Active/passive thermal control system utilizing liquid nitrogen
Solution Overview
Problem
Current methods for transporting temperature-sensitive products, particularly perishables like fish, are unreliable and complex due to limitations in maintaining extremely low temperatures, leading to quality degradation and increased energy consumption, especially in air transportation where active freezing methods are bulky and expensive, and passive methods are imprecise.
Innovation Solution
An active/passive freezer system utilizing a payload bay surrounded by insulation, a heat exchanger with a cryogenic valve for liquid Nitrogen, and a thermal battery, enabling both rapid active freezing and prolonged passive temperature maintenance, reducing heat gain and maintaining low temperatures with increased reliability and simplicity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If active freezing methods using compressors are used, then temperature control precision is improved, but device complexity and energy consumption increase
Solution Approach 1:
The patent replaces the mechanical compressor-based refrigeration system with a passive thermal control system using phase change materials and heat exchangers. This substitution eliminates complex mechanical moving parts while maintaining effective temperature control through thermodynamic principles, directly resolving the contradiction between temperature precision and device complexity.
Solution Approach 2:
The patent utilizes phase transitions of thermal energy storage materials (such as phase change from solid to liquid) to maintain stable temperatures. This passive phase-change mechanism provides precise temperature control without requiring complex active mechanical systems, thereby improving temperature precision while reducing device complexity.
2Ease of operation
If passive cooling methods using ice are used, then ease of operation is improved, but reliability deteriorates due to inability to maintain extremely low temperatures
Solution Approach 1:
The patent changes the thermal parameters of the cooling system by using phase change materials with specifically selected melting points and high latent heat values. This allows the system to maintain extremely low temperatures (below -20°C) passively, improving reliability while keeping the operation simple—no active control mechanisms are needed.
Solution Approach 2:
The patent employs composite thermal control structures combining insulation materials, heat exchangers, and phase change materials. This composite approach enhances the passive cooling capability, enabling reliable maintenance of extremely low temperatures without complicating the operational simplicity.
3Duration of action of stationary object
If insulation thickness is increased to reduce heat gain, then temperature maintenance duration is improved, but volume of the container increases
Solution Approach 1:
The patent introduces phase change materials that absorb or release large amounts of latent heat during temperature transitions. This allows the system to maintain temperatures for extended periods without requiring thick insulation, as the phase change process actively compensates for heat ingress, thereby extending temperature maintenance duration while keeping container volume compact.
Solution Approach 2:
The patent uses thermal energy storage materials as an intermediary between the external environment and the protected cargo. These materials act as a thermal buffer, absorbing excess heat during the day and releasing it during cooler periods, effectively extending temperature maintenance duration without increasing insulation thickness or container volume.
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
The system significantly enhances the reliability and efficiency of temperature control, reducing the complexity and risk in cold chain management by maintaining low temperatures for longer periods, thus preserving the quality of perishable goods during transportation.
Implementation Method 1
a heat exchanger, wherein the heat exchanger is comprised of a coolant tube within the payload bay
Implementation Method 2
a heat exchanger to transfer thermal energy from the payload bay into itself
Implementation Method 3
a payload bay surrounded by insulation, wherein the insulation can be foam, vacuum, Vacuum Insulated Panels (VIPs), or any combination therein
Implementation Method 4
a thermal battery, wherein the thermal battery is comprised of liquid water
Implementation Method 5
a thermal battery capable of significantly decreasing passive heat gain of the payload bay
Data Source
AI summary
An active/passive freezer system includes the capability to both actively cool a payload bay and passively maintain close to that temperature for extended periods of time; a freezer unit with a payload bay that can rapidly reduce its internal temperature; a thermal battery; a heat exchanger where liquid Nitrogen flows through; insulation that significantly reduces heat gain from external sources; and the capability to have separate units for cooling the payload bay and maintaining the temperature within the payload bay.