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Alaqua 7004 Boulevard East, Suite 28A,Guttenberg, NJ USA 07093    +(00-1) 551 482 7568   
Alaqua 7004 Boulevard East, Suite 28A,Guttenberg, NJ USA 07093    +(00-1) 551 482 7568   

What is the Working Principle of Evaporators?

What is the Working Principle of Evaporators?

Date:16 December, 2022   |   No Comments   |   Posted By Team Alaquainc

Evaporation is the process by which an element or compound changes from its liquid to a gaseous state below the boiling point. In most cases, it is critical that the product undergoes minimal thermal degradation. This necessitates minimizing temperature and time exposure. Along with other requirements imposed by the physical properties of the processed product,  this has resulted in the development of a diverse range of evaporator types. By all means, evaporation plants are widely used in the field of thermal concentration technology for the concentration of liquids in the form of solutions, suspensions, and emulsions.

Established in 1989, we at ALAQUA have more than 25 years of experience. We are leading manufacturers, offering a supply of evaporators, distillation plants, crystallizers, solvent recovery systems, and other process equipment. 

Types of Evaporators:

1. Falling Film Evaporators

In falling film evaporators, liquid and vapors flow downward in parallel flow. The preheated concentrated liquid reaches boiling temperature. It enters the heating tubes through a distribution device in the evaporator’s head, flows downward at boiling temperature, and undergoes partial evaporation. The co-current vapor flow augments the gravitationally-induced downward movement. Falling film evaporators can operate with very small temperature differences between the heating media and the boiling liquid. They have very short product contact times, typically only a few seconds per pass. The falling film evaporator’s properties render it ideal for heat-sensitive products, making it the most commonly employed evaporator type.

However, falling film evaporators must be carefully designed for each operating condition. Adequate wetting of the heating surface by liquid is critical for the plant’s trouble-free operation. Dry patches and incrustations will form if the heating surfaces are not sufficiently wetted; at worst, the heating tubes will become completely clogged. In critical cases, extending or dividing evaporator effects while maintaining the benefits of single-pass operation can increase the wetting rate. To achieve full and even product wetting of the tubes, the liquid distribution system must be properly designed.

2. Rising Film Evaporators

These work on the basis of the “thermo-siphon” principle. As the feed enters the bottom of the heating tubes, steam begins to form. Because of the ascending force of the steam produced during boiling, liquid and vapors flow upwards in parallel flow. At the same time, the product presses as a thin film on the walls of the tubes while increasing vapor production. As a result, the liquid rises upwards. This co-current upward movement has the advantageous effect of increasing turbulence in the liquid. This is beneficial when evaporating highly viscous products or products that tend to foul the heating surfaces.

Typically, the temperature difference between the heating and boiling sides of this type of evaporator must be quite large. Otherwise, the vapor flow’s energy is insufficient to convey the liquid and produce the rising film. Typically, the length of the boiling tubes will not exceed 23 feet. Product recirculation often accompanies the use of this evaporator type, wherein the feed inlet reintroduces some of the formed concentrates. This is to produce sufficient liquid loading inside the boiling tubes.

3. Forced Circulation Evaporator 

To prevent the product from boiling on the heating surfaces due to its fouling characteristics, we employ forced circulation evaporators. The heat exchanger heats the circulating liquid, which is then partially evaporated by reducing the pressure in the separator. This reduction in pressure allows the liquid to cool to the boiling temperature corresponding to the current pressure. Since the liquid undergoes only a slight temperature increase with each pass through the heat exchanger, maintaining a high recirculation flow rate is necessary.

This evaporator is suitable for crystallizing applications because it does not experience evaporation and, consequently, does not see a concentration increase on the heat transfer surface. In separator vessels, the liquid undergoes flash evaporation, resulting in the formation of crystals in crystallizer applications. Special separator designs are employed to separate crystals from the recirculated crystal slurry. The arrangement of the heat exchanger, whether horizontal or vertical, depends on specific requirements.

4. Plate Evaporators 

Plate evaporators are small in size. Short interconnecting pipework connects the separators to the plate packages. Minimal space requirements result in typically limiting heights to 20 to 25 feet (6-8 meters). As a result, plate evaporators can be installed in the majority of buildings. You can use framed plates as a heating surface instead of relying on tube and shell heat exchangers. These plate assemblies are similar to plate heat exchangers but have larger vapor flow passages. These units alternate the connection between a product plate and a steam plate.

The design of the product passage ensures even distribution of liquid on the plate surfaces and minimizes pressure drop in the vapor phase. The easy-to-open plate package allows for surface inspection, changing of individual plates as needed, and adjustment of the evaporation rate by adding or removing plates. The units can be customized to meet USDA Dairy sanitation standards.

Difference between an Evaporator and Condenserevaporators


The working mechanisms of evaporators and condensers differ. Despite the fact that evaporators and condensers are both heat exchange equipment, the evaporator absorbs heat while the condenser releases heat. Having said that, they are both necessary components of the refrigeration system.

Condensers’ working mechanism is an exothermic process, so you can expect them to be hot while they’re working. Power plants are excellent examples of industrial condensers. The condensers in power plants condense the vapors from the turbines.

Problems of Working with Evaporators

Realize that evaporation can lead to technical issues, particularly when applying it in the food industry. Some evaporators are sensitive to differences in dilute solution viscosity and consistency. Because of a loss of circulation, these evaporators may work inefficiently. If you intend to use an evaporator for concentrating a highly viscous solution, you may need to replace the pump. When hard deposits form on the surfaces of the heating mediums in the evaporators, fouling occurs. Proteins and polysaccharides in foods can form such deposits, reducing heat transfer efficiency.

Foaming can also be a problem because dealing with excess foam can be time-consuming and inefficient. Use antifoam agents during food processing, but limit their application to a few. Concentrated acidic solutions can cause corrosion. Surface damage can reduce the long life of evaporators. Food quality and flavor can suffer as a result of evaporation. Overall, when selecting an evaporator, the qualities of the product solution must be carefully considered.

Let’s Sum Up:

The main requirement in the field of evaporation technology is to keep the liquid’s quality while evaporating and to avoid product damage. This may necessitate exposing the liquid to the lowest possible boiling temperature for the shortest amount of time. This, along with numerous other requirements and constraints, has resulted in a wide range of designs available today. For many years, ALAQUA has been successfully supplying a wide range of evaporators to various industries. We train your employees and assist you in finding the most cost-effective solutions to increase your efficiency and profits.


  • Do you supply Internationally?

Yes, we serve a domestic and international base of customers. We also supervise installation and start-up with personnel training for every application. We respond to any troubleshooting calls 24/7.

  • How do you prevent corrosion and scaling?

Corrosion and scaling are recurring issues for evaporator operators. They begin by reducing capacity and increasing energy consumption, but can quickly lead to significant downtime and maintenance. We offer smart engineering to avoid extensive chemical softening of feed, which increases operating costs.

  • Types of evaporators you manufacture and supply?

Falling Film Evaporators, LTV Evaporators, Forced Circulation Evaporators, Plate Evaporators, etc. for more information, please contact us.

  • What is the difference between a rising and falling film evaporator?

Tubes in a typical rising film evaporator carry the liquid upward as the vertically mounted heat exchanger facilitates boiling of the water in the evaporator liquid. This boiling action helps the liquid move up and out of the tubes. In both a falling film evaporator and a rising film evaporator, we use a vertically mounted heat exchanger. In this case, the evaporator pumps the liquid to the top of the heat exchanger and directs its flow downward through the tubes. Water boils in the evaporator liquid as it flows down the tubes, helping to force the liquid down and out.

  • Do you provide personnel training?

We will actively train the personnel designated by the Customer in proper operating and maintenance procedures during commissioning and start-up. The training will pay a per diem fee and reimburse travel and living expenses at cost. To facilitate training, as well as ongoing operation and maintenance of the equipment module, we will supply an Operations and Maintenance Manual. Full specs and details on auxiliaries (pumps, motors, instrumentation) and drawings (Process Flow, Piping, Instrumentation, General Arrangement) are provided.

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