Experimental investigation of natural convection from a horizontal ice surface melting in pure water

A study on natural convection from a horizontal ice surface melting in pure water was conducted experimentally for the ambient water temperature from 2▿C to 10°C. Natural convection flow around upward-or downward-facing horizontal ice plate was divided into three regions according to the temperature variation of ambient water. The flow patterns of three regions were no flow, two-dimensional steady laminar flow and unsteady flow. Mean Nusselt number for the upward-facing surface had its maximum value at about 3°C of ambient water temperature. However, in the case of the downward-facing surface it increased as the ambient water temperature increased.     

Numerical investigations of solidification around a circular cylinder under forced convection

Journal of Mechanical Science and Technology - We present numerical investigations of solidification around a cooled circular cylinder in the presence of forced convection. The numerical method is...     

Experimental study on natural convection heat transfer from horizontal cylinders with longitudinal plate fins

The purpose of this study was to investigate the effect of various fin numbers, fin heights, and base temperatures on natural convection from horizontal cylinders with longitudinal plate fins experimentally. Experimental results were used to establish a correlation for estimating the Nusselt number under the following conditions: Rayleigh number, 300000–1000000; fin-height-to-cylinder-diameter ratio, 1/6–1/2; and fin number, 9–72. In addition, a contour map was developed to describe the thermal resistance as a function of the fin number and fin thickness.     

Mesoscopic investigation of frost crystal nucleation on cold surface based on the lattice-Boltzmann method

Journal of Mechanical Science and Technology - A lattice Boltzmann method (LBM) two-dimensional (2D) mesoscopic model is presented for studying the frost crystal nucleation process involved in...     

Experimental study of heating surface angle effects on single bubble growth

Nucleate pool boiling experiments were performed using pure R11 for various surface angles under constant heat flux conditions during saturated pool boiling. A 1-mm-diameter circular heater with an artificial cavity in the center that was fabricated using a MEMS technique and a high-speed controller were used to maintain the constant heat flux. Bubble growth images were taken at 5000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of the surface angle on the bubble growth behavior were analyzed for the initial and thermal growth regions using dimensional scales. The parameters that affected the bubble growth behavior were the bubble radius, bubble growth rate, sliding velocity, bubble shape, and advancing and receding contact angles. These phenomena require further analysis for various surface angles and the obtained constant heat flux data provide a good foundation for such future work.     

Experimental study of the effects of rough texture on surface deformation during cold metal forming

Both longitudinal and transverse frictions arising from plane strain during cold metal forming are of crucial importance for the accurate modelling, optimum design, and control of industrial processes. However, the influence of the friction and roughness along the transverse direction has been neglected in much previous research. Oblique roughness textures are considered, and the scale of roughness asperities is enlarged in this study. Four types of prism patterns, in which the angles between the longitudinal direction and the top line of prism are 90°, 60°, 30°, and 0°, and three types of pyramid patterns, in which the top angles are 151.9°, 161.1°, and 168.6°, were designed and manufactured using samples of annealed Al 6060T5. All compression tests were completed in 10 passes, and the total displacement of the pressure head was 5.4 mm. The first five passes were carried out on an Instron 8033 Materials Testing Machine, and the last five passes on a 500-ton compression-testing machine. The surface morphologies of the deformed peak were analysed, and the top areas of the deformed peak were measured. The effects of the angle between the longitudinal direction and the top line of the prism texture or the top angle of the pyramid texture on the surface morphology of the deformed peak are not obvious. The angles have a relatively significant effect on the deformation behaviour of the surface layer during cold metal forming when the deformation is small. The pattern with a top angle of 161.1°, which is the closest to the real value, shows the highest deformation resistance when the displacement of the pressure head is less than 1.2 mm.     

钛合金冷风切削表面粗糙度试验研究

为了探索汽轮机低压锁扣叶片材料Ti6Al4V钛合金的切削表面粗糙度变化规律,采用均匀设计方法设计了钛合金切削参数,在冷风降温条件下,对表面粗糙度进行试验研究。运用最小二乘法原理,对试验数据进行多元线性回归分析,建立了适用于钛合金材料在冷风切削条件下的表面粗糙度经验公式,从而找到冷风条件下切削表面粗糙度的变化规律。     

Effect of magnetic field on forced convection between two nanofluid laminar flows in a channel

This paper provides a numerical study of forced convection between hot and cold nanofluid laminar flows that are separated by a thin membrane, in a horizontal channel. Outer surface of channels' walls are thermally insulated and divide into two parts; namely NMP and MP. NMP is the channel's wall from the entrance section to the middle section of channel that is not influenced by magnetic field. MP is the channel's wall from the middle section to the exit section of channel which is influenced by a uniform-strength transverse magnetic field.The governing equations for both hot and cold flows are solved together using the SIMPLE algorithm. The effects of pertinent parameters, such as Reynolds number(10≤Re≤500), Hartman number(0≤Ha≤60) and the solid volume fraction of copper nano-particles(0≤?≤0.05), are studied. The results are reported in terms of streamlines, isotherms, velocity and temperature profiles and local and average Nusseltnumber.The results of the numerical simulation indicate that the increase in Reynolds number and the solid volume fraction lead to increase in Nusselt number. Meanwhile, the results also show that the rate of heat transfer between the flows increases as the Hartmann number increases, especially at higher values of the Reynolds number.     

Modeling of laminar forced convection in spherical-pebble packed beds

There are many parameters that have significant effects on forced convection heat transfer in packed beds, including Reynolds and Prandtl numbers of flow, porosity, pebble geometry, local flow conditions, wall and end effects. In addition, there have been many experimental investigations on forced convection heat transfer in packed beds and each have studied the effect of some of these parameters. Yet, there is not a reliable correlation that includes the effect of main parameters; at the same time, the prediction of precise correct limits for very low and high Reynolds numbers is off hand. In this article a general well-known model of convection heat transfer from isothermal bodies, next to some previous reliable experimental data has been used as a basis for a more comprehensive and accurate correlation to calculate the laminar constant temperature pebble-fluid forced convection heat transfer in a homogeneous saturated bed with spherical pebbles. Finally, for corroboration, the present results are compared with previous works and show a very good agreement for laminar flows at any Prandtl number and all porosities.     

Numerical study on the vertical bridgman crystal growth with thermosolutal convection

A numerical analysis has been carried out to investigate the influences of thermosolutal convection on the heat and mass transfer and solute segregation in crystals grown by the vertical Bridgman technique. The governing equations are solved by a finite-volume method using the power law scheme and the SIMPLE algorithm in which body-fitted coordinate system has been used. A primary convective cell driven by thermal gradients forms in the bulk of the domain, while a secondary convective cell driven by solutal gradients forms near interface. As the solutal Rayleigh number increases, secondary cell becomes to be stronger and has a great influence on the radial concentration along the interface.     

Combined free and forced convection flow of an elasto-viscous liquid through a porous channel

The combined effect of free and forced convection on the flow of an elasto-viscous liquid between two porous parallel plates with suction and injection at the walls has been studied. The effect of dimensionless numbers such as the elastic number Rc, the cross flow Reynolds number R, the Grashof number G, the Prandtl number Pr, the Brinkman number K and the wall temperature parameter N on the velocity and temperature fields, shear stresses and the rates of heat transfer at the walls have been studied.     

横圆管表面空气自然对流换热测试系统开发

为了更好地研究受热横圆管在大空间中的自然对流换热现象,设计开发了横圆管表面空气自然对流换热测试系统.该测试系统采用上下位机模式,可实现横圆管的自然对流换热系数的测定和准则关联式的验证.实际应用结果表明,该测试系统具有功能完善、测量精度高、重复性好等优点,很好地满足了自然对流换热测试的要求.     

Thermally developing forced convection and the corresponding thermal stresses in a porous plate channel

Based on the Darcy fluid model, by considering the effects of viscous dissipation due to the interaction between solid skeleton and pore fluid flow and thermal conduction in the direction of the fluid flow, the thermally developing forced convection of the local thermal equilibrium and the corresponding thermal stresses in a semi-infinite saturated porous plate channel are investigated in this paper. The expressions of temperature, local Nusselt number and corresponding thermal stresses are obtained by means of the Fourier series, and the distributions of the same are also shown. Furthermore, influences of the Péclet number (Pe) and Brinkman number (Br) on temperature, Nusselt number (Nu) and thermal stress are revealed numerically. __________ Translated from Journal of Lanzhou University (Natural Science Edition), 2006, 42(2): 114–119 [译自: 兰州大学学报(自然科学版)]     

An efficient way of convection heat transfer measurement on a curved surface

Accurate determination of convective heat transfer coefficients on complex surfaces with high spatial resolution is essential in the design and analysis of thermal systems. This study focuses on the implementation of a recently developed true color image-processing technique for the quantitative interpretation of liquid crystal images obtained from a curved surface. The interpretation includes the use of a linear hue versus temperature relation as an accurate temperature measuring tool, a color image analysis system and a transient heat transfer model for the conversion of time accurate temperature information into heat transfer coefficient maps. A square to rectangular transition duct is used as a heat transfer model representative of a curved geometry. The transient heat transfer experiments are performed with ambient temperature air in the transition duct model which is preheated by a custom designed electric heater. The measurements are performed on the curved bottom surface of the transition duct. Two dimensional surface distributions of heat transfer coefficient on the curved surface are presented with high spatial resolution. The hue-capturing technique provides extremely fine details of heat transfer coefficient when compared to other conventional discrete sensor methods. The technique is a highly automated heat transfer measurement method which reduces lengthy data reduction processes and significantly improves spatial resolution.     

Modeling forced convection in the thermal simulation of laser cladding processes

The International Journal of Advanced Manufacturing Technology - A comprehensive methodology for the implementation of thermal convection into the finite element (FE) analysis of laser direct...     

Experimental study on single bubble growth under subcooled, saturated, and superheated nucleate pool boiling

Nucleate pool boiling experiments with constant wall temperature were performed using pure R113 for subcooled, saturated, and superheated pool conditions. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant wall temperature and to measure the instantaneous heat flow rate accurately with high temporal and spatial resolutions. Images of bubble growth were taken at 5,000 frames per second using a high-speed CCD camera synchronized with the heat flow rate measurements. The bubble geometry was obtained from the captured bubble images. The effect of the pool conditions on the bubble growth behavior was analyzed using dimensionless parameters for the initial and thermal growth regions. The effect of the pool conditions on the heat flow rate behavior was also examined. This study will provide good experimental data with precise constant wall temperature boundary condition for such works.     

Experimental study and evaluation methodology on hard surface integrity

The Taguchi method is adopted experimentally to investigate the surface integrity (surface roughness, residual stress, and thermal damage layer) of hardened bearing steel in hard dry turning, and the validation experiments are consequently performed. It was revealed that the value and effect sequence of optimal hard turning parameter varies with different objectives of surface integrity. However, it is quite difficult to select or determine the optimal combination of hard turning parameters. A hard-turned component performance, which reflects an integrated impact of surface integrity, should be fully recognized to resolve the inherent conflict in the selection process. Based on it, an evaluation methodology composed of four steps is proposed that surface integrity should be evaluated by the service/fatigue life of hard-turned components and therefore turning parameters. It bears significance for super-finish hard turning further application in respect that it provides an integrated approach for hard turning parameter optimization to achieve a superior surface integrity. Funded by the Ministry of Education of China- “985” of international cooperation project “Clean Manufacturing Technology”.     

Combined heat transfer of radiation and forced convection flow of participating gases in a three-dimensional recess

This research work presents a numerical investigation of three-dimensional combined convection-radiation heat transfer over a recess including two inclined steps in a horizontal duct. To simulate the inclined surface boundaries, the blocked off method is employed for both fluid mechanic and radiation problems. The fluid is treated as a gray, absorbing, emitting and scattering medium. In numerical solution of the governing equations including conservation of mass, momentum and energy, the three-dimensional Cartesian coordinate system is used. These equations are solved numerically using the CFD techniques to obtain the temperature and velocity fields. Discretized forms of the governing equations are obtained by the finite volume method and solved using the SIMPLE algorithm. Since the gas is considered as a radiating medium, all of the convection, conduction and radiation terms are presented in the energy equation. For computation of radiative term in energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinates method (DOM) to find the divergence of radiative heat flux distribution inside the radiating medium. The effects of radiation-conduction parameter, optical thickness and albedo coefficient on heat transfer behavior of the system are presented. Comparison of numerical results with the available data published in open literature shows a good agreement.     

Experimental study of natural convection heat transfer from a nonuniformly heated flat plate simulating PV panel

Journal of Mechanical Science and Technology - In view of the characteristic of Photovoltaic (PV) conversion, an experimental study has been conducted to investigate the natural convection heat...