What are the unique design requirements for cryogenic heat exchangers?

Cryogenic challenges: materials must avoid brittle fracture at low temperatures (aluminum alloys, austenitic stainless steel, nickel alloys), high thermal expansion stresses (carefully designed expansion provisions), extremely low heat leak requirements (vacuum insulation, cold box design), and handling dense fluids and phase change. Common types: brazed aluminum plate-fin (LNG, air separation - high surface density), coil-wound (very large LNG units), and printed circuit (compact, high pressure). Design must address cooldown procedures, emergency warmup, and two-phase distribution.