产品的热设计(Thermal introduction).pptVIP

Introduction of Thermal GGT/RE – Environment Test Team Primary Mechanic of Heat Transfer Thermal energy transport: cause by temperature difference, high T - low T Conduction Heat transferring by solid medium Convection Transferring energy between solid surface and fluid Mass transport Natural (free) convection Forced convection Radiation Heat transferring by electromagnetic waves Conduction Fourier’s Law Q= -KA ΔT/ΔL Q: heat transfer rate A: cross-sectional area of heat flux ΔT/ΔL: temperature gradient K: thermal conductivity (W/mk) Ex. Al = 230 Cu = 380 Mylar = 1.8 Convection Newtonian cooling Law Qc = hc As (Ts – Ta) Qc: convection heat transfer rate As: surface area Ts: surface temperature of solid Ta: tmperature of ambient hc: heat transfer coefficient, f(flow type, body geometry, physical property, temperature, velocity, viscosity…) Natural convection Forced convction hc of air, natural convection: 0.0015~0.015 W/in2℃ forced convection: 0.015~0.15 W/in2℃ Radiation Qa = εσAF1-2( Ts4 – Ta4) Qa: radiation heat transfer rate ε: emissivity, 0 ≦ ε ≦ 1 σ: Stefan-Boltzmann constant A: surface area F1-2: view factor Ts: temperature of body s Ta: temperature of body a Thermal Resistance R = V / I V: voltage = ΔT: temperature difference I: current = Q: heat Conduction Rk = ΔL/KAk Convection Rs = 1 / hcAs Radiation Ra = (Ts – Ta) /εσAF1-2( Ts4 – Ta4) Basic Concepts for NB Thermal Design Thermal Design Target Thermal design must meet thermal spec. of CPU, all key components (HDD, FDD, CD-ROM, PCMCIA…), and all IC chips (Chipset, VGA, RAM, PCMCIA…), and all IC chips (Chipset, VGA, RAM, Audio…) in each user conditions ?Thermal Resistance Θj-a = (Tj – Ta) / Pcpu Θ j-a : CPU junction to ambient thermal resistance Tj: CPU junction temperature Ta: ambient temperature Pcpu: CPU power Basic Concepts for NB Thermal Design System Thermal Coupling effect Θj-a = (Tj – Ta – Tsys) / Pcpu Tsys: system temperatu