Combustion And Thermal Efficiencies Of Commercial Water Geysers Engineering Essay

The consumption of natural gas is speedily increasing and the reserves of gas are rapidly on the way out. Pakistan is uniquely susceptible to natural gas depletion because the hunger of the Pakistan is great and the domestic natural gas reserves are small. There is a strong potential for a natural gas crisis in the near term, which is within months or a few years. Demand and supply ratio is not showing equilibrium, so because of these reasons Pakistan is moving swiftly towards severe gas crisis. The natural gas is an important fossil fuel for its increasingly demand for domestic heating purposes, as raw material in fertilizer factories and as a source of fuel in various types of furnaces in industrial units. Keeping the importance of natural gas alive it is needed to use it as wisely as possible.

Figure1.1 Energy consumption of Pakistan

The importance of natural gas could be well understood from the figure above as it accounts for the major energy source for the country, almost half of the country’s need is fulfilled with the help of natural gas. Sector wise natural gas consumption is: Power (30.56%), fertilizer (8.27%), cement industry (0.49%), general industry (20.58%), domestic (24.11%), commercial (4.2%) and Transport (CNG; 11.8%).

Figure 1.2 Sector wise natural gas consumption in Pakistan

As the use of natural gas in countries like Pakistan is strongly season dependant, but in winters roughly water heating takes around one third of total natural gas domestic consumption. The domestic equipment such as geysers using natural gas as heating source are either ill-equipped with controlling devices or inefficient due to ill-design especially in respect of burner design and heat transfer phenomena involved. Because of these designing faults natural gas utilization and thus gas billing rises at unexpected rates.

Today’s homes demand more hot water than ever before and conventional water geysers offer unparalleled levels of performance to meet the need. In conventional geysers heat is being lost in flue gas, incomplete combustion and casing losses. Higher stack draft and uncontrolled additional excess air in the conventional water geysers results in the loss of heat in the stack. Experimental measurements show that the stack temperature is in the range of 200-240 0C. The uncontrolled excess air results in very high O2 about 16 % and low CO2 (2%) in the flue gases. Because of these effects conventional water geysers have lower efficiencies.

So the purpose of this research work was to modify conventional geysers so that it is the most advantageous as compared to conventionally used water geyser because of the less gas and time consumption. In the light of gas crisis, such gas efficient appliances are strongly needed to lessen the gap between gas supply and demand. An efficient baffle is installed in the modified geyser that results in low losses of heat in the stack and reduces the temperature of stack gases drastically. The designed baffles reduces excess air and produce more CO2 in the flue gas thus enhances the combustion efficiency. Thermal efficiency of water geyser is enhanced due to better heat exchange between mediums.

With proposed internal changes of the geyser and inclusion of a baffle, the combustion & thermal efficiencies and throughput can be substantially improved.

1.2 SCOPE OF WORK:

Higher stack draft and uncontrolled additional excess air in the conventional water geysers results in the loss of heat in the stack. Experimental measurements show the stack temperature in the range of 200-240 0C. The uncontrolled excess air results in very high O2 about 16 % and low CO2 (2%) in the flue gases. Because of these effects conventional water geysers have lower efficiencies, so the purpose here is to improve the combustion and thermal efficiency of commercial water geyser

To study the effect of

Various baffle designs in order to improve thermal efficiency by increasing inside temperature, reducing draft and increasing turbulence.

Various baffle designs to improve combustion efficiency due to decreased excess air levels by reducing draft

BChapter No. 2

LITERATURE REVIEW

2.1 What is geyser

Appliances that are used to supply hot water continuously are known as water geysers. Mostly hot water is used domestically for various needs, so these devices may also be termed as domestic gas water geysers.

heating sources in such appliances could be different such as natural gas, electricity, oil, solar radiations. But this research work is focused on gas water geysers. Gas geysers are available in variety of types and sizes. The one that is widely used in countries like Pakistan is storage water geysers.

2.2 Structure OF GAS GEYSERS

Following are the major component of the gas geysers and some safety features.

Figure 2.1 Schematic diagram of gas geyser

Burner

Gas water geysers simply consist of a steel tank with atmospheric burner at the bottom of the water storage tank. Air entering in the burners can be classified into two types, primary and secondary. Primary air is the one that is introduced into burner with fuel. Secondary air is added to aid primary air in better

combustion. In gas fired systems, primary air and fuel mixing occurs inside the mixing area. Mixture is then mixed with secondary air that ensures to some extent a good combustion. Mixture then goes to burner port to give flame.

Figure 2.2 Atmospheric gas burner

Flue gas exhaust pipe

Natural gas serves as a fuel for the water heating combines with air to give combustion products known as flue gases. These flue gases pass through exhaust pipe and are emitted to the atmosphere. Flue gas exhaust pipe has two main functions.

To exit the gases from burner

Serves as heating medium for cold water by transferring its heat.

Cold Water Inlet Pipe

The water that is to be heated enters at the bottom of the geyser with the help of a long pipe. The purpose to make the pipe long enough is to help direct the cold water at the lower portion of the geyser to avoid mixing of cold and hot water.

Hot water Outlet Pipe

This pipe is present at the top of the water geysers. Hot water on heating up rises due to thermosyphon effect and is discharged from the top of the geyser for consumption.

Anode Rod

Wherever the prolong use of water is there, chances of corrosion are maximum over there. So in order to keep the body of the geyser safe from corrosive effects, a metal rod is added that is mostly made of more reactive metals (Al, Mg) than that of the tank metal. As a result of it corrosion damages the rod only and not the whole system

Safety valve

If thermostat systems are faulty due to any reason, then it may happen that temperature may become extremely high that results in pressure increase at unsafe limits. So to avoid any sort of accident this valve is used in water geysers.

Thermostat

This device is used to set the temperature of water at a fixed value. It allows the burner to switch off when the water temperature reaches at the desired point.

Drain Valve

Scaling or sludge formation could occur due the presence of sediments in the storage tank that would be problematic if the geyser is not well maintained. By using drain valve this problem can be avoided by draining the sediments. It also gives water of better quality and increases the life of geyser.

2.3 EFFICIENCY OF WATER GEYSERS:

The efficiencies of water geysers discussed in this particular research work are

Combustion Efficiency

Thermal Efficiency

Combustion efficiency:

Combustion efficiency means how efficiently a fuel gives its energy. In other words combustion efficiency depicts the capability of burner to give heat.

Combustion is basically the oxidation of fuel that results in CO2, H2O, Sox, NOx, CO, unburnt fuel or air generation. A good combustion must result in less amount of unburnt fuel and should operate at optimum excess air.

Figure 2.3 combustion phenomena

There are two types of combustion efficiency (i) net combustion efficiency (ii) gross combustion efficiency

Net combustion efficiency

In net combustion efficiency estimation energy losses due to the presence of water molecule in the flue gases is recovered and latent energy loss term is not included.

Gross combustion efficiency

In these calculations latent energy loss term is included in combustion efficiency estimation.

Thermal efficiency

Thermal efficiency or energy factor is the indication of heat transfer rate to the cold medium with the help of heat exchange surfaces.

It can be defined in terms of geyser as the ratio of heat given out by the geyser to the total energy used by the water.

2.4 Factors affecting combustion and thermal efficiencies

The following are the key factors for understanding efficiency

Stack temperature

Fuel specification

Excess air

Radiation and convection losses

Incomplete combustion

Stack draft

Stack temperature

The temperature at which products of combustion (flue gases) leave the stack is known as flue temperature. A process is considered to be thermally efficient if these gases exit at low temperature. Because the discharge of flue gases at very high temperature results in the wastage of heat, otherwise that could be utilized in heating up the water. So as a result of this inefficiency in heat usage larger amount of fuel is required for water heating. [1] reports that fuel utilization could be reduced by 1% if the exit temperature of flue gases is lowered by 25 0C. But there is a certain limit up to which stack temperature could be decreased i-e dew point of exhaust gases. Below the dew point of flue gases, vapors start condensing that result in corrosion of geyser .Decreasing exit temperature of flue gases also results in increased thermal efficiency, with decreased fuel consumption. One percent of efficiency is enhanced by lowering 35 to 40 0F [2]

Fuel specification

The composition of fuel can have an important effect on the efficiency of the geyser. Fuel containing higher contents of H2 molecules or H2O molecules is considered to be inefficient. This is because water molecules take up latent heat from the hot flue gases in order to remain in vaporous state. The utilization of latent energy by the water molecules causes the wastage of heat due to cooling of exhaust gases.[2]

Excess air

Amount of air in excess of that required for complete combustion is known as excess air. Extra air is added into the combustion process in order to attain complete combustion. According to [2] maintaining the excess air at optimum levels is the first and foremost thing in making the heating, efficient and avoiding energy losses. Excess air makes the process inefficient in terms of combustion and thermal by stealing the heat that could otherwise be used in heating up the water. A good burner is one that uses 15% air in excess. Decreasing the excess air by 15% enhances the heating efficiency by 1% [4] . The same observation is quoted by [3] that geyser efficiency is boosted upto 2.5% if the excess O2 level is decreased by 1%.

Radiation and convection losses

Radiation and convection losses represent the heat losses from the body of geyser. These losses could be minimized by insulating these devices.

Incomplete combustion

Unburned fuel and formation of CO is an indication of incomplete combustion. Incomplete combustion occurs when

There is over excessive or too little fuel is available for combustion

Air is not present in sufficient amount.

Inadequate turbulence of air and fuel before burning.

As the following figure indicates that a very perfect amount of air gives perfect combustion. Excess air results in good combustion and too much or too little air gives incomplete combustion. Too much extra air gives large amount of inerts N2 and it takes away the energy of flue gases in heating up. As suggested by [2], formation of one CO molecule results in 70% less heat generation as compared to the CO2 molecule.

Figure 2.4 Comparison of combustion processes

EFFICIENCY STANDARDS FOR WATER HEATERS

Efficiency standards reflect minimum values of efficiency that water heaters (geysers) must exhibit in order to be implemented. Even the water geyser manufacturers in USA are required to produce their appliances with the minimum energy factor shown in table 1, by federal law [5]

Table 2.1 Energy efficiency regulations for U.S water heaters

Energy star criteria for the world wide water geysers is given in the figure 2.5

Figure 2.5 Energy star criteria for water heaters

A 40 gallon (150 liters) gas water geysers exhibits energy factor in the range of 0.42 to 0.8 and most of the geysers run at energy factor less than 0.65. [5]

The working phenomena of boilers are almost same as those of water geysers. Table 2.2 represents the combustion efficiencies of four different types

Table 2.2 combustion efficiencies of different types of boilers

2.5 IMPROVEMENT OF COMBUSTION AND THERMAL EFFICIENCIES:

Combustion and thermal efficiencies can be improved with the help of 3 T`s. good combustion occurs when the three main criterias are fulfilled.[6]

Time

Temperature

Turbulence

Time: Increasing the amount of time flue gases are contact with cold medium also increases the amount of time for heat transfer to occur.

Temperature: As the temperature difference between the source of heat and the material being heated increases, so does the rate of heat transfer.

Turbulence: Agitation of flue gases in a heat exchanger serves to provide a continual circulation of hotter flue gases in contact with the heat exchanger surfaces.

As it is already described earlier that combustion gases rises from the burner that is placed at the bottom of the water storage tank through a flue pipe placed at the centre of the water tank. Flue gases produced as a result of combustion reaction passes through the stack at very high temperature (2300 0F). These rising gases due to their high temperature transfer heat by radiation and convection to the stack walls on the cooler heat exchanging surfaces and the phenomena of conduction transfers heat within the body of water [7].

Heat transfer by convection can be augmented by increasing mixing or turbulence of the flue gases. Most commonly used method for this purpose is to increase the heat transfer surface to increase convective heat transfer. A research work done in this regard ( to increase heat transfer) concluded that enhanced heat transfer is due to increased turbulence that in turn increases pressure drop of the flue gases due to increase in friction factor. Using heat transfer enhancement devices causes an increase in heat transfer coefficient. The final suggested enhancement device suggested in this work was a type of twisted tape baffle . [7]

Baffles help to get increased heat transfer by directing hot flue gases [8]. Another report suggests that water geyser`s efficiency could be enhanced by insulating the geyser and also by using baffles in flue pipe [5]

Enhanced pressure drop across flue gases due to increase in turbulence.

More time flue gases remain in contact with cold medium

Flow of draft is effected by using flue baffles because it restricts flow of combustion gases [8] poor fuel efficiencies can be corrected with the help of control in draft [6]

The improved heat transfer leads to an increase in the thermal efficiency of the water heater [7]

Increasing thermal efficiency also reduces environmental emissions such as NOx , CO and hydrocarbons. [9]

[11] studied various aspects and factors related to heat transfer efficiency in water geysers. After relating velocity of gases, twisted tape baffles and surface emissivities, to the heat transfer modes such as convection and radiation, it was concluded that heat transfer efficiencies are enhanced 50% with flue baffling as compared to the empty flue pipe

Mostly water geysers are originally [7] manufactured with a flat plate type baffle in it that augments the heat transfer rate from hot gases towards the flue pipe wall. But various studies suggest that using modified shaped baffles thermal and combustion efficiencies could further be enhanced. Heating efficiency is highly dependant upon the geometry and design of the baffle.

[10] quotes that by using spikes on the external side of baffles increases heat transfer are and consequently enhances heat transfer efficiency of flue gases towards water.

Various configurations of baffles have different thermal efficiencies. It can be augmented by increase in heat exchanger area. But increase in thermal efficiency has a limiting point. This limiting point is the dew point of the combustion gases. Temperature of the flue gases must be always higher than the dew point of gases. The condensation of water vapors within flue gases can cause corrosion problems. So to avoid such problems thermal efficiency is limited up to 82 %[7]

Chapter No. 3

EXPERIMENTATION & METHODS

3.1.1 EXPERIMENTAL RIG

Accordingly, an experimental rig was designed and constructed for this purpose .The Water geyser used for experimentation is domestic water geyser provided by “Amber” and shown in figure 3.1. It is of 35 gallons capacity and is equipped with natural gas and water line. A burner is placed at the bottom of the water tank. Combustion gases produced as a result of burning rises through a stack. This stack is extended by attaching it with a exhaust pipe and a hole has been made into it for the access of flue gas analyzer probe. These gases on rising above heats up the water present in the storage tank. Water enters into this geyser with the help of a dip tube placed at the top of the geyser. And hot water is withdrawn from the top of the geyser because it rises due to thermosyphon effect.

Figure 3.1 Gas geyser (experimental rig)

3.1.2 FLUE GAS ANALYZER

Digital flue gas analyzer (TESTO M/XL. Testo 454) shown in figure 3.2 was used to analyze the flue gases. This analysis includes concentration of various gases in flue gas, flue gas temperature, and ambient temperature and by using these parameters it can calculate other factors like net and gross combustion efficiencies, dew point, and draft. Flue gas analyzer uses electrochemical measuring cells for the O2, CO, NO, NO2 and SO2 parameters

Figure 3.2 Digital flue gas analyzer

3.1.3 BAFFLES USED

As it is already discussed that heat transfer can be increased by increasing three factors, time, turbulence and temperature. This is what is done in this experimentation by placing a baffle in the exhaust pipe of the water geyser. Insertion of baffle augments the thermal as well as combustion performance of the geyser. Baffles used in this research work are of four types

Flat stripped baffle( original baffle)

Conical baffle

Finned baffle

Barbed razor baffle

It was investigated in the research work that which baffle is more efficient in increasing the thermal and combustion efficiencies of water geyser. The baffles tested were made of iron and is sown in figures below flat stripped baffle (figure 3.3), conical baffle (figure 3.4) finned baffle (figure 3.5) and barbed razor baffle (figure 3.6).

Figure 3.3 Flat stripped baffle

Figure 3.4 conical baffle

Figure 3.5 Finned baffle

Figure 3.6 Barbed razor baffle

Cross sectional view of the geyser after baffle insertion is shown in fig 3.7

Figure 3.7 Cross sectional view of geyser with baffle

Figure 3.8 Schematic diagram of finned baffle

Figure 3.9 Schematic diagram of barbed razor wire baffle

3.1.4 EXPERIMENTATION STRATEGY

After the detailed characterization of the geyser it was decided to first study the mechanism of heat transfer phenomena involved to improve its heating efficiency. First of all geyser was filled up properly with water. Water and ambient temperatures were noted down. Also starting values of gas and time were also noted to find out the total gas consumed and time required heating up one batch of water up to required temperature. After starting the gas burner water is allowed to heat up. Effect of various baffle designs were checked on thermal efficiency and combustion efficiency of water geyser. During all these experiments flue gas were analyzed using flue gas analyzer and at the end final water temperature, final gas reading and ending time were used to measure.

Figure 3.10 Methodology of experimentation

Chapter No. 4

RESULTS & DISCUSSION

The present research, reports the effect of inclusion of different baffles of different types on the combustion and thermal performance of water geyser that were placed in the stack pipe of geyser. The experiments were carried out in the laboratory of Chemical Engineering Department, U.E.T Lahore.

4.1 CALCULATION OF THERMAL EFFICIENCY

Thermal efficiency is actually the ratio of heat absorbed by water to the heat released by natural gas. It actually dictates that how well the heat released by fuel is consumed in heating up the water. The formula used for thermal efficiency is

Thermal efficiency = m x Cp x ( Tout – Tin) ……… equation 1

V x Hv

Where,

m = Mass of water, kg

Cp = Specific heat of water, J/Kg â-¦C = 4.184 KJ/Kg â-¦C

Tout = Outlet water temperature, â-¦C

Tin = Inlet water temperature, â-¦C

ΔT = Change in temperature, â-¦C = Tout – Tin

V = Volume of gas consumed in heating up 1 batch of water, m3

Hv = heating value of natural gas KJ/m3

All the calculations of this research work is based on one batch of geyser and the water geyser used is of 35 gallons capacity. In order to calculate mass of the water following formula was used

m = Vw x ρ ……Equation 2

m = Mass of water, kg

Vw = volume of water used, m3

ρ = density of water, m3/kg

4.2 CALCULATION OF COMBUSTION EFFICIENCY

Combustion efficiency is actually the burning ability of fuel and is calculated by subtracting dry flue gas loss, unburnt fuel loss and latent heat loss. Dry flue gas loss is actually due to the flue gases leaving at very higher temperature that could otherwise be used in heating up the water. Unburnt fuel loss is the loss due to very high excess air levels that consumes the heat that could be used otherwise in heating up the water. And latent heat loss is the loss of heat that occurs due to the presence of moisture in the fuel that consumes large amount of heat in vaporizing the water molecule.

General formulas for gross and net combustion efficiencies are shown below

EffG = 100 – (Dry flue gas loss + Wet Losses/ Latent Heat Losses) -Unburnt Fuel Loss

EffN = 100 – Dry flue gas loss – Unburnt Fuel Loss

While the formulas used for the calculations are

…….. Equation 3, 4

Where

Qgr = gross calorific value

Qnet = net calorific value

CO = % content of carbon monoxide in flue gas

CO2 = % content of carbon dioxide in flue gas

K1 = constant for natural gas (32)

Kgr = % of carbon in fuel / Qgr

Knet = % of carbon in fuel / Qnet

FT = flue gas temperature

AT = ambient temperature

X = MH2O + 9 H

MH2O = Moisture content of natural gas

H = hydrogen content of natural gas

4.3 CALCULATION OF RECOVERY RATE

Recovery rate is the number of gallons of water the geyser can raise in temperature by a certain number of degrees Celsius in one hour. In this particular research work the recovery rate is taken as amount of water in gallons that can be heated to 55 0C in 1 hr.

To find the recovery rate of water geyser for each of the baffle, numbers of experiments were performed, in which 12 gallons of water was taken as basis and the time taken by water geyser to heat up this much amount of water up to 55 0C was noted for every baffle. By applying unitary method recovery rate was calculated

UNBAFFLED:

35 minutes were consumed to heat up = 12 gallons

60 minutes were consumed to heat up = 20.6 gallons

ORIGINAL BAFFLE:

30 minutes were consumed to heat up = 12 gallons

60 minutes were consumed to heat up = 24 gallons

CONICAL BAFFLE:

28 minutes were consumed to heat up = 12 gallons

60 minutes were consumed to heat up = 25.7 gallons

FINNED BAFFLE:

26 minutes were consumed to heat up = 12 gallons

60 minutes were consumed to heat up = 27.7 gallons

BARBED RAZOR BAFFLE:

25 minutes were consumed to heat up = 12 gallons

60 minutes were consumed to heat up = 29 gallons

4.4 CALCULATION OF STACK DRAFT

Stack draft refers to the pressure difference that causes the movement of flue gases within the stack in upward direction. Flue gases when heated have lower density, as a result of it they rise in upward direction and bottom of the stack have lower pressure as compared to the ambient pressure. This difference in pressure causes the flow of flue gases inside the stack.

For efficient water heating, reduction in stack draft is very necessary so that the flue gases can remain in contact with water to be heated for longer time. Stack draft is dependent upon (i) height of the stack (ii) temperature of outside air (iii) temperature of flue gases (iv) density of flue gases. The formula used to calculate stack draft is

∆P = (PM/R) [ 1/T2 – 1/T1] g h …………….. Equation 5

Where

∆P = Pressure difference, in H2O

P = atmospheric pressure, psi= 14.7 psi

R = ideal gas constant, psi ft3 lbmol-1 R-1 = 10.73 psi ft3 lbmol-1 R-1

T2 = temperature of flue gases, R

T1 = Temperature of ambient air, R = 557 R

g= acceleration due to gravity, ft/s2 = 32.2 ft/s2

h = height of stack, ft = 4 ft

4.5 COMPARISON OF FLUE GAS ANALYSIS OF UNBAFFLED conventional geyser and geysers with designed baffles by using flue gas analyzer:

Geyser Without Baffle

Figure 4.1 Geyser without baffle

Fuel: Natural Gas

16.88 % Oxygen

20 ppm CO

2.33 % CO2

9 ppm NO

0.6 ppm NO2

172.8 â-¦C Flue temp.

10 ppm NOx

0 ppm SO2

6 ppm H2

0 ppm CxHy

74.1 %Eff N

67.4 % Eff G

0.0008 Rati.

30.4 â-¦C Amb. temp.

29.9 â-¦C Device temp.

37.0 â-¦C Dewpoint

1.09 l/m Pump flow

3.0 % O2ref

11.9 % CO2max

—— kg/h Mass. Flow CO

—— kg/h Mass. Flow SO2

—— kg/h Mass. Flow NOx

————————————————————

Heat Carrier te: —— â-¦C

————————————————————-

Geyser With Original Baffle

Figure 4.2 Geyser with original baffle

Fuel: Natural Gas

15.22 % Oxygen

20 ppm CO

3.28 % CO2

10 ppm NO

3.8 ppm NO2

146.5 â-¦C Flue temp.

14 ppm NOx

0 ppm SO2

6 ppm H2

0 ppm CxHy

85.1 %Eff N

77.3 % Eff G

0.0006 Rati.

36.0 â-¦C Amb. temp.

39.5 â-¦C Device temp.

41.1 â-¦C Dewpoint

1.09 l/m Pump flow

3.0 % O2ref

11.9 % CO2max

—— kg/h Mass. Flow CO

—— kg/h Mass. Flow SO2

—— kg/h Mass. Flow NOx

————————————————————

Heat Carrier te: —— â-¦C

4.5.3 Geyser with Conical Baffle

Figure 4.3 Geyser with conical baffle

Fuel: Natural Gas

13.00 % Oxygen

3 ppm CO

4.53 % CO2

14 ppm NO

0.8 ppm NO2

80.2 â-¦C Flue temp.

15 ppm NOx

0 ppm SO2

11 ppm H2

0 ppm CxHy

94.3 %Eff N

85.5 % Eff G

0.0000 Rati.

27.9 â-¦C Amb. temp.

28.7 â-¦C Device temp.

45.5 â-¦C Dewpoint

1.23 l/m Pump flow

3.0 % O2ref

11.9 % CO2max

—— kg/h Mass. Flow CO

—— kg/h Mass. Flow SO2

—— kg/h Mass. Flow NOx

————————————————————

Heat Carrier te: —— â-¦C

————————————————————-

4.5.4 Geyser with Finned Baffle

Figure 4.4 Geyser with finned baffle

Fuel: Natural Gas

10.43 % Oxygen

5 ppm CO

5.99 % CO2

19 ppm NO

1.8 ppm NO2

64.5 â-¦C Flue temp.

21 ppm NOx

1 ppm SO2

5 ppm H2

0 ppm CxHy

97.1 %Eff N

88.0 % Eff G

0.0000 Rati.

34.0 â-¦C Amb. temp.

36.3 â-¦C Device temp.

49.6 â-¦C Dewpoint

1.09 l/m Pump flow

3.0 % O2ref

11.9 % CO2max

—— kg/h Mass. Flow CO

—— kg/h Mass. Flow SO2

—— kg/h Mass. Flow NOx

————————————————————

Heat Carrier te: —— â-¦C

4.5.5 Geyser with Cylindrical Baffle with barbed razor

Figure 4.5 Geyser with barbed razor baffle

Fuel: Natural Gas

9.44 % Oxygen

24 ppm CO

6.55 % CO2

25 ppm NO

2.8 ppm NO2

52.1 â-¦C Flue temp.

28 ppm NOx

0 ppm SO2

7 ppm H2

0 ppm CxHy

97.2 %Eff N

88.1 % Eff G

0.0004 Rati.

22.7 â-¦C Amb. temp.

22.4 â-¦C Device temp.

51.0 â-¦C Dewpoint

1.23 l/m Pump flow

3.0 % O2ref

11.9 % CO2max

—— kg/h Mass. Flow CO

—— kg/h Mass. Flow SO2

—— kg/h Mass. Flow NOx

————————————————————

Heat Carrier te: —— â-¦C

4.6 Gas consumption comparison of different baffles

Consumption of gas for heating 1 batch of water (35 gallons) was found by noting the initial and final values of gas meter attached with the experimental rig. The difference of these values gave the total volume of gas consumed. The following table shows the volume of gas consumed for unbaffled and different configurations of baffles

Type of baffle

Gas used (m3)

Unbaffled

1.13

Original Baffle

0.86

Conical Baffle

0.778

Cylindrical Baffle with fins

0.666

Cylindrical baffle with barbed razor

0.589

Table 4.1 Gas consumption comparison of different baffles

Figure 4.6 shows the graphical trend of gas consumed for heating 1 batch of water using various baffle designs

Figure 4.6 Comparison of gas consumption by using different baffles

4.7 Time consumption comparison of different baffles

Consumption of time for heating 1 batch of water (35 gallons) was found by noting the initial and final values of time. The difference of these values gave the total time consumed. The following table shows the total time consumed for heating unbaffled and different configurations of baffled geyser

Type of baffle

Time consumed (hr)

Unbaffled

2.05

Original Baffle

1.38

Conical Baffle

1.24

Cylindrical Baffle with fins

1.18

Cylindrical baffle with barbed razor

1.10

Table 4.2 Time consumption comparison of different baffles

Figure 4.7 Comparison of time consumption by using different baffles

4.8 Exhaust temperature comparison of different baffles

Type of baffle

Flue Gas Temperature Range

(0C)

Average Flue Gas Temperature

(0C)

Unbaffled

180-220

200

Original Baffle

140-160

150

Conical Baffle

90-110

100

Cylindrical Baffle with fins

60-70

65

Cylindrical baffle with barbed razor

60-70

65

Table 4.3 Exhaust temperature comparison of different baffles

Figure 4.8 Comparison of exhaust temperature by using different baffles

4.9 Thermal Efficiency comparison of different baffles

Type of baffle

Gas used (m3)

Thermal efficiency

%

Unbaffled

1.13

35

Original Baffle

0.86

46

Conical Baffle

0.778

52

Cylindrical Baffle with fins

0.666

60

Cylindrical baffle with barbed razor

0.589

68

Table 4.4 Thermal efficiency comparison of different baffles

Figure 4.9 Comparison of thermal efficiencies by using different baffles

4.10 Combustion Efficiency comparison of different baffles

Type of baffle

Combustion Efficiency

%

Un-baffled

67.3

Original Baffle

77.4

Conical Baffle

85.5

Cylindrical Baffle with fins

88

Cylindrical baffle with barbed razor

88

Table 4.5 Combustion efficiency comparison of different baffles

Figure 4.10 Comparison of combustion efficiencies by using different baffles

4.11 Recovery rate comparison of different baffles

Type of baffle

Recovery Rate

(Gallons)

Un-baffled

20.6

Original Baffle

24

Conical Baffle

25.7

Cylindrical Baffle with fins

27.7

Cylindrical baffle with barbed razor

29

Table 4.6 Recovery rate comparison of different baffles

Figure 4.11 Comparison of recovery rate by using different baffles

4.12 Draft comparison of different baffles

Type of baffle

Draft *

(in H2O)

Un-baffled

-0.02

Original Baffle

-0.014

Conical Baffle

-0.0091

Cylindrical Baffle with fins

-0.005

Cylindrical baffle with barbed razor

-0.005

*From equation

Table 4.7 Draft comparison of different baffles

Figure 4.12 Comparison of draft comparison of different baffles

4.13 Gas savings comparison of different baffles

Type of baffle

Gas savings

(%)

Un-baffled

Original Baffle

24

Conical Baffle

31

Cylindrical Baffle with fins

41

Cylindrical baffle with barbed razor

48

Table 4.8 Gas savings comparison of different baffles

Figure 4.12 Comparison of gas savings by using different baffles

Chapter No. 5

CONCLUSIONS & RECOMMENDATIONS

5.1 CONCLUSIONS

Main goal of this study was the improvement of combustion and thermal efficiencies of water geysers using various baffle designs. As a result of utilization of these baffles a drastic change in different conditions were observed. It resulted decrease in flue gases exhaust temperature, reduction in draft, increased turbulence, less gas and time consumption. So on the whole summarizing the work, utilization of these baffles resulted increase in combustion and thermal efficiencies.

After testing baffles of different shapes and sizes it is concluded that barbed razor wire baffle gave the most efficient results in terms of time and gas consumption, draft reduction, exhaust temperature, combustion and thermal efficiencies

Barbed razor wire baffle maintains 88% combustion efficiency as compared to 67.4 % of conventional geyser.

Barbed razor wire baffle maintains 68% thermal efficiency as compared to the 35% of conventional water geysers

Using Barbed razor wire baffle, geyser consumes less time (30-40%) to fully heat up the water up to the required temperature as compared to the conventional geyser.

Less gas consumption (40-50%) that will reduce energy billing because of the utilization of Barbed razor wire baffle.

Low exhaust temperature allows venting of gases in an economical and easier way.

Less heat losses as compared to conventional water geyser because it overcomes the problem of incomplete combustion

5.2 RECOMMENDATIONS

In future several aspects may be considered:

Further research should be carried out on the design of the burner placed at the bottom of the water geyser to further improve the combustion efficiency of water geyser

Controlling the air fuel ratio by specifying the amount of air inlet to the burner will also be helpful in improving the combustion efficiency to larger extent.

Further research should be carried out on the modification of geyser structure by replacing one larger flue gases exhaust pipe with four different small exhaust pipes in order to enhance thermal efficiency of geyser due to increase in heat transfer.