Expansion valve for a refrigeration cycle
Solution Overview
Problem
Existing expansion valves in vapor compression refrigeration cycles face instability due to a hunting phenomenon caused by a mismatch in response times between the temperature sensitive medium and other components, leading to increased manufacturing complexity and costs.
Innovation Solution
The expansion valve incorporates a temperature sensitive rod with a blind hole containing a mixture of refrigerant and inert gas, where the mixing ratio of the inert gas is adjusted based on the ratio of the blind hole's equivalent diameter to its depth, allowing for a controlled time constant of heat conduction without the need for activated carbon or low heat conductivity layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If activated carbon is sealed in the blind hole of the temperature sensitive rod, then the time constant of heat conduction is ensured to limit the hunting phenomenon, but the internal structure becomes complicated and manufacturing costs increase
Solution Approach 1:
The invention extracts and removes the activated carbon from the blind hole, replacing it with a simple blind hole structure that still achieves the required time constant through geometric design (depth and diameter ratios), thereby eliminating manufacturing complexity while maintaining stability
Solution Approach 2:
The invention changes the parameters of the blind hole (depth, diameter, and their ratios) to control the heat conduction time constant, replacing the need for activated carbon with geometric parameter optimization that achieves the same stabilizing effect
2Reliability
If a low heat conductivity layer is provided to the inner wall of the blind hole, then the time constant of heat conduction is ensured to limit the hunting phenomenon, but the manufacturing steps and costs increase
Solution Approach 1:
The invention removes the low heat conductivity layer and replaces it with a geometrically optimized blind hole structure, eliminating the additional manufacturing step of applying thermal insulation layers while maintaining the required heat conduction characteristics
Solution Approach 2:
The invention uses parameter changes in the blind hole geometry (depth-to-diameter ratio) to control heat conduction characteristics, replacing the need for additional low heat conductivity layers with simple dimensional design
3Speed
If the response time period of the temperature sensitive medium is reduced, then the heat conduction response is faster, but the hunting phenomenon occurs causing instability of the refrigeration cycle
Solution Approach 1:
The invention optimizes the time constant by adjusting the blind hole geometric parameters (depth and diameter) to achieve the appropriate response speed that prevents hunting phenomenon while maintaining system stability
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 approach stabilizes the refrigeration cycle operation by adjusting the heat conduction time constant within a desired range, simplifying the valve's structure and reducing manufacturing costs while maintaining effective temperature sensing performance.
Implementation Method 1
a response time period (a time constant), which is a time period required to adjust the pressure and the temperature of the temperature sensitive medium into an equilibrium state through the heat conduction from the temperature sensitive rod
Implementation Method 2
a diaphragm (a pressure-operated member), which is displaced in response to a pressure difference between an internal pressure of a sealed space and a pressure of the low pressure refrigerant outputted from the evaporator. Here, the sealed space is a space, in which a temperature sensitive medium that changes a pressure thereof in response to a temperature is sealed
Data Source
AI summary
A temperature sensitive rod is communicated with a diaphragm that is displaceable in response to a pressure difference between an internal pressure of a sealed space, in which a temperature sensitive medium is sealed, and a pressure of a low pressure refrigerant outputted from an evaporator. A blind hole, which opens to the sealed space, is formed in an inside of the temperature sensitive rod. The temperature sensitive medium is a mixture gas of the refrigerant and an inert gas. A mixing ratio of the inert gas in the temperature sensitive medium corresponds to a ratio of an equivalent diameter of the blind hole relative to a depth of the blind hole in such a manner that a time constant of heat conduction from the temperature sensitive rod to the temperature sensitive medium is kept within a desired time constant range.