The energy consumption of a Split air conditioning unit (ACU) inside a building is extremely large, and efforts to decrease this issue are ongoing. The current work aims to experimentally investigate the thermal performance of ACU using an external cooling-water loop for pre-cooling the condenser to improve the efficiency and to reduce energy consumption by reducing refrigerant temperature before entering the condenser, thereby reducing the coefficient of performance. The experiments are performed on ACU with and without using an external coolingwater loop under different climate conditions. By using the experimental data, the systems’ performances for both cases are evaluated based on the energy, exergy, and pressure drop analysis. Effects of several parameters, e.g., ambient temperature, inlet water temperature, and water volume flow rate, on the energy and exergy performances of ACU systems are presented for the purpose of comparison. The outcomes display that the use of an external cooling water loop system has a significant impact on the system performance as compared to conventional ACU. The results display that the addition of an external cooling-water loop leads to a reduction in the compressor power consumption and to an increase in the coefficient of performance (COP) as compared to a normal ACU. The maximum reduction in compressor power consumption is obtained equal 37% at Tw = 15○C and 11 L/min, whereas the maximum enhancement in COP is obtained equal 21.5% at Tw = 30○C, 11 L/min, and Tamb = 45○C. The modified model shows an increase in exergy efficiency with the maximum enhancement of about 17% at Tw = 30○C and 15.8 L/min. The use of an external cooling water loop leads to a reduction in the irreversibility process of the compressor, evaporator and expansion valve and to an increase in the condenser losses. The outcomes show that the pressure drop is reduced by using a cooling water loop as compared to a normal ACU, where the reduction becomes more evident with a reduction in water volume flow rate and inlet temperature. Finally, the present study reveals that the use of an external cooling water loop system leads to an improvement in the performance of ACUs.

Solar energy is a renewable resource; however, high operating temperatures reduce photovoltaic (PV) performance. This study examines passive cooling and reflective enhancements on PV systems in Zakho, Iraq, during winter. Experiments were conducted on February 24 and 27 using two modified PV designs. While in Scenario I, L-shaped aluminum fins were attached to a PV module and compared with a reference panel. Scenario II combined fins with an aluminum reflector to increase the amount of incident solar radiation. Results showed notable performance gains. In Scenario I, power output rose by 14.2%, with peak efficiency improving from 10% (reference) to 12%. Scenario II achieved a 17.5% increase in power, with efficiency reaching 16.5% compared to 14% for the benchmark. Temperature decreases of 15.3°C (Scenario I) and 13°C (Scenario II) confirmed the effectiveness of passive cooling. An examination of life cycle costs (LCC) indicated reduced energy expenditures: $0.053/kWh for the reference scenario, down to $0.048/kWh with fins, and further lowered to $0.044/kWh with fins combined with a reflector. The payback periods have been decreased to 6.5, 5.9, and 5.5 years for reference, fins, and combined fins with reflector systems, respectively. The environmental analysis revealed yearly CO₂ emission reductions of 4.62, 5.25, and 5.93 tCO₂/year for reference, fins, and combined fins with reflector systems, respectively. Overall, integrating cooling fins and reflectors significantly improved PV performance, reduced energy costs, and enhanced environmental sustainability. This approach offers a practical and low-cost strategy to boost solar energy utilization in regions with similar climatic conditions.

Free convective heat transfer created from two aligned cylinders immersed inside a vented air duct is experimentally investigated. The experiments include the measurements of cylinders temperature and the air temperature inside the enclosure under steady, turbulent, and incompressible flow properties by using steady-state heat equations. The studied parameters include Rayleigh number ( ), opening sizes at lower and upper enclosure surfaces ( ), and space size between cylinders ( ) with the constant ratio of enclosure width to cylinder diameter equal to 6. The findings displayed that the average air temperature inside the enclosure for the low values of S and O is low, and it rises as S is raised. The behaviors of Nu diff er with changing Ra values. An interaction between hot cylinder and cold cylinder inside the enclosure is observed that depends on O and S values, and hence, they have a large impact on fluid temperature. The data indicated that rises with the for all and values. The value of for each cylinder depends on the values of and . The maximum value has been obtained when and with maximum enhancement between 30% and 50% depending on Ra values as compared with and , whereas the minimum average has been indicated when and . The profi les of reveal that , , and have a considerable infl uence on heat transfer.

This investigation focuses on energetic, exegetic, economical and environmental analysis of PV solar system using fixed, single- and dual-axes tracking systems under climatic weather of Zakho city/north of Iraq. Experiments are carried out on 5th September 2022. The energy and exergy analyses are used to predict the performance of three solar panels. The theoretical work includes technical, economical and environmental analysis of proposed 1 MW PV solar power plant are presented using similar characteristics of the experimental data of hourly meteorological climatic conditions during 2022. The findings display that the tracking systems have significant influences on 4–E performances. The experimental results displayed that electrical output power gain and thermal exergy output are increased when using tracking systems, where the exergy losses for single- and dual-axes tracking systems are decreased as compared to fixed solar plane. The maximum improvements in the electrical output power gain of PV solar panels using dual– and single–axes tracking systems are nearly reached to 40 % at 8 a.m., 13 % (for single) and 20 %(for dual) at 12 p.m. and 30 % at 17PM as compared to fixed solar panel. The theoretical results display that the yielded produced energy for single- and dual-axes are increased by 16.5 % and 25.5 %, respectively, as compared to fixed panel. The economic findings display that the cost of energy for single-axes, dual-axes and fixed tracking systems are 4.89, 4.41 and 8.26, respectively. Finally, the use of tracking systems reduces the CO2 emission about 4000–4500 tCO2 annually.

This study involves an investigation on fully evaporation process inside annular porous heat exchanger using Cu/ distilled water nano-fluid. Emphasis has been placed on how the use of Cu/distilled water affected two-stage flux predictions. Two-phase mixture model, based on the considerations of Local Thermal Equilibrium (LTE), has been reformulated to involve the influences of employing nano-fluid instead of only water. To display the actions of employing nano-fluid, the predictions of liquid saturation and temperature, obtained using Cu/distilled water and only water, have been presented and compared for a wide ranges of geometric conditions, operating conditions and properties of porous media. The outcomes displayed that the using Cu particle to water has a large impacts on the heat diffusivity, where the boiling and condensation fronts are considerably moved to downstream and upstream sections, respectively, as compared to the predictions of only water due to rising the axial diffusion. The temperature at the pipe exit is considerably decreased when adding Cu particles to water as compared to the pure water case. The predications of Cu/distilled water show that the nano-fluid volume fraction, geometric parameters, operating parameters and porous structure properties have high actions on the locations of initiation and termination of phase change process. Since the fluid temperature for pure water case is extremely high at the superheated vapour region, the addition of Cu particles to water considerably reduces the fluid temperature in this region and hence, the use of nano-fluid can be considered as a safety factor in the applications that used heat exchangers (boiling processes) due to it improves the mechanism of heat transfer during the boiling process.

The present study is an experimental investigation to improve the performance of the air conditioning unit (ACU) by precooling the condenser with a cooling water loop using a water heat exchanger with the employment of energy and exergy analyses under various ambient temperatures between 30 – 45C at different inlet water temperatures; 15, 19, 24 and 30C and water flowrates; 9, 11, 14 and 15.8 L/min. The results indicated that the cooling water loop have a large effect on the exergy destructions as compared with those of the no water case. When a cooling water loop is used, the compressor, evaporator, and expansion valve irreversibilities reduced. The exergy efficiency of the unit decreases as Tamb increases to about 23%; while, the exergy efficiency increases when cooling water loop is used depending on the inlet water temperature and water flowrates. The maximum enhancement in the exergy efficiency is obtained at high water flowrate for Twi = 15C with a percentage value about 13% as compared with those of the conventional ACU.

The tracking system that uses for PV solar systems has a vital role to improve the energy performance of the solar panel. In the present study, the performance of both the fixed PV solar system and single – axis tracking PV solar system is investigated experimentally. The power for each PV solar panel is 150 W. The performances of the two systems are compared to display the efficient improvement of a single-axis solar tracking (SAST) system with fixed solar (FS) system under the climate conditions in the Zakho/ Kurdistan region/ Iraq. A mechanical tracking device with a controller and linear actuator was designed, and its performance was comprehensively investigated with a PV system. The findings for a sunny day due to the use of a single axis tracking system with a solar panel as compared with those of a fixed panel, that the enhancement in the overall power generation and electrical efficiency are about 28 % and 29 %, respectively.

This work involves a numerical investigation on free convection heat transfer occurred by a hot cylinder immersed in a square duct cooled from one side under different temperatures. Simulations have been done for a large ranges of Rayleigh number (103≤ Ra ≤107) and right wall temperature (0≤Tr ≤0.75). The results displayed that Nu is enhanced with rising in Ra and decreasing in Tr. The value of Nu is decreased with rising in Tr, where the maximum reduction in Nu is about 32% for Tr=0.75 as compared to Tr=0. The maximum enhancement range for Nu is found between 50% and 100% for low Ra and between 20% and 30 % for high Ra. The variations of local Nu display that Ra has an extremely actions on the characteristics of flow and temperature fields.

The current work deals with the numerical investigation of mixed convection occurring from two hot cylinders placed inside vented ducts under different sizes of inflow and locations of outflow opening vents. The mathematical formulation is solved based on the finite volume approach. The location of the outflow section is changed to left, center, and right of enclosure. Impacts of inflow section sizes (O1=0.125 and O1=0.25), locations of outflow section (O2 =0.125), space between cylinders (0.3 ≤ S ≤ 0.45), Reynolds number (200 ≤ Re ≤ 400), and Richardson number (0.1 ≤ Ri ≤ 20) are implemented. Findings display that the average Nusselt number (Nu) is exceeded by 20% for low Ri due to the effect of nonsymmetrical inflow and outflow sections as compared with the case of equal opening vents. For large Ri, a higher Nu is obtained for nonequal opening vents in comparison with the case of equal opening vents by 10%. The difference in the average Nu between left and right cylinders is about 11%. Findings display that the enhancement in Nu due to the large spacing size between cylinders as compared with those of low spacing size is about 35%. The variations of Nu display the opening vents ratio, Re, S, and Ri have an extreme action on the characteristics of flow and temperature fields.

The mixed convection heat transfer from two horizontally aligned cylinders with one hot and one cold cylinder inside a vented square enclosure with openings on the upper and lower surfaces has been numerically investigated. The simulated behaviour of heat and flow fields has acquired the solutions using the Navier-Stokes equation and energy equation for steady, laminar and incompressible flow properties. Considering a diverse range of opening sizes O = 0.125–1, spacing sizes S = 0.3–0.45, Richardson number Ri = 0.1–10 and Reynolds number Re = 50–400 were covered with fixed Prandtl number Pr = 0.72. Velocity contours and isotherms with the average and local Nusselt numbers (Nu) have been displayed with various parameters. The method of solution uses the finite volume method (FVM). Pressure–velocity coupling and the SIMPLE method were used to solve the momentum and energy equation via the CFD software ANSYS/ FLUENT 2021 R1. The numerical solution shows the linear relationship between increasing the average Nu value with increasing Ri, Re and opening sizes O of the vents. Moreover, the increasing of spacing size to S = 0.375 positively enhances the value of average Nu around the hot cylinder. The best increase in value of average Nu resulted in S = 0.375 and O = 0.375 with 36.8 %. The average increase in Nu ranged from 10 % to 38 %.

In this article, a technical–economic study has been displayed to evaluate the productivity of grid-connected photovoltaic (PV) solar system in a campus of University of Zakho, Iraq. The feasibility of this study is based on performance ratio, capacity factor, cost of energy and yield factor. The analysis of the system has been performed using System Advisor Model (SAM) software and real data of Zakho city that is available in national renewable energy laboratory (NREL). Results show that the system produces 5205 AC MWh during the year with a maximum power generated by the arrays equal to 3.15 AC MW. The yield factor from the proposed PV system for first year is 1554 kWh/kW, whereas the capacity factor nearly equal to 17.7%. Findings indicate that the cost of energy generated by the solar system is 6.3¢/kWh. The payback period to restore the cost of the government electrical energy without using the local

Energy, economic and environment performances of 1 MWp photovoltaic power plant has been numerically investigated under climatic condition of Zakho city/Iraq using the reality metrological measurements. Results of PV system have been compared with other available power plants that used fossil fuel under identical power value. The findings displayed that the investment of PV technology is very feasible in Zakho city as compared to other power plants. The economic results displayed that the payback time nearly equal 7 years to recover the primary expense of the plant and the payback energy time is 2 years to recover the embedded energy of PV panels. The cost of PV plant is nearly 10 times less than the other fossil fuel power plants. The employment of PV plant leads to reduce CO2 emission between 600–2000 tCO2. Finally, the results illustrated that the using of PV system in Zakho city is feasible …

In this study, experimental and numerical examinations of the performance of the conventional photovoltaic panel, concentrated photovoltaic (CPV) system and water-cooled CPV system were performed. The tests are conducted under the climatic conditions of the city of Duhok, North of Iraq, on a sunny day on September 25, 2019. During the experiments, the average ambient temperature and average solar radiation were 32.6 ◦C and 930 W/m2, respectively. As well, MATLAB/Simulink modeling is developed by using PV module equations and the manufacturing data sheet. The empirical results showed that the ultimate panel temperature of the PV panel, concentrated PV system and water-cooled concentrated PV system is 57.5, 64.1 and 36.5 ◦C, respectively. In addition, the power output of the water-cooled CPV system and CPV system was improved respectively by 24.4% (effective 23%) and 10.65%. In addition, electrical efficiency was increased from 14.2% to 17% by using reflectors and water cooling with the PV panel. In the case of the water-cooled CPV system, open circuit voltage and short circuit current were increased by 9% and 5.2%, respectively. Moreover, the comparison between the experimental and numerical results agrees well.

Reducing energy consumption and providing high performance for a vapour compression refrigeration system are big challenges that need more attention and investigation. This paper provides an extensive review of experimental and theoretical studies to present the vapour compression refrigeration system and its modifications that can be used to improve system’s performance and reduce its energy consumption. This paper also presents the challenges that can be considered as a gab of research for the future works and investigations. Cooling capacity, refrigerant effect, energy consumption can be improved by using vapour injection technique, natural working fluid, and heat exchanger. Based on the outcome of this paper, vapour injection technique using natural refrigerant such as water can provide ultimate friendly refrigeration system. Future vision for the vapour compression refrigeration system and its new design technique using Computational Fluid Dynamic (CFD) is also considered and presented.

Mixed convective induced by two aligned horizontal heated cylinders embedded in a square enclosure with symmetrical openings at lower and upper surfaces of the enclosure has been numerically investigated. Navier- Stokes and energy equations have been employed to simulate the behaviours of heat and fluid flow fields. The flow has been considered to be steady, laminar and incompressible flow conditions. The parameters have been covered a wide range of the spacing size between two cylinders (0.3 ≤ S ≤ 0.45), opening vent (0.125 ≤ O ≤ 1), Reynolds number (50 ≤ Re ≤ 400) and Richardson number (0.1 ≤ Ri ≤ 10), whereas Prandtl number has been kept fixed Pr = 0.7. The average and local Nusselt numbers (Nu), streamlines and isotherms have been presented for various relevant parameters. Numerical results display that the average Nu from the heated cylinders has been increased with increasing in Ri, Re and opening vent. The increase in the spacing size to S = 0.375 leads to enhance average Nu. The spacing size has a negative effect on the average Nu when the distance between the cylinders exceeds S > 0.375. The optimum improvement in Nu has been found when the spacing size S = 0.375 under full opening size case.

Natural convection heat transfer from horizontally aligned two heated cylinders placed inside a square vented enclosure have been investigated numerically for laminar flow. The Navier – Stokes equations and energy equation have been employed to simulate the flow and thermal behaviors with finite volume (SIMPLE) method to represent and evaluate the partial differential equations in the form of algebraic equations using ANSYS – FLUENT 16.1 Package. The study is employed a range of Rayleigh number from 103 to 107 with variation of horizontal spacing between two cylinders and symmetrical open vent size with constant enclosure width. The results displayed that the average Nusselt number is increased with the increase of the Rayleigh number, spacing between cylinders and opening size. The maximum enhancement range for average Nu between 50-100 % for low Ra and 20-30 % for high Ra with full opening size and large spacing size. The variation of the local Nusselt numbers, streamlines and isotherms displayed the effect of the Rayleigh number, opening size and spacing between cylinders on the flow and thermal behaviors.

Present study involves an exhaustive analysis on hybrid photovoltaic thermal (PVT) system to display the actions of climate and operating conditions on its thermal and electrical efficiencies. The performances of the system have been evaluated based on energy and exergy analysis using the experimental data for the purpose of comparison. Experimental data have been measured for three different days in 2019 in Dohok city/north of Iraq under active mode. The results displayed that the climatic conditions have significant effect on the energy and exergy outputs. The results of energy analysis indicate that the maximum thermal and electric efficiencies in the range of (25%–58%) and (12%–16%), respectively. The results of exergy analysis displayed that the optimum thermal and electric efficiencies in the range of (2%–7%) and (10%–18%), respectively. The results also displayed that the solar panel temperature has a significant impact on the electrical energy and exergy efficiencies. The total solutions illustrated that the employ of PVT water system under active mode provides an obvious advantages and hence, the current work provides an interesting information for evaluating the performances of PVT system. As consequence, it can be advised for using in household applications at north of Iraq.

Natural and mixed convection heat transfer from a horizontal cylinder placed in a vented square enclosure has been investigated using numerical method with ANSYS Fluent 16.1 software for laminar and turbulent flow. Navier- Stokes equations and energy equation with standard k- transport equation turbulence model have been used to simulate both flow and thermal behaviors. The operating conditions covered a range of the Rayleigh number from 103 to 106 and the Richardson number range between 0.1 and 100 at variable sizes of the lower open vent with constant upper opening size. The Nusselt numbers, velocity lines and isotherms are presented to display the flow and thermal behaviors. The results displayed that the average Nusselt number is affected by Rayleigh number, Richardson number, enclosure width and lower opening size. The Nusselt number is enhanced by controlling the lower opening size. The maximum enhancement range for Nusselt number is between 20-85% depending on the Rayleigh number, Richardson number, enclosure width to cylinder diameter, and lower opening size. The velocity lines and isotherms are directly affected by the Rayleigh number, Richardson number, enclosure width to cylinder diameter, and lower opening size.

The present work deal with the experimental study to retrofit the refrigerant R407c with the refrigerant R22 in the air conditioning unit at an ambient temperature range between 30-45C. The main component of the experimental rig includes a window air conditioner with a refrigeration capacity of 2 Ton refrigeration that used refrigerant R22 as a working fluid in the experimental work. The refrigerant R22 is replaced with refrigerant R407C due to similar operation properties for the two refrigerants. The experimental results displayed the refrigeration effect and coefficient of performance COP of the R22 system are high as with those of the R407C system. The falls in the evaporator and condenser for the R407C system is lower than that of the R22 system. The temperature of discharge in the compressor for the system of refrigerant R22 is greater than that of the R407C system. Moreover, condensation temperature along the tube of the condenser is decreased with the increase of the distance for both refrigerants. The refrigerant R407C may be selected as a good alternate for R22 with an agreement difference in the two refrigerants’ performance. The system did not require replacement for any part of the AC unit.

In Australia and others developed countries, concerns about global warming have increased, and these concerns influence the use of refrigerants as working fluids in mechanical vapour compression refrigeration systems. One of the most important aspects of refrigerant selection is to reduce its impact on the environment and the ozone layer. This paper provides a comprehensive review of various theoretical and experimental studies which have been carried out on air conditioning and refrigeration applications to investigate the effect of refrigerants on the environment. The analysis in this paper reveals that alternative refrigerants are the most suitable working fluids that can be used in refrigeration systems to meet the needs of the environment. This study also suggests that natural types of refrigerants such as water, carbon dioxide, and hydrocarbon will play a significant role in protecting the environment and providing alternative friendly refrigerants to be used in refrigeration and air conditioning systems.

The study deals with the experimental and numerical investigation of the hybrid Photovoltaic-thermal solar collector system in Duhok city during seven months and includes different measurements of temperatures, water mass flow rate, wind velocity, and solar intensity. A one-dimensional mathematical model is used to simulate the transient processes with constant thermo-physical properties and heat transfer coefficients. The energy conservation equations are solved using implicit finite difference method. The numerical and experimental results showed satisfactory agreement with an error (2.36%) between two thermal efficiencies. The results include the estimation of the electrical and thermal energy, thermal, electrical and overall efficiency. The highest overall efficiency of PV/T collector occurs in May 2019 with value (72.01%) and the lowest value in January 2019 is obtained as (63.1%). The cooling method leads to an increase in the electrical efficiency to about 3% as compared with PV solar collector system.

The study deals with the experimental and numerical investigation of the hybrid Photovoltaic-thermal solar collector system in Duhok city during seven months and includes different measurements of temperatures, water mass flow rate, wind velocity, and solar intensity. A one-dimensional mathematical model is used to simulate the transient processes with constant thermo-physical properties and heat transfer coefficients. The energy conservation equations are solved using implicit finite difference method. The numerical and experimental results showed satisfactory agreement with an error (2.36%) between two thermal efficiencies. The results include the estimation of the electrical and thermal energy, thermal, electrical and overall efficiency. The highest overall efficiency of PV/T collector occurs in May 2019 with value (72.01%) and the lowest value in January 2019 is obtained as (63.1%). The cooling method leads to an increase in the electrical efficiency to about 3% as compared with PV solar collector system.

The purpose of this study is to improve the electrical performance of the photovoltaic (PV) module by using the sunlight concentration and cooling technique. Three identical polycrystalline PV modules were used in the experiments; ordinary PV module, concentrated PV module (CPV) and CPV system with cooling technique. The experiments were performed in a clear day on September 24th in Duhok, Iraq. The cooling system is developed by the water flowing on the front of the PV panel. The operating temperature of the CPV is kept very low by the cooling system, i.e., 30–35
C. The maximum power output of CPV system and CPV system with cooling compared with the reference PV module is improved by the rates of 8% and 18.5%, respectively. In addition, the maximum percentage increase in the electrical efficiency of the CPV system and CPV system with cooling technique is 6.5% and 17.7%, respectively. The CPV with the cooling system delivered more energy than the other two cases. According to the economic analysis of a typical domestic use, the payback period is 3.77, 3.52, and 3.23 years for the stand-alone PV module, CPV system and the CPV with active cooling system, respectively.

The natural convection heat transfer from a heated circular cylinder placed in a square vented enclosure was investigated considering the effect of the thermal radiation from cylinder using finite volume method with simple algorithm that used pressure-velocity coupling to solve Navier-Stockes and energy equations using Computational Fluid Dynamics CFD (Fluent software). The flow domain is filled with air. The enclosure width is 12.5 cm, two symmetrical openings at its lower and upper walls with size O = 2.5 cm and the cylinder diameter is 5 cm. Different rang of cylinder’s surface emissivity with Rayleigh number range between 103 to 106 was applied in this study as operating condition. The effect of the Ra, cylinder radiation for vented square enclosure on the convection, radiation and total Nusselt numbers Nu and flow and thermal patterns were investigated. The numerical results for pure natural convection were compared with available experimental results, good agreement was obtained. The results revealed that the natural convection heat transfer from the cylinder in the enclosure is increased as compared with that of the unbounded cylinder without radiation effect. The results also revealed that there is a linear relationship between the heat transfer enhancement and the emissivity, there is a significant effect of the cylinder surface radiation which gives high augmentation compared with that of the free cylinder and natural convection heat transfer without radiation effect. A maximum total Nusselt number is obtained at high emissivity compared with that of natural convection heat transfer, the maximum Nu enhancement ranged between 70 to 350 % for low Ra and 25 to 125% for high Ra.

The performance of hybrid photovoltaic thermal solar collector system at Duhok city for “29th” April and April month is experimentally investigated with an area of (0.864 m2) to cover the hot water, space heating and electrical loads for a home with an area of 100 m2 consists of 4 persons. The electrical production is effected by the panel temperature, and the thermal and electrical energy productions are proportional with the insolation. The cover glass has an effect on the electrical and thermal energy productions. The produced thermal energy is about 3 times of the electrical energy production. The electrical load during the specified duration is covered using 21 m2 of photovoltaic area. The thermal load includes hot water demand and space heating demand for the home. The hot water demand can be covered using 2 m2 of the collector area, the remaining collector area is be covered the space heating demand. The cost of the system may be getting back during 10 years with using the payback method.

The performance of hybrid photovoltaic thermal solar collector system at Duhok city for “29th” April and April month is experimentally investigated with an area of (0.864 m2) to cover the hot water, space heating and electrical loads for a home with an area of 100 m2 consists of 4 persons. The electrical production is effected by the panel temperature, and the thermal and electrical energy productions are proportional with the insolation. The cover glass has an effect on the electrical and thermal energy productions. The produced thermal energy is about 3 times of the electrical energy production. The electrical load during the specified duration is covered using 21 m2 of photovoltaic area. The thermal load includes hot water demand and space heating demand for the home. The hot water demand can be covered using 2 m2 of the collector area, the remaining collector area is be covered the space heating demand. The cost of the system may be getting back during 10 years with using the payback method.

Air-water two-phase flow in pipes introduces a noticeable challenge due to the complexity of the fluids. Thus, to estimate the best design and reasonable financing cost of the transportation pipelines where the bends are presenting a part of their accessories, the investigators should have been able to estimate the flow regime occurring at different directions. An experiment was carried out by using a 90o bend fixed with two pipes where the flow was upstream from a vertical to a horizontal pipe which were representing the bend inlet and outlet respectively. Two wire-mesh sensors were used for obtaining the data of the void fractions ($) at water superficial velocities (Usl) which changed from 0.052 to 0.419m/s, and air superficial velocities (Usg) from 0.05 to 4.7m/s. Furthermore, the characterization of flow regimes of the air-water flow at both bend inlet and outlet were competed accurately by using void fraction analysis of the time series, Power Spectral Density (PSD), tomographic images observed by the sensor program, and the Probability Density Function (PDF) method. The flow regimes of vertical flow lines at the bend inlet were observed as bubbly, capbubble, slug, and churn flow, whereas the flow regimes of the horizontal flow line at the bend outlet were characterized as having stratified, stratified wavy, bubbly, plug, slug, wavy annular, and semi-annular flow due to the gravity and bend effects.

This study comprises an experimental investigation of the hybrid photovoltaic thermal (PV/T) solar collector system. The performance of the photovoltaic (PV) panel is enhanced by reducing the temperature of the PV panel by passing cold water through copper pipes welded on a copper sheet plate as a heat exchanger behind the PV panel. The present work uses a flat metal plate of copper as an absorbent plate on the backside of the mono-crystalline PV solar panel. The present work has been validated by comparing the obtained results with previous experimental results from the literature, where fair agreement has been noted. The results display the performance of the PV/T solar collector during the 2nd of November 2018 and it is achieved a maximum thermal efficiency 40.3%, with a commensurate electrical efficiency of 14%, and the overall efficiency reached to 54.3%.

The present work includes the design and fabrication of the flat plate solar collector system. The performance of the system is investigated experimentally using galvanized steel sheet with 0.4mm thickness as an absorber plate with black coating, the collector area is 0.54 m2. The test is conducted in Iraq, Kurdistan region, Duhok city on January 10, 2019, for five hours. The collector efficiency is satisfactory as compared with previous study. The useful heat gain and efficiency of collector have been calculated from the collected data. The results display that there are many factors and parameters such as wind speed, collector heat removal factor, heat losses coefficient and transmission-absorption product affected on collector efficiency.

In this paper, refrigerant R407c has been experimentally investigated to retrofit the refrigerant R22 in the existing systems. Window type air conditioner with capacity of 7.0 kW using R22 as working fluid has been selected to conduct the experimental work. The two refrigerants R22 and R407C have same operation conditions are selected in order to compare these thermal performances. The results showed that the refrigeration effect of R22 is higher than those for R407C. Consequently, the coefficient of performance COP of R407C is lower than R22. Also, the discharge temperature of the R407C is lower than those of R22. The pressure drop in the evaporator and condenser of the R407C less than those for R22. Moreover, the condensation temperature decreases along the length of the condenser coil for two refrigerants. The condensation temperatures for R22 is higher than the condensation temperatures of R407C at same ambient temperature. Finally, R407C can be considered as a suitable replacement for R22 with a slight variation in the performance with no need to change any part of the refrigeration system.

In this research, the natural convection heat transfer from the horizontal circular cylinder in a vented enclosure filled with nanofluid is investigated numerically. Governing equations settling in the vorticitystream function formulation is inclusive in the numerical work, which transformed into fitted body coordinate system. The study covered the following ranges of Rayleigh number 104Ra106, nanofluid volume fraction 0 0.2, enclosure width 1.667 W/D 5, and opening size 0O/W1. The effect of Rayleigh number, nanofluid volume fraction, enclosure width, and opening size on the Nusselt number, flow patterns and isotherms were investigated. The result shows that the Nusselt number is proportional with Rayleigh number, opening size and volume fraction of nanofluid and inversely proportional with enclosure width. The isotherms and flow patterns display the temperature and flow behaviors with changing studied variables. The thickness of thermal boundary layer decreases with increasing Rayleigh number for each opening size, enclosure width and nanofluid volume fraction.

The natural convection heat transfer from horizontal circular cylinder placed in a square enclosure is investigated numerically. The study deals with the effect of magnetic field on the flow and heat transfer characteristics. The investigation employs different Hartman numbers (0, 50, 100, 200), different Rayleigh numbers (103, 104, and 105) with constant enclosure width to cylinder diameter ratios W/D = 2.5. The study included the solving of the governing equations in the form of the vorticity-stream function to be fitted with coordinate system. The algebraic grid generation is used to generate initial transformation. The elliptic grid generation is used to fit with physical domain between the heated horizontal cylinder and the enclosure into a computational domain. The resulting equations are solved using finite difference method that based on the finite volume. The research studied the influence of the variation the Hartman number on the local and average Nusselt numbers, flow patterns and temperature distributions with different Rayleigh numbers. The effect of Hartman numbers on the flow patterns and temperature distributions will be displayed using streamlines and isotherms. The results show that the conduction heat transfer is the dominant mode for low Rayleigh numbers. The convection heat transfer is the dominant mode of the heat transfer for high Rayleigh number in absence of the magnetic effect. The convection heat transfer convert to conduction mode at high Rayleigh numbers due to the effect of the magnetic field in the fluid. Also, the results show that the behavior of the local Nusselt numbers for Ha = 0 are unique and differ from those of other higher Hartman numbers for all Rayleigh numbers.

The enhancement of natural convection heat transfer using nanofluids from horizontal square cylinder placed in a square enclosure is investigated numerically. The water-based Cu is used as nanofluid. The developed model is used to investigate the performance of heat transfer of nanofluids inside an enclosure taking into account the solid particle dispersions on the flow and heat transfer characteristics. The range of Rayleigh numbers is between 104 - 106, the values of the volume fraction of nanoparticles are (0  0.2) with enclosure width to cylinder height ratio W/H equal to 2.5. The numerical investigation include the solution of the governing equations in the vorticity-stream function formulation which were mapped into body fitted coordinate system. Initially, the algebraic grid generation is used for transformations, then the elliptic grid generation is used to transform the physical domain between the heated horizontal cylinder and the enclosure into a computational domain. The resulting disecretization equation system from finite difference method is solved by using ADI method. A Fortran 90 code is built to execute the numerical algorithm. The effect of Rayleigh number and volume fractions of the nanofluids on the thermal and hydrodynamic characteristics are displayed in the results. A good agreement is achieved between the present results and the previous numerical results. The Nusselt number enhances with increasing the Rayleigh number for all ranges of the variables. An increase in average Nusselt number was achieved with increasing the volume fraction of nanofluids for the whole range of Rayleigh number. The isotherms are nearly similar when the volume fraction of nanoparticles is increased from 0 to 0.2 for each Rayleigh number, while, the streamlines are changed for same ranges.

In the present work, the natural convection heat transfer from horizontal circular cylinder situated in a square enclosure is investigated numerically. The work investigates the effect of Prandtl numbers on the flow and heat transfer characteristics. The study uses different Prandtl numbers (0.03, 0.7, 7, and 50), different Raylieh numbers (104, 105, and 106) and different enclosure width to cylinder diameter ratios W/D (1.667, 2.5 and 5). The work included the solution of the governing equations in the vorticitystream function formulation which were transformed into body fitted coordinate system. The transformations are based initially on algebraic grid generation and elliptic grid generation to map the physical domain between the heated horizontal cylinder and the enclosure into a computational domain. The disecritization equation system are solved by using finite difference method. The code build using Fortran 90 to execute the numerical algorithm. The results were compared with previous numerical results, which showed good agreement. The effect of Prandtl number variation on the average Nusselt numbers, flow patterns and isotherms with different Raylieh numbers and enclosure width ratios were investigated. The flow patterns and temperature distributions are presented by means of streamlines and isotherms, respectively. The results show that the streamlines and isotherms for Pr=0.03 are unique and differ from those of other higher Prandtl numbers for all enclosure widths and Ra≥105. The streamlines and isotherms for Pr≥0.7 are nearly similar and independent of Prandtl number. The same behaviors as streamlines and isotherms occur with Nusselt number for lower and higher values of Prandtl numbers with all ratios of enclosure width to cylinder diameter.

In the present work, the enhancement of natural convection heat transfer utilizing nanofluids as working fluid from horizontal circular cylinder situated in a square enclosure is investigated numerically. The type of the nanofluid is the water-based copper Cu. A model is developed to analyze heat transfer performance of nanofluids inside an enclosure taking into account the solid particle dispersionrs on the flow and heat transfer characteristics. The study uses different Raylieh numbers (104, 105, and 106), different enclosure width to cylinder diameter ratios W/D (1.667, 2.5 and 5) and volume fraction of nanoparticles between 0 to 0.2. The work included the solution of the governing equations in the vorticity-stream function formulation which were transformed into body fitted coordinate system. The transformations are based initially on algebraic grid generation, then using elliptic grid generation to map the physical domain between the heated horizontal cylinder and the enclosure into a computational domain. The disecritization equation system are solved by using finite difference method. The code build using Fortran 90 to execute the numerical algorithm. The results display the effect of Raylieh number, enclosure width to cylinder diameter ratio, and volume fractions of the nanofluids on the thermal and hydrodynamic characteristics. The results were compared with previous numerical results, which showed good agreement. The Nusselt number increases with increasing the Raylieh number for all cases. An enhancement in average Nusselt number was found with the volume fraction of nanofluids for the whole range of Rayleigh number. The results show that the isotherms are nearly similar when the volume fraction of nanoparticles is increased from 0 to 0.2 for each Raylieh number and enclosure width to cylinder diameter ratio, while, the streamlines are changed for same ranges.

In the present work, the enhancement of natural convection heat transfer utilizing nanofluids as working fluid from horizontal circular cylinder situated in a square enclosure is investigated numerically. Different types of nanoparticles were tested. The types of the nanofluids are Cu, Al2O3 and TiO3 with water as base fluid. A model is developed to analyze heat transfer performance of nanofluids inside an enclosure taking into account the solid particle dispersionrs on the flow and heat transfer characteristics. The study uses different Raylieh numbers (104, 105, and 106), the enclosure width to cylinder diameter ratio W/D is 2.5 and volume fraction of nanofluids is between 0 to 0.2. The work included the solution of the governing equations in the vorticity-stream function formulation which were transformed into body fitted coordinate system. The transformations are based initially on algebraic grid generation, then using elliptic grid generation to map the physical domain between the heated horizontal cylinder and the enclosure into a computational domain. The disecritization equation system are solved by using finite difference method. The code build using Fortran 90 to execute the numerical algorithm. The results display the comparisons between different types of the nanofluids based on the effect of Raylieh number, and volume fractions on the thermal and hydrodynamic characteristics. The results were compared with previous numerical results, which showed good agreement. For all types of the nanofluids, the Nusselt number increases with increasing the volume fraction of the nanofluids. The results show that the streamlines change with changing the type of the nanofluid, while the isotherms remain unchanged. The Nusselt number of Cu nanofluids is more than the those for other types of the nanofluids.

In the present work, the natural convection heat transfer from horizontal cylinder with square cross section situated in a square enclosure, vented symmetrically from the top and the bottom is investigated experimentally. The experimental work includes temperature measurements of the cylinder surface and the environment during transient state to determine Nu for the unbound and the bound cylinder. The studied variable ranges were: 107  Ra  6.6 107, 2  W/D  4, 0.25  O/D  4. The results indicated an increase in Nu with increasing Ra. Furthermore, Nu increased proportionally with the vent opening size at low enclosure widths. It showed inverse proportionality with opening size for high enclosure widths. The maximum percentage of the enhancement is more than 20% for bounded square cylinder as compared with unbounded square cylinder.

In the present work, the natural convection heat transfer from horizontal cylinder with square cross section situated in a square enclosure, vented symmetrically from the top and the bottom was investigated numerically. The work investigate the effect of the Ra, enclosure width and opening size of the enclosure on the streamlines, isotherms and heat transfer results. The numerical work included the solution of the governing equations in the vorticity-stream function formulation which were transformed into body fitted coordinate system. The transformations are based initially on algebraic grid generation and elliptic grid generation to map the physical domain between the heated horizontal cylinder and the vented enclosure into a computational domain. A hybrid scheme finite volume based finite difference method was used. The study included the following ranges of the studied variables:- 0 < Ra ≤ 6.5× 105 1.5 ≤ W/H ≤ 4 0.375 < O/H ≤ 4 The numerical results were compared with experimental results, which showed good agreement. The effect of cylinder cross section, Ra, enclosure width, and opening size on the Nu, mass flowrate, flow patterns and isotherms were investigated. The results show that the cylinder cross section has a large influence on the results especially the Nu. The Nu is proportional with Ra and inversely proportional with enclosure width and opening size. The flow patterns and isotherms display the flow and temperature behaviors with changing studied variables. The results show that the starting of natural convection heat transfer depended on the cylinder cross-section, enclosure width and opening size in addition with Ra. In addition, the results display that the hydrodynamic and thermal boundary layer thickness decreases with increasing Ra.

A solar water heating system that uses flat plate collector has been designed theoretically for a building in a Zakho city using f-chart method. The f-chart method based on some assumed collector parameters. The method, that uses weather data of Zakho city, based on the estimation of the fraction f of the total heating load supplied by the solar thermal system annually. Two design criteria were investigated in the present study; the tilt angle of the collector and the coatings of the absorber plate. The results showed that the hot water produced from solar system covers about 39-50% of the load during winter session, while, the system provide most of the heating water load during remainder sessions. The present study observed that the optimum value of the tilt angle of the flat plate collector was equal to the latitude angle of the Zakho city. The employment of different coatings displays the absorber plates that have lower emissivity factor increase the fraction of the solar energy during around the year.

In the present work, the natural convection heat transfer from horizontal cylinders with rhombic cross sections situated in a square enclosure, vented symmetrically from the top and the bottom is investigated experimentally. The experimental work includes temperature measurements of the cylinder surface and the environment during transient state to determine Nu for the unbound and the bound cylinders. The studied variables ranges were: 107  Ra  6.6 107, 2  W/D  4, 0.25  O/D  4. The results indicated an increase in Nu with increasing Ra for all cases. Furthermore, Nu increased proportionally with the vent opening size at low enclosure widths. It showed inverse proportionality with opening size for high enclosure widths.