Second hand stainless steel reboiler

Condensation is mainly divided into two types, one is called film condensation, and the other is called droplet condensation.

The condensate can form a continuous liquid film on the wall, and condensation only occurs at the interface between the liquid film and the vapor. The enthalpy of vaporization released by condensation must pass through this liquid film in order to be transmitted to the cooling wall. This type of condensation is called film condensation.

The vast majority of condensation belongs to film condensation, where the liquid film layer becomes the main heat transfer resistance. The higher the heat transfer coefficient of the liquid film or the thinner the thickness of the liquid film, the more heat is transferred. Therefore, when designing a condenser, in order to improve the condensation heat transfer coefficient, it is necessary to consider how to avoid the continuous thickening of the condensation film and how to reduce the thickness of the condensation film. For example, a condenser is usually used because the condensate continuously drips down from the tube in the shell side, so that the liquid film layer does not continuously thicken with the amount of condensation.

2. Droplet condensation

The condensate cannot form well on the wall, forming small droplets on the wall that continue to grow and enlarge. After the droplets become larger, they will continuously carry other droplets along the way down the wall due to gravity, causing the wall to repeat the formation and growth of droplets. The latent heat of vaporization released by condensation can be directly transferred to the wall, and this condensation is called droplet condensation.

The heat transfer rate of dropwise condensation is higher than that of film condensation, which can reach several times or even more than ten times that of film condensation. The reason is that the vapor is directly connected to the tube wall, and there is no liquid film with a much smaller heat transfer coefficient than the tube wall in between. At the same time, the driving force for heat transfer is the temperature difference between the vapor and the tube wall, which is larger than the temperature difference between the gas-liquid interface and the tube wall during film condensation. Although droplet condensation has a good heat transfer effect, it is difficult to operate and requires a special material for the condensation surface, so its industrial application is still limited.

A condenser is a device that condenses steam into heat, in which the steam transfers heat to the coolant. Various condensers are often used in the petrochemical industry, among which they are widely used in the condensation of two-phase flow heat transfer, such as the condensation of gas distillate at the top of the distillation tower, the condensation of water vapor, and the condensation of refrigerant vapor. The main equipment involved in condensation includes shell and tube condensers, air coolers, plate condensers, and spiral plate condensers.

Steam condensation can also be used to heat or evaporate coolant, so it can be called a condenser, evaporator, reboiler, or heater depending on the different purposes of heat exchange. This chapter mainly introduces the shell and tube condenser, with the floating head condenser structure shown in the following figure.