Flash Tank Pressure Control to Prevent High-Stage Compressor Liquid Back
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Solution Overview
Problem
Conventional systems for cooling and heating in a single unit face inefficiencies due to excessive energy consumption, decreased compressor efficiency, and safety issues, particularly in two-stage compression systems where fine droplets can enter the high-stage compressor and refrigeration oil is not effectively collected, leading to reduced system reliability and performance.
Innovation Solution
A two-stage compression heat pump system with a flash tank equipped with sensors for fluid-level and pressure control, an intercooler for enhanced sub-cooling, and a bypass valve system to prevent droplet entry into the high-stage compressor, along with a refrigeration oil collection mechanism to ensure stable operation and extend device lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a two-stage compression system is used to improve heating capacity and efficiency, then system performance is improved, but fine droplets are generated during thermal equilibrium that can enter the high-stage compressor causing liquid back or liquid compression
Solution Approach 1:
A flash tank is introduced as an intermediary device between the low-stage compressor and high-stage compressor. The flash tank receives two-phase refrigerant from the low-stage compressor, allows thermal equilibrium to occur, separates the refrigerant into vapor and liquid phases, and supplies only vapor to the high-stage compressor through a vapor outlet positioned above the liquid level. This mediator prevents fine droplets from entering the high-stage compressor while maintaining the benefits of two-stage compression.
2Device complexity
If refrigeration oil is not collected from the flash tank, then the system structure remains simple, but refrigeration oil accumulates in the flash tank reducing system reliability and performance
Solution Approach 1:
The flash tank is designed with a refrigeration oil collecting mechanism that utilizes the natural properties of the system. Refrigeration oil, being heavier than refrigerant vapor, automatically settles at the bottom of the flash tank. A refrigeration oil outlet positioned at the bottom allows the oil to be drained automatically during operation or maintenance, eliminating the need for complex external collection systems while maintaining system reliability.
3Device complexity
If conventional flash tanks are used without droplet removal devices, then the device complexity is low, but liquid back or liquid compression occurs in the high-stage compressor
Solution Approach 1:
The flash tank design utilizes the vertical dimension to separate vapor and liquid phases. The vapor outlet is positioned at the top of the tank while the liquid outlet and refrigeration oil outlet are positioned at the bottom. This vertical arrangement allows gravitational separation of phases, with vapor rising to the top outlet and liquid/droplets remaining at the bottom, effectively preventing liquid back without requiring complex mechanical separation devices.
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 achieves stable and efficient cooling and heating operations by preventing liquid backflow into the high-stage compressor, effectively collecting refrigeration oil, and enhancing system reliability and performance through complete intermediate cooling and optimized pressure control.
Implementation Method 1
induces two refrigerants to reach thermal equilibrium smoothly, wherein the refrigerants have different states from each other and flow into the flash tank
Implementation Method 2
an intercooler that maximizes cooling effect by increasing the degree of sub-cooling of a refrigerant sent to the flash tank and an evaporator
Implementation Method 3
an orifice installed so as to correspond to the refrigeration oil inlet provided at the bottom side of the U-shaped pipe, wherein the orifice is provided for filtering contaminations in the refrigeration oil
Data Source
AI summary
Disclosed herein is a flash tank of a two-stage compression heat pump system that can perform cooling and heating with a separate type intercooler and a high-stage compressor protecting device. The system comprises a fluid-level detecting sensor for detecting the fluid-level of the refrigerant, an alarm sensor for notifying the saturated state of the refrigerant filled in the flash tank, an evaporator pressure sensor for measuring and notifying the pressure of the refrigerant flowing into the evaporator, a condenser pressure sensor for measuring and notifying the pressure of the refrigerant flowing out of the condenser, a flash tank fluid-level controller for receiving signals from the above sensors and controlling intermediate pressure and the fluid-level of the flash tank, and a bypass valve controller for controlling a bypass valve that receives signals from the alarm sensor and allowing a refrigerant to directly flow from the low-stage compressor to the high-stage compressor.