Cryogen Freezer Heat Exchanger for Stable Storage Temperature
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Solution Overview
Problem
Existing freezers using liquid cryogen as a refrigerant face challenges in temperature control variability, risk of cross-contamination, high electrical power consumption, and heat rejection to the environment, as well as rapid temperature increase during power failures.
Innovation Solution
A freezer design featuring a vacuum-insulated storage chamber with a heat exchanger and a controller-managed liquid cryogen supply system that allows precise temperature control, prevents specimen contact with the cryogen, and minimizes electrical power usage by vaporizing and venting nitrogen gas outside the room.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If liquid cryogen is used as refrigerant in storage chamber, then storage temperature can be achieved, but temperature control precision deteriorates and cross-contamination risk increases
Solution Approach 1:
The system divides the refrigeration function into two separate components: a heat exchanger for temperature control and a liquid cryogen reservoir for cold source storage. This segmentation allows the heat exchanger to precisely regulate temperature by controlling heat transfer, while the reservoir maintains the cryogen supply, thereby resolving the contradiction between achieving storage temperature and maintaining temperature control precision.
Solution Approach 2:
The heat exchanger acts as an intermediary between the liquid cryogen and the storage chamber. Instead of direct contact between cryogen and specimens, the heat exchanger mediates the thermal energy transfer, enabling precise temperature control while eliminating cross-contamination risks. This intermediary approach simultaneously achieves both temperature stability and contamination prevention.
2Measurement precision
If mechanical refrigeration system is used, then temperature control is improved, but electrical power consumption increases
Solution Approach 1:
The system utilizes the natural properties of liquid cryogen (extremely low temperature and high heat transfer coefficient) to provide refrigeration without requiring electrical power for compressors or fans. The liquid cryogen spontaneously evaporates and absorbs heat from the storage chamber through the heat exchanger, making the system self-cooling and eliminating the need for external electrical power input while maintaining precise temperature control.
3Measurement precision
If mechanical refrigeration system is used, then temperature control is improved, but heat rejection to environment increases
Solution Approach 1:
The system extracts the heat rejection problem from the storage environment by using liquid cryogen that is imported from external sources. The heat absorbed from the storage chamber is transferred to the liquid cryogen, which then carries this heat away when replenished. This extraction approach eliminates the need to reject heat to the surrounding environment, thereby preventing the harmful thermal effect while maintaining improved temperature control.
4Temperature
If liquid cryogen reservoir is used, then extreme temperature is achieved, but cross-contamination risk increases
Solution Approach 1:
The heat exchanger serves as an intermediary barrier between the liquid cryogen reservoir and the storage chamber containing specimens. Thermal energy is transferred through this intermediary without direct contact between the cryogen and specimens, thereby achieving extreme storage temperatures while eliminating the cross-contamination risk that would occur with direct submersion.
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 stable temperature control, reduces the risk of cross-contamination, minimizes electrical power consumption, and maintains storage temperatures during power failures by efficiently managing the cryogen supply and venting process.
Implementation Method 1
An insulation space is defined between the inner vessel and the outer jacket. A vacuum is drawn on the insulation space so that the storage chamber is insulated.
Implementation Method 2
The storage chamber of the freezer, and thus the items stored therein, are cooled by a heat exchanger positioned within a top portion of the storage chamber.
Implementation Method 3
liquid cryogen refrigerant flows through the cooling coil and is vaporized
Implementation Method 4
liquid nitrogen refrigerant flows through the cooling coil and is vaporized
Implementation Method 5
The nitrogen gas is expanded in a vacuum breaker valve
Data Source
AI summary
A freezer that uses liquid cryogen as a refrigerant includes an inner vessel defining a storage chamber and an outer jacket generally surrounding the inner vessel so that an insulation space is defined there between. A heat exchanger is positioned in a top portion of the storage chamber and has an inlet in communication with a supply of the liquid cryogen refrigerant so that the liquid cryogen refrigerant selectively flows through the heat exchanger to cool the storage chamber while being vaporized. A purge line is in communication with the outlet of the heat exchanger and includes a purge outlet positioned over the exterior of the heat exchanger. A purge valve is positioned within the purge line so that the vaporized liquid cryogen from the heat exchanger is selectively directed to the exterior of the heat exchanger to reduce ice formation on the heat exchanger.