A heat exchanger is a heat-transfer device that is used for the transfer of thermal energy b/w two or more fluids (gas or liquid) available at different temperatures. The primary elements of a PHE include the heat transfer plates, gaskets, the supporting end frames (a fixed and a movable cover plate or frame) that house inlet & outlet fluid port nozzle, carrying and guiding bars, the supporting column, and end-frame tightening bolts. This type of heat exchanger has a highly effective heat transfer coefficient many times higher than shell & tube heat exchanger & other conventional type heat exchangers.
Typical applications include pharmaceutical plants, gearbox oil cooling systems, formaldehyde plants, Dairy products, acid cooling systems, air conditioning & refrigeration systems, hydraulic oil cooling low oil cooling marine applications, Pulp and paper industry applications, among others.
These heat exchangers further classified as Gasketed Plate Heat Exchanger, Fully Welded Heat Exchanger, Double Wall Plate Heat Exchanger, Laser Welded Plate Heat Exchanger/ Semi Welded Plate Heat Exchanger, Brazed plate heat exchanger.
Classification of Plate Heat Exchangers as follows:-
Gasketed plate heat exchanger
Gasketed PHE consists of thin, rectangular, pressed corrugated sheet metal plates (0.4 to 0.8mm thickness) that are sandwiched between full peripheral gaskets and clamped together in a frame. The frame has a fixed plate, fitted with the connecting ports, which is bolted together with a movable cover plate to hold the embossed plates in between the top and bottom carrying bars to allow proper alignment of the plates. The peripheral gaskets which are stick with corrugated plates provide the flow channel space between the adjacent plates as well as appropriate flow paths for the hot and cold fluids in alternate channels. It’s easy to maintenance & occupied less area as compared to Shell & tube heat exchanger.
Semi-welded plate heat exchanger/Laser welded plate heat exchanger
In the semi-welded heat exchanger, two heat transfer plates are welded by laser welding to make what is commercially called twin plates or modules, a semi-welded PHE is configured by assembling them in a plate and frame pack with peripheral gaskets only in the plate channels that handle the alternate fluid stream. This design is especially useful for handling relatively corrosive media where gasket heat exchangers are not suitable, which flows in the welded twin plate channels or modules. The only gaskets in contact with this medium are two circular port-hole of the peripheral gaskets between the welded plate pairs that are available in highly resistant elastomer and non-elastomer materials. The semi-welded PHEs can withstand pressures up to 30 bars on the welded twin-plate or b/w welded module fluid side, though it should be pointed out that frames are still needed to hold the plate pack. The relatively higher pressure operation extends its applications to include evaporation and condensation in refrigeration and air-conditioning systems & most commonly used for ammonia fluid.
Fully welded plate heat exchanger
The fully welded PHEs is a gasket-free plate heat exchanger, where a completely welded plate pack is fixed b/w the two end-plates in a conventional frame. By welded the plates at their edges, it’s eliminating the gaskets in PHE. However, In fully welded PHEs, we cannot increase or decrease no. of plate-like in Gasketed PHEs and semi-welded models, for increase or decrease surface area for meeting varying heat load requirements. Also, they cannot be cleaned by mechanical methods, and only chemical cleaning methods can be employed. The fully welded PHEs are specially used for thermal processes with severe duty requirements that often involve the handling of highly aggressive or corrosive fluids. They can withstand temperatures up to 1000◦C and pressures up to 40bar. Typical applications include exchangers for de-superheating in heat recovery systems, refrigeration interchangers, and heaters of organic chemicals such as solvents, vegetable oil, steam, and batch reactors, etc.
Wide-gap plate heat exchanger
In Wide gap PHEs, there is a wide-gap b/w corrugated plate which provides larger free-flow area channels for handling fluids having fibers or coarse particles and for high-viscous fluids which normally clog or chocked & cannot be satisfactorily treated in other types of PHEs. The flow cross-section has a maximum gap of up to 16 mm. typical applications of wide gap PHEs include heating of raw, limed and mixed juice in sugar mills, cooling and bleaching of plant filtrate in pulp and paper mills, and sanitization of fibrous food product slurries.
Double-wall plate heat exchangers
The double plates are constructed by laser welding two plates around the ports. The double-wall PHEs is used with either a reacting media or when product contamination between the two fluid streams must be avoided for leakage or fail-safe. In the event of the fluid, reacting with and corroding the surface of the double-wall plates, the leakage is directed in the passages between the double plates. This essentially minimizes the possibility of intermixing and the leakage also becomes easily visible on the outside of the heat exchanger. Double-wall PHEs are the compact solutions to conventionally used double wall shell & tube and double coils.
Brazed plate heat exchanger
The brazed plate heat exchanger BPHEs is essentially made up of a pack of thin corrugated plates that are brazed welded together by copper as a brazing material to form a single PHE. Brazing eliminates the need for either fixed or moving frames or gaskets; it results in a very compact PHE. Typical applications include heating and cooling (sensible or with phase change) in the process industries, evaporation and condensation in refrigeration systems, and other HVAC installations.