Abstracts:This work is aimed at studying the effect of gravity when convective condensation occurs inside a small diameter channel. An experimental apparatus has been specifically designed to perform microgravity experiments during the 62nd ESA Parabolic Flight Campaign. Convective condensation heat transfer tests have been carried out at mass velocity between 70 kg m⁻² s⁻¹ and 170 kg m⁻² s⁻¹ using HydroFluoroEther HFE-7000 (1-methoxyheptafluoropropane) as the working fluid in a circular cross section channel with an internal diameter equal to 3.4 mm. The data of heat transfer coefficient and the flow pattern visualizations show that, when gravity acts perpendicular to the channel flow, it has a beneficial effect on the heat transfer coefficient by acting on the liquid distribution along the channel perimeter. In microgravity conditions this mechanism leads to a penalization which is proportional to the mass velocity.

Abstracts:In order to study the heat transfer characteristics (HTCs) of molten salt outside the tube bundle in a shell-and-tube heat exchanger (STHE) without baffle plates, the HTCs of molten salt (204.06 °C~236.91 °C) are experimentally and numerically investigated in this paper. Firstly, the HTCs of molten salt (3514 < Re < 5482) is experimentally studied based on the test platform with HITEC salt and oil. Then the empirical heat transfer equations of molten salt applied in the shell side of STHE are fitted. Finally, the comparison between the experimental and numerical results is conducted. The results show that the fitted equations agree well with the experimental data and the fitted deviations are only 8%. The error is about 11% between the simulation and experiment results which indicates that the HTCs of molten salt STHE would be predicted well using the simulation method. The numerical results also show that there exist flow dead zones in the STHE which could weaken the molten salt HTCs.

Abstracts:Tissue engineering scaffolds combined with bioreactors are used to cultivate cells with the aim of reproducing tissues and organs. The cultivating process is critical due to the delicate in-vitro environment in which the cells should reproduce. The distribution of nutrients within the engineered construct depend on the scaffold morphology and the analysis of the fluid flow and transport phenomena under mechanical loading when the scaffold is coupled with a bioreactor is crucial for this scope. Unfortunately, due to the complicated microstructure of the scaffold, it is not possible to perform this analysis with experiments and numerical simulation can help in this sense. In this study we have computed the fluid flow and the mass transport of a parametrized scaffold in perfusion bioreactors analyzing the influence of the microstructure of the scaffold using the fluid-structure interaction approach. The latter allows considering the porous construct as compliant yet determining important structural parameters such as stresses and strains that could be sensed by the cells. The presented model considered flow perfusion that provided nutrients and mechanical compression. In particular, we have studied the effect of controllable parameters such as the diameter of the scaffold strand and the porosity on the mechanical stresses and strains, shear stress and mass transport. The results of this work will help to shed light on the necessary microenvironment surrounding the cultivated cells improving culturing scaffold fabrication.

Abstracts:The micro/mesoscale combustion system of liquid ethanol and the visualization measurement system of flame were designed and constructed on the basis of the microscale combustion theory of liquid fuels. The characteristics of the micro/mesoscale liquid ethanol diffusion flame were investigated experimentally. The flow fields of flame were visualized and measured using deflection tomography. An image sampling system was proposed for deflection tomography to obtain deflectograms and flame images in one shot. The deflection angles of rays were extracted by the wave-front retrieval of deflectograms, which was suitable for micro/mesoscale combustion. The two-dimensional temperature distributions were reconstructed using the deflection angle revision reconstruction algorithm. The three-dimensional distribution of temperature and structure of flame were obtained using a visualization toolkit equipped with the marching cube and ray casting algorithms. At the same diameter of burner, the height, width and peak temperature of flame did not change significantly as the flow rate of fuel increased in the stable combustion stage. In the oscillation combustion stage, the height and width of flame gradually increased, the peak temperature increased firstly and then decreased, and the oscillation cycle of the flame decreased with the increase in the flow rate of fuel. Under equal flow rate of fuel, the height and width of flame were independent of the diameter of burner in the oscillation combustion stage. At the same time, the distribution of temperature and the oscillation period of flame were closely related to the diameter of burner. The pulsating instability of oscillating flame interacted highly with the heat exchange effect between the flame and the liquid fuel.

Abstracts:Critical Heat Flux or CHF is a phenomenon in pool boiling, which limits the thermal flux during the nucleate heating phase. Presented research paper is an investigation of the CHF of Al2O3, Fe2O3 and CuO nanoparticles in water as base fluids. Critical Heat Flux of water and nanofluids were measured at 100 °C and 0.10325 MPa using 29 × 22 W DC power supply and NiCr 32AWG wire as the primary heater. Concentration of nanoparticles in the respective base fluids was varied from 0.01 vol% to 0.1 vol% in the step of 0.1%. Nanofluids were used as the working fluid and sent to circular bath. A significant enhancement in CHF was found of nanofluid over base fluid is found in the study. As the concentration of nanoparticles in water increases, the CHF also increases up to their optimum concentration and then starts to drop and almost becomes constant at 0.1%. The enhancement is due to enhanced surface wettability, increased heat transfer coefficient and nanoparticle deposition on heating element. The decrease in CHF over higher concentration is due to probable agglomeration due to prevalent surface charges of nanoparticles.

Abstracts:This research presents details of heat and fluid flow inside the wavy tubes with circular cross-sections at laminar regime under the Reynolds numbers in the range of 100 and 1000. To enhanced visualization, effects of non-dimensional geometric parameters such as the wave amplitude (H/D) varying between 0.1 and 0.5 and the wavelength (P/D) varying from 4 to 6 on the heat transfer process and flow nature are investigated in detail. The obtained results are validated against the available data in the literature. It is concluded that due to development of the centrifugal forces inside the wavy passage, a pair of Dean vortices appearances within the tube. The size of these vortical structures is strongly affected by the Reynolds number and geometric parameters of the wavy tube. On the other hand, at all Reynolds numbers under consideration, increasing the H/D and P/D enhances and diminishes the rate of heat transfer between the fluid flow and tube wall, respectively. Moreover, it is demonstrated that at low Reynolds numbers, the pressure drop penalty outweighs the heat transfer enhancement. It is found that the maximum thermal-hydraulic performance occurs in the case of H/D = 0.5, P/D = 6, and Re = 1000 with 42%.

Abstracts:Considering the wide range of applications of the activated carbon in different applications, the behavior of fluid flow through a packed bed of irregular shaped activated carbon grains has significant importance. Hence, an experimental investigation is conducted on axial-horizontal flow of air and argon through 5 different packed beds of granular activated carbon (GAC) with different grain sizes. Investigations are done different flow line pressure and flow rates. Based on the previous studies, a simple correlation is proposed and results are presented in terms of dimensionless friction factor versus Reynolds number. Results are presented for different grain sizes and the correlation coefficients have been estimated with excellent curve fitting to the experimental data. Outcomes of this study could be used to design the systems in which the pressure drop through a packed bed of GAC is required.

Abstracts:Effects of the mainstream boundary layer thickness and the turbulence intensity on film cooling under low Reynolds number conditions are studied in this work by the direct numerical simulation (DNS). In other to solve low-speed compressible flow problems, several methods of Roe scheme, preconditioning, dual time stepping, and LUSGS are adopted to solve governing equations. Results reveal that a horseshoe vortex appears with a thicker mainstream boundary layer, and thus the lateral coverage of the coolant fluid has increased significantly. In addition, the existence of turbulence intensity eliminates the blow-off phenomenon, which happens in a thin mainstream boundary layer condition and enhances the film cooling effectiveness.

Abstracts:Immersion of microencapsulated phase change material (MPCM) into carrying fluid to form MPCM slurry is an effective method to guarantee both heat transfer efficiency and latent heat absorption. This article reports an experimental method to evaluate the natural convective heat transfer of MPCM slurry by means of setting the test rig in three angles to represent specific heating positions, i.e., θ = 0^o (heated from bottom), θ = 90^o (heated from side) and θ = 180^o (heated from top). The thermal performances of MPCM slurry are analyzed by comparing with another two control groups: pristine PCM and MPCM particles. Results show that MPCM slurry gives the best thermal control amongst the three materials in the temperature range considered due to the thermal enhancement of natural convection, followed by pristine PCM, then MPCM particles. The surface temperature reduction of 16.3 °C is devoted by natural convection of carrying fluid in MPCM slurry, while this contribution is more pronounced (40 °C) in pristine PCM. However, the natural convection of core PCM is fully suppressed in MPCM particle. MPCM slurry with lower concentration consumes less time to reach a lower melt onset temperature at the cost of having less thermal management time.

Abstracts:Evaporation and heat transfer of the layers of water and aqueous salt solutions (H2O/LiBr, H2O/CaCl2, H2O/LiCl) have been studied experimentally. Evaporation rate is greater for a structured wall than for a smooth one. When simulating droplet evaporation and heat transfer, it is necessary to take into account free convection of air and vapor. There is a change of the heat transfer coefficient for salt solutions layers on the structured surface with the presence of an extremum. The largest value of the heat transfer coefficient α on the structured surface corresponds to water for the final stage of evaporation. For salt solutions, α is lower than that of water. The maximum excess of heat transfer coefficient of micro-structured wall above the smooth wall (20–25%) corresponds to the maximum height of the liquid layer for the initial period of evaporation. With increasing time, the excess is reduced.