2022
Cavazzini, Giovanna; Bari, Serena
Optimization of the Adsorption / Desorption Contribution from Journal Article
In: 2022.
Abstract | BibTeX | Tags: adsorption, metal-organic heat carriers, ORC, two-phase fluid, waste heat
@article{Nanoparticles2022,
title = {Optimization of the Adsorption / Desorption Contribution from},
author = {Giovanna Cavazzini and Serena Bari},
year = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
abstract = {The efficient recovery of low temperature waste heat, representing from 25% up to 55% of the energy losses in industrial processes, still remains a challenge and even Organic Rankine Cycles (ORCs) experience a strong efficiency decay in such a low temperature operating range (T < 150 C). In similar heat transfer processes, several nanofluids have been proposed as a solution for increasing heat transfer efficiency, but they produced only moderate enhancements of the heat transfer efficiency in comparison with pure fluids. This paper aims at numerically assessing the potential gain in efficiency deriving from the application of an unconventional type of nanoparticles, the metal-organic heat carriers (MOHCs), in the ORC field. In comparison with standard nanoparticles, these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption, with a theoretically high potential for boosting the heat transfer capacity of ORC systems. In this paper a numerical model was developed and customized for considering the adsorption/desorption processes of the pure fluid R245fa (pentafluoropropane) combined with a crystal structure for porous chromium terephthalate (MIL101). The R245fa/MIL101 nanofluid behavior was experimentally characterized, defining proper semi-emipirical correlations. Then, an optimization procedure was developed, combining the numerical model with a PSO algorithm, to optimize the thermodynamic conditions in the ORC so as to maximize the contribution of desorption/absorption processes. The results confirm the increase in net power output (+2.9% for 100 C) and in expander efficiency (+2.4% for 100 C) at very low heat source temperature. The relevance of tuning the operating cycle and the nanofluid properties is also demonstrated.},
keywords = {adsorption, metal-organic heat carriers, ORC, two-phase fluid, waste heat},
pubstate = {published},
tppubtype = {article}
}
The efficient recovery of low temperature waste heat, representing from 25% up to 55% of the energy losses in industrial processes, still remains a challenge and even Organic Rankine Cycles (ORCs) experience a strong efficiency decay in such a low temperature operating range (T < 150 C). In similar heat transfer processes, several nanofluids have been proposed as a solution for increasing heat transfer efficiency, but they produced only moderate enhancements of the heat transfer efficiency in comparison with pure fluids. This paper aims at numerically assessing the potential gain in efficiency deriving from the application of an unconventional type of nanoparticles, the metal-organic heat carriers (MOHCs), in the ORC field. In comparison with standard nanoparticles, these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption, with a theoretically high potential for boosting the heat transfer capacity of ORC systems. In this paper a numerical model was developed and customized for considering the adsorption/desorption processes of the pure fluid R245fa (pentafluoropropane) combined with a crystal structure for porous chromium terephthalate (MIL101). The R245fa/MIL101 nanofluid behavior was experimentally characterized, defining proper semi-emipirical correlations. Then, an optimization procedure was developed, combining the numerical model with a PSO algorithm, to optimize the thermodynamic conditions in the ORC so as to maximize the contribution of desorption/absorption processes. The results confirm the increase in net power output (+2.9% for 100 C) and in expander efficiency (+2.4% for 100 C) at very low heat source temperature. The relevance of tuning the operating cycle and the nanofluid properties is also demonstrated.
2019
Cavazzini, Giovanna; Bari, Serena; McGrail, P.; Benedetti, Vittoria; Pavesi, Giorgio; Ardizzon, Guido
Contribution of Metal-Organic-Heat Carrier nanoparticles in a R245fa low-grade heat recovery Organic Rankine Cycle Journal Article
In: Energy Conversion and Management, vol. 199, pp. 111960, 2019, ISSN: 01968904.
Abstract | Links | BibTeX | Tags: Nanofluid, Numerical Model, Optimization, ORC, waste heat
@article{Cavazzini2019b,
title = {Contribution of Metal-Organic-Heat Carrier nanoparticles in a R245fa low-grade heat recovery Organic Rankine Cycle},
author = {Giovanna Cavazzini and Serena Bari and P. McGrail and Vittoria Benedetti and Giorgio Pavesi and Guido Ardizzon},
url = {https://linkinghub.elsevier.com/retrieve/pii/S0196890419309665},
doi = {10.1016/j.enconman.2019.111960},
issn = {01968904},
year = {2019},
date = {2019-01-01},
journal = {Energy Conversion and Management},
volume = {199},
pages = {111960},
abstract = {This paper presents an in-depth investigation of the applications of an innovative nanofluid – suspensions of nanoparticles in a base fluid- in the ORC field, based on a new class of nanoparticles – termed Metal-Organic Heat Carriers (MOHCs) – molecularly engineered to reversibly uptake and release the working fluid molecules in which they are suspended. Unlike standard nanoparticles (i.e. Al2O3, Al, …), these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption which can be as much as twice the level of the latent heat of vaporization of the pure fluid phase alone. The paper illustrates the development of a nu- merical model for assessing the MOHC-based nanofluid gain in ORC systems. More specifically, the possible combination of the base fluid R245fa with the nanoparticle MIL101, a robust Metal Organic Heat Carrier, was considered. To properly model the reversible adsorption/desorption process, experimental analyses were carried out to study the uptake of the R245fa in MIL101 at different operating conditions and departing from the experimental results, proper semi-empirical correlations were defined and adopted within the numerical model. The resulting performance of the MIL101/R245fa were compared with those of pure organic fluids, whose cycle was optimized in order to maximize the area-to-power ratio. Promising results were achieved in terms of system efficiency increase and heat exchanger area reduction. 1.},
keywords = {Nanofluid, Numerical Model, Optimization, ORC, waste heat},
pubstate = {published},
tppubtype = {article}
}
This paper presents an in-depth investigation of the applications of an innovative nanofluid – suspensions of nanoparticles in a base fluid- in the ORC field, based on a new class of nanoparticles – termed Metal-Organic Heat Carriers (MOHCs) – molecularly engineered to reversibly uptake and release the working fluid molecules in which they are suspended. Unlike standard nanoparticles (i.e. Al2O3, Al, …), these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption which can be as much as twice the level of the latent heat of vaporization of the pure fluid phase alone. The paper illustrates the development of a nu- merical model for assessing the MOHC-based nanofluid gain in ORC systems. More specifically, the possible combination of the base fluid R245fa with the nanoparticle MIL101, a robust Metal Organic Heat Carrier, was considered. To properly model the reversible adsorption/desorption process, experimental analyses were carried out to study the uptake of the R245fa in MIL101 at different operating conditions and departing from the experimental results, proper semi-empirical correlations were defined and adopted within the numerical model. The resulting performance of the MIL101/R245fa were compared with those of pure organic fluids, whose cycle was optimized in order to maximize the area-to-power ratio. Promising results were achieved in terms of system efficiency increase and heat exchanger area reduction. 1.
2017
Cavazzini, Giovanna; Bari, Serena; Pavesi, Giorgio; Ardizzon, Guido
A multi-fluid PSO-based algorithm for the search of the best performance of sub-critical Organic Rankine Cycles Journal Article
In: Energy, vol. 129, pp. 42-58, 2017, ISSN: 03605442.
Abstract | Links | BibTeX | Tags: Critical temperature, Organic Rankine Cycles, PSO, System efficiency, waste heat, Working fluid
@article{Cavazzini2017a,
title = {A multi-fluid PSO-based algorithm for the search of the best performance of sub-critical Organic Rankine Cycles},
author = {Giovanna Cavazzini and Serena Bari and Giorgio Pavesi and Guido Ardizzon},
doi = {10.1016/j.energy.2017.04.090},
issn = {03605442},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
journal = {Energy},
volume = {129},
pages = {42-58},
abstract = {The present paper focuses on the thermodynamic optimization of a sub-critical ORC for heat source temperatures in the range between 80 and 150 °C. The most significant novelty of the optimization procedure is that the optimization algorithm was modified for this particular application in order to allow the swarm particles to dynamically choose the working fluid among a list of 37 candidates during their heuristic movement, by continuously and dynamically modifying the search domain of each particle iteration-by-iteration due to the different vapour saturation lines of the chosen working fluid. The significant amount of data obtained by the optimization procedure highlighted the dependency of the system efficiency on two main parameters: the Jakob number related to the optimized cycle (Jaopt) and the ratio between the critical temperature of the working fluid and the inlet heat source temperature. At closer inspection, a third new parameter Ω was identified, resulting from the combination of the previous two, whose minimization is correlated to the maximization of system efficiency. A procedure for the preliminary estimation of the optimal cycle allowing to estimate with good accuracy the Jakob number Jaopt and the corresponding value of Ω was also developed.},
keywords = {Critical temperature, Organic Rankine Cycles, PSO, System efficiency, waste heat, Working fluid},
pubstate = {published},
tppubtype = {article}
}
The present paper focuses on the thermodynamic optimization of a sub-critical ORC for heat source temperatures in the range between 80 and 150 °C. The most significant novelty of the optimization procedure is that the optimization algorithm was modified for this particular application in order to allow the swarm particles to dynamically choose the working fluid among a list of 37 candidates during their heuristic movement, by continuously and dynamically modifying the search domain of each particle iteration-by-iteration due to the different vapour saturation lines of the chosen working fluid. The significant amount of data obtained by the optimization procedure highlighted the dependency of the system efficiency on two main parameters: the Jakob number related to the optimized cycle (Jaopt) and the ratio between the critical temperature of the working fluid and the inlet heat source temperature. At closer inspection, a third new parameter Ω was identified, resulting from the combination of the previous two, whose minimization is correlated to the maximization of system efficiency. A procedure for the preliminary estimation of the optimal cycle allowing to estimate with good accuracy the Jakob number Jaopt and the corresponding value of Ω was also developed.
