lab report: heat exchanger

OBJECTIVE

The main objective for this experiment is to demonstrate the effect of the flow rate variation on the performance characteristics of a counter-flow and parallel flow concentric tube heat exchanger.

Specific objectives for this experiment include:

• Learning how the operation of concentric tube heat exchanger.
• Developing a set of experiments to obtain statistically significant trends for the overall heat transfer coefficient and the inside heat transfer coefficient as a function of water velocity.
• Observing the difference between parallel-flow and counter flow operation of the heat exchanger.

INTRODUCTION

Heat exchanger is a device built for efficient heat transfer from one medium to another. A solid wall may separate the media, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. One common example of a heat exchanger is the radiator in a car, in which the heat source, being a hot engine-cooling fluid, water, transfers heat to air flowing through the radiator (i.e. the heat transfer medium).The main purpose of heat exchanger is to remove the heat from the hot fluid and transfer it into the cold fluid. There are 3 types of heat exchanger, parallel flow, counter flow, and cross flow. However, in this experiment, we only consider the counter-flow heat exchanger and parallel flow. Counter flow exists when the two fluids flow in opposite directions. Each of the fluids enters the heat exchanger at opposite ends. Because the cooler fluid exits the counter flow heat exchanger at the end where the hot fluid enters the heat exchanger, the cooler fluid will approach the inlet temperature of the hot fluid. Parallel flow exists when two fluids flow in parallel directions. Each of the fluids enters the heat exchanger at parallel end.

The variables that affect the performance of a heat exchanger are the fluids’ physical properties, the fluids’ mass flow rates, the inlet temperature of the fluids, the physical properties of the heat exchanger materials, the configuration and area of the heat transfer surfaces, the extent of scale or deposits on the heat transfer surfaces, and the ambient conditions. The comparison between counter-flow and parallel flow also can be determined through this experiment which is explained more in discussion part in this report.

THEORETICAL BACKGROUND

One fluid (hot) convectively transfers heat to the tube wall where conduction takes place across the tube to the opposite wall. The heat is then convectively transferred to the second fluid. Because this process takes place over the entire length of the exchanger, the temperature of the fluids as they flow through the exchanger is not generally constant, but varies over the entire length. The rate of heat transfer varies along the length of the exchanger tubes because its value depends upon the temperature difference between the hot and the cold fluid at the point being viewed.

The way that a heat exchanger works is hot water and cold water entering the exchanger, where the process of cold water gaining some heat and the hot water losing some takes place, before they both exit the exchanger. What is actually happening is, the hot water is heating either the inside or the outside of the tubes in the exchanger, depending on where it is flowing, by what is known as convection.

Then the heat is conducted through the tubes to the other side, either the outside or the inside, where it is then converted back into the cold water raising its temperature. Convection is a mode of heat transfer that involves motion of some fluid that either absorbs heat from a source or gives heat to some surrounding. Conduction is a mode of heat transfer in which the heat is moving through a stationary object or fluid. For a heat exchanger that flows parallel or counter current then the coefficient of heat transfer is called the overall coefficient of heat transfer. It is calculated using the log mean temperature difference, which is found two different ways, depending on whether the flow is parallel or counter.

A heat exchanger is a device by which thermal energy is transferred from one fluid to another. The types of heat exchangers to be tested in this experiment are called single-pass, parallel-flow and counter-flow concentric tube heat exchangers. In a parallel-flow heat exchanger, the working fluids flow in the same direction. In the counter flow exchanger, the fluids flow in parallel but opposite directions.

HISTORY

The primary advantage of a concentric configuration, as opposed to a plate or shell and tube heat exchanger, is the simplicity of their design. As such, the insides of both surfaces are easy to clean and maintain, making it ideal for fluids that cause fouling. Additionally, their robust build means that they can withstand high pressure operations. They also produce turbulent conditions at low flow rates, increasing the heat transfer coefficient, and hence the rate of heat transfer. There are significant disadvantages however, the two most noticeable being their high cost in proportion to heat transfer area; and the impractical lengths required for high heat duties. They also suffer from comparatively high heat losses via their large, outer shells.

The simplest form is composed of straight sections of tubing encased within the outer shell, however alternatives such as corrugated or curved tubing conserve space while maximising heat transfer area per unit volume. They can be arranged in series or in parallel depending on the heating requirements. Typically constructed from stainless steel, spacers are inserted to retain concentricity, while the tubes are sealed with O-rings, packing, or welded depending on the operating pressures.

While both co and counter configurations are possible, the countercurrent method is more common. The preference is to pass the hot fluid through the inner tube to reduce heat losses, while the annulus is reserved for the high viscosity stream to limit the pressure drop. Beyond double stream heat exchangers, designs involving triple (or more) streams are common; alternating between hot and cool streams, thus heating/cooling the product from both sides.

EXPERIMENTAL PROCEDURE

1. This experiment was started by setting the machine for parallel-flow.
2. The hot water inlet temperature was setted 60oC with decade switch.
3. The cold water volumetric flow rate ( ... ) was set to run at a constant 2,000 cm3/min.
4. Initially, the hot water volumetric flow rate ( ... ) was set to 1,000 cm3/min.
5. This step was repeated for the volumetric flow rate of 2,000, 3,000, and 4,000 cm3/min.
6. Six temperature reading was recorded in the result table.
7. Sufficient time (approximately to be 1 to 4 minutes) is allowed, in order to achieve steady conditions.
8. Step 2 to 7 is repeated for counter-flow heat exchanger operation. 

REFERENCE

1. Heat and Mass Transfer (A Practical Approach) – 3rd Edition, Yunus A. Cengel, McGraw Hill (2006)
2. http://en.wikipedia.org/wiki/Concentric_tube_heat_exchanger
3. http://www.concentrictubeheatexchanger.com/

Determination of Specific Gravity

OBJECTIVE

To determine specific gravity of a liquid using Hydrometer Method. 

APPARATUS

Hydrometer, glass cylinders. 

THEORY

Specific gravity or relative density is the ratio of the density of the fluid to the density of water at standard temperature in example at 40C. Specific gravity can be determined directly from the density of a liquid as measured divided by standard density of water. A convenient alternative method is to use a specially calibrated instrument called Hydrometer. Hydrometer is hallows glass float designed to float upright in liquids of various densities. The depth to which it sinks in the liquid is a measure of the density of the liquid. A scale is provided on its stem which is calibrated to read specific gravity. The sensitivity of the hydrometer depends on the diameter of the stem. A very sensitive hydrometer has a large bulb and thin stem. 

PROCEDURES

1. The tall glass cylinders are placed on the flat working surface.
2. A liquid is filled to allow air to rise to the top.
3. The hydrometer is inserted carefully to allow it to settle in the center of the cylinder.
4. The scale is read after the hydrometer has settled at the bottom of the free water surface.
5. The reading is recorded. The hydrometer is taken out.
6. The procedure 3 to 5 is repeated three times for the other given liquids also.
7. The specific gravities are compared.

DISCUSSION

The specific gravity of mercury is the same on the moon. It is because specific gravity is the ratio of the density of the fluid to the density of water at 40C while density is mass per unit of volume. The mass and volume does not change even on the moon or on the earth. But, the weight will change on the moon. Thus, the specific gravity of mercury does not change on the moon. 

The hydrometer sinks more in the lighter liquids than the heavier because the lighter liquids are less dense than the heavier liquids. In this experiment, water is the lowest with its average specific gravity is 0.95 while the average specific gravity of syrup and oil are 1.25 and 0.88 respectively. From the result, we know that the density of syrup is the highest and the density of water is the lowest. Therefore, the less dense of the liquids, the lowest specific gravity will achieve. 

It is so easy to swim in the sea water than swimming pools because the density of sea water is higher than water in the swimming pools. The higher density of sea water is influenced by the existence of the salt. Thus, it is easily to swim in the sea than in swimming pools. 

CONCLUSION

The specific gravity of a liquid was successful achieved by using Hydrometer Method. Thus, the objective can be accepted.

REFERENCES

1. Andreas Alexandrou, (2001). Principle Of Fluid Mechanics, New Jersey.
2. Suhaimi Abu Talib, (2002). Fluid Mechanics, Penerbit Anda.
3. http://www.icllabs.com/Safety%20Blue%20API%20hydro.JPG

Microstructure study of ferrous and non ferrous alloys under various compositions and heat treatment conditions

ABSTRACT

This experiment was carried out in order to make students understand the differences between ferrous and non ferrous alloys from metallurgical point of view. Student will also be able to understand the phase diagram of iron-carbon and non ferrous alloys system that enables for heat treating and procedures in heat treatment involved.Furthermore, students will also be able to describe the principle engineering properties and industrial application of ferrous and non ferrous alloys.

INTRODUCTION

The properties of metals can be changed or controlled by these different processes; strain hardening or cold – working, alloying process and heat treatment. All three processes are influenced by and dependent on the crystalline nature of metals. Engineering metals are commonly categorized into two main groups; ferrous and non ferrous.

Steels are essentially alloys of carbon containing up to 1.5% carbon. By varying the manner in which carbon steels are heated and cooled, different combinations of mechanical properties for steel can be obtained. Heat treatment process is a process of ability to change the properties by applying heat. Such treatment modifies microstructures, producing a variety of mechanical properties that are important in manufacturing, such as improve formability and machinability.

Copper and aluminium are categorized as non ferrous metal which have been used in engineering either as in its pure state or as an alloy. The applications of copper and aluminium have been very wide in the electrical conductors as well as in corrosive environment. Heat treatments of these metals have in many ways improved their properties for specific or specialized applications. The properties of copper and aluminium either in their pure state or as in an alloy can be improved by heat treatment. These changes in properties are the results in the microstructures in these materials through heat treatment. Thus microstructures transformation has influenced the properties of these materials.

THEORY

Ferrous Alloy

Ferrous alloys are which iron is the prime constituents that are produced in larger quantities that any other metal type. There are especially important as engineering construction materials. Their widespread use is accounted for by three factors:

1. Iron containing compounds exist in abundant quantities within the earth's crust.
2. Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying and fabrication techniques.
3. Ferrous alloys are extremely versatile

In that they may be tailored to have a wide range of mechanical and physical properties. The principle disadvantage of many ferrous alloys is their susceptibility to corrosion. This section discusses compositions, microstructures and properties of a number of different classes of steels and cast irons.

Steels

Steels are iron-carbon alloys that may contain appreciable concentrations of other alloying elements. There are thousands of alloys that have different composition and heat treatments. The mechanical properties are sensitive to the content of carbon, which is normally less than 1.0 wt%. Some of the more common steels are classified according to carbon concentration which is:

1. Low-carbon type
2. Medium-carbon type
3. High carbon type

Subclasses also exist within each group according to the concentration of other alloying elements. Plain carbon steels contain only residual concentrations of impurities other than carbon and a little manganese. For alloy steels, more alloying elements are intentionally added in specific concentration.

• Low-Carbon Steels

Of all the different steels, those produced in the greatest quantities fall within the low-carbon classification. These generally contain less than about 0.25 wt% C and are unresponsive to heat. Microstructure consists of ferrite and pearlite constituents.

• Medium-Carbon Steels

The medium carbon steels have carbon concentration between about 0.25 wt% and 0.60 wt%. These alloys may be heat treated by austenitizing, quenching, and then tempering to improve their mechanical properties. They are most often utilized in the tempered condition, having microstructures of tempered martensite.

• High-Carbon Steels

The high carbon steels, normally having carbon contents between 0.60 wt% and 1.4 wt%, are the hardest, strongest and yet least ductile of the carbon steels. They are almost always used in a hardened and tempered condition and as such are especially wear resistant and capable of holding a sharp cutting edge.

Stainless Steel

The stainless steels are highly resistant to corrosion in a variety of environments, especially the ambient atmosphere. Their predominant alloying element is chromium; a concentration of at least 11 wt% Cr is required. Corrosion resistance may be enhanced by nickel and molybdenum additions.

Stainless steels are divided into three classes which is:

1. Martensitic
2. Ferritic
3. Austenitic

Cast Iron

Generally, cast irons are a class of ferrous alloys with carbon contents above 2.14 wt%. However, most cast irons contain between 3.0 wt% and 4.5 wt% C and in addition of other alloying elements. A re-examination of the iron-iron carbide phase diagram reveals that alloys within this composition range become completely liquid at temperatures between approximately 1150'C and 1300'C, which considerably lower than for steels. Thus, they are easily melted and amenable to casting. Furthermore, some cast irons are very brittle and casting is the most convenient fabrication technique.

Gray Iron

The carbon and silicon contents of gray cast irons vary between 2.5 wt% and 4.0 wt% and 1.0 wt% and 3.0 wt%, respectively. For most of these cast irons, the graphite exists in the form of flakes, which are normally surrounded by an α-ferrite or pearlite matrix.

Ductile Iron

Adding a small amount of magnesium and cerium to the gray iron before casting produces a distinctly different microstructure and set of mechanical properties. Graphite still forms but as a nodules or sphere-like particles instead of flakes. The resulting alloy is called nodular or ductile iron.

White Iron and Malleable Iron

For low-silicon cast irons which contains less than 1.0 wt% Si and rapid cooling rates, most of the carbon exists as cementite instead of graphite. A fracture surface of this alloy has a white appearance, and thus it is termed white cast iron. Generally, white iron is used as an intermediary in the production of yet another cast iron, malleable iron.

Compacted Graphite Iron

A relatively recent addition to the family of cast irons is compacted graphite iron. As a gray, ductile and malleable irons, carbon exists as graphite which formation is promoted by the presence of silicon. Silicon content ranges between 1.7 wt% and 3.0 wt%, whereas carbon concentration is normally between 3.1 wt% and 4.0 wt%.

Nonferrous Alloy

Steel and other ferrous alloys are consumed in exceedingly large quantities because they have such a wide range of mechanical properties, may be fabricated with relative ease and are economical to produce. However, they have some distinct limitations chiefly:

1. A relatively high density
2. A comparatively low electrical conductivity
3. An inherent susceptibility to corrosion in some common environment

Thus, for many applications it is advantageous or even necessary to utilize other alloys having more suitable property combinations. Alloy systems are classified either according to the base metal or according to some specific characteristic that a group of alloys share.

Copper and Its Alloy

Copper and copper-based alloys, possessing a desirable combination of physical properties, have been utilized in quite a variety of applications since antiquity. Unalloyed copper is so soft and ductile that it is difficult to machine. It also has an almost unlimited capacity to be cold work. Furthermore, it is highly resistant to corrosion in diverse environments including the ambient atmosphere, sea water and some industrial chemicals. The mechanical and corrosion-resistance properties of copper may be improved by alloying. Most copper alloys cannot be hardened or strengthened by heat-treating procedures; consequently, cold working and solid-solution alloying must be utilized to improved these mechanical properties.

Aluminium and Its Alloys

Aluminium and its alloys are characterized by a relatively low density, high electrical and thermal conductivities and a resistance to corrosion in some common environments including the ambient atmosphere. Many of these alloys are easily formed by virtue of high ductility; this is evidenced by the thin aluminium foil sheet into which the relatively pure material may be rolled. Since aluminium has an FCC crystal structure, its ductility is retained even at very low temperature. The chief limitation of aluminium is its low melting temperature, which restricts the maximum temperature at which it can be used.

Magnesium and Its Alloys

Perhaps the most outstanding characteristic of magnesium is its density, 1.7g/cm3, which is the lowest of all the structural metals; therefore, its alloys are used where light weight is an important consideration. Magnesium has an HCP crystal structure, is relatively soft and has a low elastic modulus. At room temperature magnesium and it alloys are difficult to deform. In fact only small degrees of cold work may be imposed without annealing.

Titanium and Its Alloys

Titanium and its alloys are relatively new engineering materials that posses an extraordinary combination of properties. The pure metal has a relatively low density, a high melting point, and an elastic modulus of 107GPa. Titanium alloys are extremely strong.

EXPERIMENTAL PROCEDURE

Students were provided with 8 specimens, which have been heat treated under the following conditions. Students were required to observe the microstructure under the optical microscope and the data obtained were recorded.

Ferrous Alloy

Specimen 1 (X17)	0.8% carbon steel, rolled bar, heated for 1 hour at 800oC, furnace cooled (annealed) to room temperature
Specimen 2 (X18)	0.8% carbon steel, rolled bar, heated for 1 hour at 800oC cooled in still air (normalized)
Specimen 3 (X19)	0.35% carbon steel bar, furnace cooled from 870oC
Specimen 4 (X20)	1.3% carbon steel bar, furnace cooled from 970oC

Nonferrous Alloy

Specimen 5 (X12)	Cu 58% / Zn 42%, reheated to 800oC for 1 hour, furnace cooled to 600oC and then water quenched
Specimen 6 (X13)	Cu 58% / Zn 42%, reheated to 800oC for 1 hour, furnace cooled to room temperature
Specimen 7 (X14)	Aluminium / 4% copper alloy, sand cast, heated at 525oC for 16 hours and then water quenched
Specimen 8 (X15)	Aluminium / 4% copper alloy, sand cast, heated at 525oC for 16 hours and then water quenched, reheated at 260oC for 70 hours

DISCUSSION
Ferrous Alloy
Specimen 1 (X17)

Specimen 1 (X17) which is containing 0.8% carbon steel, rolled bar was heated for 1 hour at 800'C. It then undergoes annealed process which is furnace cooled to room temperature. Annealing is a term that often used to define heat treatment process that produces some softening of the structure. True annealing involves heating the steel to austenite and holding for some time to create stable structure. The structure is then cooled very slowly to room temperature. This will produces a very soft structure, but also creates very large grains, which are seldom desirable because of poor toughness.

When Specimen 1 (X17) undergoes annealing process, it will produced ferrite and pearlite. The white areas are a solid solution known as ferrite. The dark areas are actually a composite called pearlite.

Specimen 2 (X18)

Specimen 2 (X18) which is containing 0.8% carbon steel, rolled bar was heated for 1 hour at 800'C. It then undergoes normalized process which is cooled in still air. Normalizing is as term of returning the structure back to normal. The steel is heated until it just starts to form austenite, It is then cooled in air. This moderately rapid transformation creates relatively fine grains with uniform pearlite.

When Specimen 2 (X18) undergoes normalizing, it will produced fine pearlite with excess of ferrite or cementite. The resulting material is soft and the degree of softness depends on the actual ambient conditions of cooling. Normalizing is more commonly used than annealing, as it is considerably cheaper that full annealing since there is not the added cost of controlled furnace cooling.

Specimen 3 (X19)

Specimen 3 (X19) which is containing 0.35% carbon steel bar. It then undergoes spheroidizing which is furnace cooled from 870'C. According to the percentage of carbon steel, specimen 3 can be classified as medium-carbon steel. When this type of carbon steel undergoes spheroidizing, it will developed the spheroidite structure. Spheroidited steels have a maximum softness and ductility and easily machined or deformed. The carbon steels will produced ferrite, cementite and also bainite microstructure.

Specimen 4 (X20)

Specimen 4 (X20) which is containing 1.3% carbon steel bar. It the undergoes spheroidizing which is furnace cooled from 970%. According to the percentage of carbon steel, specimen 3 can be classified as high-carbon steel. During cooling process of this steel, from the austenite field, the first phase to form is cementite on the austenite grain boundaries. This partitions iron and at the eutectic composition pearlite is formed from the remaining enriched austenite.

Nonferrous Alloy
Specimen 5 (X12)
Specimen 5 (X12) which is containing 58% Copper (Cu) or 42% Zinc (Zn). It then reheated to 800^oC for 1 hour. The specimen is then was furnace cooled to 600^oC and then undergoes water quenched. Hardenability means the influenced for alloy composition on the ability of steel alloy to transform to martensite for particular quenching treatment. After quenching, specimen 5 will form microstructure of martensite

Specimen 6 (X13)

Specimen 6 (X13) which is containing 58% Copper and 42% Zinc. It then reheated to 800^oC for 1 hour. The specimen is then was cooled to room temperature. The specimen undergoes hardenability just like specimen 5. The microstructure of the grains of this specimen expands.

Specimen 7 (X14)

Specimen 7 (X14) which is containing Aluminium (Al) and 4% of Copper (Cu) alloy, sand cast. It then heated at 525^o for 16 hours. It is finally undergoes water quenched. This specimen undergoes age-hardening process. Age hardening was used to designate this precipitation hardening because the strength developed by time or as the alloy ages.

Specimen 8 (X15)

Specimen 8 (X15) which is containing Aluminium (Al) and 4% Copper (Cu) alloy, sand cast. It then heated at 525^oC for 16 hours. It then undergoes water quenched. Finally, the specimen was reheated at 260^oC for 70 hours. Just like specimen 7, specimen 8 also undergoes age-hardening process.

Heat Treatment
Annealing

Applies normally to softening by changing the microstructure and is a term used to describe the heating and cooling cycle of metals in the solid state. The term annealing usually implies relatively slow cooling in carbon and alloy steels. The more important purposes for which steel is annealed are as follow:

1. To remove stresses
2. To induce softness
3. To alter ductility, toughness or electric, magnetic or other physical and mechanical properties.
4. To change the crystalline structure
5. To produce definite microstructure

Normalizing

Normalizing is a heat treatment process for making material softer but does not produce the uniform material properties of annealing. A material can be normalized by heating it to a specific temperature and then letting the material cool to room temperature outside of the oven. This treatment refines the grain size and improves the uniformity of microstructure and properties of hot rolled steel. Normalizing is used in some plate mills, in the production of large forgings such as railroad wheels and axles, some bar products. This process is less expensive that annealing.

Spheroidizing

Spheroidizing is a process of heating and cooling to produce a spherodial or globular form of carbide in steel.

Hardening

Hardening involves heating steel to its normalizing temperature and cooling (quenching) rapidly in a suitable fluid.

Alloys
Ferrous Alloys

Iron alloys containing chromium, manganese, molybdenum, silicon, titanium, tungsten, vanadium and other elements in varying proportions. Ferrous alloys are added to steel during the manufacturing process to achieve the desired degree of corrosion resistance, tensile strength, yield strength and other qualities.

Nonferrous Alloys

Nonferrous alloys are alloys that are the byproducts of non ferrous metals such as aluminium, cobalt, lead, magnesium, titanium and zinc. By definition, a non ferrous alloy is an alloy that does not intentionally contain iron. In general, non ferrous alloys are invested with non metallic properties, have higher melting point and better strength. These properties make them a favoured choice for several commercial and non commercial uses, including automobile and aircraft parts, communication equipment, water valves, musical instruments and the manufacturing of flammables and explosive.

Microstructural
Austenite

Austenite is a solid solution of ferritic carbide or carbon in iron. It cools to form pearlite or martensite.

Ferrite

Ferrite is a solid solution of carbon in body-centered cubic iron. It is a constituent of carbon steels.

Cementite

Cementite is iron carbide and an orthorhombic crystal structure. It is hard, brittle material, essentially a ceramic in its pure form. It forms directly from the melt in the case of white cast iron. In carbon steel, it either forms from austenite during cooling or from martensite during tempering.

Pearlite

Pearlite is an iron alloy phase which is characterized by the formation of distinct bands of ferrite and cementite. This iron alloy phase contains around 88% ferrite and 12% cementite. It only forms under specialized conditions which must be controlled to create this alloy phase rather than another one. Pearlite is known for being tough, thanks to the way in which it forms, and may be used in a variety of applications.

Martensite

Martensite is a solid solution of carbon in alpha-iron that is formed when steel is cooled so rapidly that the change from austenite to pearlite is suppressed; responsible for hardness of quenched steel.

CONCLUSION

From the experiment that has been carried out, we are able to understand the differences between ferrous and non ferrous alloys from the metallurgical point of view. There are differences in the microstructure of the materials. We are also able to understand the phase diagram of iron-carbon and non ferrous systems that enables for heat treating and procedures in heat treatment involved. Besides that, we are also able to describe the principle engineering properties and industrial application of ferrous and non ferrous alloys.

REFERENCES

1. http://serkanakinci.tripod.com/id19.html
2. http://sydney-harbour-bridge.bos.nsw.edu.au/engineering-studies/steel-structure.php
3. http://www.hsc.csu.edu.au/engineering_studies/transport/2522/heat_treat_answers.html
4. http://www.flickr.com/photos/core-materials/3839698246/in/set-72157622074602480/
5. http://www.engineersedge.com/heat_treat.htm
6. http://www.engineershandbook.com/MfgMethods/normalizing.htm
7. http://www.threeplanes.net/cementite.html
8. http://www.diracdelta.co.uk/science/source/s/p/spheroidizing/source.html
9. http://www.wisegeek.com/what-is-pearlite.htm
10. http://www.roymech.co.uk/Useful_Tables/Matter/Hardening.html
11. http://metals.about.com/library/bldef-Ferrite.htm

Leveling Survey (Longitudinal and Cross-section)

Learning Outcome

By the end of this practical work students should be able to:

1. Setup level equipment
2. Take back sight, intermediate sight and fore sight reading
3. Make correct booking
4. Calculate reduced level of all the point taken
5. Perform correction to the reduced level
6. Plot a longitudinal profile and cross section with a suitable scale

Theory

Leveling is the art of determining relative height or elevations of different points on the earth surface. The elevation of a point has been defined as its vertical distance above and below a given reference level surface and usually a mean sea level. The leveling work can be carried out by using direct method or indirect method. The main equipment needed to carry out leveling works is level and staffs. The elevation of the point is calculated using Height of Collimation Method or by using Rise and Fall Method. The final works of the leveling is to transform the numerical data into graphic form either in map or drawing.

Equipment

1. level
Automatic level is used to compare points on the surface of the earth and series of heights observed must be relative to a plane called datum. Automatic level is a device that gives a truly horizontal line. The telescope of this instrument need only be approximately level and the compensating device, usually a pendulum system inside the telescope corrects for the residual mislevelment. This instrument has no bubble tube; therefore preliminary leveling is carried out using the conventional three-screw leveling head and a small target bubble mounted on the tribach which brings the collimation to within 10’ of the horizontal. A prismatic compensator fitted between the eyepiece and the objective lens make correction of slight tilt automatically.

2. Leveling staff

The staff used for ordinary leveling work is sectional and assemble either telescopically or by slotting one another vertically. Most modern designs are manufactured in an aluminum alloy BS4484:Part1:1969 requires length of 3 m, 4m or 5m extension. The graduations are in the form of an E or F shape and the graduations in the 100mm interval.

3. Staff bubble

An instrument to ensure the staff is erected vertically. It is place at the side of the staff.

4. Tapes

Tape is made of synthetic material, glass fiber or linen. The length of the tape is 10m, 20, 30m and 50m are generally available. The tape is graduated at every 5mm and figures every 100mm. the first and the last meter lengths are graduated in millimeters. Whole meter figures are shown in red at every meter.

Procedures

• Longitudinal leveling (60m length)

1. The suitable position for the level to be set up is selected
2. The level is set up. The temporary adjustment is made
3. The staff is placed at the bench mark and the reading is taken
4. The reading is noted in the form provided
5. Another staff is placed at the distance of 7.5m from the first staff
6. The reading of second staff is taken and is noted as the intermediate sight
7. A distance of 7.5m is measured and the third staff position is placed. The reading is noted in the field sheet as an intermediate sight
8. Step 5 to 7 is repeated until the staff cannot be read. The last reading of the staff before the level is moved is noted in the column foresight. The staff at the foresight position must not move until the back sight reading is taken
9. The level is moved to new suitable position and the temporary adjustment is made
10. The back sight reading is taken
11. A cross section reading is taken at every 15m
12. Steps 5 to 10 are repeated until the work is completed
13. A fly level is performed back to the benchmark
14. The HOC and the reduced level of all the staff positions is calculate
15. The longitudinal and cross section profile of the road is plotted

• Cross section leveling (0m, 40m, 80m, 120m, 160m and 200m)

1. Five staff positions is selected perpendicular to the longitudinal line at position A, B, C, D and E
2. The staff is placed at point A and the reading is taken
3. The reading is entered as intermediate sight if the level is still not being moved from the previous position
4. Taking reading for points B, C, D and E is continued
5. After completed cross section leveling, taking the longitudinal leveling is continued until completed

Conclusion

From this practical, we were able to setup the compass survey stations and their equipment correctly. We have taken the reading of three points of static things that have at our location from station A. There are 3.25m, 1.80m and 3.35m from station A

We have calculated the misclosure as mentioned in the local attraction method table. The corrected bearing and the final bearing is determined by followed the correct steps

Discussion and Recommendations

1. Avoid taking measurement near magnetic sources such as hand phone, watch, electric cable and etc
2. Make sure the bubbles are properly level
3. Triple check with the work and reading
4. Make sure the plum bob properly centered over the peg

References

1. Surveying Note Chapter 1(ECG305), En. Amir Khomeiny b. Roslan, UiTM Arau, Perlis, 2010
2. Laboratory Manual Survey Practical (ECG315), UiTM Arau,Perlis, 2010