Two-Stage Compact Evaporator With Phase Separation for Vehicle WHR
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Solution Overview
Problem
Existing waste heat recovery systems for vehicles face inefficiencies in energy conversion due to the presence of fluid droplets in the expander, which can damage equipment and reduce energy recovery efficiency, especially during start-up phases.
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, thereby preventing fluid droplets from entering the expander and optimizing energy conversion with a water/organic blend working fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-stage evaporator is used in a waste heat recovery system, then the system structure is simple, but fluid droplets 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 generating vapor from liquid working fluid, and a second evaporator for superheating the vapor. This segmentation allows each stage to perform its specific function optimally, preventing liquid droplets from reaching the expander while maintaining system reliability.
Solution Approach 2:
A state separator is introduced as an intermediary component between the first and second evaporators. This separator mediates the transition by removing liquid droplets from the vapor stream, ensuring only dry vapor enters the second evaporator and subsequently the expander, thus protecting the expander without requiring direct complex design in the evaporator itself.
2Productivity
If superheating is performed in a separate second evaporator, then energy recovery efficiency is enhanced and expander protection is improved, but the system requires more heat input and larger equipment
Solution Approach 1:
The patent combines the two evaporators into a single integrated unit with shared structural components, such as a common shell and coordinated internal arrangements. This merging allows the system to achieve the energy recovery efficiency benefits of separate superheating while reducing the total heat input requirement and compacting the equipment footprint.
Solution Approach 2:
The system utilizes parameter changes in the working fluid, particularly employing an organic working fluid with specific thermodynamic properties that enable efficient phase change and superheating. By optimizing the working fluid parameters (such as selecting fluids with appropriate boiling points and heat capacities), the system achieves high energy recovery efficiency with reduced heat input requirements.
3Temperature
If a water-based working fluid is used, then higher working temperature is achieved, but freeze resistance is reduced
Solution Approach 1:
The patent employs an organic working fluid that combines the advantageous properties of different substances. This composite approach allows the working fluid to maintain higher working temperatures like water while simultaneously providing freeze resistance characteristic of organic fluids, thus resolving the contradiction between temperature performance and freeze protection.
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 efficiency by allowing superheated vapor to be formed with less heat input, improving freeze resistance and heat retention, and enabling efficient operation at lower temperatures, particularly beneficial for vehicle applications.
Implementation Method 1
a first evaporator, for evaporating liquid state working fluid to a saturated vapor state working fluid through supply of heat from a first vehicle heat source
Implementation Method 2
a state separator, or a controlled state separator function, for separating vapor state working fluid and liquid state working fluid
Implementation Method 3
a second evaporator, connected to the vapor outlet of the state separator, for superheating vapor state working fluid through supply of additional heat from a second vehicle heat source
Implementation Method 4
converting thermal energy generated in the vehicle to mechanical energy for assisting more efficient operation of the vehicle
Implementation Method 5
a condenser for condensing the vapor state working fluid back into liquid state working fluid by cooling
Data Source
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.