PROFESSIONAL RESPONSIBILITY: THE ROLE OF ENGINEERING IN SOCIETY

We argue that the practice of engineering does not exist outside the domain of societal interests. That is, the practice of engineering has an inherent (and unavoidable) impact on society. Engineering is based upon that relationship with society (inter alia).

An engineer's conduct (as captured in professional codes of conduct) toward other engineers, toward employers, toward clients, and toward the public is an essential part of the life of a professional engineer, yet the education process and professional societies pay inadequate attention to the area. If one adopts Skooglund's definition of professional ethics (1) (how we agree to relate to one another), then the codes of professional conduct lay out a road map for professional relationships. As professionals, engineers need to internalize their codes and to realize that they have a personal stake in the application of codes as well as the process of developing the codes. Yet, most engineers view professional codes as static statements developed by "others" with little (or no) input from the individual engineer. Complicating the problem, questions of professionalism (such as ethics) are frequently viewed as topics outside the normal realm of engineering analysis and design. In reality, professional responsibility is an integral part of the engineering process.

HVAC Emerging trend of Mechanical Engg..

We all know 2016 started off with a bang for the HVAC industry with the biggest ever AHR Expo in January. Since then, we’ve been hearing plenty about the newest products and trends taking over the industry. How will Iot shape how equipment communicates across other equipment and to manufactures? How will ever-shifting energy standards affect how HVAC equipment manufacturers produce new equipment and what customers are looking for when they buy? 

If you’re running an HVAC contractor business, these are the sort of questions you need answers to in order to stay on top of your customers’ wants and compete in the the ever-shifting, ever-more demanding HVAC service sphere. 

After scouring the web for the top industry executive resources for tips to try and trends to watch out for in 2015, here’s what we came up with: 

1.HVAC will Get Smarter
2. HVAC Businesses are on the Lookout for Connected, Multifaceted Software to Manage Their Business Processes
3. Construction Will Continue to Recover, which Will Lead to Growth in New HVAC System Installations

·         Non-residential: According at an article in PM Magazine, the U.S. Commerce Dept. reports that construction spending for nonresidential projects through November 2014 rose 4.2% from the year before, with lodging, office, commercial and sewage/waste disposal construction rising 11.3%, 14.7%, 8.4% and 13.6%, respectively.

·         Residential: After a yearlong study of its role in Residential HVAC, ASHRAE announced a new emphasis on Residential, the effects of which will take form as 2015 progresses.

4. HVAC Maintenance and Service will Become more Efficient through Mobile
Conclusion: Take Advantage of this Year’s Opportunity in Service with the Right Technology

In his article, “Get Smart: 5 Trends Driving the HVAC Industry in 2016,” Hal Conick of HPAC Engineering points out that there’s more smart technology than ever and HVAC is a leading industry in the movement. Smart thermostat technology, smart equipment integration, and IoT technology allows HVAC contractors to automate much of their sales and service processes, giving managers more time to leverage the financial benefits of effective asset management. 

And not only are the machines and controls getting smarter, Conick points that that EVERYTHING is getting smarter: “smarter technology will be taking center stage this year as everyone continues to battle for efficiency. There are more points of data than ever, allowing for better measurement via big data and analytics.” 

So while customers are looking for smarter equipment, HVAC contractors are also finding smart technology-driven ways to manage their businesses. 

In his post-AHR Expo article, “Simplistic Software, Comprehensive Connectivity in Demand,” Herb Woerpel of The News highlights a trend service organizations in every industry are talking about: what to look for in an enterprise mobile software solution: “Contractors are always on the lookout for simple-to-use, all-in-one software solutions that make the job of delivering indoor comfort easier and more effective.” Woerpel warns that contractors who ignore new technology do so at their own peril. 

While finding the perfect software to manage your HVAC contractor business is not a new theme in 2016, this year it’s crucial for service businesses to adopt strong mobile solutions in order to get ahead. 

With an increase in new building construction inherently comes an increase in new HVAC unit installation. In both residential and non-residential, HVAC equipment installation will be on the rise in 2016.

The HVAC professionals blog, Just Venting, highlights several expert takes on industry trends for 2016. Some of the most common and pressing included those that feature how HVAC maintenance will become more efficient and service more personal. 

According to Goodway Technologies Corp. president, Tim Kane, “Continued product innovation and improved processes in the HVAC maintenance field will yield some exciting new gains in unit efficiency and success of preventative maintenance programs.” 

Goodway digital marketing and business development director, Tim Robb, highlights how mobile applications are helping contractors improve preventive maintenance programs, which are increasing in importance since: “Companies that can specialize in these maintenance technologies are well positioned for growth as these technologies begin to dominate the commercial HVAC landscape.” 

As HVAC units become more complex, establishing regular preventive maintenance programs with technicians who understand how to service them will become more important. Industry experts and research firms are finding that technology and mobile apps are driving successful service programs in 2016. 

As the construction industry continues to recover, HVAC needs to keep up with the demand for new unit installations and efficient maintenance programs. Adopting the latest technology and advancements in mobile is one way to make your service team more productive. Mobility enables timely information delivery, more accurate dispatch to the field, stronger profits per visit, and increased worker safety. Take advantage of today’s opportunity in service by using the most advanced technology to provide the best service for your customers. 

Electricity generation from an exhaust heat recovery system utilising thermoelectric cells and heat pipes

The internal combustion engine used in majority of cars at the present time do not use their fuel input very efficiently. A majority of this energy is dissipated as heat in the exhaust. The related problems of global warming and dwindling fossil fuel supplies has led to improving the efficiency of the internal combustion engine being a priority. One method to improve the efficiency is to develop methods to utilise heat in car exhausts that is usually wasted. Two promising technologies that were found to be useful for this purpose were thermoelectric cells (TECs) and heat pipes. Therefore this project involved making a bench type, proof of concept model of power production by thermoelectric cells using heat pipes and hot engine exhaust gases. 8 cells were used and managed to produce 6.03 W when charging the battery. The system operated with a heat to electricity conversion efficiency of 1.43%. The discrepancy between the actual efficiency and the predicted efficiency of 2.31% is most likely due to the cells not operating at their optimum voltage. The predicted efficiency is approximately 1/9 of the Carnot efficiency and the actual efficiency is approximately 1/15 of the Carnot efficiency. 

THERMO ACOUSTIC REFRIGERATION

Thermo acoustic have been known for over years but the use of this phenomenon to develop engines and pumps is fairly recent. Thermo acoustic refrigeration is one such phenomenon that uses high intensity sound waves in a pressurized gas tube to pump heat from one place to other to produce refrigeration effect. In this type of refrigeration all sorts of conventional refrigerants are eliminated and sound waves take their place. All we need is a loud speaker and an acoustically insulated tube. Also this system completely eliminates the need for lubricants and results in 40% less energy consumption. Thermo acoustic heat engines have the advantage of operating with inert gases and with little or no moving parts, making them highly efficient ideal candidate for environmentally safe refrigeration with almost zero maintenance cost.

A thermo acoustic device basically consists of heat exchangers, a resonator, and a stack (on standing wave devices) or regenerator (on travelling wave devices). Depending on the type of engine a driver or loudspeaker might be used as well to generate sound waves. Compared to vapor refrigerators, thermo acoustic refrigerators have no ozone-depleting or toxic coolant. Modern research and development of thermo acoustic systems is largely based upon the work of Rottand later Steven Garrett, and Greg Swift, in which linear thermo acoustic models were developed to form a basic quantitative understanding, and numeric models for computation. Commercial interest has resulted in niche applications such as small to medium scale cryogenic applications.The aim of this report to study the basics a thermoacoustic refrigerator, its components and design.

From creating comfortable home environments to manufacturing fast and efficient electronic devices, air conditioning and refrigeration remain expensive, yet essential, services for both homes and industries. However, in an age of impending energy and environmental crises, current cooling technologies continue to generate greenhouse gases with high- energy costs.

Thermoacoustic refrigeration is an innovative alternative for cooling that is both clean and inexpensive. Thermo acoustic devices take advantage of sound waves reverberating within them to convert a temperature differential into mechanical energy or mechanical energy into a temperature differential.Refrigeration relies on two major thermodynamic principles. First, a fluid’s temperature rises when compressed and falls when expanded. Second, when two substances are placed in direct contact, heat will flow from the hotter substance to the cooler one. While conventional refrigerators use pumps to transfer heat on a macroscopic scale, thermoacoustic refrigerators rely on sound to generate waves of pressure that alternately compress and relax the gas particles within the tube.

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SOLAR SAIL

Solar sails are a form of spacecraft propulsion using the  radiation pressure from stars to push large ultra-thin mirrors to high speeds. Light sails could also be driven by  energy  beams to extend their range of operations, which is strictly beam sailing rather than solar sailing. Solar sail craft offer the possibility of low-cost operations combined with long operating lifetimes. Since they have few moving parts and use no propellant, they can potentially be used numerous times for delivery of payloads. Solar sails use a phenomenon that has a proven, measured effect on spacecraft. Solar pressure affects all spacecraft, whether in  interplanetary space or in orbit around a planet or small body. A typical spacecraft going to Mars, for example, will be displaced by thousands of kilometres by solar pressure, so the effects must be accounted for in trajectory planning, which has been done since the time of the earliest interplanetary spacecraft of the 1960s. Solar pressure also affects the  attitude of a craft, a factor that must be included in  spacecraft design. The total force exerted on an 800 by 800 meter solar sail, for example, is about 5 newtons at Earth's distance from Sol, making it a low-thrust  propulsion system, similar to spacecraft propelled by  electric engines. The concept of a huge, ultra-thin sail unfurling in space, using the pressure of sunlight to provide propellant-free transport, hovering and exploration capabilities, may seem like the stuff of science fiction. Now, a NASA team developing the "In-Space Demonstration of a Mission-Capable Solar Sail" or Solar Sail Demonstrator for short intend to prove the viability and value of the technology in the years to come.

Several upcoming missions aim to harness the subtle push of sunlight, using gossamer  "solar sails" to cruise through the heavens like boats through the sea. Such propellant-free propulsion could take craft cheaply and efficiently to a variety of destinations, from locations in near-Earth space to the edge of the solar system and beyond, advocates say.

A spacecraft equipped with a sail 1,300 feet (400 meters) wide, for example, could travel 1.3 billion miles (2.1 billion kilometers) per year, allowing it to escape the sun's sphere of influence in just a decade or so, according to researchers behind the Interstellar Probe, a NASA concept mission proposed about 15 years ago.

As the photons of sunlight strike the sail and bounce off, they gently push the sail along by transferring momentum to the sail. Because there are so many photons from sunlight, and because they are constantly hitting the sail, there is a constant pressure (force per unit area) exerted on the sail that produces a constant acceleration of the spacecraft. Although the force on a solar-sail spacecraft is less than conventional chemical rockets, such as the space shuttle, the solar-sail spacecraft constantly accelerates over time and achieves a greater velocity. It's like comparing the effects of a gust of wind versus a steady, gentle breeze on a dandelion seed floating in the air. Although the gust of wind (rocket engine) initially pushes the seed with greater force, it dies quickly and the seed coasts only so far. In contrast, the breeze weakly pushes the seed during a longer period of time, and the seed travel farther. Solar sails enable spacecraft to move within the solar system and between stars without bulky rocket engines and enormous amounts of fuel.

In order for sunlight to provide sufficient pressure to propel a spacecraft forward, a solar sail must capture as much Sunlight as possible. This means that the surface of the sail must be big – very big. Cosmos 1 is a small solar sail intended only for a short mission. Nevertheless, once it spreads its sails even this small spacecraft will be 10 stories tall, as high as the rocket that will launch it. Its eight triangular blades are 15 meters (49 feet) in length, and have a total surface area of 600 square meters (6500 square feet). This is about one and a half times the size of a basketball court.

 PRINCIPLE OF SOLAR SAIL

The fundamental principle of solar sailing is illustrated in Figure 2. If the solar sail is a perfect reflector, the combined impulse of the incident and reflected photons produce a resulting force on the solar sail that is nearly normal to the plane of the sail. By orienting the sail such that the resulting force opposes the motion of the spacecraft’s orbit, the sail causes the spacecraft to lose orbital angular momentum and spiral inwards towards the attracting body. On the other hand, if the resulting force vector is aligned such that the net force is increasing the orbital angular momentum, the orbit’s energy grows, and the spacecraft spirals out from the sun. Changing the angle of the sail’s surface normal relative to the sun can thus actuate the solar sail’s orbit in a desired manner

 The Basic Principle behind Solar Sailing

The reflective nature of the sails is key. As photons (light particles) bounce off the reflective material, they gently push the sail along by transferring momentum to the sail. Because there are so many photons from sunlight, and because they are constantly hitting the sail, there is a constant pressure (force per unit area) exerted on the sail that produces a constant acceleration of the spacecraft. Although the force on a solar-sail spacecraft is less than a conventional chemical  rocket, such as the  space shuttle, the solar-sail spacecraft constantly accelerates over time and achieves a greater velocity.

  Electromagnetism

Sunlight exerts a very gentle force. A square mirror 1 kilometer on a side would only feel about 9 Newton or 2 pounds of force. Fortunately, space is very empty and clean compared to Earth, so there is plenty of room for a 1 kilometer wide sails to maneuver, and there is no noticeable friction to interfere with your 9 Newton of thrust.

  TACKING OF SOLAR SAILS

As every sailor knows, to tack or beat a sailboat is to sail the boat at an angle into the wind. Solar sails can do their own form of tacking by using the force of sunlight pushing out from the sun to actually move closer the sun.

Spacecraft, including solar sails, travel around the sun in orbits. A spacecraft that is propelled by a rocket can shrink its orbit, and thus move closer to the sun, by thrusting the rocket in the opposite direction as the spacecraft's motion. Similarly, if a solar sail can produce thrust in the opposite direction as the spacecraft's motion, its orbit will also shrink. By producing thrust in the same direction as the spacecraft's motion, the orbit will expand, and the spacecraft will move farther away from the sun.

 Travelling towards the sun

 Travelling away from the sun

Solar sails come in three major designs:

• Square sail

• Heliogyro sail

• Disc sail 

SQUARE SAIL

 Concept design of 3-axis stabilized square solar sail system.

 HELIOGYRO SAIL

 Concept design of heliogyro solar sail system.

 SAIL DEPLOYMENT

Concept of solar sail deployment system

PROJECTS OPERATING OR COMPLETED

IKAROS 2010

On 21 May 2010, Japan Aerospace Exploration Agency (JAXA) launched the world's first interplanetary solar sail spacecraft "IKAROS" (Interplanetary Kitecraft Accelerated by Radiation of the Sun) to Venus.

  NANO SAIL D 2010

Nano sail D 2010

PROJECTS IN DEVELOPMENT OR PROPOSED

  SUN JAMMER

 LIGHT SAIL

CONCLUSION 

The major advantage of a solar-sail spacecraft is its ability to travel between the planets and to the stars without carrying fuel. Solar-sail spacecraft need only a conventional launch vehicle to get into Earth orbit, where the solar sails can be deployed and the spacecraft sent on its way. These spacecraft accelerate gradually, unlike conventional chemical rockets, which offer extremely quick acceleration. So for a fast trip to Mars, a solar-sail spacecraft offers no advantage over a conventional chemical rocket. However, if you need to carry a large payload to Mars and you're not in a hurry, a solar-sail spacecraft is ideal. As for traveling the greater distances necessary to reach the stars, solar-sail spacecraft, which have gradual but constant acceleration, can achieve greater velocities than conventional chemical rockets and so can span the distance in less time. Ultimately, solar-sail technology will make interstellar flights and shuttling between planets less expensive and therefore more practical than conventional chemical rockets. 

International space agencies and some private corporations have proposed many methods of transportation that would allow us to go farther, but a manned space mission has yet to go beyond the moon. The most realistic of these space transportation options calls for the elimination of both rocket fuel and rocket engines replacing them with sails.  Solar sail technology will eventually play a key role in long-distance  NASA missions. But just how far will these solar sails be able to take us and how fast will they get us there is still unanswerable. As we found out in the last section, solar sails would not initially be driven by the amount of force that is used to launch the space shuttle.

NASA believes that the exploration of space is similar to the tale of the "Tortoise and the Hare," with rocket-propelled spacecraft being the hare. In this race, the rocket-propelled spacecraft will quickly jump out, moving quickly toward its destination. On the other hand, a rocket less spacecraft powered by a solar sail would begin its journey at a slow but steady pace, gradually picking up speed as the sun continues to exert force upon it. Sooner or later, no matter how fast it goes, the rocket ship will run out of power. In contrast, the solar sail craft has an endless supply of power from the sun.

Additionally, the solar sail could potentially return to  Earth, whereas the rocket powered vehicle would not have any propellant to bring it back.                 

As it continues to be pushed by sunlight, the solar sail-propelled vehicle will build up speeds that rocket powered vehicles would never be able to achieve. Such a vehicle would eventually travel at about 56 miles/sec (90 km/sec), which would be more than 200,000 mph (324,000 kmph). That speed is about 10 times faster than the space shuttle's orbital speed of 5 miles/sec (8 km/sec). To give you an idea how fast that is, you could travel from New York to Los Angeles in less than a minute with a solar sail vehicle traveling at top speed. 

If NASA were to launch an interstellar probe powered by solar sails, it would take only eight years for it to catch the Voyager 1 spacecraft (the most distant spacecraft from Earth), which has been traveling for more than 20 years. By adding a laser or magnetic beam transmitter, NASA said it could push speeds to 18,600 miles/sec (30,000 km/sec), which is one-tenth the  speed of light. At those speeds, interstellar travel would be an almost certainty.

DESIGN AND FABRICATION OF BOUNDARY LAYER VISUALISATION APPARATUS

Flow visualization techniques can be classified in to three. They are particle image velocimetry, optical methods and stream linevisualization.

 Particle image velocimetry (PIV) method uses highly sophisticated software and extremely sensitive sensors to follow tracer particles which are introduced into the flow. The fundamental assumption is that the velocity of the particles and fluid is identical. The particle tracer can be solid, liquid or gas. For e.g. dust, magnesium (Mg), Al2O3, TiO2, aluminum, polystyrene, cosmetic powder, licopodium, cigarette smoke, metaldehyde, atomized DOP, glass sphere, marble dust, oil drops, water drops, hydrogen, gas, helium bubbles etc . The diameter of the particle is between 0.1 to 20 microns. PIV produces highly accurate quantitative measurement but it is not a robust system for qualitative flow visualization.

            In optical method flow can be visualized and viewed with the naked eye.  It is known that changes in the pressure and thermal energy of a body of gas will lead to a change of its refractive index. By shining a laser beam through or creating a shadow of the flow, the changes in the refractive index can be seen. Optical methods are an easy and effective way to visualize flow two dimensionally. 

Streamline flow visualization works by introducing smoke or dye into the main flow medium, resulting in streamlines. It is important to have dye solution with the same specific weight as working fluid .

Another type of classification includes surface flow visualization and off-the-surface visualization. Surface flow visualization involves tufts, fluorescent dye, oil or special clay mixtures, which are applied to the surface of a model andthe other type includes tracers such as smoke particles, oil droplets or helium filled soap bubbles.

The main problems associated with the flow visualization techniques are flow  affected by experimental setup itself, time consuming, not all phenomenon can be visualized and are expensive .Many flows are very sensitive to small changes of geometry or in other boundary condition; small changes in condition may cause a very large shift in flow pattern.such sensitivity to small changes usually means that the theoretical equations cannot be solved with sufficient  accuracy to predict the shift in flow pattern, even if all the condition affecting the flow were known with accuracy.

Considering the flow visualization of liquid common methods can be grouped in to five major types. They are marker methods, optical methods, wall trace methods, birefringence method and self visible phenomenon .Marker method is used for visualizing low speed flow while optical method is used for high speed flow. Water trace method (such as Visualization using dye, Visualization by different small particles ) and birefringence method can be used for either low speed or high speed flow.

Time line, streak line, path line plays an important role in fluid flow visualization technique . A timeline is a set of fluid particles that form a line at an instant in time. A streak line is the locus of particles which have passed through a prescribed point during a specific time interval and path line is the locus of points traversed by a given fluid particle during some specific time interval (actual path of particles during this time. Time lines can be made visible by injecting the foreign material perpendicular to the flow. A streak line arises when dye is injected in the flow from a fixed position for a period of time. A path line can be obtained by using light emitting particle. He added that in steady state path lines and streak lines are identical to stream line.

Even though the injection of foreign material to the flow is conceptually simple this technique requires careful application. The density and temperature of the injecting material should be equal to that of flow at the injection spot. The scene becomes cluttered when the number of stream lines increased . A flow visualization setup developed at Northern University that was inexpensive, multi functional and convenient for use in engineering department. Their critical requirements include size safety and cost. The product was fit for single person to operate and multi person to see what is going within the system. They used water as the flowing medium and potassium permanganate as the dye . Silver glitter dust using in cosmetic industry can be used as a foreign material. Because glitter dust is easily available, float in water and has good optical qualities. Good flow visualization image could be obtained when coupled with camera at good lighting conditions .

BOUNDARY LAYER

 Hydrodynamic boundary layer

When the solid body is immersed in a flowing fluid, there is a narrow region of the fluid in the neighborhood of the solid body, where the velocity of the fluid varies from zero to free stream velocity. This narrow region of fluid is called boundary layer. The boundary layer is the portion of fluid adjacent to the surface of an object around which the fluid is flowing. The layer is the boundary between the object and the free-flowing fluid. Due to its contact or proximity to the object, the boundary layer is affected by the object and displays flow properties that are different from those of fluid flowing farther away from the object. The boundary area is that of viscous flow, which is subject to friction from the surface of the object. . We can mainly divide the boundary layer zone in to laminar, transition, turbulent and laminar sub layer zones.

 Types of boundary layer

1. Laminar boundary layer
2. Turbulent boundary layer
3. Laminar sub layer

Boundary layer over a flat plate

Laminar boundary layer

For defining the laminar boundary layer consider the flow of fluid, having free stream velocity (U), over a smooth thin plate which is flat and placed parallel to the direction for free stream of fluid. Let us consider the flow with zero pressure gradients on one side of the plate, which is stationary. The velocity of the fluid on the surface of the plate should be equal to the velocity of the plate. But plate is stationary and hence velocity of the fluid on the surface of the plate is zero.

But at a distance away from the plate, the fluid having certain velocity. Thus a velocity gradient is set up in the fluid near the surface of the plate. This velocity gradient developed shear resistance, which retards the fluid, thus the fluid with free stream velocity (U) is retarded in the vicinity of the solid surface of the plate and the boundary layer region begins at the leading edge. At subsequent points downstream the leading edge, the boundary layer region increases because of the retarded fluid is further retarded. This is also referred as the growth of boundary layer. Near the leading edge of the surface of the plate, where the thickness is small, the flow in the boundary Layer is laminar though the main flow is turbulent. This layer of fluid is called laminar boundary layer. In this regions Reynolds number (Re) will be always less than 5×105when the flow is over the flat plate.

Turbulent boundary layer

If the length of the plate is more than the distance x, the thickness of the boundary layer will go on increasing in the downstream direction. Then the boundary layer becomes unstable and the motion of the fluid within it is disturbed and irregular which lead to transition from laminar to turbulent boundary layer. Further downstream the transition zone, the boundary layer is turbulent and continues to grow in thickness. This layer of boundary is called turbulent boundary layer. In this regions Reynolds number (Re) will be always greater than 5×105 when the flow is over the flat plate.

Laminar sub layer

This is the region in the turbulent boundary layer zone, adjacent to the solid surface of the plate. In this region the velocity variation is influenced by only by viscous effects. Though the velocity distribution would be a parabolic curve in the laminar sub layer zone.

 

 Completed design

EXPERIMENTAL CATALOGUE

To Observe Flow Patterns & To Draw Flow Patterns

AIM-: To observe the hydrodynamic boundary layer formation on different shape and to draw Flow Patterns.

Apparatus-: Flow Visualization Set up, dye, obstacle, water etc.

BOUNDARY LAYER

            When the solid body is immersed in a flowing fluid, there is a narrow region of the fluid in the neighborhood of the solid body, where the velocity of the fluid varies from zero to free stream velocity. This narrow region of fluid is called boundary layer.

TYPES OF BOUNDARY LAYER

1. LAMINAR BOUNDARY LAYER
2. TURBULENT BOUNDARY LAYER
3. LAMINAR SUB LAYER

1. LAMINAR BOUNDARY LAYER

For defining the laminar boundary layer consider the flow of fluid, having free stream velocity (U), over a smooth thin plate which is flat and placed parallel to the direction for free stream of fluid. Let us consider the flow with zero pressure gradients on one side of the plate, which is stationary. The velocity of the fluid on the surface of the plate should be equal to the velocity of the plate. But plate is stationary and hence velocity of the fluid on the surface of the plate is zero.

But at a distance away from the plate, the fluid having certain velocity. Thus a velocity gradient is set up in the fluid near the surface of the plate. This velocity gradient developed shear resistance, which retards the fluid, thus the fluid with free stream velocity (U) is retarded in the vicinity of the solid surface of the plate and the boundary layer region begins at the leading edge. At subsequent points downstream the leading edge, the boundary layer region increases because of the retarded fluid is further retarded. This is also referred as the growth of boundary layer. Near the leading edge of the surface of the plate, where the thickness is small, the flow in the boundary Layer is laminar though the main flow is turbulent. This layer of fluid is called laminar boundary layer

2.TURBULENT BOUNDARY LAYER

If the length of the plate is more than the distance x, the thickness of the boundary layer will go on increasing in the downstream direction. Then the boundary layer becomes unstable and the motion of the fluid within it is disturbed and irregular which lead to transition from laminar to turbulent boundary layer. Further downstream the transition zone, the boundary layer is turbulent and continues to grow in thickness. This layer of boundary is called turbulent boundary layer.

1. LAMINAR SUB LAYER

This is the region in the turbulent boundary layer zone, adjacent to the solid surface of the plate. In this region the velocity variation is influenced by only by viscous effects. Though the velocity distribution would be a parabolic curve in the laminar sub layer zone.

Procedure-:

Water is supplied at one end of the casing, and it is allowed to flow over the glass. Dye bottle is fixed over a stand provided on casing. Dye (solution of Potassium Permanganate) is prepared and filled in die bottle

Dye enters the Dye manifold & then into the main flow through the small tube.

Obstacles of various shapes can be kept on glass.

The flow of water is maintained very slow & dye is allowed to flow with same velocity of water through the obstacle. As the water flow speed is very slow, we can observe the Laminar flow clearly in which laminas remains separate. Record the boundary layer formation. And then, repeat the procedure by changing shape of the obstacle.

Precautions-:

• Avoid contact with the working setup
• Maintain constant velocity between the water and die
• Restrict the air disturbance

RESULT:

Design and fabrication of Boundary layer visualization apparatus is successfully done.

• Hydraulic boundary layer for different shaped obstacles such as square, disc, and triangle were visualized, It has been found that the obtained shapes of boundary layer is very similar to theoretical shape.
• The obtained boundary layer formation of the obstacle at a velocity 0.112 m/s are as shown below.

Observed result  

CONCLUSION AND FUTURE SCOPE

The design and fabrication of Boundary layer visualization apparatus is successfully done.Velocity of the points which facing the flow will be always zero. The region obtained between obstacle and the die due to the existence of high pressure. And the vortex street has been identified due to the negative pressure.

The Project can be improved by

• Constructing a device which is capable of maintaining the velocities of dye and the fluid medium equal.
• Introducing a pitot tube to measure the velocity in the boundary layer so that we can plot the velocity profile.
• Introducing a transparent film over the boundary layer will overcome the effect of wind
• Calculation of boundary layer thickness has some limitation using theoretical method , So that we can introduce new setup.

DESIGN AND REALIZATION OF A SOLAR ADSORPTION REFRIGERATION MACHINE POWERED BY SOLAR ENERGY

Among the thermal processes of solar energy, solar refrigeration is one of the most suitable processes for storage, transport and marketing of energy. Among its numerous applications, the adsorption refrigerating machine seems to be an interesting alternative to conventional refrigeration systems in isolated regions, where conventional electrical power is unavailable. However, these machines are not fully automatic because of manual interventions needed for its operation.

The adsorption refrigeration system using an adsorbent /adsorbent working pair, is composed by different elements: a solar collector which contains the adsorbent /adsorbate working pair (in our case it is the activated carbon/methanol), a condenser where the adsorbate vapor condenses, an evaporator where water plates are laid out to be transformed into ice, in order to store cold for deferred use, and a refrigeration compartment.

The development of solar adsorption refrigeration systems appeared in the late 1970s, following the needs of non-oil countries, and several studies have been undertaken  since that time. Marmottant have studied and manufactured in 1990 a solar ice maker based on adsorption/desorption phenomena which operates intermittently and uses the working pair activated carbon /methanol. A solar adsorption refrigerator was built and tested in 2000 by Hildbrand in Switzerland using the pair Silica gel-Water. The system does not contain any movable part, and the author has obtained a COP between 0.12 and 0.23. Mayor  made an adsorption refrigerator working with the pair silica gel/water. This refrigerator is characterized by its compactness and its ability to be transported. The working volume of this refrigerator is 100 liters, the surface of the solar collector is 1m2 and its mass reaches 150 kg. This machine was built with materials to minimize the mass of the system. For better insulation of refrigeration compartment, vacuum panels (VIPs) were used, while a large storage volume capacity was maintained. An independent valve was developed to eliminate any human manipulation. Abu-Hamdeh investigated some work on solar adsorption refrigerator using parabolic trough collector and uses olive waste as adsorbent with methanol as adsorbate. The author showed, from the COP values, that the optimal adsorbent mass varied between 30 and 40 kg while the optimum tank volume varied between 0.2 and 0.3 m3. Wang  developed a novel two-stage adsorption freezing machine, which is powered by the heat source with the temperature below 100°C. The composite adsorbents of CaCl2 and BaCl2 developed by the matrix of expanded natural graphite were chosen as adsorbents. The experimental results showed that the optimal coefficient of performance (COP) and specific cooling power (SCP) at 15 °C refrigeration are 0.127 and 100W.kg-1, respectively. COP and SCP increased with the increasing heat source temperature and decreased with the decreasing evaporating temperature.

The goal of this work is to develop an adsorption refrigeration system for cold production under Algeria’s climate. Experimental test was done on a prototype elaborated in laboratory in order to test the feasibility of the machine. Software was elaborated, giving an estimate of the activated carbon and methanol quantities in the adsorption refrigerator, the energy balance and the design of its various components, as well as performance coefficients of the machine.

In developed industrialised countries where there is grid electricity, there is no cost effective application for solar powered refrigeration of food, medicines etc. However, there may still be the possibility of costeffective solar air conditioning. The target cost per unit of cooling must be competitive with conventional systems, perhaps around £1 / Watt. None of the above mentioned systems are likely to achieve this figure. A few photovoltaic powered air conditioning systems have been built experimentally, but they are prohibitively expensive. Evacuated tube solar collectors have been used in conjunction with conventional Lithium Bromide - Water absorption air conditioners but are still far too costly and complex. The best possibility for cost effective solar powered air conditioning appears to be desiccant cooling. Desiccant cooling has been known and available for many years but has become popular in recent years due to two factors. The first is that the damage to the ozone layer by conventional chlorofluorocarbon refrigerants has necessitated the search for alternatives to vapour compression refrigeration. Secondly, the need to replace the peak load demand for electricity for air conditioning applications coupled with the desire of gas utilities to balance their heating loads with a summer alternative has lead to the development of heat powered refrigeration cycles. The result has been research into improved desiccant materials and cycles to both improve performance and reduce costs. Desiccants are substances that have a strong affinity for water and, because of this, can absorb moisture from an air stream. Desiccants can be solids such as lithium chloride, silica gel or molecular sieves, or liquids such as glycol, sulphuric acid or lithium bromide solution. There is a partial pressure of water vapour than can exist in equilibrium with a desiccant at a particular temperature. If the actual vapour pressure is above the equilibium value, moisture will be absorbed, but if it is lower then moisture will evaporate from the desiccant. The process is therefore reversible. The most common arrangement of desiccant system is the desiccant rotor. A desiccant rotor consists of a honeycomb support which has been impregnated with a finely divided desiccant. As air flows axially through the narrow honeycomb channels, moisture is absorbed by the desiccant. The design of the rotor gives a large surface area of contact between air and desiccant. As the air stream passes through the rotor, moisture is absorbed and the heat of absorption, almost equal to the latent heat of condensation, is released. The resulting air stream is therefore warmer but drier. The latent enthalpy contained in the moisture vapour is effectively exchanged for sensible enthalpy in the temperature of the resulting air. It is arranged that the rotor rotates slowly so that desiccant that has been exposed to moist process air moves into a separate sector. Here warm air, in which the vapour pressure is less than the equilibrium vapour pressure, carries away moisture that evaporates from the desiccant on the rotor A schematic of a desiccant cooling system is shown in Figure 6. Latent heat contained in the fresh air (1) drawn into the building is exchanged on the desiccant rotor for sensible and the air temperature rises. This warm dry air (2) is then passed through a heat wheel. The heat sink for the heat wheel is extract air (5) from the building that has been cooled by evaporative cooling (6). The resulting air stream (3) is therefore cool and dry. If moisture is added to this air stream, evaporative cooling takes place and cool air (4) is supplied to the building. The warm moist extract air (6) after the heat wheel is heated further and the hot gas (7) passed through the desiccant rotor. Moisture leaves the rotor and so a warm moist air stream (8) is discharged to outside the building. 30°C

WORKING PRINCIPLE

The following figure shows the prototype of the machine adsorption in semi pilot scale manufactured. The realization and test of a prototype at this scale allows evaluating the feasibility of the pilot scale adsorption refrigerator and its operating parameters. The prototype has the following components: a thermally insulated refrigeration compartment, an evaporator, a condenser and an adsorption tube collector. The operation principle of the machine consists in heating by solar radiation the adsorbent contained in the adsorption collector, which is disposed horizontally. This energy should be sufficient to desorb the molecules of the adsorbate (methanol) and to be transformed from its liquid phase into vapour. Then, the methanol vapours are condensed in a condenser and collected in a tank then evacuated towards the evaporator in a liquid phase. The adsorbent starts to cool gradually when solar radiation begins de decrease in the evening to reach the ambient temperature. This decrease in temperature involves the adsorption phenomenon of the activated carbon with the methanol. Cold production is the result of the energy needed to evaporate the methanol in the evaporator, which willbe adsorbed by the activated carbon. This phenomenon will cease when the adsorbent is completely saturated with methanol for a temperature slightly higher than the environmental temperature and the initial vacuum pressure.

The adsorption refrigerator Prototype with semi pilot scales.

 Adsorption solar collector scheme

SIMULATION

Refrigerated cabinet containing evaporator and ice for cold storage

Temperature evolution of ice used for cold thermal storage (time simulation: 4 hours 30 min).

THE ADSORPTION CYCLE FOR REFRIGERATION

DEVELOPMENT OF A SOLAR POWERED ADSORPTION CHILLER

CONCLUSION

The goal of this work is to develop an adsorption refrigeration system for cold production able to answer the socioeconomic requirements, in particular in term of total low costs (solar collector, equipment, maintenance) and technological simplicity (system without valve and self-adapting in the external conditions). A prototype on a semi pilot scale was elaborated, and the experimental tests were carried out in a laboratory. Cold thermal storage is used in order to store cooling energy use while shifting. Simulation of the phase change phenomena is undertaken in order to determine the quantity of PCM (ice) required to counteract the heat losses at the walls during its melting cycle (night period). Computation programme was elaborated, giving an estimate of the activated carbon and methanol quantities in the adsorption refrigerator, the energy balance and the design of its various components, as well as the thermal and solar performance coefficients of the system. A manufacture and optimization work is being done for an adsorption refrigeration machine on a pilot scale, for a refrigeration compartment volume of 100 L.