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51.
Dawid Taler 《热科学学报(英文版)》2017,26(4):339-348
Heat transfer in the turbulent flow of fluid in a pipe is analyzed. Nusselt number as a function of the Reynolds and Prandtl number is given. Power-type correlations were proposed within a wide range of Reynolds and Prandtl number. Relationships for the Nusselt number compare well with experimental data. The paper presents three power-type correlations of a simple form, which are valid for Reynolds numbers range from 3·103 ≤ Re ≤ 106, and for three different ranges of Prandtl number: 0.1 ≤ Pr ≤ 1.0, 1.0 Pr ≤ 3.0, and 3.0 Pr ≤ 103. Heat transfer correlations developed in the paper were compared with experimental results available in the literature. The comparisons performed in the paper confirm the good accuracy of the proposed correlations. They are also much simpler compared with the relationship of Gnielinski, which is also widely used in the heat transfer calculations. 相似文献
52.
Comparative analysis for flow of CNTs nanofluids is discoursed in the presence of non-Darcy porous medium. The consequences of homogeneous/heterogeneous process and heat transfer through convection are employed. The flow induced is due to non-linear stretching sheet of variable thickness. The bottom of the variable thickness sheet is heated by convective processes from a heated fluid. The velocity, temperature and concentration functions are formulated for the stretched flow problem. Convergence control variables and square residual errors for series solutions are obtained through OHAM (Optimal Homotopy Analysis Method). Biot number corresponds to larger temperature distribution in case of MWCNT than SWCNT. Comparison of nanoparicles SWCNT and MWCNT for the CNTs nanofluid fluids is highlighted. Water and engine oil CNTs fluids have higher magnitude of Nusselt number when compared with kerosene oil CNT fluid. The heat transfer rate in the presence of MWCNT is higher than SWCNT. Comparison of present study with previous published data is made. The outcomes are found in favorable agreement. 相似文献
53.
54.
Hourly mean time series of dust concentration (PM10) measured at 3 m high and a sonic-anemometer measured momentum and kinematic heat fluxes at 8 m high above the surface have been obtained from a 20-m monitoring tower located at Erdene in the Asian dust source region of Mongolia for years of 2009 and 2010. These time series were used to identify dust events and to develop optimal regression equations for the dust concentration of dust events with the friction velocity (u*) and the convective velocity scale (w*). In total, 68 dust events were identified in 2009 (except for November) and 43 dust events for the period from March to August in 2010. The duration of each dust event ranged from 3-29 h in 2009 and 5-35 h in 2010. The maximum hourly mean dust concentration of the dust event was found to be 4,107 μg m− 3 in May in 2009 and 4,708 μg m− 3 in March in 2010 while a minimum of 251 μg m− 3 in August in 2009 and 662 μg m− 3 in June in 2010. The optimal regression equation for the dust concentration (C) of dust events was found to have the form of log C = a + b(u* + cw*)n, where a, b, c and n are constants that vary month to month. The convective velocity scale (w*) that has not been taken into account in most dust modelings was found to enhance the dust concentration of dust events during the cold period from December to March when the soil temperature was below the freezing level for both the stable (w* < 0) and unstable (w* > 0) stratifications, whereas the convective velocity caused a reduction in the dust concentrations during the warm period from April to October, suggesting the importance of the convective velocity to estimate dust concentration of dust events. 相似文献
55.
S. Seghir-Ouali D. Saury S. Harmand O. Phillipart D. Laloy 《International Journal of Thermal Sciences》2006,45(12):1166-1178
This article presents an experimental identification technique for the convective heat transfer coefficient inside a rotating cylinder with an axial airflow. The method consists in heating the outer face of the cylinder using infrared lamps, and acquiring the evolution of the external surface temperature versus time using an infrared camera. Heat transfer coefficients are identified via three methods. The first one is based on an inverse model, the second one assumes the wall of the cylinder as a thermally thin wall and the third one is based on an analytical method permitting to obtain the temperature field within the whole cylinder. The experiments were carried out for a rotational speed ranging from 4 to 880 rpm corresponding to rotational Reynolds numbers varying from 1.6×103 to 4.7×105 and an air flow rate varying from 0 to which corresponds to an axial Reynolds numbers ranging from 0 to 3×104. Correlations connecting the Nusselt number to the axial and rotational Reynolds numbers are also proposed. 相似文献
56.
A convective assembly technique at the micron scale analogous to the writing action of a “pipette pen” has been developed
for the linear assembly of gold nanoparticle strips with micron scale width and millimeter scale length for surface enhanced
Raman scattering (SERS). The arrays with interparticle gaps smaller than 3 nm are hexagonally stacked in the vicinity of the
pipette tip. Variable numbers of stacked layers and clean surfaces of the assembled nanoparticles are obtained by optimizing
the velocity of the pipette tip. The SERS properties of the assembled nanoparticle arrays rely on their stacking number and
surface cleanliness.
相似文献
57.
Modeling of drying of capillary-porous materials is a mathematically complex problem. It takes into consideration simultaneous heat and mass transfer inside the material with physicochemical properties changing during the drying process. Modeling of the process mentioned above consists of describing the heat and mass transfer balances by means of differential equations. Moisture diffusion coefficient as a function of moisture content and temperature of the material is a crucial parameter that controls the process. An additional problem occurs when moving boundary of the shrinking material is taken into account. In the present work, the identification of diffusion coefficient as a function of moisture content and temperature on the basis of two different models is shown. The two models include the Pakowski model (defined in the stationary coordinates) and the Kechaou model (defined in moving coordinates). Experimental data necessary to verify the models were obtained on the basis of series of tests for different boundary conditions performed on an apple tissue. During the drying process, samples of apple undergo significant volumetric shrinkage. In this article, the comparison of the two models describing the convective drying process of shrinking material is presented together with the comparison of the identified moisture diffusion coefficient. 相似文献
58.
Heat transfer characteristics of gaseous flows in a microtube with constant heat flux whose value is positive or negative are investigated on two-dimensional compressible laminar flow for no-slip regime. The numerical methodology is based on the Arbitrary–Lagrangian–Eulerian (ALE) method. The computations are performed for tubes with constant heat flux ranging from −104 to 104 W m−2. The tube diameter ranges from 10 to 100 μm and the aspect ratio of the length and diameter is 200. The stagnation pressure, pstg is chosen in such away that the Mach number at the exit ranges from 0.1 to 0.7. The outlet pressure is fixed at the atmosphere. The wall and bulk temperatures in microtubes with positive heat flux are compared with those of negative heat flux case and also compared with those of the incompressible flow in a conventional sized tube. In the case of fast flow, temperature profiles normalized by heat flux have different trends whether heat flux is positive or negative. A correlation for the prediction of the wall temperature of the gaseous flow in the microtube is proposed. Supplementary runs with slip boundary conditions for the case of D = 10 μm conducted and rarefaction effect is discussed. With increasing Ma number, the compressibility effect is more dominant and the rarefaction effect is relative insignificant where Kn number is less than Kn = 0.0096. And, the magnitudes of viscous dissipation term and compressibility term are investigated along the tube length. 相似文献
59.
Sathaporn Thongwik Tanongkiat Kiatsiriroat Atipoang Nuntaphan 《International Communications in Heat and Mass Transfer》2008
This research studies the heat transfer phenomenon of melting slurry ice on external surface of a copper helical coil. There is water flowing inside the tube coil and exchanging heat with the slurry ice. In this experiment, the coil diameters are 6.35 mm and 9.53 mm each of 4.2 m coil length. The mass flow rate of water in the helical coil is between 0.0149–0.0562 kg/s, while the inlet temperature of water is varied in the range of 23–27 °C. The slurry ice has 60% ice and 40% water by mass at the starting. 相似文献
60.
In a heat exchanger type steam methane reformer, the temperature profiles and mole fractions along the axial distance from
the top of the reformer can be predicted by using the channel model, considering radiation heat transfer. The cross-section
of the reformer tube was divided into several channels as concentric circles and then heat transfer and mass transfer at the
interfaces between adjacent channels were considered. Because the steam reformer is operated at high temperature, the radiation
and convection were combined into one heat transfer coefficient to simplify the transfer analysis. This model predicts the
industrial plant data very well; therefore, it may be used with confidence to design the industrial heat exchanger type reformer. 相似文献