In general, heat exchangers are the devices used to exchange heat between the same or different forms of matter through conduction, convection, or radiation. Industrially, the term ‘heat exchangers’ is used for devices that assist in exchanging heat between two fluids at different temperatures without physically mixing them.
For example, room or water heaters are used to heat the ambient air or water by exchanging heat between the heating element and the surrounding air or water respectively. Also, refrigerators or air conditioners have heat exchangers to exchange the heat and cool the surrounding medium. Likewise, they have diverse applications in a wide range of fields such as the automobile industry, food, and beverage industry, nuclear power production, etc.
Types Of Heat Exchangers
There are several types of heat exchangers that are used in industries and could be mainly classified based on their design as:
Shell and Tube heat exchangers
Shell and tube heat exchangers are the most commonly discussed heat exchangers. They consist of a shell and a tube where fluids at two different temperatures are circulated parallel (co-current), perpendicular (crossflow), or anti-parallel (counter-current) to each other. A typical double pipe heat exchanger consists of only one tube inside a shell. A tube can have multiple passes before exiting a shell depending on the requisite amount of heat load to be transferred.
Plate heat exchangers
These heat exchangers consist of several metal plates that are arranged together (brazed or connected by gaskets) such that hot and cold fluids pass through alternate plates. They are more compact in size than tube heat exchangers for the same amount of heat transferred between two fluids but suffer from the drawback of having limited utility at high pressures or temperatures. Usually, the maximum pressure and temperatures that can be used are 3MPa and 260°C, respectively. (Shah, 1994)
Plate-fin/ Tube-fin heat exchangers
The exchangers are similar to the ones mentioned above except that the plates/tubes have fins attached to them. The fins provide extended surface area for the heat transfer and enhance further the quantity of heat transferred. The construction cost of these exchangers is higher than the exchangers discussed earlier.
Maintenance in heat exchangers
Fouling is the modification of the surface of plates/tubes over time due to several factors Fouling in heat exchangers is a major factor that reduces the performance of heat exchangers in due course by reducing the overall heat transfer coefficient. Fouling is the modification of the surface of plates/tubes over time due to several factors.
For example, corrosion, magnesium/calcium deposits, or biological factors such as algae settlements. Mechanical cleaning, treatment of inlet water, or circulating cleaning fluids are some of the methods used for the maintenance of heat exchangers. Some design materials such as stainless steel or titanium are more resistant to corrosion while copper alloys reduce biological fouling, thereby having higher performance.
Market Share/Demand
Technological advancement, increasing awareness of energy optimization techniques and emerging markets around the world. India and China, for instance, are greatly boosting the demand for heat exchangers.
According to the research conducted by P&S market research (P & S market research, 2016), the market size of heat exchangers was valued at 14.1 billion dollars in 2014 and is estimated to grow with a CAGR of 6.5 % during the period of 2015-2020 with the chemical industry expecting the highest growth at CAGR of 9.2% and Europe is the biggest market for heat exchangers.