Condensation Heat Transfer and Pressure Gradient Inside Multiport Minichannels

Abstract

In this paper, the experimental heat transfer coefficients measured during condensation of R134a and R410A inside multiport minichannels are presented. The frictional pressure gradient was also measured during adiabatic two-phase flow. The need for experimental research on condensation inside multiport minichannels comes from the wide use of those channels in automotive air-conditioners. The perspective for the adoption of similar channels in the residential air conditioning applications also calls for experimental research on new high pressure refrigerants, such as R410A.

Experimental data are compared against models to show the accuracy of the models in the prediction of heat transfer coefficients and pressure drop inside minichannels.     

EPDM rubber reinforced with titania generated by nonhydrolytic sol‐gel process

EPDM rubber was reinforced with titania in situ generated by using a nonhydrolytic sol‐gel (NHSG) process starting from TiCl₄ as titania precursor and tert‐butanol as oxygen donor. Titania particles in anatase form and with average diameter of 6 nm were synthesized via NHSG route and then the same procedure was adopted in presence of EPDM rubber to obtain composites containing up to 30 wt% of filler. Extraction and equilibrium swelling tests suggested an interfering effect of the NHSG reaction on the vulcanization process of the rubber resulting to a crosslink density which decreased in the presence of titania. Quasi‐static and dynamic‐mechanical characterizations indicated that the presence of titania as rigid filler in both the unvulcanized and vulcanized EPDM matrix led to a significant increase in stiffness and stress at break. The experimental values of modulus were systematically higher than the values predicted by classical equations suggesting an additional stiffening contribution deriving from the molecular interaction between the rubber and the filler. POLYM. ENG. SCI., 54:2544–2552, 2014. © 2013 Society of Plastics Engineers     

An Algebraic Approach to Shadowed Sets

After the introduction of shadowed sets and the investigation of their relation with fuzzy sets, we present BZMV^dM algebras as an abstract environment for both shadowed and fuzzy sets. Then, we introduce the weaker notion of pre-BZMV^dM algebra. This structure enables us to algebraically define a mapping from fuzzy sets to shadowed sets.     

Design and implementation of switched coil LC‐VCOs in the GHz range using the self‐inductance technique

This paper presents the design and implementation of dual‐band LC‐VCOs in the GHz‐range featuring a switched coil LC‐tank. The proposed design exploits the self‐inductance technique. The design of the coil starts from simple considerations and back‐of‐the‐envelope calculations, then electromagnetic simulations are used to optimize the coil layout. The sizing of the switch and its impact on the VCO performance are addressed as well. The VCOs have been implemented in 65 nm CMOS technology. Good correlation between simulated and measured tuning range and phase noise is obtained for all designs, thus confirming the validity and robustness of the design methodology and coil models. Copyright © 2013 John Wiley & Sons, Ltd.     

Study of the high throughput flexographic process for silicon solar cell metallisation

A commercially available silver paste was modified to match the flexographic process requirements. Rotational and oscillatory rheological tests were carried out to assess the printability and spreading behaviour of the resulting inks. Then, a multifactorial approach was used on a laboratory‐scale printing press to adapt the flexographic process for the front side metallisation of Cz‐Si solar cells, especially for the seed layer deposit of two layer contacts. To quickly identify the significant process parameters, a fractional design of experiment based on a screening approach at two levels was performed. Afterwards, two full factorial designs of experiments were implemented. While the first one allows a better understanding of the effect of the main factors and interactions, the second allows a fine tuning and a confirmation of the first results. Additionally, this methodology allows corroborating the influence of the ink rheological properties on the printing results. Following the process study and optimisation, a seed layer with an average width of 25 µm was printed at a high 0.3 m/s throughput. Additional results suggest that the line width and the throughput can be further improved, which underlines the potential of flexography for photovoltaic applications. Finally, the light‐induced process was used to thicken the seed layer after a standard firing‐through step, leading to an encouraging 17.9% efficiency on Cz‐Si solar cells. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrical ac and dc behavior of epoxy nanocomposites containing graphene oxide

This article deals with the investigation of electrical properties of epoxy‐based nanocomposites containing graphene oxide nanofillers dispersed in the polymer matrix through two‐phase extraction. Broadband dielectric spectroscopy and dc electrical conductivity as a function of electric field have been evaluated in specimens containing up to 0.5 wt % of nanofiller. Nanocomposites containing pristine graphene oxide do not show significant changes of electrical properties. On the contrary, the same materials after a proper thermal treatment at 135°C, able to provoke the in situ reduction of graphene oxide, exhibit higher permittivity and electrical conductivity, without showing large decrease of breakdown voltage. Moreover, a nonlinear behavior of the electrical conductivity is observed in the range of electric fields investigated, i.e. 2–30 kV mm^?1. A new relaxation phenomenon with a very low temperature dependence is also evidenced at high frequency in reduced graphene oxide composites, likely associated to induced polarization of electrically conductive nanoparticles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41923.     

1-Point-RANSAC Structure from Motion for Vehicle-Mounted Cameras by Exploiting Non-holonomic Constraints

This paper presents a new method to estimate the relative motion of a vehicle from images of a single camera. The computational cost of the algorithm is limited only by the feature extraction and matching process, as the outlier removal and the motion estimation steps take less than a fraction of millisecond with a normal laptop computer. The biggest problem in visual motion estimation is data association; matched points contain many outliers that must be detected and removed for the motion to be accurately estimated. In the last few years, a very established method for removing outliers has been the “5-point RANSAC” algorithm which needs a minimum of 5 point correspondences to estimate the model hypotheses. Because of this, however, it can require up to several hundreds of iterations to find a set of points free of outliers. In this paper, we show that by exploiting the nonholonomic constraints of wheeled vehicles it is possible to use a restrictive motion model which allows us to parameterize the motion with only 1 point correspondence. Using a single feature correspondence for motion estimation is the lowest model parameterization possible and results in the two most efficient algorithms for removing outliers: 1-point RANSAC and histogram voting. To support our method we run many experiments on both synthetic and real data and compare the performance with a state-of-the-art approach. Finally, we show an application of our method to visual odometry by recovering a 3 Km trajectory in a cluttered urban environment and in real-time.     

A radio‐aware worst‐case fair weighted fair queuing scheduler for WiMAX networks

This paper presents RA‐WF²Q+, a radio‐aware version of the well‐known WF²Q+ scheduler, tailored for the downlink traffic of a WiMAX system. With respect to WF²Q+, the proposed scheduler introduces the number of slots in the downlink frame as a parameter of the sharing decision process. This solution permits taking into account the information on the radio channel quality experimented by each user and, at the same time, exploiting the well‐known features of WF²Q+. The simulation study comparing the performance of the proposed scheduler with those of other well‐known scheduling algorithms highlights some interesting characteristics of RA‐WF²Q+. In particular, it permits achieving the highest overall system throughput while guaranteeing the requested quality of service for voice applications. Only when the radio resources become scarce with respect to the total offered traffic, RA‐WF²Q+ displays its opportunistic nature, favouring the users nearest to the base station. Copyright © 2012 John Wiley & Sons, Ltd.