Fundamentals

Module from the Heat Exchanger Engineering Curriculum curriculum.

Module 1 - Heat Transfer Fundamentals · Learning Objectives · 1. Compute Q = U*A*LMTD*F for any 2-stream heat exchanger · 2. Apply LMTD correction factor F for multi-pass and cross-flow · 3. Estimate U from tube-side + shell-side + fouling + wall resistance · 4. Size exchanger area given duty, approach temperature, and U · 5. Recognize when crossover (temp crossing) requires multiple shells · Typical Overall Heat Transfer Coefficients U (BTU/hr-ft2-F)

Service	U clean	U fouled	Design Margin	Notes	Source
Water/water	250-500	150-300	20%	Very high	TEMA
Light HC / water	80-200	60-150	25%	Gasoline cooler	Perry
Heavy HC / water	30-100	25-80	30%	Residuum	Perry
Light HC / light HC	70-150	50-100	25%	Process-process	Perry
Gas / water	25-60	20-50	30%	Lower density side	TEMA
Gas / gas	10-25	8-20	30%	Low U both sides	TEMA
Condensing HC / water	100-250	80-200	20%	Overhead condenser	Perry
Reboiler (kettle)	150-400	100-300	30%	Boiling shell side	Perry
Steam / water	250-750	200-500	20%	High both sides	TEMA
Air / gas (air cooler)	10-30 Ubare	-	30%	Finned tubes	API 661
LMTD and F-Factor Formulas
LMTD = (dT1 - dT2) / ln(dT1/dT2). For counterflow, dT1 = Thi - Tco and dT2 = Tho - Tci. For parallel flow, dT1 = Thi - Tci and dT2 = Tho - Tco. F = correction factor for actual pass arrangement (Tinker charts or Bowman equations). F must be > 0.75 for acceptable design. F < 0.8 suggests use more shells in series.

Source: Heat_Exchanger_Engineering_Curriculum_v1.xlsx · Sheet: Fundamentals

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