CLB21003 Process Heat Transfer- Mini Project: Design of heat exchanger

PROCESS HEAT TRANSFER ( CLB 21003) MINI PROJECT TITLE : DESIGN OF HEAT EXCHANGER

Group members : 1) Siti Hajar Mohamed (55213114225) 2) Wan Azlin Shakirah bt Wan Mohd Yusof (55213114198) 3) Syarafina Ajdrina bt Zulkipli (55213114301) 4) Tuan Nur Ayunie bt Tuan Rozam Shah ( 55213114240)

Lecturer’s name : En. Azahari bin Hamzah

1

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TABLE OF CONTENTS NO.

CONTENTS

PAGES

1

Objectives

3

2

Section 1: Executive Summary

4

3

Section 2 : Introduction

4

Section 3 : Tube Bank Analysis

5

Section 4 : Shell and Overall Heat Transfer Coefficient

5-8

9

10-12

Analysis 6

Section 5 : Product Quality Assurance

13-14

7

Section 6 : Cost Estimation

15-17

9

References

18

10

Appendices

19-21









OBJECTIVES

The main purpose in constructing and designing a heat exchanger is to implement all the knowledge about factors that influence heat exchanger. Besides, by designing a heat exchanger, we learn how to manipulate the parameter in order to minimize the weight, the cost, pressure drop and obtain most efficiency heat exchanger for the needed process. Furthermore, through this assignment, we are able to observe and decide which type of heat exchanger is suitable to be used in desired industry.









SECTION 1 : EXECUTIVE SUMMARY

The main purpose in designing a heat exchanger is to implement all the knowledge about factors that influence heat exchange and to manipulate the parameter in order to minimize the overall heat transfer coefficient, number of tubes bank, area of shell, cost, product assurance and efficiency heat exchanger for the process where we can able to observe and decide which type of heat exchanger is suitable to be used in desired industry which is important to reduce the cost for additional heating and cooling. In our design, basic structure of a shell and tube heat exchanger is a shell with a bundle of tubes inside it and the flow type is counter flow. The basic concept of a heat exchanger is based on the concept that the loss of heat on the high temperature side is exactly the same as the heat gained in the low temperature side after the heat and mass flows through the heat exchanger. The process involves two streams, which is the hot and cold stream. The cold stream (water) with temperature inlet and outlet 25°C and 65.88°C, respectively while hot stream (engine oil) with temperature inlet and outlet outlet 150°C and 100°C, 100°C, respectively where the heat is exchange between two fluids facilitate by heat exchanger where the fluid in the heat exchanger are at different temperature and do not mix with each other and without using the cooler and heater to heat up and cooled down fluid. It can be done by transferring heat from one stream to another by using heat exchanger. Selection and sizing of heat exchanger in our design is selected according few factors which is selection of tube and shell material, the diameter of tube use, the type of flow and the condition of baffles used.









SECTION 2 : INTRODUCTION

The technology of heating and cooling of systems is one of the most basic areas of mechanical engineering. Wherever steam is used, or wherever hot or cold fluids are required we will find a heat exchanger. They are used to heat and cool homes, offices, markets, shopping malls, cars, trucks, trailers, aero-planes, and other transportation systems. They are used to process foods, paper, petroleum, and in many other industrial processes. They are found in superconductors, fusion power labs, space-crafts, and advanced computer systems. The list of applications, in both low and high tech industries, is practically endless. In our basic study of thermodynamics and heat transfer, t ransfer, we studied the form f orm of the control volume energy balance and its application too many engineering problems, including to a basic heat exchanger problem. In this module, we will extend heat exchanger analysis to include the convection rate equation, and demonstrate the methodology for predicting heat exchanger performance that include both design and performance rating problems. Heat exchangers are typically classified according to flow arrangement and type of construction. In this introductory treatment, we will consider three types that are representative of a wide variety of exchangers used in industrial practice. The simplest heat exchanger is one for which the hot and cold fluids flow in the same or opposite directions in a concentric-tube (or double pipe) construction. In the parallel-flow arrangement of Figure 1.1a, the hot and cold fluids enter at the same end, flow in the same direction, and leave at the same end. In the counterflow arrangement, Figure 1.1b, the fluids enter at opposite ends, flow in opposite directions, and leave at opposite ends. A common configuration for power plant and large industrial applications is the shell-and-tube heat exchanger, shown in Figure 1.1(c). This exchanger has one shell with multiple tubes, but the flow makes one pass through the shell. Baffles are usually installed to increase the convection coefficient of the shell side by inducing turbulence and a cross-flow velocity component. The cross-flow heat exchanger, Figure 1.1d, is constructed with a stack of thin plates bonded to a series of parallel tubes. The plates function as fins to enhance convection heat transfer and to ensure cross-flow over the tubes. Usually it is a gas that flows over the fin surfaces and the tubes, while a liquid flows in the tube. Such exchangers are used for air-conditioner and refrigeration heat rejection









Figure

1.1

Types

of

heat

exchangers – (a)

concentric-tube

parallel-flow;

(b)

concentric-tube counter-flow; (c) shell-and-tube; and (d) cross flow. The list of products of heat exchanger are shell and tube heat exchangers are most commonly used in heating or cooling process fluids and gases. Typically found in applications where a need to heat or cool large volumes exist; however small volume applications are also very common. Brazed plate heat exchangers are a popular option with their compact size and high efficiency design. They are composed of a number of plate elements, each of which comprises two thin nested plates, the elements defining flow spaces between them, with adjacent elements being joined around their periphery by brazing bent edge portions. The Mueller Accu-Therm plate heat exchanger is a compact heat exchanger consisting of embossed heat transfer plates with perimeter gaskets to contain pressure and control the flow of each medium. The gasketed plates are assembled in a pack, mounted on upper and lower guide rails, and compressed between two end frames with compression bolts. ooling tower t ower is a heat rejection device that transfers waste heat from a process to the atmosphere though the cooling of the recirculated water. The type of heat rejection is commonly termed "evaporative cooling" in that the process heat energy is absorbed by the evaporation of a small portion of the circulated flow there by reducing the temperature of remaining water for reuse. Cooling towers can commonly provide lower water temperatures than are attainable with "air cooled" or "dry" heat rejection devices. (Product of heat











PROCCESS DESIGN OF HEAT EXCHANGER

In almost any chemical, electronic, or mechanical system, heat must be transferred from one place to another or from one fluid to another. Heat exchangers are used to transfer heat from one fluid to another. a basic understanding of the mechanical components of a heat exchanger is important to understand how they function and operate. a heat exchanger is a component that allows the transfer of heat from one fluid (liquid or gas) to another fluid. reasons for heat transfer include the following, which is, to heat a cooler fluid by means of a hotter fluid, reduce the temperature of a hot fluid by means of a cooler fluid, to boil a liquid by means hotter fluid, to condense a gaseous fluid by means of a cooler fluid, and boil a liquid while condensing a hotter gaseous fluid. Regardless of the function the heat exchanger fulfils, in order to transfer heat the fluids involved must be at different temperatures and they must come into thermal contact. heat can flow only from the hotter to the cooler fluid. in a heat exchanger there is no direct contact between two fluids. The heat is transferred from the hot fluid to the metal isolating the two fluids and a nd then to the cooler fluid. 3.1 Introduction Introduction

Before going through the design process, it is important to identify the properties and parameters of the heat exchange process inside the heat exchanger equipment. The parameters of the process will affect the design of the heat exchanger. Properties that must be considered is including the pressure, inlet and outlet temperature of cold stream, inlet and outlet temperature of hot stream, flow rate, etc.

Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contains









vapour. There are no chemical reaction involved in the heat exchanger, hence the inlet and outlet component is not change. In designing heat exchanger, the characteristics that should be determined from manual calculation is the tube count, heat transfer area, outer and inner diameter of tube, tube pitch, etc. There is several calculations that should be made to determine the heat balance and log mean temperature difference inside the heat exchanger in order to obtain the exact design of the heat exchanger. Before the designation process, some characteristics of the heat exchanger will be assumed based on the theoretical concept. It is including the type of the heat exchanger, number of tube and shell passes and the overall heat transfer coefficient. The assumption will be used to determine the design of the heat exchanger. The assumptions made for the heat exchanger design are:

Heat exchanger used is shell and tube



Number of tube pass = 6



Number of shell pass = 1









SECTION 3 : TUBE BANK ANALYSIS

Tube Bank 

ṁin = 35 kg/s



Tin = 150 150̊ C / 423 K



Pin = 5.5 bar / 550 kPa



Outlet Diameter (OD) = 0.019 m



Inner Diameter (ID) = 0.015 m



Length of tube (L) = 1.6 m



Heat transfer area per tube = π × L × ID = 0.0754 m2

1. QC = QH QH = ṁC p (ΔT) = (35 kg/s) (2441 J/kg.K) (50)K = 4271750 J/s 2. Velocity V = (35 kg/s)/(825.88 kg/m 3 X 0.0754 m 2 X 6) = 0.0937 m/s 3. Reynold’s number Re = (825.88 kg/m 3 X 0.0937 m/s X 0.,015 m 2)/(0.009357 kg/m.s) = 124.054 (In-Line) 4. Nusselt’s number (In-Line) Nu = 0.9 (124.054) (124.054) 0.4 (59.9)0.36 (59.9/98.31) 0.25 = 23.865

5. Heat Transfer Coefficient (in line)









SECTION 4 : SHELL AND OVERALL HEAT TRANSFER COEFFICIENT ANALYSIS

Shell 

ṁin = 23 kg/s



Tin = 25 25̊ C / 298 K



Pin = 9 bar / 900 kPa 

Tout,c = 338.88K/ 65.88 65.8 8̊C



Tout,h = 373K/ 100 10 0̊C



Tin,c = 298K/ 25 25̊C



Tin,h = 423K/ 150 15 0̊C



Outlet Diameter (OD) = 0.75 m



Inner Diameter (ID) = 0.55 m



Length of shell (L) = 3 m



Area = ӆ X 0.55m X 3m = 5.1836m2

1. To find CC QC = QH = ṁC p (ΔT 4271750 J/s = (25 kg/s) (4180 J/kg.K) J /kg.K) (T out,c – 298)K 298)K Tout,c = 338.88K/ 65.88 65.8 8̊C 2. Tavg Tavg = (65.88 + 25)/2 = 45.44K 4 5.44K 3. Velocity V = Q/A









= 0.04145m/s 6. Dinamic viscocity,µ(interpolation) (5) (0.547X10 -3 – x) x) = (4.56) (-4.9X10 -5) 2.735X10 -3 – 5x 5x = -2.2344X10 -4 x = 0.5917X10 -5 kg/s.m 7. Reynold’s number Re = [(989.92 kg/m 3) (0.04145m/s) (0.55m 2)] / 0. 5917X10 -5 kg/s.m = 38141.218 (laminar) 8. Prandtl number, Pr s (interpolation) (5) (3.55 – (3.55 – x) x) = (4.56) (-0.36) 17.75 – 17.75 – 5x 5x = -1.6416 x = 3.878 9. Nusselt’s number, Nu Nu = (0.27) (38141.218) (38141.218) 0.63 (3.878)0.36 (3.878/6.14) 0.25 = 301.7544 10. Thermal conductivity,k (interpolation) (5) (0.644 – (0.644 – x) x) = (4.56) (7X10 -3) 3.23 – 3.23 – 5x 5x = 0.03192 x = 0.6376 11. Overall Heat Transfer Coefficient 1/U = 1/hshell + 1/htube = 1/ 349.8156 + 1/213.6713 U = 132.65 W/m. W/m .̊C 12. (ΔT)LM θ1 = Tin,h – T Tout,c











P = (Tout,h – T Tin,h)/(Tin,c – T Tin,h) = (373.15 – (373.15 – 423.15)/(323.15 – 423.15)/(323.15 – 423.15) 423.15) = 0.4 R = (Tin,c – T Tout,c)/(Tout,h – T Tin,h) = (298.15 – (298.15 – 339.03)/(373.15 – 339.03)/(373.15 – 423.15) 423.15) =0.82 From the graph, the value for correction factor is 0.95

14. Overall area, A S As = Q/ (U F (ΔT) LM) = 4271750 W/(132.65 W/m 2.K X 0.95 X 79.473) =426.536 m 2 15. Number of Tubes No. Of tube = Ashell / Atube = 5.1836/ 0.0754 = 69 tubes









SECTION 5 : PRODUCT QUALITY ASSURANCE

In developing products and services, quality assurance is any systematic process of checking to see whether a product being developed is meeting specified requirements. A quality assurance systems is said to increase customer confidence and a company’s credibility, to improve work processes and efficiency, and to enable a company to a better compete with others. Quality assurance is the way of preventing defects in manufactured of products and avoiding problems when delivering a service to customers. Quality assurance refers to administrative and also procedural activities implemented in a quality systems so that requirements and goal for a product, service or activity will be fulfilled. There are a few selection that should be taken such : 1) Selection of tube and shell material

To be able to transfer heat well, the tube material should have a good thermal conductivity. Because heat is transferred from a hot to a cold side through the tubes, there is a temperature difference through the width of the tubes. Because of the tendency of the tube material to thermally expand differently at various temperatures, thermal stresses occur during operation. This is in addiction to any stress from high pressure from the fluid themselves. The tube material also should be compatible with









3) Type of flow

For this design problem, we choose counter flow. Both fluids flow in opposite directions, and are used for liquid-liquid, condensing and gas cooling applications. Units are usually mounted vertically when condensing vapour and mounted horizontally when handling high concentrations of solids.

4) Baffles

Baffles are used in shell and tube heat exchangers to direct fluid across the tube bundle. They run perpendicularly to the shell and hold the bundle, preventing the tubes from sagging over a long length. They can also prevent the tubes from vibrating. The most common type of baffle is the segmental baffle. Baffle spacing is of large thermodynamic concern when designing shell and tube heat exchangers. Baffles must be spaced with consideration for the conversion of pressure drop and heat transfer. For thermo economic optimization, it is suggested that the baffles be spaced no closer than 25 % of the shell’s inner diameter which it is double double segmental baffles. Having baffles spaced s paced too closely causes caus es a greater pressure pressu re drop because of flow redirection. Consequently having the baffles spaced too far apart means that there may be cooler spots in the corners between baffles. It is also important to ensure the baffles are spaced close enough that the tubes do not sag.









SECTION 6 : COST ESTIMATION

1 : Purchase cost for shell – shell – tube tube Heat Exchanger Determined by size factor , A ( ft 2 ) and the type of tube sheet is fixed head and the purchase cost is 19 000 USD

2 : Purchase cost









2.2 : Tube length correction factor Overall length = 3m 3m = 9.8 ft Interpolation for F L Tube length of 8 ft = 1.25 and 12 ft = 1.12

( 12 12 − 8 )( 1.1 1.12 −  ) = ( 12 12 − 9.8 )( 1.12 1.12 − 1.25 1.25 ) X = 1.1915

2.3 : Fixed head CB = exp { 11.0545 – 11.0545 – 0.9228 0.9228 ln [A] + 0.09861 ln [ A ] 2 = exp { 11.0545 – 11.0545 – 0.9228 0.9228 ln ( 426.536 m 2 ) + 0.09861 ln ( 426.536 m 2 ) } = 24.68











Cost estimation : CP * Purchase cost = 65.00 * 19,000 USD = 1,235,000 USD 1 USD = 4.34 MYR = RM 5,359,900









REFERENCES

1. Arthur H. Tuthill. The Right Metal for Heat Exchanger Tubes. Chemical Engineering. 1990, 120-124. 2. http://faculty.kfupm.edu.sa/ME/antar/experiments/Updated.Experiments/Shell_Tube/class es/index.htm [Accessed 8 December 2015]. 3. http://asq.org/learn-about-quality/quality-assurance-qualitycontrol/overview/overview.html [Accessed 12 December 2015]. 4. DoganEryener (2005), ‘Thermoeconomic optimization of baffle spacing for shell and tube heat exchangers’, Energy Conservation and Manage ment, Volume 47, Issue 11 –12, Pages

1478 –1489. 5. Perry, Robert H. and Green, Don W. (1984). Perry's (1984). Perry's Chemical Engineers' Handbook (6th Edition ed.). McGraw-Hill.









APPENDICES

















CLB21003 Process Heat Transfer- Mini Project: Design of heat exchanger

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