Technological advancement, as well as consumer demands, has motivated the miniaturization of electronic/mechanical systems and increase of device power and performance. The notebook computer is not an exception, and innovative thermal management solutions must be employed to compensate for the increased heat dissipation in the space-constrained enclosures. The majority of current cooling systems in laptop computers rely on heat pipes attached to a remote heat exchanger with micro-fans providing forced convection to reject heat to the ambient, however this technique can not accommodate the increasing heat fluxes in the confined laptop enclosure. In this study, a two-phase closed loop cooling system is designed and tested for a laptop computer. The cooling system consists of an evaporator structure containing boiling structures connected to a compact condenser with mini fans providing external forced convection. A pump is also incorporated to assist the return of the condensate back to the evaporator. The cooling system is characterized by a parametric study which determines the effects of volume fill ratio of coolant, initial system pressure, and pump flow rate on the thermal performance of the closed loop. Experimental data shows the optimum parametric values which can dissipate 25 W of chip power with a chip temperature maintained at 95C. Numerical analysis provides additional data to further enhance the heat dissipation from the external air-cooled side of the condenser by studying the effects of ventilation and air flow rate across the system. Thermal management of mobile systems must be considered during the early design phases, and this research shows the feasibility of implementing of a two-phase cooling system to dissipate 25 W in a laptop computer.

This text pursues the causes and phenomena in the course of the collapse of the molten metal layer surrounding a keyhole which is full of vapor and liquid particles during the high energy laser or electron beam drilling process. And the formation mechanism of the pores for the drilling process, to study the collapse phenomenon of the liquid layer is essential. In the research the collapse of the keyhole is taken as approximated to a transition between the slug and annular two-phase flows in a vertical pipe of varying cross-section. We develop and solve a quasi-steady, one-dimensional model for two phase flow with the assumption that the mixture in the core homogenous, ignoring the friction of the liquid layer, regarding the flow in the keyhole as supersonic, considering the mass transfer of the liquid layer to the keyhole. Two-phase flow can be liquid particle entrainment characteristics, infiltration precipitation, divided into two regions. The collapse of keyhole resulted from the infiltration of the liquid particles is chained to the pore formation. Based on the realization of annular two phase flow, In this text, that the liquid into the holes in the physical properties and caused pores formation.

This project is to explore the manufacturing and processing of laser or electron beam, formed on the surface morphology after curing and processing parts, such as surfacefilled, depression, or the formation of ripples; These reactions will directly affect the surface heat treatment and welding quality of thefinished product This study to consider the mass, momentum and energy equations, the introduction of theinterface and boundary conditions to simulate the real process In order to promote quality stability, and a large amount of production capacity and reduce costs, we must understand the institutions of the reaction In this thesis, the phase field method (Phase-field method) (Two-phase flow) two-phase flow simulation of metal surface by a concentrated source of heat melt the transient heat flow behavior

The study applies the phase-field method to simulate the behavior between bubble and liquid-solid front in the solidification. During the process, the two-phase flow module is used to match up with temperature and phase-field function to determine the percentage of- solid, liquid, and gas- in the domain. The governing equations for mass, momentum and energy contain coefficients which are related to percentage of phases.The result show that the surface tension and the temperature difference will influence the shape of bubble and the velocity of solidification.

On the efforts to provide a reliable source of experimental information on turbulent subcooled boiling ow, time resolved Particle Tracking Velocimetry (PTV) experiments were carried out using HFE-301 refrigerant ow through a vertical rectangular channel with one heated wall. Measurements were performed at liquid Reynolds numbers of 3309, 9929 and 16549 over a wall heat flux range of 0.0 to 64.0 kW=m2. From the PTV measurements, liquid two dimensional turbulence statistics are available, such as: instantaneous 2-D velocity fields, time-averaged axial and normal velocities, axial and normal turbulence intensities, and Reynolds stresses. The present results agree with previous works and provide new information due to the 2-D nature of the technique, for instance, this work shows that by increasing heat ux, the boiling bubbles influence on the liquid phase is portrayed as a persistent increase of axial velocity on regions close to the heater wall. This persistent increase on the axial velocity reaches a maximum value attributed to the terminal bubble velocity. These new observed phenomena must be considered for the development and improvement of two-phase ow turbulence models. To this end, an extensive error analysis was also performed with emphasis on the applicability of the PTV measurement technique on optically inhomogeneous flows. The error quantification exhibited negligible optically induced errors for the current conditions, making the data acquired in this work a vast and reliable source.

In this dissertation we discuss some upscaling methods for flow and transport in heterogeneous reservoirs. We studied realization-based multi-phase flow and transport upscaling and ensemble-level flow upscaling. Multi-phase upscaling is more accurate than single-phase upscaling and is often required for high level of coarsening. In multi-phase upscaling, the upscaled transport parameters are time-dependent functions and are challenging to compute. Due to the hyperbolic feature of the saturation equation, the nonlocal effects evolve in both space and time. Standard local two-phase upscaling gives significantly biased results with reference to fine-scale solutions. In this work, we proposed two types of multi-phase upscaling methods, TOF (time-offlight)- based two-phase upscaling and local-global two-phase upscaling. These two methods incorporate global flow information into local two-phase upscaling calculations. A linear function of time and time-of-flight and a global coarse-scale two-phase solution (time-dependent) are used respectively in these two approaches. The local boundary condition therefore captures the global flow effects both spatially and temporally. These two methods are applied to permeability distributions with various correlation lengths. Numerical results show that they consistently improve existing two-phase upscaling methods and provide accurate coarse-scale solutions for both flow and transport. We also studied ensemble level flow upscaling. Ensemble level upscaling is up scaling for multiple geological realizations and often required for uncertainty quantification. Solving the flow problem for all the realizations is time-consuming. In recent years, some stochastic procedures are combined with upscaling methods to efficiently compute the upscaled coefficients for a large set of realization. We proposed a fast perturbation approach in the ensemble level upscaling. By Karhunen-Lo`eve expansion (KLE), we proposed a correction scheme to fast compute the upscaled permeability for each realization. Then the sparse grid collocation and adaptive clustering are coupled with the correction scheme. When we solve the local problem, the solution can be represented by a product of Green's function and source term. Using collocation and clusering technique, one can avoid the computation of Green's function for all the realizations. We compute Green's function at the interpolation nodes, then for any realization, the Green's function can be obtained by interpolation. The above techniques allow us to compute the upscaled permeability rapidly for all realizations in stochastic space.

A new two phase separator for use in space applications has been invented. It is a vortex separator designed to accommodate gas driven two phase flows of gas and liquid. The work presented here is a first of a kind study of this newly invented separator and is meant to determine the minimum inlet gas flow rate necessary for a stable vortex inside the separator for different separator geometries. A dimensional scaling analysis was done to predict this minimum inlet gas flow rate. Experiments were performed on the ground and in conjunction with NASA using their microgravity simulating plane to determine this minimum inlet gas flow rate. The results of the experiments and scaling analysis are compared. The new design consists of two chambers, a vortex generator and a separation chamber, meant to divide the functions of vortex creation and phase separation. The two phase flow is injected tangentially into the vortex generator causing the inlet linear momentum to be transformed into azimuthal momentum. The two phase mixture in the vortex generator then moves into the separation chamber where the two phases separate due to the density difference between the phases. The dimensional scaling analysis used the Weber number to predict the minimum rotational velocity of the spinning flow in the separation chamber during a stable vortex. This rotational velocity was related to the inlet gas flow rate by the inlet momentum rate. The scaling used the dimensions of each separator tested to predict the minimum inlet gas flow rate needed for a stable vortex. In all, twelve separators were tested, eleven on the ground and one on the plane. The ground testing was a parametric study varying the sizing of the separator components. The flight experiments kept the separator geometry constant and varied the gravitational field in which the separator operated. In general, the minimum inlet gas flow rate increased with the ratio of separation chamber diameter to vortex generator diameter. This same trend was consistent with the dimensional scaling analysis. Also, the inlet flow rate increases with gravitational acceleration.

This thesis investigates the refrigerant (R-134a) flow in a minitube experimentally. The small scale heat transfer is a relatively new research area and has been in favor since the end of 1970&rsquo / s. Refrigerant flow in mini- and microscale media is a potential enhancement factor for refrigeration technology in the future. For the forthcoming developments and progresses, experimental studies are invaluable in terms of having an insight and contributing to the establishment of infrastructure in the field in addition to leading the numerical and theoretical approaches. The studies in the literature show that low mass flow rate and constant wall temperature approach in minitubes and minichannels were not among the main areas of interest. Therefore, an experimental set-up was prepared in order to perform experiments of two-phase refrigerant flow in a 1.65 mm diameter copper minitube with the constant wall temperature approach. The design, preparation, and modifications of the experimental set-up are explained in this thesis. Two-phase flow and quality arrangements were done by pre-heating the refrigerant at saturation pressure and the constant wall temperature was achieved by a secondary cycle with water and ethylene glycol mixture as the working fluid. The heat transfer coefficient and the pressure drop for the two-phase flow with varying quality values and saturation temperatures of the refrigerant were calculated and compared with the results available in literature.

A novel technique to study the two-phase flow field around an asymmetric diaphragm in a vertical pipe is presented, that enables producing data for CFD code validation in complex geometries. Main feature is a translocation of the diaphragm to scan the 3D void field with a stationary wire-mesh sensor. Besides the measurement of time-averaged void fraction fields, a novel data evaluation method was developed to extract estimated liquid velocity profiles from the wire-mesh sensor data. The flow around an obstacle of the chosen geometry has many topological similarities with complex flow situations in bends, T-junctions, valves, safety valves and other components of power plant equipment and flow phenomena like curved stream lines, which form significant angles with the gravity vector, flow separation at sharp edges and recirculation zones in their wake are present. In order to assess the quality of the CFD code and their underlying multiphase flow and turbulence models pre-test calculations by ANSYS CFX 10.0 were carried out. A comparison between the calculation results and the experimental data shows a good agreement in term of all significant qualitative details of the void fraction and liquid velocity distributions. Furthermore, the report contains a method to assess the lateral components of bubble velocities in the form of a basic theoretical description and visualisation examples. The plots show the deviation of the flow around the obstacle in term of vectors represented the average velocities of the instantaneous cross-sections of all bubbles in the time interval when they pass the measuring plane. A detailed uncertainty analyse of the velocity assessments concludes the presented report. It includes remarks about the comparison with a second method for calculating bubble velocity profiles - the cross-correlation. In addition, this chapter gives an overview about the influence of acceleration and deceleration effects on the velocity estimation.

Two-phase flow experiments at vertical pipes are much suitable for studying the action of different constitutive relations characterizing the momentum exchange at the gas/liquid interface as well as the dynamic behaviour of the gas/liquid interface itself. The flow can be observed in its movement along the pipe and, in particular, within the shear field close to the pipe wall over a considerable vertical distance and, consequently, over a comparatively long time without the immediate separation of gas and liquid characteristic for horizontal flows. Wire-mesh sensors, which were the working horse in the described experiments, supplied sequences of instantaneous two-dimensional gas fraction distributions with a high-resolution in space and time. This allows to derive from the data not only void fraction and bubble velocity profiles, but also bubble size distributions, bubble-size resolved radial gas fraction profiles as well as the axial evolution of these distributions. An interfacial surface reconstruction algorithm was developed in order to extract the extension of interfacial area from the wire-mesh sensor data. The sensors were upgraded to withstand parameters that are close to nuclear reactor conditions. Most of the experiments were performed for both air/water flow at ambient pressure and steam/water flow of up to 6.5 MPa at identical combinations of the gas and liquid superficial velocities. This offers excellent conditions for studying the influence of the fluid properties.