Mostafa Odabaee

Particle deposition effects on heat transfer from a metal foam‐wrapped tube bundle

Purpose - The purpose of this paper is to clarify the relationship between dust deposition effects on the thermohydraulic performance of a metal foam heat exchanger. Design/methodology/approach - The paper uses finite volume approximation to solve the two-dimensional volume-averaged form of governing equations through and around a metal foam-covered tube bundle. Modified porosity, permeability, and form drag coefficient for a dusty foam layer are obtained through the application of a thermal resistance network model. Findings - The paper provides novel data to predict the fouling effects on the performance of foam-wrapped tube bundles as air-cooled heat exchangers. It is observed that depending on the deposited layer thickness, the increased pressure drop and heat transfer deterioration can be very significant. Originality/value - This paper fulfils an identified need to study fouling effects on thermohydraulic performance of a foam heat exchanger.

Metal foam heat exchangers for thermal management of fuel cell systems

The present study explores the possibility of using metal foams for thermal management of fuel cells so that air-cooled fuel cell stacks can be commercialized as replacements for currently-available water-cooled counterparts. Experimental studies have been conducted to examine the heat transfer enhancement from a thin metal foam layer sandwiched between two bipolar plates of a cell. To do this, effects of the key parameters including the free stream velocity and characteristics of metal foam such as porosity, permeability, and form drag coefficient on heat and fluid flow are investigated. The improvements as a result of the application of metal foam layers on fuel cell systems efficiency have been analyzed and discussed. Non-optimized results have shown that to remove the same amount of generated heat, the air-cooled fuel cell systems using aluminum foams require half of the pumping power compared to water-cooled fuel cell systems.

Establishing sheep as an experimental species to validate ultrasound-mediated blood-brain barrier opening for potential therapeutic interventions

Rationale: Treating diseases of the brain such as Alzheimers disease (AD) is challenging as the blood-brain barrier (BBB) effectively restricts access of a large number of potentially useful drugs. A potential solution to this problem is presented by therapeutic ultrasound, a novel treatment modality that can achieve transient BBB opening in species including rodents, facilitated by biologically inert microbubbles that are routinely used in a clinical setting for contrast enhancement. However, in translating rodent studies to the human brain, the presence of a thick cancellous skull that both absorbs and distorts ultrasound presents a challenge. A larger animal model that is more similar to humans is therefore required in order to establish a suitable protocol and to test devices. Here we investigated whether sheep provide such a model. Methods: In a stepwise manner, we used a total of 12 sheep to establish a sonication protocol using a spherically focused transducer. This was assisted by ex vivo simulations based on CT scans to establish suitable sonication parameters. BBB opening was assessed by Evans blue staining and a range of histological tests. Results: Here we demonstrate noninvasive microbubble-mediated BBB opening through the intact sheep skull. Our non-recovery protocol allowed for BBB opening at the base of the brain, and in areas relevant for AD, including the cortex and hippocampus. Linear time-shift invariant analysis and finite element analysis simulations were used to optimize the position of the transducer and to predict the acoustic pressure and location of the focus. Conclusion: Our study establishes sheep as a novel animal model for ultrasound-mediated BBB opening and highlights opportunities and challenges in using this model. Moreover, as sheep develop an AD-like pathology with aging, they represent a large animal model that could potentially complement the use of non-human primates.

Modeling ultrasound propagation through material of increasing geometrical complexity

HighlightsUltrasound is increasingly being recognized as therapeutic tool for brain diseases.The acoustic properties of a set of simple bone‐modeling samples were analyzed.Wiener deconvolution predicts the Ultrasound Acoustic Response and attenuation.Finite Element Analysis observes scattering and refraction of wave propagation.Finite Element Analysis reveals differences depending on step size of models. ABSTRACT Ultrasound is increasingly being recognized as a neuromodulatory and therapeutic tool, inducing a broad range of bio‐effects in the tissue of experimental animals and humans. To achieve these effects in a predictable manner in the human brain, the thick cancellous skull presents a problem, causing attenuation. In order to overcome this challenge, as a first step, the acoustic properties of a set of simple bone‐modeling resin samples that displayed an increasing geometrical complexity (increasing step sizes) were analyzed. Using two Non‐Destructive Testing (NDT) transducers, we found that Wiener deconvolution predicted the Ultrasound Acoustic Response (UAR) and attenuation caused by the samples. However, whereas the UAR of samples with step sizes larger than the wavelength could be accurately estimated, the prediction was not accurate when the sample had a smaller step size. Furthermore, a Finite Element Analysis (FEA) performed in ANSYS determined that the scattering and refraction of sound waves was significantly higher in complex samples with smaller step sizes compared to simple samples with a larger step size. Together, this reveals an interaction of frequency and geometrical complexity in predicting the UAR and attenuation. These findings could in future be applied to poro‐visco‐elastic materials that better model the human skull.

CFD Simulation of a Supercritical Carbon Dioxide Radial-Inflow Turbine, Comparing the Results of Using Real Gas Equation of Estate and Real Gas Property File

The present study explores CFD analysis of a supercritical carbon dioxide (SCO2) radial-inflow turbine generating 100kW from a concentrated solar resource of 560oC with a pressure ratio of 2.2. Two methods of real gas property estimations including real gas equation of estate and real gas property (RGP) file - generating a required table from NIST REFPROP - were used. Comparing the numerical results and time consumption of both methods, it was shown that equation of states could insert a significant error in thermodynamic property prediction. Implementing the RGP table method indicated a very good agreement with NIST REFPROP while it had slightly more computational cost compared to the RGP table method.

Optimisation of a High Pressure Ratio Radial-Inflow Turbine: Coupled CFD-FE Analysis

The optimisation of a 5.7 air pressure ratio single stage radial-inflow turbine applied in the Sundstrand Power Systems T-100 Multipurpose Small Power Unit (MPSPU) is performed using coupled CFD-FE method. The commercial software ANSYS-Vista RTD along with a built-in module, BladeGen, is used to conduct a meanline design and, consequently, create the 3D geometry of the flow passage. Carefully examining the proposed design against the geometrical and experimental data, ANSYS-TurboGrid is applied to generate computational mesh. CFD simulations are then performed with ANSYS-CFX in which three-dimensional Reynolds-Averaged Navier-Stokes equations are solved subject to appropriate boundary conditions. Conducting the CFD simulations, the pressure and temperature distributions are imported to the ANSYS-FE module. The von Mises stress σv distribution is then calculated taking into account the centrifugal force acting on the turbine wheel. To obtain the optimised geometry, 25 major design points are regenerated where the meridional parameters, tip clearance, and blade thickness distribution are systematically changed. Furthermore, constraints are defined as high aerothermodynamic performance and acceptable vibration with a stress distribution less than yield limit of the turbine material. Results of coupled CFD-FE method show the power, efficiency, stress and deformation. Finally, performance of the optimised radial-inflow turbine indicates enhanced aero-thermodynamics (NTS and) and structural performance (σν) compared to the MPSPU turbine design.