Karl Kolmetz
A heat exchanger is a device for heat transfer from one medium to another. The personnel needs to understand the terminology of the heat transfer equipment in order to properly design, specify, evaluate bids, and check drawings for this equipment.
Heat transfer is one of the most important, as well as the most applied process, in
chemical and petrochemical plants. Economics of plant operation often are controlled by
the effectiveness of the use and recovery of heat or cold (refrigeration). The service
functions of steam, power, refrigeration supply, and the like are dictated by how these
service or utilities are used within the process to produce an efficient conversion and
recovery of heat.
The basic plate heat exchanger consist of a series of thin, corrugated plates that are
gasketed or welded together (or any combination of these) depending on the liquids
passing through and on whether it is practical to be able to subsequently separates the
plates, for whatever reason. The plates are then compressed together in a rigid frame to
create an arrangement of parallel flow channels. One fluid travels in the odd numbered
channels, the other in the even channels. All plate heat exchangers look similar from the
outside. The differences lie inside, in the details of plate design and the sealing
technologies used.
the high temperature side is exactly the same as the heat gained in the low temperature
side after the heat and mass flows through the heat exchanger. Heat exchanger simply
exchanges the heat between those two sides; as a result, it is decreasing the temperature
of higher temperature side and increasing the temperature of lower temperature side. But
designing heat exchanger might be a challenge; it needs iteration for manual calculation.
Hence, a guideline to properly select and sizing is needed.
An innovative type of heat exchanger that has found widespread use is the plate and
frame (or just plate) heat exchanger, which consists of a series of plates with corrugated
flat flow passages. The hot and cold fluids flow in alternate passages, and thus each cold
fluid stream is surrounded by two hot fluid streams, resulting in very effective heat
transfer. Also, plate heat exchangers can grow with increasing demand for heat transfer
by simply mounting more plates. They are well suited for liquid to liquid heat exchange
applications, provided that the hot and cold fluid streams are at about the same pressure.
Plate type heat exchangers (PHE) consist of a number of parallel flow channels, formed
by adjacent metal plates that are either welded or separated by gasket material around
the perimeter of each plate. The plates can be formed from a variety of metals, but
typically are made of stainless steel. The manufacturing process presses the plates into
a corrugated shape that is different for each plate type and is proprietary to each
manufacturer.
The corrugations (sometimes called ribs or chevrons) both increase the mixing of the flow
stream and add strength and support to the plate. The flow channel width between
adjacent plates ranges from 0.05 to 0.25 in. (1.27 to 6.35 mm) and the ribs of adjacent
plates have contact point with each other at regular intervals. PHEs can be designed for
true counter flow because the hot and cold flow streams pass through adjacent channels
over the entire length of the exchanger.
The main advantages of PHE are their compact size and high heat transfer effectiveness
that allow reduced number of units, smaller spaces and, for offshore platforms, and
reduced weight. They are especially attractive in cost when the equivalent shell and tube
exchanger would require in alloy shell or tubes. The minimum recommended construction
material for all types of PHEs and welded PHEs is type 304 stainless steel.
PHEs are presently operating in such liquid-liquid services as heat recovery loops,
chemical process coolers and heaters, oil platform applications, and seawater cooling.
Partially welded PHEs make good applications in product coolers using cooling water.
The plate and frame heat exchanger is not specifically considered, because steady state
design follows standard contraflow or parallel flow procedures. It is only necessary to
source sets of heat transfer and flow friction correlations before proceeding.
Plate type exchangers consist of a number of parallel flow channels, formed by adjacent
metal plates that are either welded or separated by gasket material around the perimeter
of each plate. The plates can be formed from a variety of metals, but typically are made
of stainless steel. The manufacturing process presses the plates into a corrugated shape
that is different for each plate type and is proprietary to each manufacturer. The
corrugation (sometimes called ribs or chevrons) both increase the mixing of the flow
stream and add strength and support to the plate.
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Hofmann is a Chinese manufacture of PHE, gaskets, and plates. More info,http://www.hfm-phe.com/
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