The Basics of Heat Exchangers

Heat exchangers are a staple in today's devices. They are not only present in the simplest of devices; they have also found their use in big industries and machineries in the world today. They are basically devices found in some machines that enable it to transfer heat from one medium to another. They facilitate the efficient transfer of heat from one object to another.

Use of Heat ExchangersOne example of this is the radiators found in cars or air conditioners. What usually happens is that a heat source transfers water that will cool the engine through the steam heat exchanger design. The exchanger will transfer heat from the water to air leaving the engine cooler.

They are widely used for the purposes of space heating air conditioning and even refrigeration. Heavy industries that also use this technology include power plants, chemical and petrochemical plants, oil and petroleum refineries, natural gas processors and sewage treatment facilities.

Types of Heat Exchange FlowThey can be classified into two types, mainly according to their flow arrangements. These are the parallel-flow and the counter-flow steam heat exchanger.

The parallel-flow exchange involves the two mediums going in the exchanger through the same side of the device. For example, two fluids will enter the exchanger at the same side and travel parallel each other for the whole process.

The counterflow exchange, on the other hand, is the opposite of the first process. Here, fluids will enter the device from different ends and meet each other for the process of heat exchange. Many of these use this flow since it has been proven to be the more effective of the two processes because it can transfer more heat from the heating medium to the other. In this set-up, the mediums travel to one another and are then processed by the heat exchanger.

Traditionally, exchangers are designed in a way that the surface area between the two exchanging fluids is maximised whilst minimising the resistance to the exchange flow at the same time. Additional fins installed in either direction where the fluids enter can also enhance these exchangers. These fins can add to the surface area of the exchangers whilst also helping control the flow of fluids during the exchange process.

Temperature during the Heat Exchange ProcessDepending on the size of the exchanger, temperature will vary during the exchange process. The temperature will also vary according to the position of the device. But many industries that use heat exchangers almost always have their own defined mean temperature.

This temperature is usually defined in terms of the Log Mean Temperature Difference or the LMTD. Sometimes though the temperature is still hard to determine through the LMTD method, in this case, the NTU method is then used.

TypesThere are several types of heat exchangers used today. These include shell tube exchangers, plate exchangers, adiabatic wheel, plate fin, fluid exchangers, dynamic scraped surface, phase-change exchangers, HVAC air coils, spiral exchangers and the direct contact exchangers.