Buoyancy-Driven PCM Capsules for Hot-Water Tank Heat Transfer
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Solution Overview
Problem
Existing hot-water heating systems face peaking issues due to high morning and evening demand, leading to inefficiencies and increased infrastructure costs, and phase change materials (PCMs) used in thermal storage suffer from low heat transfer performance.
Innovation Solution
The use of capsules containing PCMs with a shell that accommodates volume changes during phase transitions, combined with a heat-conducting material, to create buoyancy forces that control capsule positioning and enhance heat transfer, allowing for efficient latent heat storage and release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If phase change materials are used for thermal energy storage in water heaters, then energy storage capacity is improved, but heat transfer performance deteriorates
Solution Approach 1:
The PCM is divided into multiple small spherical capsules instead of using a large continuous block. This segmentation increases the total surface area for heat transfer while maintaining the same energy storage capacity, directly resolving the contradiction between storage capacity and heat transfer performance.
Solution Approach 2:
The invention introduces buoyancy-driven vertical movement of PCM capsules as a new dimension of heat transfer. Hot capsules rise to the top while cold capsules sink to the bottom, creating natural convection currents that enhance heat transfer throughout the water heater tank, addressing the heat transfer performance limitation.
2Strength
If PCM volume expansion during phase transition is constrained, then structural integrity is improved, but heat transfer efficiency deteriorates
Solution Approach 1:
The PCM capsules are enclosed in flexible shells that can expand and contract to accommodate the volume change during phase transition. This flexibility maintains structural integrity while allowing the PCM to fully expand, maximizing the driving force for buoyancy-driven heat transfer and preventing shell rupture.
Solution Approach 2:
The capsule shells are designed to dynamically adapt their volume during phase changes. The shells expand when PCM melts and contract when PCM solidifies, allowing the system to utilize the volume change for buoyancy-driven circulation rather than constraining it, thereby maintaining both structural integrity and heat transfer efficiency.
3Volume of stationary object
If tank size is reduced to conserve energy and cost, then space utilization is improved, but first-hour rating deteriorates
Solution Approach 1:
The invention utilizes the phase transition of PCM (solid-liquid conversion) to store and release large amounts of latent heat within a compact volume. This allows a smaller tank to provide the same first-hour rating as a larger conventional tank, as the PCM releases heat rapidly during melting without requiring large storage space.
Solution Approach 2:
The buoyancy-driven circulation creates continuous heat transfer between hot and cold PCM capsules throughout the tank. This continuous thermal circulation ensures that heat is constantly available to meet demand, maintaining high first-hour rating performance in a compact tank size.
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 design increases the first-hour rating of hot-water heaters, reduces tank size requirements, and enhances energy efficiency by improving heat transfer rates and utilization, with a 6-14% increase in coefficient of performance (COP) and 72.4% heat utilization factor.
Implementation Method 1
a phase changing material (PCM) configured to undergo a liquid-solid phase transition at a solidification temperature, TS
Implementation Method 2
The relative volume change is configured to cause a buoyancy force which acts on the capsule when the capsule is disposed in water at a water temperature, TW
Implementation Method 3
The shell comprises a first heat-conducting material... a second heat-conducting material with higher heat conductance than the first heat-conducting material
Implementation Method 4
efficient latent heat storage and release... 72.4% heat utilization factor
Data Source
AI summary
A medium for energy storage includes a plurality of capsules. Each capsule contains a phase changing material (PCM) configured to undergo a liquid-solid phase transition at a solidification temperature, TS. The PCM undergoes a relative volume change due to the phase transition. A shell is filled with the PCM. The shell contains a first heat-conducting material, and is configured to comply to the relative volume change. The relative volume change is configured to cause a buoyancy force, which acts on the capsule when the capsule is disposed in water at a water temperature, TW, to be larger than the capsule's weight for Tw>Ts, and equal to or smaller than the capsule's weight for Tw<Ts. The Ts can be within ±5° F. of a design water temperature To at the outlet of a water tank. The capsule can be neutrally buoyant in water at To.