Receiver driers and accumulators seem to have little visibility in refrigerant systems. When sourcing suppliers, it is found that most suppliers basically lack design capabilities. Does this mean these two products themselves have little technical content?

This article introduces several factors that need to be considered in the design process of these two products.

Effective Volume

Probably the most important parameter of receiver driers and accumulators is their internal volume. A large-volume cavity can adjust the total amount of refrigerant directly participating in the system cycle under different system operating conditions. When the system requires less refrigerant, it will be stored in this cavity in liquid form.

A larger volume of the receiver drier can ensure a wide refrigerant charging window, thereby ensuring the system operates properly under more working conditions. For heat pump systems, since there are two operating modes (heat pump and refrigeration), the system's demand for the total amount of refrigerant is different. Therefore, when designing a receiver drier or accumulator, it is necessary to take into account the refrigerant charging window under both modes.

Generally speaking, the receiver drier commonly used in passenger cars currently requires an internal volume of about 300ml or more, while the accumulator usually has an internal volume larger than 600ml to ensure that only gas returns to the compressor.

Internal Oil Return Design

For refrigerant systems, maintaining compressor oil circulation is particularly important, and the flow of compressor oil inside all components should be considered during the design process. Accumulators and receiver driers are no exceptions.

Especially for accumulators, the return air channel is usually designed at the upper part, but oil accumulates at the bottom due to gravity, so a special oil return channel needs to be designed. A typical structural design of an accumulator is as follows:

The diameter of the oil return channel needs to be determined through calculation and testing to prevent liquid refrigerant from entering the compressor suction through the oil return hole, which may lead to compressor liquid slugging.

Correspondingly, when designing a receiver drier, the liquid outlet should be designed at the bottom of the receiver drier as much as possible. A typical design sketch of a receiver drier is as follows:

There is an exception here: for CO₂ systems, the density ratio of oil to refrigerant varies under different operating conditions, resulting in oil inversion. That is to say, compressor oil floats on top of the refrigerant under specific operating conditions, so the oil circuit design may follow a different approach.

Desiccant Filter Packet

Generally speaking, refrigerant systems require the addition of a desiccant filter, which is usually placed inside the receiver drier or accumulator. The type and dosage of desiccant need to be confirmed. Common desiccants include AD-1, XH7, etc., whose appearance is shown in the figure. The dosage of desiccant can be simply designed according to an effective water absorption capacity of 15g.

The desiccant needs to be protected by non-woven fabric. To prevent it from entering the system and causing compressor wear, expansion valve blockage and other problems, the pore size of the non-woven fabric needs to be considered, or an additional filter screen can be added at the outlet of the receiver drier or accumulator.

Integrated Internal IHX

At present, IHX (Internal Heat Exchanger) is increasingly used, especially in heat pump models. An IHX integrated into the accumulator has also been proposed. Therefore, during the design process, it is necessary to consider whether to meet this demand. If so, more design variables need to be focused on, such as regenerative efficiency, pressure drop on both sides, etc. The figure below shows an accumulator with integrated IHX for CO₂ systems introduced by Sanhua in Patent CN 105805990 A.

Different System Control Strategies

The control strategies for the two different systems are slightly different.

For accumulator systems, due to the liquid stored in the tank, there is basically no superheat at the outlet. Therefore, the system control mostly focuses on controlling the subcooling degree at the condenser outlet, and a sensor is required at the condenser outlet to monitor the subcooling degree accordingly.

For receiver drier systems, superheat can be controlled, so a sensor is required at the evaporator outlet to monitor the superheat degree.

Others

In addition to the above considerations, other conventional requirements include internal flow resistance, structural strength, burst pressure, pressure pulse fatigue, connection structure, production process and other factors.