Test chamber and method for its control having cooling circuit accommodating small volume test chamber
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Solution Overview
Problem
Existing cooling circuits using carbon dioxide as a refrigerant are not economically viable for small volume test chambers due to their complex design, high pressure requirements, and high construction space needs, limiting their use to large installations.
Innovation Solution
A cooling circuit design incorporating an internal heat exchanger and medium-pressure bypass with a second expansion valve allows for flexible operation in subcritical and transcritical states, enabling efficient use of carbon dioxide refrigerant in compact test chambers by regulating refrigerant flow and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carbon dioxide cooling circuit is used in small volume test chambers, then cooling efficiency is improved, but device complexity increases
Solution Approach 1:
The cooling circuit is segmented into distinct functional modules: a first cooling circuit for the gas cooler and a second cooling circuit for the internal heat exchanger. This segmentation allows independent control and optimization of each module, reducing overall system complexity while maintaining high cooling efficiency through specialized carbon dioxide refrigerant circulation in each segment.
Solution Approach 2:
The internal heat exchanger is nested within the test chamber space, utilizing the available volume efficiently. The heat exchanger components are arranged in a compact, space-saving configuration that fits within the small test chamber environment, allowing the complex cooling functionality to be integrated without proportionally increasing external dimensions.
2Power
If high pressure range is used for carbon dioxide cooling, then cooling capacity is improved, but construction space increases
Solution Approach 1:
Different pressure ranges are applied locally to different components based on their specific functional requirements. The gas cooler operates at high pressure (up to 120 bar) to maximize heat rejection efficiency, while the internal heat exchanger operates at lower pressure suitable for the small test chamber volume. This localized pressure optimization maintains high overall cooling capacity while minimizing the space required for pressure-containing components.
Solution Approach 2:
The cooling circuit incorporates dynamic pressure regulation capabilities, allowing the system to adjust operating pressures based on load requirements and temperature conditions. This dynamic operation enables the system to achieve high cooling capacity when needed while reducing pressure and space requirements during partial-load operation, effectively decoupling peak capacity from continuous space occupation.
3Adaptability or versatility
If compressors are frequently switched on and off for load regulation, then cooling capacity control is improved, but compressor reliability decreases
Solution Approach 1:
The compressors are equipped with variable speed drives that enable continuous adjustment of compression capacity according to cooling load requirements. This dynamic speed control allows the system to match cooling output to actual demand without frequent on-off cycling, thereby maintaining compressor reliability and extending service life while achieving flexible cooling capacity regulation across different operating conditions.
Solution Approach 2:
The control system incorporates temperature and pressure sensors that provide real-time feedback to the compressor control. This feedback mechanism enables automatic adjustment of compressor operation to maintain optimal cooling capacity, preventing both over-compression and unnecessary shutdowns. The feedback loop ensures smooth, continuous operation that protects compressor reliability while adapting to changing thermal loads in the test chamber.
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 enables efficient temperature control in small test chambers from -20°C to 180°C, prolongs compressor life by reducing frequent switching, and reduces thermal overload risks, while maintaining high efficiency and compactness.
Implementation Method 1
an internal heat exchanger, which is connected on a high-pressure side of the cooling circuit downstream of the gas cooler and upstream of the expansion valve
Implementation Method 2
an expansion valve, refrigerant being dosed in the medium-pressure side from the high-pressure side via the internal heat exchanger by means of a second expansion valve
Implementation Method 3
a low-pressure compressor and a high-pressure compressor, which is disposed downstream of the low-pressure compressor in a flow direction of the refrigerant
Data Source
AI summary
A method for conditioning air in a temperature-insulated test space of a test chamber and a test chamber serving for receiving test material, in which a temperature ranging from −20° C. to +180° C. is generated within the test space. A cooling circuit has an internal heat exchanger, which is connected on a high-pressure side of the cooling circuit downstream of a gas cooler and upstream of an expansion valve, the internal heat exchanger being coupled with a medium-pressure bypass of the cooling circuit, the medium-pressure bypass being connected downstream of the internal heat exchanger or the gas cooler and upstream of the expansion valve on the high-pressure side as well as upstream of a high-pressure compressor and downstream of a low-pressure compressor on a medium-pressure side of the cooling circuit, refrigerant being dosed in the medium-pressure side from the high-pressure side via the internal heat exchanger by a second expansion valve.