My Name
Shell and Tube Heat Exchanger Lab Report
Objectives
Introduction
A heat exchanger refers to a gadget that aids the transfer of heat from one fluid to another. The fluids involved can either be in direct contact or separated to avoid mixing (Ramesh & Sekulic, 2003). They are in common use in sewage treatment, natural gas processing, petroleum refineries, petrochemical plants, chemical plants, power stations, air conditioning, refrigeration, and space heating. A perfect example of a heat exchanger is in the internal combustion engine (ICE) (Hiereth & Prenninger, 2010). In such a situation, a circulating fluid called engine cooler flows over the coils of a radiator. As the air flows past the coils, there is the heating of the air.
In the exchanger, the two fluids enter and exit at different temperatures and, in most cases, they remain separate. The fundamental purpose of the device may either be to add heat to a cold fluid or to remove heat from a hot fluid (Shah et al., 1988). There are several kinds of heat exchangers. The most popular types include the shell and tube heat exchangers, the plate heat and the plate and shell heat exchangers. Other kinds include the adiabatic wheel and the plate fin heat exchangers. This script is a report on a laboratory experiment conducted on shell and tube heat exchangers.
A shell and tube heat exchanger comprises a series of tubes (Thomas, 2009). One of the tube sets has the fluid to either undergo heating or cooling. The other fluid flows on the tubes to either absorb or provide the heat as desired. The tube set is referred to as the tube bundle and can contain many forms of tubes. The tube categories include the longitudinally finned and the plain amongst others. The shell and fin heat exchangers are typical for high-temperature and high-pressure applications. They are always very efficiency and robust because of their shape. While designing the tubes of the heat exchanger, one has to consider many design properties. There can be several possible designs of tubes and shells. The tubes can either be straight or curved to form You-tubes. The chief parameter to consider while designing a shell and tube exchanger include the diameter, thickness, length, pitch, corrugation, layout, and the baffle design of the tube.
We can classify shell and tube heat exchangers as either parallel or counter-flow (cross- flow) depending on the relative flow direction of the two fluids (Thulukkanam, 2013). When they flow in the same direction, the exchanger is called a parallel flow as displayed in Figure 1 below. The liquids enter the exchanger from the same end. Figure 2 shows a counter flow. In such a case, the fluids enter and exit from the opposite ends.
Figure 1: Parallel Flow
Figure 2: Counter Flow
Procedure
Parallel Flow Test
The researchers connected a parallel flow and set the heating tank at a 60 ˚C. They checked and recorded the local ambient air temperature for reference. The investigators set the hot water flow rate at approximately 3 liters per minute. They proceeded to start up the flow of the water using a hand operated flow control valve. The experimenters went on to run the first test and recorded the findings on a Data Log Table. The researchers allowed the system to achieve a steady state in which the temperatures neither decreased nor increased. It took a few minutes while the researchers were adjusting the control valves and ensuring that the flow rate remained constant. The investigators recorded the cold and hot circuit temperatures on a Data Log. The repeated the steps for three more tests.
Counter Flow Test
The researchers connected a counter flow and set the heating tank at a 60 ˚C. They achieved the set up by swapping the position for the Cin and Cout. They checked and recorded the local ambient air temperature for reference. The investigators set the hot water flow rate at approximately 3 liters per minute. They proceeded to start up the flow of the water using a hand operated flow control valve. The experimenters went on to run the first test and recorded the findings on a Data Log Table. The researchers allowed the system to achieve a steady state in which the temperatures neither decreased nor increased. It took a few minutes while the researchers were adjusting the control valves and ensuring that the flow rate remained constant. The investigators recorded the cold and hot circuit temperatures on a Data Log. The repeated the steps for three more tests.
Results
Calculations
Conversion of the volumetric flow rate into mass flow rate (kg/s)
The researchers used a volumetric flow rate of 3 liters/ second.
Mass flow rate= the density x flow rate = 1 kg / liter 3 liters/s
= 3 kg/s
Heat transfer across the heat exchanger’s walls
Parallel flow heat exchanger
Cold Stream
Using equation 1 in the calculations, Table 1 shows the findings for the heat transfer on the cold stream. The assumption is that the specific heat capacity of the water remains constant at 4.2 kJ/ kg.K.
1
Hot stream
Using equation 2 in the calculations, Table 2 shows the findings for the heat transfer on the cold stream. The assumption is that the specific heat capacity of the water remains constant at 4.2 kJ/ kg.K.
2
Counter flow heat exchanger
Using equation 1 in the calculations, Table 3 shows the findings for the heat transfer on the cold stream.
Using equation 2 in the calculations, Table 4 shows the findings for the heat transfer on the cold stream. The assumption is that the specific heat capacity of the water remains constant at 4.2 kJ/ kg.K.
Logarithmic Mean Temperature Difference
Equation 3 is the formula for finding the logarithmic mean temperature difference. We now proceed to find its value for the parallel and the counter flow types.
3
Parallel flow heat exchanger
For a parallel flow heat exchanger, the following equations apply. We apply the average values to obtain the LMTD.
ΔT1 = Thin – Tcin = 58.425 – 12 = 46.425 ˚C.
ΔT2 = Tho – Tco = 54.9 – 22.125 = 32.775 ˚C.
Therefore, ΔTlog = (46.425-32.775)/ ln (46.425/ 32.775) = 39.205 ˚C.
Counter flow heat exchanger
For a parallel flow heat exchanger, the following equations apply. We apply the average values to obtain the LMTD.
ΔT1 = Thin – Tco = 58.75 – 22 = 36.75 ˚C.
ΔT2 = Tho – Tci = 55.1– 11.7 = 43.4 ˚C.
Therefore, ΔTlog = (43.4 -36.75)/ ln (43.4 / 36.75) = 39.982 ˚C.
Energy balances against the cold flow rate
For there to be an energy balance, the heat exchanger has to obey equation four below. The formula implies that the temperature rise in the cold fluid is inversely proportional to the mass flow rate of the cold fluid provided all the other parameters remain unchanged.
mH × CpH × (TiH - ToH) = mC × CpC × (ToC - TiC) 4
Overall heat transfer coefficient (U)
Equation 5 is the formula for obtaining the total energy transfer.
Q= UAF ΔTlog 5
Where Q= heat transfer rate;
A= Mean heat transfer area = 0.02 m2;
F= Correction factor
Rearranging the equation, one obtains the formula below.
U = Q/AF ΔTlog
We, therefore, apply the formula to get the total heat transfer coefficient in the two cases
Parallel flow heat exchanger
U = Q/AF ΔTlog = 44.415/ (0.02 x 0.92 x 39.205) = 61.57 kW/m2. K
Counter flow heat exchanger
U = Q/AF ΔTlog = 45.99/ (0.02 x 0.92 x 39.982) = 62.51 kW/ m2. K
Heat Exchanger Effectiveness
Equation 6 is the formula for obtaining the heat exchanger effectiveness.
ε= Qactual / Maximum possible heat transfer
Parallel flow heat exchanger
ε= Qactual / Maximum possible
= 66.78 / (3 x 4.2 x (59.1-11.9)) = 0.1122
Counter flow heat exchanger
ε= Qactual / Maximum possible
= 70.56 / (3 x 4.2 x (59.1-12)) = 0.12
Analysis
Parallel flow parameters
Counter flow parameters
Conclusion
A heat exchanger refers to a gadget that aids the transfer of heat from one fluid to another. The fluids involved can either be in direct contact or separated to avoid mixing. They are in common use in sewage treatment, natural gas processing, petroleum refineries, petrochemical plants, chemical plants, power stations, air conditioning, refrigeration, and space heating. Counter flow heat exchangers are more effective than their parallel counterparts under similar operating conditions.
References
Hermann Hiereth, Peter Prenninger. (2010). Charging the Internal Combustion Engine (3 ed.). Washington DC: Springer Science & Business Media.
R. K. Shah, Eleswarapu Chinna Subbarao, R. A. Mashelkar. (1988). Heat Transfer Equipment Design. London: CRC Press.
Ramesh K. Shah, Dusan P. Sekulic. (2003). Fundamentals of Heat Exchanger Design (1 ed.). New York: John Wiley & Sons. Retrieved from https://books.google.co.ke/books?id=beSXNAZblWQC&pg=PA3&dq=A+heat+exchanger+fluids+contact&hl=en&sa=X&redir_esc=y#v=onepage&q=A%20heat%20exchanger%20fluids%20contact&f=false
Thomas, C. E. (2009). Introduction to Process Technology. Toronto: Cengage Learning.
Thulukkanam, K. (2013). Heat Exchanger Design Handbook (Second Edition ed.). New York: CRC Press. Retrieved from https://books.google.co.ke/books?id=ZsU5A1mANWUC&pg=PA56&dq=shell+and+tube+heat+exchangers++parallel+or+counter-flow&hl=en&sa=X&ved=0ahUKEwj7i5urwb7MAhVCGz4KHRMaCSwQ6AEINDAA#v=onepage&q=shell%20and%20tube%20heat%20exchangers%20%20parallel%20or%20counter-f
