59- 71 Al-Khwarizmi Engineering Journal,Vol. 12, No. Experimental and Numerical Study Solar Chimney Performance Aseel K. Shyaa Maryam Muayad Abbood *,**,***Department of Mechanical Engineering *** (Received http://dx.doi.org/10.22153/kej.2016.05.002 Abstract There have been many advances in the solar chimney power plant since 1930 and the first pilot work was built in Spain (Manzanares) that produced 50 KW. that needs to be investigated to enhance the perfor enhance the velocity towards the chimney to maximize design velocity. In this experimental and numerical study, the reduction area of solar collector was investigated. The reduction are the absorbing plate (h1=3.8cm, h2=2.6cm and h3=1.28cm). The numerical study was performed using ANSYS Fluent software package (version 14.0) to solve the height of reduction area to the design velocity (velocity move the blade of turbine at inlet in the chimney). The results showed that the third height (h3=1.28cm) gives the best result because when decreasing the height between th glass cover and absorbing plate, the area between them decreased and the design velocity increased then the efficiency of solar chimney model was increased. Keyword: Solar chimney, Collector, Mathematical modeling, Numerical simulation, Enhance performance 1. Introduction The solar chimney power plant consists of a solar air collector, a solar chimney and a turbine coupling with generator [1] .The mean aim from manufacture the solar chimney power plant to convert the power of solar radiation energy to thermal energy and by the rotation of turbine convert to mechanical energy and put the electric station in this to generate the electrical en that’s used in different way in the life. The solar chimney power plant is shown in Figu change of area is use to generating swirl flow inside solar collector of the solar chimney. Mark[2] The height of the roof inlet was adjustable, so that the ratio of flow areas between 1 Khwarizmi Engineering Journal,Vol. 12, No. 4, P.P. 59- 71 (2016) Numerical Study of Collector Geometry Effect Solar Chimney Performance Shyaa* Rafea A. H. Albaldawi** Maryam Muayad Abbood*** Department of Mechanical Engineering/ University of Al-Mustansiriyah aseelkhshyaa@yahoo.com :mailE* **Email: rafa_a70@yahoo.com memomoaed@yahoo.com Email:*** (Received 18 February 2016; accepted 5 May 2016) http://dx.doi.org/10.22153/kej.2016.05.002 advances in the solar chimney power plant since 1930 and the first pilot work was built in Spain (Manzanares) that produced 50 KW. The solar chimney power plant is considered of a clean power generation that needs to be investigated to enhance the performance by studying the effect of changing the area of passage of air to enhance the velocity towards the chimney to maximize design velocity. In this experimental and numerical study, the reduction area of solar collector was investigated. The reduction area that mean changing the height of glass cover from the absorbing plate (h1=3.8cm, h2=2.6cm and h3=1.28cm). The numerical study was performed using ANSYS Fluent to solve governing equations. The aim of this work was to study the height of reduction area to the design velocity (velocity move the blade of turbine at inlet in the chimney). The results showed that the third height (h3=1.28cm) gives the best result because when decreasing the height between th glass cover and absorbing plate, the area between them decreased and the design velocity increased then the efficiency Solar chimney, Collector, Mathematical modeling, Numerical simulation, Enhance performance The solar chimney power plant consists of a solar air collector, a solar chimney and a turbine [1] .The mean aim from manufacture the solar chimney power plant to convert the power of solar radiation energy to thermal energy and by the rotation of turbine convert to mechanical energy and put the electric station in this to generate the electrical energy that’s used in different way in the life. The solar Figure (1). The change of area is use to generating swirl flow inside solar collector of the solar chimney. Mark[2] The height of the roof inlet was t the ratio of flow areas between roof inlet and roof outlet could be varied. The reduction in pressure at the point of reduction area is come from the reduction in area which will draw the air flow to the region of area after the reduction. This techniqu increase heat transfer between the air flow and absorber plant and between air flow and glass cover, and to increase air velocity constructed four small-scale physical models of the solar chimney were constructed. The heigh the roof inlet was adjustable, so that the ratio of flow areas between roof inlet and roof outlet could be varied. In addition, there were plants with constant cross sectional area towers and a plant with a divergent tower. Also there was one plant with a novel roof shape. Results indicate that the Al-Khwarizmi Engineering Journal (2016) Collector Geometry Effect on ** Mustansiriyah advances in the solar chimney power plant since 1930 and the first pilot work was built in The solar chimney power plant is considered of a clean power generation mance by studying the effect of changing the area of passage of air to enhance the velocity towards the chimney to maximize design velocity. In this experimental and numerical study, the a that mean changing the height of glass cover from the absorbing plate (h1=3.8cm, h2=2.6cm and h3=1.28cm). The numerical study was performed using ANSYS Fluent . The aim of this work was to study the effect of change the height of reduction area to the design velocity (velocity move the blade of turbine at inlet in the chimney). The results showed that the third height (h3=1.28cm) gives the best result because when decreasing the height between the glass cover and absorbing plate, the area between them decreased and the design velocity increased then the efficiency Solar chimney, Collector, Mathematical modeling, Numerical simulation, Enhance performance. roof inlet and roof outlet could be varied. The reduction in pressure at the point of reduction area is come from the reduction in area which will draw the air flow to the region of area after the reduction. This technique could be utilized to increase heat transfer between the air flow and absorber plant and between air flow and glass cover, and to increase air velocity. Atit [3] scale physical models of the solar chimney were constructed. The height of the roof inlet was adjustable, so that the ratio of flow areas between roof inlet and roof outlet could be varied. In addition, there were plants with constant cross sectional area towers and a plant with a divergent tower. Also there was one plant th a novel roof shape. Results indicate that the Aseel K. Shyaa flow power increases with the decrease in the ratio of flow areas between roof inlet and roof outlet. The divergent chimney also results in significant increase in flow power compared to that of the constant area chimney. It was observed that the system with the proposed novel roof shape provides approximately the same performance as the conventional shaped system, while the ratio of flow areas between roof inlet and roof outlet for the novel system could be practically reduced. Correspondingly the increase in performance to some specific value which is much lower than the typical system could be achieved. The experimental results are different from the predicted values, but show the same trends. Fig. 1. Solar chimney power plant [4]. 2. Mathematical Model The mathematical model analyzes the flow field inside solar chimney model fig (2) governing equations. The following assumptions have been considered in mathematical model 1. A steady state condition is assumed, which is an approximation because solar radiation is transient in real conditions. 2. The working air in tests proceedings as an incompressible fluid. 3. The properties of working air in all tests such as the coefficient of viscosity and the thermal conductivity are constant. 4. The working air behaves as an ideal gas. 5. Both the solar collector and chimney tower are insulated to avoid heat losses to the environment. 6. Air enter to the solar chimney is by natural convection. 7. The flow in the collector is considered as a flow between two parallel plates. 8. The flow is assumed one-dimensional between the collector inlet and the turbine inlet. In the chimney tower the flow is assumed one Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 60 flow power increases with the decrease in the ratio of flow areas between roof inlet and roof outlet. The divergent chimney also results in significant increase in flow power compared to that of the area chimney. It was observed that the system with the proposed novel roof shape provides approximately the same performance as the conventional shaped system, while the ratio of flow areas between roof inlet and roof outlet for practically reduced. Correspondingly the increase in performance to some specific value which is much lower than the typical system could be achieved. The experimental results are different from the predicted values, but show the same trends. Solar chimney power plant [4]. analyzes the flow fig (2), using the governing equations. The following assumptions have been considered in mathematical model:- A steady state condition is assumed, which is an approximation because solar radiation is The working air in tests proceedings as an properties of working air in all tests such as the coefficient of viscosity and the thermal The working air behaves as an ideal gas. Both the solar collector and chimney tower are insulated to avoid heat losses to the Air enter to the solar chimney is by natural he flow in the collector is considered as a flow between two parallel plates. dimensional between the collector inlet and the turbine inlet. In the is assumed one dimensional between the turbine outlet and the tower outlet. 9. The flow through collector section has complete symmetry with the so ��� � 0 , and there is no flow in the directions ( v� , v� = 0). 10. The flow through chimney s complete symmetry with the so ��� � 0 , and there is no flow in the directions (v� , v = 0). Fig. 2. Solar chimney model Continuity equation [5] �� �� � � �� �� � � �� �� �� � For collector:- ρ ∂v ∂r � ρ v r � 0 For chimney:- ρ ∂v�∂z � 0 Momentum equation [5]:- For collector:- ρ. v ���� � ��� � μ !"# $� % � �%����% & � 0 For chimney:- ρv� ∂v�∂z � gρ β �T � T*� � μ +43 ∂. ∂ � 0 Energy equation[5]:- For collector Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) dimensional between the turbine outlet and the The flow through collector section has complete symmetry with the θ direction, , and there is no flow in the θ and z – = 0). The flow through chimney section has complete symmetry with the θ direction, , and there is no flow in the θ and r – = 0). Solar chimney model. � � � �� � 0 …(1) …�2� …�3� $ �� % � � ���� – . �� % 3 � …�4� � + .v�∂z. � 1 r ∂v� ∂r � ∂.v� ∂r. 5 …�5� Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 61 7 +8 .9 8:. � 1: 898: + 8 .98;.5 + 2< +=8>�8: ? . + $>�: 3 . + 12 =8>�8; ? . – 13 =8>�8: + >�: ? .@ + >� 8A8: − A BC D >� 898:@ = 0 … �6� For chimney 7 +8.98:. + 1: 898: + 8 .98;.5 + 2< +23 =8>�8; ? . + 12 =8>�8: ? . 5 + >� 8A8; − A BC D >� 898;@ = 0 …�7� 2.1. Mathematical Model in the Collector The energy balance equations for the glass cover, the absorber plate and the airflow in the collector are given in the following equation respectively [6]. For the glass cover UH�T* − TI� + h ,KLIMTK − TIN + h��TO − TI� =0 …�8� For the absorber plate S + URMT* − TKN + h.MTO − TKN+ h ,KLIMTI − TKN = 0 …�9� For the airflow in the collector h��TI − TO� + h.MTK − TON= qU …�10� Fig. 3. Heat transfer scheme of solar collector. The solar radiation absorbed by the absorber plate is S = IW αK τ … �11� where:- IW : Solar incidence on the surface of absorber plate W m.\ αK : Absorber plate absorptivity τ : Glass transmittance The mean temperature of airflow can be given by [7]:- TO = MTO,] + TO,^N2 … �12� Fig. 4. Thermal network for the collector of solar chimney. Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 62 The cover glass temperature is found from equation [6]:- TI = TK − UH MTK + T*NhKLI + h ,KLI … �13� hKLI : Convection heat transfer coefficient between the absorber plate and the glass cover is given by:- Nu = hKLI × Lk … �14� where: L : The spacing between the absorber plate and the glass cover, m k : Thermal conductivity of air W m K\ Nu : The value of Nusselt number could be obtained using the expression [8]:- Nu = 0.54 Ra� "\ For 10" ≤ Ra ≤ 10j …�15� Nu = 0.14 Ra� #\ For 10j ≤ Ra ≤ 10�� …�16� where: Ra : Rayleigh number and is given by:- Ra = Gr Pr = mβˋ∆TKLI L#ν α … �17� g: Gravitational acceleration m s.⁄ βˋ: Volumetric thermal expansion coefficient of air KL� α: Thermal diffusivity m. s⁄ ∆TKLI : The temperature difference between the absorber plate and the glass cover h ,KLI : Radiation heat transfer coefficient between the absorber plate and the glass cover. It could be calculated as suggested [6]:- h ,ILK = σ MTI + TKNMTI. + TK.N= 1ϵK + 1εI − 1? …�18� The overall top heat loss coefficient from the glass cover to the ambient obtained from empirical equation as follows [6]:- UH = vw x wy N cTK +MTK − T*N�N − f� 5 | + 1h} ~w � w� L� + σ MTK. + T*.NMTK + T*NMεK + 0.00591 N h}NL� + D2 N + f − 1 + 0.133 εKεI @ − N …�19� where: h} : The convective heat transfer coefficient due to the wind is estimated as suggested by [6]:- h} = 2.8 + 3 V … �20� V : The wind speed m s⁄ N = number of glass covers f = M1 + 0.089h} − 0.1166h}εKN�1 + 0.07866 N� c = 520 �1 − 0.000051 β.� for 0° < � < 70° . for 70° < � < 90°, use β = 70° β = collector tilt (degrees) e = 0.43 �1 − 100TK � The back loss coefficient UR is given as [6]:- UR = �� … �21� where k insulator thermal conductivity and δ thickness. The collector overall loss coefficient,U� is given by [6]:- U� = �UR + UH� Mh� h. + h� h ,KLI + h. h ,KLIN + UR UH �h� + h.�h� h ,KLI + h. UH + h. h ,KLI + h� h. …�22� Where: h�: Convection heat transfer coefficient between the glass cover and the airflow. h.: Convection heat transfer coefficient between the absorber plate and the airflow. h� and h. can be assumed to be equal and can be evaluated from the following equation:- h� or h. = Nu kD� … �23� where Nu is given by Nu = 0.0158 Re�.� …�24� R = m� D� AI μ …�25� The collector efficiency factor F� is found from the equation [6]:- F� = h� h ,KLI + h. UH + h. h ,KLI + h� h. MUH + h ,KLI + h�NMUR + h. + h ,KLIN − h ,KLI. …�26� Collector heat removal factor is given by [6]:- F� = m� C�AIU� +1 − e L =�� �� ���� �� ?5 … �27� The actual useful energy gain of the hot air in the collector can be calculated by the equation below [6]:- QU = AI F� �S − U�∆T  … �28� Then the collector efficiency which represents the indicator to its performance can be given by:- ηI = QUAI IW …�29� 2.2. Mathematical Model in the Chimney The hot air which is less denser than ambient air by overcoming the gravity and friction start rising from the chimney [7], the chimney efficiency is given as [9]:- Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 63 ηI� = PH^HQU = gHI�CKT* …�30� where, HI� is the height of the chimney, thus the power contained in the flow PH^H from equation (31) can be expressed as follows [9]:- PH^H = ηI�QU = gHI�CKT* QU … �31� QU is the actual useful energy gain can be obtained from equation (28). A pressure difference ∆p is produced between chimney base (collector outflow) and the surroundings [9]:- ∆p = ρ* g HI� ∆TT* … �32� 3. Numerical Simulation The numerical simulation includes simulation of solar chimney using ANSYS FLUENT (version14.0). ANSYS-FLUENT is a computer package used for modeling fluid flow and heat transfer in complex geometries, the present study carried out FLUENT (version 14.0) to solve continuity, momentum, and energy, equations using a finite volume method. For the simulations, steady state analysis was chosen. The working fluid used was air which was modeled as an ideal gas. The buoyancy model was activated by specifying the gravity of -g in the (y) direction which represented real life flow. The reference pressure used was 1atm. 3.1 Modeling Geometry i. The geometry creation is done by the Solid works (2013) software program. In the coordinate (x) and (z) are in the radial directions, and (y) is in the vertical direction. ii. In this model using the mesh sizing Relevance center type fin and from mesh inserting element size equal=0.0275m[10] with set the mesh shape triangle. The mesh of reduction area is shown in Fig.(5). Fig. 5. Mesh of reduction area for the solar chimney model. 3.2 Numerical Setup i. Setting Model In the present simulations, the basic settings of the fluent simulation are by activated the energy equation, select the Realizable k- ϵ full buoyancy effects in the viscous model to describe the fluid flow inside the collector and the chimney, and select the discrete ordinate (DO) radiation model to solve the radiation transfer equation for the following reasons, first only the DO model can be used to model semi-transparent walls, and second the DO model can work well across a full range of optical thicknesses. ii. Setting Materials properties Table 1, Physical properties of materials [11]. Physical property Air Glass roof Chimney wall Ground Insulation Density kg m#⁄ 1.167 2700 7833 2719 24 Thermal Conductivity W mK\ 0.0242 0.78 54 202.4 0.038 Specific heat J kg K\ 1006.43 840 465 871 700 Refractive index [-] 1 1.526 1 1 1 Emissivity [-] - 0.9 - 0.94 - Thermal Expansion Coefficient 1 K\ 0.0033 - - - - Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 64 iii. Boundary Conditions Table 2, Boundary conditions of the physical model.[12] 4. Experimental Work The simulation model with six fold collector and chimney is used in The experimental study. The diameter of collector and chimney (4.5m,20cm) respectively[13], chimney’s height is 4m, collector is inclined at 2.3°with inlet of collector is 4cm [14]. The absorption ground of collector made from black aluminum with thickness 1mm. The reduction area means that change of height of glass cover from the absorption plate at the defined distance from the center of solar chimney model .The aim from using reduction area the effect of it on air velocity. The design velocity that enters the chimney . From the simulation taken three different height of reduction area h1=3.8cm,h2=2.6cm and h3=1.28cm. making comparative with experimental work as shows in Figure(6): ¥¦§¨©ª«¬ ­® :¬¯°«¨¦­ª ©:¬© ®:­± ¨ℎ¬ «¬ª¨¬: ­® «­³³¬«¨­:´©¯¦°§ ­® «­³³¬«¨­: 2.434.10 = 0.59 �3  … �33� µ2.25 = 0.59 ↔ µ = 1.33± A:-distance of reduction area from the center of collector. And height of reduction area calculated same the calculated the far of reduction area about the center. The distance A and B shown in fig.(7b) ·¸¹º»¼ ½¾ �¸¿ÀÁ¼¹½Â Ã�¸Ã ·¸¹º»¼ Á½ÄĸÁ¼½� ¹Âĸ¼ =�.�Å�.Æ� 0.32 �3  …�34� Ç �.�" = 0.32 ↔ È = 0.0128 B:-height of reduction area (h3)in experimental work. h2 and h1 is triple and double h3 respectively.. The Scale model of solar chimney power plant and reduction area shown in figure (6),(7 a,b) respectively. Fig. 6. Scale model of solar chimney power plant. Fig. 7a. The position of reduction area. Parameter value Type Boundary T= ÉÊ , p= 1atm Pressure inlet Collector inlet T= ÉÊ , p= 1atm Pressure outlet Chimney outlet Convection + Radiation Wall Absorbing plate Convection + Radiation Wall Glass roof Fixed heat flux Ë = Ì Wall Chimney Aseel K. Shyaa Fig. 7b. Schematic diagram of shape of glass cover for the consider cases 4.1. Instrumentations The following section describes the measuring instruments used on the experimental. The data are recorded every 1 hour. Fig (8) shows the different instrumentations used in this work. solar meter model 776 is hand solar intensity meter was used to measure solar flux is ideal for measuring the solar energy abs by a flat panel collector. Has the photovoltaic cell located on the front of the meter body so it can be placed flat on the surface and the measurement read directly from the scale. The air velocity at the chimney entrance was measured by metal van anemometer model (YK-80AM). The velocity measurement range starts from (0.4) and reach to (35) m/s and temperature range (0 to 60 C°) including record function captures and displays minimum and maximum reading. The LCD shows air velocity and temperature rea simultaneously. Data logger model BTM has been used to record temperature data. 12 channels of thermocouples have been connected to this data acquisition system. Data is saved on the SD card and can be transferred to a PC and analyzed. Surface temperature of the cover (agricultural nylon) was measured using infrared thermometer model AR300.The Fig. 8. Photographic view of the Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 65 diagram of shape of glass cover for the consider cases The following section describes the measuring experimental. The data Fig (8) shows the different instrumentations used in this work. The solar meter model 776 is hand solar intensity solar flux. This model is ideal for measuring the solar energy absorbed photovoltaic cell located on the front of the meter body so it can be placed flat on the surface and the measurement The air velocity at the chimney entrance was measured by metal van 80AM). The velocity measurement range starts from (0.4) and reach to (35) m/s and temperature range (0 to 60 C°) including record function captures and displays minimum and maximum reading. The LCD shows air velocity and temperature reading Data logger model BTM-4208SD has been used to record temperature data. 12 of thermocouples have been connected Data is saved on the SD card and can be transferred to a PC and temperature of the collector (agricultural nylon) was measured using infrared thermometer model AR300.The temperature measurement range (32 to 400 C°). It offers LCD backlight for visibility in the dark, a broad temperature range, and a dual display both current and maximum measurements. points are located on the along it with 39 cm distance between each one. The first point begins at 4 cm from inlet of collector. This distribution is constant in all cases. Ten thermocouples K-type the ambient temperature, temperature inside the solar chimney. The thermocouples and its locations are defined as follows. • Five thermocouples are located on the absorber plate divided along i distance between each one. thermocouple begins at 4 cm from inlet of collector. This distribution is constant in all cases. • Five thermocouples are located in the flow direction of air to measure air temperature. These thermocouples are divided along direction with 52 cm distance between each one. All data are automatically collected and recorded in a PC through data logger. The positions of the thermocouples are as shown in Fig. (9). . Photographic view of the instrumentation. Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) diagram of shape of glass cover for the consider cases. temperature measurement range (32 to 400 C°). It offers LCD backlight for visibility in the dark, a broad temperature range, and a dual display for both current and maximum measurements. Five points are located on the collector cover divided along it with 39 cm distance between each one. The first point begins at 4 cm from inlet of collector. This distribution is constant in all cases. type were used to measure the ambient temperature, absorber plate and air temperature inside the solar chimney. The thermocouples and its locations are defined as thermocouples are located on the divided along it with 39 cm distance between each one. The first thermocouple begins at 4 cm from inlet of collector. This distribution is constant in all cases. thermocouples are located in the flow direction of air to measure air temperature. re divided along air flow with 52 cm distance between each one. All data are automatically collected and recorded in a PC through data logger. The positions of the thermocouples are as shown in Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 66 Fig. 9. Layout of thermocouples and data collecting points. 5. Results and Discussions Case studies of experimental works were taken in May month at Baghdad city under actual weather conditions of this month. The experimental data had collected from 9 AM to 2 PM. Fig. (10a) presents the behavior of the airflow velocity experimentally at the inlet chimney tower with time at various collector reduction areas . The highest velocity occurs at 1:00PM, when the levels of incident solar radiation and the airflow temperatures are higher. Higher values are found at the lower collector reduction area. For the prototype with the collector reduction area 3.8 cm, the maximum achievable velocity is 2.55 m/s at 1:00PM. By decreasing the collector reduction area to 1.28 cm, the maximum achieved velocity rises to 3.15 m/s which is about an 19.04% enhancement. A lower collector reduction area means a smaller collector flow area, giving a higher airflow velocity. Fig. (10b) shows the variation of air velocity with time among inclination angle and reduction area of collector. It is noticed that air velocity corresponding to reduction area h=1.28 cm is higher than that to inclination angle 2.3 ° resulting from the reduction of flow area. by decreasing the collector reduction area, the maximum achieved velocity rises from 2.39 m/s to 3.15 m/s which is about an 24.12% enhancement, the airflow temperature inside the solar collector increased with respect to the solar radiation intensity(I). It is also observed that the airflow temperature at h3= 1.28 cm of the solar collector is higher than those at h1= 3.8 cm, and h2= 2.6 cm during the whole testing period. Fig. (14) illustrates the history of airflow temperature, for three different values of the collector reduction areas. Higher collector reduction area reduces the airflow temperature due to the increase of the mass flow rate. Mass flow rate increased by increasing flow area in the collector. The maximum absorber ground temperature recorded at 1:00PM was 65 °C, where the collector cover temperature reached the value of 43°C and the air temperature was 40 °C these results for inclination angle of collector (2.3°) fig.(14a). While for collector reduction area (h3= 1.28 cm), the maximum absorber ground temperature was 93 °C, the collector cover temperature was 67°C and the air temperature was 62°C. The comparison showed that the reduction area was more effective than that inclination angle fig (14b). Fig.(11a) demonstrates the evolution of output power versus time for three different values of the collector reduction area. This figure illustrates that the output power increases while the collector reduction area is decreased. Current result predict higher output power with collector reduction area of h = 1.28 cm than a plants with a collector reduction area of h = 3.8 cm and h=2.6 cm. The output power for reduction area of (1.28cm) is observed higher than that for inclination angle of collector of 2.3° shown in fig.(11b) , because it is the effect of lower reduction area in collector. it can be observe the collector efficiency ( ÍͦÁÏ ÐÑ ÒÁ Ó � increases as the reduction area of the collector decreases due to its higher outlet temperature and airflow velocity. Fig. (12a) demonstrates that the collector efficiency increases from 29% to 51 % according to the decrease in collector areas from h1= 3.8 cm to h3= 1.28 cm. Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 67 Fig. 10. Variation of air velocity versus time (a)with reduction area. (b) with and without reduction area. Fig. 11. Variation output power versus time (a)with reduction area.(b)with and without reduction area. Fig. 12. Variation efficiency versus time(a) with reduction area. (b) with and without reduction area. Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 68 Fig. 13.Contours and vectors of air design velocity (m/s) (A)without reduction area.(B)at h1=3.8cm.( C)at h2=2.6cm. (D) at h3=1.28cm. Fig. 14. Contours of static air temperature(c°) (A)without reduction area.(B)at h1=3.8cm.( C)at h2=2.6cm. (D) at h3=1.28cm. Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 69 Fig. 15. Contours of static pressure(pa) (A)without reduction area.(B)at h1=3.8cm.( C) at h2=2.6cm. (D) at h3=1.28cm. 6. Conclusions According to the discussion of the obtained results, many conclusions can be extracted such as:- 1. The effects of three different collector reduction areas on solar chimney are presented. It can be concluded that decreasing the collector reduction area significantly influences on the performance of solar chimney. In the present study, collector reduction area of 1.28 cm provides the best performance. 2. The collector inclination angle is also important parameter in the solar chimney. The inclination angle of collector should be at optimum angle to provide best performance for solar chimney. 3. The reduction area is found to perform better than an inclination angle in terms of airflow velocity and temperature. 4. The thermal efficiency of the solar collector is dependent upon the magnitude of temperature 5. rise (∆T) and the airflow velocity, and also of the solar radiation. Error Analysis When experimental tests are carried out, an accurate reading should be taken, since any mistakes could reduce the accuracy of the results. There is more than one method which can be used to find the experimental error. One of these methods is that given by: Kline & Melintock [11] which depends on the assumption that when calculating a variable as R for example, which is to be calculated from a certain experimental test. This variable is assumed to be related to a number of independent variables as (v1, v2… vn) )v v,R(v=R n21 ……… …(35) For small variations in the variables, this relation can be expressed in linear form as: n n 2 2 1 1 δv v R δv v R δv v R δR ∂ ∂++ ∂ ∂+ ∂ ∂= ........ …(36) Hence, the uncertainty intervals (w) in the result can be given as 2 1                                         ∂ ∂++ ∂ ∂+ ∂ ∂= 222 Rw n n 2 2 1 1 w v R w v R w v R ............ …(37) Aseel K. Shyaa Al-Khwarizmi Engineering Journal, Vol. 12, No. 4, P.P. 59 - 71(2016) 70 Eq. (38) is greatly simplified upon dividing by Eq. (36) to non-dimensionalize                                       ∂ ∂ ++ ∂ ∂ + ∂ ∂ = R w nv R R w v R R w v R R w n 2 2 2 2 1 1 2 R ............ …(38) Hence, the experimental errors that may happen in the used variables are given in Table (3) for the measuring devices; Table 3, Uncertainties of Measuring Tools. Independent Variables (V) Uncertainty Interval (W) Temperature 0.2 ºC Velocity 0.02 Solar intensity 0.02 Error in calculating the value of collector efficiency ÔÁ = BÕ AÑ ÖÑ µ ∆9 × 3 √32 ´Á. … �39� Collector efficiency is a functional of several variables, each subject to an uncertainty. ÔÁ = ®�ÖÑ ,∆9, ×� …�40� 8ÔÁ8∆9 = BÕ AÑ ÖÑ µ × 3 √32 ´Á. …�41� 8ÔÁ8ÖÑ = BÕ AÑ µ ∆9 × 3 √32 ´Á. …�42� 8ÔÁ8× = BÕ AÑ µ ÖÑ ∆9 ×. 3√32 ´Á. … �43� Therefore the uncertainty intervals (w) in the result can be given as follows; ÙÚÛ = +=8ÔÁ8∆9 Ù∆9? . + =8ÔÁ8ÖÑ ÙÖÑ? . + =8ÔÁ8× Ù×? .5 �. … �44� ÜÝÛÚÛ = �.�Æ".�Å� = 0.00226 % 7. References [1] Schlaich Bergermann und Partner, “Solar updraft tower”, October 2011 http:\\www.solar-updraft-tower.com. [2] Mark E.Steinke,Satish G.Kandlikar, “Single- phase heat transfer enhancement techniques in microchannel and minichannel flows”, AZME,2004. [3] Atit Koonsrisuk, “Analysis of flow in solar chimney for an optimal design purpose”, thesis, 2009. [4] Hermann F. Fasel, Fanlong Meng, Ehsan Shams, Andreas Gross, “CFD analysis for solar chimney power plants”, Solar Energy 98 (2013) pp. (12–22). [5] Qahtan A. Al-Nakeeb, “Computational analysis of geometry alteration on the performance of a solar system to generate air flow”,thesis, Iraq, 2001. [6] Duffie, John A. and Beckmann, William A. (1980), “Solar Engineering of Thermal Processes”, book, John Wiley & Sons, New York. [7] M.A. dos S. Bernardes, A. Voß, G. Weinrebe, “Thermal and technical analyses of solar chimneys”, Solar Energy 75 (2003) pp. (511–524). [8] Mehrdad Ghalamchi, Alibakhsh Kasaeian, “An experimental study on the thermal performance of solar chimney with different dimensional parameters” ,Volume 91, 2016, pp. (477–483). [9] Roozbeh Sangi, “Performance evaluation of solar chimney power plants in Iran”, Renewable and Sustainable Energy Reviews 16 ,(2012), pp. (704– 710). [10] Abbas Jassem Jubear Abbas, “Numerical and experimental study of turbine - solar chimney performance”,thesis, Iraq, (2014). [11] J.P. Holman, Heat Transfer 5th edition, book ,McGraw-Hill, 1981. [12] ANSYS Fluent 12.0 user’s guide and theory guide. [13] Bashir Ahmed Danzomo, Sani Jibrin, “Similitude model design and performance evaluations of solar tower system”, ARPN Journal of Engineering and Applied Sciences, VOL. 7, NO. 4, 2012. 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