Juan Carlos Ramos

The application of spreadsheets to the analysis and optimization of systems and processes in the teaching of hydraulic and thermal engineering

This article shows the capability of current spreadsheets to define, analyze and optimize models of systems and processes. Specifically, the Microsoft spreadsheet Excel is used, with its built‐in solver, to analyze and to optimize systems and processes of medium complexity, whose mathematical models are expressed by means of nonlinear systems of equations. Two hydraulic and thermal engineering‐based application examples are presented, respectively: the analysis and optimization of vapor power cycles, and the analysis and design of piping networks. The mathematical models of these examples have been implemented in Excel and have been solved with the solver. For the power cycles, the thermodynamic properties of water have been calculated by means of the add‐in TPX (Thermodynamic Properties for Excel). Performance and optimum designs are presented in cases studies, according to the optimization criteria of maximum efficiency for the power cycle and minimum cost for the piping networks.

Film Thickness and Heat Transfer Measurements in a Spray Cooling System With R134a

Experimental measurements in a spray cooling test rig have been carried out for several heat fluxes in the heater and different spray volumetric fluxes with the dielectric refrigerant R134a. Results of the heat transfer and the sprayed refrigerant film thickness measurements are presented. The film thickness measurements have been made with a high speed camera equipped with a long distance microscope. It has been found that there is a relation between the variation in the average Nusselt number and the film thickness along the spray cooling boiling curve. The heat transfer regimes along that curve are related not only with a variation in the average Nusselt number but also with changes in the film thickness. The qualitative analysis of those variations has served to understand better the heat transfer mechanisms occurring during the spray cooling.

Linear spatial instability of viscous flow of a liquid sheet through gas

The present paper focuses on the linear spatial instability of a viscous two-dimensional liquid sheet bounded by two identical viscous gas streams. The Orr–Sommerfeld differential equations and the ...

Liver Cancer Arterial Perfusion Modelling and CFD Boundary Conditions Methodology: A Case Study of the Haemodynamics of a Patient‐Specific Hepatic Artery in Literature‐Based Healthy and Tumour‐Bearing Liver Scenarios

Some of the latest treatments for unresectable liver malignancies (primary or metastatic tumours), which include bland embolisation, chemoembolisation, and radioembolisation, among others, take advantage of the increased arterial blood supply to the tumours to locally attack them. A better understanding of the factors that influence this transport may help improve the therapeutic procedures by taking advantage of flow patterns or by designing catheters and infusion systems that result in the injected beads having increased access to the tumour vasculature. Computational analyses may help understand the haemodynamic patterns and embolic-microsphere transport through the hepatic arteries. In addition, physiological inflow and outflow boundary conditions are essential in order to reliably represent the blood flow through arteries. This study presents a liver cancer arterial perfusion model based on a literature review and derives boundary conditions for tumour-bearing liver-feeding hepatic arteries based on the arterial perfusion characteristics of normal and tumorous liver segment tissue masses and the hepatic artery branching configuration. Literature-based healthy and tumour-bearing realistic scenarios are created and haemodynamically analysed for the same patient-specific hepatic artery. As a result, this study provides boundary conditions for computational fluid dynamics simulations that will allow researchers to numerically study, for example, various intravascular devices used for liver disease intra-arterial treatments with different cancer scenarios. Copyright

Physiological outflow boundary conditions methodology for small arteries with multiple outlets: A patient-specific hepatic artery haemodynamics case study

Physiological outflow boundary conditions are necessary to carry out computational fluid dynamics simulations that reliably represent the blood flow through arteries. When dealing with complex three-dimensional trees of small arteries, and therefore with multiple outlets, the robustness and speed of convergence are also important. This study derives physiological outflow boundary conditions for cases in which the physiological values at those outlets are not known (neither in vivo measurements nor literature-based values are available) and in which the tree exhibits symmetry to some extent. The inputs of the methodology are the three-dimensional domain and the flow rate waveform and the systolic and diastolic pressures at the inlet. The derived physiological outflow boundary conditions, which are a physiological pressure waveform for each outlet, are based on the results of a zero-dimensional model simulation. The methodology assumes symmetrical branching and is able to tackle the flow distribution problem when the domain outlets are at branches with a different number of upstream bifurcations. The methodology is applied to a group of patient-specific arteries in the liver. The methodology is considered to be valid because the pulsatile computational fluid dynamics simulation with the inflow flow rate waveform (input of the methodology) and the derived outflow boundary conditions lead to physiological results, that is, the resulting systolic and diastolic pressures at the inlet match the inputs of the methodology, and the flow split is also physiological.

Computational particle–haemodynamics analysis of liver radioembolization pretreatment as an actual treatment surrogate

Liver radioembolization (RE) is a treatment option for patients with unresectable and chemorefractory primary and metastatic liver tumours. RE consists of intra-arterially administering via catheter radioactive microspheres that locally attack the tumours, sparing healthy tissue. Prior to RE, the standard practice is to conduct a treatment-mimicking pretreatment assessment via the infusion of 99m Tc-labelled macroaggregated albumin microparticles. The usefulness of this pretreatment has been debated in the literature, and thus, the aim of the present study is to shed light on this issue by numerically simulating the liver RE pretreatment and actual treatment particle-haemodynamics in a patient-specific hepatic artery under two different literature-based cancer scenarios and two different placements of a realistic end-hole microcatheter in the proper hepatic artery. The parameters that are analysed are the following: microagent quantity and size (accounting for RE pretreatment and treatment), catheter-tip position (near the proper hepatic artery bifurcation and away from it), and cancer burden (10% and 30% liver involvement). The conclusion that can be reached from the simulations is that when it comes to mimicking RE in terms of delivering particles to tumour-bearing segments, the catheter-tip position is much more important (because of the importance of local haemodynamic pattern alteration) than the infused microagents (i.e. quantity and size). Cancer burden is another important feature because the increase in blood flow rate to tumour-bearing segments increases the power to drag particles. These numerical simulation-based conclusions are in agreement with clinically observed events reported in the literature. Copyright

Thermoelectric cooling heating unit prototype

The article describes from an architectonical point of view the design, assembly, and energy behavior of a prototype for air-conditioning in residential buildings using Peltier cells, which means the application in the field of construction of a technology used in very specific areas. The new system has been designed as an independent, prefabricated, modular construction element that must fit perfectly between the structural floors and is easily adapted to the demands of different buildings. The thermoelectric cooling heating unit is designed to offer a high level of comfort to those living in the building. The only mechanical elements are the dissipation heat fans placed on the outside of the prototype, and heat sinks to transfer the heat from the power elements, reducing the possibilities of failure. The result of all these ideas is the construction of a prefabricated module, consisting of a simplified inhabited housing unit with a thermoelectric installation serving the module, which has obtained a national patent. The results of the thermal and electric behavior demonstrate that the system does not work as well as had been expected; nevertheless, the system has a high potential for its use in buildings associated with photovoltaic. Practical application : The system opens new ways to the air-conditioning without using the traditional concepts of primary and secondary loop, because the system is highly independent. Their applications could be in building refurbishment where other systems involving the use of water or air are complicated to implement, in spaces where security and resilience are crucial factors (such as surgeries or computer server rooms), or those situations with extreme maximum and minimum temperatures or irregular electrical supply, as those could exist when the army must intervene or an humanitarian disaster occurs.

Performance of Axial Fans in Close Proximity to the Electromagnetic Compatibility Screens

The performance of axial fans in close proximity to the electromagnetic compatibility(EMC) screens was analyzed by means of an experimental parametric study. The follow-ing geometrical parameters were studied: the hub-to-tip ratio, the ratio between fanthickness and fan diameter, the porosity and thickness of the perforated plate, and finally,the distance between the perforated plate and the inlet and the outlet of the fan. Screenporosity was found to be the most important parameter. Fan performance degradation isexpressed by means of two correlations: one for the deterioration in the fan pressure atthe no-flow point and the other for the flow rate reduction at the free delivery point. Bothcorrelations were formulated as functions of screen porosity and the distance betweenthe fan and the screen. We believe that the correlations can serve as a good guide for cor-rect fan placement in a telecommunications cabinet. [DOI: 10.1115/1.4005913]Keywords: fan characteristic curve, telecommunications cabinet, perforated plate,

Thermal Control of Protruding Electronic Components with PCM: A Parametric Study

This work deals with the melting and natural convection in a rectangular enclosure heated from three discrete protruding electronic components (heat sources) mounted on a conducting vertical plate (substrate). The heat sources generate heat at a constant and uniform volumetric rate. A part of the power generated in the heat sources is dissipated to the phase change material (PCM, n-eicosane with a melting temperature T m = 36°C) that filled the enclosure. To investigate the thermal behavior of the proposed heat sink, a mathematical model, based on the mass, momentum, and energy conservation equations was developed. The model has been verified and then validated comparing the melting front with available experimental results. Numerical investigations have been conducted in order to examine the effects of the electronic components thickness and the plate thermal diffusivity on the maximum temperature of electronic components. The percentage contribution of plate heat conduction on the total removed heat and temperature profile in the plate have also been analyzed. Correlations for the nondimensional secured working time (time to reach the threshold temperature, T cr = 75°C) and its corresponding melt fraction were derived.

Computational Modeling and Simulation of a Single-Jet Water Meter

A single-jet water meter was modeled and simulated within a wide measuring range that included flow rates in laminar, transitional, and turbulent flow regimes. The interaction between the turbine and the flow, on which the operating principle of this kind of meter is based, was studied in depth from the detailed information provided by simulations of the three dimensional flow within the meter. This interaction was resolved by means of a devised semi-implicit time-marching procedure in such a way that the speed and the position of the turbine were obtained as part of the solution. Results obtained regarding the turbines mean rotation speed, measurement error, and pressure drop were validated through experimental measurements performed on a test rig. The role of mechanical friction on the performance of the meter at low flow rates was analyzed and interesting conclusions about its influence on the reduction of the turbines rotation speed and on the related change in the measurement error were drawn. The mathematical model developed was capable of reproducing the performance of the meter throughout the majority of the measuring range, and thus was shown to be a very valuable tool for the analysis and improvement of the single-jet water meter studied.