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An experimental setup for pool boiling of dilute dispersions of titanium dioxide (TiO2) nanoparticle in water-ethylene glycol 50 (WEG50) as the base fluid was developed. The nanofluid was stabilized by using sodium lauryl sulfate as a surfactant. The heater surface roughness was affected by the deposition of nanoparticles during boiling which consequently changes the heat transfer characteristics. Three copper heater surface roughnesses: smooth, semi-rough and rough, were used. The effect of surface roughness and nanofluid on boiling heat transfer coefficient (BHTC), surface wettability and nucleation site density were examined. The results showed that BHTC and nucleation site density were increased by increasing the heater surface roughness in the base fluid of WEG50. The findings of this study revealed that the effect of volume concentration of nanofluid on the BHTC significantly depends on the heater surface roughness. At heater surface roughness of 0.062 μm, BHTC increases compared to WEG50 base fluid for all volume concentrations of TiO2-WEG50 nanofluid. With increasing the volume concentration of nanofluid up to 0.005%, an increasing tendency in BHTC was observed but beyond that a decreasing trend was observed for heater surface roughness of 1.213 μm. However, as heater surface roughness reaches 3.146 μm, BHTC decreased by increasing nanofluid volume concentration, compared to WEG50 base fluid. Also, increment of heater surface roughness causes the nucleation site density to increase when either base fluid or nanofluid is used. By measuring static contact angle of sessile water droplet on heater surface before and after experiment, it was found that using TiO2-WEG50 nanofluid causes to surface wettability increased.

This study has been conducted to illustrate combined heat transfer in a PolyMethylMethAcrylate (PMMA) sample. PMMA is a promising polymer utilized to optical, pneumatic actuation, sensor, analytica...

This paper investigated an optimization model for heat exchanger network by detailed design method for each heat exchanger unit. Particle swarm optimization technique is used to determine to optimum results in the mixed material heat exchanger network which included the capital and energy costs of heat exchangers. Mixed materials used in corrosive flows and included three types of exchangers such as cheap, expensive and mixed. Two methods used for achieving the optimum the total annual cost in mixed materials heat exchanger networks such as total and partial decompositions methods. The case study was used to show the application of the proposed method. The total annual cost has been reduced by detailed design in each heat exchanger by optimization technique. It has been reduced 20.7% compared with initial case in full integration method. The reduction of the total annual cost by detailed design in the partial decomposition method is 12.4% compared with the full integration method and 5.78% compared with the total decomposition method.

In this study, the synthetic jet position was optimized to obtain the maximum rate of heat transfer and the best state of temperature uniformity on a heated surface in micro-channels. Based on micro-channel length, several cases were simulated to investigate the effects of synthetic jet position on the heat transfer rate and temperature uniformity. After that, the synthetic jet position was optimized using the CFD results and the GMDH-MOGA optimization code. The obtained results show that the synthetic jet placement in all longitudinal positions of micro-channel increases the heat transfer rate, although the improvement of temperature uniformity of heated surface decreases at some positions as compared to the micro-channel without synthetic jet. The optimization results show that for obtaining the maximum value of heat transfer and the best state of temperature uniformity on the heated surface, the dimensionless longitudinal position of synthetic should be between 0.45 and 0.65. The maximum rate of heat transfer and the best state of temperature uniformity have been observed in the vicinity of lower and upper bounds of this range, respectively.

Motivation The inconvenient treatment of the current velocity-pressure coupling strategies is still a debating issue. Whether the procedures are formed on coupled or segregated solution strategy, the substituted equation for pressure, which is applied instead of the original continuity equation, is known to cause convergence problems for complex fluid flow situations. Challenge and approach The present study aims to evaluate two fully implicit, non-pressure-based coupled algorithms known as FICS and SICS (Fully/Simplest Implicit Coupled Procedures) that are able to solve the flow equations without utilizing any additional formulations (Poisson-type or else) for pressure. To do so, a numerical code using C++ was developed, and the noted coupled procedures were implemented alongside the well-known SIMPLEC (Semi-Implicit-Pressure-Linked-Equation-Consistent) algorithm, which was utilized as a benchmark procedure. The evaluations of the noted algorithms seek to compare the stability, solution speed, and compatibility to various physical phenomena such as turbulence and heat transfer that are the main subjects used to compare the fluid mechanic procedures. Significant results Obtained results indicate that coupled procedures are irrefutably stable whether only the laminar equations are solved or other highly influential scalar equations have participated. As an instance, it was observed that FICS-2 achieved convergence at least two times faster than SIMPLEC while applying the least amount of relaxation to amend for both non-linearity and the pressure-velocity coupling. Impact of the study and conclusion As a result, it is concluded that the primitive form of continuity equation is a more efficient alternative than the standard Poisson-based formulation and could be considered for future developments in commercial CFD purposes.

Thermal analysis of fluid flow is always regarded as an important research issue within cavities in order to become familiar with the characteristics of fluid flow phenomenon in enclosures. This research paper investigates the fluid and heat transfer analysis of fluid flow inside a triangular cavity using natural element methodology (NEM). This Galerkin-based methodology has been introduced for a decade and almost demonstrated its efficiency in the numerical heat transfer analysis of problems in most engineering sciences. The fluid flow contains natural convection along with conduction and radiation heat transfer with medium's walls, which have absorbing, emitting, semitransparent, and nonscattering characteristics. The final results investigate the effects of radiative and natural convection heat transfer on the fluid flow pattern as expressed in Rayleigh number, stream function, strength of natural convection regime, etc., which are checked with other similar studies presented in the literature and shows how promising NEM can be as an efficient numerical approach to improve computational precision when dealing with fluid mechanic problems.

In this paper the effects of radiation and dissipation in the entropy generation in microtube is evaluated. Governing equations are solved with analytically solution. Fluid flow in the entrance area is laminar and independent of time, and radiation is also a fluid property. Results in this paper extracted with dimensionless numbers Knudsen (k n ), Brinkman (Br) and Prandtl (Pr) that compared with the case without radiation. It is shown that entropy generation decreases with increasing Knudsen number. It can be observed that increasing Br augments the entropy generation.

In this study, effects of two different arrangements and π-radian phase difference in the oscillation of membranes of three synthetic jets, in a cross-flow of a micro-channel, on heat transfer and temperature distribution uniformity of a hot wall, located at certain distance from the synthetic jet outlet, were numerically studied by a three-dimensional model using dynamic mesh. Obtained results show that synthetic jets provide better cooling for the hot plate; however, the position and phase difference of the oscillation in the actuators of the synthetic jets are effective on the degree of cooling improvement. Depending on the position and operating conditions of the synthetic jets, reduction in the average temperature of the hot plate and increase in the Nusselt number vary from 21% to 28% and from 64% to 92% as compared to micro-channel without synthetic jet, respectively. In addition, operation of the synthetic jets improved temperature uniformity over the hot wall and improvement varies from 34% to 47% as compared to case of no synthetic jet in the micro-channel.DOI: http://dx.doi.org/10.5755/j01.mech.23.1.14091

In this paper a new model and computer code is presented by considering singular and discontinuous heat flow divergence. A hybrid model including Smith’s WSGG model and Coppale and Vervish’s model is used for calculating gas radiative properties. Energy equation is solved simultaneously to reach temperature field which specify gas radiative properties. S 8 order of discrete ordinate method is used to solve RTE. It is assumed that walls of enclosure are gray, diffuse and opaque with specified temperature. Boundary conditions are corrected in each iteration that change temperature field.

An analytical study on entropy generation considering viscous dissipation effect in the circular microchannel is reported. The fluid flow is steady, laminar, hydrodynamically fully developed and thermally developing. In the first law analysis, appropriate dimensionless variables are applied to solve the energy equation in the thermal entrance region of microchannel. Subsequently the obtained temperature field is used to derive an expression for entropy generation rate. The effect of Knudsen number and Brinkman number on the entropy generation rate and Bejan number in different axial location is presented.

The effect of MHD on steady two-dimensional laminar mixed flow about a vertical porous surface is numerically analyzed. Also the effects of radiation and heat generation and absorption are considered. A power law variation of temperature along the vertical wall is assumed. The nonlinear boundary-layer equations were transformed and the resulting differential equations were solved by an implicit finite difference scheme (Keller box method). Numerical results for the velocity distribution and the temperature distribution are presented for various values of Prandtl number Pr, magnetic parameter, porous medium parameter and internal heat generation or absorption coefficient. Further validation with previous works is carried out.

Most of two-phase heat transfer analysis involve estimation of dry-out phenomenon in order to find whether it takes place and if so, at what location in the tube it will happen. Dry-out phenomenon considerably reduces heat transfer rate and it should be avoided as far as possible. Entrainment highly affects dry-out occurrence chance and location. Therefore a great attention should be paid on simulation of entrainment in order to have a good estimation of heat transfer and to safely design thermal systems.Although there are many models available for simulation of entrainment phenomenon, few are instrumentally employed in heat and fluid flow analyses, since most of those are empirical and limitedly can be applied due to the restricted conditions of experiments. There also are few theoretical approaches in the literature for simulating entrainment phenomenon by applying the physical potential of entrainment but some of those have a considerable deviation from the available empirical models. In the present study a conceptual approach is employed to simulate entrainment. In this regard the most important potential of this phenomenon, known as interfacial waves, are studied and modeled to find how they will lead to entrainment and how much the amount of entrainment is in vertical annular two-phase flows. An entrainment correlation is proposed at the end and will be compared with the available empirical ones for the verification objectives.

Microgeometry fluid dynamics has gotten a lot interest due to the arrival of Micro-Electro-Mechanical systems (MEMS). When the mean free path of a gas and characteristic length of the channel are in the same order, continuum assumption is no longer valid. In this situation velocity slip and temperature jump occur in the duct walls. Fully developed numerical analysis for characteristic laminar slip flow and heat transfer in rhombus microchannels are performed with slip velocity, and temperature-jump boundary condition at walls. The impacts of Reynolds number (0.1 Re

Nowadays, rapid prototyping (RP) methods are widely used to produce wind tunnel testing models and thickness of layers is an important parameter that affects the aerodynamic characteristics of model. This paper described the Affects layer thickness models product with rapid prototyping on Aerodynamic Coefficients for Constructed wind tunnel testing models. Three models were evaluated. These models were fabricated from ABSi by a fused deposition method (FDM). The layer thickness was 0.178mm, 0.254mm and 0.33mm. The roughness of surfaces for each model was 25/m, 63/m and 160/m (RZ) that determined by perthometer2. A wing-body-tail configuration was chosen for the actual study. Testing covered the Mach range of Mach 0.3 to Mach 1.2 at an angle-of-attack range of -4° to +16° at zero sideslip. Coefficients of normal force, axial force, pitching moment, and lift over drag are shown at each of these Mach numbers. Results from this study show that layer thickness does have an effect on the aerodynamic characteristics in general; the data differ between the three models by fewer than 6%. The layer thickness does have more effect on the aerodynamic characteristics when Mach number is decreased and had most effect on the aerodynamic characteristics of axial force and its derivative coefficients.

For faster new product introduction aerospace companies are interested in reducing the time it takes to make wind tunnel models. The increased capability of rapid prototyping technologies has made them attractive for this purpose. An experimental study was done of rapid prototyping technology and their ability to make components for wind tunnel models in a timely and cost effective manner. This paper discusses the application of wing-body-tail configuration constructed using fused deposition method (FDM) for Subsonic and transonic wind tunnel testing. An experimental study was undertaken comparing a rapid prototyping model constructed of FDM Technologies using ABSi (Acrylonitrile butadiene styrene) to that of a standard machined steel model. Testing covered the Mach range of Mach 0.3 to Mach 1.3 at an angle-of-attack range of + 4° to +26° at zero sideslip and at angle of-sideslip ranges from –10 to +10 degrees at 16 degrees angle-of-attack.. Results from this study show relatively good agreement between the two models. It can be concluded that FDM model show promise in preliminary aerodynamic development studies and reduction in time and cost.

A method is developed for obtaining transient temperature distribution in a cooling semitransparent layer of ceramic. The layer is emitting, absorbing, isotropically scattering and heat conducting with a refractive index ranging from 1 to 2. The solution involves solving simultaneously the energy equation and the integral equation for the radiative flux gradient. The energy equation is solved using an implicit finite volume scheme and the integral equation of radiative heat transfer is solved using the singularity technique and Gaussian integration. The effects of scattering are investigated. It is shown that scattering has a significant effect on the transient temperature distribution and the transient mean temperature of the layer.

The behavior of a heat-conducting, absorbing, and emitting layer of ceramic is considered, during transient combined conductive–radiative heat transfer. The solution includes the equation of radiative transfer within the material coupled to a transient energy equation that contains both radiative and conductive terms. It is based on nodal analysis and Hottel's zonal method extended by the ray tracing method. The transient energy equation including a radiative internal energy source is solved using a time marching finite difference procedure with variable space and time increments. The effects of the influence parameters, optical thicknesses, and refractive index of the layer are considered carefully.