The scope of the PhD research was to develop a novel energy storage composite obtained by incorporating graphene-enhanced PCM into expanded clay aggregate porous media. The novel thermally enhanced PCM-based composite aggregate with improved thermal conductivity has been found to be suitable for incorporation into cementitious matrices and for use in the lightweight concrete (LWC) industry. The utilization of this lightweight graphene-enhanced PCM-based concrete within the built environment has the potential to mitigate temperature fluctuations and reduce energy demands, both for existing and newly constructed buildings. To this aim, the present study investigated a thermal energy storage aggregate (TSA) composite based on butyl stearate (BS), a low-cost commercially available PCM, and graphene nanoplatelets (GNPs, shortly named as GN in current study), as selected highly conductive agent. The liquid state graphene-enhanced PCM (nanofluid), is form-stabilized in the porous medium of expanded clay (EC) aggregates. The development of the TSA is supported by expanded clay (EC) lightweight aggregate (LWA), which is a promising material for the preparation of form-stabilized PCM (FSPCM) in the lightweight concrete industry. The study analyzed the behavior of graphene nanoplatelets embedded in PCM-EC media, and the performance of the designed composite TSA (GN-PCM-EC) was evaluated by combining experiments and finite element analysis. A finite element model was implemented for the preliminary selection of the most efficient conductive agent (nanoparticle) and prediction of the effect of its content. The thermo-chemical properties of the fabricated TSA were then fully analyzed. Finally, the thermal behavior of the TSA was investigated by embedding it within a matrix of thermal energy storage concrete (TSC). The results demonstrated that the TSA composite with 21% (wt.) 2GN-PCM (expanded clay aggregates containing 2% GN by weight of PCM), reduced the maximum temperature peaks during heating cycles by up to 5 °C compared to pristine EC (empty aggregates) and up to 2.5 °C compared to PCM-EC (aggregates containing only PCM). Analysis of the thermal performance of a thermal energy storage concrete (TSC) containing 3.5% (wt.) 2GN-PCM in a 3D setup that mimics challenging conditions where the temperature fluctuations barely reach the PCM (fully insulated with polystyrene), showed a reduction in the amplitudes of the temperature by up to 3.5 °C compared to pristine EC and by up to 1 ⁰C compared to PCM-EC. While, in a 1D heat transfer setup where the TSC is insulated at the four edges (close to building real condition, partially insulated with polystyrene), at ≤5% relative humidity, the maximum peaks were smoothed by up to 4 ⁰C when compared to PCM-EC and up to 5.1 ⁰C when compared to pristine EC, while this decrease is around 3.6 ⁰C and 5.2 ⁰C for the tests in 50% relative humidity condition. In addition, TSC, with 2 wt% GN, shows improved heat transfer, its thermal conductivity increased by 244% and 67% when comparing to pristine EC and PCM-EC, while the ultrasounds wave propagation velocity increased by approximately 20% which proves the higher degree of homogeneity in the media. Finally, the leakage test showed that the TSA is thermally stable, and the long temperature history tests on TSCs containing TSAs show potential to maintain thermal performance after at least 500 cooling-heating cycles. The results demonstrated that the novel-designed TSA composites pave the way for a practical and effective solution to improve indoor comfort and energy efficiency in buildings.
Ambito della ricerca di dottorato è stato lo sviluppo di un nuovo composito per l'accumulo di energia. Il composito è ottenuto incorporando PCM (materiale a cambiamento di fase) e grafene in aggregati di argilla espansa. Il nuovo aggregato composito a base di PCM, con caratteristiche termiche migliorate e con maggiore conduttività termica, è risultato idoneo per la produzione di calcestruzzi leggeri (LWC) quando incorporato in matrici cementizie. L’impiego di questo calcestruzzo leggero, con l’utilizzo di PCM e grafene, nell’ambiente costruito ha il potenziale di mitigare le fluttuazioni di temperatura e ridurre la domanda di energia, sia per edifici esistenti che di nuova costruzione. Per la realizzazione del compsito, idoneo per l'accumulo di energia termica (TSA), è stato utilizzato stearato di butile (BS), un PCM a basso costo e commercialmente disponibile, e nanopiastrine di grafene (GNPs), selezionato come agente ad alta conducibilità. Il PCM con grafene nello stato liquido (nanofluido) è stato stabilizzato nei pori degli aggregati di argilla espansa (EC). Gli aggregati di argilla espansa (LWA) rappresentando uno dei materiali di supporto più promettenti per la preparazione di PCM stabilizzati in forma (FSPCM) nell'industria del calcestruzzo leggero (LWC). Lo studio ha analizzato il comportamento del grafene incorporate nel PCM-EC, e le prestazioni del TSA (GN-PCM-EC) sono state valutate combinando misure esperimentali ed analisi agli elementi finiti. Un modello agli elementi finiti è stato implementato per la selezione preliminare dell'agente conduttivo (nanoparticella) più efficiente e per la previsione dell'effetto del suo contenuto. Infine, il comportamento termico del TSA è stato studiato integrandolo all'interno di una matrice cementizia per l'accumulo di energia termica (TSC). I risultati hanno dimostrato che il composito TSA con 21% (in peso) di 2GN-PCM (aggregati di argilla espansa contenenti il 2% di GN in peso di PCM) ha ridotto i picchi di temperatura massima durante i cicli di riscaldamento fino a 5 °C rispetto agli EC (aggregati base) e fino a 2.5 °C rispetto ai PCM-EC (aggregati di argilla espansa contenenti solo PCM). Le prestazioni termiche del calcestruzzo per l'accumulo di energia termica (TSC), contenente il 3.5% (peso) di 2GN-PCM, hanno mostrato una riduzione delle ampiezze delle fluttuazioni di temperatura fino a 3.5 °C rispetto agli EC (senza PCM e grapene), e fino a 1 °C rispetto a PCM-EC, con misure effettuate su una campioni completamente isolati. Mentre, in una configurazione di prova con campioni isolato su quattro lati, e con umidità relativa ≤5%, i picchi massimi sono stati ridotti fino a 4 °C rispetto a PCM-EC e fino a 5.1 °C rispetto agli EC. Questa riduzione è stata di circa 3.6 °C e 5.2 °C con umidità relativa del 50%. Inoltre, il TSC con il 2% in peso di GN ha dimostrato un miglioramento nel trasferimento di calore, con un aumento della conduttività termica del 244% e del 67% rispetto a EC e PCM-EC, mentre la velocità di propagazione delle onde ultrasoniche è aumentata di circa il 20%, dimostrando un maggiore omogeneità del materiale. Infine, le misure della variazione di massa hanno dimostrato che il TSA è termicamente stabile, e i test di lunga durata sulla storia della temperatura dei TSC contenenti TSA mostrano il potenziale di mantenere le prestazioni termiche dopo almeno 500 cicli di raffreddamento-riscaldamento. I risultati hanno dimostrato che il nuovo compositi TSA, potrebbe rappresentare una soluzione pratica ed efficace per migliorare il comfort interno e l'efficienza energetica negli edifici.
Proposal of a novel thermal energy storage aggregate composite based on graphene-modified phase change materials for energy storage concrete applications
SALIMI, MAHSA
2024/2025
Abstract
The scope of the PhD research was to develop a novel energy storage composite obtained by incorporating graphene-enhanced PCM into expanded clay aggregate porous media. The novel thermally enhanced PCM-based composite aggregate with improved thermal conductivity has been found to be suitable for incorporation into cementitious matrices and for use in the lightweight concrete (LWC) industry. The utilization of this lightweight graphene-enhanced PCM-based concrete within the built environment has the potential to mitigate temperature fluctuations and reduce energy demands, both for existing and newly constructed buildings. To this aim, the present study investigated a thermal energy storage aggregate (TSA) composite based on butyl stearate (BS), a low-cost commercially available PCM, and graphene nanoplatelets (GNPs, shortly named as GN in current study), as selected highly conductive agent. The liquid state graphene-enhanced PCM (nanofluid), is form-stabilized in the porous medium of expanded clay (EC) aggregates. The development of the TSA is supported by expanded clay (EC) lightweight aggregate (LWA), which is a promising material for the preparation of form-stabilized PCM (FSPCM) in the lightweight concrete industry. The study analyzed the behavior of graphene nanoplatelets embedded in PCM-EC media, and the performance of the designed composite TSA (GN-PCM-EC) was evaluated by combining experiments and finite element analysis. A finite element model was implemented for the preliminary selection of the most efficient conductive agent (nanoparticle) and prediction of the effect of its content. The thermo-chemical properties of the fabricated TSA were then fully analyzed. Finally, the thermal behavior of the TSA was investigated by embedding it within a matrix of thermal energy storage concrete (TSC). The results demonstrated that the TSA composite with 21% (wt.) 2GN-PCM (expanded clay aggregates containing 2% GN by weight of PCM), reduced the maximum temperature peaks during heating cycles by up to 5 °C compared to pristine EC (empty aggregates) and up to 2.5 °C compared to PCM-EC (aggregates containing only PCM). Analysis of the thermal performance of a thermal energy storage concrete (TSC) containing 3.5% (wt.) 2GN-PCM in a 3D setup that mimics challenging conditions where the temperature fluctuations barely reach the PCM (fully insulated with polystyrene), showed a reduction in the amplitudes of the temperature by up to 3.5 °C compared to pristine EC and by up to 1 ⁰C compared to PCM-EC. While, in a 1D heat transfer setup where the TSC is insulated at the four edges (close to building real condition, partially insulated with polystyrene), at ≤5% relative humidity, the maximum peaks were smoothed by up to 4 ⁰C when compared to PCM-EC and up to 5.1 ⁰C when compared to pristine EC, while this decrease is around 3.6 ⁰C and 5.2 ⁰C for the tests in 50% relative humidity condition. In addition, TSC, with 2 wt% GN, shows improved heat transfer, its thermal conductivity increased by 244% and 67% when comparing to pristine EC and PCM-EC, while the ultrasounds wave propagation velocity increased by approximately 20% which proves the higher degree of homogeneity in the media. Finally, the leakage test showed that the TSA is thermally stable, and the long temperature history tests on TSCs containing TSAs show potential to maintain thermal performance after at least 500 cooling-heating cycles. The results demonstrated that the novel-designed TSA composites pave the way for a practical and effective solution to improve indoor comfort and energy efficiency in buildings.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/238157