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Pressure drop through dimple jacket depends on various factors:
To obtain a unique equation or method of calculation of pressure drop is almost impossible as it takes a lot of computational effort, time and cost. The best practice is to use approximation methods based on experimental observations and measurements.
Many manufacturers of vessels and dimple jackets have tried to come up with some sort of approximation curves and/or equations which provides the pressure drop with the highest possible accuracy for practical applications.
Precision Stainless presents a table of pressure drop within the dimple jacket. It reads the flow rate of cooling/heating water per foot of jacket width and provides the pressure drop per length of travel.
Example:
For a tank with 64 inches diameter and 10 feet jacket height, cooling water enters from the bottom connection at flow rate of 200 gpm and exits at the top connection. Since the water travels around the vessel the width of travel would be 10 feet and the length of travel is 16.7 feet ( D x pi /12 = 64 x 3.1416 / 12). From the table pressure drop would be 0.4 psi per foot of travel for 20 gpm per foot of width. The total pressure drop would be 6.7 psi. Don’t forget to consider the static pressure difference at inlet and outlet points (here 4.33 psi).
Other companies have published similar data. Here is what Mueller suggests based on their experiments. This curve works well for cooling / heating water only, while the stainless steel dimple jacket has a depth of 1/4″.
Our experts’ suggestion would be using the following equation which is a bit more conservative that the two proposed data above.
Which f is the flow rate per width and Pd is the pressure drop per foot of travel. The illustrative curve is as following:
The next step is to add the pressure drop due to the connections to the travel pressure drop. Generally, two types of connections are used. Pipe fitting welded directly to the dimple jacket (type 1), and pipe fitting welded to box header. The box header could be rectangular (type 2) or cylindrical (type 3) as shown in the pictures above. Precision Stainless provides a table showing the pressure drop per total flow rate for both types of inlet or outlet connections.
Some more data:
For assistance on this subject please contact our experts at deconeq Engineering Group.