What is a Cross Flow Heat Exchanger?
A cross flow heat exchanger is a heat exchanger which transfers heat from one fluid to another fluid in the AHU (Air Handling Unit). The cross-flow exchanger has a vertical flow direction.
Unlike a rotary heat exchanger, a cross flow heat exchanger doesn’t transfer moisture. These heat exchangers also don’t have the risk of airstream’s short-circuiting.
The cross-flow heat exchangers are used in ventilation and cooling systems where heat needs to be shifted from one airflow to another. These heat exchangers usually consist of a thin metal panel made of aluminum. These panels are used to exchange thermal energy or heat.
The conventional cross-flow heat exchangers have square cross-sections. The thermal efficiency of the conventional cross-flow heat exchanger is from 40% to 65%. If you need higher thermal efficiency (i.e., up to 75% to 85%), you may use a dual crossflow or counterflow heat exchanger.
A shell-and-tube heat exchanger is an example of a cross-flow exchanger. In his exchanger, one fluid move inside the tubes, and the other moves around the tube in the shell side. The fluid around the tube flows at a 90o angle compared to the fluid flow inside the tube.
These types of heat exchangers are most commonly employed in two-phase systems. Another example of this exchanger is a condenser used for a steam system. In this exchanger, steam flows through a tube in the shell side and converts into the liquid phase. During this process, the heat exchanger condenses a large amount of steam.
The shell and tube heat exchangers are available for all directions of the flows, such as the cross flow, counterflow, and parallel flow. The below-given diagram represents different flow directions in the shell and tube exchangers.
The plate-fin heat exchanger is another example of cross-flow. The plate-fin exchanger has multiple fins placed between parallel plates, and the fluid flows by these fins. These fins increase the area of the heat transfer and increase the heat transfer rate. The fins have different designs like perforated, wavy, triangular, or rectangular.
Types of Cross Flow Heat Exchangers
The cross flow heat exchangers are used all over the world. These heat exchangers are divided according to the fins in the system. The cross flow heat exchanger has the following two major types:
- Unmixed flow heat exchanger
- Mixed flow heat exchanger
1) Mixed Flow Heat Exchangers
The mixed cross flow heat exchanger is also known as an unfinned heat exchanger because it has no fins (as shown in the below diagram).
In this heat exchanger, the fluid flows perpendicularly to the tubes and flows over the tubes in the shell side. In this type, the turbulence flow of the fluid can occur. This turbulence flow helps to increase the coefficient of the heat transfer. It has a lower pressure drop than types of crossflow heat exchangers.
Read Also: Working of Plate Heat Exchanger
2) Unmixed cross-flow heat exchanger
The unmixed flow heat exchanger is also known as a finned heat exchanger because it has fins installed around the tubes to allow liquid to flow over the tubes. These fins help to increase the heat transfer rate as they increase the effective heat transfer surface area.
However, these exchangers have a high-pressure loss in the system. In addition, these exchangers have high costs and weight due to the addition of fins.
Cross Flow Performance and Heat Transfer Rate
Logarithm Mean Temperature Difference (LMTD) uses to calculate the performance of the heat exchanger. You can increase LMTD to achieve higher performance. The heat transfer rate of the cross flow heat exchanger can be calculated by the below-given formula:
This formula is the same as the heat transfer rate for counter flow and parallel heat exchangers.
Design of Crossflow Heat Exchanger
The construction of the cross-flow heat exchanger allows the two fluids to move perpendicularly to each other. According to Bright Hub Engineering, this exchanger generally uses when one fluid is a gas while the other is a liquid.
For example, in a car radiator, upward and downward moving air cools the hot liquid that flows from side to side. This heat exchanger is also very ordinary in steam condensers, where liquids convert to gases at the end of the process.
Read Also: Type of shell & tube heat exchanger
Advantages and Disadvantages of Cross Flow Heat Exchangers
In a cross-flow heat exchanger, cold fluid and hot fluid flow vertically relative to one another. This is usually a convenient method to actually install the outlet and inlet ports in a small package. It is one of the most efficient designs than parallel heat exchangers.
According to the thermodynamic point of view, the cross-flow heat exchangers have more efficiency than the efficiencies of the counter-flow heat exchangers and parallel heat exchangers.
The crossflow exchangers have higher LMTD than parallel-flow heat exchangers. The cross flow exchangers require less flow area than the parallel flow exchangers for a given flow rate and inlet and outlet temperatures.
Due to these reasons, parallel flow heat exchangers are not widely employed in applications, and cross flow exchangers are ideal. Therefore, these heat exchangers are the most commonly used exchangers as it is easier to supply outlet and inlet header connections in cross-flow.
These heat exchangers have a compact design. The multi-pass cross-flow heat exchanger has easy manufacturing than counter-flow and parallel heat exchangers.
Difference between Parallel flow, Counter flow and Cross flow Heat Exchanger
|Crossflow Heat Exchanger||Counter flow Heat Exchanger||Parallel flow Heat Exchanger|
|In the cross-flow heat exchangers, the two fluids flow perpendicular to each other.||In the counter-flow heat exchanger, The tube-side fluid enters the exchanger at the opposite end of the shell-side fluid.||In the parallel flow heat exchanger, fluids flow parallel to each other.|
|It requires less flow area.||It requires a large flow area.||It also requires a large flow area.|
|These exchangers have more efficiency than parallel and counter flow exchangers.||The counter flow heat exchanger is most efficient than the crossflow and parallel flow heat exchangers.||The parallel-flow heat exchanger is more efficient than the crossflow exchanger but less efficient than the counterflow exchanger.|
Applications of Cross flow Heat Exchanger
- The crossflow heat exchangers are used in refrigerators
- They also use in the cooling industries.
- They use for automobile radiators.
- This heat exchanger uses for a condenser in the steam system.
What are the parts of the cross-flow heat exchanger?
The cross-flow heat exchanger has the following major parts:
- Tightening units
- Pressure plate
- Support column
What are cross flow heat exchangers used for?
The cross-flow heat exchangers are used to transfer thermal energy from one fluid to another. It is most commonly employed in automobile radiators and refrigerators.
What are the examples of the heat exchanger?
The most common examples of heat exchangers are HVAC, condensers, superheaters, evaporators, economizers, air preheaters, and cooling towers employed in the power plants.
What are the most common types of heat exchangers?
The heat exchangers have the following major and common types:
- Shell and tube heat exchanger
- Plate heat exchanger
- Cross flow heat exchanger
2 thoughts on “Cross Flow Heat Exchanger | Working of Cross-Flow Heat Exchanger”
thanks and great article.
you mentioned in your comparison table that the cross flow is more efficient than the counter flow heat exchanger. that make me feel little confused.
all what we learned was the opposite.
counter flow is the highest efficient
then parallel flow
lastly the cross flow
can you please elaborate more with engineering examples and numbers to show the efficiency comparison.
Thanks for your informative suggestion