Thermocompressor
Navigation: Main Page > Models > Energy Transfer Models
The Thermocompressor model is only available in SysCAD 9.3 Build 137
Contents
General Description
A Thermocompressor is a form of steam ejector in which a flow of higher pressure primary steam is used to entrain lower pressure secondary steam. The discharge stream is at an intermediate pressure between the high and low pressure steam flows. This potentially enables recovery of some of the energy in the low grade steam.
The Thermocompressor model in SysCAD is based on data sheets from the Shutte and Koerting company.
Diagram
The diagram shows the default drawing of the Thermocompressor, with the required connecting streams. The unit will not operate unless ALL of the above streams are connected.
The physical location of the connections is not important, the user may connect the streams to any position on the drawing.
Inputs and Outputs
Label  Required /Optional 
Input /Output 
No. of Connections  Description  
Min  Max  
Primary In  Required  Input  1  1  The High Pressure steam feed to the unit. 
Secondary In  Required  Input  1  1  The Low Pressure steam feed to the unit. 
Discharge  Required  Output  1  1  The discharge from the unit. This contains the steam at the Intermediate pressure. 
Behaviour when Model is OFF
If the user disables the unit, by unticking the On tick box, then the following actions occur:
 If the unit is set up in 'Demand' mode, then the demand for the high pressure steam will be set to 0;
 Otherwise, the unit will perform all calculations on the high and low pressure steams and produce an intermediate pressure steam product.
So basically, turning the unit 'Off' only has an effect if the high pressure steam is in 'Demand' mode.
Model Theory
The options for predicting the behaviour of a Thermocompressor are:
 Simple heat balance model with empirical corrections derived from the data; or
 A simple 1 dimensional model with fitted parameters from manufacturers data.
A large database, extracted from data curves produced by the Shutte and Koerting company, was used to fit a heat balance model and a simple 1D model.
Key Performance Parameters
P_{p}  Primary (motive) Pressure
P_{s}  Secondary (suction) Pressure
P_{c}  Discharge Pressure
[math]\mathbf{\mathit{\omega}}[/math]  Entrainment ratio = Mass of Secondary Steam/Mass of Primary Steam
Er  Expansion ratio = Primary Steam Pressure/Secondary Steam Pressure
Cr  Compression ratio = Discharge Pressure/Secondary Steam Pressure
Energy Balance Mode
The Energy Balance mode assumes that the flow through the Thermocompressor is adiabatic.
In this mode the user chooses the efficiency of the Thermocompressor and the enthalpy of the product steam is calculated using the following equation:
[math] \mathbf{\mathrm{h_c = h_s+\frac{\eta(h_ph_s)}{1+\omega}}}[/math]
where:
 h_{c}  Product steam Enthalpy
 h_{p}  Primary (HP) steam Enthalpy
 h_{s}  Secondary (LP) steam Enthalpy
 [math]\eta[/math]  Thermocompressor Efficiency
Assuming that the product steam is saturated, then the discharge pressure, P_{c}, can be calculated.
The entrainment ratio may also be selected if the user enables the Demand functionality for the Primary (HP) steam.
1D Model based on S&K Data
This model is based on the one dimensional analysis which:
 Is based on Shutte & Koerting data curves;
 Does not depend on any explicit assumptions about the dimensions and the internal geometry of the thermocompressor;
 Requires at the most 1 user specified parameter  The entrainment ratio, which may be selected if the user enables the Demand functionality for the Primary (HP) steam.
Assumptions, Limitations and comments
 The secondary pressure is always less than the primary pressure.
 The discharge pressure is always saturated and is less than the primary pressure and greater than the secondary pressure.
 There is an envelope of pressures and flow rates within which the device operates.
 The Entrainment ratio is restricted to between 10 and 400%.
References
 WeiXiong Chen, Ming Liu, DaoTong Chong, JunJie Yan, Adrienne Blair Little, Yann Bartosiewicz. A 1D model to predict ejector performance at critical and subcritical operational regimes. International Journal of Refrigeration 36 (2013) 17501761.
 Shutte & Koerting. Performance Data on Jet Compressors. Bulletin 4F Supp.
 Hisham ElDessouky, Hisham Ettouney, Imad Alatiqi, Ghada AlNuwaibit. Evaluation of Steam Ejectors. Chemical Engineering and Processing (2002) 551561.
 Yveline Marnier Antonio, Christelle Périlhon, Georges Descombes, Claude Chacoux. Thermodynamic Modelling of an Ejector with Compressible Flow by a One Dimensional Approach. Entropy 2012, 14, 599613.
Data Sections
The default access window consists of several sections:
 Thermocompressor tab  contains the main configuration information relating to the unit.
 Info tab  contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
 Links tab, contains a summary table for all the input and output streams.
 Audit tab  contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.
Thermocompressor Page
Class: Thermocompressor  The first tab page in the access window will have this name.
Tag (Long/short) 
Input / Calc 
Description/Calculated Variables / Options 
Requirements  
On  Tick Box  This is used to enable or disable the unit. If the unit is disabled and the unit is configured to act in 'Demand' mode, then the Primary Steam flow to the unit will be set at the minimum flow. 
Method  Energy Balance  User specifies desired efficiency and model calculates outlet pressure of Low Pressure stream. 
1D Model  S&K Data  User specifies desired outlet pressure of Low Pressure stream and model calculates efficiency.  
EfficiencyReqd / EffReqd  Input  Only visible if Method = Energy Balance. The user specifies the required efficiency of energy transfer from the High Pressure steam to the product steam. 
Entrainment.Method  User Value  The user specifies the desired entrainment ratio of High pressure to Low Pressure steam. The High pressure steam MUST be set as a 'Demand' connection, i.e. the Thermocompressor will calculate the required amount of High pressure steam = Low Pressure Steam/Entrainment Ratio and send this value to the High pressure steam connection. 
Calculated  The model will calculate the entrainment ratio of High pressure to Low pressure steam. In this case the flow of High pressure steam is set elsewhere in the project.  
EntrainmentRatioReqd / EntRatio_Reqd  Input  Only visible if Entrainment.Method = User Value. The unit will then calculate the amount of Primary (HP) steam required to satisfy the user defined entrainment ratio: Primary Steam = Secondary (LP) steam / Entrainment Ratio. The allowable range for this variable is 10 to 400% (Shutte & Koerting range). 
Prm.DemandConnection  Stand Alone  No demand connection. The High Pressure steam flow is set externally to the model. 
General Demand  The High Pressure steam feed comes from (directly or indirectly) a Feeder with Demand.On selected. The demand logic will aim to match the High Pressure steam mass flowrate to the Thermocompressor requirements.  
Results  
EntrainmentRatio / EntRatio  Calc  This is the entrainment ratio of the LP steam with the HP steam, = LP steam mass/HP steam mass. If the HP steam is in 'Demand' mode, then this value should be equal to the Entrainment Ratio specified by the user. 
ExpansionRatio / ExpRatio  Calc  This is = HP steam pressure/LP steam pressure. 
CompressionRatio / CompRatio  Calc  This is = Discharge steam pressure/LP steam pressure. 
IdealWork  Calc  The maximum amount of work that the HP steam can produce, i.e. if Efficiency = 100%. 
ActualWork  Calc  The actual amount of work available from the HP steam. 
GridDisplay  Tick Box  This is a global selection, if this is selected, then where available, variables will display in a table format, if not selected, they will be listed in separate groups as a single list. 
Feed and Product Conditions  
The following values will be displayed for the Primary, Secondary and Discharge streams. If the 'GridDisplay'box is ticked, then they will be displayed in a grid, otherwise the variables for each stream will be displayed together in a group.  
Temperature / T  Calc  The Temperature of each stream. 
Pressure / P  Calc  The Pressure of each stream. 
MassFlow / Qm  Calc  The mass flowrate of each stream. 
VapourFraction / Vf  Calc  The Vapour fraction in each stream. 
Adding this Model to a Project
Insert into Configuration file
Sort either by DLL or Group.

DLL: 
HeatExchange.dll 
→ 
Units/Links 
→ 
Heat Transfer: Thermocompressor 
or 
Group: 
Energy Transfer 
→ 
Units/Links 
→ 
Heat Transfer: Thermocompressor 
See Project Configuration for more information on adding models to the configuration file.
Insert into Project

Insert Unit 
→ 
Heat Transfer 
→ 
Thermocompressor 
See Insert Unit for general information on inserting units.