Control method for vapor compression cycle
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Solution Overview
Problem
Current vapor-compression cycles (VCCs) lack a method to combine the controllability of expansion processes with high-efficiency expansion work recovery, which is essential for improving overall cycle efficiency and cooling capacity.
Innovation Solution
A novel method involving an integrated expander and flash tank device with a metering valve, allowing for active control of compressor suction superheat by bypassing vapor from the flash tank towards the compressor inlet, and using a radial-in axial-out turbine to enhance expander power output and reduce friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an integrated expander and flash tank device is used to recover expansion work, then the Coefficient of Performance (COP) and cooling capacity increase, but the control of compressor suction superheat becomes difficult
Solution Approach 1:
The system divides the refrigerant flow into two separate paths: one through the expander for work recovery and another through the flash tank for phase separation. This segmentation allows independent control of each path, enabling the metering valve to specifically regulate the vapor bypass flow to achieve desired compressor suction superheat while maintaining the benefits of expansion work recovery
Solution Approach 2:
A metering valve is introduced as an intermediary device in the vapor bypass line between the flash tank and compressor inlet. This valve acts as a flow regulator that precisely controls the amount of vapor mixed with the compressor suction, enabling accurate control of compressor suction superheat without affecting the overall expansion work recovery process
2Ease of operation
If a conventional expansion valve is used to control the expansion process, then the compressor suction superheat can be maintained, but the expansion work is not recovered leading to lower system efficiency
Solution Approach 1:
The patent merges the expansion work recovery function with the phase separation function by integrating the expander and flash tank into a single device. This combination allows the system to simultaneously recover expansion work through the expander while separating phases in the flash tank, eliminating the need for a conventional expansion valve and preventing energy loss during expansion
Solution Approach 2:
The system changes the expansion process from a purely throttling process (isenthalpic) to a work-recovering process (isentropic or near-isentropic) by using the expander. This parameter change in the expansion process enables energy recovery while the integrated flash tank maintains proper phase separation for continued system control
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 increases the Coefficient of Performance (COP) by up to 15.3% in cooling mode and 6.9% in heating mode, while maintaining safe compressor suction superheat and reducing pressure drop, thereby improving system efficiency and cooling capacity.
Implementation Method 1
using a radial-in axial-out turbine to enhance expander power output and reduce friction
Implementation Method 2
an integrated expander and flash tank device with a vapor/liquid two-phase inlet, a first vapor outlet, and a second liquid outlet
Implementation Method 3
a metering valve with an inlet and an outlet, wherein the metering valve is disposed between the vapor outlet of the integrated expander and flash tank device, the inlet of the compressor, and the outlet of the evaporator
Implementation Method 4
an evaporator with a fan, an inlet and an outlet
Implementation Method 5
a condenser with a fan, an inlet and an outlet
Implementation Method 6
a compressor with an inlet and an outlet
Data Source
AI summary
A method for operating and controlling a vapor-compression cycle includes providing a system comprising an evaporator with a fan, a compressor, a condenser with a fan, an integrated expander, and a flash tank device with a vapor/liquid two-phase inlet and two outlets wherein a first outlet is a vapor outlet and a second outlet is a liquid outlet, and a metering valve; bringing a vapor-compression cycle up to steady-state at a fixed operating condition; opening the metering valve until the desired compressor suction superheat is achieved; and maintaining the desired degree of superheat by selectively increasing and decreasing superheat by reducing and increasing metering valve flow rate respectively.