Two-Stage Evaporator with State Separator for Waste Heat Recovery
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Solution Overview
Problem
Existing waste heat recovery systems face inefficiencies in energy conversion and freeze resistance, particularly during start-up phases, due to the mixing of vapor and liquid phases in evaporators, which can damage expanders and reduce energy recovery efficiency.
Innovation Solution
A compact two-stage evaporator system with a state separator function is introduced, separating vapor and liquid phases between the first and second evaporators, ensuring only vapor phase fluid enters the second evaporator, and liquid phase is recycled, using a water/organic blend working fluid for enhanced efficiency and freeze prevention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single evaporator is used in the WHR system, then the device complexity is reduced, but fluid droplets may enter the expander causing damage and reducing energy recovery efficiency
Solution Approach 1:
The evaporator is divided into two distinct stages: a first evaporator for vaporization and a second evaporator for superheating. This segmentation allows the system to separate the vapor generation function from the superheating function, ensuring that only vapor enters the expander while protecting against liquid droplet damage.
Solution Approach 2:
A state separator is introduced as an intermediary component between the first and second evaporators. This separator acts as a mediator that divides the mixed vapor-liquid flow into separate vapor and liquid streams, directing vapor to the second evaporator and liquid back to the first evaporator, thereby preventing liquid droplets from reaching the expander.
2Reliability
If a two-stage evaporator system is used to prevent fluid droplets, then expander protection is improved, but the device complexity increases
Solution Approach 1:
The state separator is integrated within the evaporator assembly, merging the separation function with the existing evaporator structure. The liquid return line connects the state separator back to the first evaporator inlet, creating a compact integrated system that achieves droplet prevention without requiring completely separate independent components.
Solution Approach 2:
The system uses the organic working fluid's own phase change properties and density differences to achieve automatic separation in the state separator. The liquid phase naturally settles and is redirected back to the first evaporator without requiring external power or complex control mechanisms, making the system self-regulating.
3Loss of energy
If water-based working fluid is used, then heat retention is improved, but freeze resistance is reduced
Solution Approach 1:
The system uses a composite working fluid consisting of organic components (such as alcohol) mixed with water. This composite fluid combines the advantages of both components: the organic portion provides freeze resistance and rapid vaporization, while the water portion maintains high heat retention capacity and allows operation at higher temperatures.
4Object-affected harmful factors
If organic working fluid is used, then freeze resistance is improved, but heat retention capability is reduced
Solution Approach 1:
The composite working fluid combines organic components with water to achieve a balance between freeze resistance and heat retention. The organic portion (e.g., alcohol) lowers the freezing point and enables rapid vaporization, while the water portion contributes high specific heat capacity for effective heat storage and transfer, creating a synergistic effect.
5Productivity
If superheating is implemented to eliminate fluid droplets, then energy conversion efficiency is improved, but the device complexity increases
Solution Approach 1:
The evaporator system is segmented into two functional stages: the first evaporator performs vaporization and the second evaporator performs superheating. This segmentation enables the system to achieve high energy conversion efficiency by ensuring dry, superheated vapor enters the expander, while the modular structure manages complexity through functional separation.
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 configuration enhances energy conversion efficiency by preventing fluid droplets from entering the expander, allowing for rapid start-up and improved heat transfer, while maintaining robust heat retention and freeze resistance, particularly beneficial in vehicle applications.
Implementation Method 1
The working fluid is first pumped to an evaporator where it is vaporized during a heating phase
Implementation Method 2
heat is transferred to a working fluid in an RC circuit
Implementation Method 3
a state separator, or at least a state separator function, between the respective first and second evaporators
Implementation Method 4
the vapor phase working fluid is then passed through an expander and then back through a condenser, where the vapor phase working fluid is condensed back to liquid phase working fluid
Implementation Method 5
an expander for expanding the superheated vapor state working fluid and converting that expansion into mechanical energy
Implementation Method 6
a condenser for condensing the vapor state working fluid back into liquid state working fluid by cooling
Implementation Method 7
a pump is also provided so that fluid may flow from the outlet of the condenser to the inlet of the first evaporator
Implementation Method 8
absorb heat more quickly and thus arrive at a working phase more quickly
Implementation Method 9
The water component retains the advantages of water-based vapor having a higher working temp and being a more robust retainer of heat
Implementation Method 10
Such a fluid allows for heat recovery from relatively lower temperature sources relative to other RC systems. An additional advantage of an ORC is that such systems are both more freeze resistant
Data Source
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AI summary
A compact two-stage evaporator waste heat recovery (WHR) device (7) is disclosed, and a system using the device. The device recovers energy from waste heat passing through the device and transfers that energy to a Rankine Cycle working fluid also passing through the device. The device includes a first and second evaporator (15); and, a state separator (17) connected between the outlet of the first evaporator and the inlet of the second evaporator. The state separator (17) separates the working fluid into liquid and vapor. The liquid is re-cycled to the inlet of the first evaporator (15); the vapor is sent to the inlet of the second evaporator (19) for superheating. An overall WHR system using the device further includes an expander (21), condenser (23), and pump (25). The system further includes control circuitry (26) for controlling operation of the waste heat recovery device (7) itself and the WHR system.