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Heat sinks, a type of heat exchanger used due to the simplicity of fabrication, low cost, and reliable heat dissipation, are widely employed to cool electronic devices. In recent decades, heat dissipation has remained a critical challenge in optimizing the thermal performance of heat sinks. Therefore, to ensure optimal performance and reliability, effective heat removal from these devices is essential across various operational conditions. This comprehensive review examines various methods for enhancing the thermal design of heat sinks. It includes investigations into both passive and active techniques that modify the solid or fluid domain to improve heat removal. The study encompasses different approaches, focusing on perforated plate-fin heat sinks, phase change materials (PCM) enhanced by metal foam, active cooling techniques, and cost optimization. The literature revealed a strong preference for plate fins as the primary heat sink design, comprising 70% of the investigated studies. Pin fins were utilized in 15% of cases, while a hybrid configuration incorporating both plate and pin fins was observed in the remaining 15%. The integration of fins with the chosen PCM significantly accelerated the melting process, leading to an average improvement in thermal performance. The composite incorporating foam and PCM demonstrated a substantial improvement in thermal conductivity. This study aims to summarize existing research efforts, identify limitations, and explore potential solutions for advancing the thermal performance of heat sinks.

Transient three-dimensional natural convection heat transfer due to the influences of heating from one side of an enclosure filled with a saturated porous media, whereas the opposite side is maintained at a constant cold temperature, and the other four sides are adiabatic, were investigated in the present work experimentally. Silica sand was used as a porous media saturated with distilled water filled in a cubic enclosure heated from the side,using six electrical controlled heaters, at constant temperatures of (60, 70, 80, 90, and 100oC). The inverse side cooled at a constant temperature of (24oC) using an aluminum heat exchanger, consisted of 15 channels feeded with constant temperature water. Eighty thermocouples were used to control the heated and cooled sides, and to measure the temperature in the entire enclosure. Experimental results showed that the heat transfer regime was mainly conduction for all Rayleigh numbers with small influence of convection for Ra=42 and greater for Ra=55. This effect increased with the angle of inclination of the enclosure. Numerical and experimental results showed a good agreement. There was a rapid increase in the temperature at the entire media at the early time, reduced gradually until the steady state condition reached. This temperature and heat transfer to and from the porous media, were increased as the Rayleigh number and/or inclination angle increased. The Nusselt number increased directly with the angle of inclination up to o θ = 45 and then decreased. Correlation equations are obtained from the experimental investigation, showed the change of the average and local Nusselt number with time, distance, Rayleigh number, and the inclination angle.

The brake system is one of the most important systems in all vehicles. The main objective of this system is to control the vehicle mechanical movement and stopping. Where, it can’t drive safely any vehicle without the brake system to control its acceleration rate and its stability. The effective factors that affected the brake performance are the properties of frictional material of pads and disc. The objective of the present work is to study the thermal behavior of the brake system using different types of frictional material for pads and find the optimal one of them. High amount of heat will be generated between the disc and pads during the braking process; may cause quick failure in future. In the present paper, a 3-dimensional thermal transient model of the brake system has been developed using finite element technique (COMSOL Multiphysics® 5.5). Five types of friction materials (St37-2, HCC, G95, LUK, and Tiger) are used in the numerical analyses. The results presented the variation and distribution of contact temperatures of the proposed frictional materials during braking period. The main conclusion based on the obtained results is that the optimal frictional material is HCC material and the poorest one is LUK material.

The effect of linear thermal stratification in stable stationary ambient fluid on free convective flow of a viscous incompressible fluid along a plane wall is numerically investigated in the present work. The governing equations of continuity, momentum and energy are solved numerically using finite difference method with Alternating Direct implicit Scheme. The velocity, temperature distributions and the Nusselt number are discussed numerically for various values of physical parameters and presented through graphs. ANSYS program also used to solve the problem. The results show that the effect of stratification parameter is marginalized with the increase in Prandtl number, and the increase in Grashof number does not practically vary the effect of stratification parameter.

The present work describes numerical and experimental investigation of the heat transfer characteristics in a plate-fin, having built-in piezoelectric actuator mounted on the base plate (substrate). The geometrical configuration considered in the present work is representative of a single element of the plate-fin and triple fins. Air is taken as the working fluid. A performance data for a single rectangular fin and triple fins are provided for different frequency levels (5, 30 and 50HZ) , different input power (5,10,20,30,40 and 50W) and different inlet velocity (0.5, 1, 2, 3, 4, 5 and 6m/s) for the single rectangular fin and triple fins with and without oscillation. The investigation was also performed with different geometrical fin heights ( 50mm and 35mm) and distance between the fins (3mm and 6mm). It is observed that the heat transfer increases with the increase in the frequency and Reynolds number. It is further observed that triple fins with (height=50mm and distance between the fins=3mm) gives better enhancement as compared to other cases, The study shows that the piezoelectric actuator when mounted on the rectangular fins gives great promise for enhancing the heat transfer rate

Heat transfer around a flat plate fin integrated with piezoelectric actuator used as oscillated fin in laminar flow has been studied experimentally utilizing thermal image camera. This study is performed for fixed and oscillated single and triple fins. Different substrate-fin models have been tested, using fins of (35mm and 50mm) height, two sets of triple fins of (3mm and 6mm) spacing and three frequencies applied to piezoelectric actuator (5, 30 and 50HZ). All tests are carried out for (0.5 m/s and 3m/s) in subsonic open type wind tunnel to evaluate temperature distribution, local and average Nusselt number (Nu) along the fin. It is observed, that the heat transfer enhancement with oscillation is significant compared to without oscillation for low air inlet velocity. Higher thermal performance of triple fins is obtained compared to the single rectangular fin, also triple fins with (height=50mm and fin spacing=3mm) gives better enhancement as compared to other cases. This work shows that the piezoelectric actuator when mounted on the rectangular fins shows great promise for enhancing the heat transfer rate.

The friction clutch design strongly depends upon the frictional heat generated between contact surfaces during slipping at the beginning of the engagement. Firstly, the frictional heat generated reduces the performance of the clutch system and then leads to premature failure for contacting surfaces in some cases. The experimental effort in this work included manufacturing friction facing from functionally graded material (FGM) (aluminum and silicon carbide) for the clutch system. For this purpose, a special test rig was developed to investigate the thermal behavior of FGM and compare it with other frictional materials. The Taguchi L9 orthogonal design was selected to analyze the effect of the three factors (rotational, speed, torque, and the type of the frictional material) with three levels on the surface temperature of the contacting surfaces. A three-dimensional finite element model was built to validate the experimental results where the difference between them did not exceed 5.2%. The experimental results showed that the temperatures grew with the disc radius. Furthermore, the surfaces of the pressure plates and the flywheel were affected by frictional heat flow, and this effect increased when increasing the sliding speed. The lowest temperatures occurred when using FGM, which was lower than the other materials by 10%. This study presented an integrated approach consisting of design, manufacturing, and testing to study the complex frictional materials’ effect on the clutch system’s tribological performance.

Natural convection boiling heat transfer for Refrigerant R-134a flow in a metal foam filled vertical tube is numerically investigated in the present work by using the Multiphase Mixture Model MMM at constant heat flux for both transient and steady state behavior under different parameters. The effect of changing imposed heat flux, porosity, PPI (pore per inch), and tube diameter was analyzed. It is found that liquid saturation will reach its minimum value at the exit, and the dry out point will be seen always at the 2nd half of the tube length. Results also show that smaller tube diameter and higher porosity for the same PPI caused a higher temperature variation over the entire metal foam tube. Comparisons with previous works show good agreement. Keywords: Metal foam, Natural convection, Boiling, Multiphase mixture model, Vertical tube

An investigation of thermal conductivity enhancement, melting and solidification processes of Phase Change Materials (PCMs) by using metal foams has been carried out. Two models have been used in the experiments, model I for measuring the effective thermal conductivity of metal foam embedded in paraffin wax, and model II used as a small scale thermal energy storage device with and without metal foam for investigating melting and solidification processes of the PCM under different cooling conditions (natural and forced convection). The theoretical investigation involves analytical solution of two models, the semi-infinite medium for calculating the thermal conductivity, and the thermal energy storage system TESS has been analyzed including several assumptions for determining the convective heat transfer coefficient and the factors that controlling forced convection and solidification of the PCM. The experimental results show that the thermal conductivity of wax with 10 PPI metal foam increased by (37-39) times that of pure wax. Effects of pore density (10 and 40 PPI), metal foam, and mass flow rate on solidification process have been studied and the effects of pore density and metal foam on the melting process have also been investigated. The present experimental results have been compared with the available previous studies and gave a good agreement.

A low speed open circuit wind tunnel has been designed, manufactured and constructed at the Mechanical Engineering Department at Baghdad University - College of Engineering. The work is one of the pioneer projects adapted by the R & D Office at the Iraqi MOHESR. The present paper describes the first part of the work; that is the design calculations, simulation and construction. It will be followed by a second part that describes testing and calibration of the tunnel. The proposed wind tunnel has a test section with cross sectional area of (0.7 x 0.7 m2) and length of (1.5 m). The maximum speed is about (70 m/s) with empty test section. The contraction ratio is (8.16). Three screens are used to minimize flow disturbances in the test section. The design philosophy is discussed and methods for wind tunnel calculation are outlined. Simulation of wind tunnel using ANSYS shows no separation of flow along wind tunnel. Construction steps are also included in present work.

Theoretical and experimental investigations have been carried out on developing laminar combined free and forced convection heat transfer in a vertical concentric annulus with uniformly heated outer cylinder (constant heat flux) and adiabatic inner cylinder for both aiding and opposing flows. The theoretical investigation involved a mathematical modeling and numerical solution for two dimensional, symmetric, simultaneously developing laminar air flows was achieved. The governing equations of motion (continuity, momentum and energy) are solved by using implicit finite difference method and the Gauss elimination technique. The theoretical work covers heat flux range from (200 to 1500) W/m2, Re range from 400 to 2000 and (1.36×105 ≤ Ra ≤ 1.1×107) with radius ratio of 0.555 which is the same radius ratio used in the experimental part of this study and Pr=0.7. The experimental work includes construct a rig consists essentially of an annulus with uniformly heated outer cylinder and adiabatic inner cylinder to give clear insight into heat transfer process and compare its results with that obtained in theoretical part, the range of the study are (Re= 383, 724, 1000, 1500) and heat flux equal to (q =370, 422, 588, 980) W/m2. Numerical results were represented by the temperature profile, axial velocity profile, outer surface temperature and the distribution of local Nusselt number along the dimensionless axial distance. The velocity and temperature profile results have revealed that the secondary flow created by natural convection have significant effects on the heat transfer process. Results reveal also that the experimental local Nusselt number along the annulus follows the same trend as present theoretical results with mean difference 10.23 %.

Numerical investigations of unsteady natural convection heat transfer through a fluid-saturated porous media in inclined cylindrical enclosure are studied by solving the governing (3-D) Darcy-Boussinesq equations using finite difference method. The momentum equation of flow was solved by Relaxation method and the energy equation by using Alternating Direction Implicit (ADI) method. The problem is analyzed for modified Rayleigh number with range of (50-300),angles of inclination (0°,25°,45°60°90°), amplitude of sinusoidal temperature (0.2, 0.4, 0.8) and period (0.005, 0.01, 0.02). Results indicate an increase in the heat transfer with increasing of Rayleigh number, time, amplitude, angle of inclination and period. Also average and local Nusselt number were calculated and it is found that Maximum temperature and velocity occur at angle α=45 and this indicate a strong buoyancy force effect on convective flow.

Theoretical and experimental study has been conducted on developing laminar mixed convection heat transfer air flow through an annulus for both aiding and opposing flow with uniformly heated inner cylinder and adiabatic outer cylinder for the theoretical part and with uniformly heated inner cylinder while the outer cylinder is subjected to the ambient for the experimental part. In the theoretical investigation the energy equation was first solved using (ADI) method, and then the momentum equations and continuity equation were combined as the pressure correction formula and solved by the SIMPLE algorithm. The present theoretical work covers Ra range from 4.55*10 to 5.649 10° and Re range from 300 to 1000 with radius ratio of 0.555 and Pr-0.72. The velocity and temperature profile results have revealed that the secondary flow created by natural convection have significant effects on the heat transfer process and the results reveal an increase in the Nusselt number values as Ra increases. The experimental setup consists of an annulus which has a radius ratio of 0.555 and inner cylinder with a heated length 1.2m subjected to a constant heat flux while the outer cylinder is subjected to the ambient temperature. The investigation covers Reynolds number range from 154 to 724, heat flux varied from 93 W/m² to 857 W/m², and annulus angles of inclinations a=0° (horizontal), a=20°, 60° (inclined aiding flow), u--20.-60 (inclined opposing flow) and a 90° (vertical). The experimental results show an increase in the local Nusselt number values as the heat flux increases and as the angle of the inclination moves from the positive angles (inclined aiding flow) to the horizontal position and from the negative angles (inclined opposing flow) to the horizontal position. The experimental results show that the local Nusselt number values of the aiding flow are higher than that of the opposing flow at the same Reynolds number and heat flux.

The hydrodynamic and thermal boundary layers have great effect on the fluid flow and heat transfer between rotating turbine blade. In the present work, the flow and heat transfer is analyzed numerically by solving two dimensional incompressible boundary layer equations. A ( k – ε ) turbulence modeling is used to obtain the eddy viscosity. The finite volume method is introduced to carryout all computational solution with staggered grid arrangement. Due to complex physical domain the original coordinate system is transferred to non orthogonal coordinate system. The calculation of present work done for rotating two dimensional turbine cascade with different rotating speeds (1500 rad/s, 1800 rad/s, 1900 rad/s), and for different Reynolds number (5000, 10000, 100000), in subsonic flow (M

The effects of incoming wakes of upstream rotor on the flow field in a low pressure turbine cascade are investigated. The flow field is studied numerically with and without inlet wake. The rotor effect is represented by moving bars that produce passing wakes at the entrance of the stator. The flow field is analyzed numerically by solving the steady and unsteady forms of the two-dimensional compressible Reynolds-averaged Navier-Stokes equations. Steady flow is performed without wake while the unsteady flow is performed with periodic inlet wake for Reynolds number of order 105. A k- turbulence model is used to obtain the eddy viscosity. The Cartesian velocity components and pressure on a collocated (non-staggered) grid are used as dependent variables in the momentum equations, which discretized by finite volume method, body fitted coordinates are used to represent the complex blade geometry accurately, and grid generation technique based on elliptic partial differential equations is employed. SIMPLE algorithm is used to adjust the velocity field to satisfy the conservation of mass. The results show that the wake passing produces unsteady pressure field in the direction of the rotor traverse. The comparison with the experimental data is acceptable and there is similar trend between the prediction and experimental data, except at the separation flow region due to the limitation of the turbulence model.

A computational algorithm for calculating the unsteady compressible and turbulent hydrodynamic and thermal boundary layers over a porous flat plate with uniform suction or injection is developed in the present work. The mathematical modeling involves the derivation of the governing partial differential equations of the problem. These are the continuity, the momentum, the ( κ −ε ) turbulence model and the energy equations. Besides, the perfect gas law and the Sutherland' s law of molecular viscosity are also used. A proper initial and boundary conditions are specified to be used in the solution of the governing equations. A numerical solution of the governing equations is made by using the control volume approach, with non-staggered grid technique and modified SIMPLE algorithm. The numerical solution is capable of calculating the velocity and temperature distributions of the calculation domain, the kinetic energy and dissipation of turbulence, the local and average skin-friction and heat transfer coefficients and Nusselt number, and the hydrodynamic and thermal boundary layers thicknesses. All these parameters are calculated at the transient and steady states. The numerical results show that the developed algorithm is capable of calculating the flow field, properly and accurately. The results show that injection causess light decrease in the temperature inside the thermal boundary layer, a decrease in skin – friction coefficient, a slight increase in the Nusselt number, a decrease in hydrodynamic boundary layer thickness, an increase in thermal boundary layer thickness and an increase in the time required to reach the steady state. Suction almost causes reverse effects.

A numerical calculations algorithm has been developed in the present work for a thermodynamics and aerodynamic design of an axial flow compressor. The design calculations were based on thermodynamics, gas dynamic, fluid mechanics, aerodynamic and empirical relations. A two- dimensional compressible flow is assumed with constant axial and rotor blade velocities. A free –vortex swirl distributions was used in the design. These calculations include; power of the compressor, thermodynamic properties of the working fluid, stage efficiency, number of rotor and stator blades, tip and hub diameters, blade dimensions (chord, length and space) for both rotor and stator, velocity triangles before and after the rotor, Mach number, solidity, degree of reaction, flow and blade angles (blade twist) and lift and drag coefficients along the blade and lift. A repeated stage calculation is made to calculate the above parameters along compressor stages. The twist of the blades can be calculated along the blade length at any required number of sections selected by the designers to obtain smooth blade twist profile. The developed algorithm was tested on a compressor cascade series type NACA 65(12)10 with circular camber angle of (30). The results show that; the lift coefficient decreases as mean flow angle increases, the drag coefficient increases along blade length at a mean flow angle of (15), the relative Mach number increases along blade length as mean flow angle increases, the ratio of total drag coefficient to lift coefficient increases when the mean flow angle increases, the drag coefficient decreases along blade length as the solidity increases, the cascade efficiency increases as the mean flow angle increase to (45).

A theoretical study of heat transfer and fluid flow phenomena in welding process has been carried out in the present work. The study involved the numerical solution of the transient NavierStokes and Energy equations of the weld pool region by using Finite Difference Method. The electromagnetic force field and buoyancy were included in the formulation The stream-vorticity formulation was used in the mathematical model. The numerical solution is capable of calculating the vorticity, stream function, velocity, temperature, and the interface movement of the weld pool in Gas Metal Arc Welding (GMAW). The model can be used to solve the Gas Tungesten Arc Welding (GTAW) problem. A numerical calculations algorithm was developed to carry out the numerical solution. The numerical results showed that the finger penetration phenomena occurs in the Gas Metal Arc weld is adequately explained through the application of the model. It is found that the frequency of spray transfer is a dominant factor in addition to shape of the weld pool geometry. A verification of numerical results was made through a comparison with a previous work, the agreement was good, confirming the capability and reliability of the proposed numerical algorithm in calculating fluid flow and heat transfer in Gas Metal Arc weld pools.

In the present work , a numerical study has been made for the developing compressible turbulent flow and heat transfer in circular tube with uniform injection or suction. The study included the numerical solution of the continuity, momentum and energy equations together with the two equations of the (k-ε) turbulence model, by using the Finite Difference Method (FDM). The air was used as the working fluid, and the circular passage was composed of tube with diameter (20.0) cm , and the length was 130 (hydraulic diameter) .The Reynolds number of the flow was (Re=1.78x106 ), and the Mach number (M=0.44) the ratio of the transverse velocity at the wall (vw) to the axial velocity at inlet (Uin), Ω=(vw/Uin), for suction equal(0.001) and for injection (-0.001).. The wall of the tube was heated with constant wall temperature (Tw) and in other case with constant heat flux (Qw) as a thermal boundary condition. The development of both hydrodynamic and thermal boundary layers occurs simultaneously. The computational algorithm is capable of calculating the hydrodynamic parameters such as the velocities , friction factor , turbulence structure which includes the Reynolds stress and the turbulent kinetic energy and eddy viscosity. Besides, the thermal parameters are also predicted, such as the temperature, Nusselt number, and the turbulent heat fluxes.The Results showed that the hydrodynamic and thermal entrance length is increased with the increasing of Reynolds number. The suction caused a flatten for the velocity profile and thus decreasing the hydrodynamic entrance length, and caused an increase in the Nusselt number and decreasing the local coefficient of friction, but injection caused a steeping of the velocity profile , and thus increasing the entrance hydrodynamic length and caused a decrease in the Nusselt number and increase the local coefficient of friction. Turbulent kinetic energy and turbulent heat flux are decreased with suction and increased with injection .Predictions have been obtained which are in good agreement with results obtained by past experimental and theoretical work.

A thermal layout modeling and optimization routine for a Printed Circuit Board (PCB) has been made in the present work. The thermal model includes the modeling of electronic components based on thermal resistances and the PCB as a flat plate with multiple heat sources. Isothermal and Isoflux natural convection heat transfer for horizontal and vertical PCB thermal modeling. The numerical solution method for the 2-dimensional thermal model is the superposition method for the adiabatic PCB edges. The optimization meshing model was constructed based on the Complex Method. The numerical Complex Method has been improved to a new optimization method named as "Dual Complex Method", which minimize the objective function to give the optimal step sizes in X and Y -directions. The optimization thermal layout model was constructed to accommodate the numerical SUMT mathematical optimization method. Optimization results show that in free convection, and for the optimum total heat loss objective function, the larger dimension of the PCB must be oriented horizontally rather than vertically, and the electronic components or sub-assemblies of large power should be placed near the top of the PCB. In the case of horizontal upset-down in natural convection, the components of large power must be placed near the center of the PCB.

An efficient numerical model had been developed to model the thermal behaviour of the rolling process. An Eulerian formulation was employed to minimize the number of grid points required. The model is capable to calculate the temperature distribution, the heat penetration depth, the convection heat transfer coefficient of cooling, the flow of metal through the roll gap, and the heat generation by plastic deformation and friction. The roll is assumed to rotate at constant speed, and the temperature variations are assumed to be cyclically steady state and localized with a very thin layer near the surface. The Conventional Finite Difference (CFDM) based on cylindrical coordinates was used to model the roll, and a Generalized Finite Difference Method (GFDM) with non-orthogonal mesh was employed in the deformed strip region and the roll-strip interface area. An upwind differencing scheme was selected to overcome the numerical instability resulting from the high velocity ( high Peclet number ) involved in the rolling process. The equations of the strip and roll are then coupled together and solved simultaneously. Both cold and hot rolling heat transfer behaviours, velocity distribution, and heat generation by deformation and friction under typical rolling conditions were presented to demonstrate the feasibility and capability of the developed numerical model. It has been found that, while the strip is under deformation, the bulk temperature inside the strip increases continuously; this is largely controlled by the deformation energy. On the other hand, the strip surface temperature changes much more drastically and it is mainly controlled by the friction heat and the roll temperature. The roll acts like a heat sink, because the coolant heavily cools it. Thus, as soon as the strip hits the roll its surface temperature drops. Since considerable friction and deformation heat are created along the interface and transferred from the neighboring sub-layer, the surface temperature picks up rapidly. Finally, the results of the temperature distribution for both cold and hot rolling and the heat generation by deformation and friction obtained from the present study were compared with previous published work to verify the validity of the numerical solution. Good acceptable agreements were obtained.

Experiments were carried out to study the local and average heat transfer by mixed convection to a simultaneously developing air flow in a horizontal inclined, and vertical concentric cylindrical annulus. The experimental setup consists of an annulus has a radius ratio of 0.555 and inner cylinder with a heated length 1.2m subjected to the constant heat flux while the outer cylinder is subjected to the ambient temperature. The investigation covers Reynolds number range from 154 te 845, heat flux varied from 96 W/m² to 845 W/m², and annulus angles of inclinations a (horizontal), 40°, 70°, and 90° (vertical). Results demonstrate the temperature variation along th inner cylinder surface and the local Nusselt number Nu, variation with the dimensionless axia distance, for all angles of inclinations which shows an increase in the Nu, values as the heat fit increases and as the angle of the inclination moves from the vertical to the horizontal position

Supersonic gas jets in confined liquid metal atomizing nozzle were studied by using the method of characteristics. Nitrogen at operation (stagnation) pressure of (1.65Mpa) was used in the study, with three different values of ambient pressure (1.25, 1.52 and 1.75 bar). For all the three values, the nozzle is over expanded. The Mach number at the nozzle exit for all the investigated cases was (2.64). The pressure and Mach number of the atomizing gas at various lattice points downstream of the nozzle exit were found. Besides, the effect of heat transfer from the liquid metal (aluminum) on the gas flow behavior was also investigated, The results showed that the stagnation temperature rise of nitrogen caused by heat transferred from aluminum is very small and can be neglected, and hence the flow can be assumed to be adiabatic. The results indicates that the pressure of the atomizing gas tries to adjust to the higher ambient pressure by the formation of a weak oblique "lip" shock followed by a reflected weak oblique "edge" shock. As the ambient pressure increases, the inward earvature of the jet boundary increases and hence the length of the jet decreases. As the ambient pressure increases, the point at which the oblique "lip" shock strikes the wall moves upstream toward the nozzle exit. If the shock is to be avoided, the difference between the ambient and nozzle exit pressures must be decreased. For fixed nozzle geometry, this can be done either by increasing the operaton pressure or by decreasing the ambient pressure.

The thermal behavior of an octagonal shell orbiting body in space environments had been simulated theoretically in the present work, and a simplified experimental test in a thermal vacuum chamber was also made on half-scale model of the prototype to investigate the problem. A mathematical model was built and simulated numerically by using lumped system technique and finite difference control volsme approach with explicit scheme. The body in its orbit around the earth is assumed to receive solar, albedo and earth radiation heat fluxes. The orbit is circular of (500-Km) height and (40) inclination. The developed computational algorithm is capable of calculating the heat fluxes on body faces and the temperature distribution of the body at any time instant. The results showed that the albedo and earth heat fluxes are smaller when the orbit is higher. In the side faces, the heat fluxes are maximum when orbit inclination is minimum, and vice versa, the inverse behavior is true for the upper and lower faces. The heat fluxes are maximum in winter solstice and minimum in summer solstice. If the difference between the emissivity and absorptivity values is low, the body reaches to synchronous steady state faster. The emissivity is affected more than absorptivity. The temperatures of faces, which see the carth, are more fluctuated than the other faces. Comparison between theoretical and experimental results showed good agreement.

The transient performance (acceleration and deceleration) analysis of turbojet gas turbine engire has been carried out in the present work. Transient simulation of the engines is based on the compatibility of flow and rotational speed but not of work. Gas turbine simulation is a general- purpose simulation developed for steady state (matching) study. Matching is achieved by zeroing the difference in mass flow rate of adjacent components, and work of compressor-turbine pairi Steady state is taken as an initial condition for transient simulation of the engine. The factors indicating engine limits such as surge margin, engine maximum temperature, and combustion chamber flameout that affect transient response has been studied. The results show that there is sudden change in the investigated parameters during transient operation, except for the rotational speed and the engine flow rate. Increasing the compressor surge margin and /or maximum turbine inlet temperature improves engine acceleration and decreases the acceleration time. Comparison with previous experimental work showed good agreement.