Kozak D. Heat engineering characteristics of the combined solar collector on the basis of aluminum grooved heat pipes

The work is devoted to increasing energy efficiency and simplification of integration of solar systems on the basis of the photovoltaic thermal (PV/T) collector in the facades and roofs of buildings due to use as an element of the absorbing surface of aluminum grooved heat pipes (AGHP). It is established that the efficiency of the operation of the PV/T collector with AGHP in the thermosyphon mode is significantly influenced by the thermal characteristics of the HP, which in turn depends on the following parameters: the diameter of the steam space, the thermophysical properties of the working fluid, the lengths of the heating and condensation zones, and the total length of the AGHP. Increasing the thermal conductivity of AGHP can be achieved by providing a guaranteed amount of coolant to the heating zone and selecting the optimal design parameters of the HP at the appropriate operating modes. A new approach to the implementation of PVT collectors on the basis of AGHPs is proposed. In this case, AGHPs perform a complex role – at the same time it is a highly efficient thermal conductor and a system of cooling solar cells. The design of an aluminum heat pipe with a grooved capillary structure for PVT collectors has been developed. An n-pentane is chosen as the optimum coolant for a two-phase system. The developed samples of heat pipes can provide the operation of the PVT collector in the thermal mode from 0 oC to 120 oC. In this case, the temperature range of its operation is from −40 °C to +230 °C. The analysis of calculations and experimental data showed that the PV/T collector with AGHP allows to increase the efficiency of obtaining electric energy up to 18 % due to the cooling of the PV, while the maximum electric power PV/T collector was 135 W/m2. In addition to electricity, simultaneously, it is possible to get up to 457 W of heat from 1 m2 of heat-absorbing surface, at a temperature of the output coolant 25 oС and a density of solar flux of 900 W/m2. On the basis of theoretical analysis, the most optimal modes of operation of the PV/T collector were identified – the most optimal one is the mode of PV/T collector functioning at values of 30–50 oC of the temperature difference between the absorbent surface and the environment. The new PV/T collector design has a more efficient performance compared to separate thermal solar collectors and photoelectric batteries at low temperatures on an absorbent surface (below 50 oC), and usually at higher solar flux values (over 600 W/m2). The first developed programs and methods of research of PVT collectors in artificial and natural light developed an engineering methodology for calculating the thermal characteristics of PVT collector with AGHPs during their operation in a thermosyphon mode. The recommendations for the production of PVT collectors and their use in solar power systems are given. The results of the work in the future can be used at the enterprises of LLC «Effectprof» (Kyiv), PC Sumy SPO M.V. Frunze (Sumy), PE Scientific-Implementation Firm "Thermal Technologies" (Kiev), which are engaged in the development, manufacture and implementation of heat-exchange equipment and energy-efficient systems. For further implementation, it is necessary to carry out works on designing and manufacturing an industrial design of PVT collector or facade PVT collector and to conduct tests in the field.