experiment of shell & tube heat exchanger

1.1ABSTRACTThe objective of this experiment is to study the function and the working of shell and tube heat exchanger. For this experiment, counter-current heat exchanger is used. In counter flow heat exchangers, the two fluids flow against each other, maintaining a maximum temperature difference between the hot and cold streams which allows for maximum heat transfer. Heat transfer and log mean temperature difference (LMTD) are calculated. In this experiment, we assume negligible heat transfer between the system and its surroundings, negligible potential or kinetic energy changes, constant specific heats, and that the fluids are not undergoing any phase change. In this case, the heat transfer rate across a heat exchanger is usually expressed in the form Q = mCp T. There were also calculation of Log Mean Temperature Difference (LMTD) and the formula is :LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]The basic theory in this experiment is Qh=Qc, which the amount of heat transfer is equal to the amount of heat absorb.

1.2INTRODUCTIONHeat Exchangers are used to transfer heat from one fluid to another. The shell and tube exchanger consists of a bundle of tubes with their axes parallel - much in the manner of soda straws in a carton - but supported at various points by baffles at right angles to the tube axes, which serve to keep the tubes fixed in space in a particular configuration, for example, with the axes spaced on equilateral triangles, or squares, etc. (Kessler & Greenkorn,1999). Most processes require the heating or cooling of streams to produce a desired temperature before the stream can be fed to operations. In any heat exchanger there must be a fluid that requires a change in energy (heating or cooling) and a fluid that can provide that energy change. One fluid is sent through a pipe on the inside of the heat exchanger while the other fluid is sent through a pipe on the outside. In this configuration, no mixing of the hot and cold fluids needs to take place. This is very convenient for many processes, especially when product purity needs to be ensured. This arrangement also allows for large quantities of heat to be transferred quickly, and it is relatively easy to maintain consistent operating conditions.There are three principle means of achieving heat transfer, conduction, convection, and radiation. Heat exchangers run on the principles of convective and conductive heat transfer. Radiation does occur in any process. However, in most heat exchangers the amount of contribution from radiation is miniscule in comparison to that of convection and conduction. Conduction occurs as the heat from the hot fluid passes through the inner pipe wall. To maximize the heat transfer, the inner-pipe wall should be thin and very conductive. However, the biggest contribution to heat transfer is made through convection.Heat exchangers are typically classified according to flow arrangement. In the parallel-flow heat exchanger, the hot and cold fluids enter at the same end, flow in the same direction, and leave at the same end. In the counter-flow arrangement, the hot and cold fluids enter the heat exchanger at different ends and flow in opposite directions. Each fluid arrangement leads to different heat rates and the calculations are different accordingly (Incropera, DeWitt, Bergman & Lavine, 2007Heat exchangers are widely used in refrigeration, air conditioning, power plants, food processing, and many other applications. All heat exchangers consist of two fluids at different temperatures separated by a conductive solid medium to allow heat transfer to occur between the two fluids and no mixing of the two fluids. Many types of heat exchangers exist; plate and frame, shell and tube, counter flow, and parallel flow. Heat exchangers can even have multiple passes of the fluid or fins to provide maximum heat transfer. The type of heat exchanger to provide the best heat transfer varies depending on the application.Shell-and-Tube heat exchangers shown in Figure 1 and cross-current heat exchanger which is shown in Figure 2 are among the common types of heat exchangers. A basic schematic for a single pass shell-and-tube heat exchanger is shown in Figure 3. The stream to be cooled enters the tube side and is distributed amongst the tubes shown with red arrows. The stream that cools the liquid is shown in blue enters on the shell-side and flows perpendicular to the tube bundle for maximum heat transfer. The shell-side flow passes around baffles placed around the tube bundle in order to increase both the residence time of the fluid around the tube bundle as well as to promote turbulence in order to maximize the efficiency of the heat exchanger. Figure 1 : Shell and tube heat exchanger Figure 2 : Cross flow heat exchangerShell-Side InletShell-Side Outlet

Tube-Side OutletTube-Side Inlet

Figure 3 : Schematic of a Single-Pass Shell-and-Tube Heat Exchanger with Parallel-Flow Configuration

For this experiment, counter-current heat exchanger is used. In counter flow heat exchangers, the two fluids flow against each other, maintaining a maximum temperature difference between the hot and cold streams which allows for maximum heat transfer. Figure 4 shows how the counter-current heat exchanger works

Figure 4 : The flow of hot & cold water in counter-current heat exchanger

1.3AIMS1. To study the function and the working of shell and tube heat exchanger. 2. To calculate heat transfer and heat load with constant FT1.3. To calculate Log Mean Temperature Difference (LMTD) with constant FT1.4. To calculate heat transfer and heat load with constant FT2.5. To calculate Log Mean Temperature Difference (LMTD) with constant FT2.6. To study the working principle of counter flow heat exchanger.7. To study the effect of fluid temperature on counter flow heat exchanger performance.8. To study the effect of fluid flow rated on heat exchanger performance.

1.4THEORYA heat exchanger is a piece of process equipment in which heat exchange takes place between two fluids that enter and exit at different temperatures. The primary design objective of the equipment may be either to remove heat from a hot fluid or to add heat to a cold fluid. Depending upon the relative direction of fluid motion, shell-and-tube heat exchangers are classified as parallel flow, counter flow, cross flow. In parallel flow, the hot and cold fluids flow in the same direction and therefore enter the exchanger on the same end and exit the exchanger on the same end. In counter flow, the two fluids flow in opposite directions and thus enter the exchanger and exit the exchanger from opposite ends.

Figure 5 : Parallel and counter flow in Shell & Tube Heat ExchangerThe way that a heat exchanger works is hot water and cold water enter 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 convection 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. For a heat exchanger that flows parallel or countercurrent 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 is counter-flow cheat exchanger.Heat exchangers transfer heat from one working fluid to another. For instance, steam generators, feed water heaters, re heaters and condensers are all examples of heat exchangers found in nuclear power systems. The important quantity in heat exchanger analysis is the total rate of heat transfer between the hot and cold fluid. Several different expressions for this heat transfer rate can be developed, relating the heat transfer rate to quantities such as the inlet and outlet fluid temperatures and the overall heat transfer coefficient. When these expressions are developed, care must be taken to ensure that the appropriate mean temperature expressions are used. Several assumptions can be made to simplify these expressions. We assume negligible heat transfer between the system and its surroundings, negligible potential or kinetic energy changes, constant specific heats, and that the fluids are not undergoing any phase change. The basic theory in this experiment is Qh=Qc, which the amount of heat transfer is equal to the amount of heat absorb. In this case, the heat transfer rate across a heat exchanger is usually expressed in the form Q = mCp T. Heat transfer rate for hot water, = mh Cp T Heat transfer rate for cold water, = mc Cp T Heat loss Rate = Efficiency = Dirt Factor, Q = 0.5 (Qh+Qc)where : Q is heat exchanged m is flowrate Cp is heat capacity T is the temperature difference

There were also calculation of Log Mean Temperature Difference (LMTD).LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]1.5APPARATUSThe apparatus for this experiment is the HE158C Tube Heat Exchanger. This apparatus has a tank with a heater inside to heat water to a specified temperature. The temperature setting is adjusted at the thermostat on the front panel. Once the water is heated to the desired temperature it is transferred by a water pump next to the tank. On the pump there is a knob which varies the pump pressure. When using a volumetric flow rate above 2 L/min the switch should be set to the highest pressure. The hot water is pumped through a pipe to an insulated tube for which heat will be exchanged. The actual heat exchange takes place in the insulated tubing for which cold water flows concentricity around the hot water tube in two different flow arrangements. These two arrangements, parallel and counter flow, can be changed by opening and closing certain valves within the network of hot and cold water tubing. Each flow arrangement is shown on a diagram located on the front panel. It is worthwhile to note that the temperature at cold-in changes to temperature at cold-out when a counter flow arrangement is used. The same situation applies to the temperature at cold-out, which changes to temperature cold-in for the counter flow. The other readings remain the same. The flow rates can be adjusted for both cold and hot water by turning the valve knobs on the right side of the panel. Thermometers are located at the inlet, exit and middle of the insulated heat exchanger tubing for both hot and cold water.

1.6PROCEDURE1.6.1General Start-up Procedures :1. A quick inspection was performed to make sure that the equipment is in proper working condition.2. All valves were initially closed except V1 and V12.3. Hot tank was filled via a water supply hose connected to valve V27. Once the tank is full, the valve was closed.4. The cold water tank was filled up by opening valve V28 and the valve was left opened for continuous water supply.5. A drain hose was connected to the cold water drain point.6. Main power was switched on. The heater for the hot water tank was switched on and the temperature controller was set to 50oC.7. The water temperature in the hot water tank was allowed to reach the set point.8. The equipment was now ready to be run.

1.6.2General Start-up Procedures :1. The heater was switched off. The hot water temperature was waited until it dropped below 40oC.2. Pump P1 and pump P2 were switched off.3. The main power was switched off.4. All water in the process line was drained off. The water in the hot and cold water tanks were retained for next laboratory sessions.5. All valves were closed.

1.6.3Counter-current Shell & Tube Heat Exchanger Procedures :1. General start-up procedures was performed.2. The valves to counter-current Shell & Tube Heat Exchanger arrangement was switched.3. Pumps P1 and P2 were switched on.4. Valves V3 and V14 were adjusted and opened to obtain the desired flowrates for hot water and cold water streams, respectively.5. The system was allowed to reach steady state for 10 minutes.6. FT1, FT2, TT1, TT2, TT3 and TT4 were recorded.7. Pressure drop measurements for shell-side and tube side were recorded for pressure drop studies.8. Steps 4 to 7 were repeated for different combinations of flowrate FT1 and FT2.9. Pumps P1 and P2 were switched off after the completion of experiment.

1.7RESULTSExperiment A : Counter-current Shell & Tube Heat Exchanger (constant FI 1).FI 1 (LPM)FI 2 (LPM)TT 1 (0C)TT 2 (0C)TT 3 (0C)TT 4 (0C)DPT 1 (mmH2O)DPT 2(mmH2O)

10243.530.447.549.29718

10439.230.147.049.710323

10636.829.546.349.710065

10835.029.945.648.991130

101034.730.544.848.992190

Table 1 : Counter-current Shell & Tube Heat Exchanger with constant FI 1

Experiment B : Counter-current Shell & Tube Heat Exchanger (constant FI 2).FI 1 (LPM)FI 2 (LPM)TT 1 (0C)TT 2 (0C)TT 3 (0C)TT 4 (0C)DPT 1 (mmH2O)DPT 2(mmH2O)

21031.930.437.848.75195

41032.530.542.948.85194

61033.430.544.149.15193

81034.330.644.549.760192

101035.030.845.449.882191

Table 2 : Counter-current Shell & Tube Heat Exchanger with constant FI 2

1.8CALCULATIONSEXPERIMENT 1 :1. Calculation On Heat Transfer and heat load (constant FT1) and Calculation of Log Mean Temperature Difference (LMTD) :

Heat transfer rate for hot water, = mh Cp T = 10.0 x x x 988.18 x 4175 x (43.5-30.4) C = 9007.67 W Heat transfer rate for cold water, = mc Cp T = 2.0 x x x 995.67 x 4183 x (49.2-47.5) C = 236.01 W Heat loss Rate = = 9007.67-236.01 = 8771.66 W Efficiency = = = 2.62 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /(Th,out- Tc,in)]

= = -10.38C Dirt Factor, Q = 0.5 (Qh+Qc) = 0.5 (9007.67+236.01) = 4621.84

2.Calculation On Heat Transfer and heat load (constant FT1) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 10.0 x x x 988.18 x 4175 x (39.2-30.1) C= 6257.24 W Heat transfer rate for cold water, = mc Cp T= 4.0 x x x 995.67 x 4183 x (49.7-47.0) C= 749.67 W Heat loss Rate = = 6257.24-749.67 = 5507.57 W Efficiency = = = 11.98 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]

= = -13.45C Dirt Factor, Q = 0.5 (Qh+Qc) = 0.5 (6257.24+749.67) = 3503.46

3.Calculation On Heat Transfer and heat lost (constant FT1) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 10.0 x x x 988.18 x 4175 x (36.8-29.5) C= 5019.54 W Heat transfer rate for cold water, = mc Cp T= 6.0 x x x 995.67 x 4183 x (49.7-46.3) C= 1416.06 W Heat loss Rate = = 5019.54-1416.06= 3603.48 W Efficiency = = = 28.21 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]

= = -14.76C Dirt Factor, Q = 0.5 (Qh+Qc)= 0.5 (5019.54+1416.06)= 3217.8

4.Calculation On Heat Transfer and heat lost (constant FT1) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 10.0 x x x 988.18 x 4175 x (35.0-29.9) C= 3506.80 W Heat transfer rate for cold water, = mc Cp T= 8.0 x x x 995.67 x 4183 x (48.9-45.6) C= 1832.55 W Heat loss Rate = = 3506.80-1832.55 = 1674.25 W Efficiency = = = 52.28 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]


5.Calculation On Heat Transfer and heat lost (constant FT1) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 10.0 x x x 988.18 x 4175 x (34.7-30.5) C= 2887.96 W Heat transfer rate for cold water, = mc Cp T= 10.0 x x x 995.67 x 4183 x (48.9-44.8) C= 2846.01 W Heat loss Rate = = 2887.96-2846.01 = 41.95 W Efficiency = = = 98.75 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]


EXPERIMENT 2 :1.Calculation On Heat Transfer and heat lost (constant FT2) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 2.0 x x x 988.18 x 4175 x (31.9-30.4) C= 206.28 W Heat transfer rate for cold water, = mc Cp T= 10.0 x x x 995.67 x 4183 x (48.7-37.8) C= 7566.21 W Heat loss Rate = = 206.28-7566.21 = -7359.93 W Efficiency = = = 3667.93 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]


2.Calculation On Heat Transfer and heat lost (constant FT2) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 4.0 x x x 988.18 x 4175 x (32.9-30.5) C= 660.10 W Heat transfer rate for cold water, = mc Cp T= 10.0 x x x 995.67 x 4183 x (48.8-42.9) C= 4095.47 W Heat loss Rate = = 660.10-4095.47 = -3435.37 W Efficiency = = = 620.43 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]


3.Calculation On Heat Transfer and heat lost (constant FT2) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 6.0 x x x 988.18 x 4175 x (33.4-30.5) C= 1196.44 W Heat transfer rate for cold water, = mc Cp T= 10.0 x x x 995.67 x 4183 x (49.1-44.1) C= 3470.74 W Heat loss Rate = = 1196.44-3470.74= -2274.30 W Efficiency = = = 290.09 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]

= = -14.62C Dirt Factor, Q = 0.5 (Qh+Qc)= 0.5(3470.74+1196.44)=2333.59

4.Calculation On Heat Transfer and heat lost (constant FT2) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 8.0 x x x 988.18 x 4175 x (34.3-30.6) C= 2035.32 W Heat transfer rate for cold water, = mc Cp T= 10.0 x x x 995.67 x 4183 x (49.7-44.5) C= 3609.57 W Heat loss Rate = = 2035.32-3609.57 = -1574.25 W Efficiency = = = 177.35 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]


5.Calculation On Heat Transfer and heat lost (constant FT2) and Calculation of Log Mean Temperature Difference (LMTD) : Heat transfer rate for hot water, = mh Cp T= 10.0 x x x 988.18 x 4175 x (35.0-30.8) C= 2887.95 W Heat transfer rate for cold water, = mc Cp T= 10.0 x x x 995.67 x 4183 x (49.8-45.4) C= 3054.25 W Heat loss Rate = = 2887.95-3054.25= -166.3 W Efficiency = = = 105.76 % LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]

= = -14.70C

Dirt Factor, Q = 0.5 (Qh+Qc)= 0.5 ( + )= 2971.1

1.9DISCUSSIONSIn this experiment of shell and tube heat exchanger particular apparatus, water is used as both the hot and cold fluid. The purpose of this heat exchanger is to cool a hot stream. Cooling water flows through the outer pipe (the shell), and hot water flows through the inner pipe on the inside. Heat transfer occurs in both directions; the hot water is cooled, and the cooling water is heated. This arrangement is called a shell-and-tube heat exchanger. There are many other forms of heat exchangers; most notably, the double-pipe heat exchanger.In this arrangement, a cold fluid flows through a pipe in the center of the apparatus and is heated by a hot fluid on the outside of that pipe. The hot water used in the shell-and-tube heat exchanger is produced by means of a double-pipe heat exchanger. The discharge from the shell of the shell-and-tube heat exchanger is circulated through the inner pipe of the double pipe heat exchanger. Low-pressure steam condenses on the outside of the pipe, heating the water before it enters the tubes of the shell-and-tube heat exchanger. For this experiment, counter-current heat exchanger is used. In counter flow heat exchangers, the two fluids flow against each other, maintaining a maximum temperature difference between the hot and cold streams which allows for maximum heat transfer.In this experiment we are able to determine the value of heat load (Qh and Qc) besides to calculate the LMTD. We assume negligible heat transfer between the system and its surroundings, negligible potential or kinetic energy changes, constant specific heats, and that the fluids are not undergoing any phase change. In this case, the heat transfer rate across a heat exchanger is usually expressed in the form Q = mCp T. Heat transfer rate for hot water, = mh Cp T Heat transfer rate for cold water, = mc Cp T Heat loss Rate = Efficiency =

where : Q is heat exchanged m is flowrate Cp is heat capacity T is the temperature difference

Process fluid streams may contain suspended matters or dissolved solids. When such a fluid flows through a heat exchanger over a long period of time, deposition of the tube surfaces and shell surfaces occurs. The surfaces may also be corroded by fluid slowly and the resulting corrosion products also get deposited on the surface. Formation of the deposit on a heat transfer surface is called fouling and the heat transfer resistance offered by the deposit is called the fouling factor or dirt factor commonly denoted by Rd. the dirt factor cannot be estimated. It can only be determined from the experimental data on heat transfer coefficient of a fouled exchanger and a clean exchanger of similar design operated at identical conditions. From the equation to gain Dirt factor, Q is refer to Qh or Qc. But if error happened, take average value of U, by calculating Q = 0.5 (QH+QC) Dirt Factor, Q = 0.5 (Qh+Qc)There were also calculation of Log Mean Temperature Difference (LMTD).LMTD, TLM = [( Th,in Tc,out) (Th,out Tc,in)] / ln[( Th,in Tc,out) /( Th,out - Tc,in)]The basic theory in this experiment is Qh=Qc, which the amount of heat transfer is equal to the amount of heat absorb. In this experiment, the value of Qh is not the exact value as Qc because of some errors occur during this experiment. For example, heat loss to the surroundings. Presently, the heat exchanger has no insulation and the ambient room temperature has a large effect on the results obtained in this experiment and the reading affects the calculations too.

1.10CONCLUSIONThe heat exchanger apparatus follows the basic laws of thermodynamics and this can be shown experimentally. From the other experiments that hold flow rates constant or vary the flow rates, it is clear that the First Law of Thermodynamics and conservation of energy applies to the heat exchanger apparatus. The basic theory in this experiment is Qh=Qc, which the amount of heat transfer is equal to the amount of heat absorb. Although the value of Qh obtained in this experiment is slightly different with Qc, this might due to some errors occur during this experiment and the recommendations were made to improve this experiment.

1.11RECOMMENDATIONSFor this experiment of shell and tube heat exchanger, it is recommended that the heat exchanger be well insulated in order to reduce the heat loss to the surroundings. Presently, the heat exchanger has no insulation and the ambient room temperature has a large effect on the results obtained in this experiment. Apart from that, the flowrate measure during this experiment must be taken accurately. The eyes must be perpendicular to the scale of the flow meter so that the readings will be more accurate. During the experiment, it is recommended that the readings such as FT1, FT2, DPT1, DPT2 and temperature must be taken when the system is stabilized and reach its steady state. If the readings were taken when the system are not in stabilized condition, error might be occur. Then this will affect the readings and also the calculations. Next, to improve the system of shell and tube heat exchanger, it is recommended that the shell and tube heat exchanger have alert sign or alarm that can give a sign to the engineer who handles the equipment to take the readings at the correct time in order to get accurate readings. So that, this would help in reducing the inaccuracy of the measurements in the future. Lastly, the water to the tube side should be the first and last flow rate to be turned on. The steam should be turned on only after the water is flowing through the tube side and the water should be turned on only after the steam has been turned on so that the tube and shell heat exchanger can operates more effectively.

1.12REFERENCES1) Kessler, D.P., Greenkorn, R.A. (1999). Momentum, Heat, and Mass Transfer Fundamentals, New York : Marcel Dekker Inc., pp (768-828).2) Holman, J.P. (1981), Heat Transfer, 5th Edition, New York : McGraw Hill, pp (437-467).3) http://www.ejbowman.co.uk/products/ShellandTubeHeatExchangers.html retrieved on 4.4.2015.4) http://www.alfalaval.com/about-us/our-company/key-technologies/heat-transfer/shell-and-tube-heat-exchangers/pages/shell-and-tube-heat-exchanger.aspx retrieved on 4.4.2015.5) http://www.thermopedia.com/content/1121/ retrieved on 4.4.20156) McCabe, W.L., Smith, J.C., Marriott, P. (1985), Unit Operations of Chemical Engineering, 4th Edition, McGraw-Hill.7) Incropera, DeWitt, Bergman, Lavine. (2007), Introduction to Heat Transfer, 5th Edition, New York : John Wiley.

experiment of shell & tube heat exchanger

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