scholarly journals CONVECTIVE HEAT TRANSFER CHARACTERISTICS OF AQUEOUS TiO2 NANOFLUID UNDER LAMINAR FLOW CONDITIONS

2008 ◽  
Vol 07 (06) ◽  
pp. 325-331 ◽  
Author(s):  
S. M. SOHEL MURSHED ◽  
KAI CHOONG LEONG ◽  
CHUN YANG ◽  
NAM-TRUNG NGUYEN
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Volume Fraction ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Enhancement Of Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Constant Wall Heat Flux

This paper reports an experimental investigation into force convective heat transfer of nanofluids flowing through a cylindrical minichannel under laminar flow and constant wall heat flux conditions. Sample nanofluids were prepared by dispersing different volumetric concentrations (0.2–0.8%) of nanoparticles in deionized water. The results showed that both the convective heat transfer coefficient and the Nusselt number of the nanofluid increase considerably with the nanoparticle volume fraction as well as the Reynolds number. Along with the enhanced thermal conductivity of nanofluids, the migration, interactions, and Brownian motion of nanoparticles and the resulting disturbance of the boundary layer are responsible for the observed enhancement of heat transfer coefficients of nanofluids.

scholarly journals Determination of Heat Transfer Coefficients Over Ribbed Surfaces With Infrared Thermography

1997 ◽  
Author(s):  
Francisco P. Brójo ◽  
Luís C. Gonçalves ◽  
Pedro D. Silva
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Stanton Number ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

The scope of the present work is to characterize the heat transfer between a ribbed surface and an air flow. The convective heat transfer coefficients, the Stanton number and the Nusselt number were calculated in the Reynolds number range, 5.13 × 105 to 1.02 × 106. The tests were performed inside a turbulent wind tunnel with one roughness height (e/Dh = 0.07). The ribs had triangular section with an attack angle of 60°. The surface temperatures were measured using an infrared (IR) thermographic equipment, which allows the measurement of the temperature with a good spatial definition (10.24 × 10−6 m2) and a resolution of 0.1°C. The experimental measures allowed the calculation of the convective heat transfer coefficient, the Stanton number and the Nusselt number. The results obtained suggested a flow pattern that includes both reattachment and recirculation. Low values of the dimensionless Stanton number, i.e. Stx*, are obtained at the recirculation zones and very high values of Stx* at the zones of reattachment. The reattachment is located at a dimensionless distance of 0.38 from the top of the rib. That distance seems to be independent of the Reynolds number. The local dimensionless Stanton number remains constant as the Reynolds number varies. The convective heat transfer coefficient presents an uncertainty in the range of 3 to 6%.

scholarly journals NUMERICAL STUDY OF THERMAL CHARACTERISTICS OF FUEL OIL-ALUMINA AND WATER-ALUMINA NANOFLUIDS FLOW IN A CHANNEL IN THE LAMINAR FLOW

2018 ◽  
Vol 19 (1) ◽  
pp. 251-269 ◽  
Author(s):  
Hossein Fatahian ◽  
Hesamoddin Salarian ◽  
Majid Eshagh Nimvari ◽  
Esmaeel Fatahian
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Volume Fraction ◽  
Convective Heat Transfer Coefficient ◽  
Fuel Oil ◽  
Alumina Nanofluid

The present study investigated the thermal effects of the use of nanoparticles in the fuel-oil and water-based fluids, as well as the numerical simulation of laminar flow of fuel-oil-alumina and the water-alumina nanofluids in a channel. A second order discretization method was used for solving equations and a SIMPLE algorithm was applied for pressure-velocity coupling using Fluent. Effect of nanoparticle volume fraction and particles size in different Reynolds numbers (900≤Re≤2100) on the convective heat transfer coefficient was studied. The simulation was conducted for three different volume fractions and particle sizes in the laminar flow under constant heat flux. The results showed that adding nanoparticles to the base fluid caused an increase in the thermal conductivity ratio of the fluid, which was observed to a greater degree in the fuel oil-alumina nanofluid than in the water-alumina nanofluid. The increase in nanoparticle volume fraction caused an increase in the convective heat transfer coefficient and the Nusselt number of the nanofluids. The significant point of this study was that in the same volume fraction, the effect of adding alumina nanoparticles to the fuel-oil-based fluid had more effect than adding these particles to water-based fluid, while the effect of increasing the Reynolds number in the water-alumina nanofluid on convective heat transfer coefficient was greater than the fuel-oil-alumina. Also, in the same Reynolds number and volume fraction with increasing size of nanoparticles, the value of the convective heat transfer coefficient was decreased. The results of this study can be used in refineries and petrochemical industries where the fuel-oil fluid flows in the channels. ABSTRAK: Kajian ini adalah bagi mengkaji kesan haba terhadap penggunaan bahan bakar-minyak dan cecair asas-air dalam nanopartikel, juga menjalankan simulasi pengiraan aliran laminar bahan bakar-minyak-alumina dan cecair-nano air-alumina dalam saluran. Kaedah berasingan kelas kedua telah digunakan bagi menyelesaikan persamaan dan algoritma SIMPLE telah diaplikasikan dalam gandingan kelajuan-tekanan menggunakan Fluent. Kesan jumlah pecahan nanopartikel dan pelbagai bilangan saiz zarah dalam bilangan Reynolds (900≤Re≤2100) pada pekali pemindahan haba perolakan telah dikaji. Simulasi telah dijalankan pada tiga pecahan isipadu berlainan dan pada zarah dalam aliran laminar dengan fluks haba tetap. Hasil kajian menunjukkan bahawa dengan penambahan nanopartikel dalam cecair-asas menyebabkan peningkatan nisbah daya pengaliran haba cecair pada cecair-nano bahan bakar-minyak-alumina melebihi daripada cecair-nano air-alumina. Penambahan pada pecahan isipadu nanopartikel ini menyebabkan peningkatan pada nilai pekali pemindahan haba perolakan dan bilangan Nusselt dalam cecair-nano. Perkara penting dalam kajian ini adalah pada pecahan isipadu sama, kesan penambahan nanopartikel alumina kepada cecair berasaskan minyak mempunyai kesan yang lebih besar daripada penambahan zarah-zarah ini kepada cecair berasaskan air. Pada masa sama, kesan peningkatan bilangan Reynolds dalam cecair-nano air-alumina pada pekali pemindahan haba perolakan lebih besar daripada kesan peningkatan bahan bakar-minyak-alumina. Selain itu, pada bilangan Reynolds yang sama dan dengan peningkatan saiz nanopartikel pecahan isipadu, nilai pekali pemindahan haba perolakan turut menurun. Hasil kajian ini boleh digunakan dalam industri penapisan dan petrokimia di mana bahan bakar cecair minyak mengalir dalam saluran.

Numerical Study on the Mechanism of Heat Transfer Enhancement in Fe3O4 Nanoferrofluids With Magnetic Field

2019 ◽  
Author(s):  
Chenfei Wang ◽  
Dongdong Gao ◽  
Minli Bai ◽  
Peng Wang ◽  
Yubai Li
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Fe3o4 Nanoparticles ◽  
Volume Fraction ◽  
Numerical Study ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Enhancement Of Heat Transfer

Abstract Nanofluids is reported to significantly enhance heat transfer but with little cost of pressure loss. To further the enhancement of heat transfer using Fe3O4 nanofluids, a magnetic field is employed to control the trajectory of Fe3O4 nanoparticles. A numerical study is conducted with commercial soft ANSYS FLUENT and the simulations are done with a two-phase flow approach named Euler-Lagrange. By comparing heat transfer of laminar flow in a horizontal tube with magnetic field or not, various volume fraction (0.5%/2%) and Reynolds numbers (Re = 200–1000) are considered. Results show that magnetic field contributes an average 4% promotion in convective heat transfer coefficients compared with the condition of no magnet. The mechanism of the enhancement of heat transfer with magnetic field is explored based on the analysis of velocity field. Fe3O4 Nanoparticles move up and down under the magnetic force, and convective heat transfer is enhanced because of the disturbance of the Fe3O4 nanoparticles. Slip flow between the base fluid and nanoparticles also contributes to the enhancement of heat transfer.

Experimental study on heat and mass transfer for heating milk

2011 ◽  
Vol 22 (3) ◽  
pp. 45-53
Author(s):  
Mahesh Kumar ◽  
K.S. Kasana ◽  
Sudhir Kumar ◽  
Om Prakash
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Linear Regression Analysis ◽  
Convective Heat Transfer Coefficient ◽  
Simple Linear Regression ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Rate Of Heating ◽  
Convective Heat Transfer Coefficients

In this paper, an attempt has been made to estimate the convective heat transfer coefficient for sensible heating of milk in a stainless steel pot during khoa, made by traditional method. Various indoor experiments were performed for simulation of a developed thermal model for maximum evaporation by varying heat inputs from 240 watts to 420 watts. The experimental data was used to determine values of constants in the well known Nusselt expression by simple linear regression analysis and, consequently, convective heat transfer coefficients were determined. It is found that the convective heat transfer coefficients decrease with an increase in rate of heating. The experimental error in terms of percent uncertainty was also evaluated.

Parametric Study of Convective Heat Transfer Coefficients at the Tire Surface

1980 ◽  
Vol 8 (3) ◽  
pp. 37-67 ◽  
Author(s):  
A. L. Browne ◽  
L. E. Wickliffe
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal State ◽  
Convective Heat Transfer Coefficient ◽  
Operating Conditions ◽  
Test Facility ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Abstract Analyses have shown that the thermal state of a tire is influenced by both the size of and variation in the value of the convective heat transfer coefficient at the tire surface. In the work reported here, a test facility was constructed to permit the determination of convective heat transfer coefficients under a broad range of operating conditions. Data were obtained to show the effects of air speed, boundary layer thickness and turbulence level, humidity, tire surface contamination, tire surface roughness and unevenness, and tire surface wetness on convective heat transfer coefficients. The significance of these results to tire power loss is discussed.

Experimental Performance of Natural Convection of a Semitransparent Wall With Film Coating of a Cubic Enclosure Using Infrared Imaging

2002 ◽  
Author(s):  
J. J. Flores ◽  
G. Alvarez
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Infrared Imaging ◽  
Convective Heat Transfer Coefficient ◽  
Film Coating ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Experimental Heat ◽  
Air Temperatures

This paper presents an experimental heat transfer study of the exterior side of a semitransparent wall (window) with film coating of a enclosure. The absorptance of the semitransparent wall with film coating was simulated using a film resistance on the glazing. A technique of infrared imagining thermography and a traversing system developed in Lawrence Berkeley National Laboratories (LBNL) were extended to measured from 1-D to 2-D local surface temperatures and boundary layer air temperatures of the exterior a glazing. From those measurements, the exterior heat flow and the exterior local convective heat transfer coefficients were calculated by applying a technique proposed by Truler [1]. The 2-D surface temperature distributions, the local convective heat transfer coefficient distributions and the average Nusselt number of the exterior side of the semitransparent wall with a simulated absorptance of 0.5 are presented.

Forced Convective Heat Transfer of Nanofluids in Microchannels

2006 ◽  
Author(s):  
Jung-Yeul Jung ◽  
Hoo-Suk Oh ◽  
Ho-Young Kwak
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Flow Regime ◽  
Convective Heat ◽  
Volume Fraction ◽  
Convective Heat Transfer Coefficient ◽  
Laminar Flow Regime

Convective heat transfer coefficient and friction factor of a nanofluid in rectangular microchannel were measured. An integrated microsystem consisting of a single microchannel on one side and two localized heaters and five polysilicon temperature sensors along the channel on the other side were fabricated. Aluminum dioxide (Al2O3) nanofluids with various particle volume fractions were used in experiment to investigate the effect of the volume fraction of the nanoparticles to the convective heat transfer and fluid flow in microchannels. The convective heat transfer coefficient of the Al2O3 nanofluid in laminar flow regime was measured to be increased up to 15% compared to the distilled water at a volume fraction of 1.8 volume percent without major friction loss. The Nusselt number measured increases with increasing the Reynolds number in laminar flow regime. A new type of convective heat transfer correlation was proposed to correlate experimental data of heat transfer coefficient for nanofluids in microchannels.

Convective heat transfer under different jet impingement conditions – optimum design to spray parameters

2016 ◽  
Vol 68 (2) ◽  
pp. 242-249 ◽  
Author(s):  
Yanzhong Wang ◽  
Wentao Niu ◽  
Song Wei ◽  
Guanhua Song
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Spray Parameters ◽  
Transfer Coefficients ◽  
Content Type ◽  
Heat Transfer Coefficients

Purpose – This paper aims to improve the cooling performance of the impinging jet to the machining and power transmissions, and provides more parameters to the design of the cooling system. Design/methodology/approach – A multiphase flow model with heat transfer terms is established to calculate the convective heat transfer coefficient. The computational fluid dynamics method is used to simulate the jet flow. The convective heat transfer coefficients with different spray parameters are calculated and their variations are obtained. Temperatures are tested to reflect the cooling performance (convective heat transfer coefficients) with different spray parameters. Findings – The results show that the higher convective heat transfer coefficient can be obtained with the same flow rate by decreasing nozzle diameter while increasing either the number of nozzles or the oil supply pressure. The spray distance was found to have little influence on convective heat transfer; however, the more the spray is directed parallel to the surface, the higher the convective heat transfer coefficient. The computational results coincide well with the experimental results. Originality/value – The research presented here leads to a design reference guideline that could be used in machining and power transmissions to reduce the temperature, thus improving their quality and efficiency, and preventing failure at high speeds and/or under heavy loads.

Evaluation of Convective Heat Transfer Coefficient for Pool Boiling of Milk Under Closed Condition

2015 ◽  
Vol 1 (2) ◽  
Author(s):  
Mahesh Kumar ◽  
K. S. Kasana ◽  
Sudhir Kumar ◽  
Om Prakash
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Linear Regression Analysis ◽  
Convective Heat Transfer Coefficient ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Experimental Errors

This research paper reports the study on heat and mass transfer during pool boiling of milk in an aluminum pan under closed conditions. Various indoor experiments were conducted for different heat inputs varying from 240 to 360 W. During heating of milk the evaporated water was condensed at the inner surface of the condensing cover and collected as fresh water. Experimental data were analyzed by using Rohsenow pool boiling correlation with the help of simple linear regression analysis. The convective heat transfer coefficients were estimated in the range of 186.32 to 567.56 W/m2 oC for the heat inputs varying from 240 to 360 W. The nucleate boiling heat flux was observed to increase exponentially with the increase in excess temperature. The experimental errors in terms of percent uncertainty were also evaluated.

Real-Time Determination of Convective Heat Transfer Coefficient Via Thermoelectric Modules

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Nataporn Korprasertsak ◽  
Thananchai Leephakpreeda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Thermoelectric Modules ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

In this paper, the determination of convective heat transfer coefficient under actual convection processes is proposed by using thermoelectric modules. The thermoelectric modules are positioned where cooling/heating processes take place. Based on the Seebeck effect and energy balance, voltage signals are mathematically related to the convective heat transfer coefficient in real time. In experiments, convective heat transfer coefficients of airflow in a wind tunnel are determined under heating/cooling processes at various wind speeds. The relative mean difference of the convective heat transfer coefficients between the proposed methodology and empirical formula is 2.31%. For real-time implementation, convective heat transfer coefficients of a copper plate, which is exposed to outdoor conditions during a whole day, are determined to predict copper plate temperatures from a governing equation. The performance of temperature prediction is confirmed by a coefficient of determination R2 of 0.9992. Analytical and experimental results show the effectiveness of the proposed thermoelectric modules in determining the convective heat transfer coefficient for air under actual cooling/heating conditions, in time.

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