Design and evaluation of open

volumetric air receiver for process

heat applicationsP. 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.inInt. Workshop on Design of Sub-systems for Concentrated Solar Power Technologies,

19-21 December 2013, Jodhpur.

Contents

1. Motivation

2. Objectives

3. Design Methodology

4. Volumetric Air Receiver Design and Analyses

5. SATS Facility

6. Conclusion

1. MotivationIndigenous adopted design of open volumetric air receiver(in view of local condition) for industrial process heatapplication.

Solar Convective Furnace

Avoid double conversion: Fuel Heat Electricity Process heat

Receiver

Retrofitted Furnace

1.1 Retrofitted FurnaceIn 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

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

3. Design Methodology

- Preliminary analysis “A” Design

- Detailed experiment Final Design

Need An experimental set-up: Designed and installed

3.1 Preliminary analysis

Special Consideration: Flow instability at high temperature

Analysis Capture flow instability

Need A validated tool

3.2 Validation: FLUENT is selectedSelected 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)

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

3.3 Flow instability

SiC~ 111-150 W/mKNo flow instability

Metal~ 15-30 W/mKFlow instability is expected

Condition in which the effect of thermal conductivity can be ignored: (refer to the article for derivation)

Order of magnitude analysis »

Circular (porosity ~50%) Square (porosity ~ 75%) Hexagonal (porosity ~ 55%)

RadiationRadiation

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

4.1 Circular Design

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

4.2 Receiver assembly

Components of open air receiver and assembly

All the components are designed with the help of selectively validated FLUENT code

4.3 Mixer Design (an example)Mixer plate

Convergent

nozzleCases Inlet typeNo. 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/KMaximum outlet temperature difference: 11.5°C/K

2

4

6

8

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

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 stressAir-recirculation system needs special attention

Temperature measurement

locations

Flow Rate (gm/s)

6 8 10

Expt Model CFD Expt Model Expt Model

Input Recirculating air inlet 33.6 33.6 33.6 34.6 34.6 36.7 36.7

Primary air Outlet 102.7 102.7 87.6 87.6 82.7 82.7

Output

Recirculating air

outlet 51.6 43.0 49.6 46.9 41.1 46.7 42.4

Mixed (Primary air

inlet to receiver) 53.3 40.4 47.7 40.4 46.6 45.3

Flow rate = 6g/s(in C)

0.5970.345ReNu

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

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;

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/power 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

Tem

p. (

ºC)

Time (Sec)

r = 7.75(270_deg)(2)

r = 12.25(2)

200

250

300

350

0 400 800 1200 1600

Tem

p. (

ºC)

Time (Sec)

theta = 0(2)

theta = 90(2)

r=7.75mm

Measured temperature at 1.5kWAir temperature: porous receiver outlet

200

250

300

350

400

0 600 1200 1800 2400 3000 3600

Tem

p.(

ºC)

Time(Sec)

r = 0,rec.2 r = 0,rec.3r = 0,rec.4 r = 0,rec.6r = 0, rec.7

POA = 1500 W, MFR = 5.04 g/s, POA/MFR = 300

xx

x

x

Maximum temperature is about 350 CAverage temperature is about 325 CVariation of about 7% is observed at the steady state

Evaluation of mixer

ɵ = 00

ɵ = 1800

ɵ = 00

ɵ = 900

ɵ = 1800

Z1Z5

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

te

mp

era

ture

(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)

8 equally spaced TC

2

4

6

8

125

150

175

200

225

0 400 800 1200 1600

Tem

p. (

ºC)

Time (Sec)

Outlet 2 Outlet 4

Outlet 6 Outlet 8

Fig: Components of open air receiver (a), Position of T/C to measure the outlet temperature of air (b) Outlet air temperature (c)

ab

c

Temp. at location 4 is lower thanthe other because of heat lossdue to improper insulation

Efficiency performance curve

Efficiency deceases with temperature for any given powerLinearly 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

Ou

tlet

air

tem

p.(

ºC)

Effi

cien

cy (

%)

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)

Show stopper!!!

Dust deposition Blockage Consequence??

Solution:- Removal;

- Cleaning;

- Collection;

Status: Design in progress

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

Other activities

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

How dust deposits and analysis procedure

Wind

Wind

Wind

Analysis of critical velocity for initiating saltation process

Velocity required to initiate the removal process:

Critical velocity require to lifting dust particle

ipipglgdd rFrFFrF

**)(*

Forces act on dust particles [1]

Condition for lifting dust particle [1]

2

1

'

2

3

6z

Ar

338

AC

gr

uda

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.

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

Contact

Dr. Laltu Chandra: chandra@iitj.ac.in

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