Three-dimensional numerical study of thermal exchanges in different geometry sections of mini-channels using three different nanoparticles

In the present work, we have studied the thermal exchanges of different geometry sections of mini-channels of a cooler numerically. Particularly, we have chosen a mini channels cooler copper for cooling an electronic chip IGBT. In our simulation of three-dimensional (3D), we have compared the numerical results for the different forms of the proposed mini-channels and the three different types of nano-fluids by using the Cu-water, the Ag-water, and the Diamond-water with a volume fraction of 0.02%. The numerical results are obtained by choosing a Reynolds number (Re) between 100 and 900 and considering that the flow regime is stationary. The simulation was performed using commercial software, ANSYS-Fluent 15.0. The results obtained show that the increase of the exchange surface between the walls of the mini channels and the cooling fluid makes increases the heat exchange coefficient and the improvement of the maximum junction temperature of the electronic chip IGBT with the increase of the Reynolds number. The choice of nanoparticles has considerable effects on improving the heat transfer and the maximum junction temperature of the chip IGBT

Experimental determination of the optimum working conditions of a transcritical CO2 refrigeration plant with integrated mechanical subcooling

Subcooling methods for transcritical CO2 plants are being studied in order to improve their behavior. Among them, the Integrated Mechanical Subcooling system is one of the most promising owing that performs with high efficiency and it is a total-CO2 system. This work presents the experimental determination of the optimum working conditions of a transcritical CO2 plant working with an integrated mechanical subcooling system. The plant was tested at different pressure and subcooling conditions in order to optimize the COP of the plant and determine the optimal conditions for three ambient temperatures 25.0 °C, 30.4 °C and 35.1 °C and evaporation levels between −15.6 °C and −4.1 °C. Optimum operating conditions were determined and two correlations are proposed to determine the optimal pressure and subcooling as function the gas-cooler outlet temperature and the evaporation level

Molecular astronomy of cool stars and sub-stellar objects

The optical and infrared spectra of a wide variety of `cool' astronomical objects including the Sun, sunspots, K-, M- and S-type stars, carbon stars, brown dwarfs and extrasolar planets are reviewed. The review provides the necessary astronomical background for chemical physicists to understand and appreciate the unique molecular environments found in astronomy. The calculation of molecular opacities needed to simulate the observed spectral energy distributions is discussed

Methanol synthesis in a countercurrent gas-solid-solid trickle flow reactor. An experimental study

The synthesis of methanol from CO and H2 was executed in a gas-solid-solid trickle flow reactor. The reactor consisted of three tubular reactor sections with cooling sections in between. The catalyst was Cu on alumina, the adsorbent was a silica-alumina powder and the experimental range 498–523 K, 5.0–6.3 MPa and 0.2–0.33 molar fraction of CO. Complete conversion in one pass was achieved for stoichiometric feed rates, so that the gas outlet could be closed. The experimental results are compared with the model presented in the previous paper [Westerterp, K.R. and Kuczynski, M. (1987) Chem. Engng Sci.42,]; agreement is close over the entire conversion range from 15% to 100%

Don\u27t Abandon the Water Cooler Yet: Flexible Work Arrangements and the Unique Effect of Face-to-Face Informal Communication on Idea Generation and Innovation

[Excerpt] Flexible work arrangements (FWAs), especially those offering employees a degree of control over when and where they work, have become increasingly prevalent in recent years.Research has shown that these arrangements generally lead to higher levels of job satisfaction as well as lower levels of stress, work-family conflict, absenteeism, and turnover among employees.At the same time, however, some suggest that FWAs may not be appropriate in all situations, particularly in the context of creative teamwork (i.e., in the prototypical 21st century organization). It is important, in this view, to have all team members face to face in the office to encourage informal interactions that spark insights and innovations. Surprisingly, this supposition has yet to be rigorously tested. Flexible work arrangements (FWAs), especially those offering employees a degree of control over when and where they work, have become increasingly prevalent in recent years.Research has shown that these arrangements generally lead to higher levels of job satisfaction as well as lower levels of stress, work-family conflict, absenteeism, and turnover among employees.At the same time, however, some suggest that FWAs may not be appropriate in all situations, particularly in the context of creative teamwork (i.e., in the prototypical 21st century organization). It is important, in this view, to have all team members face to face in the office to encourage informal interactions that spark insights and innovations. Surprisingly, this supposition has yet to be rigorously tested. The present study was designed to fill this void, first by examining the effects of remote work (i.e., percent of time team members work outside the office) on the frequency, spontaneity, content, and mode of their communication and, then, by assessing the extent to which variations in team communication patterns influence the level of team creativity (i.e., the degree to which teams generate novel ideas that lead to improvements in work processes and/or to new and innovative products and services). As Figure 1 on page 5 shows, the study primarily distinguished between two types of team communication: (1) formal face-to-face communication (e.g., planned meetings about work-related matters) and (2) informal face-to-face communication. Within informal face-to-face communication, two forms were examined: (2a) spontaneous communication about work-related matters and (2b) non-work-related communication. Further, in examining the efficacy of both forms of informal communication for team idea generation and innovation, the study compared electronic modes (e.g., email, instant message, audio/visual) to face-to-face interactions

Sensitivity analysis applied to the multi-objective optimization of a MCFC hybrid plant

In this paper, the multi-objective optimization of a molten carbonate fuel cell (MCFC) based hybrid plant fueled with landfill gas is performed. System operation is significantly affected by off-design conditions. These are due to variations methane concentration occurring as the landfill depletes, performance degradations of the components, particularly the fuel cell, and ambient conditions. For these reasons, the objective functions are defined considering the plant lifetime. Some of the parameters affecting the results, as the voltage degradation, the cost of fuel cell, the methane concentration and the unit cost of landfill gas can be only estimated or forecasted and their actual values are uncertain. Therefore, the optimization is performed considering a sensitivity analysis in order to estimate the effects of possible variations on the Pareto front. The following free design variables are considered: pressure and temperature operation of the MCFC, turbine inlet temperature, fuel mass flow rate. In addition, the optimal configuration of the heat exchanger network is selected for each set of the design variabl