Temperature Actuated Capillary Valve for Loop Heat Pipe
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Solution Overview
Problem
Existing two-phase heat transfer systems in aerospace applications face challenges in efficiently managing heat transfer across varying temperatures, particularly when a satellite's orientation changes, leading to uneven heating of condensers, which requires precise control of fluid flow to maintain effective cooling.
Innovation Solution
A temperature-actuated capillary flow valve is integrated into the two-phase heat transfer system, utilizing a porous wick structure and an electrical resistance heater to control vapor flow by evaporating liquid in the wick, allowing vapor passage when heated and condensing it when cooled, thus enabling dynamic adjustment of fluid flow to match changing thermal loads without mechanical valves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an electrical heater is used to maintain compensation chamber temperature, then the set-point temperature can be maintained, but the heater power increases significantly (to 15-20%) when the heat sink becomes too hot
Solution Approach 1:
The patent replaces the electrical heater with a thermal expansion-based mechanical valve system. The valve uses a bellows element that expands and contracts in response to temperature changes, automatically opening or closing the vapor passage without requiring electrical power. This substitutes an active electrical heating system with a passive thermal-mechanical response system.
Solution Approach 2:
The patent changes the operating parameter from active electrical heating to passive thermal expansion. The bellows element's volume changes in response to temperature variations, which directly controls the valve opening. This parameter change eliminates the need for continuous electrical power input while maintaining temperature control functionality.
2Ease of operation
If mechanical valves are used to control vapor flow to condensers, then fluid flow can be precisely controlled, but the device complexity increases
Solution Approach 1:
The patent extracts the complex mechanical valve components (springs, seals, actuators) and replaces them with a simple thermal expansion bellows element. The essential flow control function is retained, but the mechanical complexity is removed by using a passive thermal response mechanism that opens or closes the vapor passage based on temperature conditions.
Solution Approach 2:
The valve system is self-regulating through thermal expansion and contraction of the bellows element. The system uses the temperature differential itself to drive the valve action, requiring no external control mechanisms, actuators, or complex mechanical assemblies. The valve automatically responds to thermal conditions without additional complexity.
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 allows for efficient and adaptive heat management with minimal heater power usage, ensuring effective cooling by directing fluid flow only to operational condensers, maintaining system performance across varying solar loads and orientations without mechanical complexity.
Implementation Method 1
the housing configured to be heated by a heat source to evaporate liquid-phase working fluid from the wick and allow the vapor-phase working fluid to pass through the wick to the outlet port
Implementation Method 2
The flow valve can be cooled by a thermal strap configured to transfer heat from the valve housing to a heat sink
Implementation Method 3
a porous wick material extending across the flow passage
Implementation Method 4
at least one condenser; a vapor conduit joining the outlet of the capillary pump to the inlet of the condenser
Data Source
AI summary
A two-phase heat transfer system including at least one two-phase evaporator, at least one condenser, a vapor conduit joining a vapor outlet of the two-phase evaporator to an inlet of the condenser, a liquid conduit joining an outlet of the condenser to a liquid inlet of the two-phase evaporator, and a thermally-actuated capillary flow valve. The thermally-actuated capillary flow valve having a valve inlet, a valve outlet, a thermal connection to a heat sink for cold biasing the capillary flow valve, a porous wick extending across the flow passageway of the capillary flow valve, and a heater thermally connected to the capillary flow valve, where actuation of the heater evaporates liquid in the porous wick to allow passage of vapor through the capillary flow valve.