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Thermal Analysis Tool

Heat Sink Design Calculator
Electronics Cooling · Junction Temperature

Real-time calculation of junction temperature using fin-array thermal resistance. Switch between natural and forced convection, and visualize Bar-Cohen optimal fin pitch and fin-count optimization curves.

$$T_j = T_a + P_d \cdot R_{\text{total}}, \quad R_{\text{total}} = R_{jc} + R_{cs} + R_{sa}$$
Parameters
Power Dissipation P_d 50 W
Device Thermal Resistance θ_JC 1.0 K/W
From device datasheet
Ambient Temperature T_a 25 °C
Rated T_j max 125 °C
Material
Cooling Mode
Number of Fins N 20
Fin Height H 30 mm
Fin Length L 80 mm
Base Width W 80 mm
Fin Thickness t_f 1.0 mm
TIM Thermal Conductivity k_TIM 1.0 W/mK
TIM Thickness 0.10 mm
Over-temperature! T_j exceeds T_j_max.
Fin pitch is too small compared to the optimum (S < 0.5×S_opt)
T_j Junction
—
°C
T_case Case
—
°C
T_sink Heat Sink
—
°C
R_total
—
K/W
R_sa Heat Sink
—
K/W
h_eff Conv. Coeff.
—
W/m²K
S_opt (Bar-Cohen)
—
mm
Temperature Margin
—
K
T_j vs Fin Count N (optimization curve)
Thermal Resistance Breakdown
Theory — Heat Sink Thermal Resistance & Bar-Cohen Model

Junction Temperature

$$T_j = T_a + P_d \cdot (R_{jc} + R_{cs} + R_{sa})$$

Series thermal resistance model

Heat Sink Resistance R_sa

$$R_{sa} = \frac{1}{h_{\text{eff}} \cdot A_{\text{total}}}$$

$A_{\text{total}} = N \cdot 2HL + (N-1) \cdot SL$

Bar-Cohen Optimal Fin Pitch

$$S_{\text{opt}} = 2.714 \frac{L}{Ra_L^{1/4}}$$

Natural convection: S_opt minimizes fin-array thermal resistance

Forced Convection (Dittus-Boelter)

$$Nu = 0.023\, Re^{0.8}\, Pr^{0.4}$$

Hydraulic diameter $D_h = 2SH/(S+H)$