Flash Tank Liquid Level Feedback Control for Compressor Protection
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Solution Overview
Problem
Maintaining a desired liquid level in a flash tank within vapor compression refrigeration systems is challenging, as excessive liquid can damage compressors, while insufficient liquid can impact the performance of expansion valves.
Innovation Solution
A dynamic control system that adjusts the amount of two-phase refrigerant provided to the flash tank using a controller and an upper electronic expansion valve, based on sensor measurements to maintain the liquid level between 40-60% of the tank's height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flash tank is used to separate gas and liquid refrigerant, then compressor cost is reduced, but liquid level control becomes challenging
Solution Approach 1:
The patent implements a feedback control system using a level sensor to detect liquid level in the flash tank and an expansion valve to adjust refrigerant flow. The controller continuously monitors the liquid level and dynamically adjusts the expansion valve opening to maintain the liquid level within the target range (40-60% of tank height), resolving the liquid level control challenge while keeping the flash tank configuration.
2Reliability
If liquid level in flash tank is increased, then expansion valve performance is improved, but compressor damage risk increases
Solution Approach 1:
The feedback control system uses a level sensor to continuously monitor liquid level and adjusts the expansion valve to maintain the liquid level within the safe operating range of 40-60% of tank height. This prevents both overfilling (which could cause compressor damage) and underfilling (which would harm expansion valve performance), thereby resolving the contradiction between protecting the compressor and ensuring expansion valve performance.
Solution Approach 2:
The system dynamically changes the expansion valve opening parameter based on liquid level conditions. By adjusting the valve opening degree in response to liquid level variations, the system maintains optimal refrigerant flow to the expansion valve while preventing liquid carryover to the compressor, thus balancing the competing requirements.
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 solution effectively maintains the flash tank's liquid level within the desired range, preventing compressor damage and ensuring optimal performance of expansion valves and other system components.
Implementation Method 1
A pressure sensor configured to measure a pressure of the liquid refrigerant within the flash tank
Implementation Method 2
A first expansion valve between the condenser and an inlet of the flash tank
Implementation Method 3
A flash tank configured to receive two-phase refrigerant from the condenser and separate the two-phase refrigerant into a vapor refrigerant and a liquid refrigerant
Implementation Method 4
a flash tank to separate out the gas and liquid can often provide a lower-cost solution
Data Source
AI summary
Systems and methods for flash tank liquid level control are provided. A flash tank is a device used to separate the vapor and liquid phases of a mixture. Maintaining a desired liquid level may be important. If the flash tank overflows, liquid injected into the compressor may potentially damage the compressor. If the flash tank drains out of liquid completely, two-phase refrigerant may then be provided being into a lower expansion value, which will impact its operation. To maintain the liquid level within the flash tank within the desired range of values, a pressure sensor may be provided to measure either a pressure differential or absolute pressure of the liquid refrigerant. This measurement may then be used to calculate the liquid level within the flash tank. A controller may then send control signals to an electronic expansion valve provided between a condenser and the flash tank to either open or close depending on the liquid level within the flash tank.