A numerical simulation model for laminar flow of nanofluids in a pipe with constant heat flux on the wall was built to study the effect of the Reynolds number on convective heat transfer and pressure loss. The investigation was performed for hybrid nanofluids consisting of CuO-Cu nanoparticles and compared with CuO and Cu in which the nanoparticles have a spherical shape with size 50, 50, 50nm respectively. The nanofluids were prepared, following which the thermal conductivity and dynamic viscosity were measured for a range of temperatures (10 -60°C). The numerical results obtained were compared with the existing well-established correlation. The prediction of the Nusselt number for nanofluids agrees well with the Shah correlation. The comparison of heat transfer coefficients for CuO, Cu and CuO-Cu presented an increase in thermal conductivity of the nanofluid as the convective heat transfer coefficient increased. It was found that the pressure loss increases with an increase in the Reynolds number, nanoparticle density and particle volume fraction. However, the flow demonstrates enhancement in heat transfer which becomes greater with an increase in the Reynolds number for the nanofluid flow.

At increases the PV module temperature, electrical efficiency of a photovoltaic cells will be decreases. Due to facing the PV module to the solar irradiance to generate electricity, heating the PV cells is inevitable. A thermal channel collector can be used to absorbed heat from a PV cells, this heat absorbed from the cells can be using for other application, therefore increasing the electrical and conversion efficiency. The thermal collector system consists of a rectangular channel made from insulating materials (form) and on it the round water guides, is mounted to the backside of PV panel, through which water flow. In this modeling and numerical study, to solve this problem, was adding a cooling system to the PV panel. In the result, the benefit from this work to cooling the solar cells and increase the electrical efficiency, also to obtain heat gain in the form of hot water. Shown the simulation results, the absorber of thermal collector channel generates the maximum electrical efficiency of 14.6674% with maximum thermal efficiency of 82.532% at ambient of temperature set between 27°C to 32°C, set the temperature of inlet water at 27°C, water flow rate range (1-5) Liter/minute by increasing ratio of (1Liter/minute) and solar radiation between 300 to 1000 (W/m²) by increasing ratio of 100 (W/m ). Because high effectiveness and perfect the contact surfaces between the PV module and the thermal collector channel underneath, the recommended of (PV/T) system to enhance heat transfer.