Why textbook matters even with simulation tools

the distance between knowledge to simulation software

In thermal design and heat transfer, using Computational Fluid Dynamics (CFD) tools is practical but has its limitations. To complement CFD analysis, incorporating textbook knowledge is crucial. This article focuses on showcasing the significance of textbook knowledge through practical examples, emphasizing its benefits in thermal design work.

forced-air-cooling-at-high-altitude (flexpowermodules.com)

Operating point and model simplification

One challenge in thermal design is understanding operating points across components. Tools like GraphReader.com simplify the process of organizing data sheets by extracting plot data from graphs or images. It’s essential to consider impedance extraction in the partial model by applying mechanical principles like “total and internal equilibrium” and avoiding common mistakes such as over-accumulation in total impedance. Additionally, evaluating heat transfer requires flow and temperature data, allowing the system to be analyzed in two regions to ensure total impedance.

Presssure impedance and density impact

In thermal design, optimizing cooling performance requires a thorough understanding of various factors. Components like the bezel and IO have specific static pressure ranges, while the rest region in swith exhibits lower impedance. Estimating the operating condition at around 6 CFM per QDD2x1 or 4 CFM per QDD and aligning it with IO cooling guidance aids transceiver cooling estimations. Additionally, high altitude and challenging environmental conditions necessitate considering main flow and local heat transfers using density estimations. Main flow heat transfer relies on Cp * dT, while local heat transfer employs h * A * dT. The density order may differ due to factors like operating point movement, main flow preheating, and local heat transfer characteristics. Understanding these aspects ensures effective thermal management strategies.

Dimensionless alalysis and practical principles

As a thermal design engineer, understanding the limitations of dimensionless analysis is crucial. While dimensionless analysis is commonly used in research science to study heat transfer, its application in practical engineering poses challenges. One major hurdle is the requirement for a fixed flow area, which doesn’t align with the dynamic nature of thermal design. Adjusting heatsink sizes and venting locations based on specific requirements becomes necessary, considering factors like size and manufacturing constraints. Dimensionless analysis provides useful guidelines within a limited range but becomes less feasible when system sizes and venting areas change. Practical tools and calculators play a vital role in thermal design by enabling engineers to evaluate design drafts quickly and provide efficient customer support. By embracing these tools, thermal design engineers can adapt to real-world constraints and achieve optimal thermal management solutions.

Principles in flow and heat transfer

In the field of thermal design, understanding the principles of flow-only applications and flow with heat transfer is essential. This article explores various aspects related to model simplification, system operating points, natural convection, high altitude estimation, air/liquid cooling estimation, NIC power estimation, and operating point estimation.

Flow-Only Applications:

1. Model Simplification: Simplifying thermal models by focusing on flow aspects can significantly reduce complexity and computation time. This approach is particularly beneficial when heat transfer effects are minimal or can be separately considered. Instead of uniform airflow with the same impedance, we can approximate flow distribution and derate impedance within a duplicated simplified model using total pressure extraction. Additionally, for contact resistance, surface properties can be used to approximate the thermal conductivity of grease or thin air gap layers, simplifying meshing and computation. This simplification technique maintains consistent flow distribution while streamlining analysis and computation.
2. System Operating Point: Analyzing the flow-only conditions allows us to identify the operating point of a thermal system, considering pressure drop, flow rate, and fluid properties. This knowledge ensures optimal system performance and sufficient flow rate for heat dissipation. By utilizing tools like graph readers, extracting fan curves becomes easier, enabling accurate evaluation of the operating point and sensitivity to stall regions within the system.
3. Natural Convection: In flow-only applications, understanding the impact of natural convection is crucial for effective thermal design. Natural convection, driven by buoyancy forces, can lead to hotspots and affect cooling strategies. To keep projects moving efficiently, engineers require approximations rather than relying solely on CFD computations. Utilizing reliable tools can help provide reasonable estimations for venting size, temperature failure, and pressure requirements. By balancing industrial design requirements and early thermal input, engineers can optimize minium venting diemnsions and their thermal management strategies effectively.

Flow with Heat Transfer:

1. High Altitude Estimation: In high-altitude environments, accurate thermal design is crucial due to the decrease in air density. To address this, we must consider the operating point and heat transfer aspects. The lower air density leads to derating of impedance and fan curves, shifting the operating point. Moreover, research shows that the heat transfer coefficient exhibits specific behavior within typical length ranges. Therefore, thermal estimation at high altitude requires more than laminar formulas. Two common approaches are air cooling and uniform air preheating, which can be used for effective thermal management. When considering thermal management for ICs on the board, a combination of preheated ambient temperature and JEDEC Rja Rjc Rjb values can help determine the sufficiency of natural convection or the need for a heatsink.
2. Air/Liquid Cooling Estimation: When determining the optimal cooling method for a thermal design, such as air or liquid cooling, various factors must be considered. These include the heat load, available resources, and environmental conditions. Estimating the cooling effectiveness involves assessing parameters like density and conductivity in fluid changes. In air cooling, the dominant factor is the heat transfer area, while in liquid cooling, the higher heat transfer coefficient means that a smaller area within the cold plate can achieve the desired cooling effect compared to air cooling. The additional fin surface in liquid cooling is not effective as air cooling but may lead to significant pressure loss, making it essential to strike a balance between surface area and pressure requirements.
3. NIC Power Estimation: Accurately estimating the power dissipation of network interface cards (NICs) is crucial in thermal design to ensure effective cooling solutions. As higher speed rates require increased power, it is essential to utilize a calculator that considers power and thermal resistance (Rth) to determine the operating tier. Flow speed plays a significant role, as Rth exponentially relates to it. By calculating the temperature rise (T rise), we can determine the margin against ambient temperature. Furthermore, the T rise is linearly proportional to power, allowing us to adjust the temperature rise curve based on the power ratio. To gain a deeper understanding of NIC power estimation, check out this informative video.
4. Operating Point Estimation in Thermal Design: Analyzing flow characteristics and heat transfer requirements is crucial for estimating the system’s operating point. While system decomposition has assumptions of uniform flow, it is a highly effective collaboration approach. By analyzing individual components and their required flow rates and impedances, the coolest solution can be determined. Customers can then integrate this model into their system to finalize the absolute operating values. Examples include evaluating IO quantities and power demand, assessing the whole system’s performance, and considering decomposition changes. Utilizing reliable curve fitting with theoretical knowledge, these estimations help evaluate operating point changes and associated benefits such as improved temperature control and power savings.