Closed-Cycle Heat Transfer Pressure Control Without Air Ingress
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Solution Overview
Problem
Closed thermodynamic devices like thermosyphons and heat pipes face inefficiencies due to the presence of non-condensable gases, which reduce heat transfer efficiency and affect pressure/temperature characteristics, especially when air enters the system, and existing methods to exclude gases require vacuum conditions that can lead to air ingress.
Innovation Solution
A closed cycle heat transfer device with an expansion device connected to the condensate return duct, featuring a vessel divided by a flexible membrane, allows for gas charging to compensate for fluid vapor expansion, ensuring no non-condensable gases are present and maintaining a pressure-defined system volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vacuum conditions are used to exclude non-condensable gases during charging, then non-condensable gases are eliminated from the system, but air can ingress through leakage when the system is not operating
Solution Approach 1:
The system is charged with working fluid at atmospheric pressure before operation, eliminating the need for vacuum conditions during charging. This preliminary action of charging under normal pressure conditions prevents air ingress that would otherwise occur during vacuum maintenance, while still allowing effective exclusion of non-condensable gases during the charging process itself.
Solution Approach 2:
The charging process utilizes pressure differential changes - the system is charged at atmospheric pressure when the working fluid temperature is below its boiling point, then operated at elevated temperatures where the working fluid boils and displaces any remaining non-condensable gases to the discharge side. This parameter change from low-temperature atmospheric pressure charging to high-temperature operation resolves the contradiction between excluding gases and preventing air ingress.
2Ease of manufacture
If the system is filled with working fluid at atmospheric pressure, then charging is simplified and air ingress is prevented, but the volume available for vapour space is reduced
Solution Approach 1:
The system is preliminarily charged with working fluid at atmospheric pressure to fill the liquid space, then during operation the heated working fluid expands and creates vapour space dynamically. This preliminary charging action simplifies the manufacturing process while the operational phase creates the necessary vapour space through thermal expansion.
Solution Approach 2:
The working fluid undergoes phase transition from liquid to vapour during operation, with the vapour occupying the upper portion of the system and liquid at the lower portion. This phase transition naturally creates the required vapour space during operation without requiring excessive volume allocation during manufacturing, as the vapour space is created dynamically through heating.
3Volume of stationary object
If non-condensable gases are present in the system, then the system volume is available for all fluids, but heat transfer efficiency is reduced and pressure/temperature characteristics are affected
Solution Approach 1:
Non-condensable gases are extracted from the system during the charging process by displacing them with working fluid under pressure, then removing them through the discharge side. This extraction eliminates the harmful presence of non-condensable gases that would otherwise reduce heat transfer efficiency, while the system volume remains fully available for productive use during operation.
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 solution effectively eliminates non-condensable gases, maintains system integrity by avoiding vacuum conditions, and optimizes heat transfer by adjusting pressure and volume relationships, enhancing efficiency and reliability in thermodynamic cycles.
Implementation Method 1
a first said chamber is in communication with the second fluid duct and a second said chamber is isolated therefrom to contain a gas
Implementation Method 2
an expansion device connected to and in communication with the second fluid duct to receive liquid condensate therefrom thus to compensate for expansion of a fluid vapour phase
Implementation Method 3
heat is transferred principally via latent heat evaporation. A fixed volume of heat transfer fluid within a closed system is vaporised by application of heat in an evaporator
Implementation Method 4
Vapour then passes to a condenser where heat is transferred to some other process, the vaporised working fluid condensing against a cooling medium
Implementation Method 5
the significant difference in density between the vapour travelling to the condenser and the condensate returning to the evaporator, is exploited to create a gravity return path
Data Source
AI summary
A closed cycle heat transfer device comprising a boiler (10) and a condenser (13), the condenser being used to recover useful heat by latent heat evaporation. A circuit defined by the boiler (10), condenser (13) and ducts (12, 15) is to be liquid-filled at a pressure just above atmospheric pressure. An expansion device (16) maintains the working pressure in the circuit but will receive excess condensate in a liquid phase to compensate for expansion of the working fluid vapor which passes from the boiler (10) to the condenser (13). The expansion chamber contains a movable or flexible member which, when working liquid is received in the chamber, is displaced to compress a gas in the chamber.