers, etc. e.There are several unique advantages of CFD over an experimentally based approach to fluid system design: f.Significant reduction in new design lead time and cost.
g.The ability to investigate systems in which controlled experiments are difficult or impossible (for example, extensive systems).h.Almost infinite levels of detail in results in CFD-based simulations have been developed since the 1960s in the aerospace industry.However, CFD modeling is now widely used in manufacturing and chemical industries.The advantages of using CFD in the analysis are insight (deep understanding), foresight (overall prediction), and efficiency (time and cost efficiency).
CFD analysis is organized around numerical calculations that can handle fluid flow issues.In order to provide simple asses to their understanding control, all commercial CFD bundles incorporate modern client interfacing to input issue parameters and to look at the results.Subsequently, all code contains three primary components: 1. Pre-processor 2. Solver 3. Post-processor The procedure used to simulate a solar air collector with a CFD tool is as follows: 1. Create a 3D model of the geometry of the V-corrugated solar collector with additional dimple balls on the base plate using the ANSYS WORKBENCH software, as shown in Figure 1. 2. Make a mesh of the geometry that has been created, then mesh the volume with the TGrid type, as shown in Figure 2. Prior to taking numerical data for all variations in the diameter of the dimple balls and the distance from the front side of the base plate, a grid independence test was carried out to check whether the number of grids used was appropriate for data collection so that the right and efficient mesh could be found.3. Define the boundary conditions of the solar collector fields to be simulated with the Fluent application.4. Then check the grid, after which the scale is determined.In this study, we used a scale in meters.

Result and Discussion
Computational Fluid Dynamics (CFD) is an analytical system that uses numerical methods and algorithms to cover phenomena such as fluid flow, heat transfer, and chemical reactions in computerbased simulations.This technology is compelling and covers various industrial and non-industrial applications.Some examples are:

Grid Independency
Grid independence compares the simulation results from the most tenuous mesh (coarsen) to the densest (finest).The geometry and parameters used in the five meshes are the same.Grid independence aims to check that the number of grids used is correct to find a good and efficient mesh for numerical observations.Each tested mesh has the same boundary conditions and settings in the ANSYS Fluent software.3dimensional simulation, double precision, viscous Shear Stress Transport K-ω (SSTK-ω) model; steel material; radiation intensity set to 431 Watt/m2, discretization equation model using first-order scheme; and velocity and pressure relationship using SIMPLEC method are among the settings.Here are the results of the simulation, as shown in Table II The velocity error value in each tested mesh is then graphed.It is found that mesh 3 has an error that does not change much, and the velocity value starts to stabilize compared to mesh 4 and mesh 5 in Figure 3. Therefore, mesh 3 is considered to have met the independence grid.

Simulation Result
From the results of the independence grid, mesh 3 is used as a reference mesh for all variations of the dimple diameter.Simulations were carried out on 3 variations of the distance and diameter of the dimple with one variation of intensity, 431 Watt/m2, and the velocity of the inlet fluid, 6.5 m/s.Furthermore, from the simulations for each variation, the resulting global properties are the difference in inlet and outlet temperatures and a decrease in flow pressure.Simulations on channels without dimples were also carried out to compare the effect of dimples on increasing temperature and decreasing pressure.The simulation results can be seen in the following Table III  Table III shows the difference in temperature for each variation in diameter and dimple distance.At a distance variation of 45 mm with a dimple diameter of 10 mm, the highest temperature difference is 6.25 K, and the smallest pressure drop is 63.64 Pa.At a distance variation of 50 mm with a dimple diameter of 10 mm, the highest temperature difference is 6.29 K, and the smallest pressure drop is 73.75 Pa.The highest temperature difference value is 6.32 K at a distance variation of 55 mm with a dimple diameter of 6 mm, and the smallest pressure drop is 80.58 Pa at a dimple diameter of 10 mm.
Based on the values listed for each variation of the dimple distance and diameter, it can be concluded that the closer the distance between the dimples, the smaller the resulting pressure drop, and the larger the dimple diameter, the greater the resulting temperature value.The use of a larger dimple diameter results in an increase in the heat transfer area and further increases the outlet temperature.The variation with a dimple diameter of 10 mm at a distance of 45 mm was chosen because it shows the optimal value compared to variations between 50 mm and 55 mm. Figure 4 shows The working fluid's velocity vector when it hits the dimple with a diameter of 10 mm and a distance of 45 mm.The picture shows the fluid velocity vector seen in the Z-axis direction with an iso value of 0.0025 m on the Y-axis.The picture shows a backflow due to fluid hitting the dimple.Dimple is useful as a vortex generator, capable of directing the flow and increasing turbulence.When the flow is turbulent, the fluid particles exhibit additional motion, increasing the velocity of energy and the exchange of momentum between the particles, thereby increasing the flow's heat transfer and coefficient of friction.
Fluid flow disturbed by dimples results in a sudden decrease in flow velocity and, subsequently, a change in flow.The greater the change in flow produced, the greater the pressure drop generated.The amount of pressure drop will affect the power of the blower used.The expected ratio is the value of the largest temperature increase and the smallest pressure drop.In Figure 5, it can be seen that the calculation of the total ratio at a dimple diameter of 10 mm with a distance of 45 mm has the highest ΔT/ΔP ratio value and is considered the most optimum variation because the vortex produced is quite large and the velocity vector is higher on the side of the absorber plate so that the temperature higher average airflow and the smallest pressure drop.

Conclusion
Based on the results of CFD simulations that have been carried out for each variation of the distance and diameter of the dimple, it can be concluded that the closer the distance between the dimples, the smaller the resulting pressure drop, and the larger the diameter of the dimple, the greater the resulting temperature value.The use of a larger dimple diameter results in an increase in the heat transfer area and further increases the outlet temperature.The expected ratio is the value of the largest temperature increase and the smallest pressure drop.In the calculation of the total ratio, the dimple diameter of 10 mm with a distance of 45 mm has the highest ΔT/ΔP ratio value.

Figure 1 .
Figure 1.A 3D model for solar collector geometry

Figure 2 :
Figure 2: Mesh design on ANSYS Fluent

Figure 3 .
Figure 3. Mesh design on ANSYS Fluent P1 = Pressure value without dimple ball P2 = Pressure value with dimple ball T1 = Temperature value without dimple ball T2 = Temperature value with dimple ball

Table I :
CFD simulation parameters

Table II .
: Mesh variation simulation results

Table III .
: Simulation results of diameter variation and dimple distance