Hussam Jouhara

An Experimental Study of Small-Diameter Wickless Heat Pipes Operating in the Temperature Range 200°C to 450°C

An experimental investigation is reported for medium-temperature, wickless, small-diameter heat pipes charged with environmentally sound and commercially available working fluids. The wickless heat pipes (thermosyphons) studied have many applications in heat recovery systems since their operational temperature range is between 200°C and 450°C. The heat pipes investigated had an internal diameter of 6 mm and a length of 209 mm. The lengths of evaporator and condenser sections were 50 mm and 100 mm, respectively. The working fluids tested were diphenyl based: Therminol VP1 and Dowtherm A. High-grade stainless steel was chosen as the shell material for the heat pipes to provide chemical compatibility between heat pipe casing material and working fluids at elevated temperatures. Thermal resistances of less than 0.4 K/W have been achieved at working temperatures of up to 420°C with an effective thermal conductivity of 20 kW/m-K, which corresponds to an axial heat flux of 2.5 MW/m2. Even for such small-diameter heat pipes, the experimental data for the evaporator showed good agreement with Rohsenows pool boiling correlation.

Modelling and simulation techniques for forced convection heat transfer in heat sinks with rectangular fins

Abstract This paper provides a comprehensive description of the thermal conditions within a heat sink with rectangular fins under conditions of cooling by laminar forced convection. The analysis, in which increasing complexity is progressively introduced, uses both classical heat transfer theory and a computational approach to model the increase in air temperature through the channels formed by adjacent fins and the results agree well with published experimental data. The calculations show how key heat transfer parameters vary with axial distance, in particular the rapid changes in heat transfer coefficient and fin efficiency near the leading edges of the cooling fins. Despite these rapid changes and the somewhat ill-defined flow conditions which would exist in practice at the entry to the heat sink, the results clearly show that, compared with the most complex case of a full numerical simulation, accurate predictions of heat sink performance are attainable using analytical methods which incorporate average values of heat transfer coefficient and fin efficiency. The mathematical modelling and solution techniques for each method are described in detail.

Surface water filtration using granular media and membranes: A review

Significant growth of the human population is expected in the future. Hence, the pressure on the already scarce natural water resources is continuously increasing. This work is an overview of membrane and filtration methods for the removal of pollutants such as bacteria, viruses and heavy metals from surface water. Microfiltration/Ultrafiltration (MF/UF) can be highly effective in eliminating bacteria and/or act as pre-treatment before Nanofiltration/Reverse Osmosis (NF/RO) to reduce the possibility of fouling. However, MF/UF membranes are produced through relatively intensive procedures. Moreover, they can be modified with chemical additives to improve their performance. Therefore, MF/UF applicability in less developed countries can be limited. NF shows high removal capability of certain contaminants (e.g. pharmaceutically active compounds and ionic compounds). RO is necessary for desalination purposes in areas where sea water is used for drinking/sanitation. Nevertheless, NF/RO systems require pre-treatment of the influent, increased electrical supply and high level of technical expertise. Thus, they are often a highly costly addition for countries under development. Slow Sand Filtration (SSF) is a simple and easy-to-operate process for the retention of solids, microorganisms and heavy metals; land use is a limiting factor, though. Rapid Sand Filtration (RSF) is an alternative responding to the need for optimized land use. However, it requires prior and post treatment stages to prevent fouling. Especially after coating with metal-based additives, sand filtration can constitute an efficient and sustainable treatment option for developing countries. Granular activated carbon (GAC) adsorbs organic compounds that were not filtered in previous treatment stages. It can be used in conjunction with other methods (e.g. MF and SSF) to face pollution that results from potentially outdated water network (especially in less developed areas) and, hence, produce water of acceptable drinking quality. Future research can focus on the potential of GAC production from alternative sources (e.g. municipal waste). Given the high production/operation/maintenance cost of the NF/RO systems, more cost-effective but equally effective alternatives can be implemented: e.g. (electro)coagulation/flocculation followed by MF/UF, SSF before/after MF/UF, MF/UF before GAC.

Energy efficient HVAC systems

Abstract To achieve energy efficient Heating, Ventilation and Air Conditioning (HVAC) systems in buildings it is essential to enhance the designs of their various integrated mechanical and electrical components and to control and operate plant optimally. More efficient HVAC systems lead to a significant reduction in power consumption in buildings, which is significant bearing in mind that buildings consume over 40% of the total power consumption in many developed countries. This Special Issue on energy efficient HVAC systems was open to all contributors in the field of heating, ventilation and air conditioning systems in buildings. The invitation was for novel and original papers which extend and advance our scientific and technical understanding of efficient energy HVAC systems including Heat Pumps, water heating and cooling systems in buildings, efficient air conditioning systems, efficient component designs, energy storage (heating and cooling) and regenerative processes. In the event, all these topics were covered in the very wide-ranging submissions accepted but interesting papers on other aspects of HVAC systems and operation were also received.

Hydrophilic and hydrophobic materials and their applications

ABSTRACT Wettability of a material’s surface plays a significant role in how fluids interact with such surfaces. Wetting behavior is universal but can vary depending on the chemical nature of the solid and liquid phases. Plants and animals adapt to their environment by having evolved special properties. These properties are such as hydrophilic and hydrophobic. Hydrophilic surface has a strong affinity to water and spreading of water on such surface is preferred. The degree of hydrophilicity of the substance can be measured by measuring the contact angle between the liquid and solid phases. Hydrophobic materials are known as non-polar materials with a low affinity to water, which makes them water repelling. A contact angle of less than 90° indicates hydrophilic interaction where as an angle greater than 90° indicates a hydrophobic interaction. More recently, superwetting such as superhydrophilicity has been receiving an increased focus in the literature due to its potential significance. Superhydrophilic surface has a contact angle of less than 5°. The fabrication of hydrophilic materials can be carried out in two main ways: depositing molecules on surfaces or modification of surface chemistry. Both methods have been successful historically in achieving their intended purposes. Hydrophobic and superhydrophobic materials can be produced with many fabrication methods such as layer-by-layer assembly, laser process, the solution-immersion method, sol-gen techniques, chemical etching, and Hummer’s method. The applications of such an important property are significant. For example, hydrophilic surfaces can be used in anti-fogging applications, biomedical, filtration, heat pipes, and many others. Hydrophobic and superhydrophobic materials have been successfully applied in many sectors, such as: (I) the removal of petroleum from aqueous solutions, (II) applied to plastic, ceramics, and mesh to contribute to the oil removal from aqueous solutions, (III) hydrophobic layers have a strong self-cleaning effect on plastics, heat pipes, metals, textiles, glass, paints, and electronics, (IV) hydrophobic layers improve the anti-freezing behavior of heat pipes which prevents unwanted build-up and (V) they function as a water and dust protecting coat on electronics. The presence of this property is historic but there is still a huge potential for development for its applications in many sectors such as water treatment, heat transfer applications, biomedical devices, and many more.

Heat pipe oven for optical crystals

A heat pipe based thermal oven for crystals is presented. The crystal is placed in the adiabatic region of the heat pipe in order to have a homogenized temperature around and inside the crystal. The system ensures a steady and homogeneous temperature environment within 0.1°C precision in a wide temperature range [20°C, 100°C].This oven is used to control the temperature of the second harmonic generated from a KD*P crystal. The experimental results and modeling predictions of the temperature effect are presented and compared.

Experimental analysis of gas to water two phase closed thermosyphon based heat exchanger

P structures have been studied since the 1960’s by many scholars, most prominently, by Prof. Mead of the Institute of Sound and Vibration, Southampton University in the UK. In 2000, the author embarked on a journey with periodic structures, it took quite a while until he understood how it works, after those years, he realized, at last, that have not yet reached a good understanding! In this talk, he will be presenting an understanding of the concepts of propagation and stop bands widely used in the world of periodic structures, the forward and reverse approaches for analysis of periodic structures, conclusions of experimental and numerical research conducted by the author with his colleagues and students on periodic beams and plates, and finally, a general conclusion on the finding of the research.N play an important role in determining the hardness, fracture toughness, and strength of materials. Nanoparticles with size ranging from 1-100 nm are beginning to play a strong role as additives in metals and alloys, contributing to their high hardness and low plasticity. This presentation focuses on a class of nanomaterials called ‘nanodiamond’. Nanodiamond additives have been shown to improve tribological properties and enhance mechanical properties in varied classes of materials such as polymer composites, engine oils and lubricants. Although experimentally shown to improve mechanical properties, the nanoscale origins of how these nanoparticles interact with their host atoms and molecules is unknown. In this presentation, we explore scanning probe microscopy as a tool to study interaction between nanodiamond particles, throwing greater light on interaction forces at the nanoscale. As an example, using force-distance spectroscopy, we show that nanodiamonds show reduced adhesion with a scanning probe tip, thus making them effective as lubricant additives.Wickless heat pipes have been attracting increased attention in the last two decades due to their reliability and high heat transfer potential per unit area. Their most common application is in the process industry, when coupled to waste heat recovery devices. Heat pipe based heat exchangers offer many advantages when compared with conventional waste heat recovery systems; advantages that are detailed in the current work. The design of such devices, however, is not a straightforward process due to the complex modes of heat transfer mechanisms involved. In this paper, the characterisation of a cross-flow heat pipe based heat exchanger is studied experimentally, using correlations currently available in literature. A design tool with the purpose of predicting the performance of the test unit was also developed and validated through comparison with the experimental results. The design tool was validated with the use of a purpose-built experimental facility.F is the process by which a liquid or gas flows through a particulate solid phase, keeping it under suspension and showing fluid-like behavior. Among applications of FBs, process of energy conversion such as combustion and gasification are the focus of much research nowadays. Research in Computational Fluid Dynamics (CFD) applied to the simulation of FBs has grown in the last few years in view of the need to perform a large number of tests to define appropriate, if not optimal, operational conditions. CFD could provide a low cost test bench in FBs applications. Nevertheless, the mathematical modeling of multiphase and often reactive flows in this kind of system is indeed very complex. A possible approach that is much employed is the Euler-Granular modeling, which describes solid and gaseous phases as interpenetrating continua. Furthermore, the stresses of the solid phase, are translated into a stress tensor in the form of a fluid stress tensor, with parameters such as pressure and viscosity obtained from the Kinetic Theory of Granular Flows (KTGF). KTGF is derived from the kinetic theory for dense gases, extrapolated to describe the behavior of small particles inserted in a fluid medium. In this project we have studied the features of the Euler-Granular model and the influence of model parameters in numerical results of flows in bubbling and circulating FBs. We have employed factorial plans to quantify the influence of restitution and specularity coefficients and gas-solid drag laws, and also the interaction among these parameters.C parallel manipulator (CPM) is a 3-Dof parallel manipulator that consists of a platform which is connected to the fixed base by limbs in three perpendicular planes. In this paper smooth singularity free trajectory planning optimization of the CPM is investigated. The forward and inverse kinematic equations of CPM are obtained by the robot geometrical constraints and its dynamic equations of motion are derived using Kane’s method. Considering the actuators’ limitation and kinematical constraints originated from the closed-chain nature of the CPM, an algorithm for trajectory definition and optimization for the robot end-effector is proposed using B-Spline functions without requiring any information about the geometry of CPM endeffector. The total required energy, maximum actuator’s jerk and total time of motion are defined as three objective functions in terms of B-Spline parameters and non-dominated sorting genetic algorithm-II (NSGA-II) is used to solve the nonlinear constrained multi-objective optimization problem and calculate the optimal values of the trajectory parameters. Finally, the proposed algorithm is implemented in MATLAB software and its results are demonstrated and discussed which confirm the effectiveness of the presented method.The present study deals with the force and stress distribution within the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) in response to an anterior tibial load with the knee at full extension was calculated using a validated three dimensional finite element model (FEM) of a human ACL. The interaction between the AM and PL bundles, as well as the contact and friction caused by the ACL wrapping around the bone during knee motion, were included in the model. The AM and PL bundles of the ACL were simulated as incompressible homogeneous and isotropic hyperelastic materials. The validated FEM was then used to calculate the force and stress distribution within the ACL under an anterior tibial load at full extension. The AM and PL bundles shared the force, and the stress distribution was non-uniform within both bundles with the highest stress localized near the femoral insertion site. The contact and friction caused by the ACL wrapping around the bone during knee motion played the role of transferring the force from the ACL to the bone, and had a direct effect on the force and stress distribution of the ACL. This validated model will enable the analysis of force and stress distribution in the ACL in response to more complex loading conditions and has the potential to help design improved surgical procedures following ACL injuries.