Heat Exchanger – An Introduction
Published on : Thursday 01-06-2023
What is a heat exchanger? This article explains the concept and the types.
A heat exchanger is a device that facilitates the process of heat exchange between two fluids that are at different temperatures. Heat exchangers are used in many engineering applications, such as refrigeration, heating and air conditioning, power plants, chemical processing, food processing, automobile radiators, and waste heat recovery units. There are many instances where the use of a heat exchanger is deemed practical. For instance, high-temperature exhaust gasses from power plants and engines contain a large amount of heat which can be recovered by installing a heat exchanger before the smokestack.
Gasketed plate heat exchangers
Gasketed plate heat exchangers are efficient heat exchanger devices formed by a series of corrugated thin metal sheets and gaskets. The hot and cold fluids between the plates are separated by sealing gaskets so that they flow independently in the flow channels on both sides.
The heat transfer coefficient of gasketed plate heat exchangers is 3-5 times higher than that of the shell and tube heat exchanger because the hot and cold fluids can reach a high degree of turbulence when they flow in the plate channels which have certain corrugated shapes on the plate surface.
Gasketed heat exchangers can be fully customised to meet your exact requirements. Depending on the application media you can choose between traditional, semi-welded, free flow, sanitary plate heat exchangers as well as evaporators and condensers.
How gasketed plate heat exchanger work
In a gasketed plate heat exchanger, the plates are fitted with elastomeric gaskets which seal the channels and direct the fluids into alternate channels. The plate pack is assembled between a frame plate and a pressure plate, and compressed by tightening bolts fitted between these plates. The channel plates and the pressure plate are suspended from an upper carrying bar and located by a lower guiding bar, both of which are fixed to the support column. The physical design of the gasketed plate heat exchanger allows easy cleaning and modification of capacity by the addition or removal of plates.
Advantages of gasketed plate heat exchanger
1. High heat transfer rate
2. Less heat loss
3. Compact structure, space-saving
4. Easy to change heat transfer area
5. Easy to clean and repair
6. Wide range of application, and
7. Long service time
Welded heat exchangers
A welded plate exchanger is similar to a gasketed plate and frame heat exchanger except Welded seams replace the gasketed seals allowing this exchanger to be applied in applications of high temperatures and pressures. Built from 316 Stainless Steel, welded plate heat exchangers provide exceptional corrosion resistance. Corrugated plates produce highly turbulent flow in a true counter-current direction. This results in high efficiency and a very compact heat exchanger design. Due to the smaller size and reduced material content, they can be the most economical heat transfer choice in applications where gaskets are not acceptable.
How welded heat exchangers work
A welded plate heat exchanger is a type of heat exchanger that uses welded plates to transfer heat between two fluids. Welded plate heat exchanger consists of a series of thin metal plates, which are welded together to form a series of channels or passages. The plates are designed to create a large surface area for heat transfer and are typically made of materials that have high thermal conductivity, such as stainless steel or titanium.
The two fluids that need to be heated or cooled flow through the different passages of the heat exchanger, with each fluid flowing through alternate passages. As the fluids flow past each other, heat is transferred between them through the thin metal plates.The lack of gaskets or seals also means that welded plate heat exchangers are less prone to leakage and require less maintenance.
Welded plate heat exchangers are commonly used in applications where high pressures or temperatures are involved, such as in chemical processing, oil and gas production, and power generation. They are also well-suited for applications where the fluids being transferred are corrosive or have a high fouling potential, as the smooth surface of the welded plates makes them less prone to fouling compared to other heat exchanger designs.
Advantages of welded heat exchanger
1. High temperature and pressure resistance
2. Low investment costs through heat transfer with maximum efficiency
3. Corrosion resistance
4. Low maintenance
5. Compact structure
6. Reliable, and
7. Fully welded without gasket.
Brazed heat exchangers
A brazed plate heat exchanger consists of corrugated plates that combine to create channels through which a hot medium and a cold medium can be distributed.
Brazed plate heat exchanger can be used for a range of functions in a heating or cooling system. Brazed plate heat exchangers are widely used in many different industries and often in large-scale residential heat networks. They play an important role in delivering air conditioning process and production, refrigeration, data center cooling and residential heating.
How brazed heat exchangers work
The brazed plate heat exchanger is in principle constructed as a package of corrugated channel plates between front and rear cover-plate packages. The cover-plate packages consist of sealing plates, blind rings and cover plates. Connections are mounted on the cover plates and can be customised to meet specific market and application requirements. During the vacuum-brazing process, a brazed joint is formed at every contact point between the base and the filler material. This design creates a heat exchanger that consists of two separate channels or circuits.
Advantages of brazed heat exchanger
1. Low operational cost
2. Double-walled design that provides the ultimate protection against leaks
3. Tried-and-true fishbone technology
4. Resistance to changes in pressure and temperature, and
5. Small hold-up volume and high performance.
Common heat exchanger applications
At home
Around the home, they’re commonly found in central heating combi boilers and help to heat and cool down the water efficiently and safely. They’re also found in your refrigerator, ensuring it stays at a stable, cool temperature.
Public spaces
Car engines produce a lot of heat and this needs to be managed effectively to prevent dangers. Cars often use a combination of fans and air flow, with fins to dissipate heat, and the use of a coolant fluid.
Industrial
Heat exchangers are also used widely in different industrial applications. This includes power generation, the manufacture and storage of food, chemical engineering, and even in the running of air and marine transport
Defence
Even in the defence sector, we find heat exchangers. They are installed, for example, on the navy surface and auxiliary ships as well as on submarines. They cool nuclear submarine propulsion motors.
Durga Mechatronics Pvt Ltd, Mumbai.
www.durgamechatronics.com