In the study numerical simulations are performed to investigate the saturated fluid flow through a two dimensional microchannel (1000μm×200μm, with a superheated bottom wall) by building a comprehensive physical method and updating the standard solver in the OpenFOAM software package. On basis of previous numerical study, most of the numerical methods for the micro-scale flow boiling emphasizes the mass transfer and interfacial heat exchange. Simultaneously, geometric reconstruction technology for liquid-vapor interface is widely used, which evidently captures the interfacial boundary characteristic accurately but costs lots of computational resources. In the present study, the temperature recovery model is adopted to maintain the liquid-vapor interface temperature, and an interface-cell searching algorithm is added into the model, while the geometric interface reconstruction technology is abandoned. For the validation of the new codes developed in OpenFOAM, 1-d Stefan Problem and the experimental results of Mukherjee are both utilized to compare with our simulation results. The growth process of a single bubble in the laminar flow regime is studied in order to explore the underlying mechanism of flow boiling in microchannels. The qualitative investigation for effects of wall superheat, Reynolds number, contact angle and surface tension on heat transfer are comprehensively discussed. In general, heat flux of the bottom wall increases because of the motion of liquid-vapor interface. Wall superheat determines the rate of bubble growth on the heated wall, which is roughly proportional to wall heat flux due to the Fourier’s Law. The distribution of velocity and temperature fields in the channel refresh progressively with increasing inflow Reynolds number, which speeds up the evolution of interface position and augments the wall heat flux significantly. Furthermore, the area of thin liquid film between the wall and the bubble is enlarged by reducing the contact angle, thus augmenting the wall heat flux by several times compared with the single phase microchannel flow. However, surface tension and gravitational acceleration are found to be negligible in the present study.

A novel design of a mini heat exchanger utilizing forced convection heat transfer enhancement with electrohydro-dynamic (EHD) technique has been numerically investigated. When a high voltage is applied to a metal wire, air in its vicinity will be ionized and the injected ions will travel towards electrically grounded heat exchanger surfaces, leading to the corona wind. As a result, the corona wind disturbs the heat exchanger boundary layer and thus enhances heat transfer between the heat exchanger surface and its ambient air. A three dimensional numerical model has been developed to evaluate the heat transfer coefficient (HTC) and air side pressure drop of this EHD enhanced mini heat exchanger. Influences of position and size of the wire are evaluated in order to achieve the highest enhancement. In addition, the swirling flow pattern induced by EHD has been studied due to its important role in heat transfer enhancement. The results show a three times increase of HTC enhanced by EHD effect in present design comparing to the one without EHD effect. The most promising result shows an overall heat transfer coefficient equal to 318 W/(m 2 ·K) for a bare tube in cross flow configuration with airside pressure drop of 2.8 Pa.

Most thermal engineers will model and analyze thermal engineering cases, using any of the numerous thermal analysis software, available in the market. These commercial software need years of continuous use to be fully mastered. Large companies can afford to acquire expensive software available in the market and train their engineers; but small companies do not have the financial means to acquire such expensive software. Thus for modeling and analysis, small companies or private practice need a different alternative. Excel is one of the programs that come with Microsoft Office suite of software, which is installed on any purchased computer. Most users of Microsoft office are proficient in using Word, and can use Excel as a spread sheet to speed up calculations. Technical personnel can easily use the charting capability of Excel, but very few engineers can use Excel for intensive Numerical Analysis. Engineers should be able to use the available inexpensive Excel software to perform numerical analysis at their work place. In this article three Heat Transfer Numerical cases using Microsoft Excel are discussed in detail. the first case is two dimensional steady state heat transfer with different isothermal boundary conditions. The second shows other boundary conditions: uniform heat flux, adiabatic, and convection. The third case is transient conditions. The results from the three cases are compared with results from Patran Thermal software.

The exponential growth in electronic power has brought amazing technology but with it also comes a burden in high heat production that threatens the safety of the product since electronics’ failure rate increases by its operating temperature. As such, cooling techniques have a key role to keep the temperature of electronics devices, such as processors, memory and graphics chips, below a maximum operating temperature. In this work, a porous filled heat exchanger has been numerically modeled to investigate the cooling effectiveness and temperature distribution on the base of the heat exchanger subjected to high heat flux leaving these devices. The effects of different nanofluid coolants (0.75% double walled carbon nanotube in water (DWCNT), 1% alumina in water, and 1% diamond in 20:80 ethylene glycol/water), porous materials (copper and annealed pyrolytic graphite (APG)), and porosity values are investigated. The coolant enters from an inlet channel normal to the base, moves through the porous field, and then leaves the heat exchanger through two opposite exit channels parallel to the base. The study is performed for two and three dimensional geometries in which two different designs are studied for 3D cases. One of the designs has a rectangular cross sectional inlet channel (along transverse direction) and the other design has square one. The results indicate that utilizing APG porous matrix, for all studied coolants of pure water and water based nano fluidics, improves substantially the cooling of the base of the heat exchanger in 2D and 3D with rectangular inlet. The results also show that utilizing carbon nanofluids (DWCNT) as coolant for high porosity structures, in both copper and APG porous matrices, improves cooling efficiency and temperature uniformity over the base, for all 2D and 3D cases. The effect of inlet channel geometry, square and rectangular, is also investigated for either similar velocity or similar mass flow rate at the inlet channel entrances.

This paper investigates application of Method of Lines (MOL) and Inverse Heat Conduction techniques in spray cooling process. A flat face of a heated cylinder is cooled by using a nozzle spray and using room temperature water as a cooling fluid. The numerical analysis is done using MOL to estimate exposed surface temperature, surface heat flux, and convection heat transfer coefficient [3],[4]. Since there is no exact solution to verify the approximation result, for the verification purpose and accuracy of the result, the numerical result from this study is compared to other approximation results with experimental research done by Chen-Lee and Qiao-Chandra [1]. The results illustrate that disparity between the outcome of MOL and the one generated by Chen and Lee’s raw data is very insignificant throughout the whole time domain. This discrepancy between these two estimated results proves that MOL is a very reliable approximation technique compared to other finite element methods which require a finer mesh size and significant amount of calculations[2],[5]. However, comparing the results obtained through MOL with Qiao and Chandra shows that the difference between the estimated heat transfer coefficient and estimated heat flux converges rapidly for the short times of 0 < t < 60, but as the time passes, the MOL approximation results diverge slowly until it reaches its maximum value at ninety seconds, and the variance remains almost constant for the rest of the time period.

Three-dimensional melting problems are investigated numerically with Lattice Boltzmann method (LBM). Regarding algorithm’s accuracy and stability, Multiple-Relaxation-Time (MRT) models are employed to simplify the collision term in LBM. Temperature and velocity fields are solved with double distribution functions, respectively. 3-D melting problems are solved with double MRT models for the first time in this article. The key point for the numerical simulation of a melting problem is the methods to obtain the location of the melting front and this article uses interfacial tracking method. The interfacial tracking method combines advantages of both deforming and fixed grid approaches. The location of the melting front was obtained by calculating the energy balance at the solid-liquid interface. Various 3-D conduction controlled melting problems are solved firstly to verify the numerical method. Liquid fraction tendency and temperature distribution obtained from numerical methods agree with the analytical results well. The proposed double MRT model with interfacial tracking method is valid to solve 3-D melting problems. Different 3-D convection controlled melting problems are then solved with the proposed numerical method. Various locations of the heat surface have different melting front moving velocities, due to the natural convection effects. Rayleigh number’s effects to the 3-D melting process is discussed.

In the present work, different ventilated disc brake rotor configurations were analyzed to enhance the heat transfer rate and obtain the uniform temperature distribution in the rotor. CFD code used in this work was validated using experimental results obtained by conducting experiments on a test rig. The experimental analysis was performed to calculate the mass flow rate and heat dissipation through the rotor. Further, different types of rotor configurations viz. straight radial vane (SRV), Tapered radial vane (TRV), Alternate long and short vane (ALSV), variable diameter circular pillars (VDCP) were considered for the analysis. A rotor segment of 20° was considered for the numerical analysis due to its rotational symmetry. CFD results were in good agreement with the experimental analysis. The maximum deviation of the numerical results were about 12% from the experimental results. It is found from the analysis that among the different types of rotor configurations; variable diameter circular pillars (VDCP) rotor gives better rate of heat dissipation with more uniform temperature distribution in the flow passages. Hence for modern high speed vehicles VDCP rotor may be more appropriate.

In the present work, the performance of bi-textured micro pillar arrays has been modeled as a wicked evaporator to provide steam flow via the thin film evaporation mechanism. Bi-textured micro pillar evaporator consists of an array with rough hydrophilic pillar bases and smooth hydrophobic tips. Water wicks between the rough hydrophilic sections of the micro pillar array to cover the surface, and vaporizes from the thin films that are formed in the vicinity of the pillar walls. The stability of the phase change mechanism is increased due to the change in direction of the capillary forces at the rough-smooth interface of micro pillars. The experimental results show that the pure evaporation mechanism occurs for a surface temperature above saturation on the bi-textured micro pillar array. The numerical analysis shows that there are optimal micro pillar dimensions for each surface temperature. The evaporation mass flow rate at the optimum dimensions is higher than the pool boiling mass flow rate on a bare surface at the same surface temperature. However, the wicked evaporator performance decreases for larger evaporator sizes.

The present study examines Alternating Current (AC) electroosmotic flows in a parallel plate microchannel subject to constant wall temperature. Numerical method consists of a central finite difference scheme for spatial terms and a forward difference scheme for the temporal term. Asymmetric boundary conditions are assumed for Poison-Boltzmann equation for determining the electric double layer (EDL) potential distribution. The potential distribution is then used to evaluate the velocity distribution. The velocity distribution is obtained by applying slip boundary conditions on the walls which accounts for probable hydrophobicity of surfaces. After determining the velocity distribution numerically, the energy equation is solved by taking into account the effects of viscous dissipation and non-uniform Joule heating. The results reveal that the effect of increasing Knudsen number is a slight increase in the dimensionless temperature profile. Furthermore, the effect of increasing dimensionless time is an increase in dimensionless oscillatory temperature which leads to a steady oscillatory condition. Also, the effect of increasing dimensionless Debye-Huckel parameter is a decrease in mean oscillation value and an increase in the required time for reaching steady oscillatory condition. In addition, increasing forward or backward pressure leads to increased viscous heating near the walls. Furthermore, the effect of increasing zeta potential is an increase in the dimensionless mean velocity oscillation amplitude.

Open-cell metal foam is a class of modern porous media that possesses high thermal conductivity, large accessible surface area per unit volume and high porosities (often greater than 90%). The high porosity means very low weight. The internal structure of the foam is web-like. Internal flow inside the foam is complex and includes flow reversal, destruction of boundary layers and vigorous mixing. All of these attributes make metal foam a very attractive heat transfer core for many applications. The rather complex and intrinsically random architecture of the foam is virtually impossible to capture exactly. In this paper, we present a unit cell geometrical model that was used to represent the foam structure for numerical analysis purposes. In particular, the unit cell is used to numerically study forced convection heat transfer between aluminum foam and air. The Navier-Stokes and the governing energy equation are solved directly and the temperature fields are obtained using COMSOL. The details of the modeling process are given in this paper. The results are encouraging and lend confidence to the modeling approach, which paves the way for other investigations of the foam, as well as optimization work based on the structure of the foam.

This paper provides particulate and precipitation fouling data in five 15.54 mm I.D. copper, helically ribbed tubes taken at the condition of Re = 16000 and 800 ppm concentration. The geometries of the helical-rib tubes provided a class of internal enhancement that is typical of commercially enhanced tubes presently used in water chillers, and the ranges of geometric parameters were number of rib starts (10 to 30), helix angle (25° to 45°), and height (0.40 to 0.55 mm). A semi-theoretical model was developed to investigate the main factors of fouling formation from the fouling tests. The fouling model which started from the mass balance model considered the influences of the mass transfer coefficient, wall shear stress, sticking probability and deposit bond strength factor. The model analysis results fit the experiment data well. 3D numerical models for the experimental tubes were established, in which volume-control method and standard k-ω model were used. To explain the diversity of anti-fouling performance in different tubes, the influences of velocity field near wall to the cooling tower fouling deposition were also discussed. It is found that the fouling resistance increases with the increase of the number of starts and helix angle. The numerical results had reasonable deviations with the experimental data.

The blast furnace process is a counter-current moving bed chemical reactor to reduce iron oxides to iron, which involves complex transport phenomena and chemical reactions. The iron ore and coke are alternatively charged into the blast furnace, forming a layer by layer structural burden which is slowly descending in the counter-current direction of the ascending gas flow. A new methodology was proposed to efficiently simulate the gas and solid burden flow in the counter current moving bed in blast furnace shaft. The gas dynamics, burden movement, chemical reactions, heat and mass transfer between the gas phase and solid phase are included. The new methodology has been developed to explicitly consider the effects of the layer thickness thermally and chemically in the CFD model.

The requirement that the propellants used in launch vehicle systems must also provide the thermal energy to be converted to kinetic energy in the rocket nozzle has plagued rocket designers since the dawn of the space age. Beamed propulsion systems, however, avoid this constraint by placing the energy source on the ground and transmitting the energy to the spacecraft via microwaves. This computational work evaluates three different heat exchanger channel designs for use in a beam propulsion spacecraft. The working fluid was hydrogen and the input energy was 1.3 kW. The increase in axial temperature along the 0.1 m long channel was as high as 2000 K. In addition, it was found that despite the very small diameter of the minichannels, 1 mm, each design produced extreme temperature gradients across the channel cross section. These temperature gradients affected the velocity profile; the maximum velocity was not located at the channel center.

This paper provides a numerical analysis on precipitation and particulate fouling in a corrugated plate heat exchanger. This analysis started from the mass balance fouling model, and Realizable κ-ε model with non-equilibrium wall functions is used in the 3D numerical simulation considering the realistic geometries of the flow channel to obtained Nusselt number and wall shear stress, while Von-Karman analogy is used to obtain mass transfer coefficient. The numerical analysis is verified by experimental study. The predicted influence of fluid velocity in fouling resistance is compatible with experimental data that it can help to optimize the design of plate heat exchangers. The investigation significantly simplifies the fouling analysis of complex flow fields and can be used to assess the fouling potential of corrugated plate heat exchangers.

Heat exchangers using in-tube condensation have great significance in the refrigeration, automotive and process industries. Effective heat exchangers have been rapidly developed due to the demand for more compact systems, higher energy efficiency, lower material costs and other economic incentives. Enhanced surfaces, displaced enhancement devices, swirl-flow devices and surface tension devices improve the heat transfer coefficients in these heat exchangers. This study is a critical review on the determination of the condensation heat transfer coefficient of pure refrigerants flowing in vertical and horizontal tubes. The authors’ previous publications on this issue, including the experimental, theoretical and numerical analyses are summarized here. The lengths of the vertical and horizontal test sections varied between 0.5 m and 4 m countercurrent flow double-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The measured data are compared to theoretical and numerical predictions based on the solution of the artificial intelligence methods and CFD analyses for the condensation process in the smooth and enhanced tubes. The theoretical solutions are related to the design of double tube heat exchangers in refrigeration, air conditioning and heat pump applications. Detailed information on the in-tube condensation studies of heat transfer coefficient in the literature is given. A genetic algorithm (GA), various artificial neural network models (ANN) such as multilayer perceptron (MLP), radial basis networks (RBFN), generalized regression neural network (GRNN), and adaptive neuro-fuzzy inference system (ANFIS), and various optimization techniques such as unconstrained nonlinear minimization algorithm-Nelder-Mead method (NM), non-linear least squares error method (NLS), and Ansys CFD program are used in the numerical solutions. It is shown that the convective heat transfer coefficient of laminar and turbulent condensing film flows can be predicted by means of theoretical and numerical analyses reasonably well if there is a sufficient amount of reliable experimental data. Regression analysis gave convincing correlations, and the most suitable coefficients of the proposed correlations are depicted as compatible with the large number of experimental data by means of the computational numerical methods.

Heat exchangers using in-tube condensation have great significance in the refrigeration, automotive and process industries. Effective heat exchangers have been rapidly developed due to the demand for more compact systems, higher energy efficiency, lower material costs and other economic incentives. Enhanced surfaces, displaced enhancement devices, swirl-flow devices and surface tension devices improve the heat transfer coefficients in these heat exchangers. This study is a critical review on the determination of the condensation heat transfer coefficient of pure refrigerants flowing in vertical and horizontal tubes. The authors’ previous publications on this issue, including the experimental, theoretical and numerical analyses are summarized here. The lengths of the vertical and horizontal test sections varied between 0.5 m and 4 m countercurrent flow double-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The measured data are compared to theoretical and numerical predictions based on the solution of the artificial intelligence methods and CFD analyses for the condensation process in the smooth and enhanced tubes. The theoretical solutions are related to the design of double tube heat exchangers in refrigeration, air conditioning and heat pump applications. Detailed information on the in-tube condensation studies of heat transfer coefficient in the literature is given. A genetic algorithm (GA), various artificial neural network models (ANN) such as multilayer perceptron (MLP), radial basis networks (RBFN), generalized regression neural network (GRNN), and adaptive neuro-fuzzy inference system (ANFIS), and various optimization techniques such as unconstrained nonlinear minimization algorithm-Nelder-Mead method (NM), non-linear least squares error method (NLS), and Ansys CFD program are used in the numerical solutions. It is shown that the convective heat transfer coefficient of laminar and turbulent condensing film flows can be predicted by means of theoretical and numerical analyses reasonably well if there is a sufficient amount of reliable experimental data. Regression analysis gave convincing correlations, and the most suitable coefficients of the proposed correlations are depicted as compatible with the large number of experimental data by means of the computational numerical methods.

This study numerically examines some commercially available plate patterns of plate heat exchangers using a 3-D CFD simulation. Detailed flow distribution and heat transfer characteristics subject to three different plate patterns are examined in this study. The plate pattern include GC26 and NT10 (double chevron) and SW26. The effective surface area of the associated plate patterns are 0.8671, 0.6808, and 0.6721 m 2 , respectively. The corresponding chevron angle are 33°, 64° (double chevron) and 61°, repectively. The calculated results show that the heat transfer efficient for NT10 is higher than that of GC26 by approximately 6.35% and is higher than SW26 by 10.3%. The results indicate that the heat transfer characteristics for the double chevron plate outperform that of the single chevron plate. On the other hand, the pressure drop is also increased with the double chevron as well as chevron angle. However, it is found that the double chevron design provides a better heat transfer capability subject to identical pressure drop.

To analyze urban thermal environments more rapidly and accurately, a real urban morphology is simulated. Two models are proposed to support Reynolds Averaged Navier Stokes (RANS) simulations including: (1) a Zero-equation (ZEQ) turbulence model for outdoor airflows, and (2) convective heat transfer coefficients (CHTC) on external building surfaces. This study used commercial Computational Fluid Dynamics (CFD) software to implement the newly derived ZEQ turbulence model and CHTC wall boundary conditions. This modified version of CFD software was used to predict the thermal environment of an actual urban area including air temperatures and wind velocities. The simulated air velocities around the buildings are compared with the velocities obtained with the standard k-ε (SKE) turbulence model. The air temperatures around the buildings were compared with measured data in the actual outdoor environment. The comparisons show that this simulation method can rapidly and reliably predict a real outdoor thermal environment in an urban area.

Simulations of lithium ion batteries on a cell level are usually performed with volume averaging methods that employ effective transport properties. Bruggeman’s model, which is widely used to determine these effective properties, is solely based on the volume fraction of these porous electrodes. However, other factors like the topology and microstructure of electrodes also play a crucial role in determining effective properties. In this paper, a general derivation of the effective thermal conductivity of multiphase materials, which can be correlated with these factors, is derived using the volume averaging technique. For demonstration, three-dimensional microstructures of various porous materials are reconstructed from scanned images. These images are used to generate fully-resolved finite volume meshes representing the various constituents. The resulting mesh is then employed for numerical analysis of thermal transport, results from which are used for correlating the effective thermal conductivity with various parameters describing the microstructure. It is shown that commonly used power law exponents in the Bruggeman model for effective thermal conductivity must be recalibrated to fit the effective thermal conductivity computed from these detailed simulations.

Tripod hole film cooling designs can provide improved cooling with reduced coolant usage. It is essential to determine the impact of strong cooling near hole locations due to increased thermal gradients around the hole region. In this paper, efforts have been made to predict the same using a numerical analysis. Local temperature distribution on the blade surface causes different rates of expansion, resulting in a differential strain, furthering the impact of the numerical study and creating a need to understand the thermo-mechanical behavior of blade design. The thermal stresses that are generated near the film cooling holes are compared for different cooling hole shapes and eventually weigh the thermal advantage of a tripod hole over the cylindrical standard design. Standard k-ε was used to validate the CFD results, ensuring by a fine mesh of 5 million tetrahedrons. Validation includes comparison of the experimental results, with a numerical one where similar blade material and working temperatures are used. Upon validation, CFD was run again at engine temperature conditions with Haynes230 alloy as the blade material. Surface temperature contour enabled structural analysis using a finite element approach. Equivalent stresses (Von-Mises stresses) on the blade emerging from the analysis provided more information about stress dependency on blowing ratio.