Cascade Air Conditioner Pipe Diameter Design for Oil Return
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Solution Overview
Problem
In dual refrigerant cycle systems with a cascade heat exchanger, the flow speed of refrigerant in the secondary-side cycle is typically slow, leading to difficulties in the return of refrigerating-machine oil to the compressor.
Innovation Solution
The system incorporates a secondary-side cycle with smaller pipe diameters for the connection pipes compared to the primary-side cycle, enhancing the flow speed of refrigerant and facilitating the return of refrigerating-machine oil by adjusting the pipe diameters based on refrigerating capacity for specific refrigerants like carbon dioxide, R32, and R454B.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a cascade heat exchanger is introduced to form a dual refrigerant cycle, then heat exchange efficiency is improved, but refrigerant flow speed becomes slow causing refrigerating-machine oil to difficultly return to the compressor
Solution Approach 1:
The patent applies different pipe diameters to different locations in the system. Specifically, the secondary-side connection pipe has a smaller diameter than the primary-side connection pipe, creating local differentiation in flow characteristics. This allows the secondary-side refrigerant to achieve higher flow velocity in the connection pipe, enabling refrigerating-machine oil to return to the compressor, while maintaining adequate heat exchange capacity in the cascade heat exchanger.
2Speed
If smaller pipe diameters are used in the secondary-side cycle, then refrigerant flow speed increases facilitating oil return, but pressure loss may increase
Solution Approach 1:
The patent changes the pipe diameter parameter specifically for the secondary-side connection pipe to optimize flow velocity. By selecting an appropriate smaller diameter (7.9mm, 9.5mm, or 12.7mm based on refrigerating capacity), the system achieves sufficient refrigerant flow speed for oil return while controlling pressure loss within acceptable limits for the connection section.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration increases the flow speed of refrigerant in the secondary-side cycle, ensuring that refrigerating-machine oil easily returns to the compressor, thereby improving the overall efficiency of the refrigerant cycle system.
Implementation Method 1
a cascade heat exchanger that exchanges heat between the first refrigerant and the second refrigerant
Data Source
Figure 1
AI summary
A refrigerant cycle system (100) includes a primary-side cycle (20) that circulates a first refrigerant, a secondary-side cycle (40) that the second refrigerant, and a cascade heat exchanger (35) that exchanges heat between the first refrigerant and the second refrigerant. The primary-side cycle (20) includes a primary-side connection pipe. The secondary-side cycle (40) includes a secondary-side connection pipe. The primary-side connection pipe includes a primary-side gas connection pipe (22) and a primary-side liquid connection pipe (21). The secondary-side connection pipe includes a secondary-side gas connection pipe (42) and a secondary-side liquid connection pipe (41). The pipe diameter of the secondary-side gas connection pipe (42) is smaller than the pipe diameter of the primary-side gas connection pipe (22), or the pipe diameter of the secondary-side liquid connection pipe (41) is smaller than the pipe diameter of the primary-side liquid connection pipe (21).