Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : Heat transfer


Numerical Investigation of Thermal-Hydraulic Performance of Printed Circuit Heat Exchanger with Different Fin Shape Inserts

Ali M. Aljelawy; Amer M. Aldabbagh; Falah F. Hatem

Engineering and Technology Journal, 2023, Volume 41, Issue 1, Pages 23-36
DOI: 10.30684/etj.2022.132688.1137

The printed circuit heat exchanger is one of the most recent important heat exchangers, especially in the nuclear power plant and aerospace applications, due to its very compact geometry and small print foot. This paper presents a 3D numerical investigation of the thermo-hydraulic performance of PCHE with a new non-uniform channel design configuration. The new channel design consists of two different fins and shape inserts: the diamond and biconvex shapes. The influence of two design parameters on the heat exchanger performance was studied and optimized, the longitudinal and transverse pitch length (Pl) and (Pt). Air with constant properties as the working fluid with constant heat flux at the walls envelope. The Reynolds number varied from 200 to 2000. Different Pitch lengths were used (Pl=20, 30, 40, and 50) mm and (Pt=3, 4, and 5) mm. Three performance parameters were studied the Nusselt number, friction factor, and the overall performance evaluation factor. Results show that the thermal performance enhanced with decreasing the pitch lengths, and it was shown that this enhancement was found only at high Reynolds numbers above 1400. The higher enhancement factor was with NACA 0020 airfoil fins at pt=3 mm and pl=20mm of η=2.75 at Re=2000, while the worst performance was obtained with biconvex fins. The main reason behind the enhancement is the disruption of the boundary layer and the good mixing induced in the fluid flow.

Numerical and Experimental Investigation of Heat Transfer Enhancement by Hybrid Nanofluid and Twisted Tape

noor F. A. Hamza; Sattar Aljabair

Engineering and Technology Journal, 2023, Volume 41, Issue 1, Pages 69-85
DOI: 10.30684/etj.2022.131909.1069

This paper presents an experimental and numerical study to investigate the heat transfer enhancement in a horizontal circular tube using hybrid nanofluid (CuO, Al₂O₃/ distilled water) and fitted with twisted tape (typical twisted tape, with twist ratios (TR=9.2). Under fully developed turbulent flow and uniform heat flux conditions, the studied hybrid nanofluid concentrations are (=0.6, 1.22, and 1.8% by volume). The experimental test rig includes all the required instruments to study the heat transfer enhancement. All the tests were carried out with a Reynolds number range of 3560-8320 and uniform heat flux (13217.5 W/m². The twisted tape, manufactured from polylactic acid (PLA) by 3-dimensional printer technology, was inserted inside the tube. In this numerical study, the finite volume method (CFD) procedure was employed to pattern the forced convection turbulent flow through the tube. For hybrid nanofluid with twisted, the maximum enhancement in the maximum thermal performance factor was 2.18 for φ = 1.8%, while for a tube (water with twisted) under the same conditions, it was (2.04). A high Nusselt number was obtained with a concentration of 1.8% and an enhancement in the heat transfer of about 6.70%) than water.

Recent Development in Hydrodynamic and Heat Transfer Characteristics in the Three-phase Fluidized-bed System

Omar S. Mahdy; Amer A. Abdulrahmn; Jamal M. Ali

Engineering and Technology Journal, 2022, Volume 40, Issue 9, Pages 1-26
DOI: 10.30684/etj.2022.132506.1125

Gas–liquid-solid fluidized beds are broadly utilized in the petrochemical, pharmaceutical, refining, food, biotechnology, and environmental industries. Due to complex phenomena, such as the particle-particle, liquid-particle, particle-bubble interactions, complex hydrodynamics, and heat transfer of three-phase (gas-liquid-solid) fluidized beds, they are incompletely understood. The ability to accurately predict the essential characteristics of the fluidized-bed system, such as hydrodynamics, individual phase mixing, and heat transfer parameters, is necessary for its successful design and operation. This paper investigates the pressure drop, minimum fluidization velocity, phase holdup, heat-transfer coefficient of a fluidized bed reactor, heat transfer studies, CFD simulation, and the effect of these parameters on the extent of fluidization. Many variables (fluid flow rate, particle density and size, fluid inlet, and bed height) affect the fluidizing quality and performance of the fluidization process. The hydrodynamics parameters, mixing of phases, and the behavior of heat transfer with various modes of fluidization were investigated to predict hydrodynamics parameters. Several publications have demonstrated the utility of (CFD) in explaining the hydrodynamics, heat, and mass transfer of fluidized beds. Principles of measurement, details of the experimental configurations, and the applied techniques by various researchers are also presented. Feng's model was statistically validated using experimental data that was both time-averaged and time-dependent. Furthermore, this model successfully predicted the instantaneous flow structures, which should provide strategies for the best design, scale-up, and operation in fluidized bed columns. The divergence between the simulated and observed values can be reduced by better understanding the fluidized bed's nature.

The Influence of Convection Heat Transfers for Vertical Mini-Tubes Using Solvent Carbon Dioxide and Porous Media at Supercritical Pressure

Bilal J. Kkihlefa; Ameer A. Jaddoa; Ahmed H. Reja

Engineering and Technology Journal, 2021, Volume 39, Issue 9, Pages 1409-1419
DOI: 10.30684/etj.v39i9.2068

Porous media and solvent CO2 at supercritical pressure were investigated experimentally to study the effect of convection heat transfer in vertical mini-tubes. Mini-tubes diameter (5 and 8 mm) with medium porosity of 0.5 are proposed in experimental investigation. Experimental conditions consisted of bulk fluid, wall temperatures ranged from 33 to 55 oC, and 8 to 10 MPa of pressure. Reynolds number, Mass flow rate, and heat flux were 1750 to 21000, 0.5 to 4.5 Kg/h, and 3.25×104 to 1.1×105 W/m2 respectively. Some chemical additives like Ethanol, Chloroform, Acetone, Dimethyl sulfoxide, and Methanol were considered. A special focus was dedicated to studying the influence of heat flux, inlet temperature, and mass flow rate at measured values of wall and fluid bulk temperatures, and coefficients of local heat transfer for mini-tubes and porous media. A higher effect was noticed on the convection heat transfer by buoyancy and properties of the thermophysical variable of solvent CO2 in mini-tube at vertical position. However, when these results were compared with the controls (empty tube) shoewn dramatically different results. Heat transfer coefficient was bigger about 4 times when using the porous media tube compared with the empty type in the case of using a 5% of acetone solvent.

An Elaborate Review for Micro-Fin Heat Sink

Ibtisam A. Hasan; Sahar R. Fafraj; Israa A. Mohmma

Engineering and Technology Journal, 2020, Volume 38, Issue 1, Pages 105-112
DOI: 10.30684/etj.v38i1A.331

Heat sinks are low cost, the process of manufacturing reliability, and design simplicity which leads to taking into consideration various cutting-edge applications for heat transfer. Like stationary, fuel cells, automotive electronic devices also PV panels cooling and other various applications to improve the heat sinks thermal performance. The aim is to focus on some countless fundamental issues in domains such as; mechanics of fluids and heat transfer, sophisticated prediction for temperature distribution, high heat flux removal, and thermal resistance reduction. The outcome of this survey concluded that the best configuration of heat sinks has a thermal resistance about (0.140 K/W to 0.250 K/W) along with a drop of pressure less than (90.0 KPa) with a temperature gradient about 2 °C/mm. Heat sinks with square pin fins lead to enhance the effectiveness of heat dissipation than heat sinks with microcolumn pin fins. While other researches recommend the use of high conductive coating contains nano-particles. The present survey focuses on the researches about future heat sink with micro fin and the development to resolve the fundamental issues. The main benefits and boundaries of micro fins heat sink briefed.

Enhancement of Thermal Storage Properties of Phase Change Material by Using Metallic Swarf

Abdulkareem Khudhair; Falah Hatem; Dher Mohammed Ridha

Engineering and Technology Journal, 2018, Volume 36, Issue 5A, Pages 586-595
DOI: 10.30684/etj.36.5A.15

The phase change materials (PCM) is commonly used for storage heat as a latent heat, the main disadvantage of this method is slow response time during charging and discharging; this due to the PCM thermal properties. This work studied experimentally the enhancement of thermal properties of PCM by adding various metallic swarf such as copper, aluminum and iron swarf. Metallic swarf used as thermal conductivity promoter to produce modified paraffin wax samples. The addition of the previous enhancers was conducted with a weight fraction of (7.5%, 12.5% and 17.5%) to the whole weight of the mixture. The experimental results showed that adding of metallic swarf to the PCM decrease the charging time by (5.5 - 22.1%) for weight fractions from (7.5-17.5%) respectively. The addition of metallic swarf to PCM showed enhancement of discharging time by (27 - 77 %) compared with the case of pure wax for copper swarf weight fraction of (7.5 – 17.5%) respectively. Thermal conductivity of PW was enhanced by using aluminum, copper, and iron swarf, where it is found that the maximum enhancement about (53 times) due to the addition of (17.5%) of aluminum swarf. This method is considered a successful economic way due to the use of manufacturing waste.

Modeling the Behavior of Frost Growth on Finned Tube Heat Exchanger

Zainab Hasoun H.Naji

Engineering and Technology Journal, 2014, Volume 32, Issue 1, Pages 215-229

A quasi-steady finite-volume model was developed for modeling a plain-finround-tube heat exchanger under frosted conditions. In this study, the heat and mass transfer characteristics of heat exchangers during frost formation process are analyzed numerically. Unsteady heat and mass transfer coefficients of the air side, heat transfer coefficient of the refrigerant side, frost layer thickness, the surface efficiency of the
heat exchanger and the mass flow rate of the frost accumulated on the heat exchanger surface are calculated. The total conductivity (UA) and pressure drop of the heat exchanger are reported for different air inlet and refrigerant temperature. Results have shown that frost layer growth is faster with lower inlet air temperature. Using the developed mathematical model, the algorithm and the computer code, which have
been experimentally validated, it is possible to predict a decrease of exchanged heat flux in the heat exchanger under frost growth conditions. The model could be further extended to simulate direct expansion evaporators with varying operating conditions and variable heat exchanger geometry.

Influence of Corrosion Rate on the Double Butt Welding Shapes Design for Low Carbon Steel

Hani Aziz Ameen; Khairia Salman Hassan; Walid Khalid Abdul Kader

Engineering and Technology Journal, 2011, Volume 29, Issue 6, Pages 1094-1106

The aim of this paper is to demonstrate the influence of butt welding shapes
on the corrosion rate, microstructure and temperature of carbon steel type
St37.The double butt welding was performed by V angles 15°,30° and 45°. The
finite element analysis via ANSYS software is performed, this analysis includes a
finite element model for the thermal welding simulation. The temperature
distribution was obtained. From the results of the microscopic structure it is
evident that the geometric shape has an important role in the welding process,
when the geometric value of the welding region gets bigger, the faults get less due
to increase of heat quantity in the welding region and the corrosion rate for the
rain water is less than of sea water. The work presents the finite element model for
numerical simulation of welding in carbon steel St37 double butt welding.

Influence of Butt Welding Shapes Design on the Microstructure and Stresses of Low Carbon Steel

Hani Aziz Ameen; Khairia Salman Hassan

Engineering and Technology Journal, 2010, Volume 28, Issue 15, Pages 5036-5047

The aim of this paper is to demonstrate the influence of butt welding shapes on the microstructure, temperature and equivalent stresses of carbon steel type St- 37.The single butt welding was performed by V angles 15°,30°,45° and U shape. The finite element analysis via ANSYS software is performed , this analysis includes a finite element model for the thermal and mechanical welding simulation. The equivalent stresses and temperature distribution were obtained. From the results of the microscopic structure it is evident that the geometric shape
has an important role in the welding process, when the geometric value of the welding region gets bigger, the faults get less due to increase of heat quantity in the welding region. The work presents the finite element model for numerical simulation of welding stresses in carbon steel St-37 butt welding. The welding simulation was considered as a direct coupled thermo- mechanical analysi.s

A Study of Chaotic Behavior of Heat Transfer In Gas-Solid Fluidized Bed

e Al-Rubeai; Jamal Mane; Nabeel Majid Aliwi

Engineering and Technology Journal, 2010, Volume 28, Issue 10, Pages 2027-2042

Fluidized beds are characterized by high heat transfer rates between the
bed and internal surfaces and have uniform temperature distribution that can be
achieved in fluidized bed systems. In the same time there is a chaotic behavior of
hydrodynamic and heat transfer in gas-solid fluidized bed.
Experimental work was carried out in gas-solid (air – sand) fluidized bed to
investigate the steady state heat transfer coefficient. The bed column used was
(172) mm in diameter and (1000) mm height, fitted with immersed cylindrical
heating element of (25.4) mm in diameter. The fluidizing medium was air flowing
at different velocities from fixed bed to fluidized bed of (0.006-0.078)m/s, and
three different sizes of fine sand particles were used (i.e. 63, 112, and 145 μm),
these average particles diameters were estimated by two methods (Wide and
Narrow Range Solids).
A comparison have been done with values of the minimum fluidizing velocity that
calculated analytically, empirical, and which got experimentally. The results show
a chaotic behavior of hydrodynamic gas-solid fluidized bed.
The heat transfer coefficient and the bed viodage increase with increasing gas
fluidizing velocity and the heat transfer coefficient decreases with an increase in
particle diameter.
Two empirical correlations are proposed which can calculate wide range solids and
narrow range solids based on experimental data. The Nusselt number presented
with some dimensionless groups as follows:-
For Wide Range Solids Nu = 0.81Re0.94 Pr0.35
Where the correlation coefficient (R) was equal to (0.92) and the average absolute
relative error was (12.62 %).
For Narrow Range Solids Nu = 0.45Re0.65 Pr0.33
Where the correlation coefficient (R) was equal to (0.86) and the average absolute
relative error was (24.2 %).

Heat Transfer from an Immersed Heater in Liquid – Liquid – Solid Fluidized Beds

Asrar A. Al-Obaidy; Majid I. Abdul-Wahab; Balasim A. Abid

Engineering and Technology Journal, 2009, Volume 27, Issue 10, Pages 1901-1914

Heat transfer from an immersed heating surface to a liquid-solid and liquid-liquidsolid fluidized beds have been studied. The experiments were carried out in a (0.22) m column diameter fitted with an axially mounted cylindrical heater heated electrically. The fluidizing medium was water as the continuous phase and kerosene as the dispersed phase. Low density (Ploymethyl-methacrylate) particles were used. Previous
published heat transfer correlations, obtained for fluidized beds containing highdensity particles, gave significant deviations compared with the present data. New correlations were developed to predict the heat transfer coefficients in liquid-solid and liquid-liquid-solid fluidized beds. The new correlation is,

The heat transfer coefficients obtained from the present work were compared with those estimated from other correlations reported in the literature. The comparison shows a good agreement with the data obtained for the gas-liquid-solid fluidized beds using low-density particles.

Thermal Effects on Diesel Engine Piston and Piston Compression Rings

Isam Ezzulddinyousif; Basim M. Al-Quraishi; Ahmed A. Al-Beiruti

Engineering and Technology Journal, 2009, Volume 27, Issue 8, Pages 1444-1454

This paper introduces an analytical study on the thermal effects on the diesel
engine piston and its compresion rings during the contact between the piston and its
compression rings .A three dimensional finite element model is built for the piston
and its compression rings using the ANSYS v. 8 Finite Element Analysis Code
that serves all engineering problems . The thermal analysis is made using contact
case between the piston and its compression rings .The work in this paper did not
include a convergence study.
The study includes the effects on the piston and piston compression rings
of the thermal conductivity of piston material , and the contact area .The conclusions
of this study are that the material type of high thermal conductivity is considered better
than the material type of low thermal conductivity. This means that the aluminum
alloy is considered better than the cast-iron alloy, and tapering the compression rings
from the inner side by 1 mm , leads to a reduction in the temperature values by
1.6% , 0.84% and 0.37% compared to rectangle compression rings.