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A structure has been proposed in this paper for generating electricity from a waste heat recovery system using various experiences of research on the exploitation of thermoelectric effect, which allows the direct conversion of thermal energy into electrical energy. For this purpose, this paper has presented a new method for waste heat recovery in industry and converting it to electricity using a thermoelectric generator (TEG). The proposed system is a combination of a heat pipe and a thermoelectric generator. Indeed, the system consists of a thermoelectric generator (TEG) based on bismuth telluride (Bi2Te3), placed between two heat pipes. The proposed system is presented in two separate designs including a heat exchanger based on simple TEM1 and volumetric TEMs and has been implemented in MATLAB software. The simulation results show that the heat exchanger based on volumetric TEMs is 18% superior to the heat exchanger with simple TEM in producing electricity.

In this research, it is investigated to numerically evaluate the performance of a polymer electrolyte membrane fuel cell (PEMFC). The performance is investigated through the nonuniformity gradient loading at the catalyst layer (CL) of the considered PEMFC. Computational fluid dynamics is used to simulate a 2D domain in which a steady‐state laminar compressible flow in two‐phase for the PEMFC has been considered. In this case, a particular nonuniform variation inside the CL along the channel is assumed. The nonuniform gradient is created using a nonisothermal domain to predict the flooding effects on the performance of the PEMFC. The computational domain is considered as the cathode of PEMFC, which is divided into three regions: a gas channel, a gas diffusion layer, and a CL. The loading variation inside the catalyst is defined as a constant slope along the channel. In order to find the optimum slope, different slope angles are analyzed. The results point out that the nonuniform loading distribution of the catalyst (platinum) along the channel could improve the fuel cell performance up to 1.6% and 5% for power density and voltage generation, respectively. It is inferred that it is better to use more catalyst in the final section of the channel if the performance is the main concern.

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 paper, multi-objective particle swarm optimization method is developed for optimizing thermo-hydrodynamic journal bearings. This paper focuses on the use of multi-objective particle swarm optimization algorithm with a combination of the thermal hydrodynamic governing equations of the fluid film (i.e. momentum and energy equations) to optimize hydrodynamic partial pad journal bearings and compare with other articles. The governing equations are solved by the central difference method with a successive over-relaxation scheme and the backward difference with an iterative technique. In the paper, the lubricant viscosity changes with the temperature variation in whole fluid film. In this optimization, the bearing power loss, the minimum oil film thickness, and the maximum oil temperature are considered as objective functions and the radial clearance and length to diameter ratio are selected as design variables. The results of the objective functions are compared to other articles. Also, this study discusses the entropy and availability of two concentric cylinders with low curvature and constant wall temperature. Calculations showed that by increasing the Eckert number, the availability increases.

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.

In this study the first and the second laws of thermodynamics are evaluated for a single effect absorption chiller. Entropy generation and COP are selected as the objective functions and their variations are studied by varying the generator temperature for various condensing temperatures. For this purpose, the enthalpy and the entropy data of the super-heated steam, saturated steam and the saturated water are formulated in the mathematical equations. Also to provide the required steam of generator, prime mover in the form of internal combustion engine is applied and its partial load conditions are analyzed. A residential tower is considered as the case study for selecting the proper prime mover capacity. The number of prime movers is estimated based on the required heating power of the generator steam for each partial load. It is seen, the entropy generation would be decreased rapidly by increasing the generator temperature and after a while, the entropy generation would be approximately constant. The optimum entropy generation for each condensing temperature and the generator temperature may be decreased by increasing the evaporator temperature. It is deduced that COP is increased rapidly by increasing the generator temperature but in the following, the COP will be constant. The maximum amount of COP is decreased by increasing the condensing temperature. Also the COP is increased by increasing evaporator temperature for a certain generator and condensing temperatures.

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.

Supplying an energy source for impressed current cathodic protection is considered as the main challenge for pipelines corrosion protection in remote areas. The purpose of this study is to construct and evaluate the performance of an impressed current cathodic protection system using waste heat to replace the external electrical power supply. The system consists of four thermoelectric modules producing the electrical power from the hot combusted gas stream. Mathematical modeling and Buckingham Pi theorem were applied to obtain five dimensionless parameters and several models to estimate the system performance. According to the experimental results, the generated voltage, electrical current, and temperature difference have been increased rapidly during the experiment up to 201 mV, 44 mA, and 20 K, respectively. Moreover, mathematical modeling and Buckingham Pi theorem were also utilized to obtain three equations, two nonlinear and one dimensionless equation, to calculate the generated electrical voltage with the maximum error of 1.22%, 9.11%, and 10%, respectively. The results indicate that the temperature difference (between inlet gas and environment) and the figure of merit have a direct effect, and heat sink thermal resistance has an inverse effect on the generated electrical voltage.

In underground U-tube heat exchangers (boreholes) it is important to predict its heating performance to design and select the proper parameters such as length, diameter, material etc. to have an optimized borehole from the point of view of heat capacity and economical aspects. For this reason, having trusty equations is vital to foresee borehole heating performance and applying it in design issues. In this study a single vertical U-tube borehole with constant wall temperature is considered and analytical equations for temperature distribution in the surrounding ground around the borehole is evaluated based on one and two dimensional heat conduction respectively. The analytical equation is compared to experimental data for a borehole with 50 m depth in which warm water of 40 C is pumped into it a time period of 120 hours and the heat transfer rate per unit length is recorded. The comparison between analytical expression and experimental data shows a good agreement between them. Also the borehole entropy generation number is studied and the optimized parameters are evaluated to minimize it. It is concluded that for the considered borehole, entropy generation number is decreased by increasing its length and by decreasing the borehole radius and pipe outer radius.

This research presents different scenarios of hybrid photovoltaic-geothermal heat pump system that can provide the requirements of the heating and cooling load consumption in a residential building during the year. One of the major purposes of the present study is to explore the optimum contribution of the solar and ground source energies in which the generation energy costs are reasonable with respect to the total costs, lifetime, and energy losses. For this purpose, a numerical dynamic model consisting of different solar photovoltaic (PV) panels of polycrystalline, monocrystalline, and thin-film cells, batteries, inverter, and ground source heat pump (GSHP) was developed using the engineering equation solver and TRNSYS software. In order to reach the best performance of the system, multi- and single-objective optimizations of the life cycle cost and irreversibility were carried out using the particle swarm optimization algorithm considering all effective parameters of the system including surface area, slope, direction of PV panels and battery capacity. Moreover, the optimization tool which was developed in MATLAB software, was adopted for data interaction between TRNSYS and MATLAB. The results indicate that among various scenarios, the optimized hybrid polycrystalline PV system with an area of 35 m2 and a solar fraction of 31% can be cost-effective up to a 24% inflation rate. Also, the payback period of the optimized hybrid system compared to the regular GSHP is 3 years with the average global costs, while this value is 10 years for Iran’s economic situation.

The purpose of this research is to present a novel approach to estimate thermal design parameters with unknown values in a building equipped with radiative panels with the use of inverse methodology. A direct model is selected to analyze thermal behavior of building components in order to determine indoor temperature field using direct numerical modeling. Using inverse analysis, three thermal design parameters with unknown values, such as conductivity, internal and external convection and total heat transfer coefficients, are estimated using Levenberg–Marquardt and conjugate gradient methods with the knowledge of temperature field resulted from direct modeling. To illustrate the sufficiency of inverse technique, the results of both noisy and non-noisy estimations are presented using sensitivity analysis. To verify the accuracy of the present study, the results of inverse analysis are compared with those of numerical simulation presented in the literature, which indicates a good agreement between numerical and inverse solutions. It is shown that inverse analysis can be used as an applicable approach to increase computational precision in building thermal design phase.

U radu se istražuju karakteristike protoka i prijenosa topline mikropolarnog toka fluida preko elastičnog lima. Istražuju se utjecaji magnetskog polja, toka topline radijacije i poroznog lima, uz pretpostavku da su viskoznost i toplinska vodljivost ovisne o temperature. Primijenjene su jednadžbe formulirane aproksimacijom graničnog sloja i teorijom mikropolarnih fluida. Za rješenje problema, parcijalne diferencijalne jednadžbe transformirane su u obične diferencijalne jednadžbe primjenom rješenja sličnosti, a dobivene jednadžbe rješavane su metodom izbacivanja i metodom Runge-Kutta četvrtog reda (fourth-order Runge-Kutta). Rezultati pokazuju da djelovanje magnetskog polja i poroznosti rezultira smanjenjem vrijednosti brzine u graničnim slojevima, strujanje topline radijacije rezultira povećanjem debljine graničnog sloja. Nadalje, debljina toplinskog graničnog sloja smanjuje se porastom usisnog parametra i redukcijom učinaka radijacijskog i magnetskog polja., In this paper, the flow and heat transfer characteristics of a micropolar fluid flow over a stretching sheet are studied. The effects of magnetic field, radiation heat flux and porous sheet are investigated, and the viscosity and thermal conductivity are supposed temperature-dependent. The governing equations are formulated by boundary layer approximation and the theory of micropolar fluids. To solve the problem, the partial differential equations are transformed into the ordinary differential equations by using similarity solutions, and the achieved equations are solved by shooting method and fourth-order Runge-Kutta. The results show that the effects of magnetic field and porousness result in decrease of the velocity values in the boundary layers, but the presence of radiation heat flux results in the growth of the boundary layer thickness. Furthermore, the thickness of thermal boundary layer declines by increase of suction parameter and reduction of radiation and magnetic field effects.

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

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.

Casting, machining and additive manufacturing technologies are used in order to produce wind tunnel testing models. The models can also be analyzed by computational fluid dynamics methods. Both have their advantages and disadvantages. Since several wind tunnel models are required to accomplish aerodynamic experiments, nowadays, one of the best methods for models and airfoils manufacturing are additive manufacturing technologies. These methods are increasingly used in aerospace industry. In this research, wing and tail of a wind tunnel test model which has complicated sections, are produced by fused deposition modeling technology. In order to improve mechanical properties and surface roughness an electroplating is used on the surface of a RP model. Metal models along with fused deposition modeling models and electroplating models were tested in wind tunnels with different angels of attack. Results indicated that aerodynamic coefficients of electroplating model with a chromium coating was closer to metal model than those of AM model without electroplating. Substituting conventionally made parts with electroplating models, saves both cost and time. These models can be used in wind tunnel tests and aerodynamic data have acceptable quality.

This work presents the optimization of a solar collector surface in solar desiccant wheel cycle which for cooling process with typical configuration naming desiccant wheel, heat exchanger and water spray evaporative cooler. In this cooling cycle the thermal solar energy has used to heat the regeneration air of desiccant wheel cycle. The optimum solar collector surface has determined by taking into account of design parameters such as velocity of air, wheel speed, thickness of the desiccant and hydraulic diameter of the desiccant wheel and also operating conditions such as outside temperature, outside relative humidity, regeneration air temperature and total solar irradiance. For this purpose, effect of desiccant wheel parameters has investigated on solar collector surface. After that, optimum design parameters and minimum solar collector surface has calculated. In this cooling process, a mathematical model has used that shows physical properties of air. The calculated values for design condition show that necessary solar collector surface has decreased about 45% in comparison of an empirical model in equal operating conditions. The results of this study show that necessary solar collector surface will be decreased by increasing inlet air temperature, inlet air humidity ratio and solar irradiance and will be increased by increasing the regeneration air temperature.

Making potable water through desalination plants is a very important process in areas where clean water is highly required. One of the most common and acceptable desalination processes is multiple effect evaporation desalination (MED) process. The main objective of this paper is optimization of MED desalination with thermal vapor compression (METVC) from economical and thermodynamic point of view. Hence, first, a comprehensive thermodynamic model for METVC is developed and then the effect of operating parameters on thermal performance of the system is analyzed. Since the values of operating parameters have a great effect on both thermal performance and cost of the plant, the optimization of these parameters is very important. In this regard, some researchers have focused on improving the economical or thermodynamic aspect of the system. However, in practice it is reasonable to optimize both these criteria simultaneously. Based on this, in order to optimize the process of METVC and show influence ...

Most wind tunnel models are fabricated of all metal components using computerized numerical control (CNC) milling machines. Fabrication of metal wind tunnel models is very expensive and time consuming. The models can require months to manufacture and are often made by small high technology companies that specialize in wind tunnel model manufacture. Using rapid prototype manufacturing techniques and materials in this way significantly reduces time and cost of production of wind tunnel models. This study was done by fused deposition modelling and their ability to make components for wind tunnel models in a timely and cost effective manner. This paper discusses the application of wind tunnel model configuration constructed using FDM and FDM with chromium coating for subsonic wind tunnel testing. A study was undertaken comparing a rapid prototyping model constructed of FDM technologies using polycarbonate to that of a standard machined steel model. Results from this study show relatively good agreement among the three models and rapid prototyping method with chromium coating does have an effect on the aerodynamic characteristics which produced satisfactory results.

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

Today, engineers are aiming for performance, quality, and repeatability, to be reached in a very short delivery time. Rapid-prototyping techniques are applied to concept design and modeling. A typical aircraft development program usually needs at least four to five wind-tunnel models to adequately test the aerodynamics of a new airframe. The models are generally made of steel or aluminum. The models can require months to be manufactured. The dimensional accuracy, surface finish, and strength of such all-metal models have a distinguished history of providing high-fidelity aerodynamics data for both subsonic and supersonic aircraft. However, the fabrication of all-metal wind-tunnel models is very expensive and time-consuming. This paper describes the effects of layer-thickness models on aerodynamic coefficients to construct wind-tunnel-testing models produced with rapid prototyping. These models were fabricated from SOMOS NanoTool by stereolithography. The layer thickness for each model was 0.025, 0.05, and 0.1 mm. Testing covered the Mach range of Mach 0.10 to 0.40. Results from this study show that layer thickness does have an effect on aerodynamic characteristics. The layer thickness is more effective on the aerodynamic characteristics when Mach number is decreased and has the most effect on the aerodynamic characteristics of axial force.

This paper describes the effects of surface finish models on aerodynamic coefficients for constructed wind-tunnel testing models. Three models were evaluated. These models were fabricated from aluminum 2024-T4 by computer numerical control (CNC) machining. The roughness of surfaces for each model was 6.3, 60, and 150 μm, which was determined by PERTHOMETER2. A wing-body-tail configuration was chosen for the actual study. Testing covered the Mach range of Mach 0.3 to 1.2 at an angle-of-attack range of +6 to +26 deg at zero sideslip and an angle-of-sideslip range of -8 to +8 deg at a 16-deg angle of attack; the 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 surface finish does have an effect on the aerodynamic characteristics in general; the data differ between the three models by less than 5%. The surface finish does have more effect on the aerodynamic characteristics when the Mach number is decreased and has the most effect on the aerodynamic characteristics of axial force and its derivative coefficients.

Danas se metode brze izrade naveliko koriste u proizvodnji modela za ispitivanje u aerotunelima. Dimenzijska točnost, površinska hrapavost i čvrstoća materijala važni su parametri koji utječu na aerodinamička svojstva modela. U ovom radu ispitivane su primjene i potencijali dviju metoda brze izrade koje se koriste u konstruiranju i izradi modela za testiranje u aerotunelima, kako bi se izmjerili aerodinamički koeficijenti. Izabrani su AGARD-B model i konfiguracija nos-tijelo-rep vozila. Prvi model je bio izrađen od metala i ABS-M30 materijala strojnom obradom i oblikovanjem nanesenog rastaljenog metala. Drugi model, AGARD-B, izrađen je postupkom trodimenzijskog tiskanja. Za poboljšanje čvrstoće i krutosti modela i održavanje ravnoteže, korišteni su metalni umetci. Modeli su napravljeni što tanji kako bi se postigla prihvatljiva dimenzionalna točnost i površinska hrapavost. Mjereni su aerodinamički koeficijenti hibridnih modela uključujući silu otpora, silu uzgona i moment posrtanja pri različitim napadnim kutovima i određenim brzinama te uspoređeni sa standardnim modelima. Rezultati pokazuju da se hibridni modeli razvijeni metodama brze izrade mogu koristiti za mjerenje aerodinamičkih koeficijenata i kalibriranje aerotunela te tako smanjiti proizvodne troškove i vrijeme. Manje devijacije aerodinamičkih koeficijenata primijećene kod hibridnih modela u usporedbi s metalnim modelima mogu nastati zbog savijanja hibridnih modela kod velikog napadnog kuta., Nowadays, rapid manufacturing methods are widely used in order to produce wind tunnel test models. Dimension accuracy, surface roughness and material strength are important parameters affecting aerodynamic properties of the models. In this research, applications and capabilities of two rapid manufacturing methods used in design and development of wind tunnel test models, built to measure aerodynamic coefficients have been investigated. In this experience, the AGARD-B model and the nose-body-tail vehicle configuration have been chosen. The first model was fabricated from metal and ABS-M30 material by machining and fused deposition modelling. The other model, AGARD-B, was fabricated by the three dimensional printing process. To improve strength and stiffness of the models and maintain balance, metal inserts have been used. Models are built to the least thickness in order to achieve acceptable dimensional accuracy and surface roughness. Aerodynamic coefficients of hybrid models including drag force, lift force and pitching moment under different angles of attack and specified speed have been measured and compared with standard models. Results imply that hybrid models developed by rapid manufacturing methods can be used for measurement of aerodynamic coefficients and calibration of wind tunnels; hence save production cost and time. Minor deviation of aerodynamic coefficients observed in hybrid models compared to metal models, can be pertained to the bending of the hybrid models under large angles of attack.