Thermal Performance Of Solar Chimney Research Articles

A comparative analysis on the thermal performance of solar chimney with smooth and dimpled absorber plate

This paper presents an experimental investigation to evaluate the thermal performance of dimpled absorber plate solar chimney (DAPSC) and compare with that of smooth absorber plate solar chimney (SAPSC). The parameters measured in this study are ambient air temperature, solar intensity, outlet air temperature of solar chimney and outlet air velocity of solar chimney. The thermal performance is evaluated based on air temperature and velocity at outlet of solar chimney and heat transfer. The results indicate that the heat transfer coefficient of DAPSC system is 13.55% higher than that of SAPSC during mid sunny day. In addition to that, higher air temperature at the outlet of the DAPSC of 42.6 °C is obtained when compared with that of SAPSC of 41.6 °C. DAPSC system shows maximum air flow rate of 0.72 m/s as compared to SAPSC system with the air flow rate of 0.57 m/s.

Experimental justification of poor thermal and flow performance of solar chimney by an innovative indoor experimental setup

Power generation of solar chimneys effectively depends on their thermal performance. The manufactured samples, available in the literature, have many functional weaknesses and their obtained output power is much lower than expected. Due to the variation of operating conditions (i.e. solar radiation, wind velocity, ambient temperature etc.) of outdoor experimental setups, the thermal performance and heat transfer coefficient cannot be properly evaluated for those systems. Herein, a new indoor test setup is employed to study the steady-state thermal performance of the solar chimney collector while the effects of environmental changes on the tests are minimized. The flexibility of the custom-designed experimental setup allows the investigation of effects of angle of collector, height of chimney, and the area of collector on the convection heat transfer coefficient, velocity and temperature distribution at various points, and the ratio of energy transferred to that introduced to the collector (RET). Our analyses show that the poor performance of common solar chimneys can be justified by existence of secondary flows beneath the collector. The results are important in designing the next generation of solar chimneys with optimized geometry and enhanced thermal efficiency. Results show that, high thermal and frictional losses, due to formation of secondary flows, cause less than 9% of the input energy to enter the chimney and generate power. The collector angle is known the most responsible parameter for controlling formation of the secondary flows. For the divergent collector, increasing the collector angle from 0 to 14 reduces the thermal losses by 1.72% and enhances the heat transfer coefficient by 41.6%. On the other hand, higher amounts of secondary flows in convergent collectors, increases thermal losses by 98.8%. Based on the obtained results, increasing the collector area, as commonly suggested by many researches, while increasing the suction velocity, significantly reduces thermal efficiency of the chimney; This issue along with increasing the manufacturing costs, indicate that increasing the area acts marginally and cannot be a good idea to improve chimney performance most of the times.

CFD modelling of transient thermal performance of solar chimney used for passive ventilation in a building

The paper analysed the 24 hour performance of a solar chimney placed on a building roof in Krakow, Poland. The solar chimney was an element of as a passive ventilation system allowing energy efficient night ventilation during the summer season. The chimney was built as an air duct. Three walls of the chimney were made of glass and faced toward the sun, the opposite wall was made of a concrete absorber. The system worked in two stages: day and night. The absorber located in the chimney was heated during the day, and cooled during the night. During the night phase, the released heat provided a draft contributing to passive ventilation.Absorbers with different thermal capacities were studied. Simulations were conducted for three different absorber thickness 10 cm, 20 cm or 30 cm. The simulations were carried out using the Ansys Fluent simulation software. The hourly results of temperature distributions in the chimney allowed the authors to determine the optimal absorber thickness for the passive ventilation system. Calculations showed that the chimney with the absorber that was 10 cm thick was the optimal among analysed solutions. The absorber is warmed up to the highest temperature, up to 82°C, and induces air flow which lets removing even 3820 m3 of air during the night.

Effects of various parameters of a PCM on thermal performance of a solar chimney

A validated numerical model is established to study the effects of various parameters on thermal performance of a solar chimney integrated with phase change material (PCM) in terms of the melting/freezing time, air flow rate and air temperature difference between inlet and outlet. The numerical results showed that the phase change temperature of PCM greatly affects the thermal performance of solar chimney. The PCM having wider phase change temperature difference reaches the complete melting earlier than that with narrower one. However, it also fluctuates the room air temperature that may cause the thermal discomfort. The specific heat of PCM affects the way that sensible heat contributes to the melting/freezing process. The average mass flow rate and air temperature difference increase from 0.033 to 0.038kg/s and from 1.5 to 2°C, when the thermal conductivity of PCM is enhanced from 0.2 to 0.6W/m·°C. The initial temperature of PCM has very little influence on the melting process after the early period of melting.

Occupant Comfort and Indoor Temperature Reduction by Using Passive Air Conditioning System with Solar Chimney Concept in Hot Arid Climate

Housing in Egypt consumes high energy for cooling. Bioclimatic building design is one of the strategies of sustainable development. The aim of the present research is to investigate the thermal performance of solar chimney with passive cooling wind tower (SCPC) on occupant’s comfort. The passive cooling design is integrated on the ceiling of 30 m2 test house. Monitoring of indoor environment was carried out over a period of two months in the summer season (September and early October) with a 2 minute interval in order to calculate thermal comfort sensation, Predicted mean vote (PMV) and PPD. The results show that outlet air temperature from the wind tower is 27.3°C. The calculated predicted mean vote (PMV) is within the recommended range (-0.5<PMV<+0.5). This indicates that occupants remain satisfied with indoor thermal environment after using the passive cooling system and the difference is nearly 8 K between outdoor and indoor. The results of this research provide information of the system applicability in the climate of Assiut during day time in order to develop and install on top of real residential buildings in New Assiut, Egypt.