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Go to Editorial ManagerThe conjugate natural convection-conduction heat transfer in a domain composed of nanofluids filled porous cavity heated by a vertical solid wall is studied under steady-state conditions. The vertical left wall of the solid is kept isothermal at hot temperature Th. The vertical right wall of the solid is in contact with the nanofluid saturated porous medium contained in the cavity. The right vertical wall of the cavity is kept isothermally at the lower temperature Tc. The upper and lower horizontal walls are kept adiabatic. The governing equations of the heat transfer in the solid wall and heat and nanofluid flow, based on the Darcy model, in the nanofluid-saturated porous medium together with the derived relation of the interface temperature are solved numerically using the over-successive relaxation finite- difference method. A temperature independent nanofluids properties model is adopted. The investigated parameters are the nanoparticles volume fraction (0-0.2), Rayleigh number Ra (10-1000), solid wall to base-fluid saturated porous medium thermal conductivity ratio kwf (0.1, 1, 10), and the solid wall thickness D (0.05-0.5). The results are presented in the conventional form; contours of streamlines and isotherms and the average Nusselt number. At a very low Rayleigh number Ra=10, an enhancement in heat transfer within the porous cavity with is observed. Otherwise, the heat transfer may be unchanged or deteriorated with depending on the wall thickness D and the conductivity ratio kwf.
In this paper the conjugate heat transfer in rectangular channel is numerically investigated, where the effect of both axial heat conduction and entrance region on the internal forced convection in rectangular channels are studied. With decreasing the dimensions of channels the thickness of walls become large and in order of the channels dimensions as in microchannels. As a results the heat conduction in the walls especially in the axial direction can not be ignored, since it lead to decrease in the efficiency of heat transfer process. Also the effect of entrance region is taken into consideration where the flow is assumed developing hydro dynamically and thermally. A finite volume method is used to numerically solve the conjugate heat transfer in both the fluid and wall simultaneously. The results obtained shows that the existing of axial heat conduction lead to reduction in the heat transfer and it's effect increased with increasing the thickness of walls and Reynolds number. In this paper a correlation has been developed to calculate the value of axial heat conduction in channel's walls based on most of the affecting parameters. This correlation can be used accurately to compute the value of axial conduction in rectangular channels.
The steady-state natural convection from heat sink fin arrays was studied on horizontal, vertical, and inclined heat sinks. Under natural convection, horizontal and vertical heat sinks with parallel fins were tested by considering radiation heat transfer. The experiments were conducted with power inputs ranging from 60 W to 455 W in order to obtain different temperatures. According to the result, when heat input increases, the heat transfer coefficient increases by 38 %, 40.78 % for horizontal and vertical respectively. For horizontal and vertical cases, new correlations have been presented to calculate the Nusselt number influenced by the Rayleigh number. For the incline case, the effect of buoyancy force was studied by changing the inclination angles at 0, 30, 45, and 60 degrees from vertical position. According to comparisons between vertical and incline cases, Nusselt number and heat transfer coefficient were most improved at 30 degrees by 6 %.
In this paper friction stir welding process has been studied whereby utilized FEM method (Ansys software ver. 20). The main effective parameter in this process were rotational speed, linear speed, tool shoulder radius, heat transfer coefficient and clamping percentage to study their influence on represent temperature, von misses stress and frictional stress distribution. Because of the difficulty to obtained the number of the simulation cases in order to get the most important results, Taguchi L27 orthogonal array was apply to reduce the total number of the simulation cases. Pure copper (t = 3.18 mm) material type was applied as work plate material. ANOVA statistical tool was utilized to achieved the optimization process after the simulation cases done. Percentage of contribution of each parameter can be obtained by ANOVA table and mean of S/N ratio plot. Validation process was achieved between the Current study and experiment work in the temperature distribution field with percentage of error 2.7 %. From optimization result It is found that the optimum condition in order to obtained good results for temperature was rotational speed of (450 rpm), linear speed (2.75 mm/s), tool shoulder radius (7 mm), heat transfer coefficient (300 w/m 2 K), clamping distance percentage (40 %). And for von misses stress was rotational speed of (550 rpm), linear speed (3 mm/s), tool shoulder radius (7 mm), heat transfer coefficient (300 w/m 2 K), clamping distance percentage (20 %). While for frictional stress was rotational speed of (450 rpm), linear speed (2.5 mm/s), tool shoulder radius (7 mm), heat transfer coefficient (300 w/m 2 K), clamping distance percentage (30 %).
In this work, the turbulent buoyancy driven fluid flow and heat transfer in a differentially heated tall rectangular enclosure filled with nanofluid is quantified numerically. The two dimensional governing differential equations (continuity, momentum, energy and low Reynolds number LRN k-ω turbulence equations) are discretized using the finite volume method. SIMPLE algorithm is employed to obtain stabilized solution for high Rayleigh numbers. Two types of nanofluids namely, Al2O3-water and Cu-water, were considered. The effect of Rayleigh number (1010 to 1012), diameter of nanoparticles in the range 25-100 nm, nanoparticle volume fraction in range 0-0.08 and the aspect ratio (30, 40 and 50) on fluid flow and heat transfer are investigated. The present results are compared with previously published work and a qualitative agreement with good validation is obtained. Results show that addition of nanoparticles makes the liquid be more viscous which decreases the vertical velocity component and also decreases the temperature gradient near the walls. Also an announced heat transfer enhancement is obtained with nanoparticle volume fraction reaching a maximum point called optimal volume loading, at which the maximum convective heat transfer is obtained, and then it decreased with further increase of volume fraction.
In this study, a numerical investigation has been carried out for single phase flow behavior for thirty six internally finned tubes to demonstrate the effect of axial pitch to fin height ratio (p/e) for 0.8≤p/e≤6.345, helix angle of internal fins (β) for 30°≤β≤70°, apex angle of internal fins (α) for 0°≤α≤53.13°, internal fin height (e) for 0.6mm≤e≤1.0mm, internal tube diameter (di) with 14 mm and Reynolds number (Re) of single phase flow for 10000≤Re≤50000 on enhancement of forced convection heat transfer and reduction of friction factor by using ANSYS CFX program. It solves the three- dimensional Navier-Stokes equations for steady state turbulent with SST model and enhance wall treatment. The numerical analysis provided at fully developed velocity and temperature. Numerical results showed that the smallest axial pitch to fin height ratio (p/e) =0.8 and with apex angle α=10 degree provided enhancement of heat transfer of 2.8 to 3.55 times higher than of smooth tube. Finally, present numerical results are seen to be in good agreement with literature experimental correlations.
A numerical model has been developed to determine the effect of the wire screen mesh (wick) type on the heat transfer performance of copper–water wicked heat pipe. This model represented as steady-state incompressible flow. The governing equations in cylindrical coordinates have been solved in vapor region, wick structure and wall region, using finite difference with forward-backward upwind scheme. The results show that increasing the mesh number led to decreasing the maximum heat transfer limit and increasing the capillary pressure. While, for the same heat input the operating temperature of the heat pipe increase when the mesh number increase. Also, it was found that increasing the evaporation length, with constant condensation length, decrease the operating temperature and increase the maximum heat transfer limit. For verification of the current model, the results of liquid pressure drop for a heat pipe have been compared with the previous study for the same problem and a good agreement has been achieved.
Natural convection heat transfer in porous cavity with arc shape wall filled with nanofluid is studied numerically. The right arc shape wall of the cavity is heated at constant temperature (Th) while the left wall is kept cold at constant temperature (Tc), and the other horizontal walls are thermally insulated. The governing equations of the heat transfer and nanofluid flow are solved Flex PDE software. A temperature independent nanofluids properties models are adopted. The investigated parameters are the nanoparticles volume fraction Ø= (0-0.2), Rayleigh number Ra (10-1000) and arc center Ce (1-∞). The results are presented by contour of streamlines, isotherms and the average Nusselt number. The results have showed that the average Nusselt number decreases with increasing Ce and increases with increasing Ra and Ø.
The natural convection heat transfer in a porous media filled and isothermally heated from the bottom wall of triangular enclosure is analyzed using finite element software package (FLEXPDE). Darcy's law was used to write equations of porous media . The curved bottom wall shape, with Radii R= 0.8 , 1 and 1.5, was applied to a triangular enclosure. The boundary condition of the vertical wall is isothermal and of the inclined wall is adiabatic. The study was performed for different Rayleigh numbers (100 ≤ Ra ≤ 1000 ) and aspect ratios (0.4 ≤ AR ≤ 1 ) . Numerical results are presented in terms of streamlines, isotherms and Nusselt numbers. It was observed that heat transfer enhancement was formed with increasing Rayleigh number and aspect ratio . A comparison of the flow field and isotherm field is made with that obtained by [11], which revealed a good agreement .
This review focuses on the experimental and numerical studies of sweeping impingement jets that serve in cooling of hot surfaces. It is known that the impinging jets produce high-localized heat transfer coefficient. The sweeping jet covers a wider area on a hot target to improve the heat transfer rate, they could be used to increase the cooling rate of the impingement surface by disturbing the boundary layer. To display a readable survey, the current review was partitioned to four groups based on engineering configurations. The review shows that the sweeping nozzle gives better efficiency in heat transfer, improved Nusselt number and uniform target surface temperature, compared with the conventional normal jets. The current review reveals that the sweeping-jet mechanism can be achieved either by fluidic oscillator or by exciting a flexible wall forming an oscillating jet. Most of the fluidic oscillator researches are conducted experimentally (27%), while the researches that use flexible wall are about 24%.
In this study, a numerical investigation has been carried out for single phase flow behavior for thirty six internally finned tubes to demonstrate the effect of axial pitch to fin height ratio (p/e) for 0.8≤p/e≤6.345, helix angle of internal fins (β) for 30°≤β≤70°, apex angle of internal fins (α) for 0°≤α≤53.13°, internal fin height (e) for 0.6mm≤e≤1.0mm, internal tube diameter (di) with 14 mm and Reynolds number (Re) of single phase flow for 10000≤Re≤50000 on enhancement of forced convection heat transfer and reduction of friction factor by using ANSYS CFX program. It solves the three-dimensional Navier-Stokes equations for steady state turbulent with SST model and enhance wall treatment. The numerical analysis provided at fully developed velocity and temperature. Numerical results showed that the smallest axial pitch to fin height ratio (p/e) =0.8 and with apex angle α=10 degree provided enhancement of heat transfer of 2.8 to 3.55 times higher than of smooth tube. Finally, present numerical results are seen to be in good agreement with literature experimental correlations.
The direct-contact evaporation method is characterized by its effectiveness in applications of heat exchangers, especially in cooling systems, due to the absence of any heat resistors that prevent the transfer of heat between the cold and hot medium. The direct contact heat transfer depends mainly on how quickly the heat is taken by the bubbles of the evaporative refrigerant from the liquid and the increase in its volume up to the top of the heat exchanger, which is usually a cylindrical liquid column so that the temperature drop therein is uniform and even. There is much research on the method of heat transfer by direct contact. In this research, we collected and summarized most of the theoretical and practical researches that examined this method with the most important findings.
This study investigates the effect of rotating two rows of horizontal cylinders on forced convection heat transfer in cross flow. Each row consists a three rotating horizontal cylinders heated at constant temperature. The governing equations for the steady, laminar, two dimensional, incompressible flow and constant fluid properties are solved numerically using the finite element method with FlexPDE soft package for a two rows of rotating cylinders at the same direction and at opposite directions. The main parameters are: Reynolds number ( 40 10 Re − = ), Prandtl number ( 7.0 Pr = ), dimensionless longitudinal pitch (SL=1.5-2.5), dimensionless transverse pitch (ST=1.5-2.5) and the dimensionless angular velocity (Ω=0-3) (for both directions clockwise CW and counter clockwise CCW). It is found that the average Nusselt number increased with increasing Re and ST, and decreases with Ω and SL. The results are compared with other authors and give a agreement.
This paper explores the significance of energy conservation in the context of rising energy consumption and its impact on economic growth. With a focus on cooling systems, particularly evaporative condenser technology, the study aims to investigate its fundamentals, operating principles, and theoretical aspects. The paper delves into the various types of condensers used in cooling systems, emphasizing the role of evaporative condensers in enhancing heat transfer efficiency. The operating principles of evaporative condensers are detailed, considering factors such as air and water flow rates, wet bulb temperatures, and heat transfer coefficients. Theoretical models and mathematical approaches for evaluating evaporative condenser performance are also reviewed. The research includes an extensive review of existing literature on evaporative condenser technology, covering refrigeration models, HVAC systems, and various experimental studies. Theoretical models are discussed, highlighting the challenges in accurately modeling evaporative condenser behavior. The paper also presents achievements and advancements in research, including experiments that demonstrate the positive impact of evaporative cooling on air-cooled condenser systems. Various case studies and experimental validations showcase the potential energy savings and improved performance achieved through the incorporation of evaporative condensers in cooling systems. By switching from an air-cooled to an evaporatively-cooled condenser, one can reduce electricity consumption by 58%, according to research. This alternate condenser type improves performance by 113.4% at from 3 to 3000 kW of cooling power.
The natural convection heat transfer from horizontal isothermal three cylindrical rods inside equilateral triangular enclosure has been studied numerically. The enclosure is filled with air, and the heated rods are located at equal distances (E) from triangle center. A finite element software package (FLEXPDE) is used in the present study to solve the set of non-linear equations governing the process. Solutions are obtained for aspect ratio D/H=1/6 and range of distance E=0.2-0.6 and Rayleigh (Ra) number changes from 103 to 106. The effect of Ra and E were examined. Results are presented by streamlines, isotherms and Nusselt number and it indicates that the Nusselt number is significantly increase with increasing both Ra and E. A comparison of the Nusselt number was made with that obtained by [7], and showed substantial improvement to about 65% in some cases.
A household refrigerator represents an essential device for all houses nowadays. The electric energy consumed by the refrigerator and the fluctuation of the temperature inside the fresh food cabin is the main two problems affecting its performance. Incorporating phase change material (PCM) inside the refrigerator is one of the solutions for the previous mentioned problems. In the present study, a water PCM is added to the cabinet of 220-litters double door refrigerator. The PCM (0.5 ml of water) is added at three different locations, touch the front of the evaporator part inside the cabin, touch the rear of the evaporator part in the cabin, and far away from the evaporator part inside the cabin. The location of the PCM determines how much energy is released and stored from the evaporator. The use of phase change material (PCM) touch to the evaporator increases the rate of heat transfer due to the conduction method being used throughout the whole heat transfer process from the evaporator to the phase change material (PCM), which raises the refrigeration system's COP (coefficient of performance). The experimental test period is 24 hours for each day. Firstly, the refrigerator is tested without using PCM, and the power consumption, the temperatures at different points for the refrigerator, suction pressure, discharge pressure, the ambient temperature, and the time on period and time off period of the compressor are measured. Secondly, for same testing period all previous parameters are measured with using PCM at different locations inside the refrigerator. The results show that, adding the PCM (water) behind the evaporator led to increase the COP by 21.97%, increase the compressor off time by 73 minutes, reduction in power consumption of 14.4%, decrease of exergy losses of the system by 8% and temperature fluctuation reduced inside the fresh food cabin, that enhance the quality of stored food. Adding the PCM front the evaporator improve the previous parameters but less than that of the first case. The third location, adding the PCM far away from the evaporator has no improvement on the refrigerator's performance.
This numerical study aims to enhance the heat transfer efficiency by dissipating the heat Emitted from electronic processors. A jet impingement technique is utilized with porous layer covering a metal fin as a heat sink. Forced convection and normal convection (due to the buoyancy effect) are taken into consideration. The two equations model (Local Thermal Non-Equilibrium LTNE) employed to describe the energy equations of the two phases of the porous surface. Finite Element Method (FEM) used to discretize these equations to obtain the numerical solution. To make this study closest to the reality, constant heat flux boundary condition is applied underneath the metallic heat sink. The geometry comprises of three domains: Free flow channel, Porous layer and Metal fined heat sink. In order to simulate the heat transfer, isotherms; streamlines and Nusselt number have been considered. Investigation has been done by inspecting the effects of the pertinent non- dimensional parameters such as: Reynolds number ( Re = 100-900), Darcy number ( Da = 10 -1 -10 -6 ), Richardson number ( Ri = 0.1-100) and Porosity ( ε = 0.85-0.95). The results show that increasing Re and decreasing ε lead to enhance Nusselt number. Richardson number below 100 has no significant effects on Nu . At Re above 400, Nusselt number proportional with Darcy number. The enhancement of Nusselt number is found to be 250 % by increasing Re from 100 to 900, 290 % by decreasing ε from 0.95 to 0.85 and about 13 % by increasing Darcy number from 10 -6 to 10 -1 .
In this study, a numerical investigation has been carried out for single phase flow behavior for thirty six internally finned tubes to demonstrate the effect of axial pitch to fin height ratio (p/e) for 0.8≤p/e≤6.345, helix angle of internal fins (β) for 30°≤β≤70°, apex angle of internal fins (α) for 0°≤α≤53.13°, internal fin height (e) for 0.6mm≤e≤1.0mm, internal tube diameter (di) with 14 mm and Reynolds number (Re) of single phase flow for 10000≤Re≤50000 on enhancement of forced convection heat transfer and reduction of friction factor by using ANSYS CFX program. It solves the three- dimensional Navier-Stokes equations for steady state turbulent with SST model and enhance wall treatment. The numerical analysis provided at fully developed velocity and temperature. Numerical results showed that the smallest axial pitch to fin height ratio (p/e) =0.8 and with apex angle α=10 degree provided enhancement of heat transfer of 2.8 to 3.55 times higher than of smooth tube. Finally, present numerical results are seen to be in good agreement with literature experimental correlations.
Hydrodynamics and heat transfer in a fully developed laminar incompressible reciprocating channel flow subjected to a constant heat flux have 'been investigated analytically using similarity transfo1mat ion. An exact analytical solution for the velocity, local, and bulk temperature as well as the Nusselt number has been obtained. The effect of the parameters Pr, Ao, y, and X/Dh on u, T, Tt, Nux, and Nux are presented. The results showed that the local Nusselt number is increased with increasing Womersly number (A.) while the dimensionless temperature is increased with Womersly and decreases with amplitude (Ao). The Prandtl number has a significant effect on the local Nusselt number. The results were found in very good agreement with those obtained numerically using the finite volume method. The comparison with the experimental results of other authors gave a reasonable identification.
The solar chimney is a natural draft device that uses solar radiation to provide upward momentum to the in-flowing air, thereby converting the thermal energy into kinetic energy through an air turbine which in turn can be converted into electrical energy. The main parts of the solar chimney power plant are a large circular solar collector, a tall chimney, and an air turbine. In this paper, a theoretical study was performed to evaluate the performance of a solar chimney power plant system in Basrah City, where sunny days and solar radiation are high. A mathematical model was developed to study the effect of various parameters on the output power of the solar chimney. I1 was found that the output power depends strongly on the chimney tall and the difference between the collector air temperature and the ambient air temperature as well as the outside heat transfer coefficient, which essentially depends on the wind speed.
Solar energy is the most suitable among all renewable energy options for competing with fossil fuels in desalination due to its ability to utilize both heat and power for the process. In this study, the Parabolic Trough Solar Collector (PTSC) for powering a Single Stage Flash (SSF) desalination unit was proposed for Basrah city climate, Iraq. The desalination system comprises two directly coupled sub-systems: the PTSC and the SSF desalination unit. The preheated feed brine water coming from condenser was used as a Heat Transfer Fluid (HTF) for PTSC, which gets heated to a desired temperature referred to as the Top Brine Temperature (TBT). The numerical simulations were performed via EBSILON professional 16.02 (2022) software. The effects of TBT, mass flowrate of feed brine water to get the desired TBT, solar collector area, and vacuum pressure inside flash chamber on the performance of the desalination system was studied. A major finding of the current study can be summarized as follows: The collector efficiency is enhanced eventually as TBT increases. The maximum values of distillate water in June are around 5.5, 4.56, 3.69, 2.75 and 1.85 kg/h for 12.408, 10.434, 8.3472, 6.26, and 4.1736 m² collector area respectively, when TBT 107 °C and vacuum pressure 40 kPa. For 1.598 m² collector area, the total distillate in the 1st of June amounted to 7.9 kg, with an average production rate of around 0.7 kg/h. The solar SSF system's productivity per solar collector unit area at 20 kPa, 15 kPa, and 10 kPa vacuum pressures was 4.7 kg/day/m², 5.3 kg/day/m², and 6.25 kg/day/m², respectively. The average Performance Ratio (PR) values are determined to be 0.694, 0.577, and 0.491 for 10 kPa, 15 kPa, and 20 kPa, respectively. These results are very acceptable when compared with an existing literature.
The thermoelectric behavior of different materials under various conditions has been investigated numerically by using the heat transfer module of the COMSOL Multiphysics software platform. A simulation study of the thermoelectric materials (TEM) performance was created by altering the current applied from 0.1 to 1.0 A and setting the hot side temperature (T H ) as 273 K. The impact of different performance metrics, such as cold side temperature and output voltage, has been proven and investigated. It has been shown that the material of the thermoelectric legs', length of leg, and thickness of electrodes significantly impact the thermal and electrical performance of the thermoelectric (TE) module. Appropriate ranges have been studied in the simulation, such as the amperage values applied to the unit as mentioned above, the length of the leg within a range of 1 to 8 mm, and the thickness of the electrode with different values of 0.1 to 0.5 mm, which will achieve excellent performance for the Thermoelectric unit. Modeling and simulation results demonstrated and revealed the optimal and potential use of bismuth telluride (Bi 2 Te 3 ) as well as lead telluride (PbTe) as suitable for Peltier cooling applications. As for the use of cobalt triantimonide (CoSb 3 ), it is in contrast to the two previous metals, as it is effective and appropriate if applied to power generation. The results are validated with another study from the literature, and there is an excellent agreement with an error rate that does not exceed 0.164%.
A simulation of fluid-structure interaction (FSI) and combined convective heat exchange is accomplished in an open trapezoidal cavity-channel. A non-Newtonian (power law fluid) is inspected within the laminar region. The heat source is simulated by an isothermal hot cavity bottom wall, whereas all the rest solid walls are perfectly insulated. A deformable baffle is fixed at the top wall of the channel and its free end extends towards the open cavity. The location of the deformable baffle on the top wall is varied. The baffle position is investigated together with Richardson number ($Ri = 0.01-100$) and power law index ($n = 0.5-1.5$). The problem was solved using finite element method with Arbitrary Lagrangian-Eulerian (ALE) technique. The results are compared with the non-baffled channel. The study shows that the proposed baffled channel enhances the heat transfer notably.
In this study a two dimensional, steady state propagation of the laminar premixed flame was numerically and experimental are investigated. The energy, momentum, continuity equations for species and global reaction mechanism with equation of stat for ideal gases were solved. Constant temperature boundary condition is applied on axi – symmetric in y – direction domain. The governing equations were discretized by using computation fluid dynamics (CFD) and finite-volume method - central differencing scheme, then solved using Gauss-Seidel Iteration method on uniformed grid with VISUAL BASIC code. Effects of equivalence ratio and initial temperature of fresh gases (air – fuel mixture) were investigated for three types of fuel Methane, Propane and Butane. Also the flame speed and flame temperature were experimentally measured for air – fuel (Methane, Propane, Butane and LPG) mixtures. The burning velocity was calculated depending on the flame speed and flame temperature measuring. The flame speed and flame temperature were measured by using optical technique. Effects of equivalence ratio and initial temperature of fresh gases (air – fuel mixtures) on flame speed and flame temperature are investigated experimentally. Results were generated for the detailed description of the local fluid flow and heat transfer characteristics including temperature, axial velocity, density and mole fractions profiles. For example the flame speed reached 274.4 cm/s as a maximum value at Ø=1.1 for propane air mixture, and flame temperature comparison give a good agreement between theoretical and experimental results at rich mixtyre
The solar chimney power plant is one of the modern models studied on the world. This study presents an engineering and numerical analysis of solar chimney with different parameters. Also, it studies the comparison of two collector base shapes(circular and hexagonal) depend on the five storage material types and their effects on the heat transfer, velocity, efficiency, etc. inside the solar chimney system by considering the solar array intensity equations and the energy equation to calculate the heat transferred and stored by applying the laws of CFD. The finite volume method is used to analyze the geometry physical model by applying a commercial Fluent 6.3 code with Gambit 2.3. The obtained results show that the efficiency of solar chimney is increased by increasing the area of solar glassed collector with circular base shape than the others of polygonal or rectangular one because the circular was covered large area of system. So, the circular ground collector shape for thermal storage is the favour because it is the better to increase the velocity of entering air and to increase the efficiency of turbine. In addition to that the black Pebble storage plate is the better material for heat storage which is convected to air passed for operation of turbine than the other types aluminum, tar, copper and steel seriously.
This study presents three-dimensional numerical simulations of single-phase laminar flow and forced convection heat transfer of water in a five-layer microchannel heat sink with two channel configurations: radial arrangement and parallel divergence channels. The thermal performance and pressure drop characteristics were evaluated under identical operating conditions, including a constant mass flow rate of 3.925 × 10⁻⁴ kg/s and a uniform heat flux of 90 W/cm². The results indicated that the radial microchannel configuration significantly enhanced both hydrodynamic and thermal performance compared with the parallel divergence design. Specifically, the pressure drop was reduced by approximately 32.5%, the overall performance index increased by about 1.5, and improved temperature uniformity across the heat sink was achieved. These findings demonstrate the superiority of the radial microchannel arrangement for high-heat-flux thermal management applications.
Solar energy can only be used when it's sunny outside. Therefore, solar heating is only efficient during the day and decreases at night or on overcast days. Consumer energy needs have a distinct seasonal structure, and solar energy cannot completely meet those needs. In order to satisfy customer demand, energy storage is essential. In order to maximize the use of solar energy and to increase the energy and efficiency of the solar absorption system, superior thermal properties of sophisticated materials, such as phase change materials, are important [1]. In the current study, 20 kg of phase change material (PCM) is integrated with solar water heating and fed into a storage tank to enhance the solar water heating efficiency. Helical coil heat exchangers were added to the storage tank as an external load. The trials were conducted in four separate months (September 2021, April, May, and June 2022) that were chosen on the first day. The effectiveness, heat gain, and significance of the phase change material in increasing heating efficiency throughout the day were studied using a range of variables, including water volume flow rate (2, 3, 4, 6, and 8 L/min) and inlet water temperature (25, 30, and 35 °C). The results showed that, given an initial temperature of 25 °C, the daily efficiency range, was 0.58 to 0.65, and that the daily final outlet temperature was enhanced outlet temperature over 65 °C. Additionally, on all test days, the heat released by the phase change material was audible in the evening and increased the utilization time.
This study numerically investigates natural convection of Cu-water nanofluid in a square cavity subjected to a cooling air stream along the left wall, with the right and bottom walls maintained at cold (TC) and hot (TH) temperatures, respectively, while the top wall is adiabatic. The nanofluid flow is assumed laminar and governed by the Boussinesq approximation. The governing equations are solved using the finite volume method in ANSYS FLUENT. Simulations are performed for nanofluid volume fractions (φ = 0–0.16), Rayleigh numbers (Ra = 10³–10⁵), and free stream Reynolds numbers (Re∞ = 10³–10⁴). The effects of these parameters on stream function (ψ), temperature contours (θ), and average Nusselt number (Nuavg) are analyzed. Results indicate that heat transfer rates increase with higher φ, Ra, and Re∞. Increasing φ and Ra enhances circulation within the cavity, whereas higher Re∞ induces secondary vortices and reduces circulation in the primary vortex. Comparisons of local Nusselt numbers and temperature distributions with previous studies show good agreement, with maximum errors of 14.28% and 3.2%, respectively.
In This paper, an experimental study was carried out on a dual channel with perforating “V” corrugated absorber plate of solar air collector which the air flows both in upper channel and lower channel of the absorber plate for increasing heat transfer coefficient and improving thermal performance. The results of experimental procedures for dual channel with perforating “V” corrugated absorber plate of solar collector were compared with the flat plate dual channel of solar collector. Experimental calculations had been performed under Baghdad (33.34° North latitude, 44.4° East longitude) climatic conditions at different values of mass flow rates 0.021 kg/s, 0.027 kg/s and 0.32 kg/s. The results showed that the dual channel with perforating “V” corrugated absorber plate of solar collector is found to perform more efficiently than the flat plate dual channel of solar collector with increased 39% in thermal efficiency. Then, it showed that the efficiency increases with increasing mass flow rates. Also, it showed that the heat removal factor of the dual channel with perforating “V” corrugated absorber plate of solar collector is 36% more than the flat plate dual channel of solar collector. At the last part of the study, the exergy relations were derived for both collectors. The results of this part showed that the flat plate dual channel of solar collector is having largest irreversibility (exergy loss) and the dual channel with perforating “V” corrugated absorber plate of solar collector is having a greatest exergetic efficiency.
Evaporative cooling is a widely used energy-saving and environmentally friendly cooling technology. Evaporative cooling can be defined as a mass and heat transfer process in which the air is cooled by the evaporation of water and as a result a large amount of heat is transferred from the air to the water and thus the air temperature decreases. Evaporative cooling is mainly used in many cooling technologies used in buildings, factories, agricultural in addition to it is used industrially in cooling towers, evaporative condensers, humidification, and humidity control applications. Evaporative cooling is divided into direct evaporative cooling and indirect evaporative cooling, as well as water evaporative cooling and air evaporative cooling. This paper reviews the most important developments and technologies in evaporative cooling that lead to lower energy consumption and provide suitable cooling comfort.
In this proposed study, all environmental factors affecting the aboveground and buried pipes, such as solar radiation and temperature, and soil temperature, have been studied on the characteristics of flow inside the aboveground and underground pipelines by building a mathematical model using MATLAB based on energy balance equations. From the mathematical model, the effect of solar radiation on the aboveground section of the pipeline is significate. During March and an inlet temperature of 34 °C, the pipeline outlet fluid temperature will rise to 50 °C. Other parameters affecting the aboveground section of the pipeline, such as ambient temperature and wind speed, have a much smaller effect on the fluid temperature, and the temperature difference is approximately 4 °C between the highest and lowest pipeline outlet fluid temperature. The result for the underground section of the pipeline showed that the main affecting parameter on the fluid temperature is the burry depth of the pipeline, the deeper the pipeline depth the lower the temperature variation and the lower fluid temperature can be seen, at 1 meter of bury depth the minimum and maximum fluid temperature was 18 °C and 36 °C respectively, and at 5 meters of bury depth, the minimum and maximum fluid temperature was 26 °C and 31 °C respectively. This study also checks different process parameters. Some of these are fluid flow, pipe diameter, and pipe material. The effect of the fluid flow and pipe diameter has a similar impact on the fluid temperature (while fixing all the other parameters), the higher the fluid flow or the smaller the pipe diameter resulted in a better heat transfer and more considerable temperature difference, and vice versa. The final process parameter, pipe material, had little to no effect on the fluid temperature variation.
The panel absorbed solar radiation and majority of this radiation is transform into a heat, and it is usually wasted and useless. At higher cell temperature, the current out of the cell has an unnoticeable rise, but the voltage value will drop significantly, resulting in a reduction in maximum power produced. The cooling method is therefore beneficial to keep the panel at the operation temperature. A simulation model is developed using COMSOL Multiphysics software version 3.5 software to investigate the enhancement in performance of a PV water cooling module (PVW module) based on a passive and simple cooling technique using a wetted cotton porous wick attached on the PV panel's back side and compare with uncooled PV panel (PVREF module). Unsteady, laminar and 2-D, the flow in the proposed modules is assumed. The input parameters were taken from a real weather condition was perform in Najaf-Iraq. The effect of variation of mass flow rate is also studied in the present work. Good agreement was obtained for PVREF module with previously researches.
Mixed convection heat transfer of air in a horizontal channel with an open square cavity is studied numerically. At the center of the cavity, it is an insulated rotating circular cylinder for enhancing the efficiency of heat transmission, the location of the inner cylinder is changed vertically along the centerline of the cavity. Heat is applied to the bottom wall of the cavity at a constant temperature, and the other walls are adiabatic. The flow is steady-state, laminar, and incompressible. Using computational fluid dynamics (CFD) and the commercial software program FLUENT 2019 R1, the equations of continuity, momentum, and energy are numerically solved. The angular velocity of the cylinder range is (0 . 5 ≤ ω ≤ 4) rad/sec in a counterclockwise direction, the Richardson number range ( Ri = 0 . 1 , 1 , 10), Reynolds number is 100 and the cylinder location is ( C = 70 , 50 , 30) mm. The airflow Prandtl number is taken as ( Pr = 0 . 7). The effect of various positions of the rotating cylinder has been examined through the visualization of streamline and isotherm contour, as well as the distribution of the average Nusselt number of the heated surface. The results indicate that the flow field and temperature distributions inside the cavity are strongly dependent on the rotating circular cylinder and the position of the inner cylinder.