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Interest in renewable energy is rapidly growing due to the increase in energy demand, environmental pollution, and depletion of fossil fuels worldwide. One of these sources is solar chimney power plant, which utilizes solar energy to generate electrical energy at a relatively low operating cost. Solar chimneys also do not require cooling, indicating that water resources are not wasted, and they are expected to be widely used in developing countries with abundant solar radiation. This study involved installing a solar chimney with a height of 3 m and a diameter of 3 m for the collector. The experimental results were verified by performing numerical work using ANSYS Fluent, under the scenario that no partition was present in the collector. The exergy efficiencies with I- and C-type partitions were compared with the case without partition. The result showed that the exergy efficiencies were 7.05 % and 7.12 % for the I- and C-type partitions, respectively, and they were higher than the previous 6.44 % for no partition. This study confirmed that the power generation exergy efficiency can be increased by installing partitions in existing solar chimney power plants. [ABSTRACT FROM AUTHOR]

We studied the transient local surface temperature response that occurs when jet impinging of nitrogen gas is applied to the surface to which a pulsating heat flux is applied. After manufacturing a micro jet impinging device, which was composed of three parts—a silicon wafer, a vinyl sticker, and a Pyrex wafer—nitrogen gas was used as working fluid and the velocity was 344.8 m/s, corresponding jet Reynolds was 1467. And the amplitudes of heat fluxes varied from 5.67 to 16.17 W/cm2, the frequency also varied from 0.1 to 1000 Hz, then temperature response of RTDs was acquired. For example, when a heat flux, 8.5 W/cm2, was applied with a frequency of 0.1 Hz, the highest and lowest temperatures of RTD located on the center of the heater and under indirect jets were 30.2 °C and 20.7 °C. From the acquired results, the time constant of the device was estimated between 17 ms and 32 ms, and this result shows the conjugated mode of conduction and convection of heat transfer. To understand the dominant heat transfer, we decoupled the conduction mode and the convective heat transfer mode through analytical calculations and confirmed that the time constants were 11 µs and 128 ms, respectively. In addition, the heat transfer coefficient was inversely calculated through numerical calculation by simulating the RTD manufactured in the device, and through this, it was confirmed that the dimensionless time constant was related to the Nu number and the correlation was developed as τ/t = 3.51Nu−1.067 for f ≤ 1 Hz. [ABSTRACT FROM AUTHOR]

We studied the transient local surface temperature response that occurs when jet impinging of nitrogen gas is applied to the surface to which a pulsating heat flux is applied. After manufacturing a micro jet impinging device, which was composed of three parts—a silicon wafer, a vinyl sticker, and a Pyrex wafer—nitrogen gas was used as working fluid and the velocity was 344.8 m/s, corresponding jet Reynolds was 1467. And the amplitudes of heat fluxes varied from 5.67 to 16.17 W/cm2, the frequency also varied from 0.1 to 1000 Hz, then temperature response of RTDs was acquired. For example, when a heat flux, 8.5 W/cm2, was applied with a frequency of 0.1 Hz, the highest and lowest temperatures of RTD located on the center of the heater and under indirect jets were 30.2 °C and 20.7 °C. From the acquired results, the time constant of the device was estimated between 17 ms and 32 ms, and this result shows the conjugated mode of conduction and convection of heat transfer. To understand the dominant heat transfer, we decoupled the conduction mode and the convective heat transfer mode through analytical calculations and confirmed that the time constants were 11 µs and 128 ms, respectively. In addition, the heat transfer coefficient was inversely calculated through numerical calculation by simulating the RTD manufactured in the device, and through this, it was confirmed that the dimensionless time constant was related to the Nu number and the correlation was developed as τ/t = 3.51Nu−1.067 for f ≤ 1 Hz. [ABSTRACT FROM AUTHOR]