Boiling instabilities in microtubes

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.Microprocessor and microchip speeds are continuously increasing with their shrinking sizes. For this reason, the size of subject related heat sinks are continuously decreasing from mini size to micro size. Among many microscale heat transfer cooling applications, the most practical and extensively used micro heat sinks are plain microchannels. This study addresses the lack of information about microchannel boiling instability phenomena and includes a parametric investigation in microtubes. Experimental data were obtained from a microtube having a 250~μm inner diameter, which was tested at low mass fluxes (78.9-276.3 kg/m2s) to reveal potential boiling instabilities. De-ionized water was used as a coolant, while the microtube was heated by Joule heating. Configurations prone to boiling instabilities (low system pressures, low mass velocities) were imposed to observe boiling instabilities in microtubes. After the experiments without any inlet restriction, experiments were conducted with the configuration with inlet restriction where pressure drop over inlet restriction element was 4 times as much as pressure drop over the microtube. Temperature and pressure drop fluctuation signals were recorded and processed once boiling instabilities were observed

Bubbly cavitating flow generation and investigation of its erosional nature for biomedical applications

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.The paper presents a study of the generation of hydrodynamic bubbly cavitation in microchannels to investigate the destructive energy output resulting from this phenomenon and its potential use in biomedical applications. The research performed in this study includes the experimental results from bubbly cavitation experiments and the findings showing the destructive effects of bubbly cavitating flow on selected specimens and cells. The bubbles caused by hydrodynamic cavitation are highly destructive at the surfaces of the target medium on which they are carefully focused. The resulting destructive energy output could be effectively used for good means such as destroying kidney stones or killing infected cancer cells. Motivated by this potential, the cavitation damage (material removal) to cancerous cells and chalk pieces having similar material properties as calcium phosphate in human bones was investigated. Also the potential of hydrodynamic bubbly cavitation generated at the microscale for biomedical treatments was revealed using the microchannel configuration of a microorifice (with an inner diameter of 0.147 mm and a length of 1.52cm).This work was supported by Sabancı University Internal Grant for Research Program under Grant FRG-C47004

Implementation of a simplified method for actuation of ferrofluids

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.Magnetic actuation of ferrofluids is an emergent field that will open up new possibilities in various fields of engineering. The quality and topology of the magnetic field that is being utilized in such systems is determinant in terms of flow properties, flow rates and overall efficiency. Determining the optimal magnetic field topology to achieve the desired results, and determining the methods by which these magnetic fields are to be generated are central problems of obtaining the desired flow. A healthy comparison of various magnetic field topologies requires a varied set of examples from the most simplified to most sophisticated. Such comparisons are necessary to have a well grounded starting point. This study focuses on a particular pump design that employs a simplified magnetic field topology to obtain ferrofluid flow. The results of this paper such as flow and pressure difference are intended to form a baseline for future reference.Sabancı University Internal Research Grant, no: IACF09-0064

Septal perforators stemming from a very long left main coronary artery

We report a case of a very long left main coronary artery, 58mm,  with septal perforators before bifurcation. The coronary arteries were seen clear of plaques. To the best of our knowledge this case is a very rare case because of the existance of the first and the second septal perforator arteries originating from a very long left main coronary artery

Central region morphometry in a child brain; Age and gender differences

Background: Data on central region morphometry of a child brain is  important not only in terms of providing us with information about central region anatomy of the brain but also in terms of the help of this  information for the plans to be applied in neurosurgery.Objective: In the present study, central region morphometry of a child  brain in mid.sagittal MR images was analyzed in age and gender groups.Materials and Methods: Different points determined previously,  commissura posterior (PC) and the distances between cerebral cortex point (VCS) vertical to commissura anterior. commissura posterior line, sulcus centralis (CS), sulcus marginalis (MS), and the angle (α) between   CS-PC-MS were determined and measured together with difference of gender in three different age groups (aged 6.9, 10.13, and 14.17).Results: Central region measures of the brains of boys aged 6.17 are  higher than girls except for MS.PC distance. While VCS.PC, CS.PC, and MS-PC measures display a significant difference in the girls aged 14.17  when compared to the other age groups of 6.9 and 10.13 (P < 0.05), angle α is not significantly different in age and gender groups (P > 0.05). However, while VCS-PC, CS-PC and MS-PC distances show a significant  increase in girls beginning from the age of 14, this increase is limited in boys.Conclusion: Morphometric differences observed in different age groups in boys and girls shall contribute our evaluation of the alterations in brain development in both of genders and shall be useful in preparation of  surgical operation plans to be applied to the central region.Key words: Brain, central region, child, morphometry, magnetic resonance Imagin

A gut-to-brain signal of fluid osmolarity controls thirst satiation.

Satiation is the process by which eating and drinking reduce appetite. For thirst, oropharyngeal cues have a critical role in driving satiation by reporting to the brain the volume of fluid that has been ingested1-12. By contrast, the mechanisms that relay the osmolarity of ingested fluids remain poorly understood. Here we show that the water and salt content of the gastrointestinal tract are precisely measured and then rapidly communicated to the brain to control drinking behaviour in mice. We demonstrate that this osmosensory signal is necessary and sufficient for satiation during normal drinking, involves the vagus nerve and is transmitted to key forebrain neurons that control thirst and vasopressin secretion. Using microendoscopic imaging, we show that individual neurons compute homeostatic need by integrating this gastrointestinal osmosensory information with oropharyngeal and blood-borne signals. These findings reveal how the fluid homeostasis system monitors the osmolarity of ingested fluids to dynamically control drinking behaviour

Aurorasaurus database of real-time, crowd-sourced aurora data for space weather research

This technical report documents the details of Aurorasaurus citizen science data for the period spanning 2015 and 2016 as well as its routine data filtering protocols. Aurorasaurus citizen science data is a collection of auroral sightings submitted to the project via its website or apps and mined from social media. It is a robust data set and particularly abundant during strong geomagnetic storms when auroral precipitation models have the highest uncertainty. These data are offered to the scientific community for use through an open‐access database in its raw and scientific formats, each of which is described in detail in this technical report. Furthermore, by demonstrating its scientific utility, we aim to encourage its integration into auroral research