Hot gas defrost using fluid from high pressure tank
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Solution Overview
Problem
Existing refrigeration systems face inefficiencies and limitations in evaporator defrosting, requiring long times and high energy consumption, and may struggle with defrosting multiple evaporators effectively.
Innovation Solution
A refrigeration system that utilizes refrigerant from a high-pressure flash tank to facilitate improved evaporator defrosting, where one or more evaporators operate in a normal refrigeration mode while others are defrosted using hot gas produced by the refrigeration process, without the need for specialized high-pressure components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional defrost processes are used, then evaporators can be defrosted, but the process takes a relatively long time and consumes a relatively large amount of energy
Solution Approach 1:
The patent converts the cold refrigerant that would normally be wasted during defrost operations into a useful resource by directing it to pre-cool the evaporator before the hot gas defrost process begins. This approach transforms what was previously a harmful waste of cold into a beneficial pre-conditioning step, reducing the overall energy required for defrosting and shortening the defrost time cycle.
Solution Approach 2:
The system performs preliminary cooling of the evaporator using cold refrigerant from the flash tank before the actual hot gas defrost process starts. This pre-cooling action prepares the evaporator in advance, creating a temperature differential that accelerates the subsequent defrosting process and reduces total defrost time.
2Adaptability or versatility
If traditional defrost processes are used, then single evaporators can be defrosted, but the system is incapable of providing adequate defrosting for multiple evaporators in a multiple-evaporator refrigeration system
Solution Approach 1:
The flash tank is designed to serve multiple functions: it acts as a refrigerant storage vessel, a pre-cooling chamber for defrost operations, and a pressure regulation device. By making the flash tank multi-functional, the system can handle defrosting of multiple evaporators without adding separate dedicated components for each function, thus maintaining system simplicity while expanding capability.
Solution Approach 2:
The system divides the defrost process into distinct phases: a pre-cooling phase using cold refrigerant from the flash tank, followed by a heating phase using hot gas. This segmentation allows the system to efficiently manage multiple evaporators by cycling them through these phases independently, providing adequate defrosting capability without requiring complex simultaneous multi-evaporator handling mechanisms.
3Reliability
If high pressure components are used for hot gas defrost, then defrost performance is improved, but system complexity and cost increase
Solution Approach 1:
The system dynamically changes the pressure parameter of the refrigerant by utilizing the flash tank's ability to store refrigerant at elevated pressures and then release it as needed. By controlling the pressure regulation valve, the system can deliver hot gas at the optimal pressure for defrosting without requiring the entire system to be designed for high pressure operation, thus maintaining component simplicity while achieving improved defrost performance.
Solution Approach 2:
The flash tank acts as an intermediary device between the refrigeration cycle and the defrost process. It stores refrigerant at high pressure and releases it in a controlled manner to the evaporators needing defrost. This intermediary approach allows high-pressure hot gas defrosting without requiring all system components to be high-pressure rated, reducing overall system complexity and cost.
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 enhances defrost performance and energy efficiency, allowing for flexible operation and reducing system complexity and cost, while effectively managing the defrosting of multiple evaporators.
Implementation Method 1
A heat exchanger is positioned downstream from medium-temperature (MT) compressor(s) and transfers heat from compressed refrigerant output by the MT compressor(s) to a flow of refrigerant from the auxiliary flash tank
Implementation Method 2
The controller causes the first evaporator to operate in the defrost mode by adjusting the pressure-regulating valve to increase a pressure of the first flash tank relative to a pressure of the second flash tank, allowing flow of refrigerant from the first flash tank to the heat exchanger
Implementation Method 3
An auxiliary flash tank receives refrigerant from a gas cooler
Data Source
AI summary
A refrigeration system includes pressure-regulating valve positioned between two flash tanks and a heat exchanger is positioned downstream from a medium temperature compressor. After determining that operation of an evaporator in a defrost mode is indicated, the system causes the evaporator to operate in the defrost mode by adjusting the pressure-regulating valve to increase a pressure of a first flash tank relative to a pressure of a second flash tank, allowing flow of refrigerant from the first flash tank to the heat exchanger, and allowing refrigerant heated by the heat exchanger to flow to the first evaporator.