Luminaries-level structure improvement of LEDs for heat dissipation enhancement under natural convection

Abstract

Heat dissipation enhancement of LED luminaries is of great significance to the large-scale application of LED. Luminaries-level structure improvement by the method of boring through-hole is adopted to intensify heat dissipation. Furthermore, the natural convection heat transfer process of LED luminaries is simulated by computational fluid dynamics (CFD) model before and after the structural modification. As shown by computational results, boring through-hole is beneficial to develop bottom-to-top natural convection, eliminate local circumfluence, and finally form better flow pattern. Analysis based on field synergy principle shows that boring through-hole across LED luminaries improves the synergy between flow field and temperature field, and effectively decreases the thermal resistance of luminaries-level heat dissipation structure. Under the same computational conditions, by luminaries-level structure improvement the highest temperature of heat sink is decreased by about 8°C and the average heat transfer coefficient is increased by 45.8%.

Appendices

Nomenclature

C :

Linear-anisotropic phase function coefficient

C _1ε :

Model constants C_1ε  = 1.44

C _2ε :

Model constants C_2ε  = 1.92

C _3ε :

Model constants C_3ε  = 0.8

C _μ :

Model constants C _μ  = 0.09

E :

$E=H-p \mathord{\left/ {\vphantom {p \rho }} \right. \kern-\nulldelimiterspace} \rho +{u^2} \mathord{\left/ {\vphantom {{u^2} 2}} \right. \kern-\nulldelimiterspace} 2$

g :

Acceleration of gravity(m s^− 2)

G :

Incident radiation

G _b :

The generation of turbulence kinetic due to buoyancy, $G_b =-\displaystyle\frac{\mu_t g_i }{\rho \Pr_t }\displaystyle\frac{\partial \rho }{\partial x_i}$

G _k :

The generation of turbulence kinetic due to mean velocity gradients, $G_k = - \rho \overline{u^{\prime}_{i}u^{\prime}_{j}} \displaystyle\frac{\partial u_{j}}{\partial x_{i}}$

h :

Heat transfer coefficient(W m^− 2 K⁻¹)

H :

Enthalpy(J kg⁻¹)

k :

Turbulence kinetic energy(m² s^− 2)

k _eff :

Effective thermal conductivity(W m⁻¹ K⁻¹)

p :

Static pressure(Pa)

Pr _t :

Turbulent Prandtl number for energy Pr _t  = 0.85

Q _R :

Radiation flux(w m^− 3), $Q_R =-\Gamma \nabla G$

t :

Time(s)

T :

Temperature(K)

μ :

Velocity(m s⁻¹)

Greek Symbols

α :

Absorption coefficient

β :

Intersection angle between velocity and heat flow field, degree

ρ :

Density(kg m^− 3)

μ :

Viscosity(kg m⁻¹ s⁻¹)

μ _t :

Turbulent viscosity $\mu_t ={C_\mu k^2} \mathord{\left/ {\vphantom {{C_\mu k^2} \varepsilon }} \right. \kern-\nulldelimiterspace} \varepsilon$

ε :

Turbulence dissipation rate(m² s^− 3)

σ _k :

Model constants σ _k  = 1.0

σ _ε :

Model constants σ _ε  = 1.3

σ _s :

Scattering coefficient

Γ:

Model parameter, $\Gamma =1 \mathord{\left/ {\vphantom {1 {\left( {3\left( {\alpha +\sigma_s } \right)-C\sigma_s } \right)}}} \right. \kern-\nulldelimiterspace} {\left( {3\left( {\alpha +\sigma_s } \right)-C\sigma_s } \right)}$