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Investigation of heat transfer enhancement for a model 21 Feb 2021.pptx

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Investigation of heat transfer enhancement for a model 21 Feb 2021.pptx

  1. 1. Investigation of heat transfer enhancement for a model of external receiver solar power plant By Mahmoud Sh. Mahmoud M.Sc. Mech. Eng. / Thermal power (2001) Supervised by Asst. Prof. Dr. Ahmed F. Khudheyer Asst. Prof. Dr. Qusai Jihad Abdul Gafor
  2. 2. Motivations: Seeking to obtain energy with minimal expenses and pollution is still a challenge that is being worked on. Energy production especially in developing countries like Iraq often falls short of energy requirements which results in frequent power failure. The grow in energy consumption is continual, on the other hand fossil fuel is limited, so it is essential to consider other energy sources like renewable energy especially solar power to keep up and try to meet the energy demands in the future. The present work is conducted by building up a (CSP) model with a novel receiver design to enhance the thermal performance of it.
  3. 3. Fig 1: shows that Iraq position in area of over than 3000 hours of bright sunshine yearly [1].
  4. 4. Introduction: The renewable energy sources are available and used in many applications now a days. One of these applications is the power generation. The solar energy is the most available renewable energy sources used in the world. There are two familiar ways to convert the solar energy to electricity, direct and indirect. The direct way is presented by using photovoltaic cells (PV). The indirect way is presented by using the solar energy as a heating source for the working fluid that is used in power plant. One of the most common ways to heat the working fluid by solar energy is to concentrate solar energy. there are many concentration types, like Fresnel reflectors, trough type, compound parabolic collectors (CPC), and heliostat concentrators.
  5. 5. Concentrated solar power (CSP) thermal systems using heliostats for power generation shows better capability for improvement in performance as well as reducing the cost compared to other (CSP) systems.
  6. 6. Aims and Novelty for the present work The main objectives are to increase the (SPTS) performance:  Increase reflected sun rays from the heliostats toward the solar receiver.  Enhance solar receiver thermal efficiency. The originality of the present work could be summarized as:  Individual automated dual axis tracking system design to enhance solar plant performance.  A novel solar receiver design consisting of staggered configuration pipes is used to investigate its effect on the receiver thermal efficiency.
  7. 7. Problem Description Central tower solar power system is considered for the present study. The main losses in the traditional solar receiver are due to the presence of gaps between receiver pipes that lead to losing some of the incident sun rays. Seeking for improving and achieving the thermal efficiency of the system, sources of losses must be defined and minimized. Fig 2: (a) Traditional solar receiver. Fig 2: ( (b) novel designed solar receiver.
  8. 8. Literature review Solar power plant receiver design A review of previous researchers and studies investigated the main effecting parameters on the central tower solar power system performance are shown in the following categories. Optimization and Heat Transfer Enhancement Receiver Coating Tracking system Heliostat field
  9. 9. Solar power plant receiver design J. Yellowhair et al. (2015), Testing and optical modeling of novel concentrating solar receiver geometries to increase light trapping and effective solar absorptance. N. H. Abu-Hamdeh and K. A. Alnefaie (2016), Design considerations and construction of an experimental prototype of concentrating solar power tower system in Saudi Arabia. M. Hazmoune et. al (2016), 3D Simulation Study of a Receiver on a Solar Power Tower. S. S. Alrwashdeh (2018), The effect of solar tower height on its energy output at Ma’an- Jordan. A. K. Khlief et. al (2018), Design a New Receiver for the Central Tower of Solar Energy. Solar power plant design
  10. 10. Optimization and Heat Transfer Enhancement P. Xu et. al (2014), Numerical simulation and experimental study of the tube receiver’s performance of solar thermal power tower. D. Potter et. al (2015), Optimized Design of a 1 MWt Liquid Sodium Central Receiver System. N. Karwa et. al (2016), Receiver shape optimization for maximizing medium temperature CPC collector efficiency. A. Piña-Ortiz (2018), Experimental analysis of a flat plate receiver for measurement of low thermal power of a central tower solar system. Optimization and Heat Transfer Enhancement
  11. 11. Receiver Coating A. Hall et. al (2012), Solar selective coatings for concentrating. A. H. Alami et. al (2018), Enhancement of spectral absorption of solar thermal collectors by bulk graphene addition via high-pressure graphite blasting. S. A. Sakhaei and M. S. Valipour (2019), Investigation on the effect of different coated absorber plates on the thermal efficiency of the flat-plate solar collector. Receiver Coating
  12. 12. Tracking system M. M. Arturo and G. P. Alejandro (2010), High-precision solar tracking system. K. K. Chong and M. H. Tan (2011), Range of motion study for two different sun-tracking methods in the application of heliostat field. K. Malan (2014), A heliostat field control system. S. patil Pratik Pawar et. al (2018), Solar Tracking System Using Arduino. W. M. Hamanah et. al (2020), Heliostat dual-axis sun tracking system: A case study in KSA. Tracking system
  13. 13. Heliostat field C. J. Noone et. al (2012), A new computationally efficient model and biomimetic layout. K. Lee and I. Lee et. al (2019), Optimization of a heliostat field site in central receiver systems based on analysis of site slope effect. Heliostat field
  14. 14. From the above mentioned studies, it is obvious that there are many studies that deals with solar central tower. The present work aims to: • Fabricate new staggered configuration for the absorber heat exchanger and, • Design a new dual axes tracking system. Present Study scope
  15. 15. Mathematical Model and Numerical Analysis
  16. 16. The governing equations The present study can be described according to the assumptions, steady incompressible, viscous fully developed turbulent flow through a pipe, three-dimensional with no slip condition, single phase, conjugate heat transfer, and variable thermal physical properties for the working fluid with the bulk temperature. Continuity Equation: 𝜕 𝜌𝑢𝑧 𝜕𝑧 + 1 𝑟 𝜕 𝑟𝜌𝑢𝑟 𝜕𝑟 = 0 Momentum Equation: r - component: 𝜕 𝜌𝑢𝑧𝑢𝑟 𝜕𝑧 + 1 𝑟 𝜕 𝑟𝜌𝑢𝑟𝑢𝑟 𝜕𝑟 = − 𝜕𝑃 𝜕𝑟 + 𝜕 𝜕𝑧 𝜇eff 𝜕𝑢𝑟 𝜕𝑧 + 1 𝑟 𝜕 𝜕𝑟 𝑟𝜇eff 𝜕𝑢𝑟 𝜕𝑟 − 𝜇eff 𝑢𝑟 𝑟2 + 𝑆𝑟 𝑆𝑟 = 𝜕 𝜕𝑧 𝜇𝑒𝑓𝑓 𝜕𝑢𝑧 𝜕𝑟 + 1 𝑟 𝜕 𝜕𝑟 𝑟𝜇𝑒𝑓𝑓 𝜕𝑢𝑟 𝜕𝑟 − 𝜇𝑒𝑓𝑓 𝑢𝑟 𝑟2 − 2 3 𝜕 𝜕𝑟 𝜌𝑘 Effective viscosity is: 𝜇eff = 𝜇𝑡 + 𝜇 Turbulent viscosity is: 𝜇𝑡 = 𝐶𝜇𝑓𝜇𝜌(𝑘/𝜀)
  17. 17. The governing equations z - component: 𝜕 𝜌𝑢𝑧𝑢𝑧 𝜕𝑧 + 1 𝑟 𝜕 𝑟𝜌𝑢𝑟𝑢𝑧 𝜕𝑟 = − 𝜕𝑃 𝜕𝑧 ± 𝑔 + 𝜕 𝜕𝑧 𝜇eff 𝜕𝑢𝑧 𝜕𝑧 + 1 𝑟 𝜕 𝜕𝑟 𝑟𝜇eff 𝜕𝑢𝑧 𝜕𝑟 + 𝑆𝑧 𝑆𝑧 = 𝜕 𝜕𝑧 𝜇eff 𝜕𝑢𝑧 𝜕𝑧 + 1 𝑟 𝜕 𝜕𝑟 𝑟𝜇eff 𝜕𝑢𝑟 𝜕𝑧 − 2 3 𝜕 𝜕𝑧 (𝜌𝑘) Energy Equation: 𝜕 𝜌𝑢𝑧𝑇 𝜕𝑧 + 1 𝑟 𝜕 𝑟𝜌𝑢𝑟𝑇 𝜕𝑟 = 𝜕 𝜕𝑧 𝜇eff 𝜎𝑛,𝑡 𝜕𝑇 𝜕𝑧 + 1 𝑟 𝜕 𝜕𝑟 𝑟 𝜇eff 𝜎𝑛,𝑡 𝜕𝑇 𝜕𝑟 Using finite volume method (FVM) to discretize the governing equations for the current study.
  18. 18. Thermal efficiency q ˙ inc. = IN × AH × NH × ηcos ⋅ ηsha ⋅ ηblo ⋅ ηatt ⋅ ηspil ⋅ ρref 𝜂𝑡ℎ𝑒𝑟𝑚𝑎𝑙 = 𝑞𝑔𝑎𝑖𝑛 𝑞𝑖𝑛𝑐. = 𝑚𝐶𝑝𝛥𝑇 𝑞𝑖𝑛𝑐. 𝑞 ˙ gain = 𝑞 ˙ inc. − 𝑞 ˙ loss
  19. 19. Numerical analysis The governing equations are solved numerically with computational fluid dynamics (CFD) using ANSYS FLUENT 2019R1 commercial package, according to the mentioned assumptions and boundary conditions for the present study. Higher-order differential governing equations that were analyzed using the SIMPLE algorithm with (10-15) convergence. Upwind scheme was used in this model. The initialization was selected as a hybrid for twenty iterations to save the initialization values used for running.
  20. 20. ANSYS code validation For justifying the ANSYSFLUENT 2019R1 commercial package performance, a validation process was carried out for two different cases Fig 3: Code validation
  21. 21. Design Considerations Design Considerations Solar Receiver Profile Series Parallel Staggered Continuous Cross Pipe material Pipe diameter Working fluid Inlet position Horizontal Downward Upward Vertical Downward Upward Entrance length Heliostat Position Offset Tracking System Solar Tower height
  22. 22. Design considerations conclusions From analysis of the design consideration, the present study description had been recognized. The outcomes of the design considerations are listed below: 1. Staggered pipes configuration for the receiver, having totally (54) pipe divided into two rows with dimensions (50*50) cm. 2. Copper is selected to be the pipe material with (9.5 mm) inner diameter and (0.5 mm) thickness. 3. Heat transfer working fluid is selected to be (water) with variation in thermo-physical properties with bulk temperature. 4. Central tower high is (4.5 m). 5. Heliostat reflecting material is glass (4mm) thickness, with dimensions (80*80) cm equipped with automated dual axis tracking system. 6. Heliostat horizontal radius is (7 m) from tower base. 7. Offset angle between heliostats (opt.) is 30o, axisymmetric arrangement with the central tower normal line. 8. Duel-axes tracking system had been used.
  23. 23. Receiver’s final design Fig 4: Receiver schematic
  24. 24. Mesh generation Factor Value Recommended Status Skewness 0.2  0.25 Excellent Orthogonal element 0.88  0.9 Excellent Element quality 0.84  0.88 Excellent Aspect ratio 1.81  2 Excellent Table 1 Finest mesh metrics factors. Fig 5: Computational domain mesh
  25. 25. Mesh Independence Case No. of elements T (oC) 1 79125 38.58 2 1213250 41.63 3 6174048 47.112 4 7698288 47.161 5 27074104 47.86 Table 2 Mesh independence results.
  26. 26. Boundary conditions The boundary conditions for the present study are: o Location: Al-Nahrain University / Baghdad Latitude (33.28° N) and Longitude (44.38° E). o Solar radiation (W/m2) reflected per each heliostat is measured during the average recommended day for each selected month. o Inlet temperature (oC) is measured during the average recommended day for each selected month. o Turbulent flow, mass flow rate = 0.04 kg/s. o Velocity profile o Working fluid "Water" with variable properties as a function of temperature.
  27. 27. CFD models validation Fig. 6: Comparison among CFD models
  28. 28. Numerical results validation Fig. 8: Numerical results validation with Blasius correlation [48]. Fig. 7: Numerical results validation with Dittus-Boelter correlation [48]
  29. 29. Experimental Work
  30. 30. Design and manufacturing of the experimental rig that had been used in this study was presented, in addition to instrumentation, measurements, calibrations, test procedure, and processing gathered data. The rig was assembled, and tests were performed at Al-Nahrain University/Baghdad with Latitude (33.3152°N) and Longitude (44.3661°E) during a clear sky or partially clouded weather conditions according to the selected tested dates. The presented work is initialized from January 2018, utilizing central solar tower south oriented with heliostat automated duel axis tracking system.
  31. 31. Rig Design Rig Design Solar Receiver Assembly Flat Sheet Copper pipes Stainless steel threaded studs Coating process Heliostat Reflector Material Tracking System Control board Base linear actuators LDRs sensing system Movable central tower Instruments Digital flow meter Solar intensity data logger 48 channel Temperature data logger
  32. 32. Experimental rig setup Tower alignment in vertical position. 1 Casting the tower base using cement and sand mortar. 2
  33. 33. Experimental rig setup Locate the tower height and the position (offset angle and radius) for each heliostat. 3 Casting the heliostats bases using cement and sand mortar. 4
  34. 34. Experimental rig setup Connecting the tracking system control board with each heliostat and setting the LDRs sensors with auxiliary mirror. 5 Manually setting the tracking system for both heliostats to reflect the sun rays toward the testing board and observe the reflected image and giving feedback till the accurate positioning is achieved. 6
  35. 35. Experimental rig setup Instilling the receiver on the tower and connecting the input and output water hoses. 7 Additional fixing for the receiver using stainless steel strands to avoid wind effect on it. 8
  36. 36. Experimental rig setup Connecting all instrumentations to the system and prepare it for operating. 9
  37. 37. Experimental rig setup System is operated according to the experimental procedure. 10
  38. 38. Results
  39. 39. Results Fig. 9: Comparison between dual and single axis systems for 16 August. Fig. 10: Hourly enhancement for dual and single axis tracking systems for selected months.
  40. 40. Results Fig. 11: heliostat number one location at 9:30 in the azimuth and tilt directions for July (summer season).
  41. 41. Results Fig. 12: Friction factor comparison between Numerical and Blassius equation. Fig. 13: Pressure distribution for fluid flow in staggered solar receiver.
  42. 42. Results Fig. 14: Comparison between numerical and experimental hourly direct solar beam radiation (W/m2) at 16 August.
  43. 43. Results Fig. 15: Experimental measurements for ambient, outlet, maximum receiver surface temperatures distribution verses concentrated solar irradiance.
  44. 44. Results Fig. 16: Comparison between experimental and numerical working fluid outlet temperature. Fig. 17: Numerical and experimental maximum surface temperature.
  45. 45. Results Fig. 18: Staggered receiver surface temperature contour for 16 August Fig. 19: Staggered receiver surface temperature contour for 17 July.
  46. 46. Results Fig. 20: Temperature distribution along ZX plane at 12:00 and Y=0.05 m.
  47. 47. Results Fig. 21: Experimental and numerical surface temperature along the receiver.
  48. 48. Results Fig. 22: Comparison of experimental and numerical average Nusselt number versus Reynolds number Fig. 23: Local Nusselt number validation.
  49. 49. Results Fig. 24: Numerical and experimental thermal efficiency results
  50. 50. Results Fig. 25: comparison between present study efficiency versus numerical, one row, and evacuated tube.
  51. 51. Conclusio ns
  52. 52. Conclusions 1. The staggered configuration receiver gave 10.13%, 5.5%, and 1.5% thermal efficiency enhancement compared with conventional parallel, series, and staggered continuous configurations for the receiver, respectively. 2. The numerical results showed that the Copper pipe used in building up the solar receiver had given the highest outlet temperature with 361.7K compared with Aluminum, and Steel. 3. Automated dual axes tracking system was selected for the heliostats that provided the highest reflected solar rays with an average enhancement percent was 49.19%, 26.65%, 71.91%, and 42.28% for May, June, July, and August, respectively. 4. Optimization of tower height, heliostat radius, and offset angle were performed, and the results show that 4.5 m, 7m, and 30o respectively are the optimum values. 5. To ensure best thermal performance, a coating process was done to reduce the reflectivity and emissivity as well as increase the absorptivity of the receiver by using Ebonol C to oxidize the receiver pipes and then coated with black matt paint, this process had enhanced the thermal performance by 13.97%.
  53. 53. Conclusions 6. The highest thermal efficiency for July at 12:00 noon was 86.88% while minimum value was 75.1% for May. Thermal efficiency enhancement for June, July, and August with that for May are 11.45%, 15.68%, and 13.32% respectively. The average error percent between numerical and experimental results for May, June, July, and August are 1.28%, 1.33%, 1%, and 1.13% respectively. 7. An empirical correlation for Nusselt number had been formulated 𝑁𝑢𝑦 = 1602 ∗ 𝑅𝑒0.024463 ∗ 𝑃𝑟 −2.32751 ∗ 𝑦0.160764 The correlation conditions are, fully developed, turbulent flow (Re > 5500), L/D  3150 and Pr  7.56. 8. The present design thermal efficiency compared with one row and evacuated tube mentioned in previous studies was increased to 8% and 10.92% respectively.
  54. 54. Publications

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