Optimum design of a radial heat sink under natural convection
Introduction
The light-emitting diode (LED) market has grown recently, thanks to enhancements in LED luminous efficiency. Nevertheless, about 70% of the total energy consumed by an LED light is emitted as heat, creating a thermal problem. Without properly dissipating this heat, the performance and life of an LED light is impaired. Thus, to commercialize LED lights, the problem of heat dissipation must be solved first. Natural convection heat sinks are appropriate for LED lights, in view of their overall advantages.
There have been numerous experimental [1], [2], [3], [4], [5] and numerical [6], [7] studies of natural convection heat transfer in rectangular-fin or pin-fin heat sinks. Harahap and Setio [1] performed experiments to obtain the average heat transfer coefficients for five different rectangular heat sinks, and proposed a correlation to predict the average heat transfer coefficient. Huang et al. [2] conducted an experimental study of seven types of pin-fin heat sinks (both vertically and horizontally oriented), and the optimum shape of a pin-fin heat sink was suggested for each orientation. Bar-Cohen et al. [6] optimized a rectangular heat sink by employing existing correlations; they considered the mass of the heat sink, as well as the thermal performance. Dialameh et al. [7] carried out a numerical study to predict natural convection from arrays of aluminum horizontal rectangular thick fins with short lengths. They compared the effects of various fin geometries and temperature differences on the convection heat transfer of heat sinks, and proposed a non-dimensional correlation. However, most of these studies were concerned with heat sinks with rectangular bases, which might be not straightforward for cooling circular LED lights.
In this study, natural convection heat transfer around a radial heat sink is investigated, experimentally and numerically. The numerical model is validated by the experimental results. To determine the optimum reference model, we numerically compare the L model (long fin), the LM model (long and middle fins) and the LMS model (long, middle and short fins). Parametric studies are performed to compare the effects of the number of fins, long fin length, ratio of middle to long fin length, and heat flux on the thermal resistance and average heat transfer coefficient. Finally, optimal designs of radial heat sinks with various heat fluxes are suggested.
Section snippets
Mathematical modeling
Fig. 1 illustrates a radial heat sink, composed of a circular base and rectangular fins. The fins are assumed to be radially arranged at regular intervals. The heat sink base is horizontal, while the fins are vertical. The material of the heat sink is aluminum. Table 1 lists the properties of aluminum and air.
Experiments and validation
The numerical model is verified with experimental data, by comparing the differences between ambient and heat sink temperatures. The heat sink is made of aluminum (Al2014), with no additional surface treatment. As Fig. 3(a) shows, the experimental setup consisted of a film heater (Kapton-coated stainless steel, 25 μm), a heat sink, an insulator, type-T thermocouples (gauge 36), a data acquisition device (NI cDAQ-9172, NI9211), a power supply, a wattmeter, and a personal computer. The film heater
Results and discussion
To choose the optimum reference model, we compare the L model (long fin), the LM model (long and middle fins) and the LMS model (long, middle and short fins). Parametric studies and design optimization are carried out for the model exhibiting the best performance.
Conclusions
Numerical analyses were conducted to optimize a radial heat sink adapted to a circular LED light. Experiments were performed to validate the numerical model, and the agreement was good. To determine the optimum model, three types of heat sink (L, LM and LMS models) were compared and the LM model exhibited superior thermal performance. Parametric studies were performed to compare the effects of three geometric parameters (number of long fins, long fin length and middle fin length) and an
Acknowledgment
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2010-0008537).
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