The effects of bond, shrinkage and creep on the cracking resistance of regular, pre- and post-tensioned reinforced conrete members

Abstract

The most ordinary way to use wind energy for building heating needs is to convert mechanical wind energy into electrical energy and to use electrical energy for heating. Though there are ways to convert mechanical wind energy into thermal energy without transitional energy conversion – hydraulic systems can be implemented for this purpose. Wind rotor gives rotational motion to the pump of hydraulic system and it creates fluid circulation in the hydraulic system. A part of liquid mechanical energy due to hydraulic resistance of the system converts into the thermal energy when the liquid circulates in the close hydraulic loop and it heats up the liquid that can be used for heating purposes. Different hydraulic valves can be integrated in the hydraulic system and they can work as the load-regulating component of the system. The purpose of the study was to adjust the hydraulic load to the optimal value in order to generate a maximum amount of thermal energy. During the study, the work of a wind rotor was simulated by an electric motor, rotated at different frequencies (without feedback). The hydraulic system consisted of a gear pump, an adjustable load regulation valve, pipes, oil tank, sensors for measuring motor shaft rotational speed, oil temperature and pressure. This experimental research follow our previous researches (Ždankus et al., 2016). The experiments were carried out at additional different electric motor speeds: 12.5, 17.5, 22.5 and 27.5 Hz. The relationship between the opening degree of the valve and the amount of generated thermal energy was determined. It was noticed that an optimal work regime of system was reached by changing the opening degree of load control valve from 0.1 to 0.33. Experiments were provided in both directions of the changes of the loading, when the valve was opening and closing. The opening was provided in two different methods. Undistinguished different of the amount of generated heat was noticed. During our previous experimental research, the hypothesis appeared that a change in the kinematic fluid viscosity could influence on the amount of generated heat and the optimal value of the opening degree of the loading valve. Therefore, experiments were performed to determine the influence of rising fluid temperature on optimal regime of hydraulic system. Experimental research was performed by changing of the temperature of the liquid in the range from 20 to 50 °C. In the case of wind, mechanical energy conversion to electricity the heat emission means the energy losses. The final product and the losses are the same types of energy in the case of hydraulic system for conversion of wind mechanical energy into the thermal energy (Ždankus et al., 2016). The experimental research showed that wind energy usage could cover a significant part of the building’s thermal energy needs (Černeckienė, 2015) at the same time reducing pollution and the usage of the fossil fuel for heating purposes.