Showing papers by "Yutaka Asako published in 2018"

Numerical study on heat transfer performance enhancement of phase change material by nanoparticles: A review

Abstract: Phase change material (PCM) can be considered as an ideal solution for thermal management challenges. Owning to the large amount of heat energy can be stored or released during the phase change process, PCM widely applied for thermal energy storage (TES), cooling system and thermal comfort purpose. Nevertheless, PCM posting relative low thermal conductivity is the issues that affect its performance. Improvement in thermal performance of PCM are widely studied by former researchers. In this paper, a review on the recent study of heat transfer performance enhancement of PCM is presented. Based on the overview, dispersion of nanoparticles into PCM able to improve the heat transfer performance of PCM but there may also cause little drawback in Latent heat. Lastly, some assumptions and governing equation that applied in the numerical investigation are presented.

Review on preparation techniques, properties and performance of hybrid nanofluid in recent engineering applications

Abstract: Nanofluid has been drawing attention in various engineering applications in past decade due to its superior heat transfer characteristics than conventional working fluid. From past researchers, it is found that behavior of nanofluid can be greatly varied by various factors such as method of preparation, concentration/type of suspended nanoparticles and type of base fluid used. Due to the desire to possess nanofluid with more advantageous characteristics, dispersion of different nanoparticles into base fluid has led to a novel product which is called hybrid nanofluid. Different types of hybrid nanofluid were prepared and studied by former researchers in accordance with parameters required in their studies. Based on literature review, hybrid nanofluid shows greater heat transfer performance and rheological properties compared to base fluid and mono nanofluid. This paper reviews the preparation method, stability investigation method, thermophysical properties and heat transfer performance of hybrid nanofluid in various heat transfer applications. Apart from that, this review outlines challenges regarding hybrid nanofluid and some suggestions to improve future researches in this area.

A comprehensive review on numerical and experimental study of nanofluid performance in microchannel heatsink (MCHS)

Abstract: Microchannel heatsink is an advanced technology in the cooling system that gives a superior performance to remove high heat flux generated by a modern electronic device. Many innovations of microchannel design have been dedicated to improve the thermal performance in microchannel heatsink. Besides that, application of nanofluid as a coolant in microchannel heatsink has been attracting a lot of interest among researcher due to the enhancement of thermal conductivity in a nanofluid with a small percentage of the nanoparticle. The enhancement has contributed to heat transfer augmentation in microchannel heatsink. In this paper, a comprehensive review about nanofluid as a coolant regarding its performance based on the concentration and size of nanoparticle in microchannel heatsink was presented and analysed. The discussion of this review focused on the methodology used to analyse the performance of nanofluid in a microchannel, flow condition, channel design and type of nanofluid. Finally, the suggestion of nanofluid selection, nanoparticle concentration, nanoparticle size and flow condition have been pointed out.

Piston surface pressure of piston- cylinder system with finite piston speed

Abstract: Understanding the thermodynamics' fundamental are important for the advance of energy and environmental technologies. The study aims to derive an expression of the average pressure on the piston surface, pps in an adiabatic piston-cylinder system during an irreversible process with finite piston speed using the kinetic molecular theory. Expressions for the average pressure on the piston surface, pps are derived from the change of momentum and change of energy. The Maxwell- Boltzmann distribution is used to estimate the gas molecule velocities. The piston surface pressure obtained from the change of momentum is 37.18% lower than that obtained by the previous study. The piston surface pressure obtained from the change of energy is 26.94% lower than that obtained by the previous study.

Data reduction of average friction factor of gaseous flow in micro-channels with adiabatic wall

Abstract: This study focuses on data reduction of average friction factor of gaseous flow through microchannels. In the case of microchannel gas flow at high speed, the large expansion occurs near the outlet and the pressure gradient along the length is not constant and increases near the outlet. This results in flow acceleration and a decease in bulk temperature. Therefore both pressure and temperature are required to obtain the friction factor of the microchannel gas flow. In the past data reduction of many experiments, the friction factors have been obtained under the assumption of isothermal flow since temperature measurement of compressible flow in micro-channels is quite difficult due to the experimental technique limitations. Kawashima and Asako [1] found that the gas temperature can be determined by the pressure under the assumption of one dimensional flow in an adiabatic channel (Fanno flow) to obtain the friction factor considering the effect of a decrease in gas temperature. They also reported the data reduction of the four multiplies of Fanning friction factor for the Fanno flow defined by [2] ÷ ø ö ç è æ ÷ ø ö ç è æ ÷ ø ö ç è æ = = x T T D x p RT u Dp x p p D u f d d 2 d d 2 d d 2 2 1 4 2 2 2 w f r r t (1) To obtain a semi-local friction factor, pressures are measured at the pressure ports that are located very closely. In such a case, the change in temperature between two ports is small. Therefore, the temperature which appears in the second term in right hand side of Eq. (1) can be treated as constant. Integrating Eq. (1) with the average of the temperatures at two pressure ports, 2 2 1 T T T + = where T1 and T2 are the temperatures at the pressure ports 1 and 2, we obtain * Corresponding author migrate2018 Main room Thursday, June 28, 2018 11:55/12:00 (05min) 80 sciencesconf.org:migrate2018:209474 Proceedings of the 3 MIGRATE Workshop June 27-29, 2018 – Bastia, France 2 A Marie-Curie-ITN within H2020 ( ) ( ) ÷ ÷ ø ö ç ç è æ + + + = = ò *

Solar radiation forecast using cloud velocity for photovoltaic systems

Abstract: Today, solar energy is used in a many different ways. One of the most popular technological developments for this purpose is photovoltaic conversion to electricity. However, power fluctuations due to the variability of solar energy are one of the challenges faced by the implementation of photovoltaic systems. To overcome this problem, forecasting solar radiation data several minutes in advance is needed. In this research, a methodology to forecast solar radiation using cloud velocity and cloud moving angle is proposed. Generally, a red-to-blue ratio (RBR) color model and correlation analysis are used for obtaining the cloud velocity and moving angle. Artificial neural network (ANN) forecast models with different input combinations are established. This methodology requires lower computational time since it only uses part of the pixels in the sky image. Based on R-squared analysis, it can be concluded that the ANN model with inputs of cloud velocity and moving angle and average solar radiation showed the highest accuracy among other combinations of inputs. The R-squared value was 0.59 with only a relatively small sample size of 42. The proposed model showed a highest improvement of 75.79% when compared to the ANN model based on historical solar radiation data only.

Flat electroencephalography’s cluster centers movement tracking during epileptic seizure

Abstract: Epilepsy is a term used for a chronic disorder caused by excessive and abnormal nerve cell activity within the brain. This dynamic process is often associated with electroencephalography (EEG), which is an electrophysical method to record the electrical activity of the brain. For epilepsy patients, their EEG signals are characterized by abnormal signal flow and large spikes. This shows the excessive electrical activity within the brain can be extracted thus locating problematic cells of epilepsy is possible. However, it is very challenging due to the complexity of the signals to be analyzed. Through fEEG, the signals can be viewed in a Cartesian plane which consists of EEG’s channels and cluster center of electrical potential during epilepsy. To date, no research has been done on across time-frame of fEEG. In order to gain better insight into the dynamic process of epilepsy, a dynamic study on the cluster center movement across time-frame is necessary. Therefore, this study to shows the tracking of cluster centers movements across time-frame of fEEG. This movement tracking is essentials to understand the behavior of epilepsy such as the patterns of electrical potential. Further studies on the model could potentially assist in locating the problematic cells caused by epilepsy.