Turbulent convective heat transfer and pressure drop of dilute CuO (copper oxide) - water nanofluid Inside a circular tube

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Turbulent forced convective heat transfer and pressure drop of 0.01 vol.% CuO-water nanofluid was assessed experimentally. The nanofluids were made flow into a heated horizontal tube under uniform constant heat flux within Reynolds number range of 11,500 to 32,000. The first objective is to know how close traditional correlation/formula for, both, heat transfer and pressure drop can predict nanofluid’s heat transfer and pressure drop. The second is to know how nanofluid’s convective heat transfer and pressure drop are compared to those of its base fluid; in this case water. The results showed that the abovementioned characteristics of the nanofluid can be predicted by the traditional correlation available. It is also found that the nanofluid’s Nusselt number and friction factor, which represent the heat transfer rate and pressure drop, respectively, are close to those of water. Hence, there is no anomaly due to the dispersed nanoparticles within the water.KACST (King Abdulaziz City for Science and Technology

Modeling of Transient Cyclic Behavior of a Solid Particle Thermal Energy Storage Bin for Central Receiver Applications

AbstractOne of the emerging thermal energy storage (TES) concepts is the use of solid particles, which can potentially store thermal energy at temperatures approaching 1000°C. Efforts are underway to prepare on-sun testing of this concept at King Saud University (Riyadh, Saudi Arabia) as a part of the research activities in a SunShot project led by Sandia National Laboratories. A thorough study of this concept has been conducted and a prototype has been designed. This concept involves the use of proppants (CARBO Accucast ID50K) as the storage medium, and a thick, multilayered, cylindrical-shaped TES bin as the storage bin. Due to the complexity of building this first-of-its-kind TES bin, it was necessary to model the thermal performance of this design prior to completing the construction process. For this reason, a numerical model was built for the TES bin which is capable of determining the amount of energy loss. The model takes into account that, during daytime operation, the charging flow rate is higher than the discharging flow rate to allow the proppants to accumulate within the TES bin over about 7hours. Once the charging process is completed, the discharging phase – whose duration is about 5hours – is also modeled, followed by modeling the cooling-down process of the TES bin for 12hours to complete a 24-hour cycle. This modeling cycle is based on an assumed initial temperature in the interior of the bin. This paper extends the modeling effort to more than one cycle, such that the initial conditions at the beginning of each cycle are based on information obtained from the previous cycle, rather than on assumed values.Results show that multi-cycle modeling is important, since it shows that the assumed initial temperature may not representative and may lead to inaccurate results. Furthermore, lessons learned from the first cycle of operation, especially excessive air leakage into the TES bin during nighttime depletion, help refine modeling of subsequent cycles. Energy loss at the end of the second cycle was found to be 4.3%. While considered large, this value is primarily due to the high surface-to-volume ratio of the prototype TES bin being investigated. Preliminary analysis shows that a utility-scale TES bin using the same concept will have an energy loss of less than 1%, which conforms to the current best practice, and shows that low-cost TES solutions can be used in conjunction with the falling particle receiver concept