Alfa Laval - How does a plate heat exchanger work

How does a plate heat exchanger work

Heat transfer theory

The law of physics always allows the driving energy in a system to flow until equilibrium. Heat dissipates when there is a temperature difference.
 
A heat exchanger follows the equalisation principle. With a plate heat exchanger, heat cuts through the surface and separates the hot medium from the cold. Thus, heating and cooling fluids and gases use minimal energy levels.
 
The theory of heat transfer between mediums and fluids happens when: 
 
  • Heat is always transferred from a hot medium to a cold medium.
  • There must always be a temperature difference between the mediums.
  • The heat lost from the hot medium is equal to the amount of heat gained by the cold medium. 
 
To solve a thermal problem, let’s use the plate heat exchanger calculation method

About heat exchanger

A heat exchanger is a piece of equipment that transfers heat from one medium to another.

There are two main types of heat exchanger:

  • Direct heat exchange, where both mediums are in direct contact with each other. Eg - A cooling tower where water cools through direct contact with air.
  • Indirect heat exchange though divided media.
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What is a plate heat exchanger

The design of a plate heat exchanger (PHE) comprises several heat transfer plates. Held by a fixed plate and a loose pressure plate to form a complete unit. Each heat transfer plate has a gasket arrangement, providing two separate channel systems.
 
The arrangement of the gaskets allows through flow in single channels. This enables the primary and secondary media in a counter-current flow. The mediums are not mixed because of the gasket design.
 
The corrugated plates create turbulence in the fluids as they flow through the unit. This turbulence gives an effective heat transfer coefficient.
 
Alfa Laval has plate heat exchangers for all industries and applications - catering to heating, cooling, heat recovery, condensation, and evaporation. 

Alfa Laval’s innovative solutions are sustainable. Optimising technology for energy efficiency, emission reduction, and recovery of waste and water.

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How gasketed plate heat exchanger works

Gasketed plate heat exchangers (GPHE) optimises heat transfer. The corrugated plates provide easy heat transfer from one gas or liquid to the other.
 
Plates for a gasketed plate heat exchanger are with elastomeric gaskets. These seal the channels and direct the mediums into alternate channels. The plate pack is between the frame plate and a pressure plate. It’s then compressed with bolts between the plates. The upper carrying bar supports the channel and pressure plate. They are then fixed in a position by a lower guiding bar on the support column. This design is easy to clean and modified (by removing or adding plates).
 
Here are three steps to assemble a gasketed plate heat exchanger:
The heat transfer area of a gasketed plate heat exchanger is from corrugated plates. These are between the frame and pressure plates. The gaskets act as seals between the plates. 
 
Fluids run counter-current through the heat exchanger. This gives the most efficient thermal performance. It also enables a very close temperature approach. For instance, the temperature difference between the entering and exiting service mediums. 
 
For heat-sensitive or viscous media, cold fluid convenes with hot fluid. This minimises the risk of the media from overheating or freezing.
 
Plates are available in various pressing depths, chevron angled pattern, and corrugated shapes. All designed for optimal performance. Depending on the application, each product range has its specific plate features.
 
The distribution area ensures fluids flow to the entire heat transfer surface. This helps to avoid stagnant zones that may cause fouling.
 
High flow turbulence between plates results in higher heat transfer and pressure drop. Alfa Laval thermal designs are customisable. To suit various applications for the greatest thermal performance with the least pressure drop.
 
With the various type of gasketed plate heat exchanger available, there are advantages and disadvantages of choosing a gasketed plate heat exchanger:

Advantages of plate heat exchanger:

  1. Heat transfer precision – improved temperature approach, true counter-current flow, 80-90% less hold-up volume.
  2. Low cost - low capital investment, installation costs, limited maintenance and operating costs.
  3. Greatest reliability - less fouling, stress, wear, and corrosion.
  4. Responsible - least energy consumption for most process effect, reduced cleaning.
  5. Easy to expand capacity – adjustable plates on existing frames.

Disadvantages of plate heat exchangers:

  1. Poor sealing would case leakage occurrence which will be a replacement hassle.
  2. Limited pressure use, generally not more than 1.5MPa.
  3. Limited operating temperature due to temperature resistance of the gasket material.
  4. Small flow path, and not suited for gas-to-gas heat exchange or steam condensation.
  5. High blockage occurrence especially with suspended solids in fluids.
  6. The flow resistance is larger than the shell and tube.
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Maintaining and service for your gasketed plate heat exchanger

Maintaining a gasketed plate heat exchanger is easy.
 

Here are the two most common types of services.

Troubleshooting a plate heat exchanger, if the following occurs: 

  1. A decrease in performance 
  2. Unexplainable deviations from the temperature programme or operation requirements 
  3. External or internal leakages
  4. Disturbances in the process
  5. Need for increased capacity
  6. High energy consumption

Reconditioning of plate heat exchanger:

  1. When high thermal performance is vital to the process.
  2. For 100% reliability to prolong the heat exchanger lifetime.
  3. To restore performance should foul, corrosion or leakage occurs.