Thermosiphon Radiator Channel Sizing for Stable Nucleate Boiling
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Solution Overview
Problem
Radiators using biphasic fluids face inefficiencies in heat exchange due to incorrect dimensioning of mechanical parts and non-optimal control of boiling, leading to excessive vapor acceleration, which prevents condensate film formation, resulting in reduced heat transfer and overheating, damaging the external source and fluid.
Innovation Solution
A thermosiphon radiator design with channels sized to accommodate vapor bubbles, ensuring the smallest linear dimension is between twice and five times the diameter of the vapor bubble, along with a feedback control system to maintain nucleate boiling regime and prevent critical temperature exceedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the efflux channels are incorrectly dimensioned, then the vapor acceleration becomes excessive, but this prevents the formation of liquid film on channel walls and causes overheating
Solution Approach 1:
The patent applies parameter changes by optimizing the channel dimensioning parameter (smallest linear direction) to be between twice and five times the vapor bubble diameter. This specific parameter range controls vapor acceleration to prevent excessive speed while maintaining efficient heat exchange, resolving the contradiction between vapor speed and heat exchange reliability.
Solution Approach 2:
The patent implements feedback control through a control system that monitors the boiling regime and adjusts operating parameters to maintain nucleate boiling. This feedback mechanism ensures that vapor acceleration remains within optimal ranges, preventing the transition to film boiling and maintaining reliable heat exchange conditions.
2Power
If the vapor rises at high speed, then the heat exchange from external source to fluid increases, but the liquid film cannot return to cool the source surface
Solution Approach 1:
The patent changes the geometric parameter of the channel (smallest linear direction between 2-5 times vapor bubble diameter) to optimize the balance between vapor rise speed and liquid film return. This parameter optimization allows high heat exchange rates while maintaining sufficient liquid film flow to cool the source surface.
Solution Approach 2:
The patent creates equipotential conditions by balancing the upward vapor flow and downward liquid film flow through optimized channel dimensions. This balance ensures that both phases can move efficiently in opposite directions without one preventing the other, maintaining stable temperature conditions at the source surface.
3Reliability
If film boiling occurs, then convective heat exchange dominates, but this causes over-temperatures damaging to the external source and fluid
Solution Approach 1:
The patent employs feedback control to monitor boiling regime conditions and adjust operating parameters to maintain nucleate boiling. This feedback mechanism detects early signs of film boiling transition and corrects conditions before damaging over-temperatures occur, ensuring operational stability and preventing harm to the external source and fluid.
Solution Approach 2:
The patent applies preliminary anti-action by designing channels with dimensions that preemptively prevent film boiling formation. The optimized channel geometry (2-5 times vapor bubble diameter) creates flow conditions that favor nucleate boiling, counteracting tendencies toward film boiling before they can develop into damaging over-temperature conditions.
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
Optimized heat exchange is achieved by ensuring efficient condensate film return and maintaining the nucleate boiling regime, enhancing the reliability of the heating component, fluid, and device by maximizing the heat exchange coefficient and preventing overheating.
Implementation Method 1
the intermediate vector fluid is adapted to evaporate on contact with a hot surface of the external heat source in nucleate boiling regime, forming vapour bubbles
Implementation Method 2
A thermosiphon radiator design with channels sized to accommodate vapor bubbles
Implementation Method 3
On contact with the wall of these channels, which is colder since it is in direct contact with the external environment to be heated, the vector fluid condenses forming a condensed liquid film
Implementation Method 4
The heat exchange from the external heat source to the vector fluid is therefore governed by the conduction through the vapour
Implementation Method 5
The transfer of heat from the evaporating area to the radiant part could be governed by a convective exchange in the overheated vapour
Implementation Method 6
the condensed liquid film which provides the heat exchange with the wall, transferring the heat received from the external source to the radiator body
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3c
AI summary
A radiator of the thermosiphon type comprising a collector situated in the lowest part of the radiator, and adapted to contain an intermediate vector fluid, an external heat source, placed within the collector, wherein the intermediate vector fluid is adapted to evaporate on contact with a hot surface of the external heat source, at least one vertical tube containing therein one or more channels (4) connected to the collector and communicating with the same, characterized in that said collector and said channels are dimensioned so that each section thereof crossed by the intermediate vector fluid, excluding the thickness of the liquid film of moisture, has the smallest linear direction which is twice bigger than the diameter db of an intermediate fluid vapour bubble which, during operation, detaches itself from the hot surface of the external source during boiling of the intermediate fluid.