Balancing the amount of gas and liquid
Posted: Thu Dec 05, 2024 8:38 am
Control element is another important system component. We will learn more about it in this section.
Why is a control element necessary in a refrigeration circuit?
The control element, capillary tube or expansion valve has the function of maintaining the pressure difference between the high and low zones (condenser and evaporator respectively). This element restricts the flow of refrigerant fluid from the high pressure hot liquid through the high pressure coolant liquid at low pressure.
From there, the refrigerant reaches the evaporator and begins the heat absorption process, as explained in this article about evaporators in the 116th edition of the Club (December/2013).
How the control elements in the system work
It is a capillary tube or expansion valve. The control element creates belize whatsapp number data 5 million resistance to the passage of the refrigerant. For example, let's imagine a capillary tube. This element has an internal diameter that is about six to seven times smaller than the diameter of the connecting pipe. It is as if we have a six- to seven-lane highway for vehicles to travel on, and suddenly, from a certain point, we only provide one lane of road for traffic. This is what we call restriction.
The process is a little different than an expansion valve, but the choice of orifice and number of turns is used to tune the system for your needs. The refrigerant is throttled, reducing its temperature and pressure so that it is in ideal conditions when it evaporates in the evaporator.
The main difference between a capillary tube and an expansion valve is that when the compressor is switched off, the first pressure balance is achieved and the off time ensures that it becomes a low starting torque (LST) compressor. An expansion valve must be used with a high starting torque (HST) compressor.
General guidance for selection
Together with the correct temperature or pressure on the low-pressure side, the appropriate control element is determined. This means that for the same compressor, the capillary tubes for refrigeration and freezing are different. The control element also depends on the cooling capacity of the compressor and the refrigerant.
Capillary
In equipment with capillary tubes, the refrigerant loses pressure due to friction with the inner wall of the tube. Therefore, the inner diameter and length are important factors for capillary tubes.
Determining the refrigerant temperature of the capillary tube depends on the refrigerant temperature on the low pressure side and the compressor capacity. The determination of the capillary tube is complex. To facilitate the contractor's work, Embraco provides recommended capillary tube specifications in the compressor application manual.
Expansion valve
The purpose of the expansion valve is to keep the evaporator superheated. Two common types of expansion valves used in commercial refrigeration equipment are shown in the table on this page.
When selecting an expansion valve port, the following should be considered:
Required temperature or pressure on the low pressure side
Flow rates in compressors and refrigeration equipment
After the orifice is selected, the amount of pressure opening on the valve for the adjustment spring is adjusted. This adjustment must be made simultaneously with the opening of the system in order to seek a constant superheat on the evaporator.
It must be remembered that each valve manufacturer has its own manual, which must always be consulted to determine the model, valve port and number of turns that best suits the cooling circuit.
Which is better: expansion valve or capillary tube?
Both devices can make a refrigeration system work well if properly adjusted. The expansion valve maintains the pressure difference when it is stopped, allowing heat exchange to take place at the instant the compressor starts. However, this is more expensive.
Capillary tubes are low cost, allow pressure to be equalized, and require a motor with low starting torque, although it takes a few seconds before the heat exchange process begins.
Each control element has its advantages and disadvantages, so it is necessary to evaluate which refrigeration system is best for you.
Expansion valve model
Thermostatic expansion valve: It has a temperature measuring package with a refrigerant similar to that in the refrigeration cycle system and is usually installed at the outlet of the evaporator. Its principle is based on the pressure difference between the valve ball and the evaporator inlet, which is controlled by adjusting the number of spring turns. When the pressure of the valve ball increases, the diaphragm allows more fluid to pass through the evaporator. If the temperature of the valve ball drops, the direction of fluid flow is reversed, and the diaphragm restricts the passage of fluid. Therefore, this valve is used to maintain the temperature difference between the inlet and outlet of the evaporator.
Electronic expansion valve: It consists of a thermistor and a temperature measurement sensor, installed on the suction pipe of the compressor. The thermistor works with the microprocessor to control the movement of the electronic valve to increase or decrease the flow of liquid refrigerant to the evaporator.
Why is a control element necessary in a refrigeration circuit?
The control element, capillary tube or expansion valve has the function of maintaining the pressure difference between the high and low zones (condenser and evaporator respectively). This element restricts the flow of refrigerant fluid from the high pressure hot liquid through the high pressure coolant liquid at low pressure.
From there, the refrigerant reaches the evaporator and begins the heat absorption process, as explained in this article about evaporators in the 116th edition of the Club (December/2013).
How the control elements in the system work
It is a capillary tube or expansion valve. The control element creates belize whatsapp number data 5 million resistance to the passage of the refrigerant. For example, let's imagine a capillary tube. This element has an internal diameter that is about six to seven times smaller than the diameter of the connecting pipe. It is as if we have a six- to seven-lane highway for vehicles to travel on, and suddenly, from a certain point, we only provide one lane of road for traffic. This is what we call restriction.
The process is a little different than an expansion valve, but the choice of orifice and number of turns is used to tune the system for your needs. The refrigerant is throttled, reducing its temperature and pressure so that it is in ideal conditions when it evaporates in the evaporator.
The main difference between a capillary tube and an expansion valve is that when the compressor is switched off, the first pressure balance is achieved and the off time ensures that it becomes a low starting torque (LST) compressor. An expansion valve must be used with a high starting torque (HST) compressor.
General guidance for selection
Together with the correct temperature or pressure on the low-pressure side, the appropriate control element is determined. This means that for the same compressor, the capillary tubes for refrigeration and freezing are different. The control element also depends on the cooling capacity of the compressor and the refrigerant.
Capillary
In equipment with capillary tubes, the refrigerant loses pressure due to friction with the inner wall of the tube. Therefore, the inner diameter and length are important factors for capillary tubes.
Determining the refrigerant temperature of the capillary tube depends on the refrigerant temperature on the low pressure side and the compressor capacity. The determination of the capillary tube is complex. To facilitate the contractor's work, Embraco provides recommended capillary tube specifications in the compressor application manual.
Expansion valve
The purpose of the expansion valve is to keep the evaporator superheated. Two common types of expansion valves used in commercial refrigeration equipment are shown in the table on this page.
When selecting an expansion valve port, the following should be considered:
Required temperature or pressure on the low pressure side
Flow rates in compressors and refrigeration equipment
After the orifice is selected, the amount of pressure opening on the valve for the adjustment spring is adjusted. This adjustment must be made simultaneously with the opening of the system in order to seek a constant superheat on the evaporator.
It must be remembered that each valve manufacturer has its own manual, which must always be consulted to determine the model, valve port and number of turns that best suits the cooling circuit.
Which is better: expansion valve or capillary tube?
Both devices can make a refrigeration system work well if properly adjusted. The expansion valve maintains the pressure difference when it is stopped, allowing heat exchange to take place at the instant the compressor starts. However, this is more expensive.
Capillary tubes are low cost, allow pressure to be equalized, and require a motor with low starting torque, although it takes a few seconds before the heat exchange process begins.
Each control element has its advantages and disadvantages, so it is necessary to evaluate which refrigeration system is best for you.
Expansion valve model
Thermostatic expansion valve: It has a temperature measuring package with a refrigerant similar to that in the refrigeration cycle system and is usually installed at the outlet of the evaporator. Its principle is based on the pressure difference between the valve ball and the evaporator inlet, which is controlled by adjusting the number of spring turns. When the pressure of the valve ball increases, the diaphragm allows more fluid to pass through the evaporator. If the temperature of the valve ball drops, the direction of fluid flow is reversed, and the diaphragm restricts the passage of fluid. Therefore, this valve is used to maintain the temperature difference between the inlet and outlet of the evaporator.
Electronic expansion valve: It consists of a thermistor and a temperature measurement sensor, installed on the suction pipe of the compressor. The thermistor works with the microprocessor to control the movement of the electronic valve to increase or decrease the flow of liquid refrigerant to the evaporator.