Air Conditioning Expansion Control for Two-Phase Heat Exchange
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Solution Overview
Problem
Conventional multiple-chamber air-conditioning apparatuses experience deteriorated heat transfer performance in cooling operations due to refrigerant flowing near the outlet of indoor heat exchangers becoming superheated gas, which has a lower heat transfer coefficient compared to a gas-liquid two-phase state.
Innovation Solution
Incorporating a third heat exchanger that allows refrigerant flowing between the first and expansion devices to exchange heat with refrigerant between the expansion and second heat exchangers, along with detectors and temperature sensors to control the expansion device's opening degree, ensuring appropriate refrigerant flow for each indoor heat exchanger based on detected temperature and pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the opening degree of each expansion valve is controlled to maintain a degree of superheat within a prescribed range, then the refrigerant flow amount is adjusted for each indoor heat exchanger, but the heat transfer performance deteriorates due to superheated gas formation
Solution Approach 1:
The invention changes the control parameter from degree of superheat to degree of subcooling. By controlling the expansion valve opening degree to maintain subcooling within a prescribed range instead of superheat, the system achieves both proper refrigerant flow distribution and improved heat transfer performance, as subcooling ensures refrigerant remains in liquid or two-phase state rather than becoming superheated gas
Solution Approach 2:
The invention implements feedback control by using a detector to measure the actual degree of subcooling at the condenser outlet and adjusting the expansion valve opening degree accordingly. This closed-loop control ensures the refrigerant maintains optimal state (liquid or two-phase) for maximum heat transfer efficiency while automatically adapting to varying operating conditions
2Reliability
If the refrigerant flows through the indoor heat exchanger in gas-liquid two-phase state, then the heat transfer coefficient is high, but controlling the flow amount becomes more difficult
Solution Approach 1:
The invention simplifies flow control by changing from superheat-based control to subcooling-based control. By maintaining subcooling within a prescribed range, the system naturally ensures the refrigerant exits the condenser in liquid or two-phase state, which then flows appropriately through the expansion valve into the evaporator. This approach maintains high heat transfer performance while simplifying the control logic and reducing system complexity
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 maintains refrigerant in a two-phase gas-liquid state near the outlets of indoor heat exchangers, enhancing heat transfer performance and reducing energy consumption compared to conventional systems.
Implementation Method 1
a third heat exchanger configured to cause the refrigerant flowing through a refrigerant pipe between the first heat exchanger and the expansion device to exchange heat with the refrigerant flowing through a refrigerant pipe between the expansion device and the second heat exchanger
Data Source
Figure 1~2
Figure 3
AI summary
An air-conditioning apparatus 100 includes an internal heat exchanger 20 in which refrigerant flowing through a refrigerant pipe between an outdoor heat exchanger 3 and an expansion device 4 and refrigerant flowing through a refrigerant pipe between the expansion device 4 and an indoor heat exchanger 5 exchange heat, a pressure sensor 31, a first temperature sensor 32 that detects temperature of the refrigerant flowing into the expansion device 4 in the cooling operation, and a control unit 51 configured to control the opening degree of the expansion device 4 based on results of detection by the pressure sensor 31 and the first temperature sensor 32 in the cooling operation.