The back-and-forth movement of flow in oscillatory flow condition that can be found in blood flow, thermoacoustic energy system and ocean wave can be categorized as bi-directional flow condition and heat transfer in this flow condition is not well understood. This paper reports an experimental investigation that compares temperature and velocity values between the onedirectional (the usual flow condition) and the bi-directional flow conditions. The experiment was done using thermoacoustic's standing wave rig with two different drivers to drive the one-directional flow and bi-directional flow conditions in the test rig. Results, that were recorded using piezoresistive pressure sensor, type-K thermocouple and hotwire anemometer, indicate that care should be exercised when calculating heat transfer in bi-directional flow conditions as the temperature and velocity changes are different compared to the one-directional flow condition. Differences were recorded to be within the range of 77% for temperature and 59.5% for velocity, presumably due to the different behavior of forced and natural convection effect as flow conditions changed.
Fluid can flow in one-directional (normal flow) or oscillatory conditions. Fluid flow in some energy system involved oscillatory flow condition. The use of vortex generator has been proven to improve heat transfer in the case of one-directional flow but the impact of vortex generator in oscillatory flow condition is yet unknown. This study focusses on the heat transfer performance across a heated tube banks using a Computational Fluid Dynamics (CFD) model. Two flow conditions were modelled: steady one-directional and oscillatory flow conditions. Two-dimensional CFD models of steady flow and oscillatory flow were solved using the SST k-? turbulence model for two different cases of heated tube banks with and without the vortex generators. The heat transfer performance for both flow conditions were analysed by considering a heat transfer parameter known as Colburn-j factor. Results showed that the use of a vortex generator increased the heat transfer enhancement, regardless of the flow conditions. However, it is also noted that the heat transfer behaviour in a steady flow and an oscillatory flow is not the same, especially with the appearance of secondary flows in the system. The difference is discussed with respect to dimensionless quantity of Colburn j-factor, the non-dimensionless quantity, and the amplitude of temperature field. The result indicates that the heat equation in the steady flow condition is not very suitable to be directly used in oscillatory flow conditions. Appropriate heat equation needs to be properly addressed for situations that involve oscillatory flow motion.
Sick building syndrome (SBS) is a collection of symptoms experienced by buildings occupants such as headaches, mucous, membrane irritation, respiratory problems and fatigue. A building is claimed to have SBS if more than 20% of building occupants experience symptoms. Poor indoor air quality contributes to SBS in the building. This study aims to investigate the correlation between indoor air quality and SBS symptoms in 1st and 2nd floors of the Post office building in Bandung. The study used quantitative methods with a cross sectional study design. Data collection was carried out using particle counter, thermometer, lux meter and anemometer to measure the indoor air quality, while the questionnaire utilized random sampling technique with 119 respondents. The results of the primary data were compared with the air quality standard from Minister of Health No. 1077, 2021. The results of the Statically Compare Means and Independent T-test showed that the p-values of the temperature on the 1st floor and 2nd floors were 0.437 and 0.000, respectively. Meanwhile the p-values of PM10 and PM2.5 on the 1st and 2nd floors were 0.005 and 0.290 and 0.004 and 0.364, respectively, and the p-values of the lighting on the 1st and 2nd floors were 0.002 and 0.015. It indicates that there is a significant relationship between concentrations of PM10 and PM2.5 on the 1st floor with SBS symptoms and the temperature and humidity on the 2nd with SBS symptoms. Since 29 peoples (24% of the building’s occupants) experienced SBS, the building was considered to have a significant potential to cause SBS to its occupant.
This paper investigates a modified ejector cycle (MEC) to further enhance the COP improvement of residential air conditioner (A/C), as compared to the standard ejector cycle (SEC). This paper also presents numerical and experimental studies of the MEC. Numerical approach of MEC performances was evaluated by using SEC cycle that had been developed by many researchers. In the experimental study of MEC, three motive nozzle diameters of 0.9, 1.0 and 1.1 mm were utilized. In addition, environmentally friendly refrigerant of R290 (propane) was used as a working fluid. The modeling results of residential A/C with the cooling capacity of 2.5 kW showed higher COP improvements of MEC than SEC for all entrainment ratios of the ejector. There was no COP improvement for SEC at a low entrainment ratio, whereas there are always COP improvements for all entrainment ratios for MEC. In addition, the experimental results showed the highest COP improvement of 16.67% was achieved with the motive nozzle diameter of 1.1 mm.
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