Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Pompa Tasarımının Geliştirilmesinde Hesaplamalı Akışkanlar Dinamiğinin Kullanılması(TMMOB Makina Mühendisleri Odası, 2006) Karamanoğlu, Yılmaz; Mobedi, Moghtada; Ertöz, A. ÖzdenBilgisayar teknolojisindeki hızlı gelişmeler ve sağladığı kolaylıklar, ürün tasarım ve geliştirilmesinde yönelik hazırlanan bilgisayar yazılımların kullanılmasını kaçınılmaz hale getirmiştir. Hesaplamalı akışkanlar dinamiği (Computational Fluid Dynamics-CFD) yazılımları ise özellikle akışkan ve ısı transferi ile ilgili olan ürünlerin analizlerinin yapılmasına ve performansının sınanmasında kullanılmaktadır. Bu programlar kullanılarak, süreklilik, momentum ve enerji denklemleri bilgisayar ortamında sayısal olarak çözülmekte, sıcaklık ve akış ile ilgili verilere ulaşılmakta ve değişik parametrelerin dağılımlarının (örneğin hız, basınç, sıcaklık ve benzeri parametrelerin dağılımlarının) elde edilmesine olanak sağlamaktadır. Bu makalede, pompa tasarımı ve tasarlanan pompanın denetlenmesinde hesaplamalı akışkanlar dinamiğinin kullanılması ele alınmıştır. Pompa tasarımı safhasında, tasarımcıların en çok merak ettiği konu, tasarlanan pompadaki akışın formu ve akış ile ilgili veri (debi, basınç, tork, verim) değerleridir. Bu makalede, pompalardaki akış için geçerli olan süreklilik, momentum, türbülans denklemleri ve sınır koşulları ile ilgili özet bilgiler verilmekte, çözüm yöntemleri ve doğru çözümler elde edilebilmesi için dikkat edilmesi gereken hususlar üzerine durulmaktadır. Çözüm ağının oluşturulması, çözümün elde edilmesi safhasında karşılaşılan zorluklar ve edinilen tecrübeler aktarılmıştır.Conference Object Energy Losses From Outdoor Located Air Handling Unit and Connection Duct(Universita degli Studi di Padova, 2007) Erdoğmuş, Abdullah Berkan; Mobedi, Moghtada; Özerdem, BarışIn the present study, energy losses due to heat transmission and air leakage from outdoor located air handling unit and connection duct are investigated based on EN 1886 and NEN-EN 1507 standard. The EN 1886 standard classifies air handling unit according to heat transmission and air leakage, while NEN-EN 1507 standard specify air leakages of rectangular ducts. In this study, air leakage and heat transmission fluxes for three cities in different regions of Turkey are determined and the economical value of energy losses for a building located in the city of Izmir and services 24 hours is calculated. The ambient air temperatures are taken from Turkish State Meteorological Service. The daily average values are considered for ambient temperature. The energy losses are determined for the variable and constant supply temperatures. Tables and charts are provided to show the variation of energy losses due to transmission and air leakage for the whole year. The total amounts of heat transmission and air leakage energy losses for different classes of air handling unit and connection duct are compared and discussed.Article Citation - WoS: 62Citation - Scopus: 64Effects of Porosity on Heat and Mass Transfer in a Granular Adsorbent Bed(Elsevier Ltd., 2009) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraIn the present study, the mechanism of heat and mass transfer in an annulus adsorbent is handled. The heat and mass transfer equations for the adsorbent bed and the mass balance equation for the adsorbent granules are numerically solved to obtain the distributions of temperature, pressure, adsorptive density and adsorbate concentration in the adsorbent bed. The study is performed for the silica gel-water pair and for three different values of porosity as 0.1, 0.2 and 0.3. The distributions of temperature and adsorbate concentration are considerably influenced from the bed porosity. The adsorption period increases with the increase of the porosity value. The porosity affects the pressure and adsorptive density distributions at the beginning of the process and after a relatively short time, the averages of these dependent variables approach to the final equilibrium state.Article Citation - WoS: 27Citation - Scopus: 28Effects of Wall-Located Heat Barrier on Conjugate Conduction/Natural- Convection Heat Transfer and Fluid Flow in Enclosures(Taylor and Francis Ltd., 2008) Hakyemez, Erinç; Mobedi, Moghtada; Öztop, Hakan FehmiThe effects of a heat barrier, located in the ceiling wall of an enclosure, on conjugate conduction/natural convection are investigated numerically. The vertical walls of the enclosure are differentially heated and the horizontal walls are adiabatic. Heatline technique is used to visualize heat transport. The variations of average Nusselt number, dimensionless heat transfer rate through the ceiling wall, and dimensionless overall heat transfer rate are studied. Calculations are performed for different Rayleigh numbers (10 3≤ Ra ≤ 10 6), thermal conductivity ratios (1 ≤ K ≤ 100), dimensionless locations of the heat barrier (0 < X h < 1),and two dimensionless ceiling wall thicknesses (D = 0.05 and D = 0.20). For high thermal conductivity ratio (K = 100), the heat barrier considerably reduces the dimensionless overall heat transfer rate. The effect of the heat barrier on dimensionless heat transfer rate through the enclosure increases as the Rayleigh number decreases. For low Rayleigh number (i.e., Ra = 10 3), a location exists in the ceiling wall for which the dimensionless overall heat transfer rate is minimum.Article Citation - WoS: 57Citation - Scopus: 65Conjugate Natural Convection in a Square Cavity With Finite Thickness Horizontal Walls(Elsevier Ltd., 2008) Mobedi, MoghtadaThe effect of conduction of horizontal walls on natural convection heat transfer in a square cavity is numerically investigated. The vertical walls of the cavity are at different constant temperatures while the outer surfaces of horizontal walls are insulated. A code based on vorticity-stream function is written to solve the governing equations simultaneously over the entire computational domain. The dimensionless wall thickness of cavity is taken as 0.1. The steady state results are obtained for wide ranges of Rayleigh number (103 < Ra < 106) and thermal conductivity ratio (0 < K < 50). The variation of heat transfer rate through the cavity and horizontal walls with Rayleigh number and conductivity ratio is analyzed. It is found that although the horizontal walls do not directly reduce temperature difference between the vertical walls of cavity, they decrease heat transfer rate across the cavity particularly for high values of Rayleigh number and thermal conductivity ratio. Heatline visualization technique is a useful application for conjugate heat transfer problems as shown in this study.Article Citation - WoS: 357Citation - Scopus: 385Effect of Aspect Ratio on Entropy Generation in a Rectangular Cavity With Differentially Heated Vertical Walls(Elsevier Ltd., 2008) Gediz İliş, Gamze; Mobedi, Moghtada; Sunden, BengtIn the present study, entropy generation in rectangular cavities with the same area but different aspect ratios is numerically investigated. The vertical walls of the cavities are at different constant temperatures while the horizontal walls are adiabatic. Heat transfer between vertical walls occurs by laminar natural convection. Based on the obtained dimensionless velocity and temperature values, the distributions of local entropy generation due to heat transfer and fluid friction, the local Bejan number and local entropy generation number are determined and related maps are plotted. The variation of the total entropy generation and average Bejan number for the whole cavity volume at different aspect ratios for different values of the Rayleigh number and irreversibility distribution ratio are also evaluated. It is found that for a cavity with high value of Rayleigh number (i.e., Ra = 105), the total entropy generation due to fluid friction and total entropy generation number increase with increasing aspect ratio, attain a maximum and then decrease. The present results are compared with reported solutions and excellent agreement is observed. The study is performed for 102 < Ra < 105, 10- 4 < φ{symbol} < 10- 2, and Pr = 0.7.Article Citation - WoS: 325Citation - Scopus: 366A Review on Adsorption Heat Pump: Problems and Solutions(Elsevier, 2008) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraAdsorption heat pumps have considerably sparked attentions in recent years. The present paper covers the working principle of adsorption heat pumps, recent studies on advanced cycles, developments in adsorbent-adsorbate pairs and design of adsorbent beds. The adsorbent-adsorbate pair features for in order to be employed in the adsorption heat pumps are described. The adsorption heat pumps are compared with the vapor compression and absorption heat pumps. The problems and troubles of adsorption heat pumps are classified and researches to overcome the difficulties are discussed.Article Citation - WoS: 14Citation - Scopus: 20Natural Convection Heat Transfer From a Thermal Heat Source Located in a Vertical Plate Fin(Elsevier Ltd., 2006) Mobedi, Moghtada; Sunden, BengtA steady state conjugate conduction-convection investigation is performed on vertical plate fin in which a small heat source is located. Heat from the fin surface is transferred to the surroundings by laminar natural convection. The governing equations for the problem are the heat conduction equation for the fin and the boundary layer equations, which are continuity, momentum and energy equations, for the fluid. A computer program is written by using the finite difference method in order to solve the governing equations which are nonlinear and coupled. The best location of the heat source in the fin for maximum heat transfer rate depends on two parameters which are the conduction-convection parameter and the Prandtl number. The obtained results have shown that for the fin with large conduction-convection parameter, a heat source location for maximum heat transfer rate exists.Article Citation - WoS: 81Citation - Scopus: 89Visualization of Natural Convection Heat Transport Using Heatline Method in Porous Non-Isothermally Heated Triangular Cavity(Elsevier Ltd., 2008) Varol, Yasin; Öztop, Hakan Fehmi; Mobedi, Moghtada; Pop, IoanNatural convection heat transfer in a porous media filled and non-isothermally heated from the bottom wall of triangular enclosure is analyzed using finite difference technique. Darcy law was used to write equations of porous media. Dimensionless heatfunction was used to visualize the heat transport due to buoyancy forces. Three different boundary conditions were applied for the vertical and inclined boundaries of triangular enclosures as Case I; both vertical and inclined walls were isothermal, Case II; vertical wall was adiabatic and inclined one was isothermal, Case III; vertical wall is isothermal and inclined one is adiabatic. A cosine function was utilized to get non-isothermal wall condition. The study was performed for different aspect ratios (0.25 ≤ AR ≤ 1.0) and Darcy-modified Rayleigh numbers (100 ≤ Ra ≤ 1000). It was observed that heat transfer enhancement was formed when vertical and inclined walls were isothermal while bottom wall was at non-uniform temperature. Heat transfer from bottom wall did not vary when the value of aspect ratio was higher than 0.50. In addition, heatline visualization technique was a useful technique for non-isothermally heated and porous media filled triangular enclosures. © 2008 Elsevier Ltd. All rights reserved.Article Citation - WoS: 25Citation - Scopus: 26Visualization of Heat Transport Using Dimensionless Heatfunction for Natural Convection and Conduction in an Enclosure With Thick Solid Ceiling(Elsevier Ltd., 2008) Mobedi, Moghtada; Öztop, Hakan FehmiA conjugate conduction-(natural)convection problem is numerically studied in order to present the application of dimensionless heatfunction for entire computational domain including solid and fluid regions in an enclosure with thick solid ceiling. The modified dimensionless heatfunction for solid region is defined to provide continuity of dimensionless heatfunction on solid-fluid interface. The enclosure is differentially heated from vertical walls, and horizontal walls are adiabatic. Finite difference method is employed to solve the set of governing equations. The dimensionless governing parameters for computations are: Rayleigh number (from 103 to 106), dimensionless ceiling wall thickness (0.05 and 0.5) and thermal conductivity ratio (from 1 to 100). The obtained results shows that the heat and fluid flows in the enclosure are considerably influenced by Rayleigh number and thermal conductivity ratio. Dimensionless wall thickness comparatively has less effect on heat transfer rate through the cavity. © 2008 Elsevier Ltd. All rights reserved.