It is difficult to understand the differences between an eva...
It is difficult to understand the differences between an evaporative condenser and a cooling tower separately by the definitions surfed online, because these two things should be combined to explain as an entire system.
Let’s start from the more easy-to-understand part: Cooling Tower
Cooling Towers can be divided into two types: Open Cooling Tower and Closed Cooling Tower. Literally, in the open cooling tower, liquid waiting for cooling can contact the air directly, and in the closed cooling tower, liquid waiting for cooling is flowing in a closed pipe, which cannot contact the air.
In open cooling tower, the liquid waiting for cooling flows from the pipe into the tower, spraying down into cooling materials. The cooling materials can be plastics(PVC, PP, or CPVC), ceramics, or metal materials.
Yes, in this process, the liquid can contact air and cooling material directly, so open cooling towers commonly are used to make water cold, rather than used for complicated chemicals.
At the same time, the fans at the bottom blow cold dry wind into the tower, to help discharge hot air from the tower. The cold air stays downside, and the hot air flows upwards from top of the tower.
After being cooled by the cooling materials, the liquid flows into the bottom side pipe, then flows outside the cooling tower. Thus far, the cooling work is done.
In closed cooling towers, liquid waiting for cooling stays in pipes, and cannot contact air, thus closed type cooling towers can be used for cooling chemicals that should not contact air.
Firstly, the pump delivers cold water into the upper pipes of the closed cooling tower, sprays cold water onto the downpipes, making the tower environment cooled. At the same time, fans blow cold dry wind into the tower, removing hot air from the tower top.
Secondly, liquid waiting for cooling flows from outside pipes into the tower, cooling down by the cold pipe. Spraying Cold water is used to cool the liquid pipe, and the cold pipe cools the flowing liquid.
After flowing through the long twist pipes in the tower, cold liquid is delivered out of the closed cooling tower, thus far, the cooling work is done.
Obviously, the major difference between open cooling towers and closed cooling towers is whether the target liquid can directly contact air, the other differences are generally relevant to this major point.
Due to the first point, the cooling targets are distinguished, because open cooling towers can contaminate target liquid. As a result of that, the open cooling tower is commonly used for cooling water. In opposition, closed cooling towers can be used for sensitive or reactive chemicals.
When the target liquid directly contacts cooling materials in open cooling towers, the cooling time will be shorter, and the heat exchange space is bigger, which leads to the rapid heat elimination. By analogy, in closed cooling towers, the heat exchange space of target liquid which relies on the channel border, is less than open cooling towers.
When liquid contacts the cooling materials in open cooling towers, and evaporates by the wind of fans, liquid consumption happens. However, in closed cooling towers, the liquid stays in a closed pipe, there is no evaporation of liquid, the only consumption is the section of cold spraying water contacted air which is also recycled.
For equipment cost, closed cooling towers are higher than open cooling towers, due to the design complication. But for long term using, the maintenance and clean cost of open cooling towers will be higher.
Comparison Table:
An evaporative condenser is combined by a evaporator and a condenser.
=> Evaporative Condenser = Evaporator + Condenser
Take air conditioning as an example.
Freon is a kind of cooling material whose boiling point is -29.8℃.
In the evaporator, freon fluid affected by the environmental 26~32℃ air, boiled from liquid into gas. The boiling process will absorb heat from the environment, thus cooling down the temperature around. With fans blowing in the air conditioning evaporator, cold wind is delivered into the room.
To recycle and utilize freon, the condenser is used.
Heat dissipation happens in the process of gas condensing into liquid.
But how to make freon condense in a common temperature around 30℃?
The compressor is used for this purpose. By adding pressure to air, the air temperature will rise rapidly. When 0℃ gas freon flows through the compressor, pressure is added, and temperature rises to 80℃.
Affected by the environmental 30℃ wind blowing by fans, the freon is cooled into liquid. But this temperature dissipation(80℃->40℃) is not enough for freon to be recycled.
Then, 40 ℃ high pressure liquid freon flows through the expansion valve. By controlling the quantity of passing liquid, pressure could rapidly decrease. The slower liquid passes the valve, the quicker pressure is released, and thus temperature is cooled down.
Thus, after passing the expansion valve, the 40℃ high pressure liquid freon turns into -30℃ low pressure liquid freon, and back to the evaporator to be recycled.
To explain clearly the differences, we can add a cooling tower into the evaporative condenser system as shown in the graph below.
When adding a cooling tower into the evaporative condenser system, the wind type condenser is changed to a water type condenser. And in this system, the structure of the water condenser just looks like the structure of a closed cooling tower.
But are they the same?
- The answer is No.
The most similar component between an evaporative condenser and a closed cooling tower is the water condenser. If you understand the core difference between them, then you can get through the answer to the topic question of this whole article.
The core difference between an evaporative condenser and a cooling tower is the cooling down method.
In the water condenser, high pressure and high temperature gas turned into low temperature liquid, when the cold water sprayed onto the gas pipes, which is a process called condensation.
But in an open or closed cooling tower, the cooling down target can be high temperature liquid, and no gas-to-liquid process happens in this situation.
To understand more easily, we could cut the evaporator section as below. Because in the industrial sector, an evaporator is not used so frequently as a condenser. Evaporators are mostly used in HVAC(Air conditioning）systems and food processing.
An evaporator is not inherently required for an evaporative condenser to function. Its inclusion depends on the system's design and whether the process involves a full refrigeration cycle or a standalone condensing application.
If the cooling requirement does not involve heat absorption from an external environment (i.e., there's no need to cool a space or substance), the system may omit the evaporator.
For example: Condensation of high-pressure ammonia or CO₂ in certain chemical or petrochemical processes.
In other words, when delivering a gas target into a closed cooling tower, and spraying water onto gas pipes, relying on condensation to cool down the gas target, you can also call the closed cooling tower a condenser equipment.
However, when delivering a liquid target into the cooling tower and no condensation happens, you cannot call the closed cooling tower a condenser.
In conclusion, the differences between an evaporative condenser and a cooling tower can be listed as below:
Firstly, an evaporative condenser system commonly has an evaporator, a condenser, a compressor and an expansion valve. However, a cooling tower does not have any evaporators, compressors and valves, only the structure is similar to a condenser.
Secondly, a cooling tower can use both the gas-to-liquid method and other heat transfer methods(solid cooling materials or liquid cooling materials), but a evaporative condenser must only use evaporation and condensation cooling methods.
Lastly, an open cooling tower can be combined used with an evaporative condenser, as a part of the evaporative condenser, or be combined used with a closed cooling tower, but an evaporative condenser is not so functionally switchable.
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