VII. FREEZE PROTECTION
For freeze protection use thermostats and/or temperature controls in the connections opposite to the liquid inlet/outlet, if any, or in a temperature pocket close to the outlet.
Connect the water side pipes to ensure that the whole unit runs filled with water.
To minimize freezing risk:
- use a filter< 1-mm mesh before inlet water.
- use antifreeze when the evaporation temperature is close to waterside freezing.
- use a freeze protection thermostat and a flow switch to guarantee a constant water flow before, during and after compressor operation.
- avoid pump down operation.
- use a flow level switch and a low level pressure switch.
- if possible, use hot gas bypass system.
Insulation
Airtight insulation is recommended. It is necessary when the unit is working as evaporator at low temperatures. This can be made, among other solutions, using insulation sheets (Armaflex or similar) cut into appropriate sizes and glued together as shown. (See Figure 11.)
VIII. MAINTENANCE
Heat Transfer
The purpose of the BHE is to transfer heat from one medium to another. Heat passes very easily through the thin walls separating the two media. The pattern pressed into the plates makes the plate strong and rigid and increases the rate of heat transfer. This high rate of heat transfer can be inhibited by the formation of deposits on the plate surfaces. The corrugated pattern on Alfa Laval plates induces turbulent flow. Turbulence provides strong resistance to deposit buildup, but it cannot always eliminate fouling. The deposits may increase the total “wall thickness,” and consist of materials of a much lower thermal conductivity than of the metal plate. Thus, a layer of deposits can severely reduce the overall heat transfer rate. Corrosion can also occur under the deposits. For corrective action please see Cleaning below.
Pressure Drop
Pressure drops are wasted energy. All pipe systems, and equipment included in them, offer resistance to the media flowing through them. Some pressure drop is inevitable, but it should be kept as close as possible to the designed value for the BHE. The formation of deposits on the heat transfer surfaces reduces the free space between the plates. This means that more energy is required to achieve the desired flow in the BHE. Large particles and fibers may also clog the heat exchanger if it is not equipped with a strainer. A reduced ability to maintain the desired temperatures along with an increased pressure drop on either media, are symptoms of fouling or clogging. For corrective action please see Cleaning below.
Cleaning
Clean with detergents for fatty deposits. For heavier fouling use chemicals such as formic, citric, vinegar or other organic in concentrations compatible with copper.
Alfa Laval BHEs can be cleaned in place with the Cleaning-In-Place (CIP) system, which chemically removes calcium deposits and other forms of scaling from plate surfaces (See Figure 12.) Different solutions can be used, depending on the type of deposits. Every application has to be considered separately. The Cleaning-In-Place procedure is generally the same, regardless of the solution used.
CIP Procedure
Procedure
- Drain the unit.
- Rinse with fresh water.
- Drain water.
- Fill with fresh water.
- Add cleaning agent (solution and concentration depending on the type of fouling)
- Circulate the cleaning solution (if feasible).
- Drain the cleaning solution.
- Add and circulate the passivating liquid for corrosion inhibition of plate surfaces.
- Rinse with fresh water.
- Drain.
CAUTION: Do not use liquids that are corrosive to stainless steel or the brazing material (Copper or Nickel)! Do not leave the unit on stand-by after cleaning!
Contact your nearest Alfa Laval After Sales and Service Center for more information about cleaning-in-place equipment, detergents or service.
IX. ASSISTANCE AND FIELD SERVICE
Trouble shooting – To assure correct performance of the unit, please check that:
- it is correctly connected according to the installation.
- it is absolutely clean and free from deposits. Increased pressure drops can reveal fouling.
- the control equipment is correctly set up and that freezing does not occur.
Valutech Inc. maintains a large highly specialized engineering staff to handle your questions and problems. Your Valutech Inc. representative will be happy to provide you with quotes or answers to your questions. To assist you in finding the best solution, please provide the following sizing information along with your inquiry:
If you do not have this information, it may be sufficient to describe the existing heat exchanger.
Consult your invoice for general terms and conditions.
