منصة إيفاد العلمية

أ.م.د. ساجدة لفته غشيم

إرسال رسالة

التخصص: الهندسة الميكانيكية

الجامعة: جامعة بغداد

النقاط:

30.5

معامل الإنتاج البحثي

الخبرات العلمية

Heat transfer
Porous media
Two phase flow
Nano fluid
Free & forced convection
تقييم البحوث

الأبحاث المنشورة

Heat Transfer Enhancement in vertical Mounted Tube Subjected to Uniform Heat Flux by using Electrolysis Bubble

المجلة: International Journal of Computer Applications

سنة النشر: 2016

تاريخ النشر: 2016-05-21

In the present work, experimental and numerical investigations had been carried out to investigate the effect of sub-millimeter bubbles injection on heat transfer coefficient of upward flowing water in vertical mounted tube subjected to uniform heat flux. The experimental apparatus consists of a test rig designed and built to conduct the experiments. A circular tube, test section was designed and constructed from the copper and heated by an electrical heater on its outer surface. The dimensions of copper pipe was (length= 0.7m, diameter= 0.05 m, thickness= 1.5 mm). Water temperature at inlet was kept constant at (32°C). Thermocouples distributed longitudinally at different radial distances between cylinder surface and its center at seven sections, in addition to the fluid inlet and outlet were used to measure temperatures. Bubbles generation was performed in test section by using a proper ionization current that will be passed across the anode and cathode electrodes to produce hydrogen bubbles and oxygen bubbles at different intensities. The experiments were conducted using heat fluxes (13641 and 22736) W/m2, water mass flow of (2, 3 and 4) lit/min, mass flow rate of hydrogen and oxygen bubbles were (0.02 , 0.025) lit/min respectively and Reynolds number (1214, 1783 and 2300) for water. The results showed that an enhancement of 25.5% was obtained in the averaged Nusselt number with using ionization bubbles compared with the case without bubbles.

Experimental investigation of heat transfer enhancement in heat exchanger due to air bubbles injection

المجلة: Journal of King Saud University – Engineering Sciences

سنة النشر: 2021

تاريخ النشر: 2021-07-21

The present work experimentally investigated air bubbles injection on heat transfer enhancement and pressure drop of turbulent flow in two helical coils heat exchanger. The experience is accomplished for turbulent flow with Reynolds number (Re) of (9000 to 50000) for hot water and constant mass flow rate of cold water 0.0331 kg/s .Air bubbles injection in hot water in the range of (1.5, 2.5, and 3.5) lit/min. Experimental results represented by Nusselt number(NU), effectiveness (ε), number of thermal units (NTU) and exergy losses. It was evinced that, the presence of air bubbles in hot water causes enhanced in Nusselt number from (64 to 126) % and increased the friction factor from (66 to 85) % in the Reynolds number range from (9000 to 50000). Bubbles injection has a positive effect on enhanced heat transfer and negative effect of increased friction factor and this represent by thermal enhancement factor which was increased about (1.13 to 1.29) in mass flow rate of hot water of 0.0163 kg/s by using values of air bubbles from (1.5 to 3.5) lit/min. A quantity of number of thermal units (NTU) and effectiveness (ε) appreciably enhanced due to air bubbles. Furthermore, exergy loss with air bubbles was higher than without air bubble injection

Effect of Air Bubbles on Heat Transfer Coefficient in Turbulent Convection Flow

المجلة: Journal of Engineering

سنة النشر: 2017

تاريخ النشر: 2017-01-21

Experimental and numerical studies have been conducted for the effect of injected air bubbles on the heat transfer coefficient through the water flow in a vertical pipe under the influence of uniform heat flux. The investigated parameters were water flow rate of (10, 14 and 18) lit/min, air flow rate of (1.5, 3 and 4) lit/min for subjected heat fluxes of (27264, 36316 and 45398) W/m2. The energy, momentum and continuity equations were solved numerically to describe the motion of flow. Turbulence models k-ε was implemented. The mathematical model is using a CFD code Fluent (Ansys15). The water was used as continuous phase while the air was represented as dispersed phase. The experimental work includes design, build and instrument a test rig for that purpose. A circular vertical copper pipe test section of (length=0.7m, diameter= 0.05m, thickness= 1.5mm) is designed and constructed, heated by an electrical heater fixed on its outer surface. Water temperature at inlet is kept constant at (32°C). Water inlet and outlet temperatures, as well as radial temperature distribution within the pipe at seven sections along it between pipe surface and its center are measured. The results revealed that the secondary flow created by air bubbles have significant effects on heat transfer enhancement and temperature profile. It is observed, that averaged Nusselt number enhancement for low heat flux of 27264 W/m2 and 4 lit/min air bubbles was 33.3 % and 23% in numerical and experimental, respectively.

Numerical study of the mixed convection flow over a square cylinder

المجلة: Iraqi Journal of Chemical and Petroleum Engineering

سنة النشر: 2010

تاريخ النشر: 2010-03-21

In this work, a numerical study is performed to predict the solution of two – dimensional, steady and laminar mixed convection flow over a square cylinder placed symmetrically in a vertical parallel plate. A finite difference method is employed to solve the governing differential equations, continuity, momentum, and energy equation balances. The solution is obtained for stream function, vorticity and temperature as dependent variables by iterative technique known as successive over relaxation. The flow and temperature patterns are obtained for Reynolds number and Grashof number at (Re= -50,50,100,-100) (positive or negative value refers to aidding or opposing buoyancy , +1 assisting flow, -1 opposing flow) and (102 to 105) , respectively. The results displaced that the recirculation length above the cylinder increases with the increase in Gr number and the average Nu number is the highest at the lower surface of the cylinder, while is the lowest at the top of the cylinder surface. A comparison between the obtained results and the published computational studies has been made and it showed a good agreement.

Investigation of Optimum Heat Flux Profile Based on the Boiling Safety Factor

المجلة: Journal of Engineering

سنة النشر: 2019

تاريخ النشر: 2019-01-21

An experimental study is conducted to investigate the effect of heat flux distribution on the boiling safety factor of its cooling channel. The water is allowed to flow in a horizontal circular pipe whose outlet surface is subjected to different heat flux profiles. Four types of heat flux distribution profiles are used during experiments: (constant distribution profile, type a, triangle distribution profile with its maximum in channel center, type b, triangle distribution profile with its maximum in the channel inlet, type c, and triangle distribution profile with its maximum in the channel outlet, type d). The study is conducted using heat sources of (1000 and 2665W), water flow rates of (5, 7 and 9 lit/min). The water temperature at cooling channel inlet is kept constant at (25°C). Copper test section of (0.6 m) length (0.025m) inner diameter is used during the experiments. The electrical heater used for water heating is wrapped around the copper pipe covering (50 cm) of its length. Calibrated thermocouples are distributed along pipe surface at distances (0.1, 0.2, 0.3, 0.4 and 0.5 m) from pipe inlet to measure pipe surface temperature. The results shows that the heat source with heat flux profile of type (c) is the most reliable one from thermo-hydraulic safety point of view for both types of heat sources, as it ensures a maximum boiling safety factor (K) of (1.6, 1.7, 2) at water flow rates of (5, 7 and 9 lit/min) respectively based on maximum heat capacity of (2665 w), while the heat source with heat flux profile of type (d) which posses minimum boiling safety factors of (1, 1.2, 1.3) at water flow rates of (5, 7 and 9 lit/min) respectively based on same heat capacity value is the worst one from same point of view.

Numerical analysis of the heat transfer enhancement by using metal foam

المجلة: Case Studies in Thermal Engineering

سنة النشر: 2023

تاريخ النشر: 2023-08-21

Forced convection heat transfer in metal foam pipe under uniform heat flux was investigated numerically. Water has been used as the fluid medium in numerical simulations with copper metal foam. The test sample used metal foam for four cases (A, B, C, and D) by using varying thicknesses of foam along the pipe. In case (A), the pipe was completely filled with metal foam; in case (B), the pipe was partially embedded with metal foam and close to the wall; in case (C), the pipe was partially filled in the section's center; and in case (D), the pipe was partially filled in the form of three sections along the pipe. The foam employed in this study has a porosity of 0.90 and pore density ranges from (10–40) PPI. The fluid and energy transfers are simulated using the Forchheimer-extended Darcy equation and the local thermal non-equilibrium (LTNE) model. The simulation is performed using the commercial software FLUENT with specific boundary conditions. Turbulence was taken into account using the k- ε model. The results reveal that when the pipe is filled partially with metallic foam as indicated in case B, the Nusselt ratio rises due to the velocity gradient and temperature distribution is more homogenous inside the pipe led to enhancement in overall heat transfer. Also, the metallic foam 40PPI has a highly Nusselt number ratio, with a big value equal to 5.5 in case B due to the highly conductive surface area of heat transfer from the wall heated to the fluid. Additionally, the pipe in case A was completely filled with metallic foam, resulting in a bigger pressure drop than in the other cases, which increases flow resistance. The metal foam in case C, which is centered in the pipe's center, has the lowest pressure drop measurement. The 10PPI metallic foam exhibits the highest performance factor when compared to other metallic foam.

A mathematical analysis of nanoparticles on heat transfer in a circular pipe

المجلة: Case Studies in Thermal Engineering

سنة النشر: 2021

تاريخ النشر: 2021-12-21

The influence of various nanoparticle materials on the performance of flow in a pipe with a uniform heat flux of 10000 W/m2 is studied. The flow was simulated using Ansys 14.5 and two-dimensional governing partial differential equations. The effect of four different concentrations of nanomaterials Al2O3 and hybrid nanomaterials Al2O3–Cu were employed in this simulation. Al2O3 and Al2O3–Cu nanoparticles scattered in water at volume ratio of (0.05, 1, 2, and 3)%. The Reynolds number (Re) ranged from 254 to 1019, and the inlet temperature was 27 °C. It was shown that raising the amount of nanomaterials of Al2O3 in water enhanced some physical qualities while lowering others. As Cu is added to Al2O3 and water, the amount of heat transport is increased when compared to Al2O3 - water or water alone. Furthermore, when the concentration of nanoparticles increases, the Nusselt number (Nu) rises.

PARAMETRIC STUDY OF SUCTION OR BLOWING EFFECTS ON TURBULENT FLOW OVER A FLAT PLATE

المجلة: Journal of Engineering

سنة النشر: 2016

تاريخ النشر: 2016-12-21

The two-dimensional, incompressible, and turbulent boundary layer flow over a flat plate with suction or blowing from a spanwise slot is examined numerically. The mathematical modeling involves the derivation of the governing partial differential equations of the problems. These are the continuity, the momentum, the energy and the (K-ε) turbulence model. Besides, the perfect gas law is also used. A numerical solution of the governing equations is approximated by using a finite volume method, with staggered grid and modified SIMPLE algorithm. A computer program in FORTRAN 90 is built to perform the numerical solution.The developed computational algorithm is tested for the flow over a flat plate (4m) long with uniform suction or blowing velocity ratios of (V/U∞ =± 0.0185, ± 0.0463 and ±0.0925 m/s) are imposed on the slot for Reynolds number of (1.36 x 107 ), based on the plate length. The position of the slot change in the range of (X/L=1/4, 1/2 and 3/4) from leading edge and also, change width of slot in the value equal (0.12, 0.2 and 0.28m).The plate temperature is (70 °C), with the free stream velocity and temperature are (8.6m/s) and (25 °C) respectively. In addition, the effects of pitch angles on the flow field are investigated in the range of (30о    150о).The numerical results show that, for a uniform blowing, location of slot equal (X/L=1/4) from leading edge, a significant reduction of skin friction coefficient, wall shear stress and boundary layer thickness [displacement and momentum] to occur. While, an increase in boundary layer shape factor. Reynolds stress (uv) is more decreased than [(uu) and (vv)], mean velocity profiles in wall coordinates and dimensionless distance (U+, y+) decreases. When slot location is moved downstream to locations (X/L=1/2 or 3/4) a similar behavior can be said and most effective slot is obtained as (slot at X/L= 3m) from leading edge. While width of slot equal (0.28m) is better than values equal (0.12m and 0.2m). An opposite observations for the case of suction. The numerical results are compared with available numerical results and experimental data and a satisfactory results are obtained.

Laminar Natural Convection in nonrectangular Enclosure with and without Fins

المجلة: Journal of Engineering

سنة النشر: 2012

تاريخ النشر: 2012-04-21

In the present work, steady, laminar natural convection in nonrectangular enclosures is analyzed numerically with and without fin. Vertical walls insulated while horizontal walls maintained isothermal at different temperature and the fin was placed on horizontal surface. The length of fin was equal (B/L=0.22, 0.44 and 0.66) and thickness of fin was constant. Various parameters are studied: Rayleigh number (from 104 to 107), Prandtl number (0.7), number of fin change from (1-3) and aspect ratio (H/L= 0.15 to 0.5). The problem is formulated in terms of the vorticity-stream function procedure. A numerical solution based on program in Fortran 90 with Tec plot program. The finite difference method is used. Streamlines and isotherms are presented for different values of parameters studied. A Nusselt number correlation is derived by using program (DGA v1.00) and mean Nusselt numbers on hot walls are also calculated at different cases. The results show the mean Nusselt numbers decreases with increasing aspect ratio (H/L).Also, predictions reveal a decrease in heat transfer in the presence of fins. The results of the calculations are compared with the previous works and it showed a good agreement.

Thermal performance analysis of heat transfer in pipe by using metal foam

المجلة: Jordan Journal of Mechanical and Industrial Engineering

سنة النشر: 2023

تاريخ النشر: 2023-06-21

In this work, turbulent forced convection heat transfer in a circular horizontal pipe with insert of metal foam under the condition of constant heat flux is experimentally investigated. The Nusselt number (Nu) and friction factor (f) were tested under heat flux (31.8 and 42.4 )KW/m2 and water flow rates (3, 6 and 9) lit/min. Circular copper pipe with dimensions of 0.6 m in length, 0.025 m in diameter, and 0.001 m in thickness acts as the test section for the current investigation. It is heated by an electric heater mounted outside the pipe. The foam has pores per inch ranging from (10 to 40) PPI and porosity between ( 0.89 and 0.93).The water flowing through the pipe has a regular input temperature of 32°C.The temperature was measured along the pipe distributed in seven sections of the wall, in addition to measuring the temperature of entering and exiting the water from the pipe. The results show that, with a heat flux of 42.4 KW/m2, the copper metal foam of 40 PPI gives a higher increase in average Nusselt number up to 73% as compared to metal foam of 10 PPI of 63.74%. The difference in pressure drop between pipes with and without metal foam varies just slightly at 10 PPI, but becomes greater at 40 PPI.

The Porosity Effect of Stainless Steel Balls on Forced Convection Pipe Flow

المجلة: Al-Nahrain Journal for Engineering Sciences

سنة النشر: 2019

تاريخ النشر: 2019-06-21

An experimental study has been carried out to investigate the effects of stainless-steel balls on forced convection flow in pipe under uniform heat flux. Water is used as the working fluid and stainless-steel balls as a porous media. The Reynolds number range from (5000 to 9000) based on the diameter of the pipe. The experiments were conducted on three various numbers of stainless-steel balls (N) with various diameters (dp), which give various porosity (0.33, 0.38 and 0.41). These are (N= 2400, dp=1mm), (N=1600, dp=3mm) and (N= 750, dp=5mm). Results show that, heat transfer coefficient increases with the decrease in the porosity due to the reduction in the space between balls. This led to an increase in turbulence and produced eddies. Furthermore, enhancement in heat transfer coefficient reached its maximum value of (45%) for ball diameter with (dp=1mm) and water flow rate (9 L/min). New Correlation equations for the average heat transfer coefficient were obtained for three different diameters of balls (1, 3 and 5 mm).

Study Effect of Bubble Size on Drag Reduction

المجلة: 10th International Conference on Advances in Science, Engineering and Technology (ICASET-18)

سنة النشر: 2018

تاريخ النشر: 2018-06-21

Studied experimentally the effect of air bubbles injection on drag reduction for water flow in a vertical pipe. Test section made from transparent pipe with internal diameter of ( 0.025 m) and length (2m). Air bubbles injection in a vertical pipe from bottom by two methods nozzle and porous ring. The experiments were conducted using range of Reynolds number (13321.68 - 22202.79) and air flow rate (0.5, 1 and 1.5 L/min) . The results showed that small air bubbles injection in the pipe reduced the pressure gradient more than that large bubbles produced by nozzle. Also, it was concluded that, bubbles injection by porous ring tended to collect near the wall along the pipe .Furthermore, drag reduction reached to its maximum value at (28%) at a maximum value of void fraction (11%) and minimum value of Reynolds number (13321.68) by porous ring method .

Numerical Analysis of Laminar Natural Convection in Square Enclosure with and without Partitions and Study Effect of pPartition on the Flow Pattern and Heat Transfer

المجلة: Iraqi Journal of Chemical and Petroleum Engineering

سنة النشر: 2012

تاريخ النشر: 2012-03-21

The problem of steady, laminar, natural convective flow in an square enclosure with and without partitions is considered for Rayleigh number (103 -106 ) and Prandtl number (0.7). Vertical walls were maintained isothermal at different temperatures while horizontal walls and the partitions were insulated. The length of partition was taken constant. The number of partitions were placed on horizontal surface in staggered arrangement from (1– 3) and ratio of partition thickness (H/L= 0.033, 0.083, 0.124). The problem is formulated in terms of the vorticity-stream function procedure. A numerical solution based on a program in Fortran 90 with the finite difference method is obtained. Representative results illustrating the effects of the thickness and number of partitions on the contour maps of the streamlines and temperature are reported and discussed. In addition, the local Nusselt number is evaluated. Results show that the values of stream function (the strength of flow) in enclosure increases with the increasing Rayleigh number. As the number of partitions and thickness of partition increases, the strength of flow decreases. Mean Nusselt number increases with increasing Rayleigh number at different number of partitions. The numerical results are compared with available numerical results and experimental data and a good agreement is obtained.

New Correlation Equations for Finned Tube Heat exchangers

المجلة: journal of engineering and applied sciences

سنة النشر: 2019

تاريخ النشر: 2019-01-21

A new correlation equations were conducted on heat transfer parameters of air-side in circular finned-tube heat exchangers of staggered and in line arrangement . A Nusselt number and Euler number correlation are derived. The effects of fin height , fin spacing , fin pitch , tube outside diameter ,fin diameter , transverse tube pitch ,longitudinal tube pitch and number of rows are reflected in the correlations . The study covered the range of Reynolds number (8x103 - 5x104). Number of bundles used in this correlation 56 staggered and 33 in line. A numerical solution based on (DGA v1.00) and Excel programs were used to find constants of correlation equations. Also, Tecplot program is used to draw curves of results. Results show maximum deviation are in Nusselt number and Euler number correlations (6%, 18% for staggered and 10%, 11% for in line), respectively. in addition , the effect of fin spacing or fin height on Nusselt number and Euler number in one bundle (S1 staggered and I1 in line) are investigated. Results showed that, in staggered bundle arrangement S1, the Nu number increased and Eu number decreased when the fin spacing increased and fin height decreased. While, the effect of decreased fin spacing and increased fin height led to in increased Nu number and Eu number at bundle I1 in line arrangement.

Flow field and heat transfer characteristics in dimple pipe with different shape of dimples

المجلة: Wasit Journal of Engineering Sciences

سنة النشر: 2024

تاريخ النشر: 2024-04-21

In this work, a numerical study of a thermal performance of water flow inside a dimpled pipe. The effect of three types of dimples (circular, square and rhombus) studied in the numerical simulation. A commercial program called ANSYS was used to model the flow through a circular pipe .The threedimensional governing differential equations of mass, momentum, and energy were used together with the (K − ε ) model to evaluate the impact of dimples on a turbulent flow and the velocity field. The study was carried out in the Reynolds number (Re) range (2500–15000). The research results demonstrate that the presence of a dimple on the pipe surface greatly increases the rate of heat transmission and the friction factor compared to a normal smooth pipe . Also, the numerical study demonstrated that the Nusselt number (Nu) in case of circular dimples at diameter (4 , 6 and 8) mm was (22, 28 and 43) % greater than the smooth surface. It is discovered that the improved pipe with circular dimples have a benefit for increased heat transmission efficiency compared with the square and rhombus dimples. Additionally , circular dimples have the ability to supply the lowest friction factor (f) when compared to other types of dimple. The pipe with circular dimples with D= 4mm , at Reynolds number 2500 provided the largest thermal performance criterion (PEC) value about 1.44.