When the vapor pressure drop is more than 20% of the inlet pressure this message is printed to bring to your attention that there is an unreasonable pressure decrease in the heat exchanger.Try to rerun using a heat exchanger and/or channel type that produces a lower pressure drop.
Temperature difference between evaporating side and secondary side is very high, causing a instable gaseous film form on heat exchanger area, denying admittance of more refrigerant. Design in this region is definitely not recommended since the heat transfer will fluctuate strongly. Formation and collapse of gaseous film will result in instable evaporation. Redesign with less temperature difference to reach nucleate (normal) boiling or increase temperature difference to reach the complete film boiling zone.
Temperature difference between evaporating side and secondary side is very high, causing a stable gaseous film form on heat exchanger area. The prediction when complete film boiling is a bit uncertain. If you have a possibility of adjusting the temperature difference so that the vaporization is taking place in the nucleate boiling region, you are recommended to do so. Complete film boiling is preferred before partial film boiling.
This message is printed when the estimated two-phase channel exit velocity is greater than 100 m/s and is a very strong signal indeed to rerun the case for a heat exchanger with larger port diameter to avoid the possibility of erosion of the plate. The channel velocity refers to the velocity on the edge of the plate in the very beginning of a channel.
A high volume flow through the exit port will induce high pressure drop. For evaporators this will increase the risk of maldistribution. Lower than predicted capacity is a possible result. Higher number of plates may not increase performance since maldistribution also will increase simultaneously. Redesign using a heat exchanger with larger port diameter. Alternatively, double gas exit pipes may be fitted, halving the port velocity.
Prediction always becomes less certain because of the sensitivity of many operating parameters in deep vacuum. Some data down to a pressure of 0.015 bar indicate that the program still gives good results at that level of vacuum. However, the majority of data on hand are for higher pressures.
This message is displayed to make the user aware of the fact that there is an additional pressure drop in the fluid distribution system. The two values are displayed as an approximate min and max value, depending on the dynamic operating conditions to facilitate selection of appropriate size of expansion valve. Please note that the pressure drop through the distribution device is before the heat transfer area and will therefore not affect the evaporation temperature. SWEP recommend that the pressure drop should be above 1 bar in order to get proper distribution. However the pressure drop is generally recommended to not exceed 1/3 of the total expansion pressure drop with thermostatic expansion valves and 1/2 with electronic expansion valves.
This message is displayed to make the user aware of the fact that there is an additional pressure drop in the fluid distribution system. The two values are displayed as an approximate min and max value, depending on the dynamic operating conditions to facilitate selection of appropriate size of expansion valve. Please note that the pressure drop through the distribution device is before the heat transfer area and will therefore not affect the evaporation temperature. SWEP recommend that the pressure drop should be above 1 bar, and generally not larger than 1/3 of the total expansion pressure drop.
When parallel units are required, care must be taken at installation, so that the flow rate distribution between the units becomes as equal as possible.
This message is printed if the predicted mal distribution is greater than 12.5% and is a strong indication that a reselection is needed. A maldistribution of e.g. 50 % means that some channels will have a flow rate of 1.5 times the average and other channels will have a flow rate of only 0.5 times the average. SSP design has taken in account for the reduced efficiency of maldistribution but operation with high mal distribution is not recommended due to risk of instable operation. Reselect a BPHE by adding/changing distribution device, using a plate with higher chevron angle or using a plate with larger refrigerant outlet port.
Though the calculation is theoretically correct, this message warns that the exchanger might be thermally too short to operate properly for the displayed temperature difference. For operation with very small temperature differences the performance is more sensitive to disturbances or local and/or fluctuating differences in heat transfer. Redesign using an BPHE with a higher NTU-value and/or increase temperature difference.
Though the calculation is theoretically correct, this message warns that there might be some droplets of liquid in the leaving gas, which might cause damage to the compressor.
This warning is shown when the calculated channel velocity is less than 0.3 m/s. The value is valid for normal chiller and heat pumps temperature cases. The oil droplets might not be transported out of the heat exchanger leading to reduced heat transfer due to oil film fouling. The problem increase for low temperature evaporators (<-20°C) due to the higher viscosity of the oil. Redesign with less number of plates or higher refrigerant flow. Installing the evaporator with downwards evaporation is a possible solution to enhance oil return but it might have a negative impact on evaporator performance.
Possible erosion in the connections and ports, due to high liquid flow Try to decrease mass flow and/or select BPHE with larger ports. NB! SSP indicates the PORT velocity, never the connection velocities.
A very high velocity in the refrigerant outlet port can lead to lower performance. One consequence is an unnecessary high pressure drop will decrease the saturation pressure at the compressor. Another consequence is the impact of refrigerants distribution, which is dependent on the ratio between port and channel pressure drop. Try to select a BPHE with larger outlet port or one with higher channel pressure drop. In general, it would not be beneficial to add plates due to increased port pressure drop.
This information appears when inlet vapor quality is set to zero. Thermosyphon is another word for flooded and indicate, as said, 100% liquid in the inlet but also less than 100% gas in the outlet. Normally outlet vapor quality is 70-90% depending on case. SWEP recommend to use a B- or DB-type as evaporator since distribution is a less problem in thermosyphon evaporators. Co current flow is preferred to get boiling process started. Another important matter it the need for low pressure drop (in total often less than 10-20kPa) on the refrigerants side since the flow is often only driven by density difference.
Evaporator performance is dependent of the distribution of refrigerant between the different channels. SWEP have seen that some BPHEs benefit greatly if having specially designed connections. SSP prediction is based on test with these connections and without them the performance can be expected to decline. SWEP standard options for these BPHEs therefore only contain these connections.
Evaporator performance is dependent of the distribution of refrigerant between the different channels. This can be improved by maintaining high enough pressure drop in the distribution device (V-ring or connection pipe). SWEP recommend a pressure drop of at least 1 bar in the distribution device. Try to select another BPHE, modify number of plates or perhaps the thermal or hydraulic requirements. If no possible solution please contact your SWEP sales representative.
High liquid flow rate might lead to erosion in the connections and ports. Try to decrease mass flow and/or select BPHE with larger ports. SSP indicates the port velocity, never the connection velocity. Connection velocity can calculated in the Connection impact tool. By using titanium plates and connections, a slightly higher velocity up to 6.5 m/s is possible.
The evaporation and condensation verification tests in the SWEP laboratory are for practical reason maximized in heat flux. This warning show that design is above these test points. Design may still be valid but check with SWEP sales representative for very high values, i.e. for evaporators and condensers above 20 kW/m2.
The reason for this warning is a too high port pressure drop in relation to channel pressure drop. This leads to channel mal distribution of secondary side. High pressure drop is often due to high flow rate in small ports. SWEP recommend to rerun the selection with a heat exchanger with larger port diameters and/or higher channel pressure drop (e.g. using a heat exchanger with higher chevron angle H>M>L).
Low refrigerant temperature and/or low secondary flow can result in low temperature areas of the heat transfer surface. This can result in freezing. SWEP recommend installing freeze protection to avoid such operating conditions. Measuring leaving secondary side temperature, saturation pressure and flow rate and using cutout values (when the units is shut down) for these parameters is important. Changing secondary fluid with lower freezing temperature is also an option. For further information contact your SWEP sales representative.
Due to increased risk of refrigerant maldistribution at high NoP, SWEP does not recommend to use B-type as evaporator with NoP above 30. Above NoP 40, it is strongly recommended not to use a B-type. Please try to select a V-type or other BPHE with distribution device. For thermosiphon system (flooded) a B-type can be used with high NoP due to less risk of maldistribution
D310 performance is achieved with specific inlet pipe (between expansion valve and evaporator). Pipe diameter should be as per product recommendation. Connection should be either a coned version in the same size as the inlet pipe or a solder 28U which is then reduced to recommended pipe. For more information, please contact your SWEP sales representative.
B3 has been tested as economizer at much higher heat flux range than normally done. The heat flux range correspond to performance level seen in VRF systems. SSP has been adjusted according to these tests. Selections outside this heat flux range could be less accurate. For more information, please contact your SWEP sales representative.
If the port pressure drop is high compared to channel pressure drop the secondary fluid tends to take the shorter path and go through the first channels in the plate pack. The result is a higher flow in the first channels and less flow in the last channels. The result is maldistribution of the secondary fluid, different thermal conditions in the BPHE and eventually a lower performance. This effect has been seen at a ratio: port pressure drop vs total pressure drop above 20%. Select a BPHE will larger port or with higher channel pressure drop.
When using small pipes from expansion device to BPHE tests have shown an improved performance if using a coned connection. This give a smoother transition between the small pipe and the larger BPHE port and helps to improve distribution.
The intention with this information message is to highlight that low SH is used. The calculation is theoretically correct even if SH is low, but operation at low SH might lead to droplets of refrigerant liquid in the leaving gas. Droplets entering the compressor might cause damage to the compressor. With proper control or with higher SH the risk of damaged compressor is smaller.
For this product it has been seen in tests that best performance is achieved when water connections are the opposite side from the refrigerant connections. The effect is higher at large plate packs. If using all connections on the same side, please contact SWEP for guidance.
At full load conditions SWEP do not recommend to design with a temperature approach (leaving water temperature – evaporation temperature) closer than 2.2K. Consider to modify the thermal case slightly or select another BPHE. For more information, please contact your SWEP sales representative.
This warning is shown if the temperature difference between the two fluids in the BPHE is low. The reason could be:
An example of an issue with very tight pinch is at instable operation where fluctuating SH directly will push down the evaporation temperature and thus lower the performance of the system. Try modifying the thermal case to avoid the pinch. This will minimize uncertainty and unnecessarily large heat transfer area.
SWEP have noticed in tests that it is beneficial to use two refrigerant inlets for this BPHE. Thus both using F3 and P3 as inlet connections. This will improve refrigerant distribution and performance.