Phe Plate

• Customized: Customized
• Certification: CE, ISO, RoHS
• Sectional Shape: Square
• Performance: Pressure Resistant, Temperature Resistant, Corrosion Resistant
• Material: Stainless Steel
• Transport Package: Wooden Case
• Model NO.: SS316
• Specification: Stainless Steel
• Trademark: DGXT OR OEM
• Origin: China
• HS Code: 84195000
• Production Capacity: 100000pieces/Year

Product Description

                                                                                         Phe plate

 

A plate exchanger consists of a series of parallel plates that are placed one above the other so as to allow the formation of a series of channels for fluids to flow between them.

The space between two adjacent plates forms the channel in which the fluid flows.

Inlet and outlet holes at the corners of the plates allow hot and cold fluids through alternating channels in the exchanger so that a plate is always in contact on one side with the hot fluid and the other with the cold.

The size of a plate can range from a few square centimeters (100 mm x 300 mm side) up to 2 or 3 square meters (1000 mm x 2500 mm side). The number of plates in a single exchanger ranges from just ten to several hundred, so reaching surface exchange areas up to thousands of square meters.

Design Considerations for Plates

Because plate heat exchangers are used for wide ranging applications, they must be designed to withstand the process conditions in which they operate, this may include corrosive and erosive environments. Its possible to construct plate heat exchangers from various materials, including metals, alloys and plastics. Different materials make the plate heat exchanger more suitable for different applications. For example, if a particular flowing medium reacts aggressively when coming into contact with certain metals, polymer-based materials such as may be used instead.

Plate Heat Exchanger Advantages

There are numerous advantages associated with plate heat exchangers:

• Plate heat exchangers weigh less, require less space and are more efficient compared to other heat exchanger designs of the same size.
• Replacing and cleaning of the plates is a simple task because the plate stack can be opened easily.
• And unlike shell and tube heat exchangers, plate heat exchangers do not require additional space for dismantling.

Plate Heat Exchanger Disadvantages

But there are also some disadvantages associated with plate heat exchangers:

• Plate heat exchangers tend to be more expensive than other heat exchanger designs.
• If there is a leaking gasket causing one flowing medium to mix with the other, the leaking plate is often difficult to locate.
• Replacement of plate gaskets in-situ can be difficult, or impossible. Some plate gaskets must be returned to the manufacturer for replacement, which costs both time and money.
• When the plates are compressed together to form a plate stack, the clearance between each of the plates is small, this increases the likelihood of fouling with a corresponding reduction in heat transfer.
• When reassembling the plate stack, over-tightening the clamping bolts can lead to crushing of the plates, which damages the plate corrugations and squeezes-out the gaskets. If the gaskets are squeezed-out, the plate will no longer seal correctly.
• Plate heat exchangers are not suitable for high pressure applications because the gaskets would be expelled by the system pressure; this situation is referred to as 'gasket blow-out'. However, it is possible to get around this problem by using a gasket-less design; these designs usually use brazed or welded plates. Brazed and welded plate heat exchangers are more suitable for higher temperature and higher pressure applications, but also for applications where leakage would be hazardous/catastrophic e.g. toxic or poisonous flowing mediums.

The figure shows the flow of fluids inside the exchanger. Fluids are divided into several parallel streams and can produce a perfect countercurrent.

 

Generally, these plates are corrugated in order to increase the turbulence, the thermal exchange surface and to provide mechanical rigidity to the exchanger. Corrugation is achieved by cold forging of sheet metal with thicknesses of 0.3mm to 1 mm.

The most frequently used materials for the plates are stainless steel (AISI 304, 316), titanium and aluminium.

The corrugation on the plates forces the fluid on a tortuous path, setting a space between two adjacent plates b, from 1 to 5 millimeters.

The fluids can cross the channels in series (a less common solution) or in parallel by making counter-current or current configurations.

The serial configuration is used when there is a small flow rate for each fluid but high heat jump; the greatest problem is with a high pressure drop and an imperfect counter-current.

The parallel configuration with countercurrent channels is used for high flow rates with moderate temperature drops, and is the most widely used.

When there is a great difference between the flow rates (or between the maximum permissible pressure drop) of the two fluids, the exchanger can run twice by the fluid with a lower flow (or higher losses) to balance the values of pressure drops or specific flow rates in the channels.

The figure shows the different configurations: in parallel, in series and mixed

One of the most common problems for plate heat exchangers is an irregular supply of the all channels in parallel. In fact, the fluid tends to distribute in greater quantities in the first channels rather than the last ones in order to balance the pressure drop.

As the number of plates increases, even distribution declines, resulting in a decrease in the overall performance of the exchanger.
There are two basic types of plate heat exchangers: BPHE-Brazed Plate Heat Exchangers and PHE-Plate Heat
Exchangers.


 

In the PHE the plates create a frame where the plates are pressed with headers and tie bars, and the seal is guaranteed by gaskets. Gaskets, in addition to their sealing effect, serve to direct the flow of the fluids, and are placed along the grooves at the edges of the plates.

The maximum temperatures used for sealing heat exchangers are between 80°C and 200°C while pressures can reach 25 bar.
Gaskets are available in various types of butyl or silicone rubber.

Brazed Plate Heat Exchangers
 

Brazed plate heat exchangers have no headers, tie bars or sealing gaskets because the plates are furnace brazed at temperatures of 1100°C.

During the assembly phase, a sheet of brazing material (generally copper but also nickel) is placed between the plates, the pack is pressed and subsequently baked for some hours.

The BPHE exchanger is more compact, lighter and less bulky than one with gaskets.
The image shows the path made by the hot and cold fluid.

The brazing material carries out the function both of the gaskets and the frame.

These exchangers are generally used with chevron corrugated plates, which are assembled alternating the corrugation directions in order to create a lattice contact.

The crossing points between the corrugations of two coupled plates form a dense network of contact points that confer pressure tightness and induce swirling streams that improve heat exchange.

In this way, the turbulence of the fluids is high even at low nominal input speeds and the flow passes from laminar to turbulent for low flow rates.

The figure shows a cross section of an exchanger with 8 plates in total (6 of which are useful for heat exchange) in which the 3 channels used for the passage of the refrigerant fluid (in light blue) and the 4 for water (in red) are seen.

 

It is immediately noticeable that the path made by the fluids is chaotic, in fact, the cross section varies continuously.

The main disadvantage of these exchangers is that they are not removable and so maintenance and cleaning are not possible or at least difficult, and no flexibility exists as the number of plates can in no way be varied.

The surface of the plates is corrugated in order to increase the turbulence of the fluid during the flow into the channels.

The figure highlights the main geometrical parameters of the corrugation:

Corrugation pitch p; corrugation height b and chevron angle β compared to the main direction of the flow.

The inclination of the plate corrugations has a determining effect on thermal exchange and load losses. In fact, a pair of plates with a high β angle (> 45 °) gives a turbulence and therefore a high heat exchange with a higher pressure drop.

A smaller angle (β <45 °) causes a lower turbulence flow and lower heat exchange coefficients but also lower pressure drops.

The search for a compromising β angle between high exchange coefficients and acceptable load losses is therefore essential.

The corrugation height b has an important effect on the exchange coefficients because a greater depth causes greater turbulence.

These two picture below show an Onda case study of the flow inside the channel of a braze plate heat exchanger, you can see the flow going inside the channel in and out of the BPHE
 

The actual area is difficult to compute, so in order to compare different exchangers, reference is made to the projected area.

It should be kept in mind that heat exchangers with the same projected area (ie plates of the same size) may have different effective areas depending on the value of the surface enlargement factor φ.

The ratio between the plate length L and the plate width W also affects performance but to a lesser degree than other variables. In general, a high ratio between plate length and width gives high exchange rates but higher load losses.

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The main characteristics of these types of heat exchangers are:
- quick and easy dismantling for cleaning and control operations
- adaptation to variable operating conditions by adding or removing heat plates to modify the installed thermal flow
- any fluid leaks due to non-perfect sealing of the gaskets do not contaminate the other fluid but are directed away
- materials that are poorly adapted to soldering, such as titanium, may be used
- the gaskets limit the maximum pressure and temperature values
- potentially high costs due to the design of moulds, presses and all the production process
- high cost of the gaskets

Varying the Cooling Capacity

There are several ways to vary the cooling capacity of a plate heat exchanger:

• Regulate the outlet valves so that the flow is increased or decreased; this method is useful because no dismantling of the heat exchanger occurs. Do not throttle/regulate the inlet valves as this may starve the heat exchanger and cause localised overheating.
• Increase or decrease the number of plates in the plate stack. Increasing the number of plates in the plate stack gives a corresponding increase in cooling capacity. Decreasing the number of plates in the plate stack gives a corresponding decrease in cooling capacity. In short, more plates equals more cooling capacity and less plates equals less cooling capacity.
• Use a single pass or multi-pass design. Single pass heat exchangers allow the two flowing mediums to flow past each other only once. Multi-pass heat exchangers allow the flowing mediums to flow past each other several times. Most plate heat exchangers use the single pass design.