Heat Transfer BKF 2422 Mini Project
APPENDICES
Introduction
2
Literature Review
4
Design Problem
5
Discussion
6
Conclusion
14
Reference
14
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Heat Transfer BKF 2422 Mini Project INTRODUCTION
A heat exchanger is an equipment in which heat exchange takes place between two fluids that enter and exit at different temperature. The main function of heat exchanger is to either remove heat from a hot fluid or to add heat to the cold fluid. In this heat exchanger designation, we study only the counter-current flow. Both the hot and cold fluids flowing in the opposite direction. In this case study, we focused on the 1-2 shell and tube heat e x c h a n g e r .
We had chosen oil as hot fluid while water as cooling fluid. The decision to use thermal oil as a heat transfer medium can be based on many reasons but one of the major incentives is the use on a nonpressurised system. Steam systems operate under pressure and are subject to statutory and regulatory requirements due to the inherent risk from pressure and the increased cost of installation and routine insurance inspection requirements. Besides, thermal oils are much more thermally stable, non-toxic and able to create higher temperatures at atmospheric pressure, than their former counterparts. As a result many companies are investigating the use of the technology in their heat transfer processes. Thermal oils allow the use of low pressure heat transfer systems to achieve high temperatures which would otherwise have necessitated high pressure steam systems. Steam systems are subject to statutory and regulatory requirements due to the inherent risk from pressure and the increased cost of installation and routine insurance inspection requirements.
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Heat Transfer BKF 2422 Mini Project These are the table properties of the oil:
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Heat Transfer BKF 2422 Mini Project LITERATURE REVIEW
Heat exchanger is a devices that is vital in industries. These industries such as power production, food industry, manufacturing industry and a lot more other industries. It has various types. It funtioned according to its uses. Heat exchanger is used to transfer thermal energy between two or more fluids, between a solid surface and a fluid at different temperatures and in thermal contact. In heat exchangers, heat transfer between fluids through a separating wall or into and out of a wall. Now, we will discuss about shell and tube heat exchanger. There are several types of shell and tube of heat exchanger. For example shell and tube heat exchanger (1,2), 1 represent number of shell and 2 represent number tube. So, there is many other shell and tube heat exchanger with different number of shell and tubes. It is built with bundle of round tubes in a large cylindrical shell with the tube axis parallel to the shell. That is because it used to transfer the heat between the two fluids. The fluid flows inside the tubes and other fluid flows across and along the tubes. It consists of tubes, shells, frontend head, rear-end head, baffles and tubesheets. It is used as oil-coolers, power condensers, preheaters in power plants and also steam generators in nuclear power plants. The most common types of shell and tube heat exchanger are U-tube design and floating-head type. There are a lot of advantages using shell and tube heat exchanger. The advantages are the configuration gives a large surface area in a small volume, a good shape for pressure operation, uses of well-established fabrication techniques, can be constructed from a wide range of materials, easily cleaned and a well-established design procedures. It is also cheap except for U-tube design which is quite expensives.
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Heat Transfer BKF 2422 Mini Project DESIGN PROBLEM
Problem statement – Water, at a flow rate of
, needs to be heated from 302.59 K to 305.93 K.
Lubricant oil is available at 330.37 K. A typical shell and tube heat exchanger will be used. The plant manager recommends that the minimum temperature approach should be at least 10 K. He also recommends using 20 BWG carbon-steel tubing with a pressure drop not exceeding 10 psig (0.67 atm) for either the shell or tube side.
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Heat Transfer BKF 2422 Mini Project
DISCUSSION
(Data from Pennel Power Engineering Corp.)
Fluid A
0.00905
330.37
319.26
Fluid B
0.01
302.59
305.93
(All data express in Excel Spreadsheet Data)
Fluid A (hot fluid)
= Oil
Fluid B (cooling material)
= Water
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Heat Transfer BKF 2422 Mini Project First and foremost, we need to determine whether Fluid A should be in shell or tube pass. Stream allocation is an important decision in heat exchanger design. This decision can impact the heat exchanger life; can also make the difference between higher and lower maintenance costs. Plus, it can also have a high impact on the thermal performance the heat exchanger. From the properties, Fluid A which is oil should be place in shell pass. This is because it has lower flow rate compare to Fluid B (cooling material). Furthermore, we need to cool down the temperature of Fluid A, so it is more prefer for Fluid A place inside shell pass.
Next, we need to determine whether the flow configuration is co-current or counter-current. Based on our research, we choose counter-current for the flow configuration. For your information, a heat exchanger can have several different flow patterns. Counter-flow, parallel flow, and cross-flow are common heat exchanger types. A counter-flow heat exchanger is the most efficient flow pattern of the three. It leads to the lowest required heat exchanger surface area because the log mean temperature drop is the highest for a counter-flow heat exchanger. That’s why counter-current flow configuration is more preferable in this heat exchanger design.
For cooling material which is Fluid B to cool down Fluid A, we had chosen water. This is due to water is a universal solvent and can act the best as cooling material. Besides, water is inexpensive and non-toxic. The advantages of using water cooling over air cooling include water's higher specific heat capacity, density, and thermal conductivity. This allows water to transmit heat over greater distances with much less volumetric flow and reduced temperature difference.
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Heat Transfer BKF 2422 Mini Project Properties of Fluid B (All properties are evaluated at average temperature of Fluid B)
T(K)
p(kg/m3)
(Pa.s)
Cp(kJ/kg.K)
k(W/m.K)
Npr
299.9
996.4
4.183
0.00086
0.6109
5.89
304.26
995.7323
4.1830
0.0008
0.6177
5.3479
311
994.7
4.183
0.000682
0.6283
4.51
(Data is calculated in Excel Spreadsheet Data)
Calculate the Heat Load Heat balance:
Since
We can calculate for
:
(
)
Therefore, heat load,
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Heat Transfer BKF 2422 Mini Project Estimated overall heat transfer coefficient (
) for this heat exchanger design
For Heavy oil as hot fluid, and water as cooling material, the overall heat transfer coefficient is around
. th
(From journal and textbook, Geankopolis, 4 Edition)
Thus, we decide to take
as overall heat transfer coefficient,
Calculate the true mean temperature difference
.
is the heat exchanger
Before we calculate true mean temperature difference, we must first calculate Log mean temperature difference and determine its Fouling factor.
Log Mean Temperature Difference (LMTD)
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Heat Transfer BKF 2422 Mini Project Based on value Y and Z, we can determine the
.
th
(from textbook Geankopolis, 4 Edition)
Thus, now we can easily find the true mean temperature,
:
Calculate the heat transfer area using the estimated overall heat transfer coefficient,
.
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Heat Transfer BKF 2422 Mini Project Calculate The Tube-Side Shell And Shell-Side Transfer Coefficients.
For fluid B : T average(K)
p(kg/m3)
Cp(kJ/kg.K)
304.26
995.7323
4.1830
0.0008
k(W/m.K)
Npr
0.6177
5.3479
Assumption : 1. Fixed tube plate type 2.
0.025 m OD tubes (14 BWG) on 1.25 square pitch (PT)
3.
Tube length (Lt) = 0.609m (the tube length is increased from 0.406m)
4.
1 shell pass-6 tube pass (tube passes is increased to 6 from 2)
5.
Tube ID= 0.021m
6.
Flow area per tube=0.0352m2
7. 1 shell 6 tube
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Heat Transfer BKF 2422 Mini Project no of tube = 715.4485 /π (0.025)(0.609) = 323 NRe = 4mo (np/nt ) / π di µ = 4(0.01)(6/323)/ π (0.021)(0.0008×1000) = 14.07 u = NRe µk / di ϼk = 14.07(0.8)/0.021(995.7323) = 0.538 m/s
Tube-shell heat transfer coefficient = JH = hi di /k (µk ck / kk) -(1/3) 42= hi (0.04) / 0.6177 (0.8(4.183)/0.6177) -(1/3) hi = 4676.33 W/m2 .K Side-shell coefficient = Assumption : ID= 0.028m, OD=0.032 De = 4 (Pt2 - π/4 do2) / π do = 4(12 - π/4 (0.0322) )/ π (0.032) = 39.7567 As = π/4 (Di2) = π/4 (0.028 2) = 6.158 ×10-4 m2 NRe = ms De / As µs = 0.0095 (39.7567) / 6.158×10-4 (0.8) = 490.66 haD/k =1.86 (NRe NPr D/L ) (1/3) ha (0.032) / 0.6177 = 1.86 (490.66 (5.3479)(0.032/ 0.609 ))(1/3) ha =185.48 W/m2.K
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Heat Transfer BKF 2422 Mini Project Calculate Uo cal and heat transfer area. Uo cal =1 / [ 1/ ho +Rdg +Ao /Ai ((Do-di) /2kw) + Ao /Ai (1/hi) + Ao /Ai × Rdk ] Uo cal = 1/ [ 1/4676.33 +0.0002 + (π (0.0252)/ π (0.0212)) {(0.025/12)-(0.021/12)}/2(0.6177)} + (π (0.0252)/ π (0.0212)) (1/185.48) + (π (0.0252)/ π (0.0212)) × 0.0009 = 152.31 Error = 152.3 - 180 / 180 = 15.4% Heat transfer area = Q /Uo cal
= 139.7122 / (152.3 (19.9038)) = 0.046 m2
To reduce error : 1. Reduce the pressure drop. 2. Take the value in the correct table.
Estimation heat transfer coefficient = 2430.9 W/m2 K.
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Heat Transfer BKF 2422 Mini Project CONCLUSION
From the case study, we had already made a choice on heat exchanger plant design. We also had calculated the entire project’s requirement. Although it is quite difficult to find company with their specification heat exchanger, we finally have come out with this final report. All calculation is state and all details we have attached it in Excel Spreadsheet data. Therefore, we can conclude that the objective of this Mini Projects’ which is to apply knowledge of mathematics, science, engineering fundamentals and an engineering specialization to the solution of complex engineering problems, to - Identify, formulate, research literature and analyzed complex engineering problems reaching substantiated conclusions using first principles of mathematics, natural sciences and engineering sciences, and to Design solutions for complex engineering problems and design systems, components or processes that meet specified needs with appropriate consideration for public health and safety, cultural, societal, and environmental considerations are successfully achieved.
REFERENCE
1) http://www.power-eng.com/articles/print/volume-114/issue-2/features/supplementalcooling.html 2) http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/node131.html 3) Transport Process Textbook, Geankopolis, 4th Edition. 4) http://en.wikipedia.org/wiki/Heavy_crude_oil 5) http://www.brighthubengineering.com/hvac/62410-heat-exchanger-flow-patterns/
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