How Evaporator Works in Refrigeration

Function and Categories of Evaporator

Evaporator is an essential part in refrigeration and takes the role to evaporate refrigerants. Its function is to output refrigeration and cool down cooling medium. Evaporator is divided into flooded evaporator and dry-type evaporator based on evaporation place of refrigerants. Flooded type is the one with refrigerant evaporated in shell side while dry-type with refrigerant evaporated inside tube. At present Shini adopts dry-type evaporator and below is its structure:
 

Important points in Designing Evaporators

In heat conduction, we are known that low temperature goes down and high temperature goes up in a same object. In regard to evaporator refrigerant inlet design, where heat exchange with cooling medium has not been conducted. Therefore, the inlet temperature is lower. Thus, the refrigerant inlet is down below and outlet on top. For the design of mini evaporator, there are 1 and 2 workflows based on actual situations. One flow-in and one flow-back is referred as one cycle loop of workflow. (No.1 and No.2 in the figure). Refrigerant absorbs heats of cooling medium and it turns into gas state from liquid. As heat exchange goes, refrigerant temperature has been raised; refrigerant enters evaporator from bottom and exists from top, so in the bottom of evaporator, refrigerant exists as liquid state. After heat exchange, refrigerant turns into gas completely. Heat exchange result differs as state changes When liquid is most efficient and gas is less efficient. It should ensure return air remains gas state because compressor can not handle with liquid, thus evaporator need to evaporate all liquid into gas.

The Effect of Evaporator on Performance

In a same service environment with the same power, the scale of machine performance is reflected by the amount of refrigeration and power consumption. And machines of high performance have big refrigeration and small power consumption. The obvious change of refrigeration often manifests itself in the design of evaporator and the evaporator effect can be reflected by evaporation temperature. Every 1℃ increase of evaporation temperature will boost 3.7% of refrigeration capacity. We recommend temperature should not be increased when the effect meet the requirement for excessively enhancement of evaporator will give rise to resources wastes caused by imbalance between operation effectiveness and investment cost.

Common Faults

Common faults of evaporator include fracture of copper pipe, lowering efficiency of heat exchange and corrosion of outer shell. Causes of fracture of pipe are as followed: excessive flow velocity, corrosion effect of secondary refrigerant and bad design. Excessive flow velocity exacerbates the corrosion of pipe inwall. To decrease the flow velocity, you need to regulate the valve added to device. If flow-meter is unavailable, you can observe the index via pressure gauge. The working pressure is recommended regulated in line with product catalogue. For the corrosion from cooling medium, we need to ensure PH value of liquid in water tank is 7. For fracture of copper pipe, we may continue the normal using of machine by blocking the broken holes. To prevent water inflow into compressor, it is necessary to check if there is regular refrigerant in hi-low pressure gauge every time prior to startup (Recommended replace evaporator).

The lowering efficiency of heat exchange is mainly caused by scale formation in heat exchange tube (Evaporator is not always culprit for problems may come from condenser, refrigerant capacity and expansion valve, etc). Use solution to eliminate the scale, basically we do not recommend customers to clean scale themselves because cleaning requires professional operation. In the daily machine operation, users should fill tank with clean water and check tank regularly and replace secondary refrigerant. Plus, users may adopt anti-rust pipes to avoid scale formation. Corrosion of outer shell is also caused by poor water quality so clean water is indispensable. Newly launched Shini evaporator is equipped with anti-rust outer shell to prevent corrosion.

Maintaining and Replacement

Apart from the solutions toward flow velocity and PH value of secondary refrigerant, we recommend machine unit should renew water every three months. If water quality is consistently poor, water replace cycle should be shortened. For replacement of evaporator of standard models, you need to ensure no refrigerant inside device than welding to avoid toxic gas produced by chemical reactions of refrigerant and flame. If evaporator is damaged, we suggest customers contact us for further solutions.