🔥 Heat Exchanger

In parallel flow, both fluids enter at the same end and flow in the same direction; the exit temperatures converge toward an intermediate value. In counter-flow, fluids enter at opposite ends; the cold fluid can exit hotter than the hot fluid's exit temperature, achieving higher effectiveness.

LMTD is the effective driving temperature difference for heat transfer in an exchanger. It is calculated as (ΔT₁ - ΔT₂) / ln(ΔT₁/ΔT₂), where ΔT₁ and ΔT₂ are the temperature differences between the streams at each end of the exchanger.

Fouling is caused by scale deposits (calcium carbonate), biological growth, corrosion, and particulates that accumulate on heat transfer surfaces, increasing thermal resistance. Management includes water treatment, regular cleaning, and designing with a fouling factor allowance in the original area calculation.

Effectiveness (ε) is the ratio of actual heat transfer to the maximum thermodynamically possible heat transfer. A value of 1.0 (100%) is unachievable in practice; well-designed counter-flow exchangers can reach 0.9 or higher.

Fins extend the heat transfer surface area on the side with a lower heat transfer coefficient (usually the gas side). This compensates for the lower convective conductance of gases compared to liquids, balancing the thermal resistances and improving overall performance.