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1

Analysis of inhibiting factors in shipyards in classterizing shipyards on the Northen coastal of ACEH Indonesia using the fuzzy AHP method: a preliminary study

Rizwan T., Chaliluddin M. A., Nuvus H., Arif M., Muchlis Y., Akhyar A.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2024

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Vol. 18 No. 2

409--414

EN

The fishing shipyard in Banda Aceh City is a privately owned shipyard and is managed in a family manner. The shipyard here is active in carrying out maintenance, repair and construction of new ships when there is demand from consumers. Shipyards in Banda Aceh City generally make ships made of wood. The problem that is currently being faced is that there are many abandoned ships due to lack of finance, natural resources, human resources and the environmental, this is an obstacle to the progress and development of shipyards. The purpose of this study is to determine the inhibiting factors that exist in shipyards in the city of Banda Aceh and find alternative solutions to these problems. The method used in this study is a survey method used to look at existing symptoms and collect data on factors related to research variables and then analyzed using the Fuzzy AHP method. The results of this study indicate that the financial inhibiting factor is the most influential factor in shipyards with a resulting value of 0.4635, the inhibiting factor of Natural Resources is worth 0.35675, the inhibiting factor of Human Resources is worth 0.2865 and the inhibiting factor from the environment is the inhibiting factor which is the lowest or less influential with a value of 0.14325. The alternative solutions to financial problems are capital loans and investments. An alternative for natural resources is the addition of a minimum stock to anticipate stock scarcity and delays in the delivery of materials and tools. The alternative for human resources is the existence of an office, organizational structure, and division of tasks as well as awareness of occupational health and safety. As for the alternatives for the environment, namely the need for buildings or installation of tarpaulins for areas where ships are built, good land management and studies of other natural impacts.

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Solidification Process Modeling of Equiaxed Investment Castings with Transient Nonuniform Boundary Condition Definition

Olson Weston, Stemmler Michael, Fernandez Erik, Kapat Jayanta

Journal of Casting & Materials Engineering

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2024

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Vol. 8, no. 1

1--10

EN

The equiaxed investment casting process is a multi-physics problem which requires knowledge from engineers who have expertise in materials, metallurgy, fluid dynamics, thermodynamics, and heat transfer. Process modeling is a tool used by foundries to help predict casting defects such as shrinkage porosity, hot tears, and poor grain structure. The reliability of these predictions is strongly dependent on the accuracy of the thermal boundary conditions set in the model. In this work, a SGT5-2000E Vane 4 cast in Rene 80 nickel-based superalloy was modeled, using the FEA simulation package ProCAST, with two different methodologies. One methodology had very little effort invested into defining the thermal domain. The other methodology involved a thorough consideration of all heat transfer mechanisms acting on the mold. An extensive literature search was performed to define a unique natural convection heat transfer coefficient for each set of surfaces on the mold. The transient boundary layer development was also captured in the definition of the heat conditions. The shrinkage porosity predictions of the models were compared to real-world x-ray data and the transient nonuniform methodology predictions were much more representative than the low fidelity heat transfer methodology predictions. The low fidelity heat transfer model did predict some shrinkage, but not where it appeared in reality. The process modeler will be misdirected by the model results when deriving a solution to the casting process if the real-world physics are not appropriately accounted for in the model. This will be very counterproductive when the foundry is using the model to reduce developmental trials by running trials in model space. References and derived parameters are provided for material properties, emissivity of shell and insulation wraps, and external mold spatially varying heat transfer coefficients.

3

Employing a Combination of a Double-Glazed Flat Solar Collector and Sensible Heat Storage for Drying Agricultural Products

Efendi Mohamad, Hendrawan Yusuf, Hawa La Choviya, Argo Bambang Dwi

Ecological Engineering & Environmental Technology

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2024

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Vol. 25, iss. 5

106--118

EN

Convection heat collector technology is a promising technology for drying agricultural products. The study aimed to determine the temperature characteristics, energy efficiency, and thermal discharging of a flat plate-type collector using double-glazing technology integrated with heat storage material in the state of iron scraps in passive and active modes. Investigation was conducted for seven hours of exposure under the sun (08:00–15:00 local time). Ten temperature sensors and four humidity sensors were used during measurements to determine the thermal characteristics of the heat collector. The density of iron scraps as heat storage material is 250 kg/m3 with an irradiation time of seven hours. The results indicate that the passive mode of operation has a higher temperature characteristics than the active mode. During irradiation process, the highest temperatures on the absorber in active and passive modes were 63 °C and 55 °C, respectively. Meanwhile, the highest temperatures on the TES in passive and active modes during irradiation were 55.6 °C and 50.6 °C, respectively. The energy efficiency of the collector ranges from 23.3–55.1% (passive) and 18.6–40.7% (active). The energy efficiency of the TES (Thermal Energy Storage) has a range of 7.4–22.7% (passive) and 7.4–13.0% (active). During discharging process, it shows that the TES in passive mode can store heat for 275 minutes and active mode for 95 minutes. Heat collectors that used double glazing technology and heat storage materials using iron scraps with a density of 250 kg/m3 have a significant potential to extend the drying duration of agricultural products with limited exposure to sunlight and environmentally friendly heat collectors.

4

Numerical study on the effect of strategically placed multiple diathermal obstructions within a porous enclosure

Chordiya Jayesh, Deshmukh Padmakar, Sharma Ram Vinoy

Archive of Mechanical Engineering

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2024

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LXXI, nr 3

419--444

EN

A novel strategy to reduce the convection heat transfer across a differentially heated, fluid-saturated porous enclosure has been reported in the present investigation. This objective is achieved by sequentially and strategically embedding multiple diathermal obstructions within the enclosure. To describe it in short, the strategy is to identify the location of maximum convection strength and place a single obstruction at that location. This strategy is re-applied to find an updated location of maximum convection strength and placing another single obstruction at that newly updated location. Darcy flow model is used to describe the fluid flow in porous media and solved using Successive Accelerated Replacement scheme using finite difference method. The parameters under study are type of obstructions (horizontal, vertical, right-inclined, left-inclined, straight-crossed and inclined-crossed), number of obstructions (0 ⩽ 𝑁 ⩽ 10) and modified Rayleigh number (100 ⩽ 𝑅𝑎 ⩽ 2000). The size of obstruction (𝑍) has been fixed at 0.1. Flow and temperature distribution are plotted using streamlines and isotherms. The strength of convection is quantified using Nusselt number and maximum absolute stream function. It has been found that introducing obstructions within a differentially heated porous enclosure weakens the convection strength developed within it and the maximum reduction can be obtained for inclined-cross obstruction.

5

Role of suction/injection on electromagnetohydrodynamics natural convection flow in a porous microchannel with electroosmotic effect

Oni Michael O., Rilwan Usman

International Journal of Applied Mechanics and Engineering

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2023

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Vol. 28, no. 4

94--113

EN

This paper examined the role of suction/injection on time-dependent electromagnetohydrodynamics (EMHD) natural (free) convection flow in a vertical microchannel with electroosmotic effect. With the aid of Laplace transformation method, the governing energy and momentum equations are converted from partial differential equation (PDE) into ordinary differential equation (ODE) to obtain fluid temperature and velocity in Laplace domain. The semi-analytical solutions of the velocity profile and temperature distribution have been derived using the Riemann sum approximation. After which a MATLAB program was written to study the effects of Prandlt number Pr, Hartmann number Ha, electric field strength on x and z directions (Ex and Sz) and Grashof number Gr in fluid velocity, temperature, skin-friction and mass flow rate in terms of line graphs. Result shows the role of suction/injection parameter alters the temperature distribution and velocity profile, so also how effective the governing parameters contribute to the flow formation.

6

Entropy production due to conjugate natural convection in a nanofluid-filled enclosure with a stepped wall

Bouchoucha Abd el, Oztop Hakan F., Bessaih Rachid, Abu-Hamdeh Nidal

Engineering Transactions

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2023

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Vol. 71, iss. 2

161-183

EN

The main aim of this paper is to improve the heat transfer in a square cavity with a body at the left wall filled with a Al2O3/water nanofluid for different geometries. Numerous simulation experiments are conducted. A relative temperature is maintained at the vertical and top horizontal walls while the bottom wall is warm. The finite volume approach is considered to resolve the equations governing the thermal transfer flow in the physical domain based on the SIMPLER algorithm. In this study, different values of the following parameters are considered: Rayleigh number (104 ≤ Ra ≤ 105) and solid volume fraction (0 ≤ φ ≤ 0.1) of nanoparticles (NPs). Parameters, such as the Rayleigh (Ra) and Bejan (Be) numbers, thermal conductivity, body’s dimensions, and NPs volume fraction, which directly affect the entropy generation and heat transfer rate, are studied in a particular way. The obtained results show that entropy generation goes ahead with the Ra increase and inverse to the solid volume fraction increase. One can notice that the heat transfer has a proportional relation with φ and Ra.

7

Magnetoconvection of nanofluid in a partially heated cavity with isothermal blockage

Nagaraj Suresh, Nagarajan Nithyadevi

Journal of Applied Mathematics and Computational Mechanics

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2022

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Vol. 21, nr 2

77--90

EN

Natural convection characteristics of Al2O3-water nanofluid in a cavity is investigated numerically under the influence of a inclined magnetic field. The bottom wall is partially heated, and the top wall is cooled and the remaining regions of the cavity are kept adiabatic. An isothermally heated square blockage of the different rectangular size is placed at the centre of the cavity. The schematic model is converted into mathematical form, and the non-dimensional equations are discretized by the finite volume method using power law scheme and solved by Semi-Implicit Method for Pressure Linked Equation algorithm. The relevant parameters such as Rayleigh number (104-106), Hartmann numer (10-500), size of blockage ratio (0.25-0.75), length of the heat source (0.25-1.0) and inclination angle of the magnetic field (0°-90° on the flow and temperature fields are examined. Results are presented in terms of streamlines, isotherms, velocity profile, local and average Nusselt number. It was found that for low Hartmann numbers, the average heat transfer rate attained the maximum at the inclined magnetic field of γ = 45°. In addition, the blockage ratio of B = 0.75 enhanced the higher heat transfer rate for all values of γ.

8

Investigations of Couette flow unsteady radiative convective heat transfer in a vertical channel using the generalized method of lines (MOL)

Sowayan Ahmed S.

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 3

199--211

EN

This study describes a very efficient and fast numerical solution method for the non-steady free convection flow with radiation of a viscous fluid between two infinite vertical parallel walls. The method of lines (MOL) is used together with the Runge-Kutta ODE Matlab solver to investigate this problem numerically. The presence of radiation adds more stiffness and numerical complexity to the problem. A complete derivation in dimensionless form of the governing equations for momentum and energy is also included. A constant heat flux condition is applied at the left wall and a transient numerical solution is obtained for different values of the radiation parameter (R). The results are presented for dimensionless velocity, dimensionless temperature and Nusselt number for different values of the Prandtl number (Pr), Grashof number (Gr), and the radiation parameter (R). As expected, the results show that the convection heat transfer is high when the Nusselt number is high and the radiation parameter is low. It is also shown that the solution method used is simple and efficient and could be easily adopted to solve more complex problems.

9

Heat transfer by natural convection from a heated square inner cylinder to its elliptical outer enclosure utilizing nanofluids

Bouras Abdelkrim, Taloub Djedid, Driss Zied, Debka Siham

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 2

22--34

EN

In this paper a numerical study of natural convection of stationary laminar heat transfers in a horizontal ring between a heated square inner cylinder and a cold elliptical outer cylinder is presented. A Cu-water nanofluid flows through this annular space. Different values of the Rayleigh number and volume fraction of nanoparticles are studied. The system of equations governing the problem was solved numerically by the fluent calculation code based on the finite volume method and on the Boussinesq approximation. The interior and exterior surfaces are kept at constant temperature. The study is carried out for Rayleigh numbers ranging from 310 to 510. We have studied the effects of different Rayleigh numbers and volume fraction of nanoparticles on natural convection. The results are presented as isotherms, isocurrents, and local and mean Nusselt numbers. The aim of this study is to study the influence of the thermal Rayleigh number and volume fraction of nanoparticles on the heat transfer rate.

10

Natural convection flow in semi-trapezoidal porous enclosure filled with alumina-water nanofluid using Tiwari and das’ nanofluid model

Vedavathi Nallapati, Venkatadri Kothuru, Fazuruddin Syed, Raju G. Sankara Sekhar

Engineering Transactions

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2022

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Vol. 70, iss. 4

303--318

EN

Nowadays, optimal parameters are necessary for heat transfer enhancement in different practical applications. A numerical simulation of natural convection in a semi-trapezoidal enclosure embedded with porous medium is presented. Stream function and temperature using the Darcy–Boussinesq approximation and Tiwari and Das’ nanofluid model with new more realistic empirical correlations for the physical properties of the nanofluids are formulated. The developed partial differential equations are employed with the help of the stream function approach. The in-house developed computational MATLAB code is validated with the previously published work. The impact of a wide range of governing parameters on fluid flow patterns and temperature gradient variations is presented. The thermal Rayleigh number (Ra) can be a control key parameter for heat and convective flow. Thermal dispersion effects are also examined in this study. An increase in the Rayleigh number leads to an increase in heat transfer, where one can find a reduction of convective heat transfer with φ.

11

The natural convection inside a 3D triangular cross section cavity filled with nanofluid and included cylinder with different arrangements

Ghoben Zainab Kareem, Hussein Ahmed Kadhim

Diagnostyka

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2022

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Vol. 23, No. 2

no. art. 2022205

EN

In this paper the laminar unsteady natural convection heat transfer of (Al2O3-water) nanofluid inside 3D triangular cross section cavity was investigated. The cavity was heated differentially, the vertical walls were kept at different constant temperatures. The left hot and the right cold. The effect of the solid volume fraction was examined for two values and compared with the pure water results. The (Ra) range studied was (103≤Ra≤106). Inserting cylindrical body inside the cavity also investigated in three cases. One concentric cylinder has radius (15%) of the cavity side length. The other cases were of two cylinders having radius (7.5%) of the cavity side length, aligned vertically or nonaligned. The results show that the higher solid volume fraction gives the maximum enhancement of the average (Nu) and this enhancement increases with (Ra) increase. For the cases with inner cylinders, the average (Nu) enhanced for the case of double cylinders over single cylinder. On other hand, the nonaligned position of the cylinders giving more enhancement than other position. As like as, the location of maximum horizontal or vertical velocities were varied with the cylinders position while (Ra) has no effect.

12

Effect of aspect ratio of enclosure on free convection from horizontal cylinders in Bingham plastic fluids

Baranwal Ashok Kumar, Gupta Anoop Kumar, Tiwari Anurag Kumar, Melnik Roderick

Chemical and Process Engineering

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2022

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Vol. 43, nr 2

271--277

EN

Heat transfer in steady free convection from differentially heated cylinders enclosed in a rectangular duct filled with Bingham plastic fluids has been solved numerically for the ranges of the dimensionless groups as, Rayleigh number, 102 Ra 106; Prandtl number, 10 Pr 100 and, Bingham number, 0 Bn 50 for aspect ratios AR = 05, 0.6, 0.7, 0.8, 0.9 and 2. The streamlines, isotherm contours, yield surfaces, local and average Nusselt numbers were analysed and discussed. It is found that as the aspect ratio of the enclosure increases from 0.5 to 0.9, the average Nusselt number on the surface of the hot cylinder increases as a larger amount of fluid takes part in convection. Moreover, at sufficiently large Bingham numbers, yield stress forces dominate over buoyancy causing the flow to cease and thus the Nusselt number approaches its conduction limit. Finally, the Nusselt number approaches its conduction limit once the maximum Bingham number is reached.

13

Natural convection in a partially heated cylinder: A numerical study

Núñez José, Beltrán Alberto, Rivero Michel

Journal of Theoretical and Applied Mechanics

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2021

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Vol. 59 nr 4

623--636

EN

This work presents a numerical study on a natural convective flow in a cylindrical container heated from below, cooled from above, and partially heated from the lateral wall. Mass, momentum and energy equations were solved with a developed hybrid Fourier-finite volume code and validated with the commercial software COMSOL Multiphysics for steady-state solutions. The primary solutions correspond to steady-states Cm with azimuthal wavenumbers m. The results show mode competition between different states leading to many flow solutions including steady axisymmetric, steady non-axisymmetric, time-dependent pulsating wave solutions, and other flow states with a variety of spatiotemporal symmetries.

14

Generation of pressure oscillations in air flows in vertical channels with internal heat release

Basok Boris, Davydenko Boris, Pavlenko Anatoliy

Journal of New Technologies in Environmental Science

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2021

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Vol. 5, nr 3

106--116

EN

The characteristics of the air flow in a vertical channel, arising due to local internal heat release, are investigated by the method of numerical simulation. Heat is supplied to the flow from internal sources located in a limited volume closer to the inlet section of the channel. The problem of flow and heat transfer is described by a system of unsteady Navier-Stokes and energy equations for a compressible medium. The coefficients of viscosity and thermal conductivity are considered to be temperature dependent. From the numerical solution of this system, the velocity, pressure, and temperature fields in the channel are determined. Based on the results of the calculations, the regularities of the change in time of velocity and pressure in the channel are determined. From the analysis of the results it follows that from the moment the heat supply begins, a vertical air flow develops in the channel, which is accompanied by oscillations in velocity and pressure. Self-oscillations arising in a gas flow are a manifestation of instability of flow. It is shown that stable oscillations take place in the presence of additional local hydraulic resistance in the channel. The dependence of the amplitude and frequency of pressure oscillations and the air flow velocity on the power of the sources of internal heat release and the height of the channel has been investigated. It was determined that with an increase in the power of the source of internal heat supply and the height of the channel, the amplitudes of the velocity and pressure fluctuations increase.

15

Analysis of transient natural convective flow of a nanofluid in a vertical tube

Jha Basant K., Chitumu Ali J., Oni Michael O.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 2

31--46

EN

An analysis into the transient natural convective flow of a nanofluid in a vertical tube is made. The governing equations of momentum, heat transfer and nanoparticle volume fraction are deduced, and the influence of the thermophoresis parameter and Brownian motion is incorporated. By direct integration and variation of the parameter, analytical solutions are obtained for flow formation and heat/mass transfer at steady-state. On the other hand, due to the complexity of same problem at transient state, a numerical solution is used to solve the discretized equations of motion using the implicit finite difference technique. The influence of the thermophoresis parameter and Brownian motion is noted and well discussed. For accuracy check, a numerical comparison is made between the steady state and transient state solution at large time; this comparison gives an excellent agreement. The role of various principal parameters on velocity profile, temperature, concentration of nanoparticles, Sherwood and Nusselt numbers are presented graphically and well discussed. It is noted that the buoyancy ratio decreases the fluid velocity significantly.

16

Performance of four different nanoparticles in boundary layer flow over a stretching sheet in porous medium driven by buoyancy force

Ammani Kuttan B., Manjunatha S., Jayanthi S., Gireesha B. J.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 2

1--10

EN

This contemporary work explores the theoretical analysis of energy transfer performance of distinct nanoparticles (silver, copper, aluminium oxide and titanium oxide) adjacent to a moving surface under the influence of a porous medium which is driven by the buoyancy force. A mathematical model is presented which is converted to similarity equations by employing similarity transformation. The condensed nonlinear equations were approximated by the iterative method called RKF 45th-order. The flow and energy transference characteristics are explained through graphs and tabulated values. The notable findings are: silver- water is an appropriate nanofluid for enhancing the thermal conductivity of the base fluid. Titanium oxide – water shows a lower fluid flow movement due to porosity.

17

Effect of Rayleigh number on internal eccentricity in a heated horizontal elliptical cylinder to its coaxial square enclosure

Bouras Abdelkrim, Taloub Djedid, Driss Zied

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 3

17--29

EN

This paper deals with numerical investigation of a natural convective flow in a horizontal annular space between a heated square inner cylinder and a cold elliptical outer cylinder with a Newtonian fluid. Uniform temperatures are imposed along walls of the enclosure. The governing equations of the problem were solved numerically by the commercial code Fluent, based on the finite volume method and the Boussinesq approximation. The effects of Geometry Ratio GR and Rayleigh numbers on fluid flow and heat transfer performance are investigated. The Rayleigh number is varied from 103 to 106. Throughout the study the relevant results are presented in terms of isotherms, and streamlines. From the results, we found that the increase in the Geometry Ratio B leads to an increase of the heat transfer coefficient. The heat transfer rate in the annulus is translated in terms of the average Nusselt numbers along the enclosure's sides. Tecplot 7 program was used to plot the curves which cleared these relations and isotherms and streamlines which illustrate the behavior of air through the channel and its variation with other parameters. The results for the streamlines, isotherms, local and average Nusselt numbers average Nusselt numbers are compared with previous works and show good agreement.

18

Natural convection from four circular cylinders in across arrangement within horizontal annular space

Laidoudi Houssem

Acta Mechanica et Automatica

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2020

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Vol. 14, no. 2

98--102

EN

Numerical investigation is accomplished to study the roles of governing parameters of natural convection on the fluid motion and heat transfer rate of four heated circular cylinders placed inside a circular enclosure of cold surface. The cylinders are positioned in across arrangement. The representative results are obtained within the ranges of initial conditions as: Prandtl number (Pr = 7.1 to 1000) and Rayleigh number (Ra = 103 to 105). The average Nusselt number of each inner cylinder is computed. The effects of thermal buoyancy strength on the fluid motion and temperature are also illustrated. It was found that the heat transfer rate of cylinders depends significantly on the position inside the enclosure. Moreover, the role of Prandtl number on flow and thermal patterns is negligible. The values of Nusselt number are also given, which can be useful for some engineering applications.

19

Cieplne warunki brzegowe w przypadku obliczania stanu naprężenia w elementach grubościennych kotłów energetycznych

Wacławiak Krzysztof

Modelowanie Inżynierskie

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2019

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T. 39, nr 70

70--76

PL

Artykuł pokazuje numeryczny sposób wyznaczenia współczynnika wnikania ciepła przy przepływie pary wodnej w elementach grubościennych kotłów energetycznych. Elementy te obliczane są z warunku wytrzymałościowego na pełzanie. Literatura wskazuje również na znaczenie zmęczenia cieplno-mechanicznego powstającego w materiale w czasie rozruchu i odstawienia. Planuje się zwiększyć częstość rozruchów starszych bloków energetycznych eksploatowanych jako jednostki szczytowe. Typowe obliczenia cieplno-mechaniczne zakładają znajomość współczynnika wnikania ciepła od pary do elementu grubościennego i jej temperaturę. W obliczeniach tych pomija się izolację elementu, zakładając warunki konwekcji swobodnej do otoczenia. W pracy przeanalizowano te założenia i wykonano reprezentatywne obliczenia numeryczne.

EN

This paper presents a numerical calculation of heat transfer coefficient for steam flowing through a thick-walled elements of a power boiler. Such elements of power boilers are designed regarding creep loading. Literature shows that thermo-mechanical fatigue should also be considered especially during start-up and shut-down periods. Old boilers will be operated more frequently in upcoming years. They may be still used as steam producers during peak demand for electricity. Typical thermal and mechanical calculations used defined boundary conditions for a fluid side including heat transfer coefficient and near wall fluid temperature. Usually insulation is omitted, only natural convection to the air is included. This paper presents modeling and some exemplary calculations of proper heat transfer determination, where local and transient variables are found.

20

Natural and mixed convection of a nanofluid in porous cavities: critical analysis using buongiorno’s model

Zahmatkesh Iman, Habibi Mohammad Reza

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 1

221--233

EN

In this paper, Buongiorno’s mathematical model is adopted to simulate both natural convection and mixed convection of a nanofluid in square porous cavities. The model takes into account the Brownian diffusion and thermophoresis effects. Both constant and variable temperatures are prescribed at the side walls while the remaining walls are maintained adiabatic. Moreover, all boundaries are assumed to be impermeable to the base fluid and the nanoparticles. The governing equations are transformed to a form of dimensionless equations and then solved numerically using the finite-volume method. Thereafter, effects of the Brownian diffusion parameter, the thermophoresis number, and the buoyancy ratio on the flow strength and the average Nusselt number as well as distributions of isocontours of the stream function, temperature, and nanoparticles fraction are presented and discussed.