When sourcing an ammonia evaporator, you must prioritize material compatibility and thermal efficiency. Ensure the tubes are made of stainless steel (304 or 316L) or high-quality aluminum, as ammonia is corrosive to copper. The fin spacing is critical; for freezing applications, a spacing of 8mm to 12mm is recommended to prevent rapid frost buildup. Additionally, verify the design pressure, which should typically be rated for at least 25 bar (362 psi) to ensure safety under varying thermal loads.