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en:grundlagenhandbuch:drehmoment_und_antriebsleistung [2026/05/24 17:58] – [Power model for a melt extruder with several polymers] neelesten:grundlagenhandbuch:drehmoment_und_antriebsleistung [2026/06/16 11:11] (aktuell) – [Enthalpy model with heat flow] neelest
Zeile 48: Zeile 48:
 The estimation of the power consumption must differ in the 3 function sections in the figure on the barrel wall and in the melting section. The estimation of the power consumption must differ in the 3 function sections in the figure on the barrel wall and in the melting section.
  
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 **Figure:** Model for the power calculation. **Figure:** Model for the power calculation.
Zeile 124: Zeile 124:
 The starting point for the energetic examination is an energy balance at an extruder (see figure). The starting point for the energetic examination is an energy balance at an extruder (see figure).
  
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 **Figure:** Energy balance at a co-rotating twin screw extruder. **Figure:** Energy balance at a co-rotating twin screw extruder.
Zeile 136: Zeile 136:
 $$P = P_{Diss} + P_{Vol} = P_{Diss} + \Delta p \cdot \dot{V} \tag{24}$$ $$P = P_{Diss} + P_{Vol} = P_{Diss} + \Delta p \cdot \dot{V} \tag{24}$$
  
-{{ :en:grundlagenhandbuch:drehmoment_und_antriebsleistung:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_003.png?nolink |}}+{{ :en:grundlagenhandbuch:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_003.svg?nolink&600 |}}
  
 **Figure:** Power fractions in dependence on the dimensionless volume throughput. **Figure:** Power fractions in dependence on the dimensionless volume throughput.
Zeile 177: Zeile 177:
 The calculation is performed on the basis of the models introduced in chapter 3 of [[en:grundlagenhandbuch:drehmoment_und_antriebsleistung#references |[Kre04]]]. In the figure the variations predicted by means of the model are contrasted with the results of the flow simulation. A sufficient description of the volumetric strain energy can be recognized for the whole area. The calculation is performed on the basis of the models introduced in chapter 3 of [[en:grundlagenhandbuch:drehmoment_und_antriebsleistung#references |[Kre04]]]. In the figure the variations predicted by means of the model are contrasted with the results of the flow simulation. A sufficient description of the volumetric strain energy can be recognized for the whole area.
  
-{{ :en:grundlagenhandbuch:drehmoment_und_antriebsleistung:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_004.png?nolink |}}+{{ :en:grundlagenhandbuch:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_004.svg?nolink&600 |}}
  
 **Figure:** Dimensionless pumping capacity in dependence of the dimensionless volume throughput. **Figure:** Dimensionless pumping capacity in dependence of the dimensionless volume throughput.
Zeile 220: Zeile 220:
 The figure displays the comparative relation of the dissipated energies calculated with the Polyflow and the model predictions for a twin screw channel. The figure displays the comparative relation of the dissipated energies calculated with the Polyflow and the model predictions for a twin screw channel.
  
-{{ :en:grundlagenhandbuch:drehmoment_und_antriebsleistung:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_005.png?nolink |}}+{{ :en:grundlagenhandbuch:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_005.svg?nolink&600 |}}
  
 **Figure:** Comparison of the model predictions and the dissipated energies calculated with Polyflow for a twin screw channel. **Figure:** Comparison of the model predictions and the dissipated energies calculated with Polyflow for a twin screw channel.
Zeile 240: Zeile 240:
 For the verification of the model experiments were performed with a laboratory extruder. Silicon oil of the Baysilone 50.000 type was utilized as experimental medium. For the measurement of the power the drive unit of the extruder was suspended in an oscillating way and the section modulus was measured by means of a spring-balance, which was attached to a lever arm. Deriving from the measurement of the section modulus and the screw speed as well as the knowledge of the transmission gear ratio the drive power could thus be determined. The figure displays a comparison of the measured dimensionless drive power and the dimensionless drive power calculated with the model for closely intermeshing thread-mixing elements. The accordance is good, particularly by considering the simplifications made in the modeling. For the verification of the model experiments were performed with a laboratory extruder. Silicon oil of the Baysilone 50.000 type was utilized as experimental medium. For the measurement of the power the drive unit of the extruder was suspended in an oscillating way and the section modulus was measured by means of a spring-balance, which was attached to a lever arm. Deriving from the measurement of the section modulus and the screw speed as well as the knowledge of the transmission gear ratio the drive power could thus be determined. The figure displays a comparison of the measured dimensionless drive power and the dimensionless drive power calculated with the model for closely intermeshing thread-mixing elements. The accordance is good, particularly by considering the simplifications made in the modeling.
  
-{{ :en:grundlagenhandbuch:drehmoment_und_antriebsleistung:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_006.png?nolink |}}+{{ :en:grundlagenhandbuch:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_006.svg?nolink&600 |}}
  
 **Figure:** Comparison of the measured and the calculated dimensionless drive power for closely intermeshing thread-mixing elements. **Figure:** Comparison of the measured and the calculated dimensionless drive power for closely intermeshing thread-mixing elements.
Zeile 258: Zeile 258:
 $$P_{Diss.channel.tf} = f \cdot P_{Diss.channel.vf} \tag{37}$$ $$P_{Diss.channel.tf} = f \cdot P_{Diss.channel.vf} \tag{37}$$
  
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 **Figure:** Boundary conditions for the simplified simulation of a partly filled screw section. **Figure:** Boundary conditions for the simplified simulation of a partly filled screw section.
Zeile 264: Zeile 264:
 For the verification of this equation exemplary finite element simulations were performed with the boundary conditions as illustrated in the figure. The starting point of the simulations was a fully loaded rectangular channel with a ratio of channel height to channel width of b/h=40. For the exemplary simulations of party filled channels the depth of the reference channel is reduced. Additionally, the boundary conditions are then also changing for the simulation at the rear face of the flight, which represents the open area. In contrast to the reference computation at this area non-negligible velocities are defined; it is predetermined that at this area tangential forces do not emerge. In all cases the dissipated energy and the shear rate were calculated. For the verification of this equation exemplary finite element simulations were performed with the boundary conditions as illustrated in the figure. The starting point of the simulations was a fully loaded rectangular channel with a ratio of channel height to channel width of b/h=40. For the exemplary simulations of party filled channels the depth of the reference channel is reduced. Additionally, the boundary conditions are then also changing for the simulation at the rear face of the flight, which represents the open area. In contrast to the reference computation at this area non-negligible velocities are defined; it is predetermined that at this area tangential forces do not emerge. In all cases the dissipated energy and the shear rate were calculated.
  
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 **Figure:** Dependence of the relative dissipated energy and the relative shear rate on the loading content. **Figure:** Dependence of the relative dissipated energy and the relative shear rate on the loading content.
Zeile 317: Zeile 317:
 First of all, a specific enthalpy curve of a semi-crystalline plastic is considered (Picture 1). At the crystallite melting temperature, the plastic has a corresponding specific enthalpy depending on the type. This enthalpy is divided in PAM into $\Delta h_f$ solid enthalpy (enthalpy change to increase the solid temperature) and $\Delta h_a$ melting enthalpy (enthalpy required to dissolve the crystalline regions). First of all, a specific enthalpy curve of a semi-crystalline plastic is considered (Picture 1). At the crystallite melting temperature, the plastic has a corresponding specific enthalpy depending on the type. This enthalpy is divided in PAM into $\Delta h_f$ solid enthalpy (enthalpy change to increase the solid temperature) and $\Delta h_a$ melting enthalpy (enthalpy required to dissolve the crystalline regions).
  
-{{ :en:grundlagenhandbuch:drehmoment_und_antriebsleistung:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_009.png?nolink |}}+{{ :en:grundlagenhandbuch:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_009.png?nolink&600 |}}
  
 **Picture 1:** Specific enthalpy curve of a partially crystalline polymer **Picture 1:** Specific enthalpy curve of a partially crystalline polymer
Zeile 418: Zeile 418:
 With the relationships shown, the individual required drive powers between two support points or the individual elements can be determined and visualized in SIGMA. Finally, the individual calculated element powers must be added up to obtain the total power. The sole consideration or difference of the initial and final enthalpy to determine the power leads to errors in various cases. This is the case, for example, if the melt temperature drops once during the extrusion process due to fillers and the melt is then heated again. The subsequent heating of the melt must be done by new energy from outside. This requires a further input of power, which would be neglected if the initial and final enthalpy were simply compared. With the relationships shown, the individual required drive powers between two support points or the individual elements can be determined and visualized in SIGMA. Finally, the individual calculated element powers must be added up to obtain the total power. The sole consideration or difference of the initial and final enthalpy to determine the power leads to errors in various cases. This is the case, for example, if the melt temperature drops once during the extrusion process due to fillers and the melt is then heated again. The subsequent heating of the melt must be done by new energy from outside. This requires a further input of power, which would be neglected if the initial and final enthalpy were simply compared.
  
 +====Enthalpy model with heat flow====
 +The enthalpy model neglects the heat flow between the polymer and the barrel wall. While in larger industrial extruders the proportion of heating power to total power is small compared to the drive power, neglecting the heat flow can lead to significant errors, particularly in smaller laboratory extruders or processes with a large temperature difference between the melt and the barrel.
 +
 +To account for the heat flow, the heat transfer coefficient is calculated according to [[en:grundlagenhandbuch:drehmoment_und_antriebsleistung#references |[TM00]]]. First, the Brinkmann number is calculated and then the Nusselt number is regressed from it.
 +
 +$$Br=\frac{K*v_{0}^{n+1}}{\lambda*\Delta T*h^{n-1}}\tag{60}$$
 +
 +$$Nu=2,9*Br^{0,8}\tag{61}$$
 +
 +The heat transfer coefficient can then be calculated using the thermal conductivity of the melt and the channel height:
 +
 +$$\alpha=\frac{Nu*\lambda}{h}\tag{62}$$
 +
 +The heat flow is calculated as follows:
 +
 +$$\dot Q=\alpha*l_{Node}*U_{Barrel}*\frac{b_{eff}}{b_{max}}*\Delta T\tag{63}$$
 +
 +The heat flow is subtracted from the calculated specific enthalpy difference according to equation 46 in order to determine the corrected drive power. This calculation is performed when the 'Enthalpy w. heat flow' power model is selected.
 ==== Validation ==== ==== Validation ====
  
 The new power model was implemented and verified in SIGMA. Identical to other models, the new power model was compared with the values of the experimental investigations to validate the model. The deviations of different process points and material combinations are shown in the following picture. The new power model was implemented and verified in SIGMA. Identical to other models, the new power model was compared with the values of the experimental investigations to validate the model. The deviations of different process points and material combinations are shown in the following picture.
  
-{{ :en:grundlagenhandbuch:drehmoment_und_antriebsleistung:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_0010.png?nolink |}}+{{ :en:grundlagenhandbuch:en_sigma150_dlg_grundlagenhandbuch_drehmoment_und_antriebsleistung_0010.png?nolink&600 |}}
  
 **Figure:** Comparison of experimental investigations and simulations **Figure:** Comparison of experimental investigations and simulations
Zeile 441: Zeile 459:
  
 [TK78] Tadmor, Z.; Klein, I: Engineering Principles of Plasticating Extrusion, Robert E. Krieger Publishing Company, Huntington, New York, 1978 [TK78] Tadmor, Z.; Klein, I: Engineering Principles of Plasticating Extrusion, Robert E. Krieger Publishing Company, Huntington, New York, 1978
 +
 +[TM00] Tenge, S.; Mewes, D.: “Experimental investigation of the energy balance for the metering zone of a twin screw extruder”; Polymer Engineering & Science; Volume 40; 2000; S. 277–289