Plate heat exchanger advantages. Plate heat exchanger: pros and cons

Monoblock type plate heat exchanger is the basis of a two-stage mixed hot water supply system (hot water supply)

“Monoblock” is a type of plate heat exchanger designed to work in a two-stage hot water system, in which both stages are combined in one heat exchanger; such a heat exchanger has six pipes. (see picture).

The main and perhaps the only advantages of a monoblock are its compactness, in comparison with two heat exchangers separately and, accordingly, lower cost, which determines the breadth of application of heat exchangers of the “Monoblock” type.

Now let's try to determine its disadvantages.

Rice. Monoblock for two-stage DHW system. Location of pipes: H1 - Return coolant inlet from the heating system, H2 - DHW circulating water inlet, H3 - DHW heated water outlet, H4 - Hot coolant inlet from the heating network, F3 - Cold inlet tap water, F4 - Output of the general return coolant into the heating network.

"Simplicity" of installation.

It is believed that it is easier to install one device than several of the same ones. But the installed monoblock looks like a spider, entangled in a web of pipelines, various shut-off valves and instruments. Thus, the main advantage is lost - ease of maintenance and repair. If in a single-pass plate heat exchanger all pipes are located on the front plate H1-H4 and for its maintenance and repair you only need to use shut-off valves and dumpers, then to disassemble the monoblock system, dismantling the pipes of the movable rear plate is inevitable. Also, the back plate piping may block access to the monoblock heat exchanger. For normal operation of the monoblock, it is first worth making a competent design for connecting to the coolant, cold and hot water in order to provide easy access for maintenance and repair. A correctly mounted monoblock takes up no less space than two separate heat exchangers.

Reliability.

It is important to remember that two separate heat exchangers are more reliable than one that performs the same functions. What do we get when one of the heat exchangers fails? In this case, the system can operate at partial load while the second heat exchanger is repaired or serviced. If even one stage is inoperative, the entire monoblock must be taken out of operation, because there is only one housing for both stages.

Efficiency.

When calculating a monoblock heat exchanger, there are also some nuances. Quite often it is difficult to create a monoblock two-stage system mixed scheme DHW, comparable in efficiency to two separate plate heat exchangers. This is due to the fact that the established type of plate in the monoblock for two stages is the same. And within the limits of the thermophysical properties of this type, we need to solve the problem of arranging plate packages for both stages, while one stage may differ in flow rates from each other, especially on the coolant side. Here, for example, the requirements for the first stage are the ability to pass the total flow rate of the heating system coolant and the second stage coolant while ensuring low hydraulic resistance and average heat removal. For the second stage, these are relatively low flow rates on the coolant side and hot water supply side, higher permissible hydraulic resistances and significantly greater heat removal. That is, if these were two separate heat exchangers, then the first-stage heat exchanger should have a larger nozzle diameter and a “short” plate, and the second-stage heat exchanger should have a smaller nozzle diameter and a “longer” plate.

There is a task option for selecting equipment for a two-stage mixed circuit. The initial data are as follows: hot water supply system load 0.4 Gcal/h, heating cold water from 5° C to 60° C, total heating system load 1.2 Gcal.h, temperature graph 150-70.

Dividing the load into steps, in accordance with (SP 41-101-95), for given conditions we obtain the initial data for selecting stage heat exchangers (see table).

In fact, the NTU value characterizes the thermal regime at which the heat exchanger will operate. The higher the NTU, the greater the thermal "length" of the heat exchanger plate must be.

In this case, it is clear that the heat exchanger of the second stage must have a greater, almost 50%, heat removal capacity (thermal “length”) than the heat exchanger of the other stage. In addition, the costs on the heating side of both stages differ by almost 3 times. This means that if for the second stage heat exchanger the pipes DN32 are sufficient, then for the heat exchanger of the first stage the pipes must be larger, not less than DN50.

Plate package

As stated above, a monoblock is essentially two heat exchangers located in one frame. This means two packages of plates placed in one frame, separated by a reversal plate that has two (upper or lower) blind port holes. Often the second stage package is located closer to the fixed plate, and behind it the first stage package. Due to the different functions performed by these packages (see above), they have different layouts and numbers of plates. And since all these packages are located in one frame, there is a possibility that during the service process an error will occur when assembling the entire package of monoblock plates. That is, if, after disassembling the candy bar, the packages are swapped or arranged incorrectly, then when we reassemble the device, we will not receive from it the inherent characteristics that were originally included in it.

Table. Data for the selection of heat exchangers.

With two heat exchangers the situation is simpler. In this case, even if we assemble the entire package incorrectly, we will not get such a colossal reduction in power, costs and changes in hydraulic resistance as with a monoblock.

Eventually

Pros and cons of a plate heat exchanger with a monoblock layout:

Pros:

1. Low cost.

2. The monoblock is slightly more compact than two heat exchangers.

Minuses:

1. Difficult installation and inconvenience in maintenance due to the pipeline on the pressure plate.

2. Less reliability.

3. Less productive work.

4. Demanding requirements for assembling a package of heat exchanger plates.

Everyone has long known about the two-stage mixed hot water supply system, implemented on a type of plate heat exchanger such as a monoblock. Monoblock is a special type of plate heat exchanger for a two-stage hot water system, in which both stages are located in one housing; such a heat exchanger has six pipes.

• H1 - Input of return coolant from the heating system.
• H2 - DHW circulation water inlet.
• H3 - Output of heated hot water.
• H4 - Inlet of hot coolant from the heating network.
• F3 - Cold tap water inlet.
• F4 - Output of the general return coolant into the heating network.

The wide application of the monoblock was determined by the following factors: greater compactness compared to two separate heat exchangers, and, accordingly, lower cost. These same factors are the main and, perhaps, the only advantages of a candy bar. Let's try to decide on the disadvantages.

"Simplicity" of installation

It seems natural that it is much easier to mount a small device than two of the same ones. But what do we get as a result of installing a monoblock? The mounted monoblock looks like Spider-Man, entangled in garlands of pipelines, fittings and measuring instruments, if they are present, of course. Immediately, such an important thing as ease of maintenance is lost. If in a conventional plate heat exchanger all the pipes are located on a fixed plate (H1-H4) and its maintenance and repair only require turning off the heat exchanger and releasing the pressure, then disassembling the monoblock will require disconnecting the pipes from the movable rear plate. Further, if the back plate piping blocks access to the monoblock heat exchanger, then this also complicates access to it. That is, for normal operation of the monoblock, you should, firstly, make a competent project for linking it to existing pipelines coolant, cold and hot water in order to ensure normal access for maintenance and repair. And, secondly, a special option should be provided for attaching the pipelines to the back plate (through some removable elements) in order to ensure the mobility of the back plate without moving the heat exchanger from its place. Therefore, often a mounted monoblock occupies a volume no less than two separate heat exchangers.

Reliability issues

Naturally, two separate devices are more reliable than one that performs the same function. What do we have when one of the heat exchangers fails? In this case, we will be able to work with partial load of the hot water system while the second one is being repaired or serviced. If even one of the stages fails, the monoblock must be taken out of service as a whole, since there is only one housing for both stages.

Functionality, efficiency

The selection of a monoblock heat exchanger also has its own nuances. It is often difficult or practically impossible to create a monoblock arrangement of a two-stage mixed DHW circuit, with an efficiency equal to two separate heat exchangers. This is due to the fact that the type of plate used in the monoblock is the same for both stages. And within the limits of the thermophysical properties of this type, we have to solve the problem of arranging packages for both stages, while the first and second stages may differ, at least in terms of costs, especially on the coolant side. For example, the requirements for the first stage are the ability to pass the total flow rate of the heating system coolant and the second stage coolant while ensuring low hydraulic resistance and average heat removal. The requirements for the second stage are relatively low flow rates on the coolant and hot water side, higher permissible hydraulic resistances and significantly greater heat removal. That is, if these were two separate heat exchangers, then the first-stage heat exchanger should have a larger nozzle diameter and a “short” plate, and the second-stage heat exchanger should have a smaller nozzle diameter and a “longer” plate.

Let's consider a variant of the task for selecting equipment for a two-stage mixed circuit. The basic data are as follows: DHW system load 0.4 Gcal/h, cold water heating from 5°C to 60°C, heating system load 1.2 Gcal/h, temperature graph 150/70.

Dividing the load into stages, in accordance with SP 41-101-95 for given conditions, we obtain the initial data for selecting stage heat exchangers:

I stage

II stage

* NTU - number of heat transfer units. Heat engineering. V. N. Lukanin, M. G. Shatrov and others, Higher School, Moscow, 1999.

In fact, the NTU value characterizes the thermal regime at which the heat exchanger will operate. The higher the NTU, the greater the thermal "length" of the heat exchanger plate must be.

In our case, it is clear that the second-stage heat exchanger must have a greater, almost 50%, heat removal capacity (thermal “length”) than the first-stage heat exchanger. In addition, the costs on the heating side of both stages differ by almost three times. This means that if for the second stage heat exchanger the pipes DN32 are sufficient, then for the heat exchanger of the first stage the pipes must be larger, not less than DN50.

Plate package

As noted above, a monoblock is, in fact, two heat exchangers placed in one frame. This means two packages of plates placed in one frame, separated by a reversal plate that has two (upper or lower) blind port holes. Typically, the second stage package is located closer to the fixed plate, and behind it the first stage package. But due to the infectious functions performed by these packages (see above), they have different layouts and number of plates. Since all these packages are located in one housing, there is a possibility that during the maintenance process an error will occur when assembling the entire package of monoblock plates. That is, if, after disassembling the monoblock, the packages are swapped or arranged incorrectly (for example, plates of the first stage with a small thermal “length” are installed for the second stage and vice versa), then, having reassembled the device, we will not get from it the characteristics that were included in it from the very beginning.

With two separate devices the situation is simpler. In this case, even if we assemble the entire package incorrectly, we will not get such a fatal reduction in thermal power, costs and changes in hydraulic resistance as in the case of a monoblock.

To summarize, let's summarize all the pros and cons of a plate heat exchanger with a monoblock layout in one table.

Advantages and disadvantages

pros

• Lower initial cost.
• Separately, a monoblock is more compact than two heat exchangers.

Minuses

• More complex installation and inconvenient maintenance due to sockets on the pressure plate.
• Less reliability.
• Less efficient operation.
• Demanding when assembling a package of plates.

Result

Everyone decides for themselves what is more important to them - cost savings or more reliable operation of the equipment.

Plate heat exchangers are specialized devices that transfer heat from a hot medium to a medium that needs to be heated through corrugated plates. The plates themselves can be made of different materials, for example, graphite, copper, steel and so on. In this case, the cold and hot layers are placed one after the other.

Advantages and disadvantages

The plate heat exchanger appeared relatively recently, but has already gained popularity among consumers due to its outstanding qualities. One of the greatest advantages is that collapsible heat exchangers are very compact and save installation space.

If there is a need to increase the number of plates, then the equipment does not necessarily need to be dismantled, since the required number of plates is added or reduced during operation, and this is a big plus.

In addition, all plate units are easy to clean, and their degree of contamination is the lowest. Operating costs and cash costs for energy supply are low. And the equipment is able to fully function at very low temperatures.

The application is quite effective if there is a need for low-grade heat and its transfer. Thanks to all of the above, plate heat exchangers remain the most technologically advanced and durable, and therefore the most in demand. Get acquainted with different types plate heat exchangers, can be found at http://www.teploprofi.com/.

The disadvantages of these heat exchangers include the fact that when using low-quality coolant, the heat exchanger will quickly become clogged. And in this case, you will have to systematically clean it using a special product. There are other types of heat exchangers, for example, shell-and-tube or brazed heat exchangers, but their specialization is too narrow, so they are not as popular as plate heat exchangers.

Scope of application of plate heat exchangers

Heat exchangers of this type are used for heating, cooling and condensation:

• In heating, ventilation and air conditioning systems, including heating points.
• In swimming pools, in hot water supply systems.
• In case of separation of energy systems.
• During heat extraction and recovery in the municipal sector.
• In specialized refrigeration equipment, evaporators and condensers in refrigeration systems.
• For the purpose of cooling various media for technological needs.
• In food, automotive, steel, textile and many other areas of modern industry.

Operation of a plate heat exchanger - advantages, disadvantages, design

Heat exchangers include stamped plates that are not subject to corrosion processes. They can be used as air coolers or heaters various types liquids such as fuel oil, petroleum, water, oil and others.

For the right choice heating equipment, you need to know how the plate heat exchanger works.

The power of the device can change if the number of plates is increased or decreased. This cannot be done in other types of devices, because in them the number of heat exchange pipes is constant. Gaskets used in the production of devices strengthen the interplate channels. Rubber seals form two completely sealed channels intended for liquids that circulate during the heat exchange process.

Fluids that move towards each other produce a process whereby the hot fluid transfers heat to the cold medium. The operation of a plate heat exchanger is based on this effective principle.

Heat exchange equipment has high percentage performance and power level. It is adjusted if the number of plates changes. This device is easy to care for, disassemble and remove various contaminants. The advantage of such devices is that the plates become dirty quite slowly and do not require frequent cleaning. High-quality polishing of the plates, as well as high turbulence during operation of the device, promotes cleaning.

Flaws

But, like all devices, plate heat exchangers have their drawbacks. The main disadvantage is the use of low quality equipment. When choosing a low-quality device, the device becomes clogged in the shortest possible time, and ordinary cleaning, without the use of special chemical compositions, will not be effective. This drawback is probably the only one of heat exchange equipment.

Sometimes plate heat exchangers cost more than shell-and-tube type devices, which is a significant disadvantage in some cases.

We must not forget that the installation of heat exchange equipment requires the allocation of a separate small room. This fact can also become a disadvantage and a problem if the equipment is operated in a small space or private house. Sometimes additional space was simply not provided during the construction of the structure.

Despite some minor drawbacks, plate heat exchangers are very practical equipment that is very popular in the modern construction market.