Search for: heat-transfer-coefficients
Total 83 records
Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 48, Issue 6 , 2012 , Pages 1023-1029 ; 09477411 (ISSN) ; Sharif University of Technology
Research on convective heat transfer coefficient around a rod bundle has many diverse applications in industry. So far, many studies have been conducted in correlations related to internal and turbulent fully-developed flow. Comparison shows that Dittus-Boelter, Sieder-Tate and Petukhov have so far been the most practical correlations in fully-developed turbulent fluid flow heat transfer. The present study conducts an experimental examination of the validity of these frequently-applied correlations and introduces a manufactured test facility as well. Due to its generalizibility, the unique geometry of this test facility (hexagonal arranged, 7 vertical rods in a hexagonal tube) can fulfil...
M.Sc. Thesis Sharif University of Technology ; Shafii, Mohammad Behshad ; Saidi, Mohammad Hassan ; Saeedi, Mohammad Saeed
Modern microelectronic systems generate a large amount of heat which must be transferred out of the system without excessive temperature rise. Conventional forced air convection and microchannel cooling plates have reached their performance limits Nanofiuids are proposed as an innovative way to solve the problem. A nanofiuid is nanoscale solid particles dispersed in a traditional heat transfer liquid. Some studies show an anomalous increase in the thermal conductivity for stationary nanofiuids. However, there are only few previous studies on the convection heat transfer rate and viscosity of nanofiuids. Both convection and stationary measurements of the thermal conductivity are widely...
Evaluation of pressure effect on heat transfer coefficient at the metal-mold interface for casting of A356 al alloy, Article Iranian Journal of Materials Science and Engineering ; Volume 9, Issue 1 , 2012 , Pages 11-20 ; 17350808 (ISSN) ; Varahraam, N ; Davami, P ; Sharif University of Technology
During solidification and casting in metallic molds, the heat flow is controlled by the thermal resistance at the casting-mold interface. Thus heat transfer coefficient at the metal-mold interface has a predominant effect on the rate of heat transfer. In some processes such as low pressure and die-casting, the effect of pressure on molten metal will affect the rate of heat transfer at least at initial steps of solidification. In this study interfacial heat transfer coefficient at the interface between A356 alloy casting and metallic mold during the solidification of casting under pressure were obtained using the IHCP (Inverse Heat Conduction Problem) method. Temperature measurements are then...
Article Steel Research International ; Volume 87, Issue 3 , 2016 , Pages 330-338 ; 16113683 (ISSN) ; Fathi, A ; Škrjanc, I ; Sharif University of Technology
Wiley-VCH Verlag 2016
The paper studies the effects of solid and liquid steel properties on the heat transfer coefficient (HTC) in electric arc furnaces (EAFs). Mathematically speaking, the HTC is a function of solid and liquid steel properties. Different velocities of the bath cause different flow paths around the solid particles and therefore different HTCs - a computational issue that has not been addressed yet. Therefore, a simplified calculation model is proposed, intended for HTC estimation according to the EAF conditions. Although many studies investigated this topic, most of them either assume unconventional conditions for the EAF operation, are computationally complex or focus on a specific case; and...
Article Journal of Electrostatics ; Volume 78 , 2015 , Pages 22-30 ; 03043886 (ISSN) ; Kasaeian, A ; Ghalamchi, M ; Ghalamchi, M ; Sharif University of Technology
The effect of the corona wind on the natural convection at absorber of a solar chimney power plant pilot was investigated experimentally. The aim of the study is to improve the efficiency of SCPP through enhanced the heat transfer coefficient of absorber with corona wind. The results show that corona wind enhanced the absorber convective heat transfer coefficient leading to increment in air the velocity and the output power of the SCPP. The amount of heat transfer of pilot increased more than 14.5% when applying voltage of 15 KV and the speed in chimney experienced about 72% amelioration
Experimental assessment of convective heat transfer coefficient enhancement of nanofluids prepared from high surface area nanoporous graphene, Article International Communications in Heat and Mass Transfer ; Volume 78 , 2016 , Pages 127-134 ; 07351933 (ISSN) ; Sattari, S ; Rashidi, A. M ; Sharif University of Technology
In this research convective heat transfer coefficient enhancement of nanofluids prepared from high surface area graphene has been investigated in laminar flow in the developing region. The nanofluid has been prepared from nanoporous graphene with high surface area and with concentration of 0.025 to 0.1 wt.%. Deionized water has been used as the base fluid and a type of Ter-Polymer has been utilized as the surfactant. The results indicate that thermal conductivity of nanofluid with concentration of 0.1 wt.% remains quite constant, with only 3.8% enhancement, while convective heat transfer coefficient improves significantly, with 34% enhancement. The behavior of this enhancement related to the...
Article International Communications in Heat and Mass Transfer ; Volume 82 , 2017 , Pages 20-28 ; 07351933 (ISSN) ; Jafari, M ; Nasirivatan, S ; Osanloo, B ; Sharif University of Technology
Elsevier Ltd 2017
This work is dedicated to finding a suitable measure to judge thermal performance of nanofluids. The importance of this issue arises from misleading claim of excess heat transfer of nanofluids compared to the base fluid, neglecting the hydraulic effects such as increase in pressure drop. To clarify the issue, the experimental setup with capability to create constant Reynolds number and constant pumping power is constructed. Thermal behavior of nanofluids of silicon oxide/water and aluminum oxide/water and distilled water in developing region of laminar flow regime is investigated. In this regard, the convective heat transfer coefficient within the finned tube heat exchanger is evaluated....
Article Applied Thermal Engineering ; Volume 164 , 2020 ; Ebrahimi Dehshali, M ; Hakkaki Fard, A ; Sharif University of Technology
Elsevier Ltd 2020
The pool boiling is one of the heat transfer mechanisms used in cooling systems. Using an external force to improve the efficiency of thermo-fluid systems is among the most effective approaches, and also highly applicable in enhancing heat transfer. In this study, the pool boiling of water, as the working fluid, in the presence of a variable magnetic field, is studied. To this end, ferromagnetic beads were placed on the boiling surface, and the effect of their movements due to a variable magnetic field was observed and measured. The number of beads was selected such that they would cover 1/3, 1/2 and 2/3 of the surface in different cases and the magnetic field was controlled by altering...
Experimental investigation of the effect of copper electrodeposition on the aluminum surface and addition of ethylene glycol on boiling heat transfer coefficient, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; 2021 ; 09477411 (ISSN) ; Mahdi, M ; Abarghooei, A ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH 2021
In this research, the effect of surface characteristics on boiling heat transfer has been investigated experimentally. For this purpose, a device with the ability to automatically record the liquid temperature of the inlet and outlet of the test area, calculate the coefficient of boiling heat transfer, and heat flux has been developed. The automatic temperature stability of the working fluid and the ability to investigate the effect of surfaces with different characteristics (in terms of material and surface structure) on the boiling heat transfer parameters are the most important features of this device. The performance of the experimental setup was evaluated by the modified "Chen" equation...
Porosity and permeability effects on centerline temperature distributions, peak flame temperature, flame structure, and preheating mechanism for combustion in porous media, Article Journal of Energy Resources Technology, Transactions of the ASME ; Volume 129, Issue 1 , 2007 , Pages 54-65 ; 01950738 (ISSN) ; Safavisohi, B ; Sharbati, E ; Sharif University of Technology
The applicability and usefulness of combustion in porous media is of much interest due to its competitive combustion efficiency and lower pollutants formation. In the previous works, the focus has been on the effects of combustion and heat transfer parameters such as excess air ratio, thermal power, solid conductivity, convective heat transfer coefficient, and radiation properties on centerline temperature and pollutant formations. A premixed combustion scheme and a fixed porous medium with constant geometrical parameters have been used in these works; therefore, the effects of porous material parameters have been less considered. In this research, the effects of geometrical parameters of...
Article Proceedings of the Intersociety Energy Conversion Engineering Conference ; Volume 2 , 2000 , Pages 1261-1267 ; 0146955X (ISSN) ; Razi, Y. P ; Sharif University of Technology
The laminar natural convection from an isothermal horizontal cylinder confined between vertical walls is investigated by experimental and numerical methods. The experimental and numerical data are well correlated, independently, to equations which give the average Nusselt number in terms of the wall spacing to cylinder diameter ratio, t/D, and the Rayleigh number, Ra, for two different values of the wall height to cylinder diameter ratios, H/D=7 and 15.2. For the low Rayleigh numbers considered (Ra<1000), there are certain conditions for the confining walls under which heat transfer from the cylinder is maximum. Results are compared with the reported numerical and/or experimental results...
Article International Communications in Heat and Mass Transfer ; Volume 39, Issue 5 , 2012 , Pages 705-712 ; 07351933 (ISSN) ; Jabbari, M ; Davami, P ; Sharif University of Technology
The aim of this paper is to correlate interfacial heat transfer coefficient (IHTC) to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of casting under different pressures were obtained using the inverse heat conduction problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented for correlation between external pressure and heat transfer coefficient. Acceptable...
Article Chinese Journal of Chemical Engineering ; Volume 17, Issue 4 , 2009 , Pages 552-561 ; 10049541 (ISSN) ; Safekordi, A. A ; Jamialahmadi, M ; Sharif University of Technology
Boiling of water/triethyleneglycol (TEG) binary solution has a wide-ranging application in the gas processing engineering. Design, operation and optimization of the involved boilers require accurate prediction of boiling heat transfer coefficient between surface and solution. In this investigation, nucleate pool boiling heat transfer coefficient has been experimentally measured on a horizontal rod heater in water/TEG binary solutions in a wide range of concentrations and heat fluxes under ambient condition. The present experimental data are correlated using major existing correlations. In addition a correlation is presented for prediction of pool boiling heat transfer for the system in which...
Article Applied Thermal Engineering ; Volume 135 , 2018 , Pages 170-177 ; 13594311 (ISSN) ; Najm Barzanji, Z ; Hakkaki Fard, A ; Sharif University of Technology
Elsevier Ltd 2018
The boiling phenomena in a quiescent fluid is the nucleate pool boiling which has attracted much interest in the thermal management studies. This paper investigates the effect of the installed Twisted Tape Fins (TTFs) on the heat transfer from a surface with a temperature above the water saturation point to a coil condenser. Four different arrangements of TTFs (1, 3, 5, and 9 TTFs) are fabricated and their boiling performance in distilled water at atmospheric pressure is experimentally tested. It was observed that the increase in the boiling heat transfer coefficient of the plate with nine TTFs compared to that of the plain one is 15.5%. Furthermore, the effect of TTFs heights on the heat...
Article Applied Thermal Engineering ; Volume 133 , 2018 , Pages 276-282 ; 13594311 (ISSN) ; Alighardashi, H ; Farhadi, F ; Sharif University of Technology
Elsevier Ltd 2018
The overall heat transfer coefficient (OHTC) of air in a double-pipe helical heat exchanger is studied and experimentally investigated. In order to increase the rate of heat transfer in the annulus section, a copper-wire fin is soldered on the outside area of the internal tube. The literature correlations’ results are presented against the experimental data by changing mass flow rate and temperature, and consequently changing the Reynolds number. Further, a new method is suggested to obtain the heat transfer coefficients of double-pipe helical heat exchangers for the internal tube and the annulus section by combining two of the previously proposed approaches and making subsequent...
Experimental and numerical investigation of using pulsating heat pipes instead of fins in air-cooled heat exchangers, Article Energy Conversion and Management ; Volume 181 , 2019 , Pages 653-662 ; 01968904 (ISSN) ; Bijarchi, M. A ; Shafii, M. B ; Sharif University of Technology
Elsevier Ltd 2019
The goal of this study is the experimental and numerical investigation of using pulsating heat pipes (PHPs) as substitutes for fins in a typical air-cooled heat exchanger. Due to the small temperature difference between the cooling air and internal airflow in the case study, it was necessary that appropriate PHPs with the capability to work in small temperature difference conditions be investigated and an appropriate working fluid be selected. After reviewing various studies, R134a was selected as the best working fluid from the heat transfer standpoint. Afterward, a testing device was designed and fabricated. Additionally, in order to predict the behaviors of the main tubes with pulsating...
M.Sc. Thesis Sharif University of Technology ; Roosta Azad, Reza ; Yaghmaei, Soheyla
This project related to gas purification according to difference in the deposition point in the fludized bed.The main reason for choosing fluidized bed is increasing overall heat transfer coefficient compare in to other heat exchangers. Separation process, by cooling the wall causes the self- deposition gas phase shifts to solid phase. Solid formed on the wall, act as an insulating layer and greatly reduces the heat transfer. To solve this problem, the fluidized bed system is offered because fluid particles in addition to remove the insulating layer, improving convection heat transfer coefficient . Laboratory tests show the feasibility of preventing the formation of insulating layer by...
Modeling Evaluation of Pressure Effect on Mold/Metal Interface Heat Transfer Coefficient in A356 Alloy, M.Sc. Thesis Sharif University of Technology ; Varahram, Nasser ; Davami, Parviz
Mold/metal interfacial heat transfer coefficient (IHTC) is the most important parameter that influences the solidification and the mechanical properties of a solidified product. The present work focuses on the determination and evaluation of pressure effect on interfacial heat transfer coefficient from the experimental cooling curves during unidirectional solidification of A356 alloy against water cooled Gray iron mold (chill). For this purpose, inverse heat conduction method is used. The results showed that IHTC is not constant, but varies with time, temperature and pressure during solidification. IHTC variation is related to coherency and critical solid fraction during...
Modelling of Pressure Effect on Metal/Mold Interface Resistance in the A356 Aluminium Alloy Casting Process, M.Sc. Thesis Sharif University of Technology ; Davami, Parviz ; Varahram, Naser
The computer simulation of freezing patterns in castings has done much to broaden our understanding of casting and mold system design. The structural integrity of shaped castings is closely related to the time–temperature history during solidification, and the use of casting simulation could do much to increase this knowledge in the foundry industry. However, some uncertainties must be eradicated, particularly heat transfer at the metal/mold interface. The accurate knowledge of interfacial heat transfer coefficients is necessary for accurate modeling of castings. The present work focuses on the determination of transient mold–environment and metal–mold heat transfer coefficients during...
M.Sc. Thesis Sharif University of Technology ; Mousavi, Ali ; Aryanpour, Masood
Increasing energy consumption and limited energy resources are instances of the concerns of human societies and environmentalists today. The condensation process, as one of the most important processes in the industry, plays an important role in saving and regeneration the existing energy. Nowdays, surface optimization is one of the modern ways to improve condensation.In this research, two methods have been used to construct surfaces useful for enhancement of droplet condensation, including hybrid surfaces and solid infused surfaces. In the construction of hybrid surfaces, superhydrophobic coating with silica nanoparticles based on hydroxyl acrylic resin was used. The superhydrophilic parts...