Evaporative Gas Cooler for Subcritical CO2 Heat Rejection
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Solution Overview
Problem
Refrigeration systems using refrigerants with low critical temperatures face inefficiencies and environmental concerns, particularly in transcritical cycles, which lead to higher energy consumption and larger system sizes, and traditional alternatives like CFCs have negative environmental impacts.
Innovation Solution
An evaporatively cooled refrigeration system that includes a gas/liquid separator, expansion valve, evaporator, compressor, and a gas cooler with an indirect heat exchanger and spray system for evaporative cooling, designed to operate below the dry bulb ambient air temperature, using refrigerants like CO2 that have a low critical temperature and low environmental impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a transcritical cycle is used for refrigerants with low critical temperature, then heat rejection to ambient environment is achieved, but energy consumption increases and system size increases
Solution Approach 1:
The patent utilizes evaporative phase transition of water on the heat exchanger surfaces to achieve cooling. The water absorbs heat from the refrigerant and evaporates, providing efficient heat rejection below ambient temperature without requiring transcritical cycle operation, thus reducing energy consumption while maintaining productivity
Solution Approach 2:
The patent introduces water as an intermediary cooling medium between the refrigerant and ambient air. The water absorbs heat from the refrigerant through evaporation and is then cooled by ambient air, acting as a thermal mediator that enables efficient heat rejection without directly exposing the refrigerant to ambient conditions
2Productivity
If traditional refrigerants like CFCs are used, then refrigeration performance is achieved, but environmental impact increases
Solution Approach 1:
The patent changes the refrigerant parameter from traditional CFCs to alternative refrigerants with lower environmental impact (such as CO2 or hydrocarbons), while maintaining refrigeration performance through optimized system design including evaporative cooling and improved heat exchanger configurations
3Temperature
If evaporative cooling is applied below dry bulb ambient temperature, then cooling efficiency improves, but system complexity increases
Solution Approach 1:
The patent segments the heat rejection process into two distinct stages: first, evaporative cooling of water on the heat exchanger surfaces to achieve temperatures below ambient; second, cooling of the evaporated water vapor by ambient air. This segmentation enables efficient cooling while managing system complexity through modular design
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 system operates efficiently with lower energy consumption and reduced environmental impact by staying below the critical point of CO2, minimizing energy use and system size, while providing effective heat rejection and cooling, even in warm climates.
Implementation Method 1
Evaporative cooling provided by the evaporative coolant on the indirect heat exchanger is configured to cool the refrigerant below a dry bulb ambient air temperature
Implementation Method 2
an indirect heat exchanger to convey the refrigerant and facilitate heat from the refrigerant
Data Source
AI summary
An evaporatively cooled refrigeration system includes a refrigerant, a gas/liquid separator, an expansion valve in fluid connection to the gas/liquid separator, an evaporator to receive the refrigerant from the expansion valve, a compressor configured to compress the refrigerant in fluid connection to the evaporator, and a gas cooler in fluid connection to the compressor. The gas cooler includes an indirect heat exchanger to convey the refrigerant and facilitate heat from the refrigerant and a spray system to spray an evaporative coolant on the indirect heat exchanger. Evaporative cooling provided by the evaporative coolant on the coil is configured to cool the refrigerant below a dry bulb ambient air temperature.