Refrigerant Distribution Control for Pressure-Safe Compressor Restart
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Solution Overview
Problem
Refrigerant vapor compression systems in transport refrigeration face challenges such as high refrigerant levels in the reservoir during compressor restart, leading to pressure spikes and potential system disabling, especially due to varying ambient and cargo temperature conditions, which require efficient refrigerant redistribution and control methods to maintain system reliability and efficiency.
Innovation Solution
The system employs controlled operation of the primary expansion valve, economizer valve, and liquid refrigerant valve to manage refrigerant redistribution during unit shut-off and restart, allowing for controlled refrigerant flow and pressure management, independent of superheat conditions, to prevent liquid entry into the compressor and alleviate pressure spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressor is restarted after shutdown, then the refrigeration system can resume cooling operation, but high refrigerant levels in the reservoir cause pressure spikes and potential system disabling
Solution Approach 1:
The system performs preliminary refrigerant redistribution during the off-cycle before compressor restart by controlling the expansion valve to migrate refrigerant from the reservoir to the evaporator. This preliminary action prevents high refrigerant levels from causing pressure spikes and compressor damage upon restart, thereby resolving the contradiction between resuming cooling operation and preventing system disabling.
2Adaptability or versatility
If the system operates in varying ambient and cargo temperature conditions, then the refrigeration system can adapt to different environments, but refrigerant redistribution becomes uncontrolled leading to high reservoir levels
Solution Approach 1:
The system uses feedback control by monitoring refrigerant conditions and controlling the expansion valve to redistribute refrigerant during off-cycles. This feedback mechanism maintains stable refrigerant level distribution despite varying ambient and cargo temperature conditions, resolving the contradiction between adaptability and stability.
3Strength
If liquid refrigerant enters the compressor during restart, then the compressor may suffer damage from liquid slugging, but preventing this requires controlled refrigerant flow management
Solution Approach 1:
The system performs preliminary refrigerant redistribution during the off-cycle to ensure liquid-free conditions in the compressor before restart. By migrating refrigerant from the reservoir to the evaporator before compression begins, the system prevents liquid slugging and protects compressor durability without requiring complex additional hardware.
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 enhances compressor reliability, prevents system disabling, and ensures efficient operation across varying temperature conditions by effectively managing refrigerant redistribution and pressure control, allowing for smooth transitions between operating modes and maintaining stable performance.
Implementation Method 1
a primary expansion device disposed in the refrigerant circuit downstream of said refrigerant reservoir and upstream of said refrigerant heat absorption heat exchanger
Implementation Method 2
a refrigerant compression device, a refrigerant heat rejection heat exchanger downstream of said compression device
Implementation Method 3
a refrigerant heat rejection heat exchanger downstream of said compression device
Implementation Method 4
the vapor heat rejection heat exchanger functions as a working fluid condenser
Implementation Method 5
the heat absorption heat exchanger functions as a working fluid evaporator
Implementation Method 6
a refrigerant heat absorption heat exchanger downstream of said refrigerant reservoir
Data Source
AI summary
A method for distributing a refrigerant charge level in a refrigerant vapor compression system includes restarting a stopped refrigerant compression device in a first mode; operating a primary expansion device independent of refrigerant heat absorption heat exchanger superheat; comparing a condition at a refrigerant reservoir to a prescribed condition; wherein when the condition is below the prescribed condition for a prescribed interval, operating the primary expansion device to control the refrigerant heat absorption heat exchanger superheat; and transitioning the refrigerant vapor compression system to a second mode.