This paper presents an experimental study of gas-liquid slug flow inside a horizontal pipe. The influence of air bubble passage on liquid flow is characterized using Particle Image Velocimetry (PIV) combined with Refractive Index Matching (RIM) and fluorescent tracers. A physical insight into the velocity distribution within slug flow is presented. It was observed that the slug flow significantly influences the velocity profile in the liquid film. Measured velocity distributions also revealed a significant drop in the velocity magnitude immediately upstream of the slug nose. These findings aim to aid an understanding of the mechanism of solid transportation in slug flows.

Micro-channels are presently used extensively in applications related to biomedicine and others. These applications commonly involve flow patterns apt for separating particles in suspension, or fluid layers or fluid portions. In order to find a desired optimum performance it is necessary, among other factors, to determine the pressure gradients that would generate the required flow patterns. Presently the driving pressure gradients are produced by means of mechanical devices, such as syringe pumps, which have obvious limitations in the case where the flow time-pattern is complex. High frequency flows with varying amplitude or swift changes in acceleration imply overcoming big inertia forces in mechanisms. In this paper it is presented a novel and alternative methods for providing complex pressure pulses for the case were the working fluid changes properties when affected by magnetic fields. It is shown that an appropriate arrangement of parallel tubes, subject to different magnetic fields, can induce a wide variety of pressure pulses in selected stations of the system. These stations can be used for connecting the working channel. An analytical model is presented together with several applications.

The strategy of adding solid particles to fluids for improving thermal conductivity has been pursued for more than one century. Here, a novel concept of using liquid nanodroplets for enhancing thermal performance has been developed and demonstrated in polyalphaolefin nanoemulsion fluids with dispersed ethanol nanodroplets. The ethanol/polyalphaolefin nanoemulsion fluids are spontaneously generated by self-assembly, and are thermodynamically stable. Their thermophysical properties, including thermal conductivity and viscosity, and impact on convective heat transfer are investigated experimentally. The thermal conductivity enhancement in these fluids is found to be moderate, but increases rapidly with increasing temperature in the measured temperature range from 35 oC to 75 oC. A very remarkable increase in convective heat transfer coefficient occurs in the nanoemulsion fluids due to the explosive vaporization of the ethanol nanodroplets at the superheat limit (i.e., spinodal states, about 122 oC higher than the atmospheric boiling point for ethanol). The explosive liquid-vapor phase transition is monitored using high speed camera. The fluid heat transfer could be augmented through the heat of vaporization (which intuitively raises the base fluid specific heat capacity) and the fluid mixing induced by the sound waves. The development of such phase-changeable nanoemulsion fluids would open a new direction for thermal fluids studies.

Developing better heat pipes requires advancement of technology in all aspects of construction. In this paper I am investigating the effect of vapor pathways on the performance of biporous wicks in heat pipes. Biporous evaporator wicks, generated by sintering copper particles into semi-uniform clusters, were demonstrated to achieve high flux, heat transfer performance for use in heat pipes by Semenic (2007). The effective thermal conductivity of thick biporous wicks at high heat fluxes was found to be reduced because the region next to the wall dried out prematurely, allowing the wall interface temperature to rise well above the saturation temperature. One possible way to reduce the size of the wall-wick interface dry-out region is to sinter a thin layer of uniform size particles on the wall as suggested by Seminic. The boiling curve for this “double layer” wick diverges from a standard “single layer” biporous wick at the point of nucleation by reducing the wall temperature, and concurrently the overall temperature drop across the wick needed to drive a given heat flux. The temperature drop across the wick is reduced because the thin layer of particles between the biporous wick and the wall reduces the wall-wick interface resistance and also provides additional capillary channels underneath the biporous wick. Experimental data supports this hypothesis by showing a clear divergence between measured wall temperatures for the double layer wick from its single layer counterpart with an indication that smaller cluster sizes in the biporous wicks perform better at lowering the superheat required to obtain high fluxes. In this work, we are looking to compare the performance of these wicks to similarly sized blocks of copper in order to investigate the performance increase offered by the wicks. In order to investigate this phenomenon we ran experiments in a similar manner to previous experiments done by Reilly (2009), but a plate was inserted into the chamber above the wick to restrict the vapor flow. To determine the behavior in the copper we ran several simulations in COMSOL (a finite element software used for doing conduction analysis) of copper disks at different representative thicknesses. We ran experiments with the plate at several heights above the wick, going so far as to place the plate flush with the upper surface of the wick to force vapor back through the wick laterally. By comparing the results between these two sets of experiments we were able to deduce that even in the case where there was no open space above the wick for vapor to escape, we were still able to double the performance with respect to a system of solid copper.

Determination of Nusselt and Rayleigh numbers during natural convection heat transfer from horizontal cylinders are investigated experimentally and numerically. Experiments are done by means of the test cabin inside a conditioned room at different environmental and surface temperatures. The environmental and cylinder surface temperatures are ranging between 10–40 °C and 20–60 °C respectively. 1 m long horizontal copper cylinder is used and has outer diameters of 4.8 mm including centered silicone covered cylindrical resistant wires inside it. The experimental apparatus is designed to capable of changing the different operating parameters such as heat flux and environmental temperature. The existence of the gap on the closed surfaces in the test cabin which can cause a stack effect, affected temperature and velocity fields, disturbance of the natural convection condition is also checked. The detailed description of design and development of the test apparatus, control devices, instrumentation, and the experimental procedure are reported and the study of experimental setups from the available literature survey with the existing one are compared in this paper. The uncertainty analysis method proposed by Kline and McClintock is used and explained elaborately. Detailed information and algorithm of numerical method are given to ease the understanding of the numerical part of study. Alteration of Nusselt numbers with Rayleigh numbers, the temperature distribution on the heated horizontal cylinder surface by means of Fluent CFD program are shown in the paper. In addition to this, Morgan’s correlation is used for the comparison of Nusselt number and is found in good agreement with the experimental results.

In this study, flow and heat transfer for laminar flow in curved channels of rectangular cross section is examined. The focus of the numerical solutions is on rectangular cross sections with an aspect ratio less than one, since little information is available for heat transfer in curved rectangular pipes whose width is greater than height. The study examines the impact of the aspect ratio and Dean number on both friction factor and Nusselt number. The results show that although both friction factor and Nusselt number increase as a result of curvature effects, the heat transfer enhancements significantly outweigh the friction factor penalty. Numerical solutions in this study consider the more realistic case of hydrodynamically developed and thermally developing flow.

The present trends in the cooling technologies have marked a significant improvement in the outdoor telecommunications systems and the need of cooling has marked an important requirement for the proper functioning of these cabinets. This aim of this paper is to review all of the articles and to gather the information regarding the different cooling technologies used and their reliability in the outdoor telecommunication systems especially the telecommunication cabinets.

Special indoor air environment requirements are needed for the data center, such as ambient temperature, airflow pattern, relative humidity and ozone concentration to maintain the reliability of a computer system. In this paper, a numerical simulation based on 3-D Finite Volume Method has been conducted for a data center at Purdue University Calumet. The purpose of the simulation is to find out the most effective and low-cost air condition system. Results for temperature, relative humidity distributions as well as velocity patterns are presented. Mesh independent studies are performed. Numerical results are validated by experimental data. Suggestions are given based on the simulation results for improving the indoor environment of the data center.

This numerical investigation explores the hydrodynamic and thermal boundary layers characteristics of a liquid flow with Micro-Encapsulated Phase Change Material (MEPCM). Unlike pure liquids, the heat transfer characteristics of MEPCM slurry can not be simply presented in terms of corresponding dimensionless controlling parameters such as Peclet number. In the presence of phase change particles, the controlling parameters’ values change significantly along the tube length due to the phase change. As a result, the hydrodynamic and thermal boundary layers are significantly affected by the changing parameters. The numerical results reveal that the growth of the thermal boundary layer for MEPCM slurries is different than for pure liquids. The presence of MEPCM in the working fluid slows the growth of the thermal boundary layer and extends the thermal entry length. The local heat transfer coefficient strongly depends on the location of the melting zone interface.

Electrohydrodynamic (EHD) conduction phenomenon takes advantage of the electrical Coulomb force exerted on a dielectric liquid generated by externally applied electric field. The conduction phenomenon can be applied to enhance or control mass transport and heat transfer in both terrestrial and microgravity environments with advantages of simplicity and no degradation of fluid properties for isothermal as well as non-isothermal liquids. This paper numerically studies the heat transfer augmentation of externally driven macro- and micro-scale parallel flows by means of electric conduction phenomenon. The electric conduction is generated via electrode pairs embedded against the channel wall to solely enhance the heat transfer; it is not utilized to pump the liquid. Two cases of Poiseuille and Couette parallel flows are considered where for the former, a constant external pressure gradient is applied along the channel and for the latter, the channel wall moves with a constant velocity. The electric field and electric body force distributions along with the resultant velocity fields are presented. The heat transfer enhancements are illustrated under various operating conditions for both scales.

The performance of cross flow hollow fiber ultrafiltration (UF) membrane with molecular weight cut off (MWCO) 100 kDaltons was studied in order to effectively remove suspended solids in wastewater. Experiments were carried out to investigate the influence of the several factors such as cross flow velocity, transmembrane pressure (TMP), water temperature, and concentration of suspended solids on the membrane performance. Several cleaning methods were applied to remove the fouling. The experimental results showed that increasing TMP, temperature and cross flow velocity all resulted in increasing permeate flux. It is observed that high TMP aggravated the fouling while high cross flow velocity alleviated the fouling. High concentrations of suspended solids led to the reduction of permeate flux. It is also found that both combination of chemical, back- and forward-washing as well as soaking cleaning methods effectively removed fouling and achieved high flux recovery. The suspended solids were effectively removed by our UF system, and the water quality is significantly improved after ultrafiltration.

An experimental procedure has been developed to make in situ spectral emittance measurements of coal ash deposits. Pulverized coal is injected into a down-fired, entrained-flow reactor. Ash accumulates on a probe placed in the reactor effluent. The spectral emittance of the ash layer is calculated using measurements of the surface temperature and the spectral emissive power of the deposit. Measurements of the spectral emissive power and the surface temperature are obtained using a Fourier transform infrared (FTIR) spectrometer. The methods used to extract the spectral emissive power and surface temperature from measured infrared spectra were validated using a blackbody radiator at known temperatures. The experimental procedure was then used to find the spectral emittance of a coal ash deposit formed under oxidizing conditions.

Particle transport in ducts of square cross-section with constant streamwise curvature is studied using numerical simulations. The flow is laminar, with Reynolds numbers of Re τ = 40 and 67, based on the friction velocity and duct width. The corresponding Dean numbers for these cases are 82.45 and 184.5, respectively, where De = Re a / R , a is the duct width and R is the radius of curvature. A Lagrangian particle tracking method is used to account for the particle trajectories, with the particle volume fraction assumed to be low such that inter-particle collisions and two-way coupling effects are negligible. Four particle sizes are studied, τ p + = 0.01, 0.05, 0.1, and 1. Particle dispersion patterns are shown for each Dean number, and the steady-state particle locations are found to be reflective of the Dean vortex structure. Particle deposition on the walls is shown to be dependent upon both the Dean number and particle response time, with the four-cell Dean vortex pattern able to prevent particle deposition along the center of the outer wall.

Drilling is a highly complex machining process coupled with thermo-mechanical effect. Both the rapid plastic deformation of the workpiece and the friction along the drill-chip interface can contribute to localized heating and increasing temperature in the workpiece and tool. The cutting temperature at the tool-chip interface plays an important role in determining the tool thermal wear. This in turn affects the dimensional accuracy of the workpiece and the tool life of drill. A new embedded heat pipe technology has been proven to be able to effectively not only remove the heat generated at the tool-chip interface in drilling, but also minimize pollution and contamination of the environment caused by cutting fluids. Less tool wear can then be achieved, thus prolonging the tool life. 3D Finite Element method using COSMOS/works is employed to study coupled effects of thermal, structural static and dynamic analyses in a drilling process to check the feasibility and effectiveness of the heat pipe drill. Four different cases, solid drill without coolant, solid drill with coolant, heat pipe drill, and heat pipe drill with coolant, are explored, respectively. The results from this study can be used to define geometric parameters for optimal designs.

Scale deposition (or fouling) on metal surfaces from salt-containing water considerably reduces the efficiency and performance of heat transfer equipments. In industrial practices, scale deposition could be reduced through physical or chemical methods. However, in some cases chemical methods are unpractical due to cost and contamination issues, rendering the physical methods the only feasible options. The objective of this study was to evaluate the effectiveness of two physical treatments in reducing scale depositions. One is to decrease the surface energy of the heat exchanger wall through surface modification; the other one is to change the crystallography of the small solid particles formed in the solution by applying a magnetic field. For the first method, the scale deposition on PTFE surfaces, SAMs (self-assembly monolayers) surfaces, polished copper surfaces, and polished stainless steel surfaces are investigated respectively. Copper and stainless steel surfaces were modified by micro-scale (μm thickness) PTFE (Poly-Tetrofluorethylene) films and nano-scale (nm thickness) thiolate SAMs. The surface energy of PTFE films and SAMs layers based on copper and stainless steel were significantly reduced compared with the untreated metal surfaces. To study the magnetic treatment effect on the formation of the calcium carbonate scale, a magnetic field up to 0.6 T was implemented in a simulated recirculation cooling water system. A large number of experiments were performed to study the effects of fluid velocity, heat flux, and the bulk concentration of the solution on the fouling rate and induction period of calcium carbonate on various modified surfaces. The experiments showed that the formation rate of the calcium carbonate scale was decreased on modified surfaces and the induction period was prolonged with the decrease of the surface energy. The study also showed that the nucleation and nucleate growth of calcium carbonate particles were enhanced through magnetic water treatment. In addition, using a higher flow rate and/or filtration of suspended calcium carbonate particles achieves a longer induction period.

In this work, the numerical simulation of 2-D heat transfer problem is studied by using a meshfree method. The method is based on the local weak form collocation and the meshfree weak-strong (MWS) form. The goal of the paper is to find the temperature distribution in a rectangular plate. The results obtained are compared by those obtained by use of other numerical methods. Two types of boundary conditions are considered in this paper: Dirichlet and Neumann types. The Local Radial Point Interpolation Method (LRPIM) is used as the meshfree method. It is shown that the essential boundary conditions can be easily enforced as in the Finite Element Method (FEM), since the radial point interpolation shape functions posses the Kronecker delta property. It is also shown that the natural (derivative) boundary conditions can be satisfied by using the MWS method and no additional equation or treatment are needed. The MWS method as presented in this paper works well with local quadrature cells for nodes on the natural boundary and can be generated without any difficulty.

The increasing performance of integrated chips has introduced a growing demand for new thermal management technologies. While various thermal management schemes have been studied, thin film evaporation promises high heat dissipation rates (1000 W/cm 2 ) with low thermal resistances. However, methods to form a thin liquid film including jet impingement and sprays have challenges associated with achieving the desired film thickness. In this work, we investigated novel microstructures to control the thickness of the thin film where the liquid is driven by capillarity. Micropillar arrays with diameters ranging from 2 μm to 10 μm, spacings between pillars ranging from 5 μm to 10 μm, and heights of 4.36 μm were studied. A semi-analytical model was developed to predict the propagation rate of the liquid film, which was validated with experiments. The heat transfer performance was investigated on the micropillar arrays with microfabricated heaters and temperature sensors. The behavior of the thin liquid film under varying heat fluxes was studied. This work demonstrates the potential of micro- and nanostructures to dissipate high heat fluxes via thin film evaporation.

This study numerically explores the effect of presence of Micro-Encapsulated Phase Change Material (MEPCM) on the heat transfer characteristics of a liquid in a rectangular cavity driven by natural convection. The Natural convection is generated by the temperature difference between two vertical walls at constant temperatures. The Phase Change Material (PCM) inside the MEPCM particles melts in the vicinity of the hot wall and solidifies near the cold wall. Unlike pure liquids, the heat transfer characteristics of MEPCM slurry cannot be simply presented in terms of corresponding dimensionless controlling parameters such as Rayleigh number. In the presence of phase change particles, the controlling parameters’ values change significantly due to the local phase change. The numerical results show significant increase in the heat transfer coefficient (up to 80%). This increase is a result of the MEPCM latent heat and the increased volumetric thermal expansion coefficient due to MEPCM volume change during melting.

In this paper, the effect of the surface oscillations of a levitated droplet subject to electromagnetic and external forces, and modeled as a 3D mesh-free fluid particles system, is considered. The droplet was analyzed in a force field, which was derived from the magnetic field produced by the coil. The electromagnetic force was continuously updated with the shape and position change. To describe the fluid motion, the Navier-Stokes equations are discretized using the Moving Particle Semi-implicit (MPS) method. A numerical model based on MPS method was developed, the equations of motion were solved, the free surface of the droplet was approximated, the interface reconstructed and the oscillations frequency spectra analyzed. Two weight functions are considered and their performance compared in order to to improve the stability of MPS method.

In industrial forming processes such as extrusion or injection molding, polymeric materials experience severe thermomechanical conditions: high pressure, high deformation rates, very fast cooling kinetics and important temperature gradients. In semi-crystalline thermoplastics, such as polypropylene, these phenomena have a major influence on the crystallization occurring during cooling, which determines the final microstructure. Predicting the solidified part properties by numerical simulation requires the implementation of a crystallization kinetics model including both the thermally and flow induced effects. In this work, a numerical model simulating polymer crystallization under non-isothermal flows is developed. The model is based on the assumption that the polymer melt elasticity, quantified by the first normal stress difference, is the driving force of flow-induced extra nucleation. Two sets of Schneider equations are used to describe the growth of thermally and flow induced nuclei. The model is then coupled with the momentum equations and the energy equation. As an application, a simple shear flow configuration between two plates (Couette flow) is simulated. The relative influence of the mechanical and thermal phenomena on the crystallization development as well as the final morphology distribution is finally analyzed as a function of the shearing intensity, in terms of nucleation density and crystallite mean sizes.