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Heat resistant coatings are considered for the external surface Low-Pressure Steam Turbines (LPST). 410 stainless steel covered with nano heat resistant coatings consists of a heat resistant connecting layer enhanced by nanoparticles. A commercial paint was modified by using 20%wt of (titanium dioxide (TiO2) - aluminum oxide (Al2O3)) with different concentrations range (25,50,75wt% of TiO2) layers. These nano-coatings paints were airbrushed onto the surface of specimens of steam turbine blades. The test rig and experimental apparatus have been fabricated and collected to accomplish the thermal tests. The samples were subjected to heat resistance and a temperature test approximately similar to the steam turbine's operation condition temperature. The test results are used to choose the nano-coating layer with a concentration that ensures a composition's highest protective properties. The test sample with concentration (paint-(75% Al2O3+25% TiO2)) showed the highest thermal properties compares with the other cases.

Numerically investigated the electric double layer (EDL) Effects on the performance of the square microchannel heat exchanger (MCHE) at combined electro-osmotic and pressure-driven flow with compared pure pressure-driven with a hydraulic diameter (10 – 50) μm. We defined at any size (Dh) of microchannel heat exchanger become the impact of EDL very slight with the studied effect of electric double layer thickness λ. The diluted water 1:1 potassium chloride (KCl) solution is used as a working fluid at an ionic concentration , , silicon microchannel at zeta potential of surface -0.2 volt. A three-dimensional (3D) Poisson-Boltzmann equations and Naiver-stoke equations with applied electric field solved by using the finite volume scheme in this work. The results show an increase in pressure drop of the microchannel heat exchanger at combined flow electroosmotic and pressure-driven flow with a percentage of 31.09 % at an ionic concentration and 42.71 % at increase in pumping power, especially at low ionic concentration. Slight enhancement in average heat transfer rate and effectiveness due to an increase in average temperature difference. Decrease in overall performance at combined electroosmotic and pressure-driven flow compared with pure pressure driven.

In this paper, an experimental electrical distribution transformer was studied and a new technique was proposed to improve the performance of a new mixed cooling consisting of pure transformer oil, paraffin wax and nanoparticles. The experiment was carried out on a small transformer that was done by taking a model with dimensions (15 * 10 * 10) cm to facilitate calculations. Paraffin wax absorbs the heat generated in the transformer due to the smelting process that can be used to cool electrical appliances. Nanoparticles have good thermal properties and lead to increased oil insulation to thermal improvements in transformer oil with dispersal of solid nanoparticles and their effects on transformer cooling. Three types of solid nanoparticles were used in this experiment (Al2O3, TiO2, and Sic) with a different volume concentration (1%, 3%, and 5%) and 4% paraffin wax as a certified added percentage for each process. The obtained results showed that when mixing paraffin wax and solid nanoparticles with transformer oil, the transformer cooling performance is improved by reducing the temperature. The best selected nanoparticles were found to be Sic and the reason for this is that Sic has a higher thermal conductivity compared to (Al2O3 and TiO2). The proposed hybrid oil reduces the temperature by 10 ° C (in the case of PCM and Sic) and it is possible to improve the cooling performance of electrical transformers.

In this paper the effect of surface roughness on the performance of counter flow microchannel heat exchanger has been numerically investigated. The studied Microchannel heat exchanger is a square shape and made of aluminum as substrate material with different values of hydraulic diameters (20, 50, 110, 150 ) μm. The working fluid used is water at constant properties. Roughness- viscosity model has been used to study the roughness effect with 0.14 ratio of roughness to hydraulic diameter. The results obtained indicate that pressure drop of (CFMCHX) increased with increasing surface roughness and decrease hydraulic diameter also the results showed that there is a slight increasing in thermal performance with increasing the surface roughness.

In this paper analytical study has been made to investigate a hybrid refrigerant consists of different refrigerants with different mixing ratios and find out its effects on the performance of cycle and specify the best refrigerant that gives best performance and least environmental pollution. Firstly the performance of vapor compression refrigeration system has been analyzed with several different pure refrigerants( R11, R12, R13,R22,R23, R32, R41, R115, R116, R124, R125, R134a, R142a, R143a, R152a) by REFPROP software and the values of coefficient of performance (COP) and mass flow rate ( ) and work in compressor (Wc) for each pure refrigerant is calculated and by use other properties for every refrigerant it can determine the best refrigerants to make a new refrigerant that comes from mixing of two or three of pure refrigerants with best performance for example R22 and R134a with mixing ratios (25:75),(50:50),(75:25) respectively Assuming the evaporator temperature is (-10 °C) and the condenser temperature is (35 °C). The main parameters are calculated such as new refrigerant, mass flow rate and work used in compressor for various capacity in (kW). The results showed that the maximum performance recorded with R134a and the minimum value with R115 while the values of performance for their mixtures fluctuated between the maximum and minimum values for the pure refrigerants and the cause of this is due to combination of properties as boiling point temperature and critical temperature, latent heat of vaporization, specific heat of liquid and specific volume of the vapor

The effect of the hybrid suspension on the intrinsic characteristics of microencapsulated phase change material (MEPCM) slurry used as a coolant in counterflow microchannel heat exchanger (CFMCHE) with different velocities is investigated numerically. The working fluid used in this paper is a hybrid suspension consisting of nanoparticles and MEPCM particles, in which the particles are suspended in pure water as a base fluid. Two types of hybrid suspension are used (Al2O3 + MEPCM and Cu + MEPCM), and the hydrodynamic and thermal characteristics of these suspensions flowing in a CFMCHE are numerically investigated. The results indicated that using hybrid suspension with high flow velocities improves the performance of the microchannel heat exchanger while resulting in a noticeable increase in pressure drop. Thereupon, it causes a decrease in the performance index. Moreover, it was found that the increment of the nanoparticles’ concentration can rise the low thermal conductivity of the MEPCM slurry, but it also leads to a noticeable increase in pressure drop. Furthermore, it was found that as the thermal conductivity of Cu is higher than that for Al2O3, the enhancement in heat transfer is higher in case of adding Cu particles compared with Al2O3 particles. Therefore, the effectiveness of these materials depends strongly on the application at which CFMCHE is employed.

This paper aims to study the flow and heat transfer of hybrid suspension in counter flow micro channel heat exchanger (CFMCHE). In order to enhance the thermal properties of micro encapsulated phase change material (MEPCM) suspension. The hybrid suspension studied in this paper consists of nanoparticles and MEPCM particles, these particles are suspended in water as abase fluid, two types of hybrid suspension are used (Cu + MEPCM suspension) and (Al2O3+ MEPCM suspension) by n-octadecane as a PCM for both of them. The hydrodynamic and thermal characteristics of thes suspensions flow in micro channels of CFMCHE is numerically investigated. From obtained results, using of hybrid suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increase its effectiveness but it also lead to high increasing in pressure drop. The results showed considerable enhancement in cooling effectiveness of (Al2O3 + MEPCM suspension) above of the pure PCM suspension, Nanofluids, and water. While (Cu + MEPCM suspension) showed enhancement above of the pure PCM suspension and water, but was not best effectiveness than Nanofluids. Extra increase in pressure drop in both types of hybrid suspension above are leads to reduce the overall performance compared with pure PCM suspension. Therefore its use depends on the application at which this heat exchanger is employed

In this paper using of the phase change materials (PCMs) in a micro-channel heat sink (MCHS) is numerically investigated. The air is first used in heat sink and then four phase change materials (paraffin wax, n-eicosane, p116 and RT41) have been used as cooling mediums in different types and different configurations at different ambient temperatures. Constant heat flux is applied on the base of heat sink and mixed (convection and radiation) boundary condition is applied at the top surfaces of heat sink.The results showed that, using of the phase change materials in micro-channels heat sink with different configurations lead to enhance the cooling performance of micro heat sink. The phase change material should be selected according to its melting temperature according to the certain application as different phase change martials caused different values of reduction in heat sink temperature in range of ambient temperature due to difference in melting temperatures of PCMs. The cost of materials depends on the classification of the PCM (organic and inorganic) and quantity of PCMs used in a certain application. Keywords: Micro-channel heat sink, Heat sinks, Phase change materials, Numerical investigation, Electronic cooling

Magnetohydrodynamic micropumps received more attention due to its applications in pumping of biological and chemical specimens, such as blood, DNA, and saline buffers. In this paper the MHD flow in different cross section microchannels has been numerically investigated with different electromagnetic boundary conditions. Square, rectangular, circular and trapezoidal cross section microchannels have been used to explore the effect of channel geometry on the MHD micropump operation. The study covers a selected range of applied electric currents and magnetic flux to show their effects on MHD flow. Thermal characteristics of MHD flow have been also studied by calculation the temperature distribution through MHD micropump region. The results obtained show a considerable effect of channel geometry, the applied electric and magnetic fields on the velocity and flow rate. The circular cross section micropump gave higher velocity and flow rate compared with other cross sections, and there is a slight increase in temperature due to small effect of Joule heating.

Thermal performance of micro-channel heat sink (MHS) with different cooling mediums has been investigated numerically using 3D model of conjugated heat transfer. Four types of coolants have been used in this study starting with air as a baseline to compare its thermal performance with pure phase change material (PCM) which was paraffin wax and nanoparticles-enhanced phase change material (NEPCM) which were (Silicon carbide (Sic)-PCM and Diamond-PCM) with volume fraction values of (1, 3, and 5%). On the heat sink base, a constant and uniform heat flux of (8000, 10000, 12000, and 14000W.m−2) is applied. Numerical simulations have been performed to investigate the effect of nanoparticle material and concentrations of nanoparticles on cooling performance of heat sink. The findings elucidated the cooling performance of MHS is enhanced with PCM compared with air and suspension nanoparticles lead to improve the thermal conductivity of (NEPCM) comparing with pure PCM, that causing expedite the melting process and enhancement of cooling performance. Also, as the concentration of nanoparticles increased, the heat transfer rate for (NEPCM) enhanced and decreasing the time of the melting process.

The micro pin finned heat sink with three shapes (circular, triangular and square) of fins in addition to the unfinned micro heat sink with phase change materials of different types and different configurations is numerically investigated. The air is first used in heat sink and then two phase change materials (n-octadecane and RT44) have been used as cooling mediums at different ambient temperatures. The results obtained show that, using of the phase change materials with finned and unfinned heat sink instead of conventional cooling with air lead to improve of cooling enhancement of micro heat sink, and selected of the phase change material should be according to its melting temperature corresponding to the certain application since different phase change martials caused different values of reduction in heat sink temperature in range of ambient temperature due to difference in its melting temperatures.

The aim of this paper is to study the microencapsulated phase change materials (MEPCM) suspension as a coolant instead of pure fluid in the micro channel heat sink (MCHS) with different core and wall materials as well as different base fluids. The MEPCM suspension using in this study consist of microcapsules constructed from n-octadecane, RT44 as a phase change materials (PCM) and shell materials are poly-methylmthacrylate (PMMA), poly-alpha olefin (PAO), these capsules are suspended in (pure water, ethylene glycol and pure oil) in a concentration of (0–20)% and have been used as a cooling mediums at different ambient temperatures. Constant heat flux is applied at base of heat sink. The results obtain show that, using MEPCM suspensions as a coolant in micro heat sink instead of conventional cooling with pure fluid lead to enhance the cooling performance of micro heat sink is be 20.91% with (RT44+PMMA) pure oil, 16.91% with (RT44+PMMA) for ethyleneglycol and 12.91% with (RT44+PMMA) for pure water at concentration 2% and = 0.28 m/s. The phase change material in MEPCM suspension should be select according to its melting temperature corresponding to the certain application since different MEPCM suspension concentration caused different values of reduction in heat sink temperature in range of ambient temperature due to different in its melting temperatures

In this paper a micro pin fin heat sink is numerically investigated with three fins geometries (square, triangular and circular) in addition to the unfinned microchannel heat sink. Nanofluid is used as a cooling fluid, since the flow and heat transfer have been studied with two types of nanofluids (Diamond-water and Al2O3-water) in addition to the pure water. The volumetric concentration of selected nanofluids has been chosen in range (1–4)%. The comparison of hydrodynamic and thermal characteristics of different fin geometries and cooling fluids has been made under the same value of Reynolds number and constant wall temperature thermal boundary condition, the range of Re used is (100–900) to ensure that, the flow remains in the laminar regime. The results obtained indicated that, using of nanofluid instead of pure fluid as a coolant leads to enhanced heat transfer performance by increasing the amount of heat dissipated but it also leads to increased pressure drop for all fins shapes and nanofluids studied.

In this paper the performance of a counter flow microchannel heat exchanger (CFMCHE) is numerically investigated with a nanofluid as a cooling medium. Two types of nanofluids are used Cu-water and Al2O3-water. From the results obtained it’s found that thermal performance of CFMCHE increased with using the nanofluids as cooling medium with no extra increase in pressure drop due to the ultra fine solid particles and low volume fraction concentrations. The na-nofluids (Cu-water and Al2O3-water) volume fractions were in the range 1% to 5%. It’s also found that nanoflu-id-cooled CFMCHE could absorb more heat than water-cooled CFMCHE when the flow rate was low. For high flow rates the heat transfer was dominated by the volume flow rate and nanoparticles did not contribute to the extra heat absorption. Also the performance of CFMCHE can be increased considerably by using nanofluids with higher thermal conductivities.

The rectangular microchannel heat exchanger performance is numerically investigated in this paper. Hydrodynamic and heat transfer characteristics in a laminar, 3-D, incompressible, slip flow, steady state and counter flow are proposed. The Navier–Stokes equations and energy equation for the hot and cold fluids are solved with the slip velocity and temperature jump conditions. The governing equations are discretized using finite-volume method-upwind differencing scheme, and then these are solved using SIMPLE algorithm method on staggered grid with FORTRAN code. From the obtained results it was found that the factors affecting the effectiveness are: Reynolds number Re, thermal conductivity ratio Kr, Knudsen number Kn and aspect ratio α. Increasing of Re, Kn and α separately lead to decrease the effectiveness. While the effectiveness increases with increasing Kr until it reach a certain optimal value which gives the maximum effectiveness at Kr = 90. Also, it is found that Nusselt number decrease with increases Knudsen number. Increasing of Re and Kn separately lead to increase pressure drop.

The aim of this paper is to study the flow and heat transfer of microencapsulated phase change material (MEPCM) suspension in counter flow microchannel heat exchanger (CFMCHE) and it’s effect of the performance of this heat exchanger when using this suspension as a coolant instead of pure fluid. The hydrodynamic and thermal characteristics of this suspension flows in microchannels of CFMCHE is numerically investigated. The MEPCM suspension used in this paper consists of microcapsules constructed from n -octadecane as a phase change material (PCM) and the shell material is polymethylmethacrylate, these capsules are suspended in water in a concentration of (0–20)%. From the results, using of MEPCM suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increasing its effectiveness but it also lead to increase the pressure drop. From heat transfer (thermal performance) point of view it is better to use this type of fluid to increase cooling efficiency of a CFMCHE, but due to extra increase in pressure drop it leads to reduce the overall performance compared with pure fluids. Therefore its use depends on the application at which this heat exchanger is used.

Microchannel heat exchangers (MCHE) can be made with channels of various geometries. Their size and shape may have considerable effect on the thermal and hydraulic performance of a heat exchanger. In this paper numerical simulation is carried out to solve 3D developing flow and 3D conjugate heat transfer of a balanced counter flow microchannel heat exchanger (CFMCHE) to evaluate the effect of size and shape of channels on the performance of CFMCHE for the same volume of heat exchanger. The effect of shape of the channels on its performance is studied for different channel cross-sections such as circular, square, rectangular, iso-triangular and trapezoidal. Results show that for the same volume of a heat exchanger, increasing the number of channels lead to increase in both effectiveness and pressure drop. Moreover circular channels give the best overall performance (thermal and hydraulic) among various channel shapes. New correlations are developed to predict the value of heat exchanger effectiveness and performance index as a function of relative size of channels with overall heat exchanger volume, Reynolds number and thermal conductivity ratio.

Electrokinetic micropumps receive increasing attention due to their applications in pumping of biological and chemical fluids; such as blood, DNA, and saline PBSs. In this paper, the electroosmotic flow in square microchannels has been numerically investigated by developing a model from the basic governing equations (continuity, momentum, energy, Laplace and Poisson- Boltzmann equations). These equations were numerically solved by CFD program for two fluids (water and PBS). The study considered the external applied electric field and zeta potential to interrogate their potential effects on electroosmotic flow. Thermal characteristics of electroosmotic flow have been also studied by calculating the temperature distribution through electroosmosis micropump region. The results confirm the considerable effect of applied electric field, concentration of electrolyte fluid and zeta potential on microflow velocity and flow rate. The PBS gave higher velocity and flow rate values compared with water, and there was only a slight increase in temperature due to Joule heating effect.