Zeotropic Refrigerant Cooling Device for Test Chambers Below −80°C
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Solution Overview
Problem
Existing cooling devices struggle to achieve temperatures below −80°C in an environmentally friendly and safe manner, particularly in test chambers, due to limitations with refrigerants that have high global warming potential, flammability, and require complex adjustments for temperature glides and dynamic cooling applications.
Innovation Solution
A method using a zeotropic refrigerant mixture with a controlled expansion element, where the refrigerant partially freezes during expansion, allowing for sublimation and utilizing the enthalpy of sublimation to achieve lower temperatures, combined with an internal heat exchanger to reduce evaporation temperature, and a refrigerant composition of carbon dioxide and fluorinated components to minimize environmental impact and flammability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If carbon dioxide is used as refrigerant, then environmental safety is improved (GWP=1, nonflammable), but temperature below −56.6°C cannot be achieved due to freezing point limitation
Solution Approach 1:
The patent uses a composite refrigerant system consisting of two separate circuits: one with carbon dioxide (R744) and another with a zeotropic mixture containing hydrofluorocarbons. This composite approach allows the R744 circuit to provide environmental safety while the zeotropic circuit enables temperatures below −56.6°C through its lower freezing point components and temperature glide特性
Solution Approach 2:
The heat exchanger serves as an intermediary between the R744 circuit and the zeotropic circuit. The R744 circuit cools the zeotropic refrigerant before it enters the evaporator, enabling the zeotropic refrigerant to achieve temperatures below its normal freezing point and thus achieving temperatures below −56.6°C while maintaining environmental safety through the R744 system
2Temperature
If zeotropic refrigerant mixture is used, then temperatures below −56.6°C can be achieved, but temperature glide requires complex adjustments to expansion element and heat exchanger
Solution Approach 1:
The R744 circuit performs preliminary cooling of the zeotropic refrigerant before it enters the evaporator. This pre-cooling action prepares the zeotropic refrigerant to operate at temperatures below its normal freezing point, enabling the system to achieve temperatures below −56.6°C without requiring complex real-time adjustments to the expansion element or heat exchanger
Solution Approach 2:
The heat exchanger acts as an intermediary that decouples the temperature glide characteristics of the zeotropic refrigerant from the expansion element control. By pre-cooling the zeotropic refrigerant with R744, the system can maintain simpler control mechanisms while still achieving the desired low temperatures
3Object-affected harmful factors
If flammable refrigerant is used, then lower GWP can be achieved, but safety regulations and constructional measures increase cost and complexity
Solution Approach 1:
The patent segments the refrigerant system into two separate circuits: one using nonflammable R744 for environmental safety and another using zeotropic mixture with lower GWP components for temperature achievement. This segmentation allows each circuit to be optimized independently, with the R744 circuit providing nonflammability and the zeotropic circuit providing lower GWP characteristics without requiring extensive flammability safety measures throughout the entire system
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 approach enables the establishment of temperatures as low as −90°C or lower while maintaining environmental safety and simplicity, reducing the global warming potential and preventing clogging, with a refrigerant mixture that is nonflammable and cost-effective to use.
Implementation Method 1
the refrigerant undergoing a phase transition in the heat exchanger
Implementation Method 2
the refrigerant of a high-pressure side of the cooling circuit being cooled by means of the internal heat exchanger
Implementation Method 3
the expansion element being controlled by means of a control device of the cooling device in such a manner that the refrigerant partially freezes during an expansion at the expansion element
Implementation Method 4
allowing for sublimation and utilizing the enthalpy of sublimation to achieve lower temperatures
Data Source
AI summary
A method for operating a cooling device, a cooling device and a test chamber having a cooling device, a temperature of at least −80° C. or lower being established at the heat exchanger by means of the cooling device having a cooling circuit comprising a refrigerant, a heat exchanger, an internal heat exchanger, a compressor, a condenser and a controllable expansion element of the cooling device, the refrigerant undergoing a phase transition in the heat exchanger, the refrigerant of a high-pressure side of the cooling circuit being cooled by means of the internal heat exchanger, the cooling of the refrigerant of the high-pressure side by means of the internal heat exchanger being used to reduce an evaporation temperature at the expansion element, a zeotropic refrigerant being used as refrigerant, the expansion element being controlled by means of a control device of the cooling device in such a manner that the refrigerant partially freezes during an expansion at the expansion element.