In this work, a system of heat pipe is implemented to improve the performance of flat plate solar collector. The experiment rig consists of sun light simulator, flat plate, heat pipe (wickless), heat exchanger, and measurement instruments. The model is represented by twisting portion of the evaporator section and also inclined by an angle of 30° with a constant total length of 1140 mm. In this model the evaporator, adiabatic and condenser lengths are 780mm, 140mm and 230mm respectively. The omitted energies from sun light simulator are 200, 400, 600, 800 and 1000 W/m2 which is close to the normal solar energy in Iraq. The working fluid for all models is water with fill charge ratio of 30% and the efficiency of the solar collector is investigated with three values of condenser inlet water temperatures, namely (12, 16 and 20° C). The experimental result showed an optimum volume flow rate of cooling water in condenser at which the efficiency of collector is a maximum. This optimum agree well with the ASHRA standard volume of flow rate for conventional tasting for flat plate solar collector. When the radiation incident increases the thermal resistance of thermosyphon is decreases, where the heat transfer from the evaporator to condenser increases. The experimental results showed the performance of solar collector with twisted evaporator greater than other types of evaporator as a ratio 13.5 %.

This article reviews the construction of organic solar cell (OSC) and characterized their optical and electrical properties, where indium tin oxide (ITO) used as a transparent electrode, “Poly (3-hexylthiophene- 2,5-diyl) P3HT / Poly (9,9-dioctylfluorene-alt-benzothiadiazole) F8BT” as an active layer and “Poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate)” PEDOT: PSS which is referred to the hole transport layer. Spin coating technique was used to prepared polymers thin film layers under ambient atmosphere to make OSC.  The prepared samples were characterized after annealing process at (80 ͦ C) for (30 min) under non-isolated circumference. The results show a value of filling factor (FF) of (2.888), (0.233) and (0.28) and power conversion efficiency (PCE) of (0.0055), (3.333  10-6) and (0.0004), where these results were obtained by Keithley Electrometer Model 6517B, while spectral response is being utilized by LEOI-94 Monochromator and Keithley 6517B Electrometer.

In recent years, there has been a rising concentration in investigating and researching the boiling of micro channel flow; since they afford high thermal effectiveness, small size, and low weight. In this paper, the boiling heat transfer was experimentally examined using water as the working fluid in small diameter tubes. Experiments for the flow model were performed using the same Pyrex glass tube test facility. The experiments of heat transfer were carried out using an internal diameter copper tube (10.922 mm). The range of other parameters was varied: mass flow rate (0.008–0.0214kg/s); heat flux (17351–80529W/m2); it has been found that the average coefficient of heat transfer depends on the form of flow pattern. The average heat transfer coefficient increases by about 37% when the flow pattern varied from slug flow to churn flow at a constant mass flow rate of 0.008kg/s. Besides, the heat transfer coefficient (h) in the two-phase flow, is 39%, which is more than that for single-phase flow, when the mass flow rate is 0.0214kg/s, and heat flux) increases from 17351W/m2 to 49105W/m2. Also, when mass flow rate rises from (0.008kg/s) to (0.0166kg/s), the pressure drop increases by about (15%) and increases by about (5%) when the mass flow rate rises from (0.0166kg/s) to (0.0214kg/s). The main regime of flow was a slug, churn, bubbly, dispersed bubbly, and confined bubbly flow.

The wickless heat pipe (theroosyphon) is ordinate of three divisions the condenser, evaporator and insulated region (adiabatic region). In this work, the condenser and evaporator regions are made of copper tube with a length of 300 mm, for each an exterior diameter of 28.2 mm and an interior diameter of 26.4 mm. While the insulated region has a length of 400 mm and an exterior diameter of 28.2 mm. The evaporator region of the heat pipe bounded by a coiled heat source that represented the heat source. The condenser is encapsulated in a plastic cylinder to accommodate the flow of the cooling water. Thermosyphon has been filled by R- 134a working fluid. The effect of heat input, filling ratio and sink temperature were all tested and measurement. The results showed that the heat transfer performance increases when the applied energy to the evaporator increases while the total heat transfer efficiency of the heat pipe increases the gradient temperature between the medium of the evaporator and the condenser increases. The optimum fill rate is 119 % (250g), the sink temperature is 20°C, and it has been found to be suitable for optimum heat pipe performance.

The mixed convection investigation of various design parameters utilizing finned pipes in the cylindrical enclosure has been investigated computationally. Various geometries of fins are used (circular and longitudinal). The effect of fins number (12-16), aspect ratio (1.83-2.7), radius ratio (2-3) and fins geometry have been introduced within the present study. The observations show that when Richardson number=0.5 and 5.5 , the heat transfer decreases by 12.22% and 7.777%.,. Values of the Nusselt number rise as the number of fins increases. While, when the Rayleigh number is high, no noticeable variations in the numbers of fins (12 and 14). The purpose of using fins is to increase the surface area of heat transmission. The highest heat transfer improvement is shown to be 4.2 percent, when log (Rayleigh)=7.342 and 16 fins are utilized. The radius ratio does not affect Nusselt number throughout the whole Richardson and Rayleigh in both hot and cold locales. The turbulence sub-layer does not affect the free stream behaviour for different Richardson number. In the case of high Richardson number, the geometry does not influence the Nu. Longitudinal fins do not have dead zones, unlike circular fins, which have channelling generated by geometrical arrangement. To reach thermal equilibrium in a cold environment, the Nu in rectangular fins was reduced by 18% as compared to circular fins with a low Richardson number. Flow development would increase the impact of channelling. The heat transfer improvement decreases as the number of fins increases, as illustrated in temperature and velocity profiles for various values