Thermal Science

This paper analyzes the effects of coal grindability and its characteristics on the grinding capacity and power consumption for beater wheel mill during exploitation in thermal power plant TENT B in Obrenovac, Serbia. For this purpose, experiments were made on the mill, before and after its reconstruction. Experiments included the determination of grinding capacity, mill power consumption, and laboratory analysis of coal characteristics and Hardgrove grindability index (HGI). The analysis of experimental results found that the grinding capacity has a negative correlation with the ash content in coal. Moisture content in analysis sample of coal has a positive correlation with the consumption of electricity and grinding capacity. Between the grinding capacity and the value of HGI exists a negative correlation. Analysis of the influence of grindability of coal and coal characteristics on grinding capacity and energy consumption was carried out. Based on coal characteristics and values of HGI, mathematical expressions were derived for the calculation of grinding capacity and electric energy consumption. In addition, ability to predict specific power consumption of the mill on the basis of HGI values, were carried out. Specific power consumption obtained from HGI values showed good agreement with the experimentally determined specific power consumption of the mill.

This study discuss the application of Taguchi method in assessing maximum cooling tower effectiveness for the counter flow cooling tower using expanded wire mesh packing. The experiments were planned based on Taguchi?s L27 orthogonal array .The trail was performed under different inlet conditions of flow rate of water, air and water temperature. Signal-to-noise ratio (S/N) analysis, analysis of variance (ANOVA) and regression were carried out in order to determine the effects of process parameters on cooling tower effectiveness and to identity optimal factor settings. Finally confirmation tests verified this reliability of Taguchi method for optimization of counter flow cooling tower performance with sufficient accuracy.

In this paper we investigate theoretically the unsteady boundary layer flow and heat transfer over a permeable shrinking sheet with non-uniform heat source. The nondimensional governing equations have been solved numerically using the bvp4c function from Matlab for different values of the pertinent parameters;

Aiming at developing a more common method for predicting two-phase flow pressure drop for small channels, experiments on frictional pressure drop of air-water flow in a vertical narrow rectangular duct with a cross-section of 40 mm by 1.6 mm were conducted at atmospheric pressure. The mass flow rates of air and water covered the ranges from 0.03 to 12.5 kg/h and from 19 to 903 kg/h, respectively. It was found that the two-phase flow can be divided into three regions according to the liquid only Reynolds number, by which a modified Chisholm two-phase multiplier was proposed for predicting frictional pressure drop. Some leading correlations for predicting two-phase flow pressure drop were compared with the new correlation against current experimental data, the latter had and a mean deviation of 7.2%, showing a better agreement with the experimental results.

Numerical investigations on the turbulent fluid flow and the local heat transfer from rectangular bars for three different aspect ratios were carried out with Re=22000 and Pr=-0.71. The standard k-e turbulence model and a modified version were used in conjunction with the Reynolds-averaged momentum and energy equations for the simulations. The predictions of drag, lift, local and global heat transfer coefficients on the front, side and on the rear face of the rectangular bars are compared with available experimental results.

The convection differential models play an essential role in studying different chemical process and effects of the diffusion process. This paper intends to provide optimized numerical results of such equations based on the conformable fractional derivative. Subsequently, a well-known heuristic optimization technique, differential evolution algorithm, is worked out together with the Taylor's series expansion, to attain the optimized results. In the scheme of the Taylor optimization method (TOM), after expanding the functions with the Taylor's series, the unknown terms of the series are then globally optimized using differential evolution. Moreover, to illustrate the applicability of TOM, some examples of linear and non-linear fractional convection diffusion equations are exemplified graphically. The obtained assessments and comparative demonstrations divulged the rapid convergence of the estimated solutions towards the exact solutions. Comprising with an effective expander and efficient optimizer, TOM reveals to be an appropriate approach to solve different fractional differential equations modeling various problems of engineering.

The Lagrangian code LAG3D for dispersed phase flow modeling was implemented with the introduction of bubble break-up model. The research was restricted on bubbles with diameter less than 2 mm, ie bubbles which could be treated as spheres. The model was ...

This pa per pres ents an on-go ing re search pro ject that aims to iden tify pos si bil i ties for wider use of evap o ra tive cool ing in pro cess in dus try, es pe cially the use of evapo ra tive fluid cooler units. Ex per i men tal study is per formed on small scale evap o rative fluid cooler, while the cor re la tion based model has been car ried out to ex plore the de tailed heat and mass trans fer pro cesses in side this unit. Nu mer i cal in te gration of math e mat i cal model is ex e cuted by new ap proach, based on dif fer en tial, collo ca tion Simpson method. Pro posed mod els have been ver i fied by com par ing the com puted re sults with those ob tained by the ex per i men tal mea sure ments. The results of re search will en able the cre ation of more com pre hen sive sim u la tion software, with wider range of op er at ing and con struc tion pa ram e ters.

1. Department of Mechanical Engineering, Saga University, 1, Honjo-machi, Saga-shi, Saga 840-8502, Japan 2. Department of Mechanical Engineering, Khulna University of Engineering & Technology, Khulna-9203, Bangladesh 3. School of Mechanical Engineering, Andong ...

Large-capacity compressors in industrial plants and the compressors in gas turbine engines consume a considerable amount of power. The compression work is a strong function of the ambient air temperature. This increase in compression work presents a significant problem to utilities, generators and power producers when electric demands are high during the hot months. In many petrochemical process industries and gas turbine engines, the increase in compression work curtails plant output, demanding more electric power to drive the system. One way to counter this problem is to directly cool the inlet air. Inlet fogging is a popular means of cooling the inlet air to air compressors. In the present study, experiments have been performed to investigate the suitability of two-fluid nozzle for inlet fogging. Compressed air is used as the driving working gas for two-fluid nozzle and water at ambient conditions is dragged into the high-speed air jet, thus enabling the entrained water to be atomized in a very short distance from the exit of the two-fluid nozzle. The air supply pressure is varied between 2.0 and 5.0 bar and the water flow rate entrained is measured. The flow visualization and temperature and relative humidity measurements are carried out to specify the fogging characteristics of the two-fluid nozzle.

a Fac ulty of Elec tri cal En gi neer ing and In for ma tion Tech nol o gies, Ss. Cyril and Methodius Uni ver sity, Skopje, Mac e do nia b Re search Cen ter for En ergy, In for ma tics and Ma te ri als, Mac e do nian Acad emy of Sci ences and Arts, Skopje, Mac e do nia Orig i nal sci en tific pa per UDC: 620.97:662.767.2

In this paper multiple criteria decision making approach of alternative fuels for waste collection vehicles in southeast region of Serbia was presented. Eight alternative fuels and advanced vehicle technologies were ranked according to thirteen criteria, including financial, socio-technical, and environmental. Assessment of alternatives was performed by using the weighted aggregated sum product assessment method and results were verified using multi-objective optimization on the basis of ratio analysis method. Considered criteria were obtained from previous researches and by assessment of professional experts from manufacturing industries, public utility companies, and academics institutions. The analysis showed that both biodiesel fuels - derived from used cooking oil or from vegetable oils are the best alternative fuels for Serbian waste collection vehicles in this point of time. Compressed natural gas-powered vehicles were also ranked high in this analysis, but due to the lack of...

The behavior of the mast is non-linear due to its slenderness and compliant guy-support system, having a tendency to lose stability and even crush suddenly. Wind load is one of the main factors affecting the stability of the structure of the mast. Structural assessment of the different mast configurations has been investigated in the past. Furthermore, European standards EN 1993-3-1:2006 and EN 1993-1-6:2007 already provides some guidelines about the basis of structural analysis of masts and towers. This paper presents the results of numerical simulations of a guyed mast exposed to wind action using finite element method. Structural analyses were performed for three different constant wind loads, modal analysis provides the values of natural frequency and mode shapes, while the stability analysis was performed for the first three buckling load factor values. The motivation for this study is to investigate the contribution of finite element method to structural analysis of a lattice structure such as guyed mast as an alternative and/or improvement to the literature and codes.

A numerical investigation of the airside performance of a plain fin-and-tube heat exchanger having 4 row configurations has been presented in this study. Fluid flow is steady, incompressible and three dimensional. Laminar (400<Re H <1200) and transitional (1300<Re H <2000) flow conditions are considered for both in-line and staggered tube arrangements. For transitional flow calculations, the k-ω turbulence model is used. Uniform flow with constant velocity and temperature are considered at inlet and no-slip boundary condition and constant wall temperature is assumed at fin and tube surfaces. In this study the geometrical parameters such as fin pitches, longitudinal pitches and transverse pitches of tube spacing are studied. The results are compared with previous experimental data of Wang et al. [1]. Results are presented in the form of friction factor (f) and Colburn factor (j). For both laminar and transitional flow conditions heat transfer and friction factor decrease ...

The objective of the paper is to show the implementation of infrared thermography within world class manufacturing maintenance strategy. The results from infrared thermography inspections in a food processing and packaging solutions company were presented. Applicability of the infrared thermography, during a two-year period, caused a substantial reduction of the potential breakdown in the pilot area. Upon feasibility confirmation, the proposed method was spread to other production equipment of the company.

Two-dimensional periodically fully developed laminar forced convection fluid flow and heat transfer characteristics in a horizontal channel with staggered fins are investigated numerically under constant wall heat flux boundary condition. Study is performed using ANSYS Fluent 6.3.26 which uses finite volume method. Air (Pr 0.7) and Freon-12 (Pr 3.5) are used as working fluids. Effects of Reynolds number, Prandtl number, fin height, and distances between two fins on heat transfer and friction factor are examined. Results are given in the form of non-dimensional average Nusselt number and average Darcy friction factor as a function of Reynolds number for different fin distances and Prandtl numbers. The velocity and temperature profiles are also obtained. It is seen that as the fin distance increases, behavior approaches the finless channel, as expected. Also, thermal enhancement factors are given graphically for working fluids. It is seen that heat transfer dominates the friction as b...

A large number of producers offer a wide choice of various types of industrial cooling towers. Usually, a proper choice of pre-fabricated cooling tower satisfies end-user needs. However, if there are specific end-user requirements, it is necessary to design cooling tower according to those requirements. For the adhesive factory located in southern region of Serbia, 350 kW mechanical draught wet cooling tower was designed and built. Dimensioning of the cooling tower was done according to parameters of the ambient air, higher than the standard recommendations given in the literature. In this paper, the reasons for deviation from recommendations are given. The analysis of the cooling tower operation based on real meteorological parameters for 2015 is also shown in this paper. According to this analysis, cooling tower provides required water temperature in any season, and gives opportunity for energy savings in winter, with opportunity for heat capacity enlargement if production capacit...

Orig i nal sci en tific pa per Tri-gen er a tion sys tems are used to si mul ta neously pro duce elec tri cal, heat ing, and cool ing en ergy. These sys tems are usu ally more ef fi cient than con ven tional sys tems for sep a rate pro duc tion and have smaller dis tri bu tion losses since they are of ten located closer to the con sumer. For achieve ment of the best tech ni cal and/or fi nancial re sults, tri-gen er a tion plants have to be prop erly, i. e. op ti mally de signed and op er ated. Op er a tional op ti mi za tion is used for short term pro duc tion plan ning, con trol of tri-gen er a tion sys tems op er a tion and as a part of de sign level op ti mi zation. In this pa per an ap proach to op er a tional op ti mi za tion of tri-gen er a tion plants with re cip ro cat ing en gines is pre sented with the fol low ing math e mat i cal model. It is also ex plained how this al go rithm might be em bed ded in some larger op ti mi zation pro ce dure. In this ap proach, the im por tance of the part load per for mance of dif fer ent units of the tri-gen er a tion sys tems is em pha sized, es pe cially of co-gen er ation unit, i. e. en gine gen er a tor set and thus it re lies on man u fac tur ers' data and is char ac ter ized with rel a tively high level of de tails ex am ined. Math e mat i cal model is based on the equip ment per for mance based con straints and de mand sat is fac tion based con straints with the pos si bil ity to add more equa tions if ap pro pri ate. Ob jective func tion for op ti mi za tion is ben e fit-cost func tion. Op ti mal op er a tion re gimes for typ i cal days for each month are ob tained and an a lyzed. Im pact of elec tri cal energy price on pay-back pe riod and pri mary en ergy sav ing is an a lyzed. Pri mary energy sav ings are de ter mined and com pared to max i mal value that could be obtained.

The main objective of this study is to find a proper solution for the cross-flow water cooling tower problem, also to find an empirical correlation's controlling heat and mass transfer coefficients as functions of inlet parameters to the tower. This is achieved by constructing an experimental rig and a computer program. The computer simulation solves the problem numerically. The apparatus used in this study comprises a cross-flow cooling tower. From the results obtained, the 'characteristic curve' of cross-flow cooling towers was constructed. This curve is very helpful for designers in order to find the actual value of the number of transfer units, if the values of inlet water temperature or inlet air wet bulb temperature are changed. Also an empirical correlation was conducted to obtain the required number of transfer units of the tower in hot water operation. Another correlation was found to obtain the effectiveness in the wet bulb operation.

Study and research on arc welding have provided identification of errors in formulas for calculating the cooling time t8/5 and other dependent parameters. It is concluded that large errors are present in certain intervals which had caused fail?ures in welding technologies. Incorrect approximation of cooling temperature is replaced by a more accurate approximation used for defining of the new precise algorithm for determining relevant welding parameters.

The ce ment in dus try con trib utes about 5% to global anthropogenic CO 2 emis sions, and is thus an im por tant sec tor in CO 2 -emis sion mit i ga tion strat e gies. Car bon diox ide is emit ted from the cal ci na tion pro cess of lime stone, from com bus tion of fu els in the kiln, and from the coal com bus tion dur ing power gen er a tion. Strat e gies to reduce these CO 2 emis sions in clude en ergy ef fi ciency im prove ment, new pro cesses, shift to low car bon fu els or waste fu els in ce ment pro duc tion, in creased use of ad ditives in ce ment pro duc tion, al ter na tive ce ments, and CO 2 re moval from flue gases in clinker kilns. In creased use of fly ash as an ad di tive to ce ment and con crete has a num ber of advan tages, the pri mary be ing re duc tion of costs of fly ash dis posal, re source con serva tion, and cost re duc tion of the prod uct. Since the pro duc tion of ce ment re quires a large amount of en ergy (about 2.9-3.2 GJ/t), the sub sti tu tion of ce ment by fly ash saves not only en ergy but also re duces the as so ci ated green house gas emis sions. The pa per eval u ates the re duc tion of CO 2 emis sions that can be achieved by these mit i ga tion strat e gies, as well as by par tial sub sti tu tion of ce ment by fly ash. The latter is im por tant be cause the qual ity of the pro duced con crete de pends on the phys ical-chem i cal prop er ties of the fly ash and thus par tial sub sti tu tion as well as the type of fly ash (e. g., the con tent of CaO) has an ef fect not only on en ergy con sumption and emis sions, but also on the pro duced con crete qual ity.

Air pollution is fast becoming a serious global problem with increasing population and its subsequent demands. This has resulted in increased usage of hydrogen as fuel for internal combustion engines. Hydrogen resources are vast and it is considered as one of the most promising fuel for automotive sector. As the required hydrogen infrastructure and refueling stations are not meeting the demand, widespread introduction of hydrogen vehicles is not possible in the near future. One of the solutions for this hurdle is to blend hydrogen with methane. Such types of blends take benefit of the unique combustion properties of hydrogen and at the same time reduce the demand for pure hydrogen. Enriching natural gas with hydrogen could be a potential alternative to common hydrocarbon fuels for internal combustion engine applications. Many researchers are working on this for the last few years and the work is now focused on how to use this kind of fuel to its maximum extent. This technical note is an assessment of hydrogen enriched compressed natural gas usage in case of internal combustion engines. Several examples and their salient features have been discussed. Finally, overall effects of hydrogen addition on an engine fueled with hydrogen enriched compressed natural gas under various conditions are illustrated. In addition, the scope and challenges being faced in this area of research are clearly described.

This research work investigates the use of neat paradise tree oil in a 4-stroke natural aspirated direct injection compression ignition engine assisted with the help of superheated hydrogen (hydrogen in gaseous state or above its saturation temperature) as a combustion improver. The high calorific gaseous fuel hydrogen gas was used as a combustion improver and admitted into the engine during the suction stroke. A 4-stroke single cylinder Diesel engine was chosen and its operating parameters were suitably modified. Neat paradise tree oil was admitted through standard injector of the engine and hydrogen was admitted through induction manifold. Inducted superheated hydrogen was initiated the intermediate compounds combustion of neat paradise tree oil. This process offers higher temperature combustion and results in complete combustion of heavier molecules of neat paradise tree oil within shorter duration. The results of the experiment reveal that 40% higher NOx, 20% lower smoke, 5% low...

System, property, work and heat interactions, zeroth law, first law of thermodynamics, application of first law to closed systems and flow processes. Thermodynamic properties of fluids. Second law of thermodynamics, Carnot cycle, temperature scale, Clausis inequality, entropy increase, availability.

A mathematical model representing temperature and moisture content in bread during baking is developed. The model employs the coupled partial differential equations proposed by Luikov. Dependences of mass and thermal properties of dough on temperature and moisture content are included in the model. Resulting system of non-linear partial differential equations in time and one space dimension is reduced to algebraic system by applying a finite difference numerical method. A numerical solution of the model equations is obtained and simultaneous heat and moisture transfer in dough during baking is predicted. The changes of temperature and moisture content during the time of the process are graphically presented and commented.

The thermodynamic analyses of the triple-pressure reheat combined cycle gas turbines with duct burner are presented and discussed in this paper. The overall performance of a combined cycle gas turbine power plant is influenced by the ambient temperature, compression ratio and turbine inlet temperature. These parameters affect the overall thermal efficiency, power output and the heat-rate. In this study a thermodynamic model was development on an existing actual combined cycle gas turbine (CCGT). The code of the performance model for CCGT power plant was developed utilizing the THERMOFLEX software. The simulating results show that the total power output and overall efficiency of a CCGT decrease with increase the ambient temperature because increase the consumption power in the air compressor of a GT. The totals power of a CCGT decreases with increase the compression rate, while the overall efficiency of a CCGT increases with increase the compression ratio to 21, after that the overall efficiency will go down. Far there more the turbine inlet temperature increases the both total power and overall efficiency increase, so the turbine inlet temperature has a strong effect on the overall performance of CCGT power plant. Also the simulation model give a good result compared with MARAFIQ CCGT power plant. With these variables, the turbine inlet temperature causes the greatest overall performance variation.

Original scientific paper UDC: 536.255 BIBLID: 0354-9836, 11 (2007), 4, 143-156 Com bined cy cle power plants play an im por tant role in the pres ent en ergy sec tor. The main chal lenge in de sign ing a com bined cy cle power plant is proper uti li za tion of gas tur bine ex haust heat in the steam cy cle in or der to achieve op ti mum steam tur bine out put. Most of the com bined cy cle de vel opers fo cused on the gas tur bine out put and ne glected the role of the heat recov ery steam gen er a tor which strongly af fects the over all per for mance of the com bined cy cle power plant. The pres ent pa per is aimed at op ti mal uti liza tion of the flue gas re cov ery heat with dif fer ent heat re cov ery steam gener a tor con fig u ra tions of sin gle pres sure and dual pres sure. The com bined cy cle ef fi ciency with dif fer ent heat re cov ery steam gen er a tor con fig u ra tions have been ana lysed parametrically by us ing first law and sec ond law of ther mo dy nam ics. It is ob served that in the dual cy cle high pres sure steam tur bine pres sure must be high and low pres sure steam tur bine pres sure must be low for better heat re cov ery from heat re cov ery steam gen er a tor.

Cryogenic propellants LOx/H2 are used at very high pressure in rocket engine combustion. The description of the combustion process in such application is very complex due essentially to the supercritical regime. Ideal gas law becomes invalid. In order to try to capture the average characteristics of this combustion process, numerical computations are performed using a model based on a one-phase multi-component approach. Such work requires fluid properties and a correct definition of the mixture behavior generally described by cubic equations of state with appropriated thermodynamic relations validated against the NIST data. In this study we consider an alternative way to get the effect of real gas by testing the volume-weighted-mixing-law with association of the component transport properties using directly the NIST library data fitting including the supercritical regime range. The numerical simulations are carried out using 3D RANS approach associated with two tested turbulence models, the standard k-Epsilon model and the realizable k-Epsilon one. The combustion model is also associated with two chemical reaction mechanisms. The first one is a one-step generic chemical reaction and the second one is a two-step chemical reaction. The obtained results like temperature profiles, recirculation zones, visible flame lengths and distributions of OH species are discussed.

The fractional advection-diffusion equations are obtained from a fractional power law for the matter flux. Diffusion processes in special types of porous media which has fractal geometry can be modelled accurately by using these equations. However, the existing nonlocal fractional derivatives seem complicated and also lose some basic properties satisfied by usual derivatives. For these reasons, local fractional calculus has recently been emerged to simplify the complexities of fractional models defined by nonlocal fractional operators. In this work, the conformable, a local, well-behaved and limit-based definition, is used to obtain a local generalized form of advection-diffusion equation. In addition, this study is devoted to give a local generalized description to the combination of diffusive flux governed by Fick?s law and the advection flux associated with the velocity field. As a result, the constitutive conformable advection-diffusion equation can be easily achieved. A Dirichl...

Seemingly universal geometric forms unite the flow systems of engineering and nature. For example, tree-shaped flows can be seen in computers, lungs, dendritic crystals, urban street patterns, and communication links. In this groundbreaking book, Adrian Bejan considers the design and optimization of engineered systems and discovers a deterministic principle of the generation of geometric form in natural systems. Shape and structure spring from the struggle for better performance in both engineering and nature. This idea is the basis of the new constructal theory: the objective and constraints principle used in engineering is the same mechanism from which the geometry in natural flow systems emerges. From heat exchangers to river channels, the book draws many parallels between the engineered and the natural world. Among the topics covered are mechanical structure, thermal structure, heat trees, ducts and rivers, turbulent structure, and structure in transportation and economics. The numerous illustrations, examples, and homework problems in every chapter make this an ideal text for engineering design courses. Its provocative ideas will also appeal to a broad range of readers in engineering, natural sciences, economics, and business.

The objective of this paper is to present a fast and reliable CFD model that is able to simulate stationary and transient operations of multistage compressors and turbines. This analysis tool is based on an adapted version of the Euler equations solved by a time-marching, finite-volume method. The Euler equations have been extended by including source terms expressing the blade-flow interactions. These source terms are determined using the velocity triangles and a row-by-row representation of the blading at mid-span. The losses and deviations undergone by the fluid across each blade row are supplied by correlations. The resulting flow solver is a performance prediction tool based only on the machine geometry, offering the possibility of exploring the entire characteristic map of a multistage compressor or turbine. Its efficiency in terms of CPU time makes it possible to couple it to an optimization algorithm or to a gas turbine performance tool. Different test-cases are presented for which the calculated characteristic maps are compared to experimental ones.

The application of lignite pre-drying technologies in next generation of lignite power plants by utilizing low pressure steam as a drying medium instead of hot recirculated flue gascombined with thermal utilization of the vaporized coal moistureis expected to bring efficiency increase of 2-4 percentage points in future lignite power plants compared with today's state-of-the-art. The pre-drying concept is of particular importance in Greek boilers firing lignite with a high water and ash content. The combustion of Greek pre-dried lignite has been investigated experimentally and via numerical simulations in our previous research. This study focuses on the potential integration of a lignite pre-drying system in an existing Greek power plant with dry lignite co-firing thermal share of up to 30%. The radiative and convective heat fluxes to the boiler and the overall boiler heat balance is calculated for reference and dry lignite co-firing conditions by an in-house calculation code. The overall plant's thermal cycle is then simulated using commercial thermal cycle calculation software. The net plant efficiency is in this way determined for reference and dry coal co-firing conditions. According to the simulation results the integration of a pre-drying system and the implementation of dry lignite co-firing may bring an efficiency increase of about 1.5 percentage points in existing Greek boilers. It is therefore considered as an important measure towards improving plant efficiency and reducing specific CO 2 emissions in existing plants.

This paper presents an investigation into the effect of the laser cutting parameters on the heat affected zone in CO 2 laser cutting of AISI 304 stainless steel. The mathematical model for the heat affected zone was expressed as a function of the laser cutting parameters such as the laser power, cutting speed, assist gas pressure, and focus position using the artificial neural network. To obtain experimental database for the artificial neural network training, laser cutting experiment was planned as per Taguchi's L 27 orthogonal array with three levels for each of the cutting parameter. Using the 27 experimental data sets, the artificial neural network was trained with gradient descent with momentum algorithm and the average absolute percentage error was 2.33%. The testing accuracy was then verified with 6 extra experimental data sets and the average predicting error was 6.46%. Statistically assessed as adequate, the artificial neural network model was then used to investigate the effect of the laser cutting parameters on the heat affected zone. To analyze the main and interaction effect of the laser cutting parameters on the heat affected zone, 2-D and 3-D plots were generated. The analysis revealed that the cutting speed had maximum influence on the heat affected zone followed by the laser power, focus position and assist gas pressure. Finally, using the Monte Carlo method the optimal laser cutting parameter values that minimize the heat affected zone were identified.

The blade row interaction can alter the time-mean flow and therefore be of interest for aerodynamic design analysis. Whereas results within low subsonic turbomachines are quite numerous in the literature, there have been far fewer works which give results of blade row interaction within high speed cases. Two cases are related in this paper. First, the effects of an incoming wake on the rotor flow field of a transonic compressor are analyzed. The blade row interaction proved to be positive regarding the total pressure ratio, but negative regarding the losses.

A physical model is established in this paper to describe the heat transfer and two phase flow of a refrigerant in the evaporator and condenser of a vapor compression refrigeration system. The model is then used to determine the refrigerant charge in vapor compression units. The model is used for a sensitivity analysis to determine the effect that varing design parameters on the refrigerant charge. The model is also used to evaluate the effect of refrigerant charge and the thermal physical properties on the refrigeration cycle. The predicted value of the refrigerant charge and experimental data agree well. The model and the method presented in this paper could be used to design vapour compression units such as domestic refrigerators and air conditioners.

The objective of this study is to show the effect of guide vane geometry on the performance. In order to overcome the disadvantages of vertical axis wind turbine, a straight-bladed vertical axis wind turbine (S-VAWT) with a directed guide vane row has been proposed and tested by the authors. According to previous studies, it was clarified that the performance of the turbine can be improved by means of the directed guide vane row. However, the guide vane geometry of S-VAWT has not been optimized so far. In order to clarify the effect of guide vane geometry, the effects of setting angle and gap between rotor blade and guide vane on power coefficient and starting characteristic were investigated in the experiments. The experimental study of the proposed wind turbine was carried out by a wind tunnel. The wind tunnel with a diameter of 1.8m is open jet type. The wind velocity is 8 m/s in the experiments. The rotor has three straight blades with a profile of NACA0018 and a chord length of 100 mm, a diameter of 0.6 m and a blade height of 0.7 m. The guide vane row consists of 3 arc plates.

A steady state simulation model has been developed to evaluate the system performance of a transcritical carbon dioxide heat pump for simultaneous heating and cooling. The simulated results are found to be in reasonable agreement with experimental results reported in the literature. Such a system is suitable, for example, in dairy plants where simultaneous cooling at 4 8C and heating at 73 8C are required. The optimal COP was found to be a function of the compressor speed, the coolant inlet temperature to the evaporator and inlet temperature of the fluid to be heated in the gas cooler and compressor discharge pressure. An optimizing study for the best allocation of the fixed total heat exchanger inventory between the evaporator and the gas cooler based on the heat exchanger area has been carried out. Effect of heat transfer in the heat exchangers on system performance has been presented as well. Finally, a novel nomogram has been developed and it is expected to offer useful guidelines for system design and its optimisation. q Elimination des cristaux de givre sur une plaque froide: effets des fréquences stationnaires et de balayage des champs électriques

Improvement of the energy conversion processes efficiency helps to achieve a more reliable energy supply, a cleaner environment, more competitive businesses, and higher living standard. Industry data indicate significant potential for improving the efficiency of steam systems and minimizing their operating costs by implementing various measures. The present work is a result of a systematic approach for energy performance analysis and identification of opportunities for optimizing the steam-condensate system of the combined heat and power plant ESM Energetika, Skopje, North Macedonia. The boiler plants provide superheated steam used in a hot-water station for the district heating system, for electricity generation, and as process steam for industrial customers. As the main operating costs of the plant stem from the natural gas consumption, the implementation of a set of energy efficiency measures will lead to its reduction, accompanied by less environmental impact. As a result of the...

Numerical and experimental investigations were conducted in a transonic centrifugal compressor stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. A detailed analysis of the flow in the inducer (i.e. the entry zone of the impeller between the main blade leading edge and the splitter blade leading edge) is proposed from choke to surge. Steady and unsteady simulations were performed using the code elsA, which uses a multi-domain approach on structured meshes and solves the compressible RANS equations, associated with a two-equation turbulence model k-l in the rotating frame of reference. The 1MW LMFA-ECL test rig was used for carrying out the tests in the compressor stage. Unsteady pressure measurements up to 150 kHz and Laser Doppler Anemometry measurements were performed in the inducer. A good agreement is obtained between the experimental and numerical data even if an over dissipation is noticed in the numerical results. The change in flow pattern from choke to surge is mainly due to a change in the tip leakage flow trajectory which straightens, leading to a flow blockage of an individual passage near shroud. A spectral analysis shows that only the blade passing frequency and its harmonics compose the various spectra obtained from choke to surge.