Heat Analysis for Heat Sink Design Using Finite Element Method

This introduction paper is based on the paper "Heat Analysis for Heat Sink Design Using Finite Element Method" published by "Journal of the Korea Academia-Industrial cooperation Society".

[Fig. 1] Heat sink by direct extrusion & die casting

1. Overview:

Title: Heat Analysis for Heat Sink Design Using Finite Element Method
Author: Hyun-Suk Jang, Joon-Seong Lee and Dong-Keun Park
Year of publication: 2013
Journal/academic society of publication: Journal of the Korea Academia-Industrial cooperation Society
Keywords: Die Casting, Heat Sink, LED, Thermal Analysis, Optimal Performance

2. Abstract:

LED is standing in the limelight as a light part of the low-carbon green energy. While LEDs are eco-friendly, efficient and durable, extreme heat rises can cause their durability to decrease, with 80% of the power supply being turned into heat energy. Heat radiation systems are important because rising temperatures affect the lifetime of LED elements. Therefore, in this paper, thermal analysis was performed for the shape of heat sink to the LED bulb. Also, it is applied the temperature control systems to our products for optimal performance.

3. Introduction:

LEDs are gaining prominence as lighting fixtures in the era of low-carbon green energy. They offer advantages such as being eco-friendly, having high energy efficiency, and long lifespan. However, a significant drawback is that over 80% of the supplied power is converted into heat energy, leading to an unavoidable temperature increase. This temperature rise adversely affects the lifespan of LED elements, making the heat dissipation system critically important. This paper analyzes the thermal performance of different heat sink shapes for LED bulbs, designed with die casting manufacturing in mind, to enhance the efficiency of the heat dissipation system. Among various heat sink manufacturing methods, direct extrusion and die casting are widely utilized. This study specifically focuses on designs suitable for die casting.

4. Summary of the study:

Background of the research topic:

LEDs, despite their high efficiency and long lifespan, generate substantial heat, with approximately 80% of the input energy being converted to heat. This generated heat leads to an increase in the junction temperature of LED lighting devices. If not effectively dissipated, this can result in thermal overload, causing issues like wire breakage, delamination, solder past separation, and epoxy resin yellowing, ultimately leading to LED failure and reduced lifespan [1,2]. Therefore, effective thermal management through heat sinks is crucial.

Status of previous research:

Passive thermal management using heat sinks with cooling fins is a widely adopted technology for LED bulbs. Common manufacturing methods for heat sinks include direct extrusion and die casting. Direct extrusion produces heat sinks with fins of uniform cross-section, while die casting allows for the creation of heat sinks with varying cross-sections and more complex geometries [Fig. 1]. This study leverages die casting principles, considering factors like minimum wall thickness for aluminum die cast products, as reported by G.Lieby [7] and shown in [Table 1].

Purpose of the study:

The primary purpose of this study is to perform thermal analysis on various heat sink shapes for LED bulbs, specifically designed considering die casting manufacturing constraints. The goal is to analyze the effectiveness of these heat sink designs in dissipating heat and to identify shapes that offer optimal thermal performance for LED bulbs.

Core study:

The core of this research involves conducting transient thermal analysis using the Finite Element Method (FEM) on three different heat sink bottom designs (Type (a), Type (b), Type (c)) for an LED bulb. The LED bulb model includes components such as the LED elements, PCB, aluminum case, and the heat sink [Fig. 3]. The heat sink designs were modeled using Pro-engineer software [Fig. 4], incorporating minimum thickness applicable in die casting [Table 1]. The study evaluates the temperature distribution on the LED elements and the heat sinks to compare their thermal performance under simulated operating conditions.

5. Research Methodology

Research Design:

The research employed a comparative analysis of three distinct heat sink bottom designs (Type (a), Type (b), and Type (c) as shown in [Fig. 4]) for an LED bulb. Transient thermal analysis was conducted to observe the temperature changes over time until a state of thermal equilibrium was achieved. The heat sinks were designed based on die casting manufacturing principles, particularly adhering to minimum wall thicknesses for aluminum alloys [Table 1].

Data Collection and Analysis Methods:

The LED bulb structure, as shown in [Fig. 3], consists of a Glass cap, 16 LED elements, PCB, Aluminum case, Heat sink bottom & top, and Socket. These components were modeled in 3D using Pro-engineer. Material properties for Aluminum, Copper, Poly Carbonate, Glass, and GaN were defined as per [Table 3] and [Table 4].
A transient thermal analysis was performed. Boundary conditions included natural convection (ambient temperature of 27°C) on the external surfaces of the LED bulb. Heat generation was set at 455,000 W/m³ for each of the 16 LED elements, assuming 20-30% LED efficiency. The simulation was run for 7,200 seconds. The number of nodes and elements for the LED bulbs and heat sinks are detailed in [Table 5].

Research Topics and Scope:

The research focuses on the thermal analysis and optimal design of die-cast heat sinks for LED bulbs. The scope includes:

Modeling three different heat sink bottom shapes (Type (a), Type (b), Type (c)) integrated into an LED bulb assembly.
Applying die casting design constraints, specifically the minimum thickness for aluminum components as per [Table 1].
Performing transient thermal analysis using FEM to determine temperature distributions on LED elements and heat sink surfaces.
Comparing the thermal performance of the three heat sink designs to identify the most effective shape for heat dissipation.

6. Key Results:

Key Results:

After 7,200 seconds of operation in the transient thermal analysis, the temperatures of the 16 LED elements were recorded. [Table 6] summarizes the minimum and maximum temperatures for each LED type. For example, for Type (a), the LED temperature distribution is shown in [Fig. 7]. All LED types demonstrated temperatures within stable operating limits.
The heat sink bottom temperatures reached thermal equilibrium after approximately 3,000 seconds of operation, as indicated by the temperature-time curves in [Fig. 8]. The temperature distributions on the heat sink bottoms after 7,200 seconds are shown in [Fig. 9], with [Table 7] detailing their minimum and maximum temperatures.
The results indicated that Type (a) heat sink exhibited the highest temperatures, while Type (c) showed the lowest temperatures, signifying superior heat dissipation performance for Type (c).

LED maximum temperatures: Type (a) 67.254°C, Type (b) 57.21°C, Type (c) 57.049°C.
Heat sink bottom maximum temperatures: Type (a) 60.574°C, Type (b) 50.418°C, Type (c) 50.278°C.

[Fig. 8] Temperature distribution of heat sink

[Fig. 9] Temperature distribution of heat sink

Figure Name List:

[Fig. 1] Heat sink by direct extrusion & die casting
[Fig. 2] Default configuration of LED light bulbs[4]
[Fig. 3] Structure of LED light bulbs
[Fig. 4] Type of heat sink bottom
[Fig. 5] Use of fins to enhance heat transfer of plane wall[6]
[Fig. 6] Each elements of heat sink
[Fig. 7] Temperature distribution of LED
[Fig. 8] Temperature distribution of heat sink
[Fig. 9] Temperature distribution of heat sink

7. Conclusion:

The study conducted transient thermal analysis on three different heat sink designs for LED bulbs, based on die casting manufacturing principles, leading to the following conclusions:

(1) Thermal analysis of the three heat sink shapes, designed with minimum wall thicknesses suitable for die casting, demonstrated that all three types maintained LED element temperatures within stable operational ranges.
(2) Among the three types of heat sinks analyzed, Type (c) exhibited the best heat dissipation performance.
(3) Considering mass production via die casting, factors such as mold life, occurrence of defects, and product deformation during ejection are critical. In this regard, Type (c), which can be formed with uniformly spaced die core features rather than narrowing shapes, is considered the most suitable design.

8. References:

[1] S. H. Hwang., "Study on thermal design of LED lights", Master's thesis, pp. 1-5,13-24, 2010.
[2] S. H. Hwang, S. J. Park and Y. L. Lee, "A Study of Optimal Thermal Design for a 10W LED Lamp", J. of the Korea Academia-Industrial cooperation Society, Vol. 11, No. 7, pp. 2317-2322, 2010. DOI: http://dx.doi.org/10.5762/KAIS.2010.11.7.2317
[3] J. M. Lee, B. M. Kim, et al., "FE Analysis of Extrusion Process for Heat sink", Proceedings of annual meeting of KSTP, pp. 313-317, 2003.
[3] J. I. Park, Y. C. Yoon, et al., "Shape Optimization of Die Casting Mold for Improvement Fatigue Life Based on Fatigue Analysis", Proceedings of annual meeting of Korean Society of Machine Tool Engineers, pp. 291-296, 2009.
[4] D. I. Shin, and K. J. Park, "The Design Study for LED lightning lamp heat Sink Structure," Proceedings of Korean Society of Design Science, pp. 90 - 91, 2010.
[5] B. H. Cho, "Finite Element Heat transfer analysis of Heat sink for LED Socket", Maste- r's thesis, pp. 39-53, 2011.
[6] B. C. Park, H. K. Park, et al., "INTRODUCTION TO HEAT TRANSFER, FIFTH EDITION," TEXT BOOKS, pp. 280 – 283, 2007
[7] S. B. Park, and Y. H. Seo., "Die Casting Product Design", PRESS TECHNOLOGY, No. 11, pp. 76-87, 2000
[8] W. John, P. Shawn, et al., "100,000 Hour Lifetimes And Other LED Fairytales," 2008 LED Transformation, LLC, pp. 46 – 58, 2008.

9. Copyright:

This material is a paper by "Hyun-Suk Jang, Joon-Seong Lee and Dong-Keun Park". Based on "Heat Analysis for Heat Sink Design Using Finite Element Method".
Source of the paper: http://dx.doi.org/10.5762/KAIS.2013.14.3.1027

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Tags: aluminum alloy; ,aluminum alloys; ,CAD; ,Die casting; ,Die casting Design; ,Efficiency; ,Heat Sink; ,STP