How Does a Condenser Work?
Before we get acquainted with different types of condensers, let’s take a brief look at how a condenser works. Again, we must mention that in another article, a full description of the section was devoted to the topics of functions of a condenser.
If you haven’t read that article, we’ll briefly explain how a condenser works to make it easier for you to understand what the different types of equipment are. Each condenser has three separate phases. The first stage is called desuperheating. The vapor entering the condenser is already overheated and is under excessive pressure in the evaporator and compressor.
Desuperheating means taking the heat out of the vapor and turning it into a liquid. The next level is the changing or condensation state; Much heat continues to be lost in this state where we reach 10% of the refrigerant as vapor and 90% as a liquid.
The third and final stage is the sub-cooling stage. The sub-cooling state is there to ensure that even rising temperatures do not cause the liquid refrigerant to vaporize again. Now that you have generals insight into how a condenser works, we can safely proceed to the next sections, where we are goings to get acquainted with the types of condensers step by step.
Different Types of Condensers:
Condensers include three different types based on the condensing medium used to remove heat from the system. Neither of these three different types of condenser has any particular advantage over the other. Depending on the situation, each should be used appropriately. We are going to elaborate on the function of these three condensers types in the following.
Three main and different types of condensers:
- Air-cooled condenser
- Water-cooled condenser
- Evaporative Condenser
#1. Air-Cooled Condenser
Condensers consist of a finned continuous tube coil. Compressor discharge vapor enters the top of the coil and liquid, leaving the bottom from where it flows into receivers located under the base. A fan mounted on the compressor-motor pulleys blows air across the condenser coil.
The unit should be located in a well-ventilated and preferably cool place. The lower the ambient air temperatures, the less power is required for a given capacity. The main advantage of this type of condensers is their simplicity and low installation cost.
They are mostly used in self-contained units such as home refrigerators, freezer cabinets, display cases, water coolers, and air room conditioners. This type of condenser uses air as the external fluid to reject the heat from the system. Air-cooled condensers usually have copper coils where the refrigerant flows. But that’s not the whole story; This type is subclassified into two subsets: natural convection and forced convection.
1.1. Natural Convection
In this type of condenser, air comes into contact with the hot coil, absorbing the heat of the refrigerant inside the coil, resulting in an increase in the air temperature. As the warm air is lighter, it moves up and replaces the cold air, and again the cold air comes to touch the hot coils to reject heaters. This natural cycle continues until refrigerants lose their heat.
Since the airflow rate is low and the radiative heat transfer is also not very high, the combined heat transfer coefficients in these condensers are small. As a result, relatively large condensing surfaces are required to reject a certain amount of heat. Therefore this type of condenser is used for small capacity refrigeration systems like home refrigerators & freezers.
1.2. Forced Convection
One other type of condenser is forced convection. The fan or blower plays the most important role in removing the heat from the refrigerant inside the coil. The fan blows air into the wing coils. An important tip should be noted here, and that is that the fins of the forced convection condenser are tightly placed next to each other; Therefore, if dust and dirt fill a small space between the fins, wind blowing and heat rejection pose great trouble. Forced convection type condenser is commonly used in window air conditioners, water coolers, and packaged air conditioning plants.
#2. Water-Cooled Condenser
Water-cooled condensers are used with compressors one hp and larger. They generally constitute the most economical alternative to condensers where there is an adequate supply of clean, cheap water with minimum corrosion along with adequate and cheap means of water disposal.
This type of condenser uses water to cool the hot refrigerant and convert it into a liquid. In a water-cooled condenser, the smaller the amount of water used, the higher the condensing temperature, and the higher the cost of electricity.
Conversely, the higher the amount of water used, the lower the condensing temperature and the lower the electricity cost. Therefore, there must be an optimum sum of water flows that generate the minimum sum of water and electricity costs.
As might be guessed, this type of condenser uses water as a fluid to remove heat from the coolant. Obviously, water-cooled condensers are used where we have a sufficient supply of water. Thus, there are three different types in their own right:
2.1. Double Tube
Doubles tubes condensers have a tube of water inside a larger refrigerant tube. Water absorbs most of the refrigerants heats, but since the refrigerant tube is exposed to the natural circulations of air, part of the cooling process is over natural convection.
Although double-tube condensers have been commonly used in the past, a large number of gaskets and flanges are used in these heat exchangers, which causes maintenance problems.
2.2. Shell and Coil Condenser
In a shell-and-coil condenser, a welded shell consists of a coil of finned water tubing. In this type of water-cooled condensers, the hot refrigerants flow into the shell while cold water circulates inside the coils and condenses the refrigerants. It is generally the most compact and low cost.
2.3. Shell and Tube Condenser
One of the types of condenser processes the heat by having a cylindrical shell consisting of water tubes. In shell and tube condensers, water is pumped through pipes while refrigerant flows into the shell. The installation of fins in the pipes allows for better heat transfer.
Shell-and-tube condensers are generally low-cost & easy to maintain. The most common type of shell & tube condenser is the horizontal shell type. However, vertical shell and tube condensers are commonly used with ammonia in large capacity systems to make it possible to clean the tubes from above while the plant is running.
#3. Evaporative Condensers
This type of condenser has been developed to reduce the problem arising from the use of multiple water-cooled condensers in small air conditioning systems. Evaporative condensers are designed to combine the functions of condensers & cooling towers.
Air is blown through an opening near the bottom, flows upward into the refrigerant coil, through the spray and eliminator, and into the fan, and is discharged at the top of the unit. The refrigerant condensing coil is usually of expanded surface or finned type.
Refrigerants enter the top of the coil & flow down. The condensed fluid goes into the receiver, which is often located in the water tank to further cool the liquid refrigerant. Water is drawn from tanks by a pump mounted on the unit and released through a downward-directed spray nozzle above the refrigerant coil.
As 3 to 5% of the circulating water evaporates, the make-up water is admitted into the tank through a float-operated valve. Partial evaporation increases the salt concentration of the water, and therefore water treatment and continuous overflow are recommended.
Water treatment should also be used to reduce scale formation on the hot coil. The unit should have provision for drainage when there is a sub-freezing temperature. In cold water, no water may need to be used, and the unit then acts as an air-cooled condenser.
A Brief Comparison Between These Three Types:
Evaporators are often cheaper than water-cooled ones requiring a cooling tower. Evaporators are used in places where we usually face a lack of water supply. The evaporator is kept outside, so the water pump is turned off in cold weather to avoid freezing of water.
Air-cooled condensers are simpler to manufacture than water-cooled condensers. In addition, access to air is always available. The maintenance cost of air-cooled is less as compared to water-cooled.