design and evaluation of open volumetric air receiver.A complete analysis of volumetric receivers.

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: chandra@iitj.ac.in
Int. Workshop on Design of Sub-systems for Concentrated Solar Power Technologies,
19-21 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.
Solar Convective Furnace
Avoid double conversion: Fuel  Heat  Electricity  Process heat
Receiver
Retrofitted
Furnace

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

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)
Case PoA,
kW
MFR
(kg/s)
PoA/MFR
(kJ/kg)
Air outlet temp.
(K)
Efficiency (%)
1 2.88 0.0046 626 728 76
2 3.69 0.0046 803 850 75
3 4.41 0.0062 710 818 80
4 4.8 0.0065 743 866 83
5 5.35 0.0065 823 928 83
6 5.32 0.0066 810 936 85
7 4.33 0.0068 636 843 94
Fig. 1. 20 PPI SiC foam used for the experimental purpose by Fend et al., 2004 (Ø80X30mm)

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~ 111-150 W/mK
No flow instability
Metal~ 15-30 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. Circular (porosity ~50%) Square (porosity ~ 75%) Hexagonal (porosity ~ 55%)
Radiation
Radiation
Radiation
Porous body (receiver) type Channels/inch2 Df,eff/L
SolAir 200 receiver (square channel) 90 1.401
Circular design (IIT Jodhpur) 104 0.713
Hexagonal design (IIT Jodhpur) 144 0.837
Square design (IIT Jodhpur) 154 0.974
4. Volumetric Air Receiver Design and Analyses
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. 4.3 Mixer Design (an example)
Mixer plate
Convergent
nozzle
Cases Inlet type
No. of Inlet
(quarter)
Arrangement R’ Dp (mm)
I Circular 2 Non staggered 1 14.4 Angle: 9.54°
Length:139.4mm
Outlet diameter:
50.8mm
II Circular 3 Non staggered 1.5 14.4
III Elliptical 3 staggered 1 and 1.5 9 and 5.56
IV Circular 3 staggered 1 and 1.5 14.4
• Design case IV is selected based on detailed analysis
Maximum inlet temperature difference: 50 °C/K
Maximum outlet temperature difference: 11.5°C/K
2
4
6
8

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

16. Surface temperature on porous receiver
with 6 inlet
Temperature contour (RANS CFD analyzed)
Turbulence model: Reynolds stress
2nd Order approximation
Experiment and CFD analysis: Power = 0.45 kW
Non-uniform temperature leads to thermal stress
Air-recirculation system needs special attention
Temperature measurement
locations
Flow Rate (gm
6 8
Expt Model CFD Expt M
Input
Recirculating air inlet 33.6 33.6 33.6 34.6 3
Primary air Outlet 102.7 102.7 87.6 8
Output
Recirculating air
outlet
51.6 43.0 49.6 46.9 4
Mixed (Primary air
inlet to receiver)
53.3 40.4 47.7 4
Flow rate = 6g/s
(in C)
0.597
0.345Re
Nu 

17. 5. 4kWth Solar Air Tower Simulator
(SATS) Facility
Open volumetric air
receiver assembly (A)
Electrically
heated
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 ~ 210- 420;
- Volumetric heating is ensured;

19. 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)
250 286 270 33 78 >90%
5.2 Experiment: Measured data for 1.25kW
Fig. : Receiver Temperature: Radial and Azimuthal (solid)
200
250
300
350
0 400 800 1200 1600
Temp.
(ºC)
Time (Sec)
r = 7.75(270_deg)(2)
r = 12.25(2)
200
250
300
350
0 400 800 1200 1600
Temp.
(ºC)
Time (Sec)
theta = 0(2)
theta = 90(2)
r=7.75mm

20. Measured temperature at 1.5kW
Air temperature: porous receiver outlet
200
250
300
350
400
0 600 1200 1800 2400 3000 3600
Temp.(ºC) Time(Sec)
r = 0,rec.2 r = 0,rec.3
r = 0,rec.4 r = 0,rec.6
r = 0, rec.7
POA = 1500 W, MFR = 5.04 g/s, POA/MFR = 300
x
x
x
x
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
ɵ = 00
ɵ = 1800
ɵ = 00
ɵ = 900
ɵ = 1800
Z1
Z5
Experiment 1 A B D
PoA (Watt) 750 750 1250 1250
Equivalent
Concentration (Sun)
210 210 350 350
PoA/MFR (kJ/Kg) 100 200 200 300
125
150
175
200
225
250
0 100 200 300
Air
temperature
(ºC)
Theta(ɵ)
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)
Z1: Non-uniform (azimuthal)
Z5: Uniform (mixing)

22. 8 equally spaced TC
2
4
6
8
125
150
175
200
225
0 400 800 1200 1600
Temp.
(ºC)
Time (Sec)
Outlet2 Outlet4
Outlet6 Outlet8
Fig: Components of open air receiver (a), Position of T/C to measure
the outlet temperature of air (b) Outlet air temperature (c)
a
b
c
Temp. at location 4 is lower than
the other because of heat loss
due to improper insulation

23. Efficiency performance curve
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
0
50
100
150
200
250
300
350
50
60
70
80
90
100
0 100 200 300 400 500
Outlet
air
temp.(ºC)
Efficiency
(%)
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)

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
Dust deposition on heliostat  Reduces reflectivity  Consequences??
(surprise)
Objective: Understanding of the physics of deposition and analysis
Solar radiation Reflection towards
receiver
Sun Heliostat Central Receiver

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:
Critical velocity require to lifting dust particle
ip
ip
g
l
g
d
d r
F
r
F
F
r
F







*
*
)
(
* 


Forces act on dust particles [1]
Condition for lifting dust particle [1]
 
2
1
'
2
3
6z
Ar
3
3
8


























A
C
gr
u
d
a
p


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:
47.55.Kf, 92.60.Mt, 92.40.Gc, 45.70.Qj, 45.70.Mg, 45.70.-n, 96.30.Gc, 96.30.Ea, 96.30.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: chandra@iitj.ac.in

32. Pf = pressure of fluid (Pa) ρf = density of fluid (kg/m3) p = static pressure (Pa)
R = gas constant (J/kg K) Tf = temperature of fluid (K) k = turbulence kinetic
energy (J)
A = area (m2) S = source term (W/m3) τ = stress tensor (N)
Uf = velocity of fluid (m/s) CPf = Specific heat capacity of
fluid (J/KgK)
Es = total solid energy
(J)
Ts = temperature of solid (K) Ef = total fluid energy (J) R’ = (Rs/Rout)
λf = Thermal conductivity of
fluid (W/mK)
ε = porosity (%) T = mass averaged
temperature (K)
m = mass flow rate of air
(kg/m3)
RS = Radial position of the plate
opening (m)
DP = Diameter of pore
(mm)
λs = Thermal conductivity of
solid (W/mK)
λeff = effective thermal
conductivity
= ε λf + (1- ε) λs (W/mK)
Rout = radius at mixer
outlet (m)
Nomenclature