General mounting advice
Never expose the unit to pulsations or excessive cyclic pressure or temperature changes. It is also important that no vibrations are transferred to the heat exchanger. If there is a risk of this, install vibration absorbers. For large connection diameters, the use of an expanding device in the pipeline is recommended. It is also suggested that a rubber mounting strip, for example, should be used as a buffer between the BPHE and the mounting clamp.
In single-phase applications, e.g. water-to-water or water-to-oil, the mounting orientation has little or no effect on the performance of the heat exchanger. In two-phase applications, however, the orientation of the heat exchanger becomes very important. In two-phase applications, SWEP's BPHEs should be mounted vertically, with the arrow on the front plate pointing upwards.
Several mounting suggestions for SWEP BPHEs are shown in Figure 8.8. Mounting stud bolts (see Figure 8.9) in various versions and locations are availableas an option on BPHEs. These stud bolts are welded to the unit. For smaller BPHEs, it is also possible to mount the unit by simply suspending it from the pipes/connections.
Connections in general
All connections are brazed to the heat exchanger in the general vacuum brazing cycle. This process gives a very strong seal between the connection and the cover plate. However, take care not to join the counterpart with such force that the connection is damaged.
Depending on the application, there are many different versions and locations available for the connections, e.g. Compac flanges, SAE flanges, Rotalock, Victaulic, threaded connections and welding connections (see Figure 8.10). It is important to have the correct international or local standard of connection, because they are not always compatible.
Some connections have an external heel (see Figure 8.12) to simplify the pressure and leakage testing of the BPHE in production.
Some connections are fitted with a special plastic cap to protect the threads and sealing surface (see Figure 8.11) of the connection, and to prevent dirt and dust from entering the BPHE. This plastic cap should be removed with care, to prevent damage to the thread or any other part of the connection. Use a screwdriver, pliers or knife.
Threaded connections can be female or male (see Figure 8.12), in wellknown standards such as ISO-G, NPT and ISO 7/1.
The soldering connections (sweat connections) (see Figure 8.13) are in principle designed for pipes with dimensions in mm or inches. The measurements correspond to the internal diameter of the connections. Some of SWEP's soldering connections are universal, i.e. fit both mm and inch pipes. These are denominated xxU, such as the 28U, which fits both 1 1/8" and 28.75 mm.
All BPHEs are vacuum-brazed with either pure copper filler or nickelbased filler. Under normal soldering conditions (no vacuum), the temperature should not exceed 800°C. The material's structure can be altered if the temperature is too high, resulting in internal or external leakage at the connection. It is therefore recommended that all soldering uses silver solder containing at least 45% silver. This type of solder has a relatively low soldering temperature and high moistening and fluidity properties.
When soldering flux is used to remove oxides from the metal surface, this property makes the flux potentially very aggressive. Consequently, it is very important to use the correct amount of soldering flux, because too much may lead to severe corrosion. No flux should be allowed to enter the BPHE.
It is important to degrease and polish the surfaces when soldering. Apply chloride flux with a brush. Insert the copper tube into the connection and braze with minimum 45% silver solder. Point the flame towards the piping and braze at max. 650°C. Avoid internal oxidation, e.g. by protecting the inside of the refrigerant side with nitrogen gas (N2).
Welding is recommended only on specially designed welding connections (see Figure 8.14). All SWEP's welding connections are made with a 30° chamfer on top of the connection. Do not weld pipes on other types of connections. The measurement in mm corresponds to the external diameter of the connection.
During the welding procedure, protect the unit from excessive heating by:
a.using a wet cloth around the connection.
b.making a chamfer on the joining tube and connection edges.
Use TIG or MIG/MAG welding. When using electric welding circuits, connect the ground terminal to the joining tube, not to the back of the plate package (see Figure 8.15). Internal oxidation can be reduced by using a small nitrogen flow.
If any of the media contain particles larger than 1 mm, a strainer (see Figure 8.16) with a size of 16-20 mesh (number of openings per inch) should be installed before the exchanger. The particles could otherwise block the channels, causing low performance, increased pressure drop and risk of freezing. Some strainers can be ordered as BPHE accessories.
BPHE insulation (see Figure 8.17) is recommended for evaporators, condensers and district heating applications, etc. For refrigeration, use extruded insulation sheets, e.g. Armaflex or equivalent, which can also be supplied by SWEP.
Normally, the circuit with the higher temperature and/or pressure should be connected on the left side of the heat exchanger when the arrow is pointing upwards. For example, in a typical water-to-water application, the two fluids are connected in a counter-current flow, i.e. the hot water inlet in connection F1 and its outlet in F3, and the cold water inlet inconnection F4 and its outlet in F2 (see Figure 8.18). This is because the right-hand side of the heat exchanger contains one more channel than the left-hand side, and the hot medium is thus surrounded by the cold medium to prevent heat loss.
In single-phase applications, e.g. water-to-water or water-to-oil, the mounting orientation has little or no effect on the performance of the heat exchanger. This means that it is possible to mount the unit horizontally, on its side or back, without affecting performance. However, make sure that no air is trapped inside the heat exchanger when it is on its side.
Evaporators; V-type BPHEs
In all refrigerant applications, it is very important that every refrigerant channel is surrounded by a secondary fluid channel on both sides. Normally, the refrigerant side must be connected to the left-hand side and the secondary fluid circuit to the right-hand side of the BPHE (see Figure 8.19).
If the refrigerant and secondary fluid connections are transposed, the evaporation temperature will fall, with the risk of freezing and very low performance. SWEP BPHEs used as condensers or evaporators should always be fitted with adequate connections on the refrigerant side.
V-type BPHEs are equipped with a special distribution device at the refrigerant inlet, i.e. normally port F3. The purpose of the distribution device is to distribute the refrigerant evenly in the channels.
The refrigerant liquid should be connected to the lower left connection (F3) and the refrigerant gas outlet to the upper left connection (F1). The secondary fluid circuit inlet should be connected to the upper right connection (F2) and the outlet to the lower right connection (F4).
In two-phase applications such as evaporators, the orientation of the heat exchanger becomes very important. For evaporators, SWEP's BPHEs should be mounted vertically, with the arrow on the front plate pointing upwards.
Although evaporators normally have the refrigerant inlet in the bottom, it is possible to evaporate downwards. This means that refrigerant will enter the evaporator in connection F1 and gas will leave the evaporator from connection F3. In these circumstances, performance will be reduced. Ensure that no refrigerant liquid enters the compressor. This installation may also lead to control problems.
For DX-evaporators, counter-current flow is the normal flow arrangement because it results in the highest MTD. For flooded evaporators, cocurrent flow is a common flow arrangement because a high inlet temperature difference is needed to initiate the evaporation process.
In cases of very high outlet port velocity, double outlet connections may be needed. This will decrease the velocity and pressure drop in the outlet port and thus increase the performance of the evaporators.
In the case of parallel installed evaporators with one compressor, it is important to make sure that the pressure drops in the suction lines are the same. This is to minimize maldistribution and prevent poor performance.
For evaporators, it is practical to measure the water temperature inside the heat exchanger. This can be achieved by equipping the evaporator with sensor connections on the back of the evaporator (P2/P4). The sensor connections are internally threaded where a temperature sensor can be attached. It is important here to ensure that the sensor is long enough to reach at least the middle of the port.
As with evaporators, the orientation of the heat exchanger is also very important for condensers. For condensers, SWEP's BPHEs should be mounted vertically, with the arrow on the front plate pointing upwards.
In a SWEP condenser, the refrigerant gas should be connected to the upper left connection, F1, and the condensate to the lower left connection, F3 (see Figure 8.20). The secondary fluid circuit inlet should be connected to the lower right connection, F4, and the outlet to the upper right connection, F2.
Counter-current flow is the normal flow arrangement, resulting in the highest MTD. Condensers can be tilted with some performance loss. The condenser is normally less sensitive to tilting compared with evaporators, for which the performance losses are significant.