PCM Heat Exchanger Flow Reversal for Efficient Thermal Storage
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Solution Overview
Problem
Conventional latent heat storage systems using phase change materials (PCMs) face challenges such as high cost, low heat transfer efficiency, and thermomechanical stresses due to changes in PCM density during phase transitions, leading to suboptimal flow directions and increased system complexity.
Innovation Solution
A thermal storage system design with a bundle of conduits configured for single or multi-pass flows based on PCM density characteristics, using hydraulic separators and passive valve systems to manage flow direction and enhance heat transfer efficiency without additional inserts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If downward flow is used during charging for PCMs with higher solid density, then thermomechanical stresses are reduced, but heat transfer efficiency decreases due to lower Reynolds numbers
Solution Approach 1:
The system dynamically changes flow direction based on operational mode (charging vs discharging) and PCM properties. During charging, downward flow is used to reduce thermomechanical stresses on the heat exchanger. During discharging, upward flow is used to enhance heat transfer efficiency by increasing Reynolds numbers and promoting turbulent flow. This dynamic adaptation resolves the contradiction between stress management and heat transfer efficiency.
Solution Approach 2:
The system changes the flow direction parameter based on operational requirements. By reversing flow direction from downward (during charging) to upward (during discharging), the system optimizes both thermomechanical stress management and heat transfer efficiency at different operational stages. This parameter change allows the system to achieve high heat transfer coefficients during discharging while protecting the heat exchanger during charging.
2Productivity
If upward flow is used during discharging, then heat transfer efficiency increases due to higher Reynolds numbers, but thermal stratification may be compromised
Solution Approach 1:
The system dynamically adjusts flow direction based on operational mode. During discharging, upward flow is employed to maximize heat transfer efficiency through higher Reynolds numbers and turbulent flow conditions. During charging, downward flow is used to maintain thermal stratification. This dynamic switching allows the system to optimize for heat transfer efficiency during discharge while preserving thermal stratification during charge operations.
Solution Approach 2:
The system periodically reverses flow direction according to the charging/discharging cycle. During the discharge phase, upward flow enhances heat transfer. During the charging phase, downward flow maintains stratification. This periodic reversal of flow direction allows the system to achieve high heat transfer efficiency during discharge while maintaining thermal stratification during charge, resolving the contradiction between these two requirements.
3Device complexity
If conventional single-pass flow is used, then system complexity is reduced, but heat transfer performance is insufficient due to low Reynolds numbers
Solution Approach 1:
The system uses passive hydraulic valves that automatically change the flow path based on pressure differential and flow direction. During charging, the valve directs flow in one pattern; during discharging, it directs flow in another pattern. This dynamic, passive flow control achieves multi-pass flow enhancement without complex active control systems, resolving the contradiction between system complexity and heat transfer performance.
Solution Approach 2:
The hydraulic valve system operates autonomously based on the natural pressure differential and flow direction in the system. No external control signals or active components are needed - the valve automatically directs flow to optimize heat transfer during charging and discharging based on the operational state. This self-service approach achieves enhanced heat transfer performance without increasing system complexity through active control.
4Productivity
If flow direction is optimized for heat transfer, then energy efficiency increases, but thermomechanical stresses on the heat exchanger increase
Solution Approach 1:
The system dynamically changes flow direction based on operational mode. During charging, downward flow is used to minimize thermomechanical stresses on the heat exchanger. During discharging, upward flow is used to maximize heat transfer efficiency through higher Reynolds numbers. This dynamic adaptation allows the system to optimize for energy efficiency during discharge while protecting the heat exchanger during charging, resolving the contradiction between these two requirements.
Solution Approach 2:
The system periodically reverses flow direction according to the charging/discharging cycle. During discharge operations, upward flow enhances energy efficiency. During charge operations, downward flow reduces thermomechanical stresses. This periodic reversal allows the system to achieve high energy efficiency during discharge while minimizing stress during charging, resolving the contradiction between energy efficiency and stress management.
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
Enhances heat transfer performance and reduces system complexity and cost by optimizing flow patterns, achieving higher Reynolds numbers and stable convection modes, thus improving energy density and efficiency.
Implementation Method 1
The two fluids exchange heat energy by conduction through the tube walls
Implementation Method 2
the phase change material undergoes a phase change, for example, its melting
Implementation Method 3
During a charge, the heat transfer fluid reaches a temperature that is higher than a phase change temperature of the material, for example its melting temperature, and gives up energy to it, which causes a phase change of the material
Implementation Method 4
The phase change material is then considered stagnant, i.e., static (apart from natural convection currents in the liquid phase of the phase change material)
Data Source
Figure 1A~2
Figure 3~4
Figure 5
AI summary
The invention relates to a thermal storage system (1) implementing a phase change material (2), comprising a heat exchanger (11) having a bundle (111) of at least three conduits (14a), (14b) and (14c), configured, for a conventional PCM, to receive a flow of the heat transfer fluid in a single, downward pass during charging and in multiple passes during discharging of the thermal storage system, and for a "water" type PCM, to receive a flow of the heat transfer fluid in multiple passes during charging and in a single, upward pass during discharging of the thermal storage system.