Steam Water Heater

Chapter 1

INTRODUCTION

In the early 1900s, the electric power generation industry was experiencing rapid growth and change. The steam engines used for power in the previous century had been displaced by turbines which generated electricity as they were rotated by pressurized steam generated in boilers. Turbines and boilers were operating at higher temperatures and pressures (and also in increasingly complex cycles, which required more sophisticated thermal design and analysis) in order to attain greater thermodynamic efficiency. They were also becoming larger as the demand for electricity skyrocketed. A major source of growing pains for the industry was the lack of accurate and standardized values for the properties of water and steam. For the design of power plants and the boilers and turbines within them, it is necessary to have accurate values of thermodynamic quantities such as the vapor pressure (pressure at which water boils at a given temperature) and the enthalpy of vaporization or latent heat (amount of heat required to generate steam from liquid water). More important, the evaluation of the performance of purchased equipment depends on the calculation of these properties. The efficiency of a turbine is measured as the fraction of the energy available in the steam that is converted to electricity, but that available energy is calculated to be a different number depending on the values used for the thermodynamic properties. A turbine might appear to be 28 % efficient with one set of properties and only 27 % efficient with another set; because of the large flows involved, these small differences could mean large sums of money. It therefore became imperative to settle on internationally standardized values for the properties of water and steam, so that all parties in the industry could have a “level playing field” on which to compare bids and equipment performance.

Chapter2

STEAM

Steam is the technical term for the invisible water vapor, the gaseous phase of water formed when water is boiled, In common language it is used to refer to the visible mist of water droplets formed when 'water vapor condenses in the presence of cooler air. At lower pressures, such as in the upper atmosphere or on a high mountain, water boils at a lower temperature than the nominal 100 °C (212 °F) at standard temperature and pressure.

Superheated steam is steam at a temperature above its boiling point for the given pressure. The Enthalpy of vaporization is the energy required to turn water into water vapour during a process which increases the volume by 1,600 times at standard temperature and pressure. Steam engines convert this difference in volume into mechanical work were important to the Industrial Revolution; more recently steam turbine have become popular for the generation electricity.

2.1 Types of steam

A gas can only contain a certain amount of steam (the quantity varies with temperature and pressure). When a gas has absorbed its maximum amount it is said to be in vapor-liquid equilibrium ^[1] and if more water is added it is described as 'wet steam'.

Superheated steam is steam at a temperature higher than its boiling point for the pressure which only occurs where all the water has evaporated or, in the case of steam generators (boilers), the saturated steam has be conveyed out of the steam drum.

 Steam tables contain thermodynamic data for water/steam and are often used by engineers and scientists in design and operation of equipment where thermodynamic cycles involving steam are used.

2.2 Water and Steam

Consider the heating of water at constant pressure. If various properties are to be measured, an experiment can be set up where water is heated in a vertical cylinder closed by a piston on which there is a weight. The weight acting down under gravity

on a piston of fixed size ensures that the fluid in the cylinder is always subject to the

same pressure. Initially the cylinder contains only water at ambient temperature. As

this is heated the water changes into steam and certain characteristics may be

noted.

Initially the water at ambient temperature is subcooled. As heat is added its

temperature rises steadily until it reaches the saturation temperature corresponding

with the pressure in the cylinder. The volume of the water hardly changes during

this process. At this point the water is saturated. As more heat is added, steam is

generated and the volume increases dramatically since the steam occupies a

greater space than the water from which it was generated. The temperature however remains the same until all the water has been converted into steam. At this point the steam is saturated. As additional heat is added, the temperature of the steam increases but at a faster rate than when the water only was being heated. The volume of the steam also increases. Steam at temperatures above the saturation temperature is superheated.

If the temperature T is plotted against the heat added q the three regions namely subcooled water, saturated mixture and superheated steam are clearly indicated. The slope of the graph in both the subcooled region and the superheated region depends on the specific heat of the water and steam respectively.

cp = q / ΔT

The slope however is temperature rise )T over heat added q. This is the inverse of specific heat cp.

Slope = 1 / cp

Since heat added at constant pressure is equal to the enthalpy change this plot is really a temperature-enthalpy diagram. As has already been demonstrated, a temperature-entropy diagram is useful is showing thermodynamic cycles. The temperature-enthalpy diagram may be converted into a temperature-entropy diagram by using the two relations:

cp = q / ΔT

Δs = q / T

Combining these gives:

cp ΔT = T Δs

ΔT / Δs = T / cp

The ratio of change in temperature over change in entropy ΔT/Δs is the slope of the graph on a temperature-entropy diagram. If cp is constant in one or other region of the plot the slope is proportional to temperature T and will increase as the temperature rises. The area under the curve represents the heat added q up to any point or between any points.

This plot shows just one line of a temperature-entropy chart. If the experiment is repeated under different conditions, families of lines can be developed to obtain a complete chart.

2.3 Temperature-Entropy Chart

Consider the heating of water at different pressures each time maintaining the selected pressure constant. A series of similar lines will be obtained with those at higher pressures being above those at lower pressures. As pressure increases however the amount of latent heat added to completely evaporate the water decreases. This is because, at higher pressure, since the increase in volume from

liquid to vapour is not as great, less energy is required to expand the fluid to its new condition. Eventually, at very high pressures, the density of the steam becomes equal to that of the water and no latent heat is required to expand the fluid. If the points at which the water and steam respectively become saturated are joined up a saturated water line and a saturated steam line are formed. These join at the critical point where steam and water densities are equal to form the characteristic bell shaped curve.

The sub cooled water region is to the left and the superheated steam region to the right of the bell curve. The saturated water-steam mixture region lies under or within the bell.

Within the saturated water-steam mixture region there are intermediate conditions. When only part of the total latent heat to evaporate the water has been added a unique point X on the particular constant pressure line is reached. At this point the mass fraction of vapour is x and the mass fraction of liquid is (1 - x). Each fraction has associated with it either the enthalpy of the water at saturation conditions hf or the enthalpy of the steam at saturation conditions hg. The total enthalpy of the mixture is therefore:

h = x hg + (1 - x) hf

h = hf + x (hg - hf)

h = hf + x hfg

The value hfg is equivalent to the latent heat required to convert the water into steam. Similar formulae may be derived for internal energy u and entropy s

u = uf + x ufg

s = sf + x sfg

If all these unique points X for a given mass fraction of vapour under different pressures are joined, a line of constant mass fraction or steam quality is obtained. For other unique mass fractions, other lines of steam quality can be drawn to create a whole family of lines. Note that these lines all meet at the critical point.

Another important family of lines is that showing constant enthalpy conditions. The change in enthalpy h is equal to the heat added q under constant pressure conditions. If given amounts of heat are added from an arbitrary zero condition for different pressure conditions, this heat q will be represented by the area under the respective constant pressure lines. These areas must all be equal for a given amount of heat added and thus a given change in enthalpy. Joining up the points on each constant pressure line at which the given amount of heat has been added will produce a line of constant enthalpy. Adding different amounts of heat will produce a family of constant enthalpy lines. Note that these have a steep slope in the saturated region but a lesser slope in the superheated region.

2.4 Fluid Properties

            The following properties for liquids and gases may be determined by experiment and are plotted on thermodynamic diagrams:

Pressure p

Temperature T

Specific volume v

Internal energy u

Enthalpy h

Entropy s

Pressure and temperature can be measured directly. Specific volume can be obtained by measurement of the physical size of the container. Enthalpy can be obtained by measurement of the amount of heat added at constant pressure. Internal energy can be calculated from the formula for the definition of enthalpy:

h = u + p v

Entropy can be calculated from its formula in terms of temperature:

s = cp ln (T / To)

Temperature To is an arbitrary base temperature (273°K for water) and specific heat cp may be obtained from the formula:

cp = q / ΔT

cp = Δh / ΔT

In the saturated water-steam mixture region the change in entropy is obtained as follows:

Δs = q / T

Δs = hfg / Saturation

All relevant parameters may thus be obtained and plotted as families of curves on a temperature-entropy diagram. It is not always sufficiently accurate to read values from such a diagram. To overcome this problem the calculated values which would be plotted are instead presented in tabular form in a set of thermodynamic tables. These have high accuracy but, since only discrete values in a continuum are presented, interpolation is often necessary to obtain the desired values.

2.5 Thermodynamic Equations

Certain steam and water properties can be determined by experiment and others subsequently by calculation from basic formulae already given. Steam does however follow to some degree the gas laws, that is, as pressure increases specific volume decreases and as temperature increases specific volume increases. Experimental determination of the properties allows the deviation from the gas laws to be ascertained. Thus using a combination of the gas laws, the equations already derived and experimental results it is possible to develop suitable semi-empirical equations which will allow the properties of water and steam to be computed. Such equations are used for developing steam tables where each tabulated value is calculated. These equations are usually polynomials with several constants. The more complex the polynomial the more accurate the results and often as many as six constants are used in the equation. Equations of this type are also used in computer routines to find required properties.

Chapter 3

THERMODYNAMIC PROPERTIES OF WATER AND STEAM FOR POWER GENERATION

It describes the accurate measurements carried out at NBS that were essential in reaching agreement on the needed standards. In the United States, this problem was first addressed in 1921 by a group of scientists and engineers brought together by the American Society of Mechanical Engineers (ASME). The 1921 meeting led to the formation of the ASME Research Committee on Thermal Properties of Steam. This committee, recognizing the need for reliable data, collected subscriptions from industry and disbursed the money to support experimental measurement of key properties of water and steam at Harvard, MIT, and the Bureau of Standards. Because the ASME committee was not as successful in their fundraising as they had hoped, all three institutions ended up subsidizing some of the research themselves in recognition of its importance. The need for standard, reliable data was also recognized in other countries (notably England, Germany, and Czechoslovakia), and research efforts were coordinated internationally.

In the late 1920s and early 1930s, three international conferences were held with the purpose of agreeing on standardized values for the properties of water and steam. This culminated in 1934 with the adoption of a standard set of tables, covering the range of temperatures and pressures of interest to the power industry at that time. These tables gave the vapor pressure as a function of temperature, values of the volume and enthalpy for the equilibrium vapor and liquid phases along the vapor-pressure curve, and volumes and enthalpies at points on a coarse grid of temperatures and pressures. Each value had an uncertainty estimate assigned to it. The data those tables were based on also became the basis for a book of “Steam Tables” produced by J. H. Keenan and F. G. Keyes  the Keenan and Keyes tables were the de facto standard for the design and evaluation of steam power generation equipment worldwide for the next 30 years. The most important data behind these new steam tables came from the laboratory of Nathan S. Osborne at the National Bureau of Standards. Through most of the 1920s and 1930s, Osborne and his coworkers painstakingly built equipment and conducted measurements. The ASME had originally hoped for data within three years of the project’s 1921 start, but fortunately they were patient (and grateful to the NBS for subsidizing the work) and continued to support the project through years of pioneering, but often frustrating, apparatus development. Finally, beginning in the late 1920s, their patience was rewarded as data of unparalleled quality began coming from Osborne’s laboratory. The primary experimental technique was calorimetry, in which a measured amount of heat is added to a fluid under controlled conditions. Osborne and coworkers had previously performed calorimetric measurements on ammonia. For measurements on water, several new calorimeters were developed. One of these, constructed from copper and used for the region below 100 _C, has been preserved in the NIST museum; it is shown in Fig. 1.

The region of most industrial importance, however, was at much higher temperatures (and correspondingly higher pressures), well beyond what had been encountered in the ammonia work. Experiments at these conditions were also more difficult because water is very corrosive at high temperatures. We briefly describe the calorimeter that was built to overcome these difficulties and that was used to take the data reported in the Osborne, Stimson, and Ginning paper.

Fig. 1. Calorimeter used by Osborne et al. to study water properties at temperatures

 below 100⁰C.

The heart of the calorimeter was a heavy-walled 325 cm3 vessel of chromium-nickel steel. The contents were not stirred to achieve thermal equilibrium; instead, heat was diffused by 30 internal silver fins. The vessel contained a heater and carried a miniature platinum resistance thermometer. The calorimeter was shielded from the environment by two concentric silver shields that were maintained at the calorimeter temperature at all times. The calorimeter had two valves. The valve at the top allowed a measurable amount of vapor to be extracted, and the bottom valve allowed extraction of a known amount of liquid water. The water simultaneously served as a pressure transfer medium to allow measurement of the saturation pressure. During extraction of either vapor or liquid, the remaining liquid would partially evaporate, and heat was supplied to the calorimeter in order to keep the temperature constant.

Chapter 4

BOILERS & THERMIC FLUID HEATERS

            This section briefly describes the Boiler and various auxiliaries in the Boiler Room. A boiler is an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam. The hot water or steam under pressure is then usable for transferring the heat to a process. Water is a useful and inexpensive medium for transferring heat to a process. When water at atmospheric pressure is boiled into steam its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be an equipment that must be treated with utmost care. The boiler system comprises of: a feed water system, steam system and fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system. The water supplied to the boiler that is converted into steam is called feed water. The two sources of feed water are:

·         Condensate or condensed steam returned from the processes

·         Makeup water (treated raw water) which must come from outside the boiler room and plant processes. For higher boiler efficiencies, an economizer preheats the feed water using the waste heat in the flue gas.

Chapter 5

TYPE OF BOILERS

            This section describes the various types of boilers: Fire tube boiler, Water tube boiler, Packaged boiler, Fluidized bed combustion boiler, Stoker fired boiler, Pulverized fuel boiler, Waste heat boiler and Thermic fluid heater.

5.1 Fire Tube Boiler

            In a fire tube boiler, hot gases pass through the tubes and boiler feed water in the shell side is converted into steam. Fire tube boilers are generally used for relatively small steam capacities and low to medium steam pressures. As a guideline, fire tube boilers are competitive for steam rates up to 12,000 kg/hour and pressures up to 18 kg/cm2. Fire tube boilers are available for operation with oil, gas or solid fuels. For economic reasons, most fire tube boilers are of “packaged” construction (i.e. manufacturer erected) for all fuels.

Figure 2. Sectional view of a Fire Tube Boiler

(Light Rail Transit Association

5.2 Water Tube Boiler

            In a water tube boiler, boiler feed water flows through the tubes and enters the boiler drum. The circulated water is heated by the combustion gases and converted into steam at the vapour space in the drum. These boilers are selected when the steam

demand as well as steam pressure requirements are high as in the case of process cum power boiler / power boilers. Most modern water boiler tube designs are within the capacity range 4,500 – 120,000 kg/hour of steam, at very high pressures. Many water tube boilers are of “packaged” construction if oil and /or gas are to be used as fuel. Solid fuel fired water tube designs are available but packaged designs are less common. The features of water tube boilers are:

·         Forced, induced and balanced draft provisions help to improve combustion efficiency.

·         Less tolerance for water quality calls for water treatment plant.

·         Higher thermal efficiency levels are possible

Figure 3. Simple Diagram of Water Tube Boiler

5.3 Packaged Boiler

            The packaged boiler is so called because it comes as a complete package. Once delivered to a site, it requires only the steam, water pipe work, fuel supply and electrical connections to be made to become operational. Package boilers are generally of a shell type with a fire tube design so as to achieve high heat transfer rates by both radiation and convection

Figure 4. A typical 3 Pass, Oil fired packaged boiler

The features of packaged boilers are:

·         Small combustion space and high heat release rate resulting in faster evaporation.

·         Large number of small diameter tubes leading to good convective heat transfer.

·         Forced or induced draft systems resulting in good combustion efficiency.

·         Number of passes resulting in better overall heat transfer.

·         Higher thermal efficiency levels compared with other boilers.

These boilers are classified based on the number of passes - the number of times the hot

combustion gases pass through the boiler. The combustion chamber is taken, as the first pass after which there may be one, two or three sets of fire-tubes. The most common boiler of this class is a three-pass unit with two sets of fire-tubes and with the exhaust gases exiting through the rear of the boiler.

5.4 Fluidized Bed Combustion (FBC) Boiler

            Fluidized bed combustion (FBC) has emerged as a viable alternative and has significant advantages over a conventional firing system and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, biogases & other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr.

            When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream – the bed is called “fluidized”. With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized bed”. If sand particles in a fluidized state are heated to the ignition temperatures of coal, and coal is injected continuously into the bed, the coal will burn rapidly and the bed attains a uniform temperature. The fluidized bed combustion (FBC) takes place at about 840OC to 950OC. Since this temperature is much below the ash fusion temperature, melting of ash and associated problems are avoided.

            The lower combustion temperature is achieved because of high coefficient of heat transfer due to rapid mixing in the fluidized bed and effective extraction of heat from the bed through

in-bed heat transfer tubes and walls of the bed. The gas velocity is maintained between minimum fluidization velocity and particle entrainment velocity. This ensures stable operation of the bed and avoids particle entrainment in the gas stream.

5.4.1 Atmospheric Fluidized Bed Combustion (AFBC) Boiler

Most operational boiler of this type is of the Atmospheric Fluidized Bed Combustion.

(AFBC). This involves little more than adding a fluidized bed combustor to a conventional shell boiler. Such systems have similarly being installed in conjunction with conventional water tube boiler.

            Coal is crushed to a size of 1 – 10 mm depending on the rank of coal, type of fuel fed to the combustion chamber. The atmospheric air, which acts as both the fluidization and combustion air, is delivered at a pressure, after being preheated by the exhaust fuel gases. The in-bed tubes carrying water generally act as the evaporator. The gaseous products of combustion pass over the super heater sections of the boiler flowing past the economizer, the dust collectors and the air pre-heater before being exhausted to atmosphere.

5.4.2 Pressurized Fluidized Bed Combustion (PFBC) Boiler

In Pressurized Fluidized Bed Combustion (PFBC) type, a compressor supplies the Forced Draft (FD) air and the combustor is a pressure vessel. The heat release rate in the bed is proportional to the bed pressure and hence a deep bed is used to extract large amounts of heat. This will improve the combustion efficiency and sulphur dioxide absorption in the bed.

The steam is generated in the two tube bundles, one in the bed and one above it. Hot flue gases drive a power generating gas turbine. The PFBC system can be used for cogeneration (steam and electricity) or combined cycle power generation. The combined cycle operation (gas turbine & steam turbine) improves the overall conversion efficiency by 5 to 8 percent.

5.4.3 Atmospheric Circulating Fluidized Bed Combustion Boilers (CFBC)

            In a circulating system the bed parameters are maintained to promote solids elutriation from the bed. They are lifted in a relatively dilute phase in a solids riser, and a down-comer with a cyclone provides a return path for the solids. There are no steam generation tubes immersed in the bed. Generation and super heating of steam takes place in the convection section, water walls, at the exit of the riser.

            CFBC boilers are generally more economical than AFBC boilers for industrial application requiring more than 75 – 100 T/hr of steam. For large units, the taller furnace characteristics of CFBC boilers offers better space utilization, greater fuel particle and sorbent residence time for efficient combustion and SO2 capture, and easier application of staged combustion techniques for NOx control than AFBC steam generators.

Figure 5. CFBC Boiler

5.5 Stoker Fired Boilers

            Stokers are classified according to the method of feeding fuel to the furnace and by the type of grate. The main classifications are spreader stoker and chain-gate or traveling-gate stoker.

5.5.1 Spreader stokers

            Spreader stokers utilize a combination of suspension burning and grate burning. The coal is continually fed into the furnace above a burning bed of coal. The coal fines are burned in suspension; the larger particles fall to the grate, where they are burned in a thin, fast burning coal bed. This method of firing provides good flexibility to meet load fluctuations, since ignition is almost instantaneous when the firing rate is increased. Due to this, the spreader stoker is favored over other types of stokers in many industrial applications.

5.5.2 Chain-grate or traveling-grate stoker

            Coal is fed onto one end of a moving steel grate. As the grate moves along the length of the furnace, the coal burns before dropping off at the end as ash. Some degree of skill is required, particularly when setting up the grate, air dampers and baffles, to ensure clean combustion leaving the minimum of unburnt carbon in the ash.

            The coal-feed hopper runs along the entire coal-feed end of the furnace. A coal gate is used to control the rate at which coal is fed into the furnace by controlling the thickness of the fuel bed. Coal must be uniform in size as large lumps will not burn out completely by the time they reach the end of the grate

Figure 7. View of Traveling Grate Boiler

5.6 Pulverized Fuel Boiler

            Most coal-fired power station boilers use pulverized coal, and many of the larger industrial water-tube boilers also use this pulverized fuel. This technology is well developed, and there are thousands of units around the world, accounting for well over 90 percent of coal-fired capacity.

            The coal is ground (pulverized) to a fine powder, so that less than 2 percent is +300 micrometer (μm) and 70-75 percent is below 75 microns, for a bituminous coal. It should be noted that too fine a powder is wasteful of grinding mill power. On the other hand, too coarse a powder does not burn completely in the combustion chamber and results in higher unburnt losses.

            The pulverized coal is blown with part of the combustion air into the boiler plant through a series of burner nozzles. Secondary and tertiary air may also be added. Combustion takes

place at temperatures from 1300-1700 °C, depending largely on coal grade. Particle residence time in the boiler is typically 2 to 5 seconds, and the particles must be small enough for complete combustion to have taken place during this time.

            This system has many advantages such as ability to fire varying quality of coal, quick responses to changes in load, use of high pre-heat air temperatures etc. One of the most popular systems for firing pulverized coal is the tangential firing using four

burners corner to corner to create a fireball at the center of the furnace.

Figure 8: Tangential firing for pulverized fuel

5.7 Waste Heat Boiler

            Wherever the waste heat is available at medium or high temperatures, a waste heat boiler can be installed economically. Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbinegenerator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.

Figure 9: A simple schematic of Waste HeatBoiler

5.8 Thermic Fluid Heater

            In recent times, thermic fluid heaters have found wide application for indirect process heating. Employing petroleum - based fluids as the heat transfer medium, these heaters provide constantly maintainable temperatures for the user equipment. The combustion system comprises of a fixed grate with mechanical draft arrangements.

            The modern oil fired thermic fluid heater consists of a double coil, three pass construction and fitted a with modulated pressure jet system. The thermic fluid, which acts as a heat carrier, is heated up in the heater and circulated through the user equipment. There it transfers heat for the process through a heat exchanger and the fluid is then returned to the heater. The flow of thermic fluid at the user end is controlled by a pneumatically operated control valve,

based on the operating temperature. The heater operates on low or high fire depending on the return oil temperature, which varies with the system load.

Figure 10. A typical configuration of Thermic Fluid Heater

The advantages of these heaters are:

·         Closed cycle operation with minimum losses as compared to steam boilers.

·         Non-Pressurized system operation even for temperatures around 250 0C as against 40 kg/cm2 steam pressure requirement in a similar steam system.

·         Automatic control settings, which offer operational flexibility.

·         Good thermal efficiencies as losses due to blow down, condensate drain and flash steam do not exist in a thermic fluid heater system.

            The overall economics of the thermic fluid heater will depend upon the specific application and reference basis. Coal fired thermic fluid heaters with a thermal efficiency range of 55-65 percent may compare favorably with most boilers. Incorporation of heat recovery devices in

the flue gas path enhances the thermal efficiency levels further.

Chapter 6

DESIGN AND FABRICATION OF STEAM WATER HEATER

Materials used:

(a)    Two mild steel pipes.

(b)   Copper tube

(c)    Mild steel base plates

(d)   Heating coil

Construction details:

Height of outer cylinder=30cm

Height of inner cylinder=30cm

Total length of the copper tube taken=1.5m

Diameter of the copper tube=.8cm

Power of the heating coil=2000watts

Distance between two cylinders=5mm

Diameter of the inner cylinder=11.5cm

Diameter of the outer cylinder=16.5cm

FABRICATION:

1.      The base plate is drilled on two places for fixing the heating element and also for the copper tube outlet.

2.      The inner cylinder is welded on to the base plate with the heating element inside.

3.      Another plate is fixed on the top of the inner cylinder, with two holes drilled.

                (a) One for refilling the water inside the inner cylinder

                (b) One for the steam to pass through the copper tube

4.      The copper tube is fixed to one of the holes and wound around the cylinder to the exact winding needed for the steam to convert into water at the outlet

5.      The outer cylinder is welded to the plate.

6.      Cold water is poured in between the two cylinders for heating.

Chapter 7

ANALYSIS

Pressure and temperature can be measured directly or can be find out from the steam table. Specific volume can be obtained by measurement of the amount of heat added at constant pressure. Internal energy can be calculated from the formula for the definition of enthalpy

h=u+pV

Here pressure 1.5 bar

 And temperature corresponding to it is 127.617⁰ c.

Amount of heat added 130⁰ c.

Internal energy can be calculated from the formula from the definition of the enthalpy

h=u+pv

130=u+1.5×3.168

U=130-(1.5×3.168)

Internal energy, h=125.248

Entropy can be calculated from it’s formula in terms of temperature.

S=C_p×ln (T/T₀)

Temperature T₀ is an arbitrary base temperature (273⁰k for water) and specific heat C_p may be obtained from the formula

C_p=q/ΔT

q=127.617

ΔT=T₁-T₂

T₁=Final temperature

T₂=Initial temperature

T₁-T₂=120-90=30

C_p=127.617/30=4.2539

Specific heat of water=4.2539

Entropy, S=4.2539×ln (393/273)

                  =4.2539×ln (1.439)

                  =1.548

Chapter 8

COMPARISON BETWEEN STEAM HEATING AND DIRECT HEATING

·         Pressure and temperature in steam heating is higher than direct heating.

·         Heating efficiency is high in steam heating.

·         Steam heating includes convection.

·         Saves time and is a faster process.

·         Saves energy and high efficiency.

Chapter 9

CONCLUSION

            Prior to executing the test protocol on the steam water heater systems, individual components were tested, resulting in: (1) Identification of experimental biases from use of the steam water heater in discrete single stage mode, (2) Selection of dip copper tube of varying lengths and an optimum exterior piping configuration and, (3) The effect of the quality of hot water flows induced by the circulating pump.

Using the experimental results as a guideline, this water system has a good economic payoff and we can save a great deal of money by building our own system. Some of the steam water heating systems are simple, low cost and are manageable systems to install or build.