共查询到20条相似文献,搜索用时 0 毫秒
1.
A water-based functionalized nanofluid was made by surface functionalizing the ordinary silica nanoparticles. The functionalized nanoparticles were water-soluble and could still keep dispersing well even at the mass concentration of 10% and no sedimentation was observed. An experimental study was carried out to investigate the pool boiling heat transfer characteristics of functionalized nanofluid at atmospheric and sub-atmospheric pressures. The same work was also performed for DI water and traditional nanofluid consisted of water and ordinary silica nanoparticles for the comparison. Experimental results show that there exist great differences between pool boiling heat transfer characteristics of functionalized and traditional nanofluid. The differences mainly result from the changes of surface characteristics of the heated surface during the boiling. A porous deposition layer exists on the heated surface during the boiling of traditional nanofluid; however, no layer exists for functionalized nanofluid. Functionalized nanofluid can slightly increase the heat transfer coefficient comparing with the water case, but has nearly no effects on the critical heat flux. It is mainly due to the changes of the thermoproperties of nanofluids. Traditional nanofluid can significantly enhance the critical heat flux, but conversely deteriorates the heat transfer coefficient. It is mainly due to effect of surface characteristics of the heated surface during the boiling. Therefore, the pool boiling heat transfer of nanofluids is governed by both the thermoproperties of nanofluids and the surface characteristics of the heated surface. 相似文献
2.
The effect of SiO2 particles on heat transfer performance of a pulsating heat pipe(PHP) was investigated experimentally.DI water was used as the base fluid and contrast medium for the PHP.In order to study and measure the character,there are SiO2 /H2 O nanofluids with different concentration and applying with various heating powers during the experiment investigation.According to the experimental result,the high fraction of SiO2 /H2 O will deteriorate the performance of PHP compared with DI water,i.e.the thermal resistance and the temperature of evaporation section increases.It is in contrary in the case of low fraction of SiO2 /H2 O.Finally,the comparison of the thermal performances between the normal operation system and the static settlement system is given.It is found that both the thermal resistance of nanofluid PHP and the temperature of the evaporation section increase after standing for a period,and it is the same trend for the temperature fluctuation at the identical heating power for PHP. 相似文献
3.
M. NasiriS.Gh. Etemad R. Bagheri 《International Communications in Heat and Mass Transfer》2011,38(7):958-963
This paper is related to heat transfer performance of Al2O3/H2O and TiO2/H2O nonofluids through an annular channel with constant wall temperature boundary condition under turbulent flow regime. The constant temperature is applied on the outer wall of the channel. Experimental investigation was done for a wide range of Al2O3 and TiO2 nanoparticle concentrations and Reynolds number. Based on the experimental results, for specific Peclet number, Nusselt number of nanofluids is higher than that of the base fluid. The enhancement increases with increase of nanparticle concentration for both employed nanofluids. Based on the results of this investigation there is no significant difference on the heat transfer enhancement associated with two employed nanofluids. 相似文献
4.
Amir Houshang Mahmoudi Mina Shahi Abbas Honarbakhsh Raouf 《International Communications in Heat and Mass Transfer》2011,38(1):119-127
The objective of this paper is to investigate the conjugated heat transfer in a thick walled cavity filled with copper-water nanofluid. The analysis uses a two-dimensional rectangular enclosure under conjugated convective-conductive heat transfer conditions and considers a range of Rayleigh numbers. The enclosure was subjected to a constant and uniform heat flux at the left thick wall generating a natural convection flow. The thicknesses of the other boundaries are assumed to be zero. The right wall is kept at a low constant temperature while the horizontal walls are assumed to be adiabatic. A moveable divider is located at the bottom wall of the cavity. The governing equations are derived based on the conceptual model in the Cartesian coordinate system. The study has been carried out for the Rayleigh number in the range of 105 ≤ Ra ≤ 108, and for the solid volume fraction at 0 ≤ ? ≤ 0.05. Results are presented in the form of streamlines, isotherms, average Nusselt number and input heat absorption by the nanofluid. The effects of solid volume fraction of nanofluids, the location of the divider and also the value of the ambient convective heat transfer coefficient on the hydrodynamic and thermal characteristics of flow have been analyzed. An increase in the average Nusselt number was found with the solid concentration for the whole range of Rayleigh number. In addition, results show that the position of the divider and the ambient convective heat transfer coefficient have a considerable effect on the heat transfer enhancement. 相似文献
5.
D. Ashtiani M.A. Akhavan-Behabadi M. Fakoor Pakdaman 《International Communications in Heat and Mass Transfer》2012
An experimental investigation on heat transfer characteristics of MWCNT-heat transfer oil nanofluid flow inside horizontal flattened tubes has been carried out under uniform wall temperature condition. Nanoparticle weight fractions were 0%, 0.1%, 0.2%, and 0.4%. The copper tubes of 14.5 mm I.D. were flattened and used as the test section of oblong shape with inside heights of 13.4 mm, 11.7 mm, 10.6 mm, and 8.6 mm. The nanofluid flowing inside the tube was heated inside a steam chamber to keep the temperature of the tube wall constant. The required data were acquired for laminar hydrodynamically fully developed regime. The effects of different parameters such as volumetric flow rate, nanoparticle weight fraction, and hydraulic diameter on the heat transfer behavior of the tested systems have been investigated experimentally. For a given flattened tube at a constant nanoparticle weight fraction, increasing volumetric flow rate results in heat transfer enhancement. In addition, as the tube profile becomes more flattened and the hydraulic diameter decreases, the heat transfer coefficient goes up at constant volumetric flow rate. Utilizing nanofluids instead of the base fluid, the heat transfer rate enhances remarkably. The higher the nanoparticles weight fraction, the more the rate of heat transfer enhancement. Finally, the results show that the amount of increase in heat transfer coefficient caused by employing nanofluid instead of the base fluid is comparable to what caused by flattening the tube. 相似文献
6.
M.A. Akhavan-Behabadi M. Fakoor Pakdaman M. Ghazvini 《International Communications in Heat and Mass Transfer》2012
In this study, heat transfer enhancement of a nanofluid flow inside vertical helically coiled tubes has been investigated experimentally in the thermal entrance region. The temperature of the tube wall was kept constant at around 95 °C to have isothermal boundary condition. Experiments were conducted for fluid flow inside straight and helical tubes. In these experiments, the effects of a wide range of different parameters such as Reynolds and Dean numbers, geometrical parameters and nanofluid weight fractions have been studied. In order to investigate the effect of the fluid type on the heat transfer, pure heat transfer oil and nanofluids with weight concentrations of 0.1, 0.2 and 0.4% were utilized as the working fluid. The thermo-physical properties of the working fluids were extremely temperature dependent; therefore, rough correlations were proposed to predict their properties. Based on the experimental data, utilizing helical coiled tubes instead of straight ones enhances the heat transfer rate remarkably. Besides, nanofluid flows showed much higher Nusselt numbers compared to the base fluid flow. Finally, it was observed that combination of the two enhancing methods has a noticeably high capability to the heat transfer rate. 相似文献
7.
Turbulent convective heat transfer performance and pressure drop of very dilute (less than 0.24% volume) CuO/water nanofluid flowing through a circular tube were investigated experimentally. Measurements showed that addition of small amounts of nanosized CuO particles to the base fluid increased heat transfer coefficients considerably. In average 25% increase in heat transfer coefficient was observed with 20% penalty in pressure drop. Enhancement ratio did not show significant variation with concentration of CuO in nanofluid in the range studied in this work. 相似文献
8.
Mostafa Keshavarz Moraveji Seyyed Mohammad Hossein HaddadMehdi Darabi 《International Communications in Heat and Mass Transfer》2012
In this paper, convective heat transfer effect on the non-Newtonian nanofluid flow in the horizontal tube with constant heat flux was investigated using computational fluid dynamics (CFD). For this purpose, non-Newtonian nanofluid containing Al2O3 and Xanthan aqueous solution as a liquid single phase with two average particle sizes of 45 and 150 nm and four particle concentrations of 1, 2, 4 and 6 wt.% and two concentrations of Xanthan aqueous solutions (0.6,1.0 wt.%) were used. Effect of particle size and concentration of Xanthan solution on convective heat transfer coefficient was investigated in different Reynolds numbers (500 < Re < 2500) for various axial locations of tube. The results showed that heat transfer coefficient and Nu number of non-Newtonian nanofluid increased with increasing concentration of Xanthan solution. By applying the modeling results, an equation was obtained for Nusselt number prediction using the dimensionless numbers. The results showed that the correlated data were in very good agreement with predicted data. The maximum error was around 5%. 相似文献
9.
Nor Azizah YacobAnuar Ishak Roslinda NazarIoan Pop 《International Communications in Heat and Mass Transfer》2011,38(2):149-153
An analysis is carried out to study the problem of the steady flow and heat transfer over a static or moving wedge with a prescribed surface heat flux in a nanofluid. The governing partial differential equations are transformed into a set of nonlinear ordinary differential equations using similarity transformation, before being solved numerically by the Keller box method and the Runge-Kutta-Fehlberg method with shooting technique. The features of the flow and heat transfer characteristics are analyzed and discussed. Three different types of nanoparticles are considered, namely copper Cu, alumina Al2O3 and titania TiO2 with water as the base fluid. It is found that the skin friction coefficient and the heat transfer rate at the surface are highest for copper-water nanofluid compared to the alumina-water and titania-water nanofluids. Moreover, the heat transfer rate at the surface increases with the Falkner-Skan power law parameter m. 相似文献
10.
Dorin Lelea Catalin Nisulescu 《International Communications in Heat and Mass Transfer》2011,38(6):704-710
The numerical modeling of the conjugate heat transfer and fluid flow of Al2O3/water nanofluid through the micro-tube was presented in the paper. The laminar flow regime was considered along with viscous dissipation effect. The diameter ratio of the micro-tube was Di/Do = 0.1/0.3 mm with a tube length L = 100 mm. The heat transfer rate was fixed to Q = 0.5 W with three different Br = 0.1, 0.5 and 1. The water based Al2O3 nanofluid was considered with various volume concentrations of Al2O3 particles ? = 1, 4, 6, 9% and two diameters of the particles Dp = 10 nm and 47 nm. The analysis was performed on the results for local heat transfer coefficient. 相似文献
11.
Khwanchit WongchareeSmith Eiamsa-ard 《International Communications in Heat and Mass Transfer》2011,38(6):742-748
Heat transfer, friction and thermal performance characteristics of CuO/water nanofluid have been experimentally investigated. The nanofluid was employed in a circular tube equipped with modified twisted tape with alternate axis (TA). The concentration of nanofluid was varied from 0.3 to 0.7% by volume while the twisted ratio (y/W) of TA was kept constant at 3. The experiments were performed in laminar regime (Reynolds number spanned 830 ≤ Re ≤ 1990). The uses of nanofluid together with typical twisted tape (TT), TA alone and TT alone were also examined. To evaluate heat transfer enhancement and the increase of friction factor, the Nusselt number and friction factor of the base fluid in the plain tube were employed as reference data. The obtained results reveal that Nusselt number increases with increasing Reynolds number and nanofluid concentration. By the individual uses of TA and TT, Nusselt numbers increase up to 12.8 and 7.2 times of the plain tube, respectively. The simultaneous use of nanofluid and TA improves Nusselt number up to 13.8 times of the plain tube. Over the range investigated, the maximum thermal performance factor of 5.53 is found with the simultaneous employment of the CuO/water nanofluid at 0.7% volume and the TA at Reynolds number of 1990. In addition, the empirical correlations for heat transfer coefficient, friction factor and thermal performance factor are also developed and reported. 相似文献
12.
M.A. Ahmed N.H. Shuaib M.Z. Yusoff A.H. Al-Falahi 《International Communications in Heat and Mass Transfer》2011,38(10):1368-1375
In this paper, heat transfer and pressure drop characteristics of copper–water nanofluid flow through isothermally heated corrugated channel are numerically studied. A numerical simulation is carried out by solving the governing continuity, momentum and energy equations for laminar flow in curvilinear coordinates using the Finite Difference (FD) approach. The investigation covers Reynolds number and nanoparticle volume fraction in the ranges of 100–1000 and 0–0.05 respectively. The effects of using the nanofluid on the heat transfer and pressure drop inside the channel are investigated. It is found that the heat transfer enhancement increases with increase in the volume fraction of the nanoparticle and Reynolds number, while there is slight increase in pressure drop. Comparisons of the present results with those available in literature are presented and discussed. 相似文献
13.
Yali Guo Daoyang Qin Shengqiang Shen Rachid Bennacer 《International Communications in Heat and Mass Transfer》2012
The lattice Boltzmann method is applied to simulate the thermal field and flow field of nanofluid natural convection in a square cavity. The heat transfer characteristics of nanofluid are compared with that of water to explore nanofluid heat transfer mechanism. The flow field shows different characters at different Rayleigh number and the average Nusselt number is obtained changing with Rayleigh number. 相似文献
14.
Mostafa Keshavarz Moraveji Sina Razvarz 《International Communications in Heat and Mass Transfer》2012
In this research, the effect of using aluminum oxide nanofluid (pure water mixed with Al2O3 nanoparticle with 35 nm diameter) on the thermal efficiency enhancement of a heat pipe on the different operating state was investigated. 相似文献
15.
An investigation on the effects of solid particles on boiling heat transfer enhancement is performed. The range of particle diameter is from millimeter to nanometer. The experimental results show that boiling heat transfer can be enhanced greatly by adding the solid particle into the liquid whether in fixed particle bed or in fluidized particle bed. The boiling enhancement is closely related to the particle size, the initial bed depth and the heat flux applied. The experiments show that boiling characteristics are greatly changed when a particle layer is put on the heated surface. The major effects of fixed particle bed on nucleate pool boiling heat transfer are the nucleation, bubble moving and thermal conductivity effect. A boiling heat transfer correlation is obtained to predict the boiling heat transfer coefficients in a liquid saturated porous bed. A volumetric convection mechanism of boiling heat transfer enhancement by fluidized particles is proposed. The calculated results from the model suggested in this paper agree reasonably with the experimental values. 相似文献
16.
H. Demir A.S. DalkilicN.A. Kürekci W. DuangthongsukS. Wongwises 《International Communications in Heat and Mass Transfer》2011,38(2):218-228
In this study, forced convection flows of nanofluids consisting of water with TiO2 and Al2O3 nanoparticles in a horizontal tube with constant wall temperature are investigated numerically. The horizontal test section is modeled and solved using a CFD program. Palm et al.'s correlations are used to determine the nanofluid properties. A single-phase model having two-dimensional equations is employed with either constant or temperature dependent properties to study the hydrodynamics and thermal behaviors of the nanofluid flow. The numerical investigation is performed for a constant particle size of Al2O3 as a case study after the validation of its model by means of the experimental data of Duangthongsuk and Wongwises with TiO2 nanoparticles. The velocity and temperature vectors are presented in the entrance and fully developed region. The variations of the fluid temperature, local heat transfer coefficient and pressure drop along tube length are shown in the paper. Effects of nanoparticles concentration and Reynolds number on the wall shear stress, Nusselt number, heat transfer coefficient and pressure drop are presented. Numerical results show the heat transfer enhancement due to presence of the nanoparticles in the fluid in accordance with the results of the experimental study used for the validation process of the numerical model. 相似文献
17.
Soheil Soleimani M. SheikholeslamiAuthor VitaeD.D. GanjiAuthor Vitae M. Gorji-BandpayAuthor Vitae 《International Communications in Heat and Mass Transfer》2012
To investigate natural convection heat transfer in a semi-annulus enclosure filled with nanofluid, the Control Volume based Finite Element Method (CVFEM) is used. The fluid in the enclosure is Cu–water nanofluid. The inner and outer semi circular walls are maintained at constant temperatures while the two other walls are thermally insulated. The Navier Stokes equations in their vorticity-stream function form are used to simulate the flow pattern and isotherms. The numerical investigation is carried out for different governing parameters namely; the Rayleigh number, nanoparticle volume fraction and the angle of turn for the enclosure. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. The results reveal that there is an optimum angle of turn in which the average Nusselt number is maximum for each Rayleigh number. Moreover, the angle of turn has an important effect on the streamlines, isotherms and maximum or minimum values of local Nusselt number. 相似文献
18.
Natural convection heat transfer from a heated cylinder contained in a square enclosure filled with water–Cu nanofluid is investigated numerically. The main objective of this study is to explore the influence of pertinent parameters such as Prandtl number (Pr) and diameter (D) of the heated body on the flow and heat transfer performance of nanofluids while Rayleigh number (Ra) and the solid particle volume fraction (?) of nanoparticle are considered fixed. The results obtained from finite element method clearly indicate that heat transfer augmentation is possible using highly viscous nanofluid resulting in the compactness of many industrial devices. 相似文献
19.
Mina Shahi Amir Houshang Mahmoudi Farhad Talebi 《International Communications in Heat and Mass Transfer》2011,38(4):533-542
Laminar conjugate heat transfer by natural convection and conduction in a vertical annulus formed between an inner heat generating solid circular cylinder and an outer isothermal cylindrical boundary has been studied by a numerical method. It is assumed that the two sealed ends of the tube to be adiabatic. Governing equations are derived based on the conceptual model in the cylindrical coordinate system. The governing equations have been solved using the finite volume approach, using SIMPLE algorithm on the collocated arrangement. Results are presented for the flow and temperature distributions and Nusselt numbers on different cross sectional planes and longitudinal sections for Rayleigh number ranging from 105 to 108, solid volume fraction of 0‹φ‹0.05 with copper-water nanofluid as the working medium. Considering that the driven flow in the annular tube is strongly influenced by orientation of tube, study has been carried out for different inclination angles. 相似文献
20.
This work examines the natural convection heat and mass transfer near a sphere with constant wall temperature and concentration in a micropolar fluid. A coordinate transformation is used to transform the governing equations into nondimensional nonsimilar boundary layer equations and the obtained boundary layer equations are then solved by the cubic spline collocation method. Results for the local Nusselt number and the local Sherwood number are presented as functions of the vortex viscosity parameter, Schmidt number, buoyancy ratio, and Prandtl number. For micropolar fluids, higher viscosity tends to retard the flow and thus decreases the natural convection heat and mass transfer rates from the sphere with constant wall temperature and concentration. Moreover, the natural convection heat and mass transfer rates from a sphere in Newtonian fluids are higher than those in micropolar fluids. 相似文献