FRAUNHOFER INSTITUTE FOR SOLAR ENERGY SYSTEMS ISE

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1 FRAUNHOFER INSTITUTE FOR SOLAR ENERGY SYSTEMS ISE Performance evaluation and optimization of adsorption modules Dr. Gerrit Füldner Fraunhofer Institute for Solar Energy Systems ISE Sorption Friends 2015 Milazzo, Sicily,

2 AGENDA Motivation: Optimization of adsorption modules for different applications Questions: Which transport processes are occuring? How should they be described and measured? Which (transport) process is dominating the module dynamics for a given module? How does a good adsorber configuration (geometrical etc.) and a good adsorber/evaporator combination look like, taking into account the requirements from a specific application? 2

3 Adsorption Module for Heat Transformation Most simple case: One ad-/desorber and one evaporator/condenser in a vacuum shell 3

4 Different modelling depth Detailed PDE model (only AdHEX) Simpler RC nodes model (full physical transport parameters sorption module) description of detailed heat empirical lumped parameters and mass transfer phenomena evaluation of influence of geometrical configuration can be derived from more detailed model or parametrization of experimental data parameters only valid for one specific geometrical configuration 4

5 PDE modelling of aluminum fibre composite adsorber 5 Non-isothermal bidisperse model of adsorption kinetics Calibrated by LPJ kinetics, porosimetry, permeability measurements, heat conductivity, diffusion coefficients (PFG-NMR, IR imaging)

6 Average Temperature Levels - Desorption T T in T out T HX ΔT Desorber Ad-HX T cm Composite/ Adsobent Adsorbent T eq (p ch, X) ΔT Module ΔT Material (Thrust) T s (p ch ) ΔT Condenser Chamber E/C-HX T echx T out T in 6

7 Average Temperature Levels Adsorption T Ad-HX T HX Composite/ Adsorbent T ads Adsorbent T eq (p ch, X) ΔT Adsorber T in T out ΔT Module ΔT Material (Lift) T in T echx T out ΔT Evaporator T s (p ch ) E/C-HX Chamber 7

8 Cycle simulations - average pressures in AdHEX Idealized simulation: constant pressures from evap/cond PDE model: average pressures in macroand micropores p micropores: p(x,t) 8

9 Cycle simulations - average temperatures in AdHEX Fluid temperature: step changes Average temperatures in different parts of AdHEX: Obviously main heat transfer limitation by fluid- HX heat transfer 9

10 Duehring diagram - Adsorption Heat and mass transfer limitations both as T-differences no time information 10

11 Relative influence of different transport processes average temperature difference equivalents Heat and mass transfer limitations both as T-differences Now with time information No macropore influence, but almost equal influence of heat transfer and micropore diffusion 11

12 Adsorber optimization 12 Parameter variation: cycletime and composite layer thickness Optimization criteria: COP, VSHP/VSCP, MSHP/MSCP COP rising with cycletime and layer thickness, VSHP dropping -> Where is the optimum?

13 Multicriterial Pareto optimization Pareto front All optimal combinations to be found on Pareto front Layer thickness of e.g. 2.5mm allows broad variation of cycletime -> Good part-load behaviour! 13

14 SUMMARY AND CONCLUSION Driving T differences are needed for power output reduce theoretical temperature lift, increase necessary driving temperature difference (thrust) When heat and mass transfer mechanisms are known and described by a validated model, it is possible to make their influence comparable on one common scale using temperature difference equivalents Multiple optimization criteria can be tackled by Pareto approach 14

15 ACKNOWLEDGEMENTS This work was partly supported by the German Federal Ministery for Education and Research BMBF (WasserMod, FKZ 03SF0469B). PhD scholarship from Deutsche Bundesstiftung Umwelt (DBU) to Gerrit Füldner is gratefully acknowledged. Thanks to Ursula Wittstadt, Eric Laurenz and Lena Schnabel for their contributions to this presentation. 15

16 Thank you for your attention! Fraunhofer Institute for Solar Energy Systems ISE Gerrit Füldner 16