Design and analysis of a wire-driven flexible manipulator for bronchoscopic interventions

Bronchoscopic interventions are widely performed for the diagnosis and treatment of lung diseases. However, for most endobronchial devices, the lack of a bendable tip restricts their access ability to get into distal bronchi with complex bifurcations. This paper presents the design of a new wire-driven continuum manipulator to help guide these devices. The proposed manipulator is built by assembling miniaturized blocks that are featured with interlocking circular joints. It has the capability of maintaining its integrity when the lengths of actuation wires change due to the shaft flex. It allows the existence of a relatively large central cavity to pass through other instruments and enables two rotational degrees of freedom. All these features make it suitable for procedures where tubular anatomies are involved and the flexible shafts have to be considerably bent in usage, just like bronchoscopic interventions. A kinematic model is built to estimate the relationship between the translations of actuation wires and the manipulator tip position. A scale-up model is produced for evaluation experiments and the results validate the performance of the proposed mechanism

Dynamic simulation and exergetic optimization of a Concentrating Photovoltaic/ Thermal (CPVT) system

The development of a dynamic, theoretical model suitable for the prediction of the long-term performance of a parabolic-trough Concentrating Photovoltaic/Thermal CPVT system is discussed in the present study. The formulation of the mathematical model and the considered geometrical and operational parameters of the system, such as the characteristics of the employed PV modules and active cooling system are described in detail. The effect of heat capacity is taken into consideration in the thermal balances and thus the model is able to capture the transient behavior of the system. Besides, the model is validated using available experimental data of a manufactured prototype CPVT system. The daily performance of system is predicted for different values of the cooling fluid flow rate and temperature under various environmental conditions. At a second stage, an exergy analysis is conducted in order to point out the effect of the characteristics of the main system sub-components on the exergetic efficiency and exergy output of the CPVT system. It was established that the system exergetic performance is primarily influenced by the optical quality of the parabolic trough and the electrical efficiency of the PV module. Increasing these two factors to achievable values, e.g. ηopt = 0.75 and ηel = 0.25, can yield an increase of the system exergetic efficiency from 12% to 24%

A new methodology for estimating cavitation erosion: Application on a high speed cavitation test RIG

In this work a new methodology for the prediction of flow areas of cavitation erosion is presented. The new methodology is a post processing procedure utilizing the results of the flow field solution; it is based on tracking the cavity boundaries in near-wall regions where the material derivative of the vapour volume fraction is reducing, meaning that in these areas the vapour structures are collapsing. Three cavitation erosion indexes are proposed and tested, by simulating the flow formed in a high-speed cavitation tunnel at Laboratoire des Ecoulements Géophysiques et Industriels (LEGI) of the University of Grenoble, where experimental erosion results have been obtained in the past. Agreement between the experimental data and the predictions is satisfactory, indicating the research road for developing an accurate prediction methodology of erosion and material loss

Off-centre binary collision of droplets: A numerical investigation

The paper presents results from a numerical investigation of the non-central binary collision of two equal size droplets in a gaseous phase. The flow field is two phase and three dimensional; the investigation is based on the finite volume numerical solution of the Navier–Stokes equations, coupled with the Volume of Fluid Method (VOF), expressing the unified flow field of the two phases, liquid and gas. A recently developed adaptive local grid refinement technique is used, in order to increase the accuracy of the solution particularly in the region of the liquid–gas interface. The reliability of the solution procedure is tested by comparing predictions with available experimental data. The numerical results predict the collision process of the two colliding droplets (permanent coalescence or separation) and in the case of separation the formation and the size of the satellite droplets. The time evolution of the geometrical characteristics of the ligament, for various Weber numbers and impact parameters, is calculated and details are shown of the velocity and pressure fields particularly at the ligament pinch off location not hitherto available. Gas bubbles due to collision are trapped within the liquid phase as it has also been observed in experiments and their volume is calculated

A cavitation aggressiveness index within the Reynolds averaged Navier Stokes methodology for cavitating flows

The paper proposes a methodology within the Reynolds averaged Navier Stokes (RANS) solvers for cavitating flows capable of predicting the flow regions of bubble collapse and the potential aggressiveness to material damage. An aggressiveness index is introduced, called cavitation aggressiveness index (CAI) based on the total derivative of pressure which identifies surface areas exposed to bubble collapses, the index is tested in two known cases documented in the open literature and seems to identify regions of potential cavitation damage

Insight into the Greek electric sector and energy planning with mature technologies and fuel diversification

The numerous available options for the development of the Greek electric sector in combination with the various techno-economic and political constraints make energy planning rather complex. Furthermore, as full auctioning of CO 2 allowances shall be the rule from 2013 onwards for the electric sector following free allocation, even more uncertainties emerge. This work aims at investigating the main characteristics of the Greek electric system taking into consideration the various allowance allocation schemes, evaluates fundamental energy scenarios and ultimately performs energy planning. The reliability of the algorithm utilised is assessed by predicting successfully key figure energy results for years 2004-2008. Main parameter under investigation in the study is the cost of CO 2 emissions allowances, while expansion scenarios are evaluated according to a newly developed set of indices standing for feasibility, environmental performance, cost effectiveness and energy safety. Many expansion scenarios examined were proved unrealistic as led to extremely high utilization of imported fuels for electricity production, while others proved inefficient on environmental or economic basis. Finally, it was proved that if a "conservative" energy planning is adopted, emissions reduction in 2020 can reach 6.3% over 2005

Numerical investigation on the evaporation of droplets depositing on heated surfaces at low Weber numbers

The evaporation of water droplets, impinging with low Weber number and gently depositing on heated surfaces of stainless steel is studied numerically using a combination of fluid flow and heat transfer models. The coupled problem of heat transfer between the surrounding air, the droplet and the wall together with the liquid vaporisation from the droplet’s free surface is predicted using a modified VOF methodology accounting for phase-change and variable liquid properties. The surface cooling during droplet’s evaporation is predicted by solving simultaneously with the fluid flow and heat transfer equations, the heat conduction equation within the solid wall. The droplet’s evaporation rate is predicted using a model from the kinetic theory of gases coupled with the Spalding mass transfer model, for different initial contact angles and substrate’s temperatures, which have been varied between 20–90° and 60–100 °C, respectively. Additionally, results from a simplified and computationally less demanding simulation methodology, accounting only for the heat transfer and vaporisation processes using a time-dependent but pre-described droplet shape while neglecting fluid flow are compared with those from the full solution. The numerical results are compared against experiments for the droplet volume regression, life time and droplet shape change, showing a good agreement

Numerical investigation of the evaporation of two-component droplets

A numerical model for the complete thermo-fluid-dynamic and phase-change transport processes of two-component hydrocarbon liquid droplets consisting of n-heptane, n-decane and mixture of the two in various compositions is presented and validated against experimental data. The Navier–Stokes equations are solved numerically together with the VOF methodology for tracking the droplet interface, using an adaptive local grid refinement technique. The energy and concentration equations inside the liquid and the gaseous phases for both liquid species and their vapor components are additionally solved, coupled together with a model predicting the local vaporization rate at the cells forming the interface between the liquid and the surrounding gas. The model is validated against experimental data available for droplets suspended on a small diameter pipe in a hot air environment under convective flow conditions; these refer to droplet’s surface temperature and size regression with time. An extended investigation of the flow field is presented along with the temperature and concentration fields. The equilibrium position of droplets is estimated together with the deformation process of the droplet. Finally, extensive parametric studies are presented revealing the nature of multi-component droplet evaporation on the details of the flow, the temperature and concentration fields

Transient heating effects in high pressure Diesel injector nozzles

The tendency of today’s fuel injection systems to reach injection pressures up to 3000 bar in order to meet forthcoming emission regulations may significantly increase liquid temperatures due to friction heating; this paper identifies numerically the importance of fuel pressurization, phase-change due to cavitation, wall heat transfer and needle valve motion on the fluid heating induced in high pressure Diesel fuel injectors. These parameters affect the nozzle discharge coefficient (Cd), fuel exit temperature, cavitation volume fraction and temperature distribution within the nozzle. Variable fuel properties, being a function of the local pressure and temperature are found necessary in order to simulate accurately the effects of depressurization and heating induced by friction forces. Comparison of CFD predictions against a 0-D thermodynamic model, indicates that although the mean exit temperature increase relative to the initial fuel temperature is proportional to (1 − Cd2) at fixed needle positions, it can significantly deviate from this value when the motion of the needle valve, controlling the opening and closing of the injection process, is taken into consideration. Increasing the inlet pressure from 2000 bar, which is the pressure utilized in today’s fuel systems to 3000 bar, results to significantly increased fluid temperatures above the boiling point of the Diesel fuel components and therefore regions of potential heterogeneous fuel boiling are identified