How Do Ammonia Evaporators Work in Refrigeration Systems?

Ammonia (R717) evaporators are the core low-pressure heat exchange components of industrial ammonia refrigeration loops, widely deployed in cold storage, seafood processing, dairy plants, food factories and blast freezers. Their core function is to absorb heat from cold rooms or production spaces by enabling liquid ammonia to vaporize, creating the low-temperature environment required for product preservation.

Ammonia refrigeration follows the standard vapor-compression cycle: compressor → condenser → expansion device → evaporator → back to compressor. The ammonia evaporator carries out the critical heat-absorbing phase change step. Below is a step-by-step working principle, plus a breakdown of two mainstream evaporator types used in cold storage: dry expansion unit coolers and flooded evaporators.

Step 1: Low-temperature, low-pressure ammonia enters the evaporator

High-pressure liquid ammonia flows out from the water-cooled condenser after releasing heat. It passes through an expansion valve (or orifice plate, float valve for flooded systems), which sharply reduces its pressure and temperature.

The output is a cold mixture of liquid and vapor ammonia, which is fed into the evaporator coil shell or tube bundle. For standard ceiling-hung ammonia unit coolers, the two-phase ammonia flows inside stainless steel heat exchange tubes.

Step 2: Heat transfer & ammonia vaporization (core working process)

Warm air from the cold storage or processing facility is blown across the outside of the finned ammonia tubes by axial fans. Heat transfers from the warmer air through tube walls into the cold liquid ammonia inside.

Ammonia has an extremely high latent heat of vaporization. As it absorbs sensible heat from surrounding air, liquid ammonia boils and turns into pure ammonia vapor. This phase change consumes massive heat rapidly, dropping the air temperature drastically. The cooled air circulates back into the warehouse to maintain set low temperatures from +5°C fresh storage down to -40°C blast freezing.

Key note: Copper tubing cannot be used for ammonia coils. Ammonia chemically reacts with copper to form corrosive complexes, so all evaporator tubes adopt carbon steel, SS304 or SS316 stainless steel.

Step 3: Ammonia vapor exits for compression

After complete vaporization inside the coil, low-pressure, low-temperature ammonia vapor accumulates at the top of the evaporator.

- For dry expansion unit coolers: A small superheat margin prevents liquid droplets from being drawn into the compressor.

- For flooded evaporators: An integrated mist separator removes entrained liquid ammonia to avoid liquid slugging, a serious fault that damages centrifugal or screw compressors.

The dry ammonia vapor is then sucked into the ammonia compressor. The compressor raises vapor pressure and temperature, pushing high-pressure hot gas into the condenser to reject heat to cooling tower water, restarting the full refrigeration cycle.

Our custom ammonia evaporators are engineered to match all industrial refrigeration scenarios: seafood cold storage, dairy processing plants, fruit & vegetable preservation warehouses, meat freezing facilities and large-scale logistics cold chains. We offer full customization of capacity, fin spacing, stainless steel materials and defrost modes to match unique site operating environments.

Contact our official email info@cstheatexchanger.com to view full technical specifications and project cases of industrial ammonia evaporators.