IR Window Cooling with Throttled Two-Phase Flow
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Solution Overview
Problem
Infrared windows used in hypersonic vehicles face challenges with high temperatures and heat fluxes, leading to thermal distortion and reduced optical transmission due to existing cooling methods that either compromise optical clarity or fail to maintain uniform temperature distribution.
Innovation Solution
The implementation of internally cooled IR windows using two-phase flow in channels with hydraulic diameters less than 0.118 inch, equipped with throttling devices to initiate adiabatic nucleation and prevent boiling hysteresis, ensuring uniform temperature and low mass flow rates while maintaining optical clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling passages are made larger to improve heat transfer, then heat transfer coefficient improves, but pressure drop increases and flow distribution becomes non-uniform
Solution Approach 1:
The patent changes the hydraulic diameter parameter to be less than 0.118 inch, which optimizes the balance between heat transfer surface area and pressure drop. This specific parameter threshold creates sufficient cooling efficiency while maintaining acceptable pressure losses and flow distribution across the window assembly.
Solution Approach 2:
The patent implements throttling devices at specific locations within the cooling passages to create localized flow resistance. This local modification of flow characteristics ensures uniform coolant distribution across different regions of the window, preventing some areas from being over-cooled while others remain insufficiently cooled.
2Stress or pressure
If cooling passages are made smaller to reduce pressure drop, then pressure drop decreases, but heat transfer coefficient reduces
Solution Approach 1:
The patent establishes a critical hydraulic diameter threshold of less than 0.118 inch that prevents pressure drop from becoming excessive while maintaining adequate heat transfer. This parameter optimization ensures that smaller passages do not sacrifice cooling efficiency unnecessarily.
Solution Approach 2:
Throttling devices are strategically placed in smaller cooling passages to regulate local flow rates. This local flow control compensates for the reduced passage size, ensuring that each region receives adequate coolant flow for effective heat removal despite the smaller overall passage dimensions.
3Temperature
If throttling devices are added to uniformize flow distribution, then temperature uniformity improves, but device complexity increases
Solution Approach 1:
The patent introduces throttling devices only at specific locations within the cooling passage system where flow maldistribution is most problematic. This selective application of flow control elements achieves temperature uniformity across the window while avoiding the need to complexify the entire cooling system.
Solution Approach 2:
The throttling devices modify local flow resistance parameters to balance coolant distribution. By adjusting these local resistance parameters, the system achieves uniform temperature distribution without requiring a complete redesign of the entire cooling architecture.
4Temperature
If two-phase flow is used to enhance cooling efficiency, then heat transfer coefficient improves, but flow stability deteriorates under high g-forces
Solution Approach 1:
The patent optimizes the hydraulic diameter to be less than 0.118 inch, which creates sufficient flow resistance to maintain stable two-phase flow patterns even under high g-forces. This parameter control prevents flow maldistribution and boiling hysteresis that would otherwise occur in larger passages during hypersonic flight.
Solution Approach 2:
Throttling devices are positioned to create localized flow control zones that stabilize two-phase flow distribution. These local flow control mechanisms counteract the destabilizing effects of high g-forces on evaporating coolant, ensuring consistent heat removal across the window surface.
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 provides improved heat transfer coefficients, reduced temperature variations, and smaller system size, enhancing the survivability and performance of IR windows under extreme conditions by maintaining a uniform temperature and minimizing pressure drops.
Implementation Method 1
throttling device upstream of an evaporation section of the cooling passages to initiate adiabatic nucleation
Implementation Method 2
cooling passages arranged inside the window to provide cooling
Implementation Method 3
two-phase flow in channels with hydraulic diameters less than 0.118 inch
Implementation Method 4
upstream of the evaporation section of the cooling passages
Implementation Method 5
adiabatic nucleation (i.e., evaporation) and prevent boiling (evaporation) hysteresis
Data Source
AI summary
A window assembly heat transfer system is disclosed in which a window member has a selected transparency to monitored or sensed light wavelengths. One or more passages are provided in the window member for flowing a single-phase or two-phase heat transfer fluid, the passages being optically non-transparent to the monitored or sensed light wavelengths. A mechanism allows either evaporation or condensation of the fluid and/or balancing of a flow of the fluid within the passages. In one embodiment, the window assembly can be made by producing passages in a top surface of a first single plate, optionally producing passages in a bottom surface of a second single plate and bonding the top surface of the first plate to a bottom surface of a second single plate to form the window member with the passage or passages. In another embodiment, the window assembly can be made by providing a core around which the window member material is grown and thereafter removing the core to produce the passage or passages.