Experimental Study and Thermal Modelling of Cocoa Shell Convective Drying in an Indirect Solar Dryer

The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced in the drying chamber. Then at steady time intervals, the sample is withdrawn from the drying chamber, for a rapid weighing. After each weighing, the sample is reintroduced in the dryer. At each time interval, the ambient temperature of the drying chamber and its relative humidity γ are measured by a thermo-hygrometer. From the experimental data, a theoretical determination of the moisture evaporated from the product was performed and a good agreement was found between the theoretical and experimental values, confirmed by the value of the RMSE. Those calculations used the constants in the Nusselt number found in literature. Then those constants were evaluated again, to get new values more suitable with the experimental data. The dimensionless numbers of Nusselt, Grashof and Prandtl were calculated. That allowed the calculation of the average value of the Nusselt number. The average convective heat transfer coefficient was determined.

Numerical and theoretical investigations of heat transfer characteristics in helium-xenon cooled microreactor core

Helium-xenon cooled microreactors are a vital technological solution for portable nuclear reactor power sources.To exam-ine the convective heat transfer behavior of helium-xenon gas mixtures in a core environment,numerical simulations are conducted on a cylindrical coolant channel and its surrounding solid regions.Validated numerical methods are used to determine the effect and mechanisms of power and its distribution,inlet temperature and velocity,and outlet pressure on the distribution and change trend of the axial Nusselt number.Furthermore,a theoretical framework that can describe the effect of power variation on the evolution of the thermal boundary layer is employed to formulate an axial distribution cor-relation for the Nusselt number of the coolant channel,under the assumption of a cosine distribution for the axial power.Based on the simulation results,the correlation coefficients are determined,and a semi-empirical relationship is identified under the corresponding operating conditions.The correlation derived in this study is consistent with the simulations,with an average relative error of 5.3%under the operating conditions.Finally,to improve the accuracy of the predictions near the entrance,a segmented correlation is developed by combining the Kays correlation with the aforementioned correlation.The new correlation reduces the average relative error to 2.9%and maintains satisfactory accuracy throughout the entire axial range of the channel,thereby demonstrating its applicability to turbulent heat transfer calculations for helium-xenon gas mixtures within the core environment.These findings provide valuable insights into the convective heat transfer behavior of a helium-xenon gas mixture in a core environment.

Influence of the Inclination Angle on Mixed Convection and Heat Transfer in a“T”Shaped Double Enclosure

The effect of the tilt angle on mixed convection and related heat transfer in a“T”shaped double enclosure with four heated obstacles on the bottom surface is numerically investigated.The considered obstacles are constantly kept at a relatively high(fixed)temperature,while the cavity’s upper wall is cooled.The finite volume approach is used to solve the mass,momentum,and energy equations with the SIMPLEC algorithm being exploited to deal with the pressure-velocity coupling.Emphasis is put on the influence of the tilt angle on the solution symmetry,flow structure,and heat exchange through the walls.The following parameters and related ranges are considered:Rayleigh number 104≤Ra≤5.105,tilt angle 0°≤φ≤90°,Reynolds number 100≤Re≤1000,Prandtl number Pr=0.72,block height B=0.5,opening width C=0.15,and distance between blocks D=0.5.The results reveal different branches of solutions on varying Re andφ.They also show that the symmetry of the solution regarding the P_(2)axis is retained for all cases with no tilt and for values of Re between 100 and 1000.

Convective Heat Transfer Characteristics of the Elliptic Cylinder with Axis Ratio 4∶1 in Crossflow

The heat transfer features around the elliptic cylinder of axis ratio 4∶1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthalene sublimation technique, the local heat transfer distribution and the mean heat transfer coefficient are clarified. The result shows that the mean heat transfer coefficient is higher than that of a circular cylinder in most Reynolds number range regarded, and this superiority turns to be more significant with the increase of flow speed. Moreover, the effect of axis ratio on mean heat transfer coefficient was investigated tentatively. The oil-lampblack technique was employed to enable visualization of the flow pattern around the cylinder and on the cylinder wall.

Comprehensive Molten Salt Storage Shell and Supporting Structure Design and Analysis-Part I:A Conductive and Convective Theoretical Heat Transfer Analysis for Molten Salt Cylindrical Shells at 565℃ and 700℃

In this paper a full theoretical thermal analysis of a large molten salt container,80-foot in diameter and 46-foot high,including a four-foot elliptic shell roof,is presented for two temperatures,the standard 565℃ and a futuristic 700℃,which substantially improves the efficiency of the molten salt containers through the use of a highly stable chloride salt called SS700(SaltStream 700).The theoretical analysis includes conductive and convective heat transfer analysis in the steel container,elliptic roof shell,the fiberglass insulation,and firebrick insulation,and includes thermal insulation designs to safeguard against energy losses at high temperatures.The underlying soil and the high temperature concrete foundation were analyzed theoretically using conductive heat transfer,however the area surrounding the soil surface around the bottom of the molten salt storage tank had convective heat transfer analysis included.The final designs presented in this paper seek to limit heat losses to a maximum of 250 W/m^(2) while being able to operate at a minimum external ambient temperature of-10℃,which determines the thicknesses of the fiberglass and firebrick insulation.

THE PREDICTIONS OF CONVECTIVE HEAT TRANSFER ON TURBINE BLADE AIRFOIL BY USING LOW－REYNOLDS NUMBER TURBULENCE MODEL

A development of Schmidt-Patankar low-Reynolds number turbulencemodel is made to simulate heat transfer on turbine blades.Examination calculation iscarried out for 18 conditions of six turbine vanes.The parameter regions are outletReynolds number ranging

An Investigation into the Influence of the Airflow Path on the Convective Heat Transfer for an Eddy Current Retarder Turntable

In order to improve the convective heat transfer relating to an eddy current retarder,the finite element model has been used to assess the performances of different possible designs.In particular,assuming the steady running state of retarder as the working condition,flow and temperature fields have been obtained for the rotor.The influence of airflow path on heat dissipation has been analysed,and the influence of the temperature field distribution on the performance of retarder has been discussed accordingly.The results show that when the steady running state of the turntable is considered,the maximum temperature is lower,the level of turbulence flow is mitigated,and the temperature distribution becomes more regular.These factors contribute to improve the heat dissipation ability of the retarder.

Comprehensive Molten Salt Storage Shell and Supporting Structure Design and Analysis-Part II:A Conductive and Convective Numerical Finite Element Heat Transfer Analysis for Molten Salt Cylindrical Shells at 700℃,and Comparison with Theoretical Analysis

In this paper a finite element thermal analysis model-using COMSOL-of a large molten salt container,80-foot in diameter and 46-foot high that includes a four-foot elliptic shell roof,is presented for a futuristic 700℃ design,which uses a highly stable chloride salt called SS700(SaltStream 700)that improves the efficiency of the tank when compared to the traditional 565℃.The FEA(finite element analysis)includes conductive and convective heat transfer analysis in the steel container,elliptic roof shell,the fiberglass insulation,and firebrick insulation,and includes thermal insulation designs to safeguard against energy losses at high temperatures.The underlying soil and the high temperature concrete foundation were analyzed by finite element using conductive heat transfer,however the area surrounding the soil surface around the bottom of the MS storage tank had convective heat transfer analysis included.The finite elements analyses presented are to verify the final fiberglass and firebrick insulation designs,which seeks to limit heat losses to a maximum of 250 W/m^(2) while being able to operate at a minimum external ambient temperature of-10℃.These results are also compared to previously calculated theoretical results.

Influence of Brownian Motion, Thermophoresis and Magnetic Effects on a Fluid Containing Nanoparticles Flowing over a Stretchable Cylinder

The influence of Brownian motion and thermophoresis on a fluid containing nanoparticles flowing over a stretchable cylinder is examined.The classical Navier-Stokes equations are considered in a porous frame.In addition,the Lorentz force is taken into account.The controlling coupled nonlinear partial differential equations are transformed into a system of first order ordinary differential equations by means of a similarity transformation.The resulting system of equations is solved by employing a shooting approach properly implemented in MATLAB.The evolution of the boundary layer and the growing velocity is shown graphically together with the related profiles of concentration and temperature.The magnetic field has a different influence(in terms of trends)on velocity and concentration.

Improving Heat Transfer in Parabolic Trough Solar Collectors by Magnetic Nanofluids

A parabolic trough solar collector(PTSC)converts solar radiation into thermal energy.However,low thermal efficiency of PTSC poses a hindrance to the deployment of solar thermal power plants.Thermal performance of PTSC is enhanced in this study by incorporating magnetic nanoparticles into the working fluid.The circular receiver pipe,with dimensions of 66 mm diameter,2 mm thickness,and 24 m length,is exposed to uniform temperature and velocity conditions.The working fluid,Therminol-66,is supplemented with Fe3O4 magnetic nanoparticles at concentrations ranging from 1%to 4%.The findings demonstrate that the inclusion of nanoparticles increases the convective heat transfer coefficient(HTC)of the PTSC,with higher nanoparticle volume fractions leading to greater heat transfer but increased pressure drop.The thermal enhancement factor(TEF)of the PTSC is positively affected by the volume fraction of nanoparticles,both with and without a magnetic field.Notably,the scenario with a 4%nanoparticle volume fraction and a magnetic field strength of 250 G exhibits the highest TEF,indicating superior thermal performance.These findings offer potential avenues for improving the efficiency of PTSCs in solar thermal plants by introducing magnetic nanoparticles into the working fluid.

Experimental Investigation on Convective Heat Transfer Characteristics in Ribbed Channel

The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.

Fluid Flow and Convective Heat Transfer in a Water Chemical Condenser

In this paper,a detailed investigation of water(Pr=7.0)convection in a chemical condenser is carried out.Two openings are located along one side of the cavity.The Navier-Stokes equations are solved in the frame of a control volume method using the SIMPLEC algorithm to implement adequate coupling of pressure and velocity.Special emphasis is given to the influence of the Reynolds number,the tilt of the channel and the Rayleigh number on the convective heat transfer.Results are presented and discussed allowing the control parameters to span relatively wide intervals:Rayleigh number(10^(4)≤Ra≤5×10^(5)),channel inclination(0°≤90°)and Reynolds number(10≤Re≤1000).On the basis of these results,a new correlation of the Nusselt number is elaborated.

Heat Transfer Characteristics of Boiler Convective Heating Surface Under Pressurized Oxygen-fuel Combustion Conditions

增压富氧燃烧是一项极具前景的减排CO2新技术。对增压富氧燃烧条件下,对流受热面换热特性进行研究具有重要的意义。该文以一台实际300MW等级机组煤粉锅炉为计算对象,采用维里方程及Chun等的计算方法计算确定增压富氧燃烧烟气物性,采用宽带关联k模型计算富氧燃烧烟气辐射特性。进行了常规空气燃烧以及φ（O2）：φ（CO2）=21：79、φ（O2）：φ（CO2）=30：70两种比例的0.1、0.5、1.0、1.5、6 MPa五种压力下增压富氧燃烧各对流受热面的热力计算,分析了增压富氧燃烧条件烟气压力变化对各受热面换热特性的影响。研究结果表明：随烟气压力的升高,烟气流速下降,但烟气的Re却基本保持不变,对流换热系数有所增加。增压富氧燃烧烟气的辐射换热系数比空气燃烧烟气辐射换热系数大。实现同样的换热量,增压富氧燃烧条件下（φ（O2）：φ（CO2）=21：79、φ（O2）：φ（CO2）=30：70）对流受热面所需换热面积比常规空气燃烧条件下少。

An Experimental Study on Nanofluids Convective Heat Transfer Through a Straight Tube under Constant Heat Flux

In this work, the laminar convective heat transfer performance and the pressure drop of water-based nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles flowing through a straight circular tube were experimentally investigated. The experimental results showed that addition of small amounts of nano-sized Al2O3 and TiO2 particles to de-ionized water increased heat transfer coefficients considerably, while the SiO2 nanofluids showed the opposite behavior attracting the authors' interests. An average of 16% and 8.2% increase in heat transfer coefficient were observed with the average of 28% and 15% penalty in pressure drop for Al2O3 and TiO2 nanofluids.

Numerical investigation on convective heat transfer over two heated wall-mounted cubes in tandem and staggered arrangement

In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated.Two cubes, which are under constant heat flux, are placed in different tandem and staggeredarrangements on a base plate. This problem is studied for different streamwise and spanwisedistances between two cubes in different Renolds number （Re）, by using finite-volume method.Effects of these parameters are considered on flow and heat transfer characteristics. The resultsshow that the temperature distribution is strongly dependent on flow structure and varies with anychange of flow pattern in different arrangements of cubes. In addition, it is observed that the dragcoefficient, which is influenced more by pressure forces, in staggered arrangement, is greater thantandem arrangement. Results show that by increasing the spanwise distance the amount of meanNusselt number （Nu） of Cube 2 becomes the same as Cube 1.

Heat transfer study on solid and porous convective fins with temperature-dependent heat generation using efficient analytical method

A simple and highly accurate semi-analytical method, called the differential transformation method(DTM), was used for solving the nonlinear temperature distribution equation in solid and porous longitudinal fin with temperature dependent internal heat generation. The problem was solved for two main cases. In the first case, heat generation was assumed variable by fin temperature for a solid fin and in second heat generation varied with temperature for a porous fin. Results are presented for the temperature distribution for a range of values of parameters appearing in the mathematical formulation(e.g. N, εG, and G). Results reveal that DTM is very effective and convenient. Also, it is found that this method can achieve more suitable results in comparison to numerical methods.

Mixed convective heat and mass transfer analysis for peristaltic transport in an asymmetric channel with Soret and Dufour effects

The present investigation addresses the simultaneous effects of heat and mass transfer in the mixed convection peristaltic flow of viscous fluid in an asymmetric channel. The channel walls exhibit the convective boundary conditions. In addition, the effects due to Soret and Dufour are taken into consideration. Resulting problems are solved for the series solutions. Numerical values of heat and mass transfer rates are displayed and studied. Results indicate that the concentration and temperature of the fluid increase whereas the mass transfer rate at the wall decreases with increase of the mass transfer Biot number. Furthermore, it is observed that the temperature decreases with the increase of the heat transfer Biot number.

Heat transfer in a porous saturated wavy channel with asymmetric convective boundary conditions

The viscous flow in a wavy channel with convective boundary conditions is investigated. The channel is filled with a porous viscous fluid. Two cases of equal and different external convection coefficients on the walls are taken into account. Effect of viscous dissipation is also considered. The governing equations are derived employing long wavelength and low Reynolds number approximations. Exact closed form solutions are obtained for the simplified equations. Important physical features for peristaltic flow caused by the wavy wave are pumping, trapping and heat transfer rate at the channel walls. These are discussed one by one in depth and detail through graphical illustrations. Special attention has been given to the effects of convective boundary conditions. The results show that for Bi1≠Bi2, there exists a critical value of Brinkman number Brc at which the temperatures of both the walls become equal. And, for Bi1>Bi2 and Br>Brc, the temperature of the cold wall exceeds the temperature of hot wall.

Validation of Heat Transfer between Theoretical and Experimental from the Internal Surface of Vertical Tubes with Internal Rings Heated by Electrical Heating Coils

The comparison between experimental and theoretical heat transfer inside heated vertical channels that dissipate heat from the internal surface with and without internal rings is studied.The experimental setup consists of a circular pipe which is heated electrically by providing constant heat flux on the wall.The theoretical and experimental analysis is conducted in several pipes of same diameter but different lengths.The length of the pipe varies from 450 mm to 850 mm.The length to diameter ratios are taken as L/D=10,12.22,15.56,and 18.89.The value of imposed heat flux varies from 250 to 3340 W/m2.The internal ring thickness varies from 4 mm to 8 mm.separation distance between the internal rings varies from 75mm to 300 mm.The theoretical results are compared with experimental data to ascertain numerical accuracy of the method.The effects of L/D ratio,thickness of internal rings and separation distance on the heat transfer performance are studied.The experimental result is compared with theoretical,theoretical results are found by using ANSYS.In this study theoretical result for wall temperature along the height of tube,fluid temperature at exit of tube are compared with experimental data.

Nanofluids Transport Model Based on Fokker-Planck Equation and the Convection Heat Transfer Calculation

In current research about nanofluid convection heat transfer, random motion of nanoparticles in the liquid distribution problem mostly was not considered. In order to study on the distribution of nanoparticles in liquid, nanofluid transport model in pipe is established by using the continuity equation, momentum equation and Fokker-Planck equation. The velocity distribution and the nanoparticles distribution in liquid are obtained by numerical calculation, and the effect of particle size and particle volume fraction on convection heat transfer coefficient of nanofluids is analyzed. The result shows that in high volume fraction （ 0 _-- 0.8% ）, the velocity distribution of nanofluids characterizes as a ＂cork-shaped＂ structure, which is significantly different from viscous fluid with a parabolic distribution. The convection heat transfer coefficient increases while the particle size of nanoparticle in nanofluids decreases. And the convection heat transfer coefficient of nanofluids is in good agreement with the experimental result both in low （0 ~〈 0.1% ） and high （ q = 0.6% ） volume fractions. In presented model, Brown motion, the effect of interactions between nanoparticles and fluid coupling, is also considered, but any phenomenological parameter is not introduced. Nanoparticles in liquid transport distribution can be quantitatively calculated by this model.