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Ensuring adequate ventilation during tunnel construction is a critical issue that directly affects construction efficiency. A good ventilation environment can effectively guarantee the construction progress. In this paper, by repeatedly selecting the flow field simulation parameters and continuously summarizing the calculation methods, a reasonable model is selected to simulate the tunnel engineering. Specifically, the eddy current zone near the working face is obtained by analysing the flow field of forced ventilation tunnels. Furthermore, we analyse the dispersion and accumulation of harmful gases in the tunnel. The CO concentration at typical locations in the tunnel is also examined in order to determine areas with the lowest likelihood of harmful gas discharge. We then propose adding a jet fan to the tunnel to create an extraction plus ventilation tunnel. Simulation results reveal that the addition of a jet fan causes eddy currents that improve the extraction of harmful gases, thereby greatly reducing ventilation time and increasing efficiency. The results of the model can effectively guide the actual project, and help them save the construction time.

Experimental investigation of various heat transfer mechanisms associated with isolated nucleate pool boiling have been presented. Measurements have been made in a complete non-intrusive manner using rainbow schlieren deflectometry technique. Boiling experiments have been performed for two levels of superheat with the bulk fluid maintained under saturated conditions. The rainbow schlieren images have first been subjected to qualitative interpretation wherein various sub-processes associated with the boiling phenomenon, such as development of thermal boundary layer on the substrate surface, inception of single bubble, growth of the vapor bubble till it departs, and scavenging of the superheat layer following the bubble departure have been discussed. Contributions of individual sub-processes towards the overall heat transfer rates achieved for a given superheat level have been determined through quantitative analysis of the images. Schlieren observations revealed the effect of varying superheat levels on parameters such as bubble diameter and departure time. Detailed heat transfer analysis revealed the dominance of evaporative heating in contributing towards the overall heat transfer rates. On the other hand, the contribution of natural convection from the heated substrate was found to be relatively small. In quantitative terms, the evaporative heating was seen to have an individual contribution as high as approximate to 66% to the overall heat transfer and approximate to 88% to the growth of the vapor bubble in the case of superheat level of 7 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.

The phenomena of nanofluids-based natural convection heat transfer around a heated cylinder have been studied using nonintrusive real-time diagnostics. Experiments have been performed with a horizontally placed heated cylinder immersed in bulk ambient conditions with water and alumina oxide/water-based dilute nanofluids as the working fluids. Volumetric concentrations of alumina nanoparticles have been varied from 0.005 to 0.02%. A classical Mach-Zehnder interferometer has been used to record the line-of-sight projection data of the convective field around the heated cylinder. The strength of thermal gradients prevailing around the surface of the heated cylinder was seen to be clearly affected by the variations in the nanofluid concentration, thus indicating the plausible role of nanoparticles in disrupting the thermal boundary-layer profiles around the cylinder surface. Significant enhancement in the heat transfer coefficient was observed at the highest levels of concentration of the dilute nanofluids employed, whereas the spatially averaged Nusselt numbers around the cylinder surface showed a marginal deterioration at the lower range of volumetric concentrations. With a further increase in nanoparticles concentration, the Nusselt numbers showed an increasing trend, although not as significant as observed in the case of the heat transfer coefficient. Plausible mechanisms responsible for these observations have been delved upon using purely nonintrusive whole field measurements.

The present study is concerned with the simultaneous estimation of thermal and solutal diffusivities of salt-water solutions from a single-shot dual-color interferometric image recorded using real-time dual wavelength interferometric technique. The experimental scheme consists of a two-layered salt stratified medium created in a quartz cell while diffusing thermal conditions have been created by imposing stabilizing temperature boundary conditions at the two horizontal surfaces. The line-of-sight projection data of variations in the refractive index field caused due to changes in the thermal and solutal fields have been recorded using a dual wavelength Mach-Zehnder interferometer. Two distinct monochromatic laser sources i.e. He-Ne (lambda(1)= 632.8 nm) and Ar-ion (lambda(2) = 457.9 nm) have been employed for recording the changes in the density field and the corresponding phase changes in the path of the traversing beam have been recorded simultaneously by using Bayer mosaic color CCD sensor. The experiments have been performed with an initial concentration step of Delta C-i = 0.25 (wt/wt)% and a temperature gradient of Delta T= 1.2 degrees C. The results have been presented in the form of dual-color interferometric images, contours of two-dimensional temperature and concentration fields, corresponding profiles of temperatures and concentrations along the central vertical axis at various time instants. The temporal fringe shifts observed in the fringe patterns of two colors enable the simultaneous measurements of solutal and thermal diffusivities in real time. The thermal and solutal diffusion coefficients have been estimated by ensuring the fidelity between the experimentally determined respective fields with the analytical solutions and the values estimated in the present work are in close agreement with the standard values reported in the literature. (C) 2016 Elsevier Inc. All rights reserved.

The present work reports the development and application of a lens-based rainbow schlieren deflectometry technique for non-intrusive investigation of heat transfer characteristics of dilute nanofluids. The experiments have been performed under natural convection regime. Buoyancy-driven convection has been set up in the vicinity of a heated vertical flat plate that is immersed in a quiescent ambient fluid medium with de-ionized water as the base fluid and Al2O3/water-based dilute nanofluids. The experiments have been carried out for three different volumetric concentrations of alumina nanoparticles i.e. 0.01%, 0.02% and 0.03%. The color variant of the classical schlieren technique namely the rainbow schlieren deflectometry has been employed to record the projection data of the temperature gradient field in the test cavity. The optical configuration of the imaging technique employs a specially-designed color filter for generating the desired schlieren effects. The recorded schlieren images are characterized by a gradation of hue distribution that is proportional to the strength of the temperature gradients prevailing in the test section. Results have been discussed in the form of two-dimensional rainbow schlieren images, whole field distribution of temperature gradients in the vicinity of the heated plate and local distribution of heat transfer coefficients as a function of the length of the plate for the varying concentrations of nanofluids. The profiles of local heat transfer coefficients along the length of the heated plate as obtained with nanofluids show a considerable difference when compared with that of the de-ionized water. Significant enhancement in the average values of heat transfer rates is achieved with nanofluids as the ambient fluid medium in comparison with the base fluid. The study clearly reveals the potential of rainbow schlieren deflectometry technique in the context of heat transfer measurements with nanofluids as the working medium. (C) 2016 Elsevier Ltd. All rights reserved.

Based on frequently used internal partitions in offices, the effects of pollutant source characteristics and an internal partition on airflow and contaminant distribution under different ventilation modes are studied in this paper. The indoor flow field measurement is implemented in a 1:1 single environmental chamber under different ventilation patterns, and then the numerical model is established. The numerical method is verified and analyzed by comparing the measured and simulated results. According to the verification results, the numerical simulation is introduced to study the influence of different supply and return air mixes and pollutant source distributions on the flow field and diffusion performance with an internal partition. The indoor flow field and concentration distribution under different conditions are compared, and the discharge efficiency under different working conditions is analyzed. The results indicate that internal partitions have a greater influence on the down-supply up-return ventilation mode than the floor-supply up-return and top-supply down-return ventilation mode. Furthermore, if the room is zoned, the effect of source position is larger under the down-supply up-return ventilation mode than under the other two modes.

After conducting the intensive research on the distribution of fluid’s velocity and biochemical reactions in the membrane bioreactor (MBR), this paper introduces the use of the mass-transfer differential equation to simulate the distribution of the chemical oxygen demand (COD) concentration in MBR membrane pool. The solutions are as follows: first, use computational fluid dynamics to establish a flow control equation model of the fluid in MBR membrane pool; second, calculate this model by adopting direct numerical simulation to get the velocity field of the fluid in membrane pool; third, combine the data of velocity field to establish mass-transfer differential equation model for the concentration field in MBR membrane pool, and use Seidel iteration method to solve the equation model; last but not least, substitute the real factory data into the velocity and concentration field model to calculate simulation results, and use visualization software Tecplot to display the results. Finally by analyzing the nephogram of COD concentration distribution, it can be found that the simulation result conforms the distribution rule of the COD’s concentration in real membrane pool, and the mass-transfer phenomenon can be affected by the velocity field of the fluid in membrane pool. The simulation results of this paper have certain reference value for the design optimization of the real MBR system.