Two-Stage Compressor Engine Cooling Using Two-Phase Refrigerant Flow
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Solution Overview
Problem
Existing methods for cooling engines in refrigerant circuits with two-stage compressors either reduce system efficiency or are costly, requiring additional lines and expansion valves with complex control systems.
Innovation Solution
Cooling the engine using a two-phase refrigerant main flow at a medium pressure level, which contains both gaseous and liquid refrigerant, eliminating the need for additional expansion valves and allowing waste heat to be reintegrated without affecting efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the engine is cooled with suction gas before compression in the second compression stage, then the engine cooling is achieved, but the efficiency of the refrigerant circuit is reduced due to heating of the suction gas and decrease in density and mass flow
Solution Approach 1:
The refrigerant flow is segmented into a main flow that bypasses the engine cooling system and a separate flow that is used for engine cooling. This allows the majority of the refrigerant to maintain optimal conditions for heat pump operation while a portion is dedicated to engine cooling, thus resolving the contradiction between cooling effectiveness and system efficiency
Solution Approach 2:
An intermediary cooling system is introduced that uses a separate refrigerant flow path with its own expansion valve and heat exchanger. This intermediary system allows engine cooling to occur without directly impacting the main refrigerant circuit's efficiency, as the two systems operate semi-independently
2Temperature
If the engine is cooled with compressed gas after compression in the first compression stage, then the engine cooling is achieved, but losses occur and the temperature of the compressed gas increases, increasing demands on temperature resistance of the motor
Solution Approach 1:
The engine cooling is performed using refrigerant at an intermediate pressure level before the second compression stage, rather than after the first compression stage. This preliminary cooling action prevents the refrigerant from undergoing excessive compression and heating, thereby reducing energy losses and temperature demands on the motor
3Temperature
If a separate bypass connection with expansion valves is used to cool the motor, then the engine cooling is achieved, but the device complexity and control effort increase
Solution Approach 1:
The refrigerant circuit is designed to serve multiple functions: the main refrigerant flow handles the primary heat pump operation, while a portion of this same flow is diverted through a relatively simple bypass system to provide engine cooling. This multi-functionality allows one system to perform both cooling and engine temperature control without requiring entirely separate systems
Solution Approach 2:
The refrigerant circuit serves itself by using its own flow to cool the engine through a simplified bypass system. The system's existing refrigerant, after completing its primary heat pump cycle, automatically flows through the bypass to absorb engine heat, eliminating the need for external cooling systems or complex control mechanisms
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 simplifies the cooling process, reduces manufacturing and control costs, and maintains system efficiency by utilizing the entire refrigerant flow for engine cooling without requiring additional bypass connections or valves.
Implementation Method 1
the waste heat from the engine is fed into the main refrigerant flow which has a medium pressure level
Implementation Method 2
the engine is cooled with a two-phase refrigerant main flow, which is the medium has pressure level
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a method and a device for cooling an engine, wherein the engine drives at least one at least two-stage compressor (2) of a refrigerant circuit (1), which compressor comprises at least a first compression stage (3) and a second compression stage (4), wherein a refrigerant is conducted through the refrigerant circuit (1), which refrigerant is raised from a low pressure level to a medium pressure level in the first compression stage (3) and from the medium pressure level to a high pressure level in the second compression stage (4) and, subsequently to the second compression stage (4), is expanded to the medium pressure level with a release of heat.