Refrigerant control system for a flash tank

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Solution Overview

Problem

Conventional refrigeration systems with flash tanks and shell-side evaporators face challenges in controlling refrigerant levels and flow, particularly when evaporators do not produce superheated refrigerant, leading to unstable operation, high costs, and unsuitability for certain evaporator types like flooded or falling film designs.

Innovation Solution

A system using a tube-side condenser and shell-side evaporator with a flash tank, where condenser outflow subcooling regulates inflow to the flash tank, and an orifice controls outflow from the flash tank, with multi-parameter control including compressor capacity, reducing the need for expensive sensors and valves.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional superheating-based control is used in flash tanks, then refrigerant level control is stable, but it is incompatible with shell-side evaporators that cannot superheat refrigerant

Engineering Contradiction:

Improvecompatibility with shell-side evaporatorsVSAvoidcontrol stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the control parameter from superheating (temperature-based) to subcooling (temperature differential-based). By measuring the temperature difference between the condenser outlet and the flash tank inlet, the system can control refrigerant flow without requiring superheating at the evaporator outlet, thus enabling compatibility with shell-side evaporators while maintaining control stability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces subcooling as an intermediary control mechanism. Instead of directly controlling based on evaporator outlet conditions (which require superheating), the system uses subcooling at the condenser outlet as a proxy parameter that indirectly controls flash tank refrigerant levels, enabling work-around the limitation of non-superheating evaporators

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If expensive sensors and valves are used for precise refrigerant control, then control precision is improved, but system cost increases

Engineering Contradiction:

Improverefrigerant level control precisionVSAvoidsystem cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent replaces expensive, complex sensors and control valves with simpler, more economical components. By using subcooling measurement (which can be achieved with basic temperature sensors already present in the system) and controlling refrigerant flow through the natural flash tank mechanism, the system achieves adequate control precision without investing in costly specialized equipment

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent enables the flash tank to self-regulate refrigerant levels through the subcooling control mechanism. The temperature differential naturally indicates when the flash tank needs more or less refrigerant, allowing the system to control itself without requiring expensive external sensors and actuators for each control point

Inventive Principle:

Principle #25Self-service

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 refrigerant flow, improves chiller performance, reduces costs, and is suitable for various evaporator types by using subcooling and orifice control, enhancing overall system efficiency and reliability.

Implementation Method 1

Condenser outflow subcooling may be used to regulate the inflow to the flash tank

Methodology Applied

Scientific EffectSubcooling: Supercooling

Implementation Method 2

Outflow from the flash tank to the evaporator may then be controlled by an orifice

Methodology Applied

Scientific EffectOrifice flow control: Pressure Drop

Implementation Method 3

the liquid refrigerant at least partially evaporates. 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

Methodology Applied

Scientific EffectPhase separation: Density Gradient

Implementation Method 4

the process fluid is cooled by an evaporator that absorbs heat from the process fluid by evaporating refrigerant

Methodology Applied

Scientific EffectEvaporation: Evaporation

Implementation Method 5

The refrigerant is then compressed by a compressor and transferred to a condenser

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 6

In the condenser, the refrigerant is cooled, typically by air flow and recondenses into a liquid

Methodology Applied

Scientific EffectCondensation: Condensation

Data Source

PatentUS9657978B2Refrigerant control system for a flash tank

Publication Date: 2017.05.23 TYCO FIRE & SECURITY GMBH

AI summary

A refrigeration system is provided, such as for use with chillers. The system uses a tube-side condenser, such as a microchannel condenser, along with a shell-side evaporator such as a falling film evaporator. A flash tank economizer is disposed between the condenser and the evaporator, and an inlet valve 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 to a system compressor. Liquid phase refrigerant combined with some gas phase refrigerant exits the flash tank and is directed through an orifice before entering the evaporator.