Haq, Syed Mohammad Hameed Ul (2018-12). Numerical Simulation of Uniform Circular Microjet and Mono Dispersed Micro Droplet Streams for Impingement Cooling. Master's Thesis. Thesis uri icon

abstract

  • Effective cooling of electronic chips is essential for optimum performance. With the exponential growth of computers, there has been a sharp rise in the heat generation of these devices. Therefore, an utmost need has developed to utilize alternative cooling methods to ensure low operating temperatures. Some of the cooling techniques under consideration include spray cooling and jet impingement cooling. While jet impingement cooling is fairly easy to understand, Spray cooling still remains one of the most parameter intensive physical mechanisms. A common practice to simplify spray cooling is modeling it as a continuous stream of droplets, which is also followed in this study. A comparison between the two aforementioned techniques is necessary to understand which of them performs better for this particular application. For this purpose, a study based on computational fluid dynamics simulations was performed. Both cooling technique were simulated with parameters in line with the experimental conditions. To accurately depict the impingement process and fluid flow, a 2D axisymmetric structured grid was constructed. For accurate spatial resolution, grid was refined using static mesh adaption for jets and dynamic mesh adaption for droplets. A time dependent patching method was utilized to simulate a single stream of droplets. A Volume of Fluid approach coupled with the Level Set method (CLS-VOF) was employed in ANSYS Fluent for simulating the flow. A good agreement was reached between experimental and numerical data for both cooling techniques, in terms of temperature profile, heat transfer coefficient, Nusselt number, impact crater diameter and film thickness in the impingement zone. Heat transfer characteristics and hydrodynamics of jet impingement and droplet train impingement were compared and it was found that droplet train impingement outperformed the latter. Improved performance of droplet train impingement was due to the convective heat transfer across the surface, which was driven by fluid momentum. Droplet train impingement produced higher momentum across the impingement zone, compared to jet impingement, resulting in greater heat transfer. Higher momentum also led to larger crater diameters for droplet impingement. Despite its periodic behavior, a smooth temperature profile, with lower temperature gradients across the heat surface, was produced by droplet impingement as compared to jet impingement. This was attributed to the sweeping motion of the fluid at higher momentum, removing the generated heat, further away from the impingement zone. Thermal boundary layer of droplets was thinner than the thermal boundary layer of jets, indicating better heat transfer.
  • Effective cooling of electronic chips is essential for optimum performance. With the exponential growth of computers, there has been a sharp rise in the heat generation of these devices. Therefore, an utmost need has developed to utilize alternative cooling methods to ensure low operating temperatures. Some of the cooling techniques under consideration include spray cooling and jet impingement cooling. While jet impingement cooling is fairly easy to understand, Spray cooling still remains one of the most parameter intensive physical mechanisms. A common practice to simplify spray cooling is modeling it as a continuous stream of droplets, which is also followed in this study. A comparison between the two aforementioned techniques is necessary to understand which of them performs better for this particular application. For this purpose, a study based on computational fluid dynamics simulations was performed. Both cooling technique were simulated with parameters in line with the experimental conditions.
    To accurately depict the impingement process and fluid flow, a 2D axisymmetric structured grid was constructed. For accurate spatial resolution, grid was refined using static mesh adaption for jets and dynamic mesh adaption for droplets. A time dependent patching method was utilized to simulate a single stream of droplets. A Volume of Fluid approach coupled with the Level Set method (CLS-VOF) was employed in ANSYS Fluent for simulating the flow. A good agreement was reached between experimental and numerical data for both cooling techniques, in terms of temperature profile, heat transfer coefficient, Nusselt number, impact crater diameter and film thickness in the impingement zone.
    Heat transfer characteristics and hydrodynamics of jet impingement and droplet train impingement were compared and it was found that droplet train impingement outperformed the latter. Improved performance of droplet train impingement was due to the convective heat transfer across the surface, which was driven by fluid momentum. Droplet train impingement produced higher momentum across the impingement zone, compared to jet impingement, resulting in greater heat transfer. Higher momentum also led to larger crater diameters for droplet impingement. Despite its periodic behavior, a smooth temperature profile, with lower temperature gradients across the heat surface, was produced by droplet impingement as compared to jet impingement. This was attributed to the sweeping motion of the fluid at higher momentum, removing the generated heat, further away from the impingement zone. Thermal boundary layer of droplets was thinner than the thermal boundary layer of jets, indicating better heat transfer.

publication date

  • December 2018