Study on High-Performance PDLC Optical Devices

修士論

Thermophysical Properties Of CNF-Based Nanocoolant As A Heat Transfer Media

High heat flux removal is one of the major challenges in designing for the future electronic devices. The trend to address these high heat fluxes is to introduce microchannel arrays directly in the heat generating by the electronic component. Commonly, water is suggested to be used as a single-phase coolant in combination with the microchannel heat sinks for cooling of electronics applications. However, one of the major problems faced by the existing coolants is the limited amount of heat that can be absorbed by the fluids. An innovative way to overcome this limitation is by utilizing a nanocoolant as the heat transfer medium in a cooling application. This research was aimed at formulating an efficient nanocoolant from PR-24 HHT carbon nanofibers (CNF) in a base fluid consisting of deionized water (DI) and ethylene glycol (EG). The dispersion of nanofibers was enhanced by the presence of polyvinylpyrrolidone (PVP) as the stabilizing agent through two-step preparation process. The experiment was conducted by setting the variable weight percentage of CNF from 0.1wt% to 1.0wt%, with the base fluid ratio range from 100:0 (DI:EG) to 0:100 (DI:EG). The characterization testing was performed to study the surface species of the nanofiber using nitrogen gas adsorption technique, fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). The detailed study of the thermophysical properties such as thermal conductivity, viscosity, and specific heat capacity of stable CNF-based nanocoolant was also been investigated at three different temperatures (6°C, 25°C and 40°C). The maximum thermal conductivity enhancement of 29.95% was noticed for the nanocoolant with 0.6wt% at 0:100 (DI:EG). The rheological analysis showed that when the temperature increases, the viscosity diminishes. Whereas, due to a lower specific heat of the CNF, the specific heat of the nanocoolant decreased in proportion with the CNF concentration. Experimental investigations into the forced convective heat transfer performance of the CNF-based nanocoolant in a laminar flow through a mini heat transfer test rig showed that the presence of nanoparticles enhanced the heat transfer coefficient as opposed to the original base fluid. The highest heat transfer coefficient was reported with 30:70 (DI:EG) by the 0.7wt% nanocoolant at 40°C with the value of 265.28 x 103 W/m2.K. The enhancement of the heat transfer coefficient was due to the higher thermal conductivity value. The Nusselt number was also calculated and presented in this research. Overall, this study shows that the CNF-based nanocoolant has a huge potential to replace existing coolants in electronic cooling applications. Thus, in order to commercialize nanocoolant in practice, more fundamental studies are needed to understand the crucial parameters that affect their thermal characteristics

Decision-making support in vehicle routing problems : A review of recent literature

The Vehicle Routing Problem (VRP) involves a set of customers with known locations, each having a certain demand for goods or services. There is also a fleet of vehicles available, each with limited capacity and often a fixed starting point. With the aid of mathematical programming tools, this paper offers an overview of the most recent VRP research. This study also examines the algorithms for solving VRP models and categorizes them in terms of their application areas. For these reasons, related publications that appeared in the international journal have been compiled and studied. According to the literature review, multi-criteria decision-making (MCDM) techniques have yet to constitute the most mathematical programming methods used to solve the VRP problem

Thermal conductivity and viscosity of deionised water and ethylene glycol-based nanofluids

This paper focused on thermal conductivity and viscosity of deionised water and ethylene glycol-based nanofluids at three different temperatures (6C, 25C and 40C). For the preparation of nanofluids, a two-step method, comprised of homogenisation and sonication, was used on a mixture of MWCNT-OH, PVP and the base fluid. The results revealed that thermal conductivity was enhanced by about 8.86% for 0.8 wt% deionised water-based MWCNT-OH nanofluid, and by 5.37% for 0.2 wt% ethylene glycol-based MWCNT-OH nanofluid. Meanwhile, in viscosity test, the highest temperature of 40C exhibited lowest viscosity. This phenomenon happened only with ethylene glycol-based nanofluid, whilst the data on the viscosity of deionised water-based nanofluid was inconsistent at certain nanofluid concentrations . In conclusion, addition of MWCNT-OH into base fluid enhanced base fluid performance , giving it the potential to be used in cooling system applications. Keywords: Nanofluids; thermal conductivity; viscosity

Investigation of thermal characteristics of CNF-based nanofluids for electronic cooling applications

A major problem being faced by existing coolants is the limited amount of heat that can be absorbed by the fluids. An innovative way to overcome this limitation is by utilizing a nano-coolant as a heat transfer medium in a cooling application. This paper was aimed at formulating an efficient nanofluid from Pyrograf III HHT24 carbon nanofibers (CNF) in a base fluid consisting of deionized water (DI) and ethylene glycol (EG) with polyvinylpyrrolidone (PVP) as the dispersant. The experiment was conducted by setting the variable weight percentage of CNF from 0.1 wt% to 1.0 wt%, with the base fluid ratio of 90:10 (DI:EG) weight percent. Then, the thermal properties of the formulated nanofluids were investigated. The test on the thermal conductivity of the nanofluids showed that the highest thermal conductivity of 0.642 W/m.K in this experiment was produced when the concentration of nanofluid is 0.5 wt% at a temperature of 40°C. Experimental investigations into the forced convective heat transfer performance of the CNF-based nanofluid in a laminar flow through a mini heat transfer test rig showed that the presence of nanoparticles enhanced the heat transfer coefficient as opposed to the original base fluid. The highest heat transfer coefficient was reported using nanofluid with a concentration of 0.6 wt% at 40°C. The enhancement of the heat transfer coefficient was due to the higher thermal conductivity value. The Nusselt number was also calculated and presented in this paper. This study showed that the CNF-based nanofluids have a huge potential to replace existing coolants in electronic cooling applications. Thus, in order to commercialize nanofluids in practice, more fundamental studies are needed to understand the crucial parameters that affect their thermal characteristics. Keywords: carbon nanofibers; nanofluid; thermal conductivity; heat transfe

The Mediating Role of Institutional Support on Relationship between Technology Acceptance Model (TAM) and Student Satisfaction to Use eLearning during Covid-19 Pandemic: The Study of Private University in Malaysia

In these two years, E-learning system has fully become the teaching tools of higher education institutions in Malaysia after lockdowns due to Covid-19 pandemic. Universities strive hard to work with E-learning platforms in providing an effective learning environment and rich online courses for university’s students, but many research findings show that the e-learning teaching outcome is not up to expectation. This study aims to assess the role of institutional support as a mediator on the relationship between variables of Technology Acceptance Model (TAM) and satisfactions of university’s student to use e-learning during COVID-19 pandemic period. Respondents are among 344 students from different study major who had to study through e-learning education amidst pandemic in private university in Malaysia. The data collected used structures questionnaire and are analyzed by using SPSS. The result of this study reveals that institutional support has partially been mediated on the relationship between satisfaction of student and variables from TAM model namely perceive usefulness and perceive ease of use. The result of this study provides an idea for higher education institution to develop successful online platform in enhancing student’s learning satisfaction

Thermal properties characteristics of MWCNT-OH based Nanofluids in mixture of Ethylene Glycol and Deionized water / Amirah Abdullah...[et al.]

Conventional fluids have lower thermal properties. Moreover, the low freezing and high boiling point of water are another issues have made limitation occurred. Therefore, inclusion of MWCNT-OH nanoparticles in mixture of ethylene glycol and deionized water is an alternative way to solve these problems. Then, two-step method is used in nanofluids synthesizing through homogenized and sonicated all materials together such as MWCNT-OH nanoparticles (0.1 wt% to 1.0 wt%) and PVP surfactant (0.01 wt%) in mixture of ethylene glycol to deionized water (20:80) for five minutes. The nanofluids were tested in thermal conductivity test, heat transfer coefficient test and specific heat test. Thus, the thermal conductivity results show positive enhancement for all concentrations and 0.9 wt% of MWCNT-OH based nanofluids have the highest thermal conductivity. It is followed by 0.3 wt% and 0.6 wt% of MWCNT-OH based nanofluids. The percentage enhancement of thermal conductivity is about 0.812% to 17.0%. Whilst, high heat transfer coefficient has given increment of nanofluids Nusselt number. However, specific heat test have decrement values with increment of weight loading even though has high thermal conductivity values. This thermal properties results are affected by dispersion and suspensions of nanoparticles possess higher thermal conductivity. In addition, functionalized group attached on nanoparticles, quantity of surfactant, ultrasonication process and nanofluids stability are factors which influenced the thermal conductivity. Moreover, heat absorption and capacity of nanofluids and as well as temperature are another factors that capable to enhance the thermal conductivity. The small size and high surface area of nanoparticles, low surface roughness, nanoparticles concentration, temperature and nanoparticles interaction are others influenced factors in these test. Whilst, lower specific heat value on nanoparticles and agglomeration form affected in specific heat test. In conclusion, addition of MWCNT-OH nanoparticles in mixture of base fluids is capable to improve thermal properties of nanofluids

The good doctor

This work sought to observe the response of a nanofluid put along in an electrical circuit while seeing the behaviour of the fluid. Would the nanofluids have a characteristic of an electrolyte? Two mini channels were constructed using additive manufacturing approach. The nanofluids were flooded in the channels where they were connected in series with a generic resistor in a low voltage circuit. The fluids' behaviours were observed through the recorded voltage drops at the resistor and also at the channel's start and end points, respectively. The results showed minute currents were flowing in the circuit as the fluids recorded high resistances. Therefore, the nanofluids are naturally high resistance electrolytes. However, the real nature of the fluids exposed to electrical potentials for a longer duration is unknown