Flow boiling heat transfer of a non-azeotropic mixture inside a single microchannel

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.This study moves from the need to study flow boiling of zeotropic mixture in microchannels. In the recent years much attention has been paid to the possible use of fluorinated propene isomers for the substitution of high-GWP refrigerants. The available HFOs (hydrofluoroolefins) cannot cover all the air-conditioning, heat pump, and refrigeration systems when used as pure fluids because their thermodynamic properties are not suitable for all operating conditions and therefore some solutions may be found using blends of refrigerants, to satisfy the demand for a wide range of working conditions. In the present paper a mixture of R1234ze(E) and R32 (0.5/0.5 by mass) has been studied. The local heat transfer coefficient during flow boiling of this mixture in a single microchannel with 0.96 mm diameter is measured at a pressure of 14 bar, which corresponds to a bubble temperature of 26.3°C. The flow boiling data taken in the present test section are discussed, with particular regard to the effect of heat flux, mass velocity and vapor quality. The heat transfer coefficients are compared against some predicting models available in the literature. Furthermore, the new experimental data are compared to flow boiling data of pure R1234ze(E) and pure R32 to analyze the heat transfer penalization due to the mass transfer resistance of this zeotropic mixture

Plano nacional de políticas para as mulheres : necessidades práticas ou interesses estratégicos?

Este artigo analisa, utilizando as categorias Necessidades Práticas (das mulheres) e Interesses Estratégicos (de gênero), a efetividade das ações incluídas nos três Planos Nacionais de Políticas para as Mulheres (período: 2003-2015), considerando especificamente o eixo sobre o mundo do trabalho. A pesquisa qualitativa, bibliográfica e documental, evidenciou que essa recente política pública, executada pelo Estado brasileiro, não alterou substancialmente a realidade vivenciada pelas trabalhadoras. No artigo, defendemos a utilização das categorias Necessidades Práticas e Interesses Estratégicos como método de análise para a formulação, monitoramento e avaliação de políticas de gênero a fim de orientar as transformações para além do atendimento às necessidades básicas das mulheres, visando à superação da divisão sexual do trabalho.This article analyze, using the categories Practical Women Needs and Gender Strategic Interests, the effectiveness of the actions of the three National Plans of Policies for Women (2003-2015), emphasizing the axis of job market. The qualitative research, support on literature revision and documents analysis, revealed that recent public policy carried out by the Brazilian government, has not substantially altered the reality experienced by women workers. We advocate the use of categories Needs Practice and Strategic Interests as an analytical method for the formulation, monitoring and evaluation of gender policies to guide the transformation further the women practical needs to overcome the sexual division of work

Are Land Based Surveys a Useful Tool for Managing Marine Species of Coastal Protected Areas?

One goal of the LIFE project “Del.Ta.” (NAT/IT/000163) was the preparation of an Action Plan to protect the bottlenose dolphin community in the Pelagie Archipelago (Sicily, Italy). It stressed the importance of regular monitoring of the spatial and temporal distribution of dolphins in order to evaluate the impact of local activities. This study assesses whether land-based surveys could be an effective alternative to vessel-based surveys. During the summer of 2006, both surveys’ methodologies were used at Lampedusa, with 35 sightings recorded from land and 31 from a boat. Comparison was based on the assessment of the type of information they provided in relation to the presence of the animals and their behavior. Both methodologies were applicable, but there were differences in their requirements, potential information generated, costs, and sensitivity to weather conditions. Vessel-based surveys require well trained observers and enable photo-identification and observation of social interaction and morphology. Animal movements, interactions with anthropogenic elements and group dynamics are better collected from land but spatial data can be documented up to 1 nautical mile from the coast. Weather conditions have a significant platform specific effect on sighting frequencies. The high sighting frequency during land surveys provides support for the development of zero-impact land-based dolphins watching activity

Two-Phase Flow and Heat Transfer of a Non-Azeotropic Mixture inside a Single Microchannel

In the recent years much attention has been paid to the use of fluorinated propene isomers for the substitution of high-GWP refrigerants. However, the HFOs (hydrofluoroolefins) cannot cover all the air-conditioning, heat pump, and refrigeration applications. In a recent study, it was found that the coefficient of performance (COP) and the capacity of heat pump cycles using HFO-1234ze(E) are significantly lower than those of R410A (Koyama et al., 2010). The main causes are the small latent heat and vapor density of R1234ze(E). To improve the COP and capacity, in the latest literature it was attempted to blend R1234ze(E) into another refrigerant, R32 Although R32 is one of the HFCs, it has relatively low GWP and excellent thermodynamic characteristics. Therefore, a zeotropic mixture of R1234ze(E) and R32 can be used in the field of air-conditioning due to its mild impact on environment. In this paper, a mixture of R1234ze(E) and R32 (0.5/0.5 by mass) is under study. In particular the frictional pressure gradient and the local heat transfer coefficients during flow boiling and condensation of this mixture in a single minichannel with 0.96 mm diameter are measured. Tests are carried out in the experimental apparatus available at the Two Phase Heat Transfer Lab of the University of Padova. As a peculiar characteristic of the present technique, the flow boiling heat transfer coefficient is not measured by imposing the heat flux; instead, the boiling process is governed by controlling the inlet temperature of the heating secondary fluid. For the determination of the local heat transfer coefficient, three parameters are measured: the local heat flux, the saturation temperature and the wall temperature. The heat flux is determined from the temperature profile of the secondary fluid in the test section. The wall temperature is directly measured along the test section and the saturation temperature is obtained from the pressure measurements at the inlet and outlet of the test tube. During condensation tests, the heat is subtracted from the fluid by using cold water. As in flow boiling, the heat transfer coefficient is obtained through the measurement of the local heat flux and the saturation-to-wall temperature difference. The heat transfer coefficients are compared against predicting models available in the literature. The new experimental data are also compared to heat transfer data of pure R1234ze(E) and R32. This allows to analyze the heat transfer penalization due to the mass transfer resistance of this zeotropic mixture and to assess available predicting models for condensation and evaporation of zeotropic mixtures in minichannels. Pressure drop data are also used to assess predicting pressure gradient correlations

A Reproducible Protocol to Assess Arrhythmia Vulnerability in Silico: Pacing at the End of the Effective Refractory Period

In both clinical and computational studies, different pacing protocols are used to induce arrhythmia and non-inducibility is often considered as the endpoint of treatment. The need for a standardized methodology is urgent since the choice of the protocol used to induce arrhythmia could lead to contrasting results, e.g., in assessing atrial fibrillation (AF) vulnerabilty. Therefore, we propose a novel method—pacing at the end of the effective refractory period (PEERP)—and compare it to state-of-the-art protocols, such as phase singularity distribution (PSD) and rapid pacing (RP) in a computational study. All methods were tested by pacing from evenly distributed endocardial points at 1 cm inter-point distance in two bi-atrial geometries. Seven different atrial models were implemented: five cases without specific AF-induced remodeling but with decreasing global conduction velocity and two persistent AF cases with an increasing amount of fibrosis resembling different substrate remodeling stages. Compared with PSD and RP, PEERP induced a larger variety of arrhythmia complexity requiring, on average, only 2.7 extra-stimuli and 3 s of simulation time to initiate reentry. Moreover, PEERP and PSD were the protocols which unveiled a larger number of areas vulnerable to sustain stable long living reentries compared to RP. Finally, PEERP can foster standardization and reproducibility, since, in contrast to the other protocols, it is a parameter-free method. Furthermore, we discuss its clinical applicability. We conclude that the choice of the inducing protocol has an influence on both initiation and maintenance of AF and we propose and provide PEERP as a reproducible method to assess arrhythmia vulnerability

Experimental study of phase change heat transfer in minichannels for ground and space applications

Two-phase heat transfer is widely encountered in minichannels heat exchangers such as air-cooled condensers and evaporators for automotive, compact devices for electronic cooling, aluminum condenser for air-conditioning applications, loop heat pipes and capillary pumped loops for space applications. Nowadays there is also an increasing interest on new refrigerants, pure and blended, with a low-GWP. This thesis aims at studying the physical phenomena of condensation by investigating the effect of gravity inside small channels, presenting an experimental analysis during normal gravity and microgravity conditions. Another objective of this thesis is to analyze the two-phase heat transfer performance of non-azeotropic mixtures, with low-GWP, in minichannels. Regarding mixtures the work focused not only on condensation heat transfer but also on flow boiling and two phase pressure drop. In the first part of this thesis the design and the realization of a new test section to study the effect of gravity during convective condensation is presented. The new test section has an internal diameter of 3.38 mm and it allows to measure quasi-local heat transfer coefficients and to visualize the flow pattern. Quasi-local heat transfer coefficients measured on ground during condensation of R134a at 40°C and mass velocities between 50 and 200 kg m-2 s-1 are presented. The flow patterns visualized are compared with flow pattern maps available in the literature and the experimental heat transfer coefficients with different models for condensation. The new test section has been also used to study convective condensation in microgravity conditions during the 62nd ESA Parabolic Flight Campaign. This has been one of the first attempts to perform heat transfer coefficients measurements and flow pattern visualizations on normal gravity and microgravity conditions during convective condensation inside tubes. The deep connection between gravity effect and flow pattern are shown in the images. Regarding on-ground applications, in the recent years much attention has been paid to the possible use of fluorinated propene isomers for the substitution of HFC fluids being in most cases high-GWP refrigerants. However, the available HFOs (hydrofluoroolefins) cannot cover all the air-conditioning, heat pump, and refrigeration systems when used as pure fluids because their thermodynamic properties are not suitable for all operating conditions; therefore some solutions may be found using blends of refrigerants, to satisfy the demand for a wide range of working conditions. The second part of this thesis presents an experimental study of the two-phase heat transfer for a R32/R1234ze(E) non-azeotropic mixture, at different mass compositions, inside a 0.96 mm inner diameter minichannel. As first step, frictional pressure gradient during adiabatic two-phase flow has been investigated. The experimental data are also compared with several models available in the literature. Local heat transfer coefficients have been then measured during condensation of the R32/R1234ze(E) mixture at three different mass compositions (23/77%, 46/54 and 75/25% by mass). The new experimental data are compared to those of pure R1234ze(E) and R32. This allows to analyze the heat transfer penalization due to the mass transfer resistance occurring during condensation of this zeotropic mixture and to assess about suitable predicting models. The present work reports also the local heat transfer coefficient measured during flow boiling of the R32/R1234ze(E) mixture (50/50% by mass) at a pressure of 14 bar, which corresponds to a bubble temperature of 26.2 °C. The flow boiling data, taken in the 0.96 mm minichannel, are discussed with particular regard to the mass transfer mechanism. The new experimental data are also compared to flow boiling data of pure R1234ze(E) and pure R32. This flow boiling database, encompassing more than 300 experimental points at different values of mass velocity, heat flux and vapor quality, is compared with available correlations in the literature. The introduction of a correction to account for the additional mass transfer resistance is discussed and such correction is found to be necessary and proper to provide a correct sizing of the evaporator