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engines
Thermal-resistance network
Thermal-resistance network
串并联R=L/kA · 复合墙U值 · Q=ΔT/ΣR+温度分布
Composite wall as resistors in series · ΣR, U-value and heat flow Q
Fin heat transfer
Fin heat transfer
m=√(hP/kA) · 肋效率η=tanh(mL)/mL · 温度分布
Extended surface · m = √(hP/kAc), fin efficiency η = tanh(mL)/(mL)
Conduction shape factor
Conduction shape factor
二维稳态Q=S·k·ΔT · 埋管/边/角几何
2D steady conduction · Q = S·k·ΔT with the geometry in S
Biot number · lumped-capacitance criterion
Biot number · lumped-capacitance criterion
Bi=hLc/k · Bi<0.1集总有效 · vs内部梯度
Compare internal conduction vs surface convection resistance
Lumped capacitance · cooling curve
Lumped capacitance · cooling curve
θ/θ0=exp(−t/τ) · τ=ρVc/hA · 冷却曲线
θ/θ₀ = exp(−t/τ), τ = ρVc/(hA)
Critical insulation radius · cylinder
Critical insulation radius · cylinder
rc=k/h · r<rc加保温反增散热 · Q峰值
r_c = k_ins/h · adding insulation can raise heat loss
Convection · Newton's law of cooling
Convection · Newton's law of cooling
牛顿冷却Q=hAΔT · 自然vs强制h · 热流密度
Q = h·A·(Ts − T∞) — surface heat transfer by convection
Nusselt correlation · Nu = C·Reᵐ·Prⁿ
Nusselt correlation · Nu = C·Reᵐ·Prⁿ
Nu=C·Reᵐ·Prⁿ · Dittus-Boelter · h=Nu·k/L
Forced convection — dimensionless correlation gives h = Nu·k/L
LMTD · heat exchanger driving force
LMTD · heat exchanger driving force
ΔTlm=(ΔT1−ΔT2)/ln(ΔT1/ΔT2) · Q=UAΔTlm · 顺/逆流
Q = U·A·ΔT_lm — the log-mean temperature difference
Radiation view factor F₁₂
Radiation view factor F₁₂
F12几何 · 互易A1F12=A2F21 · 求和ΣFij=1
Configuration factor from geometry · reciprocity A₁F₁₂ = A₂F₂₁ · summation ΣF = 1
Net radiation exchange (two gray surfaces)
Net radiation exchange (two gray surfaces)
Q=σ(T1⁴−T2⁴)/Σ辐射热阻 · 发射率 · 角系数
Radiative-resistance network · Q = σ(T₁⁴−T₂⁴) / (R_surf1 + R_space + R_surf2)
Heat-exchanger effectiveness (ε-NTU)
Heat-exchanger effectiveness (ε-NTU)
NTU=UA/Cmin · Cr=Cmin/Cmax · 效能ε · Q=εCminΔTmax
Cr = Cmin/Cmax · NTU = UA/Cmin · ε = Q/Qmax · Q = ε·Cmin·(Th,in − Tc,in)