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The turbulence intensity is an important feature of the turbulent airflow and draught sensation in ventilated rooms. The turbulence is often measured with hot-wire (in fluid mechanics applications) and hot-sphere sensors (in indoor air comfort investigations). In this paper the turbulence was measured with hot-wire and hot-sphere sensors in a full-scale single office room based on air speed measurements. Isothermal air injection was applied and the measurements were conducted on eight different inlet volume flow rates. The two applied sensors resulted two independent samples, which were evaluated with different statistical methods. The results showed that there was not significant difference between the standard deviation and average of the measured samples. Thus, the two sensors statistically gave the same results on probability level 95%.
The referred international standards suggest an average turbulence intensity 40% for draught comfort design in mixing ventilation. The results showed that most of the measured turbulence intensities were less than the recommended standard turbulence intensity.
Abstract
Thermodynamic efficiency is a crucial factor of a power cycle. Most of the studies indicated that efficiency increases with increasing heat source temperature, regardless of heat source type. Although this assumption generally is right, when the heat source temperature is close to the critical temperature, increasing the heat source temperature can decrease efficiency. Therefore, in some cases, the increase in the source temperature, like using improved or more collectors for a solar heat source can have a double negative effect by decreasing efficiency while increasing the installation costs. In this paper, a comparison of the CO2 subcritical cycle and the Trilateral Flash Cycle will be presented to show the potential negative effect of heat source temperature increase.
Abstract
Carbon-dioxide-based trans-critical power cycle is a novel technology for waste heat recovery. This technology can handle the high-temperature exhaust gas and can be built in a compact size, which is an important feature for the auxiliary equipment for an internal combustion engine. To obtain the best output, four configurations were constructed: the basic system; one with preheater, another with regenerator and a fourth with preheater and regenerator. Special features of supercritical CO2 make these cycles able to recover more energy than the traditional organic Rankine cycle. According to this study, heat regeneration increases thermal efficiency while preheating influences the net power output. Thus, it is beneficial to add both regenerator and preheater to the basic cycle.
