Index

Heat Exchangers

A heat exchanger is a device which transfers heat from one medium to another. The heat is transferred by conduction through the exchange materials separating the media used. The medium through which this heat exchange occurs is what determines the different kinds of heat exchangers there are.

PIROBLOC designs and manufactures heat exchangers whose fluid is primary thermal fluid. The heat exchangers can be grouped into the following basic categories according to their application:

  • Thermal fluid / others
  • Thermal fluid / vegetable oil
  • Thermal fluid / steam
  • Thermal fluid / air
  • Thermal fluid / water (with storage tank)

The main application of heat exchangers is to heat fluids. There are many designs, as well as products to be heated. We design and manufacture customized heat exchangers to meet the particular requirements of each case and process.

Specifications

Technical features

  • Power range: 0.1 to 10,000 kW
  • Maximum permissible pressure: 50 bar
  • Test pressure: 80 bar
  • Maximum operating pressure: 40 bar
  • Operating temperature: up to 340°C
  • Design temperature: 350°C
  • Design code: ASME VIII Div. 1, EN 13445, AD2000

OPERATION OF HEAT EXCHANGERS

The primary fluid is usually thermal oil from a boiler. There are many secondary fluids, which may be either liquid or gaseous. Usually, the U-tube and housing system is used. The arrangement of the primary and secondary fluids by the tubes or the shell, and vice versa, will depend on each case.

The excess heating surface, fouling factor and others ensure proper service even under the most unfavorable conditions.

Thanks to the most powerful calculation tools, we can satisfy the vast majority of industrial heating process needs, regardless of flow rate, operating pressure or product heating conditions: e.g. viscosity and temperature.

Versions with corrugated tubing, to increase the heating surface, or expansion compensation, to minimize the effects of expansion following high temperature differences, are sometimes recommended.

Versions with a double head can be supplied for processes subject to possible soiling in the tubes which require periodic cleaning. Here, the inner tubular bundle can be easily completely isolated, both at the front and back, for total, chemical and mechanical cleaning of the tubing interior.

TYPES OF HEAT EXCHANGERS

There is a great variety of heat exchangers, but the three important types into which they may be classified are as follows:

  • Shell and tube heat exchanger: Shell and tube heat exchangers consist of a large number of small tubes placed inside a cylindrical shell. The tubes are placed in the cylinder in a tube bundle which may have tube plates permanently fixed to the body or a battery of floating tubes allowing the tube bundle to expand and contract with heat conditions. The tube battery can be removed easily for cleaning and maintenance.
  • Plate heat exchanger: Plate heat exchangers work in the same way as tube exchangers, although they use a series of stacked plates instead of tubes. Exchangers of this type have a compact, stainless steel construction, making them an ideal solution for use with refrigerants, as well as in food and drink processing.
  • Air-cooled heat exchanger: Air-cooled heat exchangers are commonly used in vehicles and other moving applications where there is no available permanent source of cold water.  Thermex designs and supplies combined cooling assemblies (or combined refrigerators), which combine a water cooler, and oil cooler and a charge air cooler in a single unit, reducing space requirements and improving efficiency. Cold air is provided by a fan or the flow of air produced by the vehicle’s movement.

HOW IS A HEAT EXCHANGER DESIGNED?

The following information is needed for it to be possible to select a heat exchanger meticulously matching each customer’s needs:

  • Type of fluid, temperature and flow in the primary circuit (normally the hot fluid)
  • The objective of the primary circuit (heat dissipation or target output temperature)
  • Type of fluid, temperature and flow in the secondary circuit (normally the refrigerant)

Beginning from these data, an initial proposal is produced, which is then customised according to the customer’s specifications and needs of the project.

WHAT FLUIDS CAN A HEAT EXCHANGER WORK WITH?

Selection of a fluid for a heat exchanger directly depends on the type of heat exchanger being used, and materials available.

A standard heat exchanger made by Pirobloc is adequate for most usual fluids, including oil, water and glycol. For fluids of a more corrosive nature, such as fluorinated salt water, refrigerants and acids, it is necessary to build the heat exchanger using other materials such as stainless steel or titanium.

MORE EFFICIENT HEAT EXCHANGERS

There is a series of parameters normally used to measure a heat exchanger’s performance and efficiency:

Temperature difference – The temperature difference between the hot fluid and the coolant is very important when a heat exchanger is being designed. The coolant always need to be at a considerably lower temperature than the hot fluid. The lower the temperatures of the coolant fluid are, the more heat they will extract from the hot fluid.

Flow – Another important factor is the flow of the fluids in both the primary and secondary sides of the heat exchanger. Greater flow increases the exchanger’s heat transfer capacity, but also means greater mass, which may make elimination of energy more difficult, as well as greater speed and pressure loss.

Installation – Normally, the most efficient way of installing a heat exchanger is to have the fluids circulate in in a countercurrent arrangement, i.e., if the coolant is moved from left to right, the hot fluid is moved from right to left. In shell and tube heat exchangers, the coolant must enter at the lowest entry position to ensure that the heat exchanger is always full of water. For air-cooled heat exchangers, it is important to take the air flow into account when a cooler is installed, because blockage of any part of the core would compromise the cooling capacity.

HEAT EXCHANGER MAINTENANCE RECOMMENDATIONS

Heat exchangers are made of robust materials, do not have moving parts and work at a variety of different pressures and temperatures, so if a heat exchanger is properly used, there is no reason why it should not be possible for it to remain in operation for many years. There are several steps which should be taken to help to increase the working life of a heat exchanger:

Make sure the design data are accurate. If you send data to our engineers for heat exchanger selection, it is best to ensure that they are as accurate as possible. This will ensure not only that your heat exchanger is thermally efficient, but also that it will be capable of operation for a long period of time. If flows are too high, erosion may be a problem; if pressures are too high, leaks may occur; and if there is any unusual chemical in the fluids (e.g. acids in the coolant water), get in touch with us to check compatibility. If our standard materials are not suitable, we can usually supply an alternative which is.

All Pirobloc’s heat exchangers are designed for ease of maintenance. The end covers can be removed, enabling the tube bundle inside to be extracted for cleaning.



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References

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