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Table of Contents Table of Contents .................................................................................................. 1

Explanations to Information and Warnings in SSP G7 ......................................... 2 Single phase .......................................................................................................... 2

Port velocity on primary side is high (XXX) ......................................................... 2 Min wall temperature on primary/secondary side is below the freezing point (XXX) ................................................................................................................. 2

Condenser ............................................................................................................. 2 Pressure drop in condenser is XXX % of inlet pressure ...................................... 2 Double vapor inlet connections .......................................................................... 2 Inlet port velocity on primary side is high (XXX m/s > 100 m/s) .......................... 2 Port velocity on secondary side is high (XXX > 5.5 m/s) ..................................... 2 Inlet channel velocity on primary/secondary side is high (XXX m/s > 100 m/s) ... 2 Inlet port recovery unreasonably high. Design questionable ............................... 2 Maldistribution on secondary side may reduce HTC more than 5 % ................... 3 Very high heat flux not experimentally certified (XXX kW/m²) ............................. 3 Pressure drop for full gas flow: XXX kPa ............................................................ 3

Evaporator ............................................................................................................. 3 The vapor pressure drop is XXX ........................................................................ 3 Partial film boiling in the two-phase zone ............................................................ 3 Complete film boiling in the two-phase zone ...................................................... 3 Exit channel velocity primary side XXX > 100 m/s .............................................. 3 High exit port pressure drop, greater than 30% of total pressure drop ................ 4 Low vaporization pressure, less than 0.015 bar .................................................. 4 Pressure drop in V-ring is X.X - Y.Y bar ............................................................. 4 The distribution must be perfect between parallel units ...................................... 4 The vaporization side maldistribution is XX % .................................................... 4 Too small temperature difference might cause underperformance ..................... 4 Superheat less than 5 K might cause underperformance. .................................. 4 Vapor velocity probably too low to carry oil ......................................................... 5 Port velocity on primary/secondary side > XXX .................................................. 5

Manual to create user defined fluid file in SSP G7 ................................................ 6 Connection Impact tool......................................................................................... 11

Introduction .......................................................................................................... 11 Functionality ........................................................................................................ 11

Selecting the connections ................................................................................ 11 Pressure drop calculation ................................................................................. 12 Print out function .............................................................................................. 13

Results ................................................................................................................ 13 Recommendations ........................................................................................... 13

Evaporator calculations........................................................................................ 15 Flow Patterns ................................................................................................... 15 Inlet and outlet connection recommendations for evaporators .......................... 16

Pressure Drop Tool - Help document .................................................................. 17 Two Stage system design in SSP ........................................................................ 21 Support .................................................................................................................. 22


Explanations to Information and Warnings in SSP G7

Single phase

Port velocity on primary side is high (XXX)

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. If you are using titanium plates and connections, you can tolerate a slightly higher velocity up to 6.5 m/s.

Min wall temperature on primary/secondary side is below the freezing point (XXX)

The minimum wall temperature is below the freezing point of the specific fluid. Design during these conditions is not recommended.

Condenser

Pressure drop in condenser is XXX % of inlet pressure

The pressure drop through the condenser is not negligible in relation to the total pressure. The relatively high pressure drop may affect the condenser performance negatively.

Double vapor inlet connections

This message just points out that the calculation was performed using the double vapor connection option set, i.e. with two vapor inlet connections.

Inlet port velocity on primary side is high (XXX m/s > 100 m/s)

This message is shown when the estimated two-phase channel inlet velocity is greater than 100 m/s and is a very strong signal indeed to rerun the case using 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.

Port velocity on secondary side is high (XXX > 5.5 m/s)

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.If you are using titanium plates and connections, you can tolerate a slightly higher velocity up to 6.5 m/s.

Inlet channel velocity on primary/secondary side is high (XXX m/s > 100 m/s)

This message is shown when the estimated two-phase channel inlet velocity is greater than 100 m/s and is a very strong signal indeed to rerun the case using a heat exchanger with larger port diameter to avoid the possibility of erosion of the plate.

Inlet port recovery unreasonably high. Design questionable

The pressure recovery in the inlet port is more than one third of the total pressure drop causing a pressure increase of more than 5 %. If this message is shown, it is


recommended that the case is rerun using a heat exchanger with larger port diameters.

Maldistribution on secondary side may reduce HTC more than 5 %

Channel mal distribution of secondary side (side 2) might reduce the heat transfer coefficient with more than 5 %. Warning comes for very high flows through the heat exchanger. Rerun with an exchanger having a higher NTU-value and/or larger port diameters.

Very high heat flux not experimentally certified (XXX kW/m²)

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.

Pressure drop for full gas flow: XXX kPa

When you run the program using the heat recovery option, this message displays the total pressure drop in the heat exchanger if the gas of inlet conditions was flowing alone without condensation, i.e. if secondary side is inactivated.

Evaporator

The vapor pressure drop is XXX

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.

Partial film boiling in the two-phase zone

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.

Complete film boiling in the two-phase 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.

Exit channel velocity primary side XXX > 100 m/s

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.


High exit port pressure drop, greater than 30% of total pressure drop

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.

Low vaporization pressure, less than 0.015 bar

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.

Pressure drop in V-ring is X.X - Y.Y bar

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 max and min 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.

The distribution must be perfect between parallel units

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.

The vaporization side maldistribution is XX %

This message is printed if the predicted mal distribution is greater than 12.5 %. A maldistribution of 50 % means that the channel closest to the inlet will have a flow rate of 1.5 times the average and the channel at the other end will have a flow rate of only 0.5 times the average. SSP design have taken in account for the reduced efficiency of maldistribution but operation with high mal distribution effects is not recommended due to risk of instable operation. Redesign using an BPHE with a higher NTU-value and/or port hole diameters or use a BPHE with a distribution device.

Too small temperature difference might cause underperformance

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.

Superheat less than 5 K might cause underperformance.

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.


Vapor velocity probably too low to carry oil

When the channel velocity becomes less than 0.3 m/s SSP show this warning. The oil droplets may not be transported out of the heat exchanger leading to reduced heat transfer due to oil film fouling. Problem increase for low temperature evaporators (<-20°C) due to the high viscosity of the oil. Redesign with less number of plates or higher refrigerant flow. Downwards evaporation is also a possible solution.

Port velocity on primary/secondary side > XXX

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.


Manual to create user defined fluid file in SSP G7 Open the Fluid Editor that is found under the tools menu.

The Fluid Editor window will appear. I. Start by filling out the blank boxes in the top of the window as below

1. Fluid name: Choose a proper name for the fluid, it could be explanatory, such as “Methane gas 22bar”

2. Reference: Write which source the thermal data is coming from, e.g. internet, customer or other source

3. Approved by: Write your own name as reference

4. Choose if this is a single phase fluid (no phase change) or a two phase fluid that will evaporate or condense

II. Fill out the thermal data for your fluid. The data can be written manually in each box, but you can also copy and paste an entire table from e.g. excel. Make sure that you put in data with the correct units!

1

2

3

4


You can put in as many values as you want, recommended is to put in values for at least 3 temperatures. Remember that the more values you put in, the more accurate the simulation will be! If you press Plot Data, you are able to see the curve fit that SSP has made for your input data.


III. Save and start using the fluid file:

1. Press Save

Choose your preferred folder to save the file. The file name will automatically be the same as the fluid name that you gave as input.


2. Press Export fluid to SSP


3. Close the fluid editor and open a new calculation, the fluid that you created is now available under My Fluids:


Connection Impact tool

Introduction Connection impact tool is a new tool introduced in SSP G7 that will allow users to check the effect of different connections in different ports of the selected BPHE. It will allow choosing connections available as art no. Connection impact provides fluid speed and pressure drop in the interface between BPHE and connection, incorporates these values to the BPHE total pressure drop. It also guides and warns on the correct connection selection.

Functionality

Selecting the connections

Once a user have calculated and selected a BPHE it is possible to click the connection impact icon in the tool bar as per picture 1.

Picture 1 Connection impact tool icon

In the connection impact tool it is possible to specify:

1.- Connection material 2.- Pressure range 3.- Port configuration 4.- NND size for each port 5.- Connection for each port

See picture 2 for further reference. Drop down menus 1 to 3 act as filters that will display only the connections for art no for the selected BPHE. If a connection is not shown, please make sure that connection material and pressure drop down menus are set to all, so that all available connections are shown. It´s possible to increase the window size in order to see the article number if they aren´t visible using the original size.


Picture 2. Drop down menus

Pressure drop calculation

Pressure drop in the connection is calculated as a sudden expansion/contraction pressure drop calculation. Inlet connections Inlet connections pressure drop is calculated as sudden expansion pressure drop equation:

Outlet connections Outlet connections pressure drop is calculated as sudden contraction pressure drop equations:

1 2 3

4

5


Print out function

When clicking print out button, the user will obtain a word document with all the BPHE data for the calculation case, same function as print button in SSP main interface. The difference is that the “pressure drop – total” now include the connection pressure drop.

Picture 3 Print out function

Results

Recommendations

Velocity limits for single phase fluids: Connection velocity is limited due to pressure drop issues. When the pressure drop increases, the pump power increases for a given water flow. The velocity limit in the connection is different from the velocity limit in the plates and ports. This velocity limit is considered in normal SSP calculations, where warnings are given on excessive velocity in ports and/or channels, which may cause erosion in the BPHE. For liquids, velocity limit in ports and plates is set to 5,5m/s.

iV


For gases, velocity limit in ports and plates is set to 100m/s For steam applications velocity in ports and plates is set as per graph below:

Picture 4 Velocity vs Temperature of saturation

Velocity limits for evaporators The size of the inlet connection should correspond to a velocity between 10 and 25 m/s in order to ensure a good distribution of the fluid, see “Flow patterns” below. Connection outlet velocity should be higher than 5m/s to avoid oil retention in the evaporator. It should be below 25 m/s to avoid maldistribution and instable evaporation.

It is possible to use double outlet connections when velocity is over 25m/s. Velocity limits for condensers Condenser inlet velocity should be 5 – 25 m/sec to ensure good distribution and condenser performance. For condenser outlet the recommendation is 1 – 10 m/sec to ensure good condensate control.


Evaporator calculations Picture 3 is representative for selections of connections for an evaporator. This and below is also valid for selections for dual evaporators and cascade units. Once the connection is selected, the tool provides the user with pressure drop and velocity values in the connection. (red circle). It also provides with some messages in the bottom part (blue circle) There are three types of messages:

Error messages: Critical message that indicate an improper selection of a connection Warning messages: Important message that indicate information the user

should be aware of. Information: It mentions interesting information about the calculation.

Finally, the graph below the BPHE (green circle), shows the impact of the choice of connection on the flow pattern at the BPHE inlet. In order to reach a good refrigerant distribution it´s important to achieve appropriate conditions such as suitable flow pattern. This graph is just shown for evaporator calculations.

Picture 5 Connection impact values

Flow Patterns

The homogeneous flow patterns (Bubble and Froth) flow are desired flow patterns at the inlet of the evaporator. Annular, annular-slug or even wavy-stratified is not recommended since this increase the risk of maldistribution. Bubble and froth can be obtained by choosing the correct inlet connection.


Picture 6 Mist flow (left) with a good mixture. Stratified flow (right) with separated gas and

liquid

The flow pattern that provides the best distribution is the mist fluid regime. Mist regime cannot be achieved in BPHEs. The second best distribution is achieved in the froth or bubble flow regime, which can be obtained in BPHEs according to above. By increasing the dimension of the connection, we move vertically upwards in the graph. By increasing the X inlet value, we move horizontally to the left in the graph, see figure 7 below.

Figure 7 How to change flow regime. Froth and bubble is recommended

Inlet and outlet connection recommendations for evaporators

In addition to velocity and flow pattern the connection and pipes should be selected to fit port size. This is important to avoid extra pressure drop (if the diameter changes several times) and to avoid regions where liquid refrigerant can be stagnant.

Figure 8 Pipe and connections setup (inlet on the left and outlet on the right)

Possible by changing the connection diameter

Possible only by changing the inlet vapor quality

Aimed area


Pressure Drop Tool - Help document

Heat exchanger

- Select the heat exchanger

- You may choose the heat exchanger by clicking on the drop down.

- Only one heat exchanger can be selected at a time.

Number of Passes

- Set the required number of passes. - By default the no. of passes is set to 1. - The maximum allowed number of passes is 6. -

Number of Channels

- Used to set the no. of channels. - By default the no. of channels is set to 10. - The minimum allowed number of channels is 1 and the maximum is 999.

Fluid Name

- Choose the required fluid from the dropdown. Only one fluid can be selected at a time.

Reference Temperature

- Set the reference temperature. - By default the temperature is set to 25.


- The reference temperature value should be between 0 to 250°C (32 to 482°F).

Specific pressure drop calculation

If you want to know the flow rate for a specific pressure drop or vice versa, use this feature .Just fill in one of the values and get the corresponding value in other textbox. Range of pressure drop calculation

- Press 'Calculate range' and the flow rate will be calculated for the given range and vice versa. The range is editable.

- By selecting a column in the grid either pressuredrop or flow the grid column will be grayed, which will be considered as the input for calculation.

- On every cell to be considered for the calculation the entered values in the grid should be committed by clicking Enter/moving to another cell.

Export list to Excel It is possible to export the calculated list into MS Excel. Mark the list and copy ('Ctrl' and 'c') and paste ('Ctrl' and 'v') when you moved to Excel work sheet. Copy

To copy the content in the list i.e. the range of pressuredrop and flow. Copy the list and paste it in MS Excel sheet or notepad. We can copy the values from excel sheet to the list even. Paste

Paste the values into the grid


Print

To get the printout of the calculated range in the list and the graph displayed. Graph [pressure v/s flow]

It is an add on feature available in Pressuredrop, based on the calculation range displayed in the list, a graph is plot between the pressuredrop and flow rate and is displayed on the right side of the form. The graph can be plot between Pressuredrop v/s flow and flow v/s pressuredrop by choosing it from the dropdown provided there. Unit conversion The units of pressuredrop and flow can be changed in the grid by changing the units in the Pressuredrop textbox and flow textbox respectively. The same units will be displayed in the graph. Restore Grid:

Reset the grid and the graph to default values. Copy Graph:

Copies the generated graph to the clipboard. Save As:

To save the generated graph Print:


To print the graph. Restore Graph:

Restores the graph to its original state.


Two Stage system design in SSP

Calculation steps: 1. Specify fluids used if other than water

2. Specify Radiator working conditions (Temperatures and Pressure drops: Winter case) 3. Specify Two Stage working conditions (Temperatures: Summer case; Pressure drops: Winter case) 4. If the Radiator and Two stage are coupled, select “Include flow from radiator” (*)

5. To enable flow optimization of the primary return from the Radiator needed to calculate the actual district return and tap water outlet temperatures , select “Auto Performance” (**). Performance mode works in a similar manner as Auto Performance for a given design.

*

**

Radiator Two Stage – Stage 2 or After Stage

Two Stage – Stage 1 or Pre Stage

Two Stage system: Radiator and Two Stage

Two Stage

single unit


Support For general questions regarding calculations and products please contact your SWEP sales contact. Please report technical issues and bugs to [email protected], in English only.

mailto:[email protected]

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