Homework-2
ME-6105, spring 2009
Group members: Muhammad Sadiq, Wei Ye, Khalil Gouia
Task 1: Identify the decision situation
1.1 Application domain
Design of a Thermo-Chemical system
The main objective of this project is to design a Solar Water Purifier that converts
many types of contaminated water such as well water and river water to ‘Potable Healthy
Drinking Water’.
1.2 Description of system:
By using the sun’s energy to convert impure water into clean, safe and healthy
drinking water, the Solar Water Purifier is an efficient solar evaporation water
purification system. Working at an ambient temperature between 35°C and 40°C, the
water within the Solar Water Purifier will heat to more than 85°C. This pasteurizing
effect partially kills bacteria and pathogens dramatically reducing the risk of water born
diseases. Before supplying water for drinking a few drops of chemical is added for the
bleaching of water. The quantity of bleach to be added is proportional to the flow rate.
Fig 1 Plumbing layout for arrays of solar water purifiers
Since the Solar Water Purifier uses the sun’s energy, it is very simple to use and it has no
moving parts, therefore there is hardly any maintenance. The cleaning maintenance is an
easy procedure which is generally completed by filling the panels with a solution of citric
acid in clean water and leaving the panels to soak for about 2 hours, then flushing to
remove the citric acid.
1.3 Description of specific design decision:
Our design decision is to choose the proper combination of different components for
providing the required quality of drinking water. One of the main objectives is to achieve
the best PPR (Performance Price Ratio). The overall performance will be evaluated by
the following important parameters.
Quality and quantity of water
This is the primary goal of our project to provide the desired amount of water with the
standard quality of drinking water.
Cost
In order to make it available for common man, not only the fabrication cost should be
reduced but also the operating cost should be minimized.
Reliability
The product should be robust and should provide the standard drinking water in different
environments
Environmental impacts
It should be environment friendly. The water waste should be minimized
1.4 Authority of decision maker in different scenarios:
Unfortunately, we can not control all of the design parameters. We have control on many
design parameters like cost, storage capacity, solar panel geometry and its area and the
flow rate. Beside these parameters, there are many design terms which are out of our
control e.g. the initial temperature of the water, sun shine, rain, and environmental
temperature.
Task 2: Determine an Objectives Hierarchy
In this project, according to the purpose of solar water purifier and designing it from the
aspect of an industry product, we have chosen our fundamental objective as to maximize
the PPR (Performance Price Ratio) of our system. From this point of view, it’s straightforward to come up with the following means objectives:
Performance, cost and reliability. Here it’s remarkable to make an emphasis on the
performance of our solar water purifier. As it is described in Task 1, one of our specific
design decisions is to provide standard quality drinking water with specific quantity, so
the performance of the system should at least take these two aspects into account. From
the branch of performance shown in Fig 2, the “flow rate” determines the quantity of the
final output of drinking water, while the “health” part concerns environmental effects and
quality of the water.
Maximize the
PPR of the
system
Maximize
Performance
Health
Flow rate
Maximize
Reliability
Minimize Cost
Minimize
Fabrication
cost
Minimize
Operating cost
Structure &
Configuration
Environmental
effects
Material
Electrical
operating cost
Quality of
water
Assembly
Mechanical
operating cost
Fig 2. Objectives Hierarchy of Solar Water Purifier
The objectives hierarchy of the solar water purifier gives us the outline of our
system, and it also allows us to have a clear idea of what we are pursuing and what we
are dealing with. To be more specific on this project, we can draw out the objectives
network of the solar water purifier, which is shown in Fig 3 below.
Although most of the relationships in this network diagram are quite obvious, it
still provides us a better understanding of our system. For example, the material of the
solar panel plays a very important role in our system. Obviously with better material we
can optimize the reliability of the solar water purifier, but from this diagram, we can see
that it will also increase the fabrication cost of the whole system, which leads to higher
total cost. So if we are going to choose the suitable material for the solar panel, we should
take consideration of both the fabrication cost and the reliability of the system and this
could remind us to make a trade-off of these two sides effects.
Material
Maximize PPR of the system
Maximize performance
Minimize
environmental
effects
Maximiz
e quality
of water
Select suitable
flow rate
Minimize
mechanical
operating cost
Minimize cost
Minimize
operating
cost
Minimize
electrical
operating cost
Maximize reliability
Minimize
fabrication
cost
Minimize
assembly cost
Select
suitable
structure
Select
suitable
material
Fig 3. Objectives Network of Solar Water Purifier
After we find out the fundamental and means objectives of our solar water
purifier, we can derive those attributes that measure them. However, when considering
the objectives, some of them are also related to the components of the system, e.g. when
we consider the performance and cost of the system, one important component is the
solar panel which is used to convert the solar energy into the heat for the flow, and this
will give us the attributes such as the panel material, its area and geometry. Similarly,
when the flow rate is concerned, we can think of the pump used here and also the water
tank. The former gives us the attributes of the flow rate, power consumption and head
pressure of the pump and the latter gives us the attributes of the storage or capacity of the
tank. So after we go through all of those objectives and components, we can decide all
the attributes of the solar water purifier in our design, which are listed in table 1.
After we thought about all these objectives and corresponding attributes, we
found out that, the most important objectives are to maximize the quality of the water and
minimize the cost of the system. As for those attributes, the kernel of our system is the
solar panel, so we need to design its attributes (the proper material, area …) with our
model and simulation. Moreover, we can see that some objectives cannot be simulated
like reliability of the solar water purifier and the structure configuration of the system.
Finally, in our design, we will focus on the following: flow rate, solar panel (material,
area and orientation angle) and the quality of the water.
Table 1. Attributes for objective measurements
objectives
Maximize performance
Minimize cost
Maximize reliability
Attributes
Quality of water, flow rate, solar panel efficiency
Solar panel area, material
System structure and configuration
Task 3: Identify the Design Alternatives
3.1 Level of details of decision alternatives
There are many decision alternatives which mainly include the design of solar panel.
The solar panel could be of different shapes and areas. Since the solar panel is the most
important part of the project, so varying its shape and area has a major influence on the
design of the whole project.
(i) The solar panel can be of curvilinear shape. It may have no motor to get rotation
during the day with the change of the sun location.
(ii) The solar panel can be of straight geometry. In this case, the efficiency of the
solar panel cannot be uniform during the whole day. Since the performance of
solar panel directly depends on the radiations that it gets from the sun, so it
varies the whole day. In order to get uniform heat, the panel should be rotated
in such a way that it remains perpendicular to sun all the times. By keeping
the panel perpendicular to the sun, we can ensure the maximum exposure area
and hence the maximum heat gain. For this purpose, we can install a motor to
provide uniform rotation to the solar panel.
(iii)In order to make sure that the water got boiled and it is completely purified, we
have to make sure that it got the proper amount of heat. In this case, there
could be an extra resistance, battery and solar panel in order to provide the
extra heat to water which is already treated by the solar panels. This heat is
just to assure that the water is properly heated and the treated water is good
enough to drink.
(iv) Most of the parameters are related to the heat transfer. Heat transfer is also a
function of the material properties. There could be different combinations of
materials to come up with a final design that optimizes the heat transfer and
minimizes the heat losses in flowing water.
Task 4: Identify the Structure of the Design Problem
4.1 Influence Diagram
As mentioned earlier, the geometry and area of the panel has a direct influence on
the solar energy transfer and cost. The solar energy depends upon sun shine. On a cloudy
day, the energy available from sun is reduced and it directly influences the amount of
solar energy transfer. Beside the solar energy transfer, the environmental temperature and
flow rate influence the water temperature. Pump should be powerful enough to supply the
desired/optimal flow rate which influences the water quality. It should be ensured that the
water is getting proper amount of heat to get purified. Water quality also depends on the
inlet water. In case of rain, the inlet water is dirtier and needs more purification.
Sun shine
Geometry of
the panel
Area of
panel
Material of
panel
Cloudy
day
Environmental
temperature
Cost
Solar energy
transfer
Reliability
Water
temperature
Utility
Water
quality
Pump power
Flow rate
Rain
Water tank
Fig. 4, Influence diagram of solar water purifier
Task 5: Simulation Scenario for an Energy-Based System Model
5.1 Modeling of the Design Objectives
To satisfy the design objective of maximizing the PPR of the Solar Water Purifier, we
have to model the following systems:
 Thermal energy transfer from sunshine to water;
 Fluid flow rate regulation;
 Fluid circuit from the input to the output;
 Electrical consumption of the pump;
 Pump power;


Sun orientation;
Properties of the solar panel (Geometry, conductance, orientation and
area).
At a further stage, it is possible to add a modeling of:
 An additional electric circuit that can improve the overall performance of
the system.
5.2 Energy-based models to be addressed later
The design team has identified two major energy aspects in Solar Water Purifier system
that needs to be addressed in the computer simulation and modeling. These include the
following:


Energy transfer from the sun to the water
Energy transfer from the electric energy to the pump.
5.3 Physical Phenomena & Energy-Domains





The planned model, as described in Section 5.1, will address many of the
physical phenomena associated with the system, such as:
Gravity (pumping water);
Heat transfer (conductance);
Water evaporation and condensation (Chemical phenomena);
Electric phenomena (resistance, heat generation and electric energy
storage) in case of addition of an electric circuit to the system.
5.4 significant assumptions
Several assumptions will be made to simplify this problem and make “inside” (and fit it into)
the scope of our project. The most significant assumptions will probably include:
 Uniform/Permanent sunlight during the functioning time of the system;
 The solar panels are always perpendicular to sunlight;
 The water is pure and healthy enough to be dunk after being evaporated, condensed
and treated with some drops of chemicals (such as bleach);
 Homogeneous heat distribution inside the system;
 Isothermal fluid circuit. It means that the a mbient temperature does not cool the
fluid inside the system.
Task 6: Plan Assessment
Currently, there are some uncertainties in our plan. The most significant one is
whether we will be able to calculate/model the efficiency of the energy transfer from the
sun to the system or not. The energy transfer efficiency depends largely not only on the
properties of the used material but also on the geometry of the panel and its orientation.
We will use our knowledge of conductance, geometry optics (optimize the focus of the
sunlight on the panels) and thermal systems to be as close as possible to the real physical
phenomena.
Besides, several external factors could have a impact on the final result. For instance, a
very low initial temperature of the water (at the input of the system) could slow down the
functioning of the system (low fluid rate at the exit).
Finally, the final tank at the exit of our system, where the drinkable water will be
stored should meet some standards. For example, this tank has to be made of stainless
steel in order to prevent the degradation of the quality of the water.
If it turns out that modeling the energy transfer from the sun to the system is so
difficult, maybe we can assume a fixed amount of energy transfer. Of course, this fixed
amount should be realistic but does not take into account relative positions of the panel
and the sun. This is equivalent to assume an average energy transfer amount. In
mathematical words, it would be an integration of heat transfer over a period of time
(probably the duration of sun presence per day).
Muhammad Sadiq
I am doing my PhD in the laboratory of “Design of multifunctional materials”.
We develop different models to describe the behavior of these materials. It’s a wonderful
opportunity for me to take advantage of this course and get maximum benefit of the core
ideas of designing, modeling and simulation. Further, I am trying to learn the concepts of
Dymola and apply it on my PhD project. I am working on the project of Lead Free
Soldering for harsh environments. I would develop different models that could give me a
feedback of the PCB’s (Printed Circuit Boards) developed with lead free solders.
Wei YE
The topic of this project attracted us when Muhammad proposed it at the first
group meeting. After we begin to work on the design of solar water purifier, I feel that I
am not only learning the modeling knowledge but also learning to interact with other
group members and try to make my own contribution to our project. I am very happy to
join this group and work with Muhammad and Khalil. During the work, we are
discussing and it makes me realize that, before someone stresses on his opinion, he must
understand the ideas of the other members. I’m looking forward that the project will be
done nicely with our diligent efforts and seamless communication.
Khalil GOUIA
The idea of modeling a Solar Water Purifier seduced me right from the beginning of our
group discussion. We discussed other systems but clearly the SWP was our favourite so
there was no big dilemma to opt for it.
The idea to provide pure water for the world’s poorest people attracted me. Clearly, we
are not manufacturing this product and not providing help for these peoples. However,
just “simulating” the system is satisfactory enough for me at this level.
Besides, the SWP involves several physical phenomena such as gravity, heating,
evaporation, condensation, etc. This assumes the learning of many new concepts for an
ECE student…