Post on 20-Dec-2015
description
A Dissertation Presentationon
Thermo-Hydraulic Performance of Square Perforated Solar Air
Heater
Guided By: Submitted By:
Dr. B. K. Maheshwari Rahul TripathiAssistant professor M.E. (Thermal Engg.)
DEPARTMENT OF MECHANICAL ENGINEERINGM. B. M. ENGINEERING COLLEGE
FACULTY OF ENGINEERING AND ARCHITECTUREJ. N. V. UNIVERSITY, JODHPUR
June, 2014
April 18, 2023 M.E. Dissertation by Rahul Tripathi 2
Contents Of Dissertation
Performance Enhancement Of Solar Air Heater Using
Baffles
Experimental Setup And Programme
Result And Graphs
Conclusions
References
April 18, 2023 M.E. Dissertation by Rahul Tripathi 3
PERFORMANCE ENHANCEMENT OF SOLAR AIR HEATER USING BAFFLES
Perforated Rectangular Blocks
Asymmetrically Heated Rectangular Duct with
Perforated Baffles
Use of Porous Baffles to Enhance Heat Transfer
Fully perforated ribs
Half perforated turbulence promoters
Fins provided with baffles
April 18, 2023 M.E. Dissertation by Rahul Tripathi 4
Perforated Rectangular Blocks
• Sara et al. (2001) had investigated perforated rectangular cross-sectional.
• Results from the perforated blocks concluded that as the degree of the perforation increased the heat-transfer enhancement capability of the blocks also increased.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 5
A typical variation in the heat transfer with Re for varying degree of the perforated open-area ratio (φ=0.05, 0.10 and 0.15) is shown in Figure.With their experimental studies they have concluded that perforations in the blocks enhance the heat transfer and the enhancement increases with increasing the degree of perforations.
Fig. Variation of with Re (Sara et al, 2001)
April 18, 2023 M.E. Dissertation by Rahul Tripathi 6
Asymmetrically Heated Rectangular Duct with Perforated Baffles
• Maheshwari et al. (2005) has experimentally studied the heat transfer and friction factor of rectangular ducts with baffles (β = 18.4%, 28.4%, 41.7% & 46.8%)
They have concluded that the baffles with the highest open area ratio (46.8%) give the best performance compared with the smooth duct at equal pumping power.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 7
Fig. (a) Schematic of the baffled duct, (b) sketch of a baffle with perforations. (Karwa et al 2005).
The longitudinal section of the duct is shown in Fig.(a) and (b) shows two views of a perforated baffle.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 8
Fig. Thermal performance at equal pumping power. (Karwa et al. 2005)
April 18, 2023 M.E. Dissertation by Rahul Tripathi 9
Use of Porous Baffles to Enhance Heat Transfer
Anand and Ko (2003) have experimentally studied heat transfer enhancement in a rectangular channel by using a porous baffle made up of aluminum foam. Baffles were mounted on bottom and top walls in a staggered fashion. Porous baffles as shown in Fig.
Fig. Aluminium foam structure (Anand and Ko 2003)
April 18, 2023 M.E. Dissertation by Rahul Tripathi 10
The heat transfer enhancement ratio (Nu+) decreases with increase in Reynolds number and increases with increase in pore density.
Fig. Heat transfer enhancement ratio of different pore density. ( Anand and Ko,2003 ).
April 18, 2023 M.E. Dissertation by Rahul Tripathi 11
Fully Perforated Ribs
Hwang and Liou (1995) investigated heat transfer and friction in a rectangular
channel (W/H=4) with symmetrically mounted solid and fully perforated ribs on
parallel broad walls (β=50%, e/H=0.13 and 0.26, δ/e=0.38 and 0.76, Re=10,000–
50,000, p/e=5–20).
Their studies had also concluded that the perforated ribs are thermohydrolically
better than the solid ribs.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 12
Half Perforated Turbulence Promoters
Tanasawa et al. investigated the effect of the half perforated turbulence promoters
symmetrically mounted on two opposite walls on the heat transfer and friction in a
rectangular channel.
They found that surfaces with the half perforated turbulence promoters with
perforations on the lower half of the ribs performed better than those with the solid
type promoters.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 13
Fins Provided with Baffles
Yeh and Chou (1991) experimentally investigate the efficiency of solar air heaters with baffles as shown in Fig. and found considerable improvement in the collector efficiency of solar air heaters with fins in the collector are provided with attached baffles to create air turbulence and an extended heat transfer area and on increasing the density of baffles.
Fig. Baffle attached to absorber plate. (Yeh and Chou, 1991)
April 18, 2023 M.E. Dissertation by Rahul Tripathi 14
Roughness elements of larger height give a high increase in the heat transfer but increase in pressure drop is a serious concern. Hot zones develop in the wake of these elements because of re-circulating flow. This leads to lower heat transfer from these zones; thus an attempt has been made by the designers to overcome this effect by putting perforation in the baffles which increase the heat transfer from these zones and help in reducing the pressure drop across the channel. The perforated elements allow a part of the flow to pass through these perforations and thus the hot zones and form drag are reduced.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 15
Experimental Setup And ProgrammeExperimental investigation of heat transfer and friction characteristics of a
rectangular duct with square perforated baffles on one broad wall which is subjected to solar radiation has been carried out using an outdoor test facility available in department of mechanical engineering. The test facility has been designed according to the guide line of ASHRAE standard 93-1986 for testing of solar collector operating in an open-loop mode.
Instrumentation
Solar Radiation Measurement
A pyranometer (shown in figure ) was used to measure the total short wave
radiation from both sun and sky and a pyrheliometer wad used to measure the
direct normal insulation.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 16
Fig. Pyranometer Solar radiation measuring instrument
April 18, 2023 M.E. Dissertation by Rahul Tripathi 17
Temperature Measurement
In present investigation a Butt-welded 1 mm dia Chromel Alumel bead (K-type) thermocouples having temperature range 0o-1200oC , calibrated against mercury thermometer of 0.1oC least count, was used for the temperature measurement.
Fig. Thermocouple measurement circuit
April 18, 2023 M.E. Dissertation by Rahul Tripathi 18
The thermocouples(3/24 inch diameter “K type” – CR/AL (Compensating)PVC
THERMOCOUPLE Indian Standards IS – 8784 STANDARD. confirmation ECO
SERIES) were provided along the axial center line of the absorber plate in small
holes on the span-wise variation of absorber plate temperature as shown in fig.
Nineteen (19) thermocouple arranged span-wise in the duct, as shown in the fig.
To measure the exit air temperature after the mixing section three thermocouples
were provided as shown in figure.
Inlet temperature of air to the duct was also measured using a thermocouple in
the same manner.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 19
Fig. (a) Thermocouple positions of baffled absorber plate.(b) Thermocouple positions of smooth absorber plate.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 20
Fig. Thermocouple locations on Smooth and Baffled plates in Solar Air Heater.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 21
Air Flow Measurements
For flow measurement an orifice plate (as shown in fig.) and inclined manometers with tilt of 5:1 had been used to achieve the desired accuracy in present investigation.
Fig. Detailed view of orifice plate (Gharai et al, 2011)
April 18, 2023 M.E. Dissertation by Rahul Tripathi 22
Pressure Drop across Collector
The static pressure drop across the solar collector was measured using a differential pressure measuring device. Each side of the device was connected to four externally main folded pressure taps as shown in Fig. The pressure taps consist of 6.4 mm nipples soldered to the duct and centered overt mm diameter holes. The edge of these holes on the inside surface of duct was made sure to be free from burrs and other surface irregularities.
Fig. Schematic representation of the measurement of pressure drop across the solar collector.(ASHRAE Codes ,93-1986)
April 18, 2023 23
Wind VelocityThe wind velocity was measured with an instrument (shown in figure) and
associated readout device that can determine the integrated average wind velocity for each test period accuracy of ± 0.8 m/s (1.8 mph)
Fig Wind velocity measurement device
M.E. Dissertation by Rahul Tripathi
April 18, 2023 M.E. Dissertation by Rahul Tripathi 24
Apparatus and Method of Testing
The experimental test facility, designed and fabricated as per ASHRAE
Standard for testing of solar collectors (ASHRAE Standards, 1986), consists of
300 mm wide parallel ducts with entrance, test, exit and mixing sections, a
blower, control valves, orifice plates and provision for temperature and pressure
drop measurements as shown in Fig. (a) and (b). It works in an open loop mode.The ducts are made of good quality smooth faced plywood and wooden
boards. Each duct is 2880 mm long consisting of 1.64 m long test section, 550
mm long insulated entry and exit sections are installed to reduce any upstream and
downstream effect due to entrance and exit section respectively on the test section.For the turbulent flow regime, ASHRAE Standard recommends entry and
exit lengths of 5(WH) and 2.5(WH), respectively, i.e. 526 mm and 263 mm,
respectively for the duct cross-section employed in the present investigation.The height of both the ducts has been kept fixed at 38.4 mm. The combined
width of ducts (with side walls) is 850 mm where ducts being 300mm wide as
shown in figure.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 25
Fig (a) and (b) Plan and Elevation of Solar Air Heater.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 26
The test section length is 1.64 m resulting in length to hydraulic diameter (D=38.4
mm) ratio of 24.3. Topside of the heated test section carries 12 pieces of 3.25 mm
thick aluminium plate with square perforated baffles on the lower side.
Fig. Sectional view of solar air heater
April 18, 2023 M.E. Dissertation by Rahul Tripathi 27
The sun facing sides of both the absorber plates are smooth and blackened.
Glass plates of 5 mm thickness have been used as cover over the absorber plates at a
height of 60 mm. The top side of entry and exit lengths of each duct is covered with
the plywood.A 100 mm long baffled mixing section is provided to get uniform temperature
of the exit air in the measuring section just after the mixing section. The exit end of
each duct is connected, through a rectangular to circular transition piece, to a 70 mm
ID G.I. pipe with orifice plate assembly.The other end of the each pipe is connected through control valve to the
suction of a 10 HP blower using flexible pipe and a Y-section (not shown in the
figure).50 mm thick thermocole insulation has been provided on the back of the
collector from test section inlet to outlet of twin duct while the transition pieces and
orifice plate assembly pipes (up to the orifice plates) are covered with foam blanket
insulation.All joints are properly sealed with putty.The set-up was installed horizontal (in north-south orientation) on the roof top
at a height of 750 mm on an iron stand.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 28
thermocouples have been fixed with M-seal in the sun facing side of
absorber plate in small diameter holes drilled about 2.5 mm deep at nineteen axial
and span wise locations on the smooth and baffled absorber plates, respectively.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 29
Assembly and Fabrication of the Experimental setup
Below are images for the sequence of assembly and fabrication of solar air heater experimentation.
Fig Wooden Frame of the solar air heater
April 18, 2023 M.E. Dissertation by Rahul Tripathi 30Fig. Valves, Pipe fitings, and insulation used for solar air heater
April 18, 2023 M.E. Dissertation by Rahul Tripathi 31
Fig. Rectangular (300x38.4 mm2) to circular transition piece(70 mm ID), G.I. pipe with orifice plate assembly. The throat diameter of the orifice plate is 38 mm. The other end
of the each pipe is connected through control valve
April 18, 2023 M.E. Dissertation by Rahul Tripathi 32
Fig Finished Solar Air Heater Wooden Frame and pipe fitting
April 18, 2023 M.E. Dissertation by Rahul Tripathi 33
Fig 3.25 mm thick Aluminium sheet used for fabrication of smooth and
baffled absorber plates
Fig. .Final Assembly of transition piece and control valves on solar air heater
April 18, 2023 M.E. Dissertation by Rahul Tripathi 34
Fig. Hand punching machine used for fabrication of baffles
April 18, 2023 M.E. Dissertation by Rahul Tripathi 35
Fig Punching die of square shape.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 36
Fig Assembly of Smooth and Rough Plates on Twin Duct Solar Air Heater.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 37
Fig. Attachment of Thermocouples on absorber plates
April 18, 2023 M.E. Dissertation by Rahul Tripathi 38
Fig Blackened Absorber plates for increased absorptivity
April 18, 2023 M.E. Dissertation by Rahul Tripathi 39Fig. Complete Fabrication of solar air Heater with Glass plate Covers
April 18, 2023 M.E. Dissertation by Rahul Tripathi 40
Experimental Conditions and Procedure
All components of the experimental set up and the instrument have been
checked for proper operation. The blower was then switched on and the joints of the
setup were properly sealed to prevent leakage.Micro-manometer and inclined U-tube manometer were properly leveled.
Blower was switched on and the flow control valve was adjusted to give a
predetermined rate of air flow through the test section. Before the covers were put off, it was ensured that all the thermocouples gave
the same output.All reading was noted under steady state condition, which was assumed to
have been obtained when the plate and air outlet temperature did not deviate over a
10 minute period. The steady state for each run was obtained in about 1 hour and two Reynolds
numbers was investigated throughout the day in the following manner.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 41
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6
Nov.-13 Nov.-14 Nov.-15 Nov.-16 Nov.-17 Nov.-18
β=42.70% β=42.70% β=51.98% β=51.98% β=60.69% β=60.69%
Re=3000and
Re=6000
Re=9000and
Re=12000
Re=3000and
Re=6000
Re=9000and
Re=12000
Re=3000and
Re=6000
Re=9000and
Re=12000
Table : Experimentation Plan
April 18, 2023 M.E. Dissertation by Rahul Tripathi 42
Reynolds number, Re 3034 – 12003
Duct depth, H 38.4 mm
Width of duct, W 300 mm
Hydraulic Diameter, D 68.16 mm
Duct aspect ratio, W/H 7.81
Test section length, L 1640 mm
Test section length to hydraulic diameter ratio,
L/D
24.06
Thickness of baffle, δ 0.643 mm
Baffle height, e 19 mm
Spacing between baffles (pitch), p 134.1 mm
Baffle height-to-duct height ratio, e/H 0.495
Baffle thickness-to-height ratio, δ/e 0.034
Baffle pitch-to-height ratio, p/e 7.06
Open area ratio of perforated baffle, β Type I β = 42.70%
Type II β = 51.98%
Type III β = 60.69%
Table : Experimental conditions and dimensions of baffle and duct
April 18, 2023 M.E. Dissertation by Rahul Tripathi 43
Fig. Details and dimensions of square perforated baffles of open area ratio β=60.69%.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 44
Fig. Details and dimensions of square perforated baffles of open area ratio β=51.98%.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 45
Fig. Details and dimensions of square perforated baffles of open area ratio β=42.70%.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 46
Fig. Detailed nomenclature and various parameters of baffle
April 18, 2023 M.E. Dissertation by Rahul Tripathi 47
The studies (Han et al., 1978; Han and Park, 1988; Han et al., 1989) show that
the effect of the values of the friction factor and the heat transfer either vanishes or is
only marginal when the aspect ratio is greater than 8. It is to be noted that the solar air
heaters have generally high aspect ratio duct. Keeping the above information in the
mind, the value of the baffle height-to-duct height ratio, (e/H), baffle thickness-to-
height ratio, (δ/e), baffle pitch-to-height ratio, (p/e), and the duct aspect ratio, (W/H)
have been fixed for the present study. Only Open area ratio of perforated baffle, (β),
have been varied and three values were selected, (i.e. 60.69%, 51.98%, and 42.70%).
While the baffles height has been fixed at 19 mm. The airflow rate was varied to
give flow Reynolds number of about 3034 to 12003.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 48
Perforated Baffles
The details of baffles used in this study and other relevant system parameters
are given in previous Tables and figures. In the present study, the baffle height-to-duct
height ratio e/H has been fixed at 0.495, which reduces flow passage blockage effect
and simultaneously the baffles extend sufficiently deeper into the flow into the buffer
zone. The baffle pitch- to- height ratio p/e is 7.06 and the flow Reynolds number study
ranges from 3000-12000.
The ratio of the area of the perforations to the baffle frontal area is known as
open area ratio and is given by
= n a2 / (be)
where n is the number of the holes punched through the baffle and a is the side
of a square hole
April 18, 2023 M.E. Dissertation by Rahul Tripathi 49
Data Reduction
Mass flow rate of air has been determined from pressure drop measurement across the orifice plate using the following relationship:
The heat transfer coefficient for the heated test section was calculated from:
Where the heat transfer rate Qu, to the air is given by
The heat transfer coefficient has been used to determine the Nusselt number using the equation
Where
April 18, 2023 M.E. Dissertation by Rahul Tripathi 50
The Reynolds number was determined from the value of the mass flow rate, m, using the equation:
Where
The friction factor was determined from the measured values of pressure drop,
The thermo physical properties of the air have been taken at the corresponding mean temperature Tm = Tfm or Tmpg. The following relations of
thermo physical properties, obtained by correlating data from NBS (U.S.), have been used:
April 18, 2023 M.E. Dissertation by Rahul Tripathi 51
RESULT AND GRAPHS
Variation of Nusselt Number with Reynolds Number
The Comparative plot of Nusselt number v/s Reynolds number has been shown in Fig. for smooth and baffled duct of different perforations (i.e., β= 60.69%, 51.98%, and 43.70%).
2000 4000 6000 8000 10000 12000 140000
20
40
60
80
100
120
Smooth Plate β=42.70% Perforated Bafflesβ=51.98% Perforated Baffles β=60.69% Perforated Baffles
Reynolds Number (Re)
Nus
selt
Num
ber
(Nu)
Fig Variation of Nusselt Number with Reynolds Number
April 18, 2023 M.E. Dissertation by Rahul Tripathi 52
2000 4000 6000 8000 10000 12000 140000
0.5
1
1.5
2
2.5
3
Smooth Plate
β=42.70% Perforated Baffles
β=51.98% Perforated Baffles
β=60.69% Perforated Baffles
Reynolds Number (Re)
Nus
selt
Num
ber
ratio
(N
u/N
u s)
Variation of Nusselt Number ratio (Nu/Nus) with Reynold Number (Re)
Fig. Plot of Nusselt number ratio versus the Reynolds number
The enhancement in Nusselt number for baffled plate of open area ratio β=42.70% is found highest and is order of 1.36-2.09 times more than smooth plate. It is to be noted that value of Nusselt number is directly related to change in heat transfer coefficient. And eventually we get better heat transfer coefficient for baffled plates as compared to the smooth plate.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 53
Variation of Friction Factor with Reynolds Number
2000 4000 6000 8000 10000 12000 140000
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Smooth β=60.69% Perforated Bafflesβ=51.98% Perforated Baffles β=42.70% Perforated Baffles
Reynolds Number (Re)
Fric
tion
Fact
or (f)
As shown in Fig variation of friction factor has been found in good agreement with theoretical value given by Moody’s Chart
Fig Variation of Friction factor with Reynolds Number
April 18, 2023 M.E. Dissertation by Rahul Tripathi 54
In the present experimentation study there was an enhancement of 1.36-
2.09 times in Nusselt number while friction factor increased 1.91-2.19 times for
the baffle of open area ratio β=42.70%.It is found in the study that friction factor increment for other two baffles
of open area ratio β=51.98% and 60.69% are 1.77-2.10 and 1.49-1.7
respectively.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 55
Variation of Temperature Rise with Mass Flow Rate
0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.040
2
4
6
8
10
12
14
16
18
Smooth β=60.69% Perforated Bafflesβ=51.98% Perforated Baffles β=42.70% Perforated Baffles
Mass Flow Rate (m/s)
(To-T
i) T
empe
ratu
re R
ise
(oC
)
From the figure 4.4 if is cleat that Temperature Rise for baffled plates are higher than smooth plates with same value of mass flow rates and solar insolation
Fig Variation of Temperature Rise with Mass Flow Rate
April 18, 2023 M.E. Dissertation by Rahul Tripathi 56
Thermo-Hydraulic Performance Parameter
Lewis [1975] proposed a thermo-hydraulic performance parameter known as efficiency parameter h, which evaluates the enhancement of heat transfer for same pumping power requirement and is defined as,
2000 4000 6000 8000 10000 12000 140000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Smooth Plate β=60.69% Perforated Baffles β=51.98% Perforated Bafflesβ=42.70% Perforated Baffles Series9
Reynolds Number (Re)
(St/
Sts)
/(f/
fs)1/
3
Fig Thermo-hydraulic Performance Parameter
April 18, 2023 M.E. Dissertation by Rahul Tripathi 57
Thermo-hydraulic Performance Parameter for square perforated baffle
are found greater than unity it is found 1.49, 1.75, 1,86 and 1.87 for baffle of
open area ratio β=60.70% for different Reynolds number range investigated in
the study between 3034 to 12003.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 58
Comparison of Square and Circular Perforated Baffles
2000 4000 6000 8000 10000 12000 140000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
β=60.69% square perforated baffles β=46.8% circular perforated baffles
Reynolds Number (Re)
Rat
io o
f Nus
selt
Num
ber
(Nu/
Nus
)
Maheshwari et. al, 2005, experimentally investigates the circular perforated baffles of four different open area ratios 18.4%, 28.4%, 41.7% and 46.8%. He found that the baffle of open area ratio of 46.8% give the greatest performance advantage.
Fig. Plot of Nusselt number ratio versus the Reynolds number for circular and square perforated baffles.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 59
They concluded that increasing the open area ratio increase the performance
of the heater but in case of circular perforation it is not possible to increase the open
area ratio more than 46.8%. I opted square perforation and in it, it is possible to
increase the perforation to a limit of 60.69%.In this experimental study it is found that for the square perforated baffle of
open area ratio of 60.69% is the best one. By comparing it with circular perforated
baffle of 46.8% perforation, increment in Nusselt number is more by 21%.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 60
2000 4000 6000 8000 10000 12000 140000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2β=60.69% Perforated Baffles β=46.8% circular perforated baffles
Reynolds Number
(St/
Sts)
/(f/
fs)1/
3
Fig Comparison of thermo hydraulic performance of 60.69% square perforated baffles and 46.8% circular perforated baffles
By the comparing of thermo hydraulic performance of 60.69% square perforated baffles and 46.8% circular perforated baffles it is found that 60.69% square perforated baffles are thermo hydraulically better than 46.8% circular perforated baffles by 18%
April 18, 2023 M.E. Dissertation by Rahul Tripathi 61
CONCLUSIONSNusselt number enhancement by use of square perforated baffles of different
open area ratios was found to be in the range of 1.36 to 2.09 times to the
corresponding values of smooth plate for the Reynolds Number 3034 to 12003.
Increment in Friction factor (power penalty) was found 1.91-2.19, 1.77-2.10 1.49-1.7
for the baffle of open area ratio β=42.70%, β=51.98% and 60.69% respectively to the
corresponding values of smooth plate for the Reynolds Number 3034 to 12003.Nusselt number increases whereas friction factor decreases with increase of
Reynolds number. Values of friction factor and Nusselt number were highest for
perforated baffle of open area ratio β=42.70% and was lowest for perforated baffle of
open area ratio β=60.69% but . This is due to change in flow characteristics because of
baffles that cause flow separation, reattachments and generation of secondary flow.Thermo-hydraulic Performance Parameter for square perforated baffle are
found greater than unity it is found 1.87, 1.70, and 1.55 for baffle of open area ratio
β=60.69%, 51.98% and 42.70% respectively for different Reynolds number range
investigated in the study between 3034 to 12003.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 62
The ratio of Nusselt number of baffled duct to smooth duct was found in the
range of 1.59 to 1.88 for the Reynolds no. of 3034 to 12003 for square perforated
baffles of open area ratio of 60.69% but for circular perforated baffles of open area
ratio of 46.8% it was reported in the range of 1.45 to 1.55 by Maheshwari et. al,
2005. So it is concluded that square perforated baffles of 60.69% perforation are
better than circular perforated baffles of 46.8% perforation.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 63
REFERENCE1) F. Bayrak, H. F. Oztop and A. Hepbasli, Energy and exergy analyses of
porous baffles inserted solar air heaters for building applications, Energy and Buildings 57 pp 338–345, 2013.
2) S. Chamoli, N.S. Thakur and J.S. Saini, A review of turbulence promoters used in solar thermal systems, Renewable and Sustainable Energy Reviews 16 pp 3154– 3175, 2012.
3) P. Promvonge, Heat transfer and pressure drop in a channel with multiple 60° V-baffles, International Communications in Heat and Mass Transfer 37 pp 835–840, 2010.
4) P. Promvonge, W. Jedsadaratanachai and S. Kwankaomeng, Numerical study of laminar flow and heat transfer in square channel with 30_ inline angled baffle turbulators, Applied Thermal Engineering 30 pp 1292-1303, 2010.
5) R. Karwa, B. K. Maheshwari, Heat transfer and friction in an asymmetrically heated rectangular duct with half and fully perforated baffles at different pitches, International Communications in Heat and Mass Transfer 36 pp 264-268, 2009.
6) H. Esen, "Experimental energy and exergy analysis of a double-flow solar air heater having different obstacles on absorber plates," Building and Environment, vol. 43, no. 6, pp. 1046-1054, June 2008.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 64
7) Sen Zekai, Solar energy fundamentals and modeling techniques: atmosphere, environment, climate change and renewable energy, 1st ed. Springer-Verlag London Limited, 2008.
8) D. Rojas, J. Beermann, S. A. Klein, and D. T. Reindl, "Thermal performance testing of flat-plate collectors," Solar Energy, vol. 82, no. 8, pp. 746-757, August 2008.
9) B. S. Romdhane, "The air solar collectors: Comparative study, introduction of baffles to favor the heat transfer," Solar Energy, vol. 81, no. 1, pp. 139-149, January 2007.
10) M. Ramadan, A. El-Sebaii, S. Aboul-Enein, and E. El-Bialy, "Thermal performance of a packed bed double-pass solar air heater," Energy, vol. 32, no. 8, pp. 1524-1535, August 2007.
11) T. Liu, W. Lin, W. Gao, C. Luo, M. Li, Q. Zheng, and C. Xia, "A parametric study on the thermal performance of a solar air collector with a v-groove absorber," International Journal of Green Energy, vol. 4, no. 6, pp. 601-622, November 2007.
12) El-Sebaii AA, Aboul-Enein S, Ramadan MRI, El-Bialy E. Year round performance of double pass solar air heater with packed bed. Energy Convers Manage;48:990–1003. 2007
13) J. A. Duffie and W. A. Beckman, Solar Engineering of Thermal Processes, 3rd ed. Hoboken, NJ: Wiley, 2006.
14) M. Mittal and L. Varshney, "Optimal thermohydraulic performance of a wire mesh packed solar air heater," Solar Energy, vol. 80, no. 9, pp. 1112-1120, September 2006.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 65
15) T. Koyuncu, "Performance of various design of solar air heaters for crop drying applications," Renewable Enegy, vol. 31, no. 7, pp. 1073-1088, June 2006.
16) S. C. Tzeng, T. M. Jeng and Y. C. Wang, Experimental study of forced convection in asymmetrically heated sintered porous channels with/without periodic baffles, International Journal of Heat and Mass Transfer 49 pp 78–88, 2006.
17) R. Karwa, B. K. Maheshwari and N. Karwa, Experimental study of heat transfer enhancement in an asymmetrically heated rectangular duct with perforated baffles, International Communications in Heat and Mass Transfer 32 pp 275-284, 2005.
18) P. Naphon, Effect of porous media on the performance of the double-pass flat plate solar air heater, International Communications in Heat and Mass Transfer 32 pp 140–150, 2005.
19) C. Ho, H. Yeh, and R. Wang, "Heat-transfer enhancement in double-pass flatplate solar air heaters with recycle," Energy, vol. 30, no. 15, pp. 2796-2817, November 2005.
20) M. Sahu and J. Bhagoria, "Augmentation of heat transfer coefficient by using 90 degree broken transverse ribs on absorber plate of solar air heater," Renewable Energy, vol. 30, no. 13, pp. 2057-2073, October 2005.
21) K. H. Ko and N.K. Anand, Use of porous baffles to enhance heat transfer in a rectangular channel, International Journal of Heat and Mass Transfer 46 pp 4191-4199, 2003.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 66
22) H. Sugiyama, M. Akiyama, Y. Nemoto and F.B. Gessner, Calculation of turbulent heat flux distributions in a square duct with one roughened wall by means of algebraic heat flux models, International Journal of Heat and Fluid Flow 23 pp 13–21, 2002.
23) C. Kennedy, "Review of mid- to high-temperature solar selective absorber materials," National Renewable Energy Laboratory, Tech. Rep., 2002.
24) O. N. Sara, T. Pekdemir, S. Yapici and M. Yilmaz, Heat transfer enhancement in a channel flow with perforated rectangular blocks, International journal of heat and fluid flow 22 pp 509-518, 2001.
25) A. Hachemi, "Technical note: Comparative study on the thermal performances of solar air heater collectors with selective and nonselective absorber-plate," Renewable Enegy, vol. 17, no. 1, pp. 103-112, May 1999.
26) K. K. Matrawy, "Theoretical analysis for an air heater with a box-type absorber," Solar Energy, vol. 63, no. 3, pp. 191-198, September 1998.
27) A. Mohamad, "High efficiency solar air heater," Solar Energy, vol. 60, no. 2, pp. 71-76, February 1997.
28) C. Choudhury and H. P. Garg, "Performance of air-heating collectors with packed airflow passage," Solar Energy, vol. 50, no. 3, pp. 2005-221, March 1993.
29) V. K. Sharma, S. Sharma, R. B. Mahajan, and H. P. Garg, "Evaluation of a matrix solar air heater," Energy Conversion and Management, vol. 30, no. 1, pp. 1-8, 1990.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 67
30) N. Bansal, "Thermal performance of plastic film solar air and water heaters," International Journal of Energy Research, vol. 11, no. 1, pp. 35-43, Jan-March 1987.
31) A. Severson and et. al., "Solar air heater," U.S. Patent 4085 730, 1978.32) O. A. Schmidt, "Solar air heater," U.S. Patent 4085729, 1976.33) Vincent, "Dome solar air heater," U.S. Patent 4 236 507, 1977.34) S. Satcunanathan and S. Deonarine, "A two-pass solar air heater," Solar
Energy, vol. 15, no. 1, pp. 41-49, May 1973.35) C. L. Gupta and H. P. Garg, "Performance studies on solar air heaters," Solar
Energy, vol. 11, no. 1, pp. 25-31, January-March 1967.36) C. L. Gupta and H. P. Garg, "Performance studies on solar air heaters," Solar
Energy, vol. 11, no. 1, pp. 25-31, January-March 1967.37) A. Whillier, "Plastic covers for solar collectors," Solar Energy, vol. 7, no. 3,
pp. 148-151, July-September 1963.38) G. Lof, M. El-Wakil, and J. Chiou, "Residential heating with solar-heated air
- colorado solar house," ASHRAE Journal, vol. 5, no. 10, pp. 77-86, 1963.
April 18, 2023 M.E. Dissertation by Rahul Tripathi 68
Thank You
Any Queries