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Solar chimney has been applied on various aspects of building physics and green design. It makes natural ventilation based on stack effect from absorbing solar radiation. A Computational Fluid Dynamics (CFD) method has been widely utilized to model the heat transfer and air flow inside the chimney. The appearance of reverse flow is one of the elements affecting induced results from CFD models. In this study, we examined influences of the suction flow to suppress the reverse flow at the outlet of the air channel. The suction height, suction width and the velocity of the exhaust fan were investigated. The induced flow rate and temperature rise of the chimney were compared to the base case, which has no suction flow. It is observed that the ratio of Qsc and Qbase, which are the induced flow rate at the outlet of the chimney which has exhaust fan and induced flow rate of the base case, respectively, increases with the width, w, and the height above the inlet, h, of the suction port then gradually approaches a constant of about 1.25 when w and h are higher than 0.02 m and 0.15 m correspondingly. Additionally, one advantage of the suggested solution is to lower the noise from the fan to the room.

Using solar energy, a Trombe wall is a passive solar design in an attempt to improve the energy efficiency inside buildings. Trombe walls absorb thermal energy through a glass panel on the outside. This energy is used to heat the cold air from inside the buildings through the inlet at the bottom of the air gap between the glaze and the wall. The warm air rises and it is redirected back into the building through the outlet at the top of the air gap. The performance of Trombe walls can be improved by adding discrete heat sources. In this study, an investigation on the temperature rise and the induced flow rate of the air flow was studied with the presence of a heat source placed at different positions on the air channel. By Computational Fluid Dynamics (CFD) technique, the dimension of the heat source was varied to obtain their effects on the efficiency of the Trombe wall. An increase of 18°C in temperature was attained when the heat source was placed near the outlet of the air gap. The presence of discrete heat sources is an approach to improve the performance of Trombe walls.

Solar chimney has been studied extensively by many researchers and proved to be an effective method for natural ventilation of buildings. Once properly designed, a solar chimney can help to save energy significantly and maintain thermal comfort conditions inside the building. In ideal configurations, a vertical solar chimney has been studied in the form of a straight air channel with constant flow area. In this study, we considered a solar chimney in practical applications where the outlet area of the air channel may be contracted due to other required elements, such as those for weatherproofing. The flow and heat transfer inside the air channel were simulated with a Computational Fluid Dynamics model. Effects of reducing the outlet area were examined under different heights and gaps of the air channel. The results show that reducing the outlet area significantly reduces the flow rate but increases the temperature rise through the chimney. Based on the results, one may select suitable configurations depending on the priority of the application of the chimney, i.e. higher flow rate for ventilation or higher temperature rise for heating applications.

With a good design, solar chimney is able to provide sufficient natural ventilation for buildings. In practice, natural ventilation performance depends on many factors, such as solar radiation, which is intermittent. Therefore, in this study, a proposed combined natural–forced flow solar chimney is investigated. Induced ventilation rate is estimated under the effects of the temperature of the forced flow and compared to that of the base case which has no forced flow. The results show that, with a forced flow velocity of 1.0 m/s and a heat flux of 500 W/m2, the induced mass flow rate increases when the forced flow temperature increases from 20 to 35oC. Compared with the base case, the combined natural–forced flow offers more flow rate as the gap G is above 0.05 m at the height, H, of solar chimney H of 0.45 m; 0.1 m at H=0.95 m; 0.15 m at H=1.45 m, and 0.2 m at H=2.0 m. It is expected that with a proper design, improvement of ventilation performance of a solar chimney can be achieved by this combined natural–forced flow.

Numerical simulations have been widely employed in buildings, particularly for prediction of natural ventilation. The Computational Fluid Dynamics (CFD) has been utilized successfully for prediction of the airflow and heat transfer in solar chimney, one of the common devices for natural ventilation. However, CFD requires expensive computational resources. In this study, an Adaptive Neuro-Fuzzy Inference System (ANFIS) model was tested for quick prediction of the heat transfer in a vertical solar chimney based on the data provided by a CFD model. The Nusselt number in solar chimneys at different heights and heat flux were predicted with the CFD model. The generated data were used to train two ANFIS models which were then validated with the remaining CFD data. The results show that the ANFIS models can predict the Nusselt number and mass flow rate with the maximum discrepancy between the two results of less than 5.0%.

Natural ventilation, one of the key elements of green buildings, can be achieved with solar chimneys. This device based on buoyancy effects induced by solar radiation to create air flow for ventilation. Among the factors influencing performance of a solar chimney is the area of the inlet. In this study, effects of reducing the inlet area on the performance of a vertical solar chimney was examined numerically. A CFD (Computational Fluid Dynamics) model was built on the ANSYS Fluent CFD code to simulate the air flow and heat transfer inside the solar chimney at different heights and gaps. The results showed that, as the inlet area decreases, the flow rate is almost unchanged until a critical ratio of the inlet area and the gap of the air channel. As the inlet area decreases further, the flow rate decreases at a constant rate. The temperature rise is always enhanced as the inlet area decreases. The changes of the thermal efficiency depend on the gap – to -height ratio. These observations can serve as references for design of air damper at inlet of solar chimney for a specific application, such as ventilation where higher flow rate is desired, or heating where higher temperature rise is preferred.

An accurate simulation will assist to understand the behavior of rarefied gas flows in MEMS devices. This is useful for obtaining an optimal design for these devices. In this paper, we will comprehensively investigate the effect of viscous heat generation on the rarefied gas microflows in the microcavity and Couette flows. The considered cases have the Knudsen number ranging from 0.05 to 1, and working gas as argon. Both of the temperature jump conditions were recently derived including the viscous heat generation term such as the new type of Smoluchowski and the modified Patterson temperature jump conditions are adopted in the present work. The simulation results show that the viscous heat generation significantly affects the gas temperatures, and it makes a reduction of the gap between the CFD and DSMC data. The simulation results of the modified Patterson jump condition are close to the DSMC data for the high Kn cases, Kn = 0.5 and 1 while those of the new type of Smoluchowski jump condition are not.

Exploring solar radiation, solar chimneys are widely used in sustainable building design. Solar chimneys can ensure thermal comfort in a house by generating a heating or cooling air flow. For heating applications, the induced air flow is heated and supplied back to the house. In this study, the air flow and heat transfer in a solar chimney for heating were modelled by a numerical simulation based on Computational Fluid Dynamics (CFD) technique. An investigation on the system performance was carried out with the presence of a heated cavity above the top and below the bottom of the air channel. The length and the width of the cavity and the chimney gap have a strong influence on the flow rate and temperature rise through the chimney. The results showed that an appropriate dimension of the heated cavity can enhance the performance of the solar chimney.

Integrated passive cooling technique in building is expected to save energy and create thermal comfort. Solar chimney has been adopted to building design as an effective technique for natural ventilation. The working principle of solar chimney is based on thermal effect, particularly natural convection heat transfer. In this paper, heat transfer performance of a solar chimney with different contracting inlet areas is presented. Furthermore, the effects of major dimension, i.e. ratio of chimney gap and height G/H, are also investigated. As the ratio of the inlet area and the gap, Ai/G, from 90% to 20%, the Nusselt number is strongly affected for G/H below or equal to 5%; while for G/H above or equal to 20%, it showed minor influence. In addition, with G/H of 10% and inlet area from 40% to 60% of the gap, heat transfer coefficient have considerable improvement from 5.3% to 6.1%. The result suggests that G/H = 10% and Ai/G in the range of 40% to 60% are optimal design.

Solar chimney has been widely employed for natural cooling or heating of buildings. Of its forms, wall-attached solar chimney is common. Most of previous studies examined solar chimneys with the heat source on one side of the air channel of a solar chimney. In practical applications, depending on the materials, the absorption of solar radiation can be on both sides of the air channel. Therefore, this study examines a wall-attached solar chimney with the heat source distributed on both sides of the air channel. The Computational Fluid Dynamics (CFD) model was utilized to simulate the flow dynamics and heat transfer of the problem. Performance of the solar chimney was described in terms of the heat transfer coefficient, or Nusselt number, the induced flow rate, and the temperature rise through the chimney. The results shows that the examined parameters can be improved, reduced, or unchanged depending on the gap of the air channel and the heat distribution ratio. The findings may be useful for designing wall-attached solar chimney as they show the conditions for maximizing the flow rate or the temperature rise.

Solar chimney has been applied widely in many aspects, such as civil engineering and building physics and demonstrated to be a good solution for natural ventilation of dwellings. It uses absorbed solar radiation to create stack effect which induces air flow and increases ventilation of building. Therefore, solar chimney is one of the most common methods used for energy saving, especially in the field of green design. In this study, we examined a solar chimney integrated with a cover plate at the outlet of the chimney. In other words, the outlet area of the chimney is contracted. A Computational Fluid Dynamics (CFD) model was utilized to simulate the air flow and heat transfer throughout the air channel. The effects of lowering the outlet area were investigated at various air channel heights and gaps. The results indicate that limiting the outlet area strongly affected the computed Nusselt number.

As one of the most common methods for natural ventilation of building, solar chimney has been studied widely in the literature. Various forms of solar chimney have been proposed for enhancing its performance for a specific application, i.e ventilation and/or heating. In this work, we examined performance of an L-shaped comprising horizontal and vertical air channels connected serially by a numerical model based on the Computational Fluid Dynamics (CFD) method. Two different total lengths and gaps of the chimney were tested. The considered parameters included the flow rate, temperature rise, and thermal efficiency. The results show that as the horizontal portion is longer than the vertical one, the flow rate decreases while the temperature rise increases. The variation of the thermal efficiency depends on the ratio between the gap and the total length of the air channel. The findings can help to select suitable configurations of an L-shaped for a specific cooling or heating application.

A Trombe wall can be installed in buildings to reduce electricity consumption. Trombe walls are designed to absorb and store solar radiation. By thermal effects, cool air enters the air channel from the inlet and is heated during the channel’s passage. The warm air rises and is fed back into the building to achieve energy efficiency. In this study, an investigation on the induced flow rate and temperature rise was carried out with a fin’s presence by a numerical method based on Computational Fluid Dynamics (CFD) technique. The location and length of the fin were changed to improve the system performance. This work demonstrated that an increase of 16° C in temperature at the outlet can be achieved with a distance of 0.1 m between the fin and the inlet. The fin added inside the Trombe wall channel is an approach to achieve thermal comfort in sustainable building design.

Solar chimneys have been widely used for natural ventilation of buildings. It absorbs solar radiation to create stack effect to induce air flow for ventilation. To model air flow and heat transfer inside solar chimneys, numerical models based on Computational Fluid Dynamics (CFD) have been broadly employed. The size of the computational domain is one of the factors influencing computed results from CFD models. In this study, we investigated effects of the extension of the domain above the outlet of the air channel as the gap and the height of the air channel changes. Two types of the computational domains were studied. The small domain has identical physical size with a cavity inside the solar chimney while the large domain contains both the cavity and the ambient air surrounding the chimney. The induced flow rate and temperature rise of the chimney were computed and compared between those domains. It is seen that to ensure the changes of both flow rate and temperature below 1.0%, the required extension, h, of the domain above the outlet of the air channel is a function of the gap – to – height ratio G/H, not only the gap. Specifically, for G/H in the range of 0.1 – 0.4 in this study, the required h/G rises from 10 to 30.

With passive designs, such as solar chimney, solar radiation absorbed on building envelopes can help to reduce the energy consumption of the building. Solar chimneys can be employed for natural ventilation and/or heating. The performance of a solar chimney has been reported in the literature to depend mainly on the dimensions and designs of the air channel where the air flow is induced. Particularly, the design of the inlet area plays an important role. In this study, effects of the expansion of the inlet area of a vertical solar chimney were investigated numerically with a Computational Fluid Dynamics (CFD) model. The induced flow rate and temperature rise through the chimney were assessed when the inlet area was expanded in both horizontal toward the right side of the air channel and vertical directions and at different heat fluxes. With the expansion, the induced flow rate is always enhanced as the expanded height is equal to and more than the gap of the air channel due to the reduction of the area of the recirculation zone in the air channel. However, no significant enhancement of the temperature rise or the thermal efficiency is seen as the thermal boundary layer along the heated (left) wall changes insignificantly. Similar trends are seen for both values of the heat fluxes. The findings in this study can serve as a reference for different design options for the inlet of solar chimneys.

This study investigates flow field around a building with triangular cross section by experiments and numerical simulations. The experiments were conducted in an open wind tunnel. Pressure distribution on the surfaces of a scaled model of the building was recorded at different wind speeds and wind angles. The simulation was based on Computational Fluid Dynamics (CFD) technique with computational conditions similar to those in the experiments. It was revealed that the pressure distribution on the building surfaces changed significantly with the wind angles, the direction of the surface relative to the wind angle, and position on the surface. The effect of the different wind angles in determining the drag coefficient on the building was also performed. Flow visualization with smoke and the CFD results reveal flow structure around and behind the building which strongly correlate with the measured pressure distribution on the building surface.

Solar chimneys absorb solar radiation for natural ventilation or cooling of buildings. In typical solar chimneys, the air flow is induced by the thermal effect which causes pressure gradient inside the chimney to deviate from that of the ambient air. The induced flow is employed to ventilate the connected building naturally. In this study, we aimed to boost the induced flow rate through a typical solar chimney by a forced flow at the inlet of the air channel which is divided into two ports for the forced and the induced flows. The air flow and heat transfer were modeled with a Computational Fluid Dynamics (CFD) model with the ANSYS Fluent CFD code. Changing factors included the forced velocity, the dimensions of the inlet port for the forced air flow and the length of the partition between the ports of the naturally induced and forced air flows. It is seen that the forced flow significantly reduces the pressure in the air channel compared to that of a typical chimney; hence increasing the induced flow rate. The flow rate was significantly enhanced as the forced velocity was above 0.2 m/s; the area of the inlet port for the forced flow was 12.4% of the total inlet area; and the partition height was less than 5.0% of the total height of the air channel. In this configuration, the forced flow can be the waste exhaust air flow from other mechanical ventilation systems of the building. Therefore, no additional energy is required for this solution.

Solar chimneys absorb solar radiation heat to create stack effect which induces airflow for natural ventilation of buildings. Solar chimneys have been studied mainly in two forms: vertical air channel and inclined one. In this paper, a solar chimney with a horizontal absorber surface was proposed. Its performance in term of the induced air flowrate through the channel and the thermal efficiency was predicted by a CFD (Computational Fluid Dynamic) model. Examined factors included the heat flux and major dimensions of the chimney: length of the absorber surface, gap of the air channel, and height and width of the inlet and outlet sections. The results show that increasing of all examined factors enhances the flowrate but has minor effect on the thermal efficiency. However, excessive large outlet width results in reduction of the flowrate and thermal efficiency due to appearance of reverse flow at the outlet.

Solar chimneys absorb solar radiation heat and induce natural convective airflow for natural ventilation of buildings. In this study, we simulate induced airflow in a two-dimensional vertical solar chimney by Lattice Boltzmann Method (LBM) and focus on laminar flow region at low Rayleigh (Ra) number. Standard D2Q9 and D2Q4 models with single relaxation time are used for flow and temperature fields, respectively. Airflow and air temperature distributions inside the chimney are investigated under effects of main parameters of solar chimneys: heat flux, chimney height H, and chimney width b. Typical characteristics of a solar chimney were well reproduced in our simulations. Particularly, we analyze flow reversal region near the outlet of the chimney. The flow separation regions were observed at low ratio of H/b at a given Ra number or at high Ra number at a given H/b ratio and significantly reduced the induced flowrate. To suppress the flow reversal, we propose a simple method of rearranging the heat transfer surface on the opposite side in the upper and lower halves of the chimney. The results show that this method can eliminate the separation region and increases the induced flowrate at low ratio of H/b at a given Ra number.

Formation of the initial bedforms, known as sand-wavelets, developing from a flat erodible bed in hydrodynamically smooth flow has been studied numerically. The computational model consists of hydrodynamic and sediment transport equations. The unsteady hydrodynamic equations are solved by Large-Eddy-Simulation (LES) and Immersed-Boundary-Method (IBM) on a non-bodyfitted grid. Dynamics of individual grains are neglected and only bedload is considered, as calculated from Van Rijn's equation (1984, Journal of Hydraulic Engineering, Vol. 110) . Two-dimensional (2D) bed evolution is coupled with the above 3-dimensional (3D) hydrodynamic equations. The computed wavelength agrees with linear stability analysis and with experimental data in the literature. The length of the sand-wavelets is observed to correspond to the disturbance region of bed shear stress caused by discontinuities on the bed surface, as postulated by Yalin (1977, Mechanics of Sediment Transport, Pergamon press) .