The Experimental Investigation of Double Pipe Heat Exchangers Prepared from Two Techniques

9th Thai Society of Mechanical Engineers, International Conference on Mechanical Engineering, TSME-ICoME (2018: Tavorn Palm Beach Resort Phuket, Thailand)Heat exchangers are the equipment used in variety of industries at all levels related to heat and thermal systems. Using heat exchangers at maximum efficiency are to reduce the amount of energy lost that impacts on environment and manufacturing cost in the industry. This research focused on comparing performances of two heat exchangers; two double-pipe heat exchangers were fabricated domestically with two different welding techniques (flare and Argon welding techniques). Both heat exchangers were tested on the same experimental setup and investigated for their thermal efficiency. Their working fluid was water, hot water and cold water flowed inside the heat exchangers were arranged as parallel (co-current) and counter flow configurations. Thermal efficiency when hot water and cold water flow rates varied in the range from 0.5 to 2 liters per minute, were also investigated. The results showed that the second heat exchanger fabricated with the Argon-welding technique showed the better thermal performance than that of the first heat exchanger fabricated with the flare technique. The thermal performances of the second heat exchanger were varied from 92% to 99% while the performances of another heat exchanger were varied from 32% to 38%. Therefore, the heat exchanger manufacturing played an important role to the heat exchanger performance. The same heat exchanger design but different fabricating technique caused lost in heat transfer process which affected the thermal performance and operating cost of the industry. © Published under licence by IOP Publishing Ltd.We would like to thank our students; Patpong WONGTHAM, Phathai KOONCHONNABOT, Apichat KEAWHON., The research described in this paper was financially supported by Faculty of Science and Engineering and Office of Campus, Kasetsart University, Chalermphrakiat Sakon Nakhon Province Campus, and Kasetsart University Research and Development Institute, Kasetsart University

Tek hücre jel elektroforezi için görüntü analizi

Genetik bilginin nesilden nesile sağlıklı olarak aktarılabilmesi için deoksiribonükleik asit (DNA) yapısının korunması son derece önemlidir. Ancak, hücrenin normal metabolik süreçlerinde ya da fiziksel veya kimyasal etkilerle DNA’da hasar oluşabilmektedir. Yaşam bilimlerinin çeşitli alanlarında ve bazı patofizyolojilerin klinik tanısında DNA hasarının tespiti oldukça önemlidir. Tek hücre jel elektroforezi (THJE) veya diğer adıyla Comet analizi fiziksel ve kimyasal etkilerin canlılar üzerinde yol açtığı genotoksik ve sitotoksik etkilerin bir göstergesi olan DNA hasar seviyelerinin ölçülmesinde kullanılan güvenilir ve kolay uygulanabilir bir yöntemdir. Yöntem genel olarak, canlı dokulardan izole edilen çekirdek içindeki DNA’nın, ince bir agaroz jel içine yerleştirilip elektroforetik ortamda yürütülmesini temel alır. Comet protokolü ile elde edilen DNA görüntüleri gözle değerlendirilebileceği gibi günümüzde çeşitli yazılımlar kullanılarak da analiz edilmektedir. Bu tür yazılımlar sayesinde kısa sürede ve araştırmacının deneyimine bağlı kalınmayarak objektif sonuçlar elde edilebilmektedir. Literatürde bulunan mevcut çalışmalar, Comet analiz sistemlerinin yarı otomatik ve otomatik olarak ikiye ayrıldığını göstermektedir. Yarı otomatik yazılımlar çoğunlukla kullanıcıdan bir eşik değeri, DNA’yı seçme ve Comet görüntüsünün baş kısmını seçmelerini ister. Otomatik yazılımlar ise kullanıcı tarafından seçilen veya görüntü boyunca yer alan Comet analiz görüntülerini otomatik olarak analiz edip ölçüm sonuçlarını sunar. Bu çalışmada, HepG2 (ATCC HB-8065) hepatosellüler karsinom karaciğer kanser hücrelerinden elde edilen Comet analiz görüntüleri kullanılmıştır. Kullanıcı tarafından seçilen bu görüntülerde, ölçüm sonuçlarının hesaplanması ve kullanıcıya parametrik veriler sunulması amaçlanmıştır. Preservation of the structure of dioxyribonucleic acid (DNA) is crucial so that genetic information can be transmitted in a healthy way from generation to generation. However, DNA could be damaged by metabolic processes of a cell or by chemical or phsycial activity. Detection of DNA damage is very crucial in various areas of life sciences and in the clinical diagnosis of some pathophysiologies. Single cell gel electrophoresis, also called Comet Assay, is a reliable and easily applicable method to measure/detect level of DNA damage which is an indicator of an genotoxic and cytotoxic effect on living organisms caused by chemical and phsyical activity. The method is generally based on the fact that the DNA in the nucleus isolated from living tissues is placed in a thin agarose gel and run on an electrophoretic medium. DNA images obtained with the Comet protocol can be evaluated visually as well as can be analyzed using various software today. With such software, objective results can be obtained in a short period of time and without adhering to the researcher's experience. Current studies in the literature show that Comet analysis systems are categorized into two as semi-automatic and automatically. Semi-automated software often requires the user to select a threshold value, the DNA, and the head of the Comet image. The automatic software automatically analyzes the Comet analysis images selected by the user or located throughout the image and presents the measurement results. In this study, Comet analysis images obtained from HepG2 (ATCC HB-8065) hepatocellular carcinoma liver cancer cells were used. Calculation of measurement results of these user-selected images and presenting parametric data to the user are intended

BANKA PERSONELLERİNİN PERFORMANS DEĞERLENDİRMESİNE BAKIŞ AÇILARI: ÇORUM İLİ ÖRNEĞİ

Günümüzde sürekli ve hızlı değişim içerisinde olan bankacılık sektöründe, bankaların rekabet ortamına ayak uydurabilmek, getirilerini maksimum seviyede tutmak ve hedeflerine ulaşabilmeleri için performans değerlendirme önemli bir araç haline gelmiştir. Performans, bir iş veya görev ile ilgili önceden belirlenen şartlara, standartlara bu sorumluluklar yerine getirilirken uyulması ve bu iş veya görev ile ilgilinin beklenen amaçlara ulaşılma derecesidir. Performans değerlendirme ise performansı değerlendirilecek kişi veya kuruluşun performans ile ilgili yapmış olduğu çalışmalarını tüm yönleri ile ele alan bir yöntemdir.Performans değerlemesi oldukça zor ve uzun çaba gerektiren bir süreçtir. Bu süreç performans değerlendirme çalışmaları, kurum tarafından personellerin performanslarının değerlendirilme aşamaları, personellere değerleme sonuçlarının iletilmesi ve de son olarak personellerin bu geri dönüş sayesinde kendilerini geliştirmek için yapabileceklerini planlaması gibi işlemleri kapsamaktadır. Görüldüğü üzere performans değerleme süreci sadece personelin ne kadar etkin çalıştığını ortaya çıkarmamaktadır. Kuruma verimliliğin artması için gerek faaliyetler konusunda gerekse personelleri konusunda yapılması gerekenleri planlama fırsatı verirken aynı zamanda personele de kariyer planlaması için yapması gerekenler konusunda yol gösterici olmakta ve kişiyi kendini geliştirme konusunda teşvik etmektedir.Özellikle bankaların da içinde yer aldığı hizmet sektöründe çalışanların performans değerlemeye karşı tutumları çok daha önemli bir yere sahiptir. Bu sektörde çalışanlar müşteri kesimi ile direkt temas halindedir. Personelin çalışma ortamındaki memnuniyeti ve mutluluğu bir şekilde tutum ve davranışlarına da yansıyacaktır. Önemli olan personellerin performans değerlendirme sürecine objektiflik, adalet gibi konularda güvenmesidir. Personel bu değerlemeye ne kadar güvenirse çalışma performansı o kadar artacaktır. Bu durumda bankanın faaliyetlerinin de kalite ve verimliği artacak ve de banka sektördeki rekabet gücünde de önemli bir avantaj sağlamış olacaktır. Bu çalışmada, banka personellerinin performans değerlendirme konusunda yaşadıkları sorunlar ve bu konudaki beklentileri araştırılmıştır. Araştırmada veriler anket yöntemiyle elde edilmiştir. Anketler Çorum merkezindeki banka personellerine uygulanmıştır. Araştırma verileri SPPS programı ile analiz edilmiştir. Performansı etkileyen birçok sebep bulunmaktadır. Bunların başında çalışma ortamı, yöneticinin tutumu ve ücret gibi konular yer almaktadır. Analizden, personellerin kendilerini işlerini yapmada yeterli beceride gördükleri, aldıkları ücreti yetersiz buldukları ve yöneticilerle yaşadıkları sorunların performanslarını kötü etkilediği gibi sonuçlara ulaşılmıştır

Heatline visualization of natural convection in a porous cavity occupied by a fluid with temperature-dependent viscosity

Temperature dependent viscosity effect in buoyancy driven flow, of a gas or a liquid, in an enclosure filled with a porous medium is studied numerically, based on the general model of momentum transfer in a porous medium. The Arrhenius model, which proposes an exponential form of viscosity-temperature relation, is applied to examine three cases of viscosity-temperature relation: constant, decreasing and increasing. Application of arithmetic and harmonic mean values of the viscosity is also investigated for their ability to represent the Nusselt number versus the effective Rayleigh number. Heatlines are illustrated for a more comprehensive investigation of the problem

A consistent methodology for the derivation and calibration of a macroscopic turbulence model for flows in porous media

This work aims to model turbulent flows in media laden with solid structures according to porous media approach. A complete set of macroscopic transport equations is derived by spatially averaging the Reynolds averaged governing equations. A two-scale analysis highlights energy transfers between macroscopic and sub-filter kinetic energies (dispersive and turbulent kinetic energies). Additional terms coming from the averaging procedure and representing solids/fluid interactions and turbulent contributions are modeled. Connections between turbulence modeling and dispersion modeling are presented. Other closure expressions are determined using physical considerations and spatial averaging of microscopic computations. A special care is given to the calibration methodology for the phenomenological coefficients. Results of the present model are successfully compared to volume-averaged reference results coming from fine scale computations and show significant improvements with respect to previous macroscopic models

Parametric investigation of a non-constant cross sectional area air to air heat exchanger

The present article addresses the design, mathematical modelling and analysis of a novel highly exergy-efficient air to air heat exchanger. An intricate design based on an hexagonal mesh is proposed for the cross-sectional area of the heat exchanger with aims to explore the performance gains that can be obtained by exploiting the capabilities and benefits offered by modern fabrication techniques such as additive manufacturing. Special attention is paid to understanding the relationship or trade-off that exists between the overall exergy efficiency of the heat exchanger and its cost. The iterative algorithm used to find the geometrical parameters that yield the best performance in terms of volume of material required per unit of exergy transfer at a certain level of efficiency, as well as the assumptions and simplifications made, are comprehensively explained. It has been found through the analyses carried out performed, which are thoroughly discussed throughout the paper, that if the characteristic dimension of the heat exchanger is scaled up by a factor of n, the volume of material per kW of exergy transfer at certain exergy efficiency will increase by a factor of n squared. This is a very important observation, possibly applicable to other types of heat exchangers, that indicates that performance improves dramatically at smaller scales. The overall performance of the case study presented is satisfactory, a volume of material as low as 84.8 cm3 for one kW of exergy transfer can be achieved with a 99% exergy efficiency

Effects of temperature dependent viscosity on Bénard convection in a porous medium using a non-Darcy model

Temperature-dependent viscosity variation effect on Benard convection, of a gas or a liquid, in an enclosure filled with a porous medium is studied numerically, based on the general model of momentum transfer in a porous medium. The exponential form of viscosity-temperature relation is applied to examine three cases of viscosity-temperature relation: constant (mu = mu(C)), decreasing (down to 0.13 mu C) and increasing (up to 7.39 mu(C)). Effects of fluid viscosity variation on isotherms, streamlines, and the Nusselt number are studied. Application of the effective and average Rayleigh number is examined. Defining a reference temperature, which does not change with the Rayleigh number but increases with the Darcy number, is found to be a viable option to account for temperature-dependent viscosity variation. (C) 2007 Published by Elsevier Ltd

Construction and configuration of convection-powered asphalt solar collectors for the reduction of urban temperatures

In this paper, an analysis of a convection-powered asphalt solar collector prototype is approached by the means of experimental trials and computational fluid dynamics (CFD) simulations in order to evaluate how to optimise its design for the reduction of high urban pavement temperatures. Since the energy harvesting setup consists of a series of pipes buried in the pavement, their arrangement is here studied and experimentally compared to a possible construction technique consisting of concrete corrugations that aim at replacing the pipes. CFD simulations are employed to optimise the air collection chamber which is placed immediately before the heated air leaves the asphalt solar collector prototype. The data gathered is analysed in terms of energy harvested and exergy. The results obtained show that for an overall optimal performance, pipes should be installed in a single row under the pavement wearing course. This allowed a surface temperature reduction of up to 5.5 °C in the pavement prototype studied and the highest absorbed energy and exergy measured. In addition, the CFD simulations showed that care has to be put in finding the optimal shape and size for the air collection chamber, as they significantly influence the behaviour of the system

Solid oxide fuel cell reactor analysis and optimisation through a novel multi-scale modelling strategy

The simulation of a solid oxide fuel cell (SOFC) that incorporates a detailed user-developed model was performed within the commercial flowsheet simulator Aspen Plus. It allows modification of the SOFC's governing equations, as well as the configuration of the cell's fuel-air flow pattern at the flowsheet level. Initially, the dynamic behaviour of single compartment of a cell was examined with a 0D model, which became the building block for more complex SOFC configurations. Secondly, a sensitivity analysis was performed at the channel (1D) scale for different flow patterns. Thirdly, the effect of fuel and air flow rates on the predominant distributed variables of a cell was tested on a 2D assembly. Finally, an optimisation study was carried out on the 2D cell, leading to a robust, optimal air distribution profile that minimises the internal temperature gradient. This work forms the foundation of future stack and system scale studies