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  1. Presenting Author- Mukul Sharma (Energy Centre, MANIT, Bhopal) Co-author- Anil Kumar (Energy Centre, MANIT, Bhopal) Co-author- Prashant Baredar (Energy Centre, MANIT, Bhopal) Co-author- A. Palamanit (Energy Systems Research Institute, Prince of Songkla University, Hat Yai, Songkhla, Thailand) Co- author- V.P. Chandramohan (Mechanical Engineering Department, NIT, Warangal )
  2.  Basics of solar drying  Computational fluid dynamics (CFD) simulation  Objective  Description of domestic direct type multi-shelf solar dryer  Experimental Conditions  Observations  Design of domestic direct type multi-shelf solar dryer  Assumptions for simulation  Boundary conditions for simulation  Results after simulation  Conclusion  References
  3.  Solar food drying is world wide known process which is adopted by our ancestors from ancient era.  Open food drying is currently most preferred by the people of developing nations like India.  There are some disadvantages of Open food drying such as contamination by dust and insects , deterioration of food by rain, birds, animals and human etc [1].  To overcome these disadvantages , Various dryers were developed by the researchers. Some of them work on conventional power and some works on Renewable Energy.  The devices works on conventional energy were used initially but they were found to be costly and very energy intensive.  There are three types of solar dryers [3].  Direct Type Solar Dryer  Indirect Type Solar Dryer  Mixed Type Solar Dryer Fig.1. Domestic direct type multi- shelf solar dryer[2]
  4.  Direct Type solar dryers uses direct solar radiation for food drying. They are of two types viz. cabinet dryers and greenhouse dryers.  In Indirect type solar dryer, there are two separate parts: one is solar collector and another is dryer.  The solar radiation’s heat is collected at solar collector and with the help of air , it is transferred to drying chamber where drying of food takes place.  The mixed type solar dryers use both direct and indirect type technology simultaneously.
  5. CFD is a branch of fluid mechanics that utilises the mathematical modelling and numerical simulation algorithms to analyse and solve the problems that involve flow of any fluid [4]. Various CFD simulation tools are: • ANSYS- Fluent, COMSOL , OpenFOAM, Altair’s AcuSolve, Star-CCM+ , Autodesk Simulation CFD and many more.. Some of the advantages of CFD simulation are as follows: • The CFD analysis gives the exact result which empowers the researcher to analyse the optimal design and overall performance of the model [5]. • CFD analysis software saves a significant time and money which would get wasted in the experimental observations for performance validation of a model [6].
  6. To Validate the design of domestic direct type multi-shelf solar dryer using Computational fluid dynamics simulation. To demonstrate the temperature distribution and radiation heat flux distribution inside domestic direct type multi-shelf solar dryer.
  7.  A domestic direct type multi-shelf solar dryer (fig.1) was developed by Singh et al. for Indian conditions.  The dryer has three perforated trays arranged one above other.  The air flows through the dryer by natural circulation.  It has variable inclination to capture more solar radiation. The inclination was set as per the latitude of installed location of dryer. The dryer was set up initially at Ludhiana, India (31oN).  The main parts of dryer were hot box, base frame, trays and shading plates. The top, back, one side and gate of the box were insulated.  For air flow, 40 holes of 8mm diameter were given in bottom and 20 holes were given at the top.  A 4mm thick glass sheet was fixed as glazing in the front side of solar dryer.  The interior of dryer was painted with dull black paint for absorption of solar rays. Fig 1: Domestic direct type multi- shelf solar dryer[2]
  8. [2]  The experiment at no load condition was carried out at Ludhiana(Punjab) on 21 November.  Initially, the inlet and outlet holes were blocked , so maximum stagnation temperature was attained.  The dryer was placed facing to south direction at 9:30 am to 4:00 pm.  The average overall heat loss coefficient (U1) based on aperture area for dryer was calculated using: 𝐼 𝜏𝛼 = 𝑈1 (𝑇𝑆 − 𝑇𝑎) (1) where, I = solar radiation intensity in W/m2, 𝜏 = transmissivity, α = absorptivity, 𝑇𝑆= maximum stagnation temperature, 𝑇𝑎= ambient temperature.
  9. The following experimental results were obtained at no load condition:  The maximum stagnation temperature attained by the dryer was observed 100oC.  The corresponding solar radiation intensity and ambient temperature were 750 W/m2 and 30oC, respectively observed during mid-noon.  The overall heat loss coefficient U1 based on aperture area for dryer was found to be 8.5 W/m2 K .
  10. Fig.2: Wireframe model of domestic direct type multi-shelf solar dryer Fig.3: Meshed wireframe view of domestic direct type multi-shelf solar dryer Trays Top Holes Bottom Holes
  11.  Mass conservation equation [7]: 𝜕𝜌 𝜕𝑡 + 𝛻. 𝜌𝒗 = 0 (2) where ρ is the fluid density and 𝒗 is the fluid velocity.  Momentum conservation equation [7]: 𝜕 𝜕𝑡 𝜌𝒗 + 𝛻. 𝜌𝒗𝒗 = −𝛻p + ρ𝐠 + 𝐅 (3) where, p is the static pressure,ρ𝐠 and 𝐅 are the gravitational and external forces, respectively.  Energy Conservation equation [7]: 𝜕 𝜕𝑡 𝜌𝐸 + 𝛻. 𝑣 𝜌𝐸 + 𝑝 = 0 (4) where, E is the total energy of fluid.
  12. For simulation of temperature distribution, the little amount of air flow is assumed from the lower and upper holes of 8 mm diameter. To reduce the complexity of the simulation, the perforated tray mesh size is considered of 2×2 cm2 and shading trays are neglected. Lower holes are considered as inlet and upper holes are considered as outlet.
  13.  Total Elements- 2,88,343  Radiation model- Surface to surface, Solar Loading- Solar ray tracing  Latitude – 31o N , Longitude- 75o E (For Ludhiana), Fair weather Conditions  Date and time- 21 Nov. ,12:00 P.M.  Direct solar irradiance- 750 W/m2 , Diffused Solar irradiance- 200 W/m2  Inlet and outlet – openings  Fluid- Air with density 1.225 kg/m3 and specific heat -1006.43 j/kg-k, Thermal conductivity- .0242 w/m-k.  Ambient air temperature -300 K  Outer walls- insulated
  14. The temperature near the trays can be observed about 320 K. Further the temperature rise can be seen as air move upwards towards outlet to a range of 328 K which is significant rise in temperature as per the design of dryer. Fig. 4: Contour of static temperature of the trays inside the dryer cabinet. Fig. 5: Contour of static temperature of the dryer cabinet.
  15. As the absorptivity of the dryer is fixed to 0.9 as per data used in experiments due to this the most of the radiation are absorbed inside the dryer and this is clearly seen in the contours. The maximum radiation is incident on the trays and this can be seen in Fig. 6. This high heat flux helps in increasing the circulating air temperature continuously inside the dryer to a significant level which is required for food drying. Fig.6 : Heat radiation flux contour of trays inside the dryer cabinet.
  16. An attempt has been made to carry out CFD based analysis using ANSYS-FLUENT 14.0 software to get heat transfer and radiation fluxes of Domestic direct type solar dryer at no load condition. The temperature of the air inside the cabinet dryer increases to a significant value of 326K with continuous flow of fresh air from the atmosphere at natural circulation mode. The major area inside the cabinet dryer such as trays, dryer walls gets sufficient radiation flux which validates the design of the Domestic direct type solar dryer. Hence, the design of the dryer formulated by Singh et al. has been validated by this CFD simulation.
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