Design and evaluation of open volumetric air receiver for process heat applications

Transcription

1 Design and evaluation of open volumetric air receiver for process heat applications P. Sharma, R. Sarma, D. Patidar, G. Singh, D. Saini, N. Yadav L. Chandra*, R. Shekhar, P. S. Ghoshdastidar Centre for Solar Energy Technologies Indian Institute of Technology Jodhpur, Rajasthan, India. *Corresponding author: Int. Workshop on Design of Sub-systems for Concentrated Solar Power Technologies, December 2013, Jodhpur.

2 Contents 1. Motivation 2. Objectives 3. Design Methodology 4. Volumetric Air Receiver Design and Analyses 5. SATS Facility 6. Conclusion

3 1. Motivation Indigenous adopted design of open volumetric air receiver (in view of local condition) for industrial process heat application. Receiver Solar Convective Furnace Retrofitted Furnace Avoid double conversion: Fuel Heat Electricity Process heat

4 1.1 Retrofitted Furnace In Design Stage for Aluminum Heat Treatment Furnace Hearth Hot Air Ducts Hot Air in Hot Air in Backup (existing) electric heaters Aluminum Ingots Hearth grid

5 2. Objectives Design aspects of open volumetric air receiver a. Flow instability; b. Components, such as, mixer, air-recirculation system, porous receiver; Evaluation of the designed receiver

6 3. Design Methodology - Preliminary analysis A Design - Detailed experiment Final Design Need An experimental set-up: Designed and installed

7 3.1 Preliminary analysis Special Consideration: Flow instability at high temperature Analysis Capture flow instability Need A validated tool

8 3.2 Validation: FLUENT is selected Selected experiment: Fend et al. (2004) Fig PPI SiC foam used for the experimental purpose by Fend et al., 2004 (Ø80X30mm) Case PoA, MFR PoA/MFR Air outlet temp. Efficiency (%) kw (kg/s) (kj/kg) (K)

9 3.2 Validation: Analyses - CFD analyzed results within experimental error limit ± 5%. - Larger deviation only in 1 out of 7 cases is observed. - Best practice: Temperature dependent material properties should be carefully modeled

10 3.3 Flow instability SiC~ W/mK No flow instability Metal~ W/mK Flow instability is expected Condition in which the effect of thermal conductivity can be ignored: (refer to the article for derivation) Order of magnitude analysis»

11 4. Volumetric Air Receiver Design and Analyses Radiation Radiation Radiation Circular (porosity ~50%) Square (porosity ~ 75%) Hexagonal (porosity ~ 55%) Porous body (receiver) type Channels/inch 2 D f,eff /L SolAir 200 receiver (square channel) Circular design (IIT Jodhpur) Hexagonal design (IIT Jodhpur) Square design (IIT Jodhpur) Target: 1. Effect of porosity; 2. Effect of geometry

12 4.1 Circular Design Design consideration: Porous receiver assembly with foot piece; air re-circulation system; mixing plate; mixer etc.

13 4.2 Receiver assembly Components of open air receiver and assembly All the components are designed with the help of selectively validated FLUENT code

14 Cases Inlet type 4.3 Mixer Design (an example) No. of Inlet (quarter) Mixer plate Arrangement R Dp (mm) Convergent nozzle I Circular 2 Non staggered Angle: 9.54 II Circular 3 Non staggered Length:139.4mm III Elliptical 3 staggered 1 and and 5.56 Outlet diameter: IV Circular 3 staggered 1 and mm Design case IV is selected based on detailed analysis Maximum inlet temperature difference: 50 C/K Maximum outlet temperature difference: 11.5 C/K

15 Air re-circulation system Why? Non-uniform cooling of porous receiver Thermal Stress Failure Solution: Ensure uniform cooling Velocity (m/s) Contour: Injection plane Air-recirculation system (injection) Velocity Contour: outlet plane Uniform velocity Uniform cooling Mitigation of thermal stress

16 Surface temperature on porous receiver with 6 inlet Experiment and CFD analysis: Power = 0.45 kw Temperature measurement locations (in C) Flow rate = 6g/s Flow Rate (gm 6 8 Expt Model CFD Expt M Input Output Recirculating air inlet Primary air Outlet Recirculating air outlet Mixed (Primary air inlet to receiver) Temperature contour (RANS CFD analyzed) Turbulence model: Reynolds stress 2 nd Order approximation Non-uniform temperature leads to thermal stress Air-recirculation system needs special attention Nu 0.345Re

17 5. 4kWth Solar Air Tower Simulator (SATS) Facility Electrically heated Open volumetric air receiver assembly (A) A Receiver assembly, B Heat exchanger, C Blower, D Thermal energy storage, E Direct storage line, F Secondary line Target air temperature: 450

18 5.1 Experiment: Conditions Receiver: Electrically heated - Receiver material: Brass; - Power input = 750kW - 1.5kW; - Equiv. suns on porous receiver ~ ; - Volumetric heating is ensured;

19 Temp. (ºC) 5.2 Experiment: Measured data for 1.25kW Temp. (ºC) POA/MFR (kj/kg) Average receiver Temp. (C) Air Temp. (C) at the outlet of porous receiver Re-circulating air inlet temp. (C) Re-circulating air outlet temp. (C) Efficiency (heat removal/po wer input) >90% r = 7.75(270_deg)(2) r = 12.25(2) Time (Sec) Fig. : Receiver Temperature: Radial and Azimuthal (solid) theta = 0(2) theta = 90(2) r=7.75mm Time (Sec)

20 Measured temperature at 1.5kW Air temperature: porous receiver outlet Temp.(ºC) 400 POA = 1500 W, MFR = 5.04 g/s, POA/MFR = x x x x r = 0,rec.2 r = 0,rec.4 r = 0, rec.7 r = 0,rec.3 r = 0,rec Time(Sec) Maximum temperature is about 350 C Average temperature is about 325 C Variation of about 7% is observed at the steady state

21 Evaluation of mixer Air temperature (ºC) Z5 Z1 ɵ = 0 0 ɵ = 0 0 ɵ = 90 0 Temp.(ºC) at Z1 (1) Temp.(ºC) at Z5 (2) Temp. at Z1(A) Temp. at Z5(A) Temp. at Z1(D) Temp. at Z5(D) Temp at Z1 (B) Temp at Z5 (B) 250 Z1: Non-uniform (azimuthal) 225 Z5: Uniform (mixing) 200 ɵ = ɵ = Theta(ɵ) Experiment 1 A B D PoA (Watt) Equivalent Concentration (Sun) PoA/MFR (kj/kg)

22 Temp. (ºC) 8 equally spaced TC a 6 4 b Outlet 2 Outlet 4 Outlet 6 Outlet Time (Sec) c Temp. at location 4 is lower than the other because of heat loss due to improper insulation Fig: Components of open air receiver (a), Position of T/C to measure the outlet temperature of air (b) Outlet air temperature (c)

23 Efficiency (%) Outlet air temp.(ºc) Efficiency performance curve POA/MFR(kJ/kg) Effciency(P=1250W) Efficiency (P=1500W) Effciency (P=1000W) Efficiency (P=750W) T_out(P=1250W) T_out(P=1500W) T_out(P=1000W) T_out(P=750W) Efficiency deceases with temperature for any given power Linearly decreasing trend of efficiency with PoA/MFR and outlet temperature is observed (see e.g. Hoffschmidt et al. (2003)) A correlation, such as, Efficiency = f(power, mass flow rate, temperature) will be derived

24 Show stopper!!! Dust deposition Blockage Consequence?? Solution: - Removal; - Cleaning; - Collection; Status: Design in progress

25 Conclusion - The first design of volumetric air receiver is being evaluated - Experiment and analyses indicate potential for application to process heat - Cleaning strategy is under development

26 Other activities

27 Motivation and Objective God plays Dice!! Sunny regions are usually blessed with dust Solar radiation Reflection towards receiver Sun Heliostat Central Receiver Dust deposition on heliostat Reduces reflectivity Consequences?? (surprise) Objective: Understanding of the physics of deposition and analysis

28 How dust deposits and analysis procedure Wind Wind Wind

29 Analysis of critical velocity for initiating saltation process Velocity required to initiate the removal process: F d * r ( F F )* r F d g l g ip * r ip Condition for lifting dust particle [1] Forces act on dust particles [1] Critical velocity require to lifting dust particle u 8 3 pgr 3 ' C A a d 3 Ar 2 6z 1 2 Small dust size Higher Threshold Velocity More difficult to remove Reference : [1] J. F. Kok, Eric J. R. Parteli, T. I. Michaels, and D. BouKaram, The physics of wind-blown sand and dust, PACS: Kf, Mt, Gc, Qj, Mg, n, Gc, Ea, nd.

30 Acknowledgement The R & D activities are funded and realized with support from: Ministry of New and Renewable Energy (MNRE), Govt. of India IIT Jodhpur, Ministry of Human Resource Development (MHRD), Govt. of India All students and staff members

31 Contact Dr. Laltu Chandra:

32 Nomenclature P f = pressure of fluid (Pa) ρ f = density of fluid (kg/m 3 ) p = static pressure (Pa) R = gas constant (J/kg K) T f = temperature of fluid (K) k = turbulence kinetic energy (J) A = area (m 2 ) S = source term (W/m 3 ) τ = stress tensor (N) U f = velocity of fluid (m/s) C Pf = Specific heat capacity of fluid (J/KgK) E s = total solid energy (J) T s = temperature of solid (K) E f = total fluid energy (J) R = (R s /R out ) λ f = Thermal conductivity of ε = porosity (%) T = mass averaged fluid (W/mK) m = mass flow rate of air (kg/m 3 ) R S = Radial position of the plate opening (m) temperature (K) D P = Diameter of pore (mm) λ s = Thermal conductivity of solid (W/mK) λ eff = effective thermal conductivity = ε λ f + (1- ε) λ s (W/mK) R out = radius at mixer outlet (m)