Transported by centrifugal pump

The pressure of the medium at the inlet of the centrifugal pump can be increased, for example by raising the operating pressure of the equipment at the pump inlet or increasing the installation height of such equipment; if conditions permit, cooling systems can also be used to lower the temperature of the medium at the pump inlet.

At high temperatures, gas is easily generated, which can lead to cavitation in the pump. The main reason is that negative pressure occurs at the pump’s inlet; when the pressure is low, the boiling point drops, making vaporization more likely. The solution is to find a way to prevent negative pressure from occurring at the pump’s inlet, or to ensure that the liquid does not vaporize under such negative pressure. Increase the pressure at the pump inlet, or lower the temperature.

The expert has learned some more knowledge: lol

If it is at the design stage, there are several solutions: 1. Raise the installation elevation of the inlet equipment ； 2. Increase the operating liquid level of the inlet equipment, of course, under permissible conditions. 3. Reduce the pressure drop loss at the pump inlet, for example by increasing the inlet pipe diameter or shortening the length of the inlet pipe ； 4. Maintain the temperature of the pumped liquid, for example, by increasing the capacity of the heat exchanger in the upstream section, 5. Modify the pump design, such as selecting a suitable pump (one with low NPSH requirements) or lowering the pump’s installation height.

The installation height of the equipment can be increased, or an exhaust pipeline can be installed on the pump inlet line; however, this pipeline can only be used for venting before the pump is put into operation. It is recommended that the user opt for a positive-displacement pump, such as a vane pump, as this will basically solve the problem

Increase the pressure or raise the installation height.

The principle is as explained on the 3rd floor. Once you know the cause, it’s easy to think of targeted solutions. Many netizens have already proposed solutions; another option to consider is increasing the diameter of the inlet pipe.

Strictly speaking, whether a centrifugal pump experiences cavitation is not only related to whether the fluid is at a high temperature; what plays a decisive role is the effective NPSH at the pump inlet. Raising the equipment installation height at the pump inlet merely due to the high inlet temperature may incur unnecessary engineering costs. For example, when the medium is residue at 200 degrees, since the medium is generally in a subcooled state, the installation height of the equipment at the pump inlet does not need to be very high ； The medium is LPG at room temperature; generally, the medium is in a saturated state, which requires the installation height of the equipment at the pump inlet to be relatively high. The selection of high-temperature pumps is also important; attention should be paid to the net positive suction head, material, sealing, etc. Stress analysis should be conducted for the layout of the pump inlet and outlet pipes.

I’m not quite sure about one thing: is there any connection between the installation height of the equipment and cavitation?

If the equipment is installed at a high height (relative to the pump), the resulting static head is sufficient to effectively prevent cavitation

1. Negative pressure at the inlet. 2. The temperature of the medium being transported is high. 3. High outlet pressure. 4. The requirement exceeds the head capacity of the transfer pump. Once the cause is identified, the problem can be solved:victory: :victory:

If the temperature is not too high and it is not a toxic liquid, the problem can be resolved by venting

This issue can be easily found in the chemical machinery sector. The main issue is cavitation; below are its causes and manifestations: When a centrifugal pump is in operation, the liquid pressure decreases from the pump inlet to the inlet of the impeller, with the liquid pressure pK being at its lowest at a certain point near the inlet of the blades. Thereafter, as the impeller does work on the liquid, the liquid pressure rises rapidly. When the pressure pK near the inlet of the impeller blades is less than the saturated vapor pressure pv at the liquid transport temperature, the liquid vaporizes. At the same time, it allows the gases dissolved in the liquid to escape. They form many bubbles. When the bubble moves with the liquid to a region of higher pressure within the flow channel, the external liquid pressure is greater than the vaporization pressure inside the bubble; as a result, the bubble re-condenses and collapses, forming a cavity. Instantly, the surrounding liquid rushes toward this cavity at extremely high speeds, causing the liquids to collide with each other and leading to a sudden increase in local pressure (which can reach several hundred atmospheres). In this way, it not only hinders the normal flow of the liquid; more seriously, if these bubbles burst near the wall of the impeller, the liquid acts like countless small projectiles, continuously striking the metal surface. Its impact frequency is very high (reaching 2000–3000 Hz in some cases), causing the metal surface to crack due to impact fatigue. If the bubbles contain some active gas (such as oxygen), they utilize the heat released during bubble condensation (with local temperatures reaching 200–300°C) to form thermocouples, thereby inducing electrolysis and electrochemical corrosion, which further accelerates the rate of metal degradation. The combined phenomenon of vaporization, condensation, impact of such liquids, resulting in high pressure, high temperature, and high-frequency impact loads that cause mechanical cracking and electrochemical corrosion damage to metal materials is known as cavitation. The term “saturated vapor pressure at the liquid transfer temperature” mentioned here is the key to the aforementioned issue. Whether it is necessary to raise the installation height of the pump inlet equipment depends on the saturated vapor pressure of the medium at that temperature and the pump’s own net positive suction head.

Hehe, isn’t this that Bernoulli equation from chemical engineering principles? You need to review Chemical Engineering Principles, OP!