Effect of tube arrangement on the performance of shell and tube heat exchanger

Research aim: “To determine the effect of tube arrangement on the performance of shell and tube heat exchanger”

Research Objectives: 

• To evaluate the working procedure of shell and tube heat exchanger
• To determine different patterns of tube layout in heat exchanger devices
• To analyse the way on which performance of shell and tube heat exchanger influence

Research Question:

• How tube layout patterns influence the performance of shell and tube exchanger devices?

Chapter 2: Literature Review

Theme 1: Working procedure of shell and tube heat exchanger

A heat exchanger is used for transferring enthalpy (thermal energy) between a fluid and solid surface, two or more fluids, etc. in thermal contact with varies in temperatures. Usually, in such devices, work interactions and external heat not occurs. Therefore, typical applications in heat exchangers involves the cooling or heating of a fluid stream as well as evaporation or might be condensation of multi / single component fluid streams (Cai and et. al., 2019). The objectives in other applications may include sterilize, distilled, pasteurize, concentrate, crystallize or more, to control the fluid process or recovery / rejection of heat. In some heat exchangers, the fluids that exchanges heat are might be in direct contact. While in most devices, heat transfer among fluids are taken place by separating the wall transiently. According to the views of Brogan (2020), the shell and tube heat exchanger is a type of heat exchanger in which fluid is transferred into gaseous state. It also includes the process of heat exchanger that consist of both warmed and chilled fluid (Dandotiya and Banker, 2017). In this, two fluids having different temperatures are flow in this exchanger process. The fluid can be transform through tube walls. It consists of pressure and temperature from which heat exchanger process occur. The one fluid flow outside the tube but inside the shell while other fluid flows inside the tube. The shell and tube exchanger mainly consist of various parts. These tubes are present in cylindrical form. In shell tube bundle are present.

The tube bundle consists of tube sheets, baffles, tubes and tie rods, etc. in order to hold bundle. In Front header, fluid enters inside of tube side. In rear header, the fluid leaves from this part and returned to front header through multiple passes of tube side. The plenum is present on the end of shell. This work by collecting or discharge the bundle of fluid. The baffles help in removing barriers that occur at time of heat exchangers. As this improve regulation of shell by creating turbulence in shell (Wang  and et. al., 2017). It also decreases concentration of cold and hot liquid. These are essential to work properly as it depends on proper functioning of heat exchanger. In pressure, sometimes unexpected leak occurs but with pressure differential, leakage or contamination of fluid can be prevented or minimized. The pressure has increased in tube sheet so that leakage can be easily flow in cooling medium. This prevents from costly failures in the process of fluid. In such type of exchanger, heat external and interactions between work are not occur.

Some heat exchangers consist of direct contact with fluid that exchange through heat. While in others, walls are separately used in heat transfer process of fluid. In shell and tube heat exchanger, liquid and gases both are used as fluids (Jiang and et. al., 2017). As per views of Brogan (2020), this process is an efficient mode of energy conservation as large number of tubes are used in which heat transfer occur at large number of area. In this, only one phase or single phase used as heat exchangers for both liquid and gas on each side. The two fluids are used in this heat exchanger process. One is for processing and other used as cooling medium. The small diameter tubes are placed in shell in which process fluid are run after being cooled. The cooling medium is present on outer part of shell. In order to keep function properly of, both fluid cooling and process are regulated continuously in exchanger (Riahi and et. al., 2017). This exchanger consists of small tubes which creates large surface area that help in proper functioning of shell and tube exchanger. The cooling fluid is necessary to be choose in this exchanger as most plants are require water supply.

There are some mediums that can be used as cooling fluid such as water, ethylene glycol and propylene glycol in context of plants. The water is the most effective medium that are used in this as it is easily available. The ethylene glycol has lower freezing point and higher boiling point when it is mixed with water (SHELL AND TUBE HEAT EXCHANGERS, 2020). The propylene glycol is less toxic and is used in coolant medium high as it reduces the issue of coolant. This medium has qualities of freezing and boiling point and transfer of thermal heat.  There are some standard set in working of shell and tube exchanger. The Tubular exchanger manufactures association set some standards that identify power of manufacturing  of shell and tube exchanger (Singh and Sarkar, 2018). With the help of this standard, workers get to know standard of industry that can linked with heat exchanger as it can produce quality. In this, there are three types of standards are included such as R, C and B.  This exchanger can be used in power plant or feed water.

Theme 2: Different patterns of tube layout in heat exchanger devices

 Heat exchanger is basically a device which converts heat from one medium to another. It is used in both heating and cooling processes (Abd, Kareem and Naji, 2018). Tube layouts in heat exchanger devices refers to tubes which are located in a shell. There are four different types of tube layouts in a heat exchanger devices such as square (90°), triangular (30°), rotated triangular(60°)and rotated square (45°). Triangular patterns are used to provide greater heat transfer as they make the fluid to flow in a turbulent manner around the piping. However, square patterns of the tube layout are used where large fouling is experienced and cleaning is in a constant manner (Geete and et. al., 2018). The prior function of tube layout in a heat exchanger device is to involve large number of tubes in a shell in order to acquire maximum area for heat transfer. A triangular pattern of tube layout will adapt more tubes in comparison to square or a rotated square patterns. A triangular pattern is more often employed to produce high turbulence and eventually leads to high amount of heat transfer. At the crucial tube pitch of 1.25 times the tube O.D, it does not allow any mechanical cleaning of tubes, hence access lanes are not available. Eventually, a triangular layout in the tube of a heat exchanger device is only limited to clean shell side services (Kayabasi, Alperen and Kurt, 2019). As per the perspective of Chemical Engineering World, (2013) it has been analysed that for the services which require mechanical cleaning on the shell side, square patterns of the tube must be utilized. Access lanes are not necessary for the chemical cleaning process, so it is important to use a triangular layout patten for dirty shell side services to offer a suitable and an effective chemical cleaning. A triangular pattern could be used for fixed tube sheets exchangers and square pattern is used for floating head exchangers (Esapour and et. al., 2016). For U-tube exchangers a triangular pattern can be utilise to provide a shell side stream and square pattern is used when it is dirty. Such different patterns of tube layout in Shell and Tube Heat Exchangers would be helpful in effective heat transfer. A tube layout angle is referred in context to the flow direction and is not linked with vertical or horizontal reference line arrangement (He and et. al., 2016). For a given O.D ratio, about 15% of the more tubes could be accommodated within a given shell diameter using a triangular layout. High heat transfer is often link with this specific pattern of tube layout. Only water jet cleaning is possible in this kind of layout. The effect of square pattern of tube on performance of STHEs would be beneficial as it is used for dirty shell side services which require mechanical cleaning method. It would probably increase the functioning of STHE and would result in a effective heat transfer (Ma and et. al., 2017). It would be beneficial to use rotated square pattern as square pattern may produce much amount of turbulence which may leads to higher efficiency of transformation of pressure drop to heat transfer.

Theme 3: Influence of tube layout pattern on performance of heat exchanger devices

As per Tubular Exchangers Manufacturers Association (TEMA) standard, it has been analysed that for tube layouts in the form of rotated triangular (with 60º angle) and triangular (with 30º angle) patterns has accommodated more tubes than other layouts that are square (90º) and rotated square (45º) patterns having on same tube pitch (Pal and et. al., 2016). Under there type of arangements, a triangular pattern of tube layout produces high turbulence. So, a high heat-transfer rates can be used but at expense of higher pressure drop (a square, or rotated square arrangement), for heavily fouling fluids. But here, in this process, it is necessary that outside of the tubes must be mechanically cleaned (Chahartaghi, Eslami and Naminezhad, 2018). As flow characteristics in tube bundles around some rows of tube is highly influenced by pattern of arrangement, therefore, it has the direct influence on exchange of heat between fluids. Along with this, some other factors that might influence performance of shell-side of STHEs include baffle spacing, inlet and outlet zones’ size, number of tubes, baffle cut, etc. Furthermore, it has been investigated that there is a high impact of baffle inclination angle on fluid flow and different characteristics of STHE’s heat transfer (Shahril and et. al., 2017). With various degrees or baffle inclination angles such as 0⁰, 10⁰, 20⁰ etc. with 35% as baffle cut, inclination angle 20⁰ shows the better performance than others. Along with this, rate of transfer heat also increased up to 30⁰ angular orientation of baffles, while decreases at 45⁰.

Taking the geometrical modelling, with parameters like Baffle (number of baffles, cutting, spacing etc.), Tube (diameter, layout pattern, pitch, number of tubes) and shell-side (inlet and outlet diameter) will be taken to draw the tube bundle arrangement, in following way –

Figure 1: Pattern of Tube Layout Arrangement

Figure 2: Tube Bundle Arrangement -

1. Triangular STHE
2. Rotated STHE
3. Combined patterns

Taking the thickness of tube material negligible, thermal properties of fluid; engine oil and water as varied within shell-side and tube-side respectively, the governing equations for such an analysis include RANS Model with k – ε, turbulence in following way –

∇.(𝛒u) = 0  as continuity equation … (i)

𝛒u. ∇ u = ∇. [-pI + (µ + µ_T ) ((∇u + (∇u)^T ) – â…” (∇.u) I ) - â…” pkI  ] + F          as momentum equation … (ii)

Using this momentum equation, turbulent KE equation will be –

𝛒u. ∇ k = ∇. [(µ + µ_T / σ_k) ∇k ] + µ_T P(u) – (⅔𝛒k)∇.u) – ð›’ε    …(iii)

Energy Equation –

𝛒C_p u. ∇ T = ∇ . (k ∇T) + Q

Under these equations, constants of RANS model –

C_µ = 0.09, C_ε1 = 1.44

C_ε2 = 1.92 and σ_k = 1.0 to 1.3

So, through numerical investigation, it has been identified that in each STHE, the viscosity of fluid increases from tubes inlet to outlet and it may be result in elimination of fluid density as the shell side is heated up as its viscosity increases (Cai and et. al., 2019). It has been analysed that portions with higher amount of viscosity arise between baffles which is due to cross flow heating of tubes from the shell. Pressure drop in STHEs is more pronounced in the shell zones rather than in the baffle window. It is majorly because of cross-flow obstructions occurred through tube bundles (Panahi and Zamzamian, 2017). Within the lower pressure drop region, the overall heat transfer enhance at a faster rate than the increase which has observed in higher pressure drop area. This incarnate some of the facts found in the study that mass flow rate has increase and drops in heat transfer rate and pressure are directly proportional to each other. STHE produce high amount of heat transfer coefficient for combined patterns. Heat transfer is high in combined patterns rather than rotated triangular pattern for same pressure drop. Performance factors for rotated triangular pattern and combined pattern in STHE reduce crucially (Abdelkader, Jamil and Zubair, 2019). Thus, it has been critically identified that triangular pattern of tube lay out in Shell and Tube Heat Exchangers has higher performance in relation to transfer of heat rather than rotated triangular and combined patterns.

Chapter 3: Research Scope

Significance of research

Enhancement of heat transfer via devices like Shell and Tube Exchangers stills, carried a high attention of researchers. Therefore, working on this topic and investigating how tube layout pattern influence the performance of STHE, helps researchers in widening their skills about concept of transfer (Wang, Zheng, Liu and Liu, 2018). Through investigation, a number of concepts like whether shell diameter and length of tube also effect heat transfer coefficient or not, including pressure drop towards shell side with square and triangular pitches can be analysed. In this regard, to conduct study, the present research will be carried on secondary basis, where a number of articles will be chosen, under which shell and tube heat exchanger are designed via utilising a number of equipment, like various parameters for studying the effect of cutting space, baffle window, shell diameter and tube length, fouling rate on pressure drop and heat transfer coefficient for shell and tube sides etc. (Saffarian, Fazelpour and Sham, 2019). This would help in studying the impact of each parameter of such design, which will further lead to make quick prediction.

Chapter 4: Research Method

To conduct a study on such a complex project of engineering, secondary articles will be explored from authenticate websites. This would help in addressing mention objectives and maintaining accuracy as well (Du, Chen, Du and Cheng, 2019). While to numerically investigate the effect of tube arrangement on performance of STHEs, Geometrical Modelling will be used, which includes three distinct set of tube bundles by negligence the material of tube – triangular, rotated triangular and combined patterns.

Chapter 5: Project Budget, Resources and Time Line

Project Budget

Project budget is a tool that utilised the project mangers to analyse and determine the total cost of the project which is investing by project administrator to [perform all the actions and activities of the specific project. This document consist a brief information about all the fund and finance that are likely to be obtained before the project is completed. Before starting a project, the project manager formulate a budget on the basis of approximation regarding that cost which is required to complete particular work. This budget consist different cost like labour cost, material procurement cost and operating cost. At the time of formulation of this document, the individual meet all the financial needs of the project so that it can design an effective statement regarding finance. Project budget is important because its permits administrators to monitor that how much cost will require for the project.

In this current project, the researcher will required £700 to complete the investigation project in appropriate manner. This mentioned cost will be needed to surveyor to gather information by using different sources of data collection like internet and authenticate website. Because the research is doing towards an engineering project so collecting accurate information, the person uses authenticate sites which are cost consuming. Apart from it, the person required cost for instruments, equipment and others so that they can accomplish this project report in effective manner.

Resources

It refers to those sources that are used by the investigator to gather and collect information for the completion of the report. It can be those assorted substantial that serve as a basis for different studies that including survey, interviews, articles, research papers, academic journals, articles etc. In this current project, the investigator uses secondary method of data collection so it will use different resource of this method regarding information gathering like collect data from authentic websites, articles, research papers and others. Other resources that are needed to complete this investigation report are time, cost, instruments, equipments, internet, human resource and machinery etc. and surveyor will require critical thinking, knowledge, skills, expertness and potential etc.

Time Line

It refers to that time frame and duration which is needed to project managers to complete research report so that the work can be finished on time. It can be that time period which can be consumed by the research activity to perform a specific task. In context of this report, it is a display of a list of activities which are mentioned in chronological order. It is a visual communication by which it is represent that how much time is taken by a particular research work for accomplish it. For example, how much time duration consume by researcher to set aims and objective, selecting research method, gathering data, interpretation of information and others. For performing all the research activity of this project the surveyor will be require 4 months. Within this duration, the person set aims and objective, use appropriate methodologies and collect information so that the individual can accomplish desired outcomes and set objective of report.

Chapter 6: Team Charter and Communication strategy

Team charter indicates to a document that is designed in a team setting that clarifies group direction while setting boundaries. It can be a report that is created by the project manager to establish a group of people to complete research project, provide direction to them to work in research and inform them about the limitations of the project so that they can do their work in set boundaries. In this research project, surveyor design a team charter to make group of people by analysing their skills as per the research so that they can perform in adequate manner. With the help of it, the person share information about the aims, objectives and time frame of research. The person also provide guidance to team members so that they can do their work as per the project and provide instructions. The main motive of team charter is that team should work regarding the common gaol of the respective report. With the help of this document, the investigator can direct teammates regarding this engineering project so that those people who are working in this kind of research project very first time, they can familiar with the activities and way of working.

Communication strategy refers to a plan and way of making communication to share and deliver information to others. In context of research, communication strategy states to those tools and techniques of communication which is used by the researcher to share and transfer information regrading research project to its other members of teammates. There are different kinds of communication like visual, verbal and non-verbal communication so to share information by using through these kind of communication methods, surveyors use different communication tools. For example, if the person make visual communication then investigator use graphs, models, tables, photographs, diagrams and others so that they can present actual things that they want to deliver to team. In this research report, the person can make verbal and visual communication. For making effective communication, they can use different tools like chat box, messages, phone calls, email, direct communication etc. Effective communication strategy is important because it help in maintains connection, update individual with latest info and allowing them to work effectively regarding their project goal.

Chapter 7: Summary

Under this research, to predicate the performance in overall process of shell and tube heat exchangers, numerical investigations have been done, with different-different layout patterns. So, it has been summarised that heat transfer as well as pressure drop during cross-flow of shell-fluid has much occurred through tube bundles. By comparing with triangular arrangement of shell heat-transfer, average deviations of coefficients of heat transfer are 11.2% & 8.3% for other tube arrangements that are rotated and combined patterns. While pressure drops for both patterns as comparison with STHE_T are 16.0% and 18.8% respectively. Therefore, from these two results, it has been evaluated that performance of shell heat exchangers is much effected by tube layout arrangements. Along with this, STHE_T (tube layout arrangement in triangular way) is more desirable then others as it exhibits transfer of higher heat coefficient than others, for pressure drop within shell-side.  

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