So when a cross cannot be avoided, you split the exchanger into 2 or more shells and avoid the cross in each shell because the hotter cold fluid never meets the colder shell fluid.

Temperature cross over is a term used to describe the scenario where the temperatures of both circuits in a liquid cooled heat exchanger begin to cross over. This can be an important factor in a heat exchanger design as the efficiency of a cooler will be significantly reduced when the temperatures cross over.

A temperature cross is very difficult to achieve in an exchanger with multiple tube passes, because the value of the LMTD correction factor F would become very low, and therefor it would require much more area just to achieve a little more duty.

High fluid velocity, high turbulence, high surface area and a large temperature differential all contribute to more efficient heat transfer. However, different designs are more efficient than others depending on the application. There are three common kinds of heat exchangers.

It is the smallest difference between the temperatures of the cold and hot streams. For example, if you heat a cold fluid from 80°C up to 100°C using a hot fluid at 105°C, the approach temperature of the heat exchanger is 105-100 = 5°C.

… and temperature cross. If the final temperature of the cold stream is lower than the hot fluid outlet temperature for counter current flow as shown in Fig. 4(a), then it is the temperature approach. Obviously, there can never be temperature cross for co-current flow since it vio- lates second law of thermodynamics.

Generally temperature crosses are best avoided with a single shell S exchanger. That is because the exchanger’s effectiveness drops rapidly as the temperatures cross. However, there are configurations and strategies, including use of multiple shells, that can overcome this problem.

If you have a temperature cross in your simulation you most likely accidentally specified it that way. it happens when you add a specific constraint that is insensible for example, it happens when the temperature of the shell tube outside is chosen to be higher than the temperature of the tube side inlet.

The natural laws of physics always allow the driving energy in a system to flow until equilibrium is reached. Heat leaves the warmer body or the hottest fluid, as long as there is a temperature difference, and will be transferred to the cold medium. Heat will always be transferred from a hot medium to a cold medium.

Below Pinch Note that stream 4 starts at the pinch temperature and so cannot provide any cooling below the pinch. We cannot match stream 1 or 2 with stream 3 at the pinch. Split stream 3 to reduce CP.

What is “Approach Temperature”? This term refers to the temperature difference between the leaving process fluid and the entering service fluid. If air is cooled from 300 F to 100 F using 90 F cooling water, the air temperature approaches the water by 10 F (100 – 90 = 10).

Temperature cross. The terms describe the scenario where the outlet temperature of the cold fluid is higher than the outlet temperature of the hot fluid. The cross temperature point is where the two fluids have the same temperature. In order to get a temperature cross, fluids need to flow in opposite directions.

The internal passes of fluids. In a heat exchanger, the fluid flowing on the tube side can make either one pass or two or more, before reaching the outlet valve. The number of back and forth passes can be up to eight.

Dear Moscos, When the cold fluid outlet temperature goes higher than the hot fluid outlet temperature, a CROSS is supposed to take place in a counter current exchanger. Beyond this point, the temperaure of cold fluid will be higher than the hot one and heat transfer will take place in the opposite direction to that desired.