Two step oil motive eductor system
Solution Overview
Problem
Hermetically sealed chiller assemblies face challenges in maintaining efficient refrigerant flow and oil viscosity due to the mixing of lubricating oil and refrigerant, leading to reduced heat transfer capacity and potential cavitation, especially under low head pressure conditions where traditional eductor systems experience performance reduction or failure.
Innovation Solution
A two-step oil motive eductor system is implemented, comprising a gas motive eductor and an oil motive eductor, which uses pressurized oil and refrigerant gas to manage the oil and refrigerant mixture, ensuring stable oil suction conditions and minimizing refrigerant load in the oil sump, thereby maintaining consistent operation across varying refrigerant pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional single eductor system is used, then the structure is simple, but the system fails under low head pressure conditions and cannot maintain stable oil suction
Solution Approach 1:
The single eductor system is divided into two separate eductors: a first eductor for oil suction from the oil sump and a second eductor for refrigerant gas suction from the evaporator. This segmentation allows each eductor to be optimized for its specific function, enabling reliable operation under low head pressure conditions while maintaining manageable system complexity through functional specialization.
2Reliability
If oil and refrigerant mix extensively, then lubrication is provided to the compressor, but heat transfer capacity reduces and cavitation risk increases
Solution Approach 1:
The second eductor extracts refrigerant gas from the evaporator and delivers it directly to the compressor plenum, separating the refrigerant flow path from the oil flow path. This extraction prevents excessive mixing of oil and refrigerant in the heat exchangers, maintaining heat transfer capacity while still providing necessary lubrication to the compressor through the first eductor's oil delivery system.
3Use of energy by moving object
If head pressure is low, then energy efficiency improves, but eductor performance reduces and system stability deteriorates
Solution Approach 1:
The two eductors are designed with different local characteristics optimized for their specific functions: the first eductor is optimized for oil suction with appropriate nozzle geometry for liquid handling, while the second eductor is optimized for refrigerant gas suction with geometry suited for vapor handling. This local optimization allows each eductor to maintain reliable performance across a wider range of head pressure conditions, including low head pressure operation.
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
The two-step system stabilizes oil suction conditions and maintains efficient refrigerant flow, even under low head pressure conditions, by utilizing a high-pressure oil motive fluid to manage the oil and refrigerant mixture, reducing the risk of cavitation and ensuring consistent operation of the chiller assembly.
Implementation Method 1
The first eductor includes a first suction inlet that receives a first oil and refrigerant mixture from a plenum of a compressor, a first motive inlet that receives a first motive fluid from an oil sump, and a first outlet that discharges a first outlet mixture to the oil sump
Implementation Method 2
The second eductor includes a second suction inlet that receives a second oil and refrigerant mixture from an evaporator, a second motive inlet that receives a second motive fluid from a condenser, and a second outlet that discharges a second outlet mixture to the plenum of the compressor
Data Source
AI summary
An eductor system for a chiller assembly is provided. The system includes a first and a second eductor. The first eductor includes a first suction inlet that receives a first oil and refrigerant mixture from a plenum of a compressor, a first motive inlet that receives a first motive fluid from an oil sump, and a first outlet that discharges a first outlet mixture to the oil sump. The first outlet mixture includes both the first oil and refrigerant mixture and the first motive fluid. The second eductor includes a second suction inlet that receives a second oil and refrigerant mixture from an evaporator, a second motive inlet that receives a second motive fluid from a condenser, and a second outlet that discharges a second outlet mixture to the plenum of the compressor. The second outlet mixture includes both the second oil and refrigerant mixture and the second motive fluid.