Views: 0 Author: Site Editor Publish Time: 2026-09-04 Origin: Site
For blast freezer / IQF tunnel operating at ‑40 °C evaporating temperature, used for meat, seafood, poultry quick‑blast freezing. This unit is pump‑liquid‑overfeed (recirculation) type; DX direct‑expansion is not recommended at this low temperature.
Item | Specification for‑40°C Ammonia Blast Freezer Evaporator |
|---|---|
Refrigerant | R717 Ammonia, liquid overfeed pump circulation |
Evaporating temp | ‑40 °C |
Blast room air temp | ‑30 ~‑35 °C |
Air velocity | 3.0‑4.5 m/s (high‑speed blast requirement) |
Recirculation ratio | 3:1 ~ 4:1 (critical for‑40 °C low‑temp operation) |
Fin pitch | 8‑12 mm wide pitch, anti‑frost blockage; narrow‑pitch fins forbidden |
Defrost mode | Hot‑gas ammonia defrost (primary); optional auxiliary water spray defrost |
Capacity range | 50 kW ~ 500 kW, modular multi‑unit combination for large IQF tunnel |
❗ Copper / copper alloy strictly forbidden for ammonia system.
Heat‑exchange tubes: Seamless carbon steel / 304 stainless steel. Must satisfy low‑temperature impact test for‑40 °C service.
Fins: Aluminum (epoxy coated) / 304 stainless steel fins. Avoid thin‑fins frost‑bonding at ultra‑low temp.
Casing & drain pan: 304 stainless steel. Drain pan + drain pipe with heat tracing to prevent ice plugging during defrost.
Fans: Low‑temperature resistant axial fans, IP55/IP66 motor, anti‑condensation heater. VFD‑speed adjustable optional.
Headers & joints: Full steel/stainless steel, full penetration welding, ammonia‑resistant gaskets.
Liquid overfeed pump recirculation is mandatory At‑40 °C low suction pressure, insufficient liquid supply creates local dry‑out inside coil, heavy performance drop. Maintain 3‑4 times recirculation ratio, guarantee full tube inner wetting.
Hot‑gas defrost sequence control is vital
Perform pump‑out before defrost: evacuate liquid ammonia inside evaporator coil, prevent liquid hammer / liquid‑shock risk at ultra‑low temperature.
Good hot‑gas distribution across all coil passes; avoid partial coil no‑defrost and permanent ice build‑up.
Drain‑pan tracing must run together with defrost; melted water cannot stay and re‑freeze.
Frost management ‑40 °C blast freezer builds frost extremely fast. Wide 8‑12 mm fin pitch extends running time between defrost cycles. Too small fin pitch causes airflow blockage in short production time.
Mechanical low‑temperature resistance All coil, header, support structure shall consider thermal contraction stress under‑40 °C; material low‑temperature impact property must meet pressure‑code requirement.
Safety requirement Pressure relief ports, strict leak test, ammonia‑resistant sealing. Comply with local industrial ammonia refrigeration codes.
Using small fin pitch → frost bridging, sharp capacity drop.
Low liquid‑overfeed ratio → partial dry‑out inside tubes, poor cooling effect.
Missing pump‑out step before hot‑gas defrost → liquid hammer risk for coil and pipeline.
Drain system without heat tracing → drain outlet frozen solid after defrost.
