211 optical and numerical study of direct steam generation in parabolic trough collector module...
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C. S. Ajay & K. S. Reddy
Heat Transfer and Thermal Power Laboratory
Department of Mechanical Engineering
Indian Institute of Technology Madras, Chennai - 600036
International Conference on Advances in Energy Research
IIT Bombay, Powai, 10th-12th December 2013
Optical and Numerical study of Direct Steam Generation in Parabolic Trough Collector module
by
Organization of Talk
• Introduction
• Development of Optical and Thermal model
• Numerical Investigations of Direct Steam Generation in solar parabolic trough collectors.
• Summary
• Parabolic trough collector is a
– medium temperature (100oC to 400oC) concentrated solar power technology
– two dimensional concentrator that concentrates solar radiation over a line focus
• The basic components in the Parabolic Trough Collector are
– a concentrator which a reflective mirror, bend on to a shape of a parabola
– Receiver mounted at the focus
Parabolic trough collector and DSG operation
Source: asiaenergy.net
• In a solar power plant working in DSG mode,
the boiler in conventional power plant is
replaced by solar collector
• Water from the outlet of the steam condenser
is sent through the collector and is directly
converted to steam
• The steam from the collector outlet is used to
run turbines to generate power
Development of coupled Optical and Thermal model
• A standard collector (Euro-trough) corresponding to has been considered for the simulation.
• The inner wall is applied with heat flux boundary condition, given in terms of inside heat transfer
co-efficient and free stream temperature.
• The flux distribution obtained from the MCRT code is applied outside of the absorber
• The radiative heat transfer between the receiver and the glass tube is modeled using Discrete
Transfer Radiation Model (DO) model
• The length of the DSG collector considered is 500m.
q(θ)
ql,g-a
qin=hdi(Tw-Tfi)
Glass tube
Receiver
Ql,r-g
( ) u
i
Q zH z H
m
( )u ap op lossQ z SW l Q z
• Enthalpy at a given node of
the receiver is given as,
(1)
(2)
Development of coupled Optical and Thermal model
Algorithm of thermal model
Development of coupled Optical and Thermal model
Heat transfer co-efficient in two phase region
θwet
Si
Sv
Sl
(3)
(4)
Stratified flow
Stratified flow
• Heat transfer co-efficient in the liquid region is given by,
0.8 0.4cb,l
,
h 0.023Re Pr lDl v
h lD
1
3,l cb l nbh h h
• Dh,l ,Dh,v are the hydraulic diameters for liquid and vapor region given by
• Heat transfer co-efficient in the vapour region is given by,
0.8 0.4
,
0.023Re Pr vv v v
h v
hD
4 (1 )hl
i l
AD
S S
4
hvv l
AD
S S
• hl and hv are obtained from these equations and are applied in the nodes
of the wet and wet and dry regions depending upon the wetting angle
-0.550.12 -0.5 0.67nb 10h =55Pr -log Pr M q
θwet,sw
φ
ξ=θwet,sw-φ
O
Ro
Si
Sv
Sl
Stratified wavy flow
Development of coupled Optical and Thermal model
• For annular flow the inner diameter of the receiver is assumed to be completely wet and
the uniform heat transfer co-efficient is applied inside the tube.
1
3,l cb l nbh h h
• Where Reδ is the film Reynolds no and δ is the film thickness
• ul is the superficial liquid velocity and δ is the film thickness
(5)
(6)
(7)
(8)
(9)
Mathematical formulation
Annular flow
0.6965 0.4, 0.1361Re Pr l
cb a l
kh
-0.550.12 -0.5 0.67nb 10h =55Pr -log Pr M q
4Re l
l
u
(1 )
(1 )l
G xu
(1 )
D
Sl
D
δ
Results and Discussion:
• The simulations are carried out for different mass flow rates, different irradiance conditions.
The maximum temperature of the absorber tube is limited to less than 450oC.
• Five irradiance conditions which were considered are 1000W/m2, 850W/m2, 600W/m2,
400W/m2, and 200W/m2.
• The collector is also analyzed for different receiver thicknesses (5mm, 7mm, 10mm) to
study its effect of thermal gradient under two phase conditions
• The collector position are varied from 0 to 50o to study the asymmetric temperature profile
resulting from stratified flow conditions
• The position of the water-steam interface with respect to the flux distribution at different
collector positions is shown in figure
Collector position : 0o Collector position : 50o
q’ q’
V
L
V
L
Results and Discussion
Temperature distribution around the absorber
Results and Discussion
Non-dimensional temperature distribution around the absorber (thickness =10mm)
Operating conditions:
m=1kg/s; DNI= 1000W/m2;
Collector position = 0o (solar noon)
Operating conditions:
m=1kg/s; DNI= 1000W/m2;
Collector position = 50o
•Non-dimensional temperature profile (Tw-Tmin(z)) obtained around the receiver for the whole entire
collector length
Tw
-Tf
Angular position around the receiver (degrees)
Collecto
r length (m
)
Tw
-Tf
Angular position around the receiver (degrees)
Collecto
r length (m
)
Results
Non-dimensional temperature distribution around the absorber (Thickness =10mm)
Collecto
r length (m
)
Angular position around the receiver (degrees)
Non
-dim
ensi
onal
tem
pera
ture
gra
dien
t (K
)
Operating conditions:
m=0.155kg/s; DNI= 200W/m2;
Collector position = 0o (solar noon)
Operating conditions:
m=0.155kg/s; DNI= 200W/m2;
Collector position = 50o Tw
-Tf
Angular position around the receiver (degrees)
Collecto
r length (m
)
Tw
-Tf
Angular position around the receiver (degrees)
Collecto
r length (m
)
Results and DiscussionCross-sectional view of receiver at the point of maximum thermal gradient in the sub-cooled,
superheated and stratified two phase regions
Collector inclination = 0o
Collector inclination = 50o
Sub-cooled region Stratified region Super heated region
Collecto
r length (m
)
Angular position around the receiver (degrees)
Non
-dim
ensi
onal
tem
pera
ture
gra
dien
t (K
)
Collecto
r length (m
)
Angular position around the receiver (degrees)
Non
-dim
ensi
onal
tem
pera
ture
gra
dien
t (K
)
Results
m=1kg/s; DNI= 1000W/m2;
Collector position = 0o (solar noon)
m=0.155kg/s; DNI= 200W/m2;
Collector position = 50o
Non-dimensional temperature distribution around the absorber (thickness =5mm)
m=0.155kg/s; DNI= 200W/m2;
Collector position = 50o
Tw
-Tf
Angular position around the receiver (degrees)
Collecto
r length (m
) Tw
-Tf
Angular position around the receiver (degrees)
Collecto
r length (m
)
Tw
-Tf
Angular position around the receiver (degrees)
Collecto
r length (m
)
Results and DiscussionCross-sectional view of receiver at the point of maximum thermal gradient in the sub-cooled,
superheated and stratified two phase regions
Sub-cooled region Stratified region Super heated regionCollector inclination = 0o
Collector inclination = 50o
Conclusion and Summary
• A coupled MCRT-DSG model has been developed for finding thermal performance characteristics of
the DSG collector
• Thermal analysis on the receiver revealed that the thermal gradient higher in the stratified flow and
this effect is higher at higher collector inclination
• The collector inclination increases the temperature gradient across the cross-section by 18%
• The maximum temperature gradient across the receiver cross-section in the DSG collector is
obtained in the stratified region as 1022 K/m at an irradiance of 200W/m2
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