Flash Tank Economizer Control for Shell-Side Chillers
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Solution Overview
Problem
Conventional refrigeration systems with flash tank economizers face challenges in controlling refrigerant levels and flow, especially when using shell-side evaporators that do not produce superheated refrigerant, leading to unstable operation, high costs, and unsuitability for certain evaporator types.
Innovation Solution
A refrigeration system employing a control system with a flash tank feed valve acting as an expansion valve, a fixed orifice for liquid-rich mixture flow to the evaporator, and a level switch to prevent overfilling, along with compressor speed control for feed-forward adjustments, to maintain subcooling and optimize chiller performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional superheating-based control is used, then control precision is improved, but applicability deteriorates because shell-side evaporators cannot superheat refrigerant
Solution Approach 1:
The patent changes the control parameter from superheating (temperature above boiling point) to subcooling (temperature below condensation point). This allows the control system to work with shell-side evaporators that cannot superheat refrigerant, while maintaining precise control capability through the subcooling-based feed valve regulation.
2Stability of the object's composition
If flash tank level control is implemented, then operational stability is improved, but system complexity increases due to additional sensors and control loops
Solution Approach 1:
The patent implements a feedback control loop where the subcooling sensor monitors condenser outlet conditions and automatically adjusts the feed valve position. This closed-loop feedback mechanism maintains flash tank level stability while integrating smoothly into the existing refrigeration cycle without requiring complex additional systems.
3Productivity
If subcooling control is used, then chiller performance is improved, but manufacturing complexity increases
Solution Approach 1:
The subcooling control system uses the refrigerant's own thermal properties and the existing condenser outlet conditions to generate control signals. The system self-regulates by measuring subcooling directly at the condenser outlet and automatically adjusting feed valve position, eliminating the need for external control devices or complex manufacturing modifications.
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 reduces system costs, improves reliability, and enhances performance by stabilizing condenser pressures and evaporator efficiency, while being suitable for various evaporator types, including shell-side evaporators, and reduces refrigerant charge.
Implementation Method 1
In the condenser, the refrigerant is cooled, typically by air flow and recondenses into a liquid
Implementation Method 2
the refrigerant is cooled, typically by air flow
Implementation Method 3
the process fluid is cooled by an evaporator that absorbs heat from the process fluid by evaporating refrigerant
Implementation Method 4
an evaporator that absorbs heat from the process fluid
Implementation Method 5
the condensed refrigerant may then be directed to the flash tank where the liquid refrigerant at least partially evaporates
Implementation Method 6
The vapor may be extracted from the flash tank and redirected to the compressor, while liquid refrigerant from the flash tank is directed to the evaporator
Data Source
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AI summary
A refrigeration system is provided, such as for use with chillers. The system uses a tube-side condenser (24), such as a microchannel condenser, along with a shell-side evaporator (32) such as a falling film evaporator. A flash tank economizer (26) is disposed between the condenser and the evaporator, and an inlet valve (28) to the flash tank is controlled based upon subcooling of condensate from the condenser. The vapor exiting the flash tank may be fed via an economizer line (60) to a system compressor (50). Liquid phase refrigerant combined with some gas phase refrigerant exits the flash tank and is directed through an orifice (30) before entering the evaporator.