Numerical Assessment of Nanofluids in Recharging Microchannel: Thermo-Hydrodynamic and Entropy Generation Analysis

In this work three-dimensional numerical study is presented that deals with thermo-hydrodynamic performance and entropy generation in recharging microchannel using water-based nanofluids. Four different water-based nanofluids (Al2O3, CuO, SiO2, and ZnO) are considered with volume concentration and nanoparticle diameter varied in the range of 1% to 5%, and 10 nm to 50 nm respectively to understand their effect on thermo-hydrodynamic performance and entropy generation. Constant wall heat flux of 100 W/cm2 is applied on the substrate bottom surface while coolant flows through recharging microchannel with Reynolds number Re = 100 to 500. It is revealed that among all the nanofluids under investigation, water/Al2O3 provides enhanced thermal performance with higher effectiveness parameter (η), and it also shows reduced entropy generation in recharging microchannel. With increasing volume concentration of water/Al2O3 nanofluid, heat transfer coefficient increases, effectiveness parameter increases, and entropy generation reduces. Water/Al2O3 nanofluid with smaller particle diameter shows enhanced heat transfer coefficient, and reduced entropy generation, whereas it shows decreased effectiveness parameter. This is attributed to increased pressure drop with decreasing particle diameter. This study suggest that optimized combination of particle diameter and volume concentration should be chosen for using nanofluid based coolants for high heat flux removal.

COVID19 Pandemic: How Effective Are Interventive Control Measures and Is A Complete Lockdown Justified? A Comparison of Countries and States

Background For fighting the COVID-19 pandemic, countries used control measures of different severity, from ‘relaxed’ to lockdown. Drastic lockdown measures are considered more effective, but also have a negative impact on the economy. When comparing the financial value of lost lives to the losses of an economic disaster, the better option seems to be lockdown measures.Methods We developed a new parameter, the effectiveness of control measures, calculated from the 2nd time derivative of daily case data, and normalised to the average of the daily case data during the effective phase; and also calculated from the derivative of the logarithm of the reproductive number. We calculated this parameter and two associated parameters, i.e. effectiveness, duration of effective phase, and ratio of the 2 former parameters, for 92 countries, states and provinces, whose effective phase ended the latest on 15 May 2020. We compared these effectiveness parameters, and also the mortality during and after the effective phase, for countries with and without lockdown measures by means of the Mann-Whitney test.Results We did not find any statistically significant difference in the three effectiveness parameters, between countries with and without lockdown (p > 0.76; very small effect size). There was also no significant difference in mortality during the effective phase (p > 0.1; very small to small effect sizes), however a significant difference after the effective phase, with higher mortality for lockdown countries. The effectiveness parameter derived from the daily case data correlated well with the parameter derived from the reproductive number (R2 = 0.9480). The average duration of the effective phase was 17.3 ± 10.5 days.Conclusions The results indicate that lockdown measures are not necessarily superior to relaxed measures, which in turn are not necessarily a recipe for failure. Relaxed measures are, however, more economy-friendly. The higher mortality of lockdown countries is explained from the fact that, in our database, more lockdown countries than no-lockdown countries have higher mortality already during the effective phase that became significant only after the effective phase.

How the Italian Residential Sector Could Contribute to Load Flexibility in Demand Response Activities: A Methodology for Residential Clustering and Developing a Flexibility Strategy

This work aims at exploring the potential contribution of the Italian residential sector in implementing load flexibility for Demand Response activities. In detail, by combining experimental and statistical approaches, a method to estimate the load profile of a dwelling cluster of 751 units has been presented. To do so, 14 dwelling archetypes have been defined and the algorithm to categorise the sample units has been built. Then, once the potential flexible loads for each archetype have been evaluated, a control strategy for applying load time shifting has been implemented. That strategy accounts for both the power demand profile and the hourly electricity price. Specifically, it has been assumed that end users access a pricing mechanism following the hourly trend of electricity economic value, which is traded day by day in the Italian spot market, instead of the current Time of Use (TOU) system. In such a way, it is possible to flatten the dwellings cluster profile, limiting undesired and unexpected results on the balancing market. In the end, monthly and yearly flexibility indexes have been defined along with the strategy effectiveness parameter. From calculations, it emerges that a dwelling cluster for the Italian residential sector is characterised by a flexibility index of 10.3% and by a strategy effectiveness equal to 34%. It is noteworthy that the highest values for flexibility purpose have been registered over the heating season (winter) for the weekends.

Application of the Concept of Total Productive Maintenance in Automatic Bottle Filling Machines

Guwatirta Sejahtera is one of the companies engaged in the bottled drinking water industry. Problems that occur at PT. Guwatirta Sejahtera is the absence of routine maintenance on the machine so that damage, especially on automatic bottle filling machines, often occurs. This study applies a total productive maintenance method to determine the level of damage and identify the source of the problem as a basis for making recommendations for improvement in reducing the level of damage that often occurs in automatic bottle filling machines. The stage of the study begins by determining the engine efficiency and six big losses using the Overall Equipment Effectiveness parameter (OEE). Then proceed with identifying the source of the problem using the Failure Mode and Effect Analysis (FMEA) method. Recommendations for improvement include making: a daily inspection checklist, small working groups, Standard Operating Procedures for operating the machine and routine maintenance schedules. Based on the estimated calculation if the recommendation for improvement is applied, the value of the original engine efficiency of 84.26% increased to 98.97% and the initial maintenance costs of Rp.81,232,369.48 decreased to Rp.75,355,764.39 per year

Investment on human capital in a dynamic contest model

Although most contest games are modeled in such a way that the outcome depends only on the efforts exerted by the contestants, what is arguably more important is the contestants’ effective efforts which may be influenced also by their ability, human capital, strength, etc. In this paper, we investigate an extensive model including such an effectiveness parameter and analyze the optimal investment behavior in a dynamic conflict framework. At each period, two contestants compete for a common prize by choosing contest efforts and investment levels. Each contestant’s investment accumulates as his/her human capital which depreciates through time. Who wins the component contest at a particular period is determined by the contestants’ effective efforts, defined as increasing functions of their efforts and human capitals. Following the analysis of subgame perfect Nash equilibrium in a two-period model and of open-loop equilibrium in an infinite-horizon model, we provide intuitive comparative static results.

A New Approach for Centrifugal Impeller Preliminary Design and Aerothermal Analysis

This paper introduces a new approach for the preliminary design and aerothermal analysis of centrifugal impellers using a relative diffusion effectiveness parameter. The relative diffusion effectiveness is defined as the ratio of the achieved diffusion to the maximum available diffusion in an impeller. It represents the quality of the relative diffusion process in an impeller. This parameter is used to evaluate impeller performance by correlating the relative diffusion effectiveness with the impeller isentropic efficiency using the experimental data acquired on a single-stage centrifugal compressor (SSCC). By including slip, which is appropriate considering it is an inviscid effect that should be included in the determination of maximum available diffusion in the impeller, a linear correlation between impeller efficiency and relative diffusion effectiveness resulted for all operating conditions. Additionally, a new method for impeller preliminary design was introduced using the relative diffusion effectiveness parameter, in which the optimal design is selected to maximize relative diffusion effectiveness. While traditional preliminary design methods are based on empirical loss models or empirical knowledge for selection of diffusion factor (DF) in the impeller, the new method does not require any such models, and it also provides an analytical approach for the selection of DF that gives optimal impeller performance. Validation of the method was performed using three classic impeller designs available in the open literature, and very good agreement was achieved. Furthermore, a sensitivity study shows that the method is robust in that the resulting flow angles at the impeller inlet and exit are insensitive to a wide range of blockage factors and various slip models.