Liquid Nitrogen Blast Freezer Design for Rapid Cryogenic Cooling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Blast Freezers are limited by the boiling point of their refrigerants, which restricts the ability to freeze products quickly, requiring over two hours to reach -40°C, whereas the new freezer system achieves this in one hour using liquid nitrogen and enhanced convective cooling.
Innovation Solution
The freezer employs a high-pressure liquid nitrogen system with evaporators, fans, and a thermal box for rapid cooling, along with a heating system using electric pads and heat tubes for efficient temperature control, allowing for freezing and heating of products to -160°C and room temperature respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional refrigerants with boiling point of -100 C are used in mechanical blast freezers, then the freezing capability is limited, but the system complexity is reduced
Solution Approach 1:
The patent changes the fundamental parameter of the refrigerant from conventional refrigerants with boiling point of -100 C to liquid nitrogen with boiling point of -196 C. This parameter change enables the freezer to achieve lower temperatures and faster freezing rates, directly resolving the temperature limitation while accepting the increased system complexity of handling cryogenic liquids
Solution Approach 2:
The patent replaces the conventional mechanical compression system with a liquid nitrogen evaporation system. Instead of using compressors and mechanical refrigeration cycles, the system uses the evaporation of liquid nitrogen to provide cooling, substituting a mechanical system with a phase-change-based system that achieves superior performance
2Loss of time
If conventional blast freezers are used, then the freezing time is extended beyond 2 hours, but the operational simplicity is maintained
Solution Approach 1:
The patent changes the refrigerant parameter from conventional refrigerants to liquid nitrogen, which has a boiling point 96 degrees Celsius lower than conventional refrigerants. This parameter change enables the system to freeze 100 bags to -40 C in one hour, reducing freezing time by 50% compared to conventional systems
Solution Approach 2:
The patent employs periodic action through the controlled evaporation of liquid nitrogen and the use of fans to circulate cold air periodically throughout the payload bay. This ensures uniform and rapid freezing across all products, achieving fast freezing times while maintaining operational control
3Productivity
If liquid nitrogen is used as coolant with high pressure of 90 psi and high flow rate of 80 gallons per hour, then the freezing speed is doubled, but the energy consumption increases
Solution Approach 1:
The patent utilizes the phase transition of liquid nitrogen evaporating to gaseous nitrogen as the primary cooling mechanism. This phase transition absorbs large amounts of heat (latent heat of vaporization), providing extremely efficient cooling that doubles the freezing speed compared to conventional systems, while the energy is drawn from the thermal energy of the products themselves rather than external power sources
Solution Approach 2:
The liquid nitrogen system is self-service in that it uses its own evaporation process to provide cooling without requiring external compressors or additional energy input. The high pressure and high flow rate are maintained by the natural properties of the liquid nitrogen supply system, and the cooling effect is generated automatically as the nitrogen evaporates, reducing the need for external energy consumption
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 design reduces freeze time by half, enabling the freezing of 100 bags in one hour and heating of products efficiently, while maintaining precise temperature control and reducing heat gain through advanced sealing and insulation techniques.
Implementation Method 1
a cryogenic flow system that operates at a predetermined Nitrogen flow; a plurality of evaporators inside the payload bay
Implementation Method 2
evaporators coupled to the payload bay with a multiplicity of coolant tubes in each evaporator, wherein each tube enters and then exits the payload bay
Implementation Method 3
a plurality of fans to circulate cooled air in the payload bay; a plurality of fans that distribute the cooled air from the evaporators to the payload bay
Implementation Method 4
a thermal box immediately outside the evaporators and payload bay, that effectively thermally seals the payload bay from the outside environment, significantly reducing heat gain
Implementation Method 5
A 2-inch rubber pneumatic seal is strategically placed to not only seal the gap between the main door and the thermal box but also to seal the gap between the inner door and the thermal box
Implementation Method 6
When the customer requirement is to heat product from these extremely low temperatures to room temperature or even warmer, a heating system has been designed for fast temperature recovery. Electric pads in the airflow path reduce the heating time
Implementation Method 7
In addition multiple heat tubes, similar in diameter to the copper cooling tubes are placed into the evaporator fins for heating
Data Source
AI summary
A freezer includes a plurality of shelves in an insulated payload bay; a plurality of evaporators coupled to the payload bay with a multiplicity of coolant tubes in each evaporator, wherein each tube enters and then exits the payload bay, further comprising one or more cryogenic valves coupled to the coolant tubes; a pump to force coolant flowing through the evaporators with a pressure of at least 90 psi to supply the coolant at each evaporator with at least 80 gallons per hour of coolant; and a plurality of fans to circulate cooled air in the payload bay.