CFD Modeling and Optimization Analysis of Thermal Energy Storage Based Solar Collectors

Among various types of solar collectors, evacuated tube solar collector (ETC) has attracted much attention, especially for their application in solar water heating systems (SWHs). However, due to the intermittency in solar intensity, the ETCs may not work at their maximum functionality. In this study, the computational fluid dynamics (CFD) modeling of a heat pipe ETC (HPETC) with and without the integration of phase change materials (PCMs) is performed. In order to cross-validate the obtained results from CFD and recent experimental analysis, the boundary conditions are set as the field-testing data. The simulation results show an acceptable agreement with the experimental data with an average deviation of 4.8%. In order to further increase the accuracy of a numerical model, the volume of fluid (VOF) approach is adopted to simulate two-phase (evaporation-condensation process) phenomena inside a heat pipe. The result showed a 0.78% increase in numerical model accuracy when the heat pipe is simulated as a two-phase device in comparison with the simplified approach (in which HP is considered a high thermal conductive device). The result of this study showed improvement in numerical model accuracy when the VOF model is adopted. However, the VOF approach is found very time-consuming. As a result, a simplified numerical approach is adopted to optimize the thermal performance of an HPETC system. The performance of an HPETC is optimized by investigating the effect of HP position and various energy storage materials in both normal and on-demand operations. The results show that the solid-to-liquid phase change process was expedited by 48 minutes when the HP shifted from the top to the center of the glass tube. On the other hand, during normal operation, the maximum liquid fraction of PCM reached up to 98% in an optimized system whereas the conventional system reached up to only 74%. During normal operation, It is observed that the HPETC system integrated with PCM struggled to reach a melting fraction of 100% due to its poor thermal conductivity. The issue of poor thermal conductivity is addressed by impregnation of high thermal conductive porous metal to the PCM. To demonstrate the viability of the proposed approach, experimental analysis is carried out. The proposed system has reported maximum thermal efficiency of 71.71% while the conventional system showed maximum thermal efficiency of only 29.14%. Impregnation of porous metal to the PCM showed promising results and improved thermal performance in the HPETC system. The same approach is used to improve the electrical and thermal performance of a photovoltaic-thermal (PVT) system. CFD analysis is performed to assess the effect of integrating PCM + Cu porous metal with the PVT system. In addition, during the simulation, a real-time transient solar radiation boundary condition is applied to accurately predict the performance parameters such as the surface temperature of the PV cell, melting fraction of PCM, and the thermal energy stored by the system. The PVT system integrated with PCM + Cu porous metal system exhibited electrical efficiency of 11.49% which is 12.09% higher compared with the PVT system integrated with pure PCM. In addition, PV cell temperature is also decreased by 23.03 oC for the PVT system integrated with PCM + Cu porous metal. The outcome of this study can be a benchmark for further optimization of thermal energy storage-based solar collectors.

Name thesis:degree_name

Ph.D. (Doctor of Philosophy)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Engineering (UMKC)

Grantor

University of Missouri--Kansas City

Year dc:date.issued

2022

Author dc:creator

• Pawar, Vivek R.

Advisor dc:contributor.advisor

• Sobhansarbandi, Sarvenaz

Handle dc:identifier.uri

https://hdl.handle.net/10355/90341

OAI identifier oai:identifier

oai:mospace.umsystem.edu:10355/90341