The objective of the study is to find a relation for the predicting convective and evaporative heat transfer coefficient and distillate output for 200 mm and 160 mm water depth. In this present work an attempt is to be made to use inner glass cover temperature instead of outer glass temperature as done by other researchers. The sides of the wall of the condensing cover are made up of FRP sheet to avoid heat losses from sides and to provide the desired inclination to the cover to the bath. It is exposed to room condition to increase the difference between water temperature and the condensing cover temperature to increase the heat transfer rate and thus the condensate output. The operating temperature range for the experiment is to be maintained at steady state from 50oC to 90oC by using a constant temperature bath. The yield obtained for a 1/2 hour intervals were used to determine the values of constant C and n and consequently convective and evaporative heat transfer coefficient. It is therefore expected that higher yield is to be obtained at higher temperature and at minimum depth of water

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IJMET
© I A E M E
EFFECT OF WATER DEPTH AT 30° INCLINED CONDENSING COVER IN
THE PERFORMANCE OF A WATER DISTILLATION SYSTEM IN AN
INDOOR SIMULATION
Abhishek Gaikwad1, Dhananjay Kumar Singh2, Abhay Singh3
Assistant Professor1, Scholars2, 3
Department of Mechanical Engineering, SSET, SHIATS, Naini, Allahabad
90
ABSTRACT
The objective of the study is to find a relation for the predicting convective and evaporative
heat transfer coefficient and distillate output for 200 mm and 160 mm water depth. In this present
work an attempt is to be made to use inner glass cover temperature instead of outer glass temperature
as done by other researchers. The sides of the wall of the condensing cover are made up of FRP sheet
to avoid heat losses from sides and to provide the desired inclination to the cover to the bath. It is
exposed to room condition to increase the difference between water temperature and the condensing
cover temperature to increase the heat transfer rate and thus the condensate output.
The operating temperature range for the experiment is to be maintained at steady state from
50oC to 90oC by using a constant temperature bath. The yield obtained for a 1/2 hour intervals were
used to determine the values of constant C and n and consequently convective and evaporative heat
transfer coefficient. It is therefore expected that higher yield is to be obtained at higher temperature
and at minimum depth of water.
Keywords: Distillate Output, Constant Bath Temperature, Dunkle, Convective Heat Transfer
Coefficient and Evaporative Heat Transfer Coefficient.
1. INTRODUCTION
There is an important need for clean, pure drinking water in many developing countries.
Often water sources are brackish (i.e. contain dissolved salts) and contain harmful bacteria and
therefore cannot be used for drinking. In addition, there are many coastal locations where sea water
is abundant but potable water is not available. Pure water is also useful for batteries and in hospitals
or schools. Distillation is one of many processes that can be used for water purification. This requires

2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME
an energy input, as heat, solar radiation can be the source of energy. In this process, water is
evaporated, thus separating water vapor from dissolved matter, which is condensed as pure water.
Requirement of distilled water for human beings is approx. 5 liters per person per day.
Therefore 2m2 of still are needed for each person served.
A simple solar still consisting of a water basin and a single glass cover is the first proposed
design of solar still that is easy to construct and it has virtually no operating cost. It is generally
classified as a passive and active distillation system
Solar stills should normally only be considered for removal of dissolved salts from water. If
there is a choice between brackish ground water and polluted surface water, it will usually be
cheaper to use a slow sand filter or other treatment device. If there is no fresh water then the main
alternatives are desalination, transportation and rainwater collection.
91
2. MATERIALS AND METHODS
The experimental set-up includes a constant temperature bath; the condensing covers at
inclination of 30°, digital temperature indicators, well calibrated thermocouples (by Zeal
Thermometer), two transparent pipes of small diameter and measuring jars. The output from the still
is collected through a channel. Two plastic pipes are connected to this channel to drain the distillated
water to an external measuring jar. The total capacity of the constant temperature bath is 40 L, and its
effective evaporative surface area is 300 mm × 400 mm. The water is heated by bath heating coils. It
is conducted from 50°C to 90°C (temperature range) for 200 mm and 160 mm water depth at
intervals of 5°C. Constant temperature bath was started at 8:30 am 1 hour before to take the readings
and to make sure that steady state has been reached after 1 hour at 9:30 am. After steady state
continuous readings for every 1/2 hour has been taken i.e., 10:00,10:30,11:00,11:30,12:00,12:30,1:00
under no fan conditions..i.e., natural mode. Same process has been applied for temperature range
50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C. Same method is applied for both water
depths at 30° inclinations of condensing cover.
Condensing cover is made of glass reinforced plastic (GRP) of 3 mm thickness. This glass
reinforced plastic is manufactured by sticking many layers of corrugated sheets with special
chemicals in such a manner that air is entrapped between its corrugated cavities, which provide a
high degree of insulation for heat flow, which is a highly desired quality for the solar still material.
Condensing cover made of plane glass of 4 mm thickness is fixed to the top of the vertical walls of
the stills using a rubber gasket on both side of glass and clamp fixed iron frames made of angles. To
avoid the spilling of basin water into the distillate channel and to prevent the contact of distillate
channel with the glass cover as well as with the water level.
Fig 1: Condensing cover of the solar distillation system

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME
92
3. INDENTATIONS AND EQUATIONS
In this experiment characteristic length is calculate by using half of the vertical height at
central axis of condensing cover, this is 89 mm for 200 mm water depth, 129 mm for 160 mm water
depth.
Difference = Height of bath – Height of water
= 230 – 160 = 70 mm (for 160 mm water depth)
= 230 – 200 = 30 mm (for 200 mm water depth)
Vertical height of smaller end of solar still (df) = 59 mm (for all cases of water depth)
Characteristic Length (Lv) = Difference + df
1. For 200 mm water depth = 59 mm + 30 mm = 89 mm = 0.089 m.
2. For 160 mm water depth = 59 mm + 70 mm = 129 mm = 0.129 m.
In general for heat transfer the following equations may be applied the rate of convective heat
transfer is described by the general equation.
(1)
Where:-
hcw = Convective heat transfer Coefficient
A = Evaporative surface area, m2
Tw = Evaporative surface temperature, C
Tg = Temperature of boundary from evaporation surface, C
Q = Rate of heat transfer by convection.
Convective heat transfer coefficient is not a property of material, it is dependent on the
following factors:-
1. Operating range of temperature and temperature difference.
2. Geometry of condensing cover.
3. Flow characteristics of the fluid.
4. Physical properties of the fluid within the operating temperature.
The relation of the non dimensional Nusselt number carries the convective heat transfer
coefficient as
(2)
(3)
Where:-
Nu = Nusselt Number
Gr = Grashof Number
Pr = Prandtl Number
Kv = Thermal conductivity

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME
Lv = Characteristics length of condensing cover, m
C n = Constant
The distillate output in kg from the unit can be obtained by the relation:
93
(4)
L = Latent heat of vaporization of water, J/kg
Aw = Surface area, m2
t = time interval in seconds
Rate of evaporative heat transfer
(5)
Evaporative heat transfer coefficient, W/m² °C
(6)
Pw = Partial saturated vapor pressure at water temperature, N/m²
Pg = Partial saturated vapor pressure at condensing cover temperature, N/m²
By substituting the expression for hcw from equation (3) into equation (6), we get
(7)
Substituting hew from equation (7) into equation (5), we get
(8)
Substituting qew from equation (8) into equation (4), we get
(9)
(10)
Where,
(11)
Taking the logarithm to both side of equation (10) comparing it with the straight line
equation.
y = mx + C (12)

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME
94
We get
(13)
(14)
By using linear regression analysis the coefficient in equation (12),
(15)
(16)
Where:-
N = number of experiment observations
Co = ln C; C = Exp (Co) (17)
n = m (18)
3.1 Temperature – dependent physical properties of vapor
1. Specificheat(Cp)
2. Density()
3. Thermal Conductivity(Kv)
4. Viscosity(μ)
5. Latent heat of vaporization of water (L)
6. Partial saturated vapor pressure at condensing cover temperature (Pg)
7. Partial saturated vapor pressure at water temperature (Pw)
8. Expansion factor ()

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME
95
4. FIGURES AND TABLES
Table 1: Average values calculated for 200 mm water depth
S.NO BATH TEMP
(°C)
WATER TEMP
(°C)
VAPOR TEMP
(°C)
INNER GLASS
TEMP (°C)
1 50 40.9 38.3 37.0
2 55 45.1 41.0 37.3
3 60 49.3 43.4 40.7
4 65 54.1 47.3 43.3
5 70 59.0 52.0 48.6
6 75 65.0 56.0 51.6
7 80 68.4 60.9 55.3
8 85 71.9 65.9 61.1
9 90 79.1 72.1 70.9
Table 2: Average values calculated for 160 mm water depth
S.NO BATH TEMP
(°C)
WATER TEMP
(°C)
VAPOR TEMP
(°C)
INNER GLASS
TEMP (°C)
1 50 38.9 36.0 34.4
2 55 45.0 40.9 37.3
3 60 49.0 43.0 40.0
4 65 53.6 47.3 43.0
5 70 58.9 51.7 48.6
6 75 63.0 55.3 51.3
7 80 69.0 60.0 55.3
8 85 74.0 65.1 61.1
9 90 78.7 69.9 65.7
Table 3: Comparison of Tw, Tv and Tg at different water depths.
S.NO Bath
Temp
Water Temp(°C) Vapor Temp(°C) Inner Glass Temp(°C)
At 200 mm At 160 mm At 200 mm At 160 mm At 200 mm At 160 mm
1 50 40.9 38.9 38.3 36.0 37.0 34.4
2 55 45.1 45.0 41.0 40.9 37.3 37.3
3 60 49.3 49.0 43.4 43.0 40.7 40.0
4 65 54.1 53.6 47.3 47.3 43.3 43.0
5 70 59.0 58.9 52.0 51.7 48.6 48.6
6 75 65.0 63.0 56.0 55.3 51.6 51.3
7 80 68.4 69.0 60.9 60.0 55.3 55.3
8 85 71.9 74.0 65.9 65.1 61.1 61.1
9 90 79.1 78.7 72.1 69.9 70.9 65.7

7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME
Table 4: Comparison of distillate output (Mew Practical) of present model
S.NO BATH TEMP (°C) Mew at 200 mm Mew at 160 mm
1 50 3.0 1.1
2 55 5.4 3.4
3 60 9.1 6.8
4 65 11.8 8.1
5 70 16.2 12.2
6 75 22.3 17.0
7 80 29.0 27.5
8 85 35.3 33.0
9 90 46.0 41.5
Table 5: Comparison of distillate output between Dunkle, present model theoretical value for 200
mm water depth
S.NO BATH TEMP (°C) Mew T(ml) Mew P (ml) Mew D (ml)
1 50 2.6 3.0 3.2
2 55 6.3 5.4 9.3
3 60 8.3 9.1 12.7
4 65 12.8 11.8 21.1
5 70 17.5 16.2 30.5
6 75 25.0 22.3 45.9
7 80 29.1 29.0 54.5
8 85 33.5 35.3 64.0
9 90 36.8 46.0 72.4
Table 6: Comparison of distillate output between Dunkle, present model theoretical value for
160 mm water depth
S.NO BATH TEMP (°C) Mew T(ml) Mew P (ml) Mew D (ml)
1 50 2.0 1.1 3.4
2 55 3.8 3.4 12.8
3 60 6.5 6.8 13.2
4 65 8.6 8.1 17.9
5 70 11.8 12.2 25.3
6 75 16.0 17.0 36.0
7 80 24.1 27.5 57.3
8 85 28.5 33.0 68.7
9 90 35.4 41.5 77.9
96

8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME
97
5. RESULTS AND DISCUSSION
Fig.2: Comparison of water temperature for 200 mm 160 mm water depth
Fig.3: Comparison of vapor temperature for 200 mm 160 mm water depth
Fig.4: Comparison of inner glass temperature for 200 mm 160 mm water depth

9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME

10. 98

11. Fig.5: Comparison of average values of practical distillate output recorded for different water depths
Fig.6: Comparison of distillate output between Dunkle, present model theoretical value for 200
mm water depth

12. Fig.7: Comparison of distillate output between Dunkle, present model theoretical value for 160
mm water depth

13. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 6, June (2014), pp. 90-100 © IAEME
99
6. CONCLUSIONS
The values obtained at higher operating temperatures for the convective and evaporative heat
transfer coefficients and values of unknown constant C and n obtained by the present experiment.
The present model gives more accurate and realistic values of distillate output as compared with the
theoretical values of distillate output. It obtains high distillate output at higher operating temperatures
and at higher water depth at 30° inclination of the condensing cover.
It is clearly seen (Fig.2,3 4) that at 30° inclination angle condensing cover the water
temperature for 200 mm water depth is higher than 160 mm up to 75°C bath temperature. Vapor
temperature and inner glass temperature for 200 mm water depth is higher than 160 mm water depth
at all stages of bath temperature. So here we are observing that the water temperature, vapor
temperature and inner glass temperature of the condensing cover for 200 mm water depth at
30°inclination angle of the condensing cover is maximum than the 160 mm water depth at
30°inclination angle of the condensing cover.
The distillate output obtained from present model at 200 mm water depth is much higher than
the values recorded for 160 mm water depth. It shows that at 30° inclination angle condensing cover
minimum the water depth maximum the distillate. (See fig. 5)
The values of Dunkle distillate output are higher in both the cases as our research is in indoor
simulation. The environment change and some losses of distillate output as well as not using stirrer is
also the drawbacks of this research which does not compete with the Dunkle.
Fig 6 7 shows that the theoretical and practical values are very close to each other in both
the cases. Practical values of distillate output are always greater than the theoretical values for both
the water depths. Its shows our results are genuine and satisfactory.
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14. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
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12. Later on Kumar and Tiwari (1996), “Estimation of a convective mass transfer”.
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× 105. However, this Relation has its own limitations which have been discussed by many
researchers.
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100
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Still Orientation on Productivity of Passive Solar Still”, International Journal of Mechanical
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