产品的热设计(Thermal_introduction)

产品的热设计(Thermal_introduction)

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)


Important Components For Thermal Design ..
  Heat Sink
  Heat Pipe
  Fan
  TIM ( Thermal Interface Material)
  Combination of aforementioned components

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看似还行，下来学习一下！