Heat Transfer Expert

Before Starting

1. Which mode? (conduction, convection, radiation, or combined)
2. Steady state or transient?
3. Internal or external convection?

Core Expertise Areas

Conduction

Fourier law: q = negative k A dT over dx, heat flows down temperature gradient. Thermal resistance: R = L over kA for flat wall, ln(r2 over r1) over 2 pi k L for cylinder. Composite walls: resistances in series and parallel, total R determines heat flux. Fins: extended surfaces increase heat transfer area, fin efficiency eta_f. Biot number: Bi = hL over k, ratio of convection to conduction resistance.

Convection

Newton cooling law: q = h A delta T, h is convection coefficient. Nusselt number: Nu = hL over k, dimensionless convection coefficient. Forced external: flat plate Nu correlations, cylinder in cross flow. Forced internal: Dittus-Boelter for turbulent pipe flow, Sieder-Tate with viscosity correction. Natural convection: buoyancy driven, Rayleigh number Ra = Gr times Pr.

Radiation

Stefan-Boltzmann: q = epsilon sigma A T4, radiation from surface at T. View factor: F_12 is fraction of radiation from 1 intercepted by 2. View factor reciprocity: A1 F12 = A2 F21. Radiation network: analogous to electrical resistance for enclosures. Gray body: emissivity constant with wavelength, simplifies radiation calculations.

Heat Exchangers

LMTD method: Q = UA times LMTD, log mean temperature difference. Effectiveness-NTU: useful when outlet temperatures unknown. Parallel flow vs counterflow: counterflow achieves closer temperature approach. Fouling: additional thermal resistance from deposits, reduces performance over time.

Best Practices

• Identify dominant heat transfer mode before detailed analysis
• Check Biot number to determine if lumped capacitance is valid
• Use appropriate correlation for flow geometry and regime
• Account for fouling in heat exchanger design with fouling factors

Common Pitfalls

Pitfall	Fix
Lumped capacitance when Bi greater than 0.1	Use spatial analysis or numerical method
Wrong correlation for flow regime	Check Re and geometry match correlation assumptions
Ignoring radiation at high temperature	Radiation scales as T4, dominates above 500 C
LMTD undefined for equal inlet-outlet temperatures	Use effectiveness-NTU method instead

Related Skills

• fluid-mechanics-expert
• thermodynamics-mech-expert
• manufacturing-processes-expert