Cryogen Freezer Heat Exchanger Purge for Ice-Free Temperature Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing freezers using liquid cryogen as a refrigerant face challenges in temperature control and risk of cross-contamination, while mechanical refrigeration systems require significant electrical power and contribute to environmental heating.
Innovation Solution
A freezer design incorporating a heat exchanger with a purge line and controller to manage liquid cryogen flow, allowing precise temperature control and minimizing contact with cryogenic liquids, combined with vacuum insulation to reduce energy consumption and prevent ice formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If liquid cryogen reservoir is used for cooling, then storage temperature can be maintained at very low levels (-90°C to -195°C), but temperature control precision deteriorates because temperature varies dependent upon the amount of liquid cryogen
Solution Approach 1:
The system segments the cryogen delivery into controlled portions through a heat exchanger, allowing precise metering of cryogen flow rather than relying on bulk reservoir levels. This enables precise temperature control while maintaining very low storage temperatures.
Solution Approach 2:
A heat exchanger is introduced as an intermediary between the cryogen source and the storage chamber. This intermediary device allows controlled heat transfer and precise temperature regulation without direct contact between the cryogen and stored materials, resolving the contradiction between achieving extreme cold and maintaining temperature precision.
2Object-affected harmful factors
If specimen containers are placed in cold vapor above the cryogenic liquid reservoir, then cross-contamination risk is reduced, but temperature control effectiveness deteriorates because containers may still contact the liquid cryogen
Solution Approach 1:
The system extracts the cooling function from direct liquid cryogen contact and relocates it to a heat exchanger system. This separates the cooling mechanism from the storage space, eliminating cross-contamination risk while ensuring reliable temperature control through controlled heat transfer.
Solution Approach 2:
The heat exchanger acts as an intermediary that provides cooling without requiring specimen containers to be positioned above or near liquid cryogen. This eliminates the cross-contamination hazard while maintaining effective temperature control through the mediated heat transfer process.
3Measurement precision
If mechanical refrigeration system is used, then temperature control precision is improved, but electrical power consumption increases significantly
Solution Approach 1:
The system replaces the mechanical refrigeration system (compressor, condenser, evaporator) with a passive heat exchanger-based cryogen delivery system. This substitution eliminates the need for high-power mechanical components while achieving precise temperature control through controlled cryogen flow and phase change.
Solution Approach 2:
The system utilizes the phase transition of cryogen (liquid to vapor) in the heat exchanger as the primary cooling mechanism. This phase change process provides efficient heat transfer and precise temperature control without requiring the continuous operation of high-power mechanical refrigeration components.
4Temperature
If mechanical refrigeration system removes heat from storage chamber, then temperature control is achieved, but environmental heating increases because rejected heat adds to the room
Solution Approach 1:
The system extracts the heat removal process from the storage chamber environment by using a heat exchanger that transfers heat directly to the cryogen. The cryogen absorbs heat and undergoes phase change, removing heat from the system without requiring a separate heat rejection mechanism that would add heat to the surrounding room.
Solution Approach 2:
The system converts the harmful effect of heat accumulation into a beneficial process by using the cryogen's phase change to absorb and remove heat. The heat that would otherwise be rejected into the room environment is instead captured by the cryogen during vaporization, converting a potential harmful thermal load into an effective cooling mechanism.
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 enables controlled temperature maintenance, reduces energy usage, prevents cross-contamination, and minimizes environmental heating, providing efficient and reliable cryogenic storage without the drawbacks of traditional systems.
Implementation Method 1
the liquid cryogen refrigerant may flow through the heat exchanger to cool the storage chamber while being vaporized
Implementation Method 2
the liquid cryogen refrigerant may flow through the heat exchanger to cool the storage chamber while being vaporized
Implementation Method 3
a heat exchanger positioned in the storage chamber, said heat exchanger having an outlet and an inlet adapted to communicate with a supply of the liquid cryogen refrigerant
Implementation Method 4
an outer jacket generally surrounding the inner vessel so that an insulation space is defined there between
Implementation Method 5
an outer jacket generally surrounding the inner vessel so that an insulation space is defined there between
Implementation Method 6
a purge line in communication with the outlet of the heat exchanger, said purge line including a purge outlet positioned adjacent to an exterior of the heat exchanger; and a purge valve positioned within the purge line so that the vaporized liquid cryogen from the heat exchanger may be selectively directed to the exterior of the heat exchanger to reduce ice formation on the heat exchanger
Data Source
Figure 1
Figure 2
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.