One-dimensional mechanistic model for flow boiling pressure drop in small- to micro- passages

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Accurate predictions of two-phase pressure drop in small to micro diameter passages are necessary for the design of compact and ultra-compact heat exchangers which find wide application in process and refrigeration industries and in cooling of electronics. A semi-mechanistic model of boiling two-phase pressure drop in the confined bubble regime is formulated, following the three-zone approach of Thome et al. (2004) for heat transfer. The total pressure drop is calculated by time-averaging the respective pressure drop values of single-phase liquid, elongated bubble with a thin liquid film and single-phase vapour. The model results were compared with experimental data collected for a wide range of diameter tubes (4.26, 2.88, 2.02, 1.1 and 0.52 mm) for R134a at 6 – 12 bar

Electrical conductivity for Copper Oxide (CuO) nanofluids in the superconducting phase. A generalization of Type II superconductivity hydrodynamics behavior

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Copper oxide superconducting nanofluids exhibit a lot of very interesting technological properties and their behaviour is typical of a two- phase nanofluid. Near the superconductivity trasition temperature, their electrical conductivity is the sum of a normal conductivity component and a flux flow superconducting contribution from the unpinned motion of vortices within the sample. Armed with recent experimental results for regular type II superconductivity nanosamples, we review the corresponding expected behaviour for CuO High Temperature Superconducting (HTSC) systems. The equivalent Navier-Stokes equations that go under the name Ginzburg–Landau equations for the superconducting density are briefly reviewed and their solutions are presented in a clear way for the particular problem. Contribution of fluctuations of the structural vortex lattice, which is a stable solution of the Time Dependent Ginzburg-Landau (TDGL) equations, to the flux flow two -phase conductivity is briefly presented. The corresponding discussion for the two-phase thermal conductivity of a superconducting nanosample is going to be presented in a separate future publication

Design optimisation of air-fed full pressurised suits

This article is a post-print version of the published article which may be accessed at the link below.The JET machine and associated facilities require significant maintenance and enhancement installation activities in support of the experimental exploitation programme. A proportion of these activities are within radiological and respiratory hazardous environments. As such, breathing air-fed one-piece pressurised suits provide workers with protection from the inhalation of both airborne tritium and beryllium dust. The design of these suits has essentially developed empirically. There is a practical necessity to improve the design to optimise worker performance, protection and thermal comfort. This paper details the complexity of modeling the three-dimensional thermofluid domain between the inner surface of the suit and under garments that includes mass as well as heat transfer, suiting geometry, human metabolism and respiration and effects of limb movements. The methods used include computational fluid dynamics (CFD), theoretical adaptations of mixed-phase turbulent flow, profile scanning of a suit and actuating life size mannequin and data processing of the images and experimental validation trials. The achievements of the current programme and collaborations are presented in the paper and future endeavors are discussed.The author gratefully acknowledges the loan of the articulated mannequin from the Defence Science and Technology Laboratories. This work was funded jointly by EPSRC and by the European Communities under the contract of Association between EURATOM and UKAEA. The views and opinions expressed herein do not necessarily reflect those of the European Commission. This work was carried out within the framework of EFDA

Acute Postoperative Changes in Body Composition and Muscle Function Among Patients with Pancreatic Cancer Undergoing Pancreaticoduodenectomy

Aim: To observe changes in the nutritional status of patients during the acute postoperativedays following pancreaticoduodenectomy and to evaluate their influence onpostoperative complications.Methods: Nutritional status was assessed in 72 patients on the preoperative day beforesurgery and postoperative days (PD) 3 and 8, included measurements of bodycomposition by bioimpedance impedance analysis, biochemical values and musclefunction by maximum handgrip strength (HGS). The presence of postoperative complicationswas collected over 30 post operative days. Changes at PD were calculatedfor all variables. Non-parametric statistics were used and results are given as median(25th–75th quartiles).Results : Significant changes occurred on PD 3 in body weight +2.3 (0.8–3.6) kg, totalbody water +2.8 (1.1–5.9) l, extracellular water +2.5 (1.2–3.7) l, intracellular water+1.1 (-0.4–1.9) l, phase angle -1.0 (-1.2 to -0.7)°, C-reactive protein +58.0 (36.0–100.8)mg/l, serum albumin -12 (-16.5 to -10.0) g/l, and HGS -4.8 (-7.3 to -3.0) kg. Higher butno significant changes were observed at PD 3 in patients with postoperative complications(n=28) compared to those without (n=44). The hospital stay was longer inpatients with complications (12.5 days, p=0.005).Conclusion: Changes in body composition, biochemical values and muscle functionwere observed during the first 8 PDs. Changes at PD 3 did not influence significantlythe outcomes, but trends in body fluids and phase angle were found among patientswith postoperative complications

Heat transfer correlation for flow boiling in small to micro tubes

This article is available open access under a Creative Commons license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Copyright © 2013 The Authors. Published by Elsevier Ltd. All rights reserved.There is a large discrepancy in the open literature about the comparative performance of the existing macro and microscale heat transfer models and correlations when applied to small/micro flow boiling systems. This paper presents a detailed comparison of the flow boiling heat transfer coefficient for R134a in stainless steel micro tubes with 21 macro and microscale correlations and models. The experimental database that was used in the comparison includes the data for 1.1 and 0.52 mm diameter tubes, mass flux range of 100–500 kg/m2 s and system pressure range 6–10 bar obtained in the course of this study. The effect of the evaporator heated length on the comparative performance of the correlations and models was investigated using three different lengths of the 1.1 mm diameter tube (L = 150, 300 and 450 mm). This comparative study demonstrated that none of the assessed models and correlations could predict the experimental data with a reasonable accuracy. Also, the predictability of most correlations becomes worse as the heated length increases. This may contribute in explaining the discrepancy in the comparative performance of the correlations from one study to another. A new correlation is proposed in the present study based on the superposition model of Chen. The database used in developing the correlation consists of 5152 data points including the current experimental data and data obtained previously with the same test rig, fluid and methodology for tubes of diameter 4.26, 2.88, 2.01 mm. The new correlation predicted 92% of the data within the ±30% error bands with a MAE value of 14.3%

Velocity profile development and friction in compressible micro flows

From Poiseuille theory, it is known that incompressible laminar fully-developed flow of a Newtonian fluid in a constant cross-section channel is characterised by steady parabolic velocity profiles after a fully-developed flow condition is attained. In turbulent fully-developed flow the velocity profiles are non-parabolic and become more flat for higher Reynolds numbers. When the incompressible hypothesis does not hold, as in the case of high velocity ideal gas flow, the velocity profile becomes flatter, as if more turbulent, due to the superposition of compressibility and turbulence effects, if applicable. This is typical in microchannel flows, where pressure gradients are high and the gas is rapidly accelerating, eventually up to the sound velocity. As the flow accelerates the effects of compressibility grow stronger and the velocity profile keeps changing shape. The radial velocity component does not zero as in fully-developed flow but reverses after the entrance effects have damped out and grows with the Mach number. A net mass transfer toward the walls is thus generated making the velocity profile more flat. This affects the friction factor which is no longer constant, being proportional to the normal-to-wall velocity gradient, and needs to be evaluated. In the present work, the compressible friction factor is numerically investigated and correlations are proposed based on the velocity profile shape evolution as a function of the Mach number. This, together with other considerations on the velocity profile shape change, is shown to enhance the predictive capability of the Fanno theory for compressible flows

Pool boiling on modified surfaces using R-123

This article has been made available through the Brunel Open Access Publishing Fund.Saturated pool boiling of R-123 was investigated for five horizontal copper surfaces modified by different treatments, namely, an emery-polished surface, a fine sandblasted surface, a rough sandblasted surface, an electron beam-enhanced surface, and a sintered surface. Each 40-mm-diameter heating surface formed the upper face of an oxygen-free copper block, electrically heated by embedded cartridge heaters. The experiments were performed from the natural convection regime through nucleate boiling up to the critical heat flux, with both increasing and decreasing heat flux, at 1.01 bar, and additionally at 2 bar and 4 bar for the emery-polished surface. Significant enhancement of heat transfer with increasing surface modification was demonstrated, particularly for the electron beam-enhanced and sintered surfaces. The emery-polished and sandblasted surface results are compared with nucleate boiling correlations and other published data. © 2014 Syed W. Ahmad, John S. Lewis, Ryan J. McGlen, and Tassos G. Karayiannis Published with license by Taylor & Francis