# StaticDrum


## Copyright © EDF 2002 - 2026   
## ThermoSysPro Version 4.2  
This component model is documented in Sect. 14.6 of the ThermoSysPro book.   
# Static drum   

The static drum is a reservoir at the top end of the boiler. It separates water from steam in the mixture generated in the boiler and stores them.  
This component can also be used as a simple steam generator.  

The static drum is modeled according to the following assumptions:  
- heat exchanges between the liquid and steam phases, as well as between drum and external medium, are negligible,  
- pressure losses are negligible,  
- water is always saturated.  



## Modelica component model  

The equations mentioned below are implemented in the component *StaticDrum*, located in the *WaterSteam.Junctions* sub-library.   
This component has 9 connectors:  
- Ce_eva: saturated water inlet from the evaporator,  
- Cs_eva: saturated water outlet toward the evaporator,  
- Ce_sup: supplementary water inlet,  
- Cs_sup: supplementary water outlet,  
- Ce_eco:  water inlet from a money saver,  
- Ce_steam: steam inlet,  
- Cs_sur: saturated steam outlet toward the overheater,  
- Cs_purg: saturated water outlet toward the drain,  
- Cth: thermal port.  
   
![ThermoSysPro.WaterSteam.Junctions.StaticDrum.svg](./icons/ThermoSysPro.WaterSteam.Junctions.StaticDrum.svg)  

## Nomenclature  

| Symbol| Description| Unit| Definition | Modelica name |  
| :--------------------------------------- | :---------------------------------------------------------------------------------------- | :--------------------------- | :---------------------- | :----------- |  
| $h_{\text {eco, } i}$| Specific enthalpy of the liquid at the inlet of the drum, coming from the economizer| $\mathrm{J} / \mathrm{kg}$ || Ce_eco.h |  
| $h_{\text {eva }, \mathrm{i}}$| Specific enthalpy of the fluid at the inlet of the drum, coming from the evaporator| $\mathrm{J} / \mathrm{kg}$ || Ce_eva.h |  
| $h_{\text {steam }, \mathrm{i}}$| Specific enthalpy of the steam at the inlet| $\mathrm{J} / \mathrm{kg}$ || Ce_steam.h |  
| $h_{\text {sup }, \mathrm{i}}$| Specific enthalpy of the fluid at the additional inlet| $\mathrm{J} / \mathrm{kg}$ || Ce_sup.h |  
| $h_{\text {drain,o }}$| Specific enthalpy of the liquid at the outlet, going to the drain| $\mathrm{J} / \mathrm{kg}$ || Cs_purg.h |  
| $h_{\mathrm{eva}, \mathrm{o}}$| Specific enthalpy of the fluid at the outlet, going to the evaporator| $\mathrm{J} / \mathrm{kg}$ || Cs_eva.h |  
| $h_{\mathrm{sup}, \mathrm{o}}$| Specific enthalpy of the liquid at the additional outlet| $\mathrm{J} / \mathrm{kg}$ || Cs_sup.h |  
| $h_{\mathrm{sur}, \mathrm{o}}$| Specific enthalpy of the steam at the outlet, going to the super-heater| $\mathrm{J} / \mathrm{kg}$ || Cs_sur.h |  
| $\dot{m}_{\text {drain }, \mathrm{o}}$ | Mass flow rate of the liquid at the outlet, going to the drain| $\mathrm{kg} / \mathrm{s}$ || Cs_purg.Q |  
| $\dot{m}_{\mathrm{eco}, \mathrm{i}}$| Mass flow rate of the fluid at the inlet, coming from the economizer| $\mathrm{kg} / \mathrm{s}$ || Ce_eco.Q |  
| $\dot{m}_{\text {eva }, \mathrm{i}}$| Mass flow rate of the fluid at the inlet, coming from the evaporator| $\mathrm{kg} / \mathrm{s}$ || Ce_eva.Q |  
| $\dot{m}_{\mathrm{eva}, \mathrm{o}}$| Mass flow rate of the liquid at the outlet, going to the evaporator| $\mathrm{kg} / \mathrm{s}$ || Cs_eva.Q |  
| $\dot{m}_{\text {steam, } \mathrm{i}}$ | Mass flow rate of the steam at the inlet| $\mathrm{kg} / \mathrm{s}$ || Ce_steam.Q |  
| $\dot{m}_{\mathrm{sup}, \mathrm{i}}$| Mass flow rate of the fluid at the additional inlet| $\mathrm{kg} / \mathrm{s}$ || Ce_sup.Q |  
| $\dot{m}_{\mathrm{sup}, \mathrm{o}}$| Mass flow rate of the liquid at the additional outlet| $\mathrm{kg} / \mathrm{s}$ || Cs_sup.Q |  
| $m_{\mathrm{sur}, \mathrm{o}}$| Mass flow rate of the steam at the outlet, going to the super-heater| $\mathrm{kg} / \mathrm{s}$ || Cs_sur.Q |  
| $W$| Thermal power exchanged from the heat source to the fluid| $\mathrm{W}$|| Cth.W |  
| $x$| Steam mass fraction at the outlet going to the super-heater \(steam separation efficiency\) | $-$|| x |  


## Governing equations  

### Static mass balance equation  


    
    

- Validity domain:   
   
 $\forall \dot{m}$  

- Mathematical formulation:   
   
$$ 0 =\dot{m}_{\mathrm{eco}, \mathrm{i}}+\dot{m}_{\mathrm{eva}, \mathrm{i}} +\dot{m}_{\mathrm{sup}, \mathrm{i}}+\dot{m}_{\text {steam, }} -   
\dot{m}_{\text {drain }, \mathrm{o}}-\dot{m}_{\mathrm{eva}, \mathrm{o}}-\dot{m}_{\mathrm{sup}, \mathrm{o}}-\dot{m}_{\mathrm{sur}, \mathrm{o}} $$  

- Comments:   
   



### Static energy balance equation  


    
    

- Validity domain:   
   
 $\exists \dot{m}$ such that $\dot{m} 
\neq 0$  

- Mathematical formulation:   

$$   0=\dot{m}_{\text{eco }, \mathrm{i}} \cdot h_{\mathrm{eco}, \mathrm{i}}+\dot{m}_{\mathrm{eva}, \mathrm{i}} \cdot h_{\mathrm{eva}, \mathrm{i}}+\dot{m}_{\mathrm{sup}, \mathrm{i}} \cdot h_{\text{sup }, \mathrm{i}}\    \quad +\dot{m}_{\text{steam,i }} \cdot h_{\text{steam,i }}-\dot{m}_{\text{drain,o }} \cdot h_{\text{drain,o }}-\dot{m}_{\mathrm{eva}, \mathrm{o}} \cdot h_{\mathrm{eva}, \mathrm{o}}\    \quad -\dot{m}_{\mathrm{sup}, \mathrm{o}} \cdot h_{\mathrm{sup}, \mathrm{o}}-\dot{m}_{\mathrm{sur}, \mathrm{o}} \cdot h_{\mathrm{sur}, \mathrm{o}}+W$$  

- Comments:   
   
 This equation is valid if some mass flow rates are non-zero. Otherwise, the mixing specific enthalpy is undefined.  


### Specific enthalpy at the drum liquid outlets  


    
    

- Validity domain:   
   
 $\exists \dot{m}$ such that $\dot{m} 
\neq 0$  

- Mathematical formulation:   
   
 $$h_{\mathrm{eva}, \mathrm{o}}=h_{\mathrm{sup}, \mathrm{o}}=h_{\text {drain }, \mathrm{o}}=h_{l}^{\mathrm{sat}}$$   

- Comments:   
   
 The liquid inside the drum is assumed always at saturation.  


### Specific enthalpy at the drum vapor outlet  


    
    

- Validity domain:   
   
 $\exists \dot{m}$ such that $\dot{m} 
\neq 0$ and $x \approx 1$  

- Mathematical formulation:   
   
 $$h_{\mathrm{sur}, \mathrm{o}}=(1-x) \cdot h_{l}^{\mathrm{sat}}+x \cdot h_{\mathrm{v}}^{\mathrm{sat}}$$  

- Comments:   
   
 The vapor inside the drum is assumed always at saturation with possibly small amounts of water.  

## References   
   
El Hefni, Baligh and Bouskela, Daniel (2019). [Modeling and Simulation of Thermal Power Plants with ThermoSysPro](https://link.springer.com/book/10.1007/978-3-030-05105-1), sect. 14.6. Springer Nature Switzerland AG.