Direct-Expansion Evaporator Flash-Gas-Driven Liquid Recirculation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Direct expansion refrigeration systems face a reduction in cooling capacity due to reduced liquid refrigerant flow through the evaporator, which is exacerbated by the inefficiency in utilizing flash gas generated during the expansion process.
Innovation Solution
A vapor ejector and separator combination is used to recirculate additional refrigerant liquid from the evaporator outlet to the inlet, leveraging flash gas generated during throttling to increase the heat-absorbing capacity by enhancing liquid flow and heat transfer within the evaporator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If liquid refrigerant flow is reduced to achieve superheat at evaporator outlet, then superheat is improved, but cooling capacity deteriorates
Solution Approach 1:
The evaporator outlet stream is segmented into two paths: the original superheat generation path and a new recirculation path through the vapor ejector. This segmentation allows simultaneous achievement of superheat and increased liquid flow for enhanced cooling capacity.
Solution Approach 2:
A feedback loop is established where flash gas from the expansion device drives the vapor ejector to recirculate liquid refrigerant back to the evaporator inlet. The recirculated liquid enhances heat transfer and cooling capacity while the expansion valve continues to regulate superheat at the outlet.
2Device complexity
If flash gas is discharged without utilization, then system simplicity is maintained, but energy efficiency deteriorates
Solution Approach 1:
The flash gas, previously considered a parasitic loss, is converted into a useful resource to drive the vapor ejector. The ejector uses flash gas as motive flow to recirculate liquid refrigerant, transforming energy waste into a capacity-boosting mechanism.
Solution Approach 2:
The system uses its own flash gas to power the vapor ejector, creating a self-service mechanism that requires no external energy input. The flash gas automatically drives the recirculation process, improving efficiency without adding external complexity.
3Productivity
If vapor ejector is added to recirculate liquid refrigerant, then cooling capacity is improved, but device complexity increases
Solution Approach 1:
The vapor ejector is merged with the existing evaporator and expansion device components. The ejector utilizes the flash gas already present in the system and integrates with the liquid refrigerant circulation path, combining multiple functions into a unified system that minimizes additional complexity.
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 effectively boosts the refrigeration capacity by increasing liquid refrigerant flow, improving heat transfer and maintaining system integrity by recycling excess liquid, thereby addressing the capacity reduction issues in direct expansion systems.
Implementation Method 1
The liquid refrigerant flow is increased through local recirculation of liquid from evaporator outlet to evaporator inlet through a vapor ejector which pumps liquid refrigerant from a lower pressure to a higher pressure
Implementation Method 2
The vapor-liquid separator generates vapor to power the ejector through flashing of warm refrigerant liquid from a higher temperature and pressure to a lower pressure
Implementation Method 3
After the throttling process, as in a standard refrigeration cycle, the mixture of liquid and vapor enters the inlet vapor-liquid separator
Data Source
AI summary
A system and method for increasing the refrigeration capacity of a direct expansion refrigeration system having a vapor separator and a vapor ejector. After the throttling process at the expansion device, the mixture of liquid and vapor enters the inlet separator. The vapor separator generates vapor to power the ejector through flashing of warm refrigerant liquid from a higher temperature and pressure to a lower pressure. The cooler refrigerant liquid then goes to the evaporator coil inlet. Furthermore, the system stabilizes the superheat of the outlet vapor and reduces fluctuations in outlet superheat caused by excess unevaporated liquid flowing from the outlets of the tubes due to mal-distribution at the inlet.