Direct Expansion Evaporator With Vapor Ejector Flash Gas 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 throttling process, leading to parasitic losses and suboptimal heat transfer.
Innovation Solution
The integration of a vapor ejector and separator combination that recirculates liquid refrigerant from the evaporator outlet to the inlet, utilizing flash gas to increase refrigerant flow and enhance heat transfer by pumping liquid from lower to higher pressure, thereby boosting the evaporator's heat absorbing capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid refrigerant flow through the evaporator is reduced to achieve superheat at the evaporator outlet, then compressor safety is improved, but cooling capacity is reduced
Solution Approach 1:
The system uses a superheat sensor to detect the temperature of refrigerant vapor at the evaporator outlet and provides feedback to a controller. The controller adjusts the expansion valve opening based on this feedback to maintain optimal superheat while maximizing refrigerant flow and cooling capacity.
Solution Approach 2:
The expansion valve opening is dynamically adjusted based on real-time superheat measurements rather than being fixed. This dynamic control allows the system to optimize the balance between achieving necessary superheat for compressor protection and maintaining maximum refrigerant flow for cooling capacity.
2Device complexity
If flash gas generated during throttling is discharged without utilization, then system simplicity is maintained, but energy loss increases
Solution Approach 1:
The system captures the previously wasted flash gas and converts it into a useful resource by using it as motive flow in a vapor ejector. The flash gas that was simply discharged now powers the ejector to recirculate liquid refrigerant, transforming an energy loss into a beneficial effect that enhances cooling capacity.
Solution Approach 2:
The vapor ejector acts as an intermediary device that utilizes flash gas as motive flow to drive the recirculation of liquid refrigerant. The ejector converts the kinetic energy of the flash gas into a useful function, mediating between the throttling process and the evaporator to improve overall system efficiency.
3Productivity
If additional components (vapor ejector and separator) are added to recirculate liquid refrigerant, then heat transfer efficiency is improved, but device complexity increases
Solution Approach 1:
The vapor ejector performs multiple functions: it acts as a recirculation pump for liquid refrigerant, utilizes flash gas as motive flow, and enhances heat transfer in the evaporator. The outlet separator also serves dual purposes by separating vapor-liquid mixture and returning liquid to the evaporator while directing vapor to the compressor.
Solution Approach 2:
The system utilizes phase transitions of refrigerant, particularly the flashing of liquid to vapor during throttling, to drive the ejector operation. The phase change of flash gas from liquid to vapor provides the motive flow needed for recirculation without requiring additional energy input.
4Productivity
If liquid refrigerant flow rate is increased to improve cooling capacity, then heat transfer is enhanced, but superheat at evaporator outlet is reduced
Solution Approach 1:
The refrigerant flow is segmented into multiple paths: the primary flow through the evaporator and an additional recirculated flow injected at the evaporator inlet through the ejector. This segmentation allows independent optimization of total refrigerant flow for cooling capacity while maintaining adequate superheat through the expansion valve control.
Solution Approach 2:
Liquid refrigerant is recirculated and injected at the evaporator inlet before entering the evaporation process. This preliminary injection of additional liquid refrigerant enhances the total refrigerant flow and heat transfer capacity while the expansion valve maintains proper superheat conditions at the outlet.
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 regenerative method increases the evaporator's heat transfer efficiency by recycling additional liquid refrigerant, improving cooling capacity and preventing refrigerant loss, while maintaining compressor safety by capturing and re-delivering excess liquid.
Implementation Method 1
The flash gas generated in the expansion device before the evaporator inlet
Implementation Method 2
a vapor ejector which pumps liquid refrigerant from a lower pressure to a higher pressure
Implementation Method 3
The mixture of liquid and vapor enters the inlet vapor-liquid separator
Implementation Method 4
After the throttling process, as in a standard refrigeration cycle, the mixture of liquid and vapor enters the inlet vapor-liquid separator
Implementation Method 5
The liquid refrigerant flow is increased through local recirculation of liquid from evaporator outlet to evaporator inlet
Implementation Method 6
The increased liquid improves heat transfer through higher internal surface contact with boiling liquid
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.