Commercial heating


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Heat transfer made simple


Heat exchangers represent a well-established, and proven technology that offers a host of advantages in a range of applications. Nathan Andrews of ECEX has some insight


H


eat transfer happens whenever there is a difference in temperature between two objects; this transition occurs in the direction


of decreasing temperature, in other words from a hot object to a cold object.


This scientific principle is at the heart of a technology that has proven invaluable in the HVAC sector for decades – the heat exchanger. There are essentially two types of heat exchanger to choose from – shell & tube, and flat plate. Most of both types move heat by conduction (rather than convection or radiation) through the exchanger materials (shells and tubes, or plates) which


separate the mediums being used (usually water, sometimes gas). With shell & tube heat exchangers, two fluids are


placed in thermal contact using tubes housed within an outer cylindrical shell – the more tubes, the more powerful the heat exchanger. Shell & tube heat exchangers tend to be specified


for comfort applications and industrial settings to heat and cool fluids. They can often be found in power generation, oil refineries and other chemical processes, metals and mining, chilled water systems and refrigeration, cooling for turbines and compressors, and pulp and paper applications.


The construction of flat plate heat exchangers


Typically, every plate in a flat plate heat exchanger has an alternating gasket pattern. The hot medium flows into the space between a pair of plates but will not flow into the space between the next pair of plates because the gaskets prevent it. The process continues so that every second set of plates is filled with the hot flow medium. At the same time, the cold medium enters a heat exchanger through the cold medium inlet, but this time the gaskets are positioned to allow the cold medium to flow into the space where no hot medium is present. This means the heat exchanger is filled with both hot and cold flowing mediums between each alternate plate. Heat is transferred from one side of the plate to the other, thereby removing heat from the hot medium. There are two principal ways to seal flat plate heat exchanger plates together. Nitrile rubber gaskets running around the edges of the plates have a very good coefficient of elasticity which means they can be heated and cooled without breaking. Alternatively, the plates can be brazed or welded (although this tends to reduce flexibility because it is more of a fuss to add or remove plates).


Flat plate heat exchangers employ the same


heat conducting principles as shell & tube units but differ in design. They are constructed from a series of corrugated metal plates stacked one after another and housed within a large frame. Hot and cold (usually) liquid or (sometimes) gas is passed between the plates. There are three main benefits of flat plate heat


exchangers. These are: ¡ Efficiency – The corrugated plate gives the PHE a larger contact surface area than a traditional shell & tube heat exchanger of similar size; this increases the heat transfer rate and makes a heat exchanger more efficient. ¡ Serviceability – PHEs are smaller and lighter than the shell & tube alternative. They are simple to disassemble should a defect be discovered in a plate, making them particularly easy to clean and maintain. PHEs don’t need access space to dismantle. Should a defect be discovered in a plate, it can be removed, and the PHE can be returned to service at a marginally lower capacity until a replacement is installed. ¡ Flexibility – The number of plates in these units can quickly and easily be increased or decreased depending on capacity requirements. The best way to specify and service heat


exchangers is by talking to the experts. My own company installs and maintains plate heat exchangers as part of its mechanical engineering services. Working with leading manufacturer, Thermo Logistics (which has more than 25 years’ experience in heat exchanger servicing and maintenance), ECEX delivers plate heat exchanger services to a variety of commercial applications, including hospitals, industrial and manufacturing processes, district heating systems, and swimming pools. The company provides technical expertise


on all aspects of heat exchangers, supplying comprehensive service and support for flat plate heat exchangers, including accessories, loan packs, and certification of heat exchanger plates


24 November 2022


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