Cryogenic freezer
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Solution Overview
Problem
Conventional cryogenic freezers face challenges in maintaining uniform low temperatures, particularly with mechanical freezers that rely on electricity and are limited in temperature range, and liquid nitrogen freezers that suffer from temperature stratification and high operational costs due to the need for continuous LN2 replenishment.
Innovation Solution
A cryogenic freezer design incorporating a mechanical refrigeration system with a cryocooler using a cryogenic fluid and a vacuum-insulated dewar with a central cryogenic reservoir, where the cryocooler modulates cooling based on pressure changes to maintain consistent temperatures and minimize LN2 consumption, combined with a system controller to manage heat loads and ensure temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a mechanical refrigeration system is used to achieve lower temperatures, then the temperature range is improved, but the reliability deteriorates due to dependence on electricity and refrigeration system failures
Solution Approach 1:
The system divides the refrigeration function into two independent segments: a mechanical refrigeration system for active cooling and a liquid nitrogen reservoir for passive backup cooling. This segmentation allows the system to achieve extended temperature range while maintaining reliability through the autonomous nitrogen reservoir that activates automatically upon mechanical system failure.
Solution Approach 2:
The system changes the operational parameters by introducing a dual-mode refrigeration approach. The mechanical system operates during normal conditions to achieve lower temperatures, while the liquid nitrogen reservoir provides backup at extreme temperatures, allowing the system to adapt to different temperature requirements and failure scenarios.
2Temperature
If liquid nitrogen is used to achieve extremely low temperatures, then the temperature is improved, but the loss of substance worsens due to continuous LN2 replenishment requirements
Solution Approach 1:
The mechanical refrigeration system acts as an intermediary that reduces the direct contact and consumption of liquid nitrogen. By handling the bulk of the cooling demand through the mechanical system, the nitrogen reservoir serves only as a backup, dramatically reducing LN2 replenishment frequency and consumption.
Solution Approach 2:
The system transitions from continuous liquid nitrogen consumption to periodic replenishment. The mechanical refrigeration system handles continuous cooling demands, while the liquid nitrogen reservoir provides intermittent backup cooling only when the mechanical system fails or requires maintenance, converting a continuous loss into a periodic one.
3Ease of operation
If a mechanical freezer configuration is used, then the ease of operation is improved, but the temperature uniformity deteriorates due to box-shaped design and door-equipped configuration
Solution Approach 1:
The patent embeds the mechanical refrigeration system within the vacuum-insulated dewar structure, creating a nested configuration where the mechanical system operates inside the well-insulated container. This nesting allows the mechanical system to maintain temperature uniformity throughout the storage space while preserving ease of operation through the dewar's access design.
4Loss of energy
If vacuum insulation is used to improve thermal insulation, then the loss of energy is improved, but the device complexity worsens due to additional insulation layers and structure
Solution Approach 1:
The vacuum-insulated dewar structure serves multiple functions simultaneously: it provides thermal insulation to reduce energy loss, contains the mechanical refrigeration system, and supports the liquid nitrogen reservoir. This multi-functionality reduces the need for additional separate insulation components, thereby limiting the increase in device complexity while achieving superior thermal performance.
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 solution provides reliable, energy-efficient, and cost-effective low-temperature storage with minimal temperature variation, eliminating the need for continuous LN2 replenishment and ensuring the preservation of valuable biological materials even in the event of power or refrigeration failures.
Implementation Method 1
a vacuum-insulated dewar with a central cryogenic reservoir
Implementation Method 2
a mechanical refrigeration system with a cryocooler using a cryogenic fluid
Implementation Method 3
A number of stainless steel storage racks, one of which is illustrated at 22, holding boxes containing biological specimens are positioned inside the dewar. The racks rest on a circular turn tray platform 26. To access storage racks 22, a user rotates the tray 26 using handles 28. At the bottom of the dewar is a pool 32 of liquid nitrogen (−196° C.) which keeps the biological specimens in the dewar cool by evaporating.
Data Source
AI summary
A cryogenic freezer features a dewar defining a storage space. A reservoir is positioned within or adjacent to the storage space and is configured to contain a cryogenic liquid with a headspace above the cryogenic liquid in a reservoir interior space that is sealed with respect to the storage space. A refrigeration module is in heat exchange relationship with the reservoir. A sensor is configured to determine a temperature or pressure within the reservoir. A system controller is connected to the sensor and the refrigeration module and configured so that the refrigeration module is adjusted to provide additional cooling to the reservoir when a pressure or temperature within the headspace increases.