Plate heat exchangers are devices designed to perform a variety of thermal operations, such as heating and cooling. They can withstand very high temperatures and pressures, and consist of several separate stainless steel chambers. The principle of the exchanger is to transfer heat between two fluids located in the chambers. Inside these chambers, the hot and cold liquids can circulate without touching. Plate heat exchangers are found in stratified storage heaters. It’s a flexible, expandable device that adapts to every need. Find out exactly what a plate heat exchanger is, the different models on the market and how they work.
What is a plate heat exchanger?
A plate heat exchanger is an element that heats and cools liquids and gases at low energy levels. Its function is to separate cold and hot fluids by passing heat across its surface. This heat exchange is based on specific laws. A temperature difference is required between these two fluid bodies. In fact, the heat exchanger’s driving energy is created by the temperature difference. Similarly, the function of this device is always to transfer heat from a hot body to a cold one, and not vice versa. The equalization principle is respected with the plate heat exchanger. Seven fundamental parameters need to be taken into account in order to solve a thermal problem with this type of device. To do this, we need to know :
- Heat capacity or quantity of heat to be transferred;
- Fluid types;
- Inlet and outlet temperatures on both sides (primary and secondary);
- Maximum operating pressure;
- Maximum acceptable pressure drop on both primary and secondary sides;
- Flow rate;
What are the different types of heat exchanger?
Different types of heat exchanger exist. These thermal devices are designed to respond optimally to a number of specific process conditions and applications. The best-known plate heat exchangers are as follows:
● Brazed plate heat exchanger ;
● Gasketed plate heat exchanger;
● Gas-liquid plate heat exchanger;
● Fused plate heat exchanger;
● Spiral heat exchanger ;
● Printed circuit heat exchanger ;
● Welded plate and shell heat exchanger;
● Semi-welded plate heat exchanger and frame ;
● Welded plate heat exchanger and block.
Heat exchangers by fluid type
Depending on the fluids to be transferred, different heat exchangers are used. These include
● Water-gas heat exchangers: shell-and-tube evaporator, double-tube heat exchanger, shell-and-tube condenser, shell-and-tube heat exchanger, shell-and-tube heat exchanger ;
● Air-water heat exchangers: air heater, air-cooled liquid coolers, air-cooled condenser, air cooler/cooler, air-cooled gas cooler ;
● Water-oil heat exchanger: brazed heat exchanger.
● Water-to-water heat exchanger: brazed heat exchanger, plate and gasket heat exchanger ;
Plate heat exchanger operating mode
Made up of several thin, closely-spaced plates in fluted (herringbone) or ribbed shapes, exchangers can be manufactured from stainless steel, aluminum or synthetic materials. The plates may be welded together, or compressed inside a frame and sealed against each other. To operate, the heat exchanger has channels between each plate, whose role is to circulate the two fluids in parallel, but also in opposite or crossed directions. This function enables it to cool a hot liquid and heat a cold one. One of the fluids flows through the odd-numbered ducts, the other through the even-numbered ducts. The heat transfer zone covers the entire surface of the plates (heat energy transfer). Conductivity is improved and heat exchange simplified, thanks to the creation of a turbulence zone in the channel or chevron plate heat exchanger. The unit’s mode of operation is simple and is based on well-known physical principles:
● Convection ;
● Conduction ;
● Radiation.
Primary and secondary fluids pass through the channels in the same direction, with plate heat exchangers that have a parallel flow. This is anti-method or co-current circulation. This type of device has an inlet on the same side for both fluids. For heat exchangers with methodical or counter-current flow, these two fluids have the same inlet.
Heat exchangers with methodical or countercurrent circulation also have parallel flow, although the fluids flow in opposite directions. To optimize the heat exchanger’s performance, the most efficient configuration is co-current circulation.
How do I clean plate heat exchangers?
Various techniques can be used to clean plate heat exchangers. These include:
● mechanical cleaning under pressure or using a brush. For this type of cleaning, which involves dismantling the plates, the bolts (loosening), tie rods and frame must be carefully removed. The user must then clean the exchanger or, if necessary, carefully replace each plate.
● chemical cleaning with 10% sulfuric acid. For cleaning without disassembly, simply leave the product to act for 60 minutes before rinsing the unit thoroughly with clean water;