Numerical-2-project.docx

Abstract Computational Fluid Dynamic (CFD) is a useful tool in solving and analysing problems that involve fluid flows, while shell and tube heat exchanger is the most common type of heat exchanger and widely use in oil refinery and other large chemical processes because it suite for high pressure application. The processes in solving the simulation consist of modelling and meshing the basic geometry of shell and tube heat exchanger using the CFD. Then, the boundary condition will be set before been simulate based on the experimental parameters. Parameter that had been used was the same parameter of experimental at constant mass flow rate of cold water and varies with mass flow rate. CFD model is validated by comparison to the experimental results Introduction A shell and tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and it is suite for high pressure applications. As its name implies, this type of heat exchanger consists of a shell with a bundle of tubes inside. The basic principle of operation is very simple as flows of two fluids with different temperature brought into close contact but prevented from mixing by a physical barrier. Then the temperature between two fluids tends to equalize by transfer of heat through the tube wall. The fluids can be either liquids or gases on either the shell or the tube side. In order to transfer heat efficiently, a large heat transfer area should be used, leading to the use of many tubes. In this way, waste heat can be put to use. The tubes may be straight or bent in the shape of a U. The heat exchanger is used to boil water recycled from a surface condenser into steam to drive a turbine to produce power. Computational Fluid Dynamics or CFD is the analysis of systems involving fluid flow, heat transfer and associated phenomena such as chemical reactions by means of computer based simulation. The technique is very powerful to perform the millions of calculations required to simulate the interaction of fluids and gases with complex surfaces used in engineering. CFD not just spans on chemical industry, but a wide range of industrial and nonindustrial application areas such as:         

Aerodynamics of aircraft and vehicles. Combustion in IC engines and gas turbines in power plant. Loads on offshore structures in marine engineering. Blood flows through arteries and vein in biomedical engineering. Weather prediction in meteorology. Flows inside rotating passages and diffusers in turbo-machinery. External and internal environment of building like wind loading and heating or ventilation system. Mixing and separation or polymer moulding in chemical process engineering. Distribution of pollutants and effluents in environmental engineering

Increasingly CFD is becoming a vital component in the design of industrial products and processes. The development in the CFD field provides a capability comparable to other Computer Aided Engineering (CAE) tools such as stress analysis codes.

Literature Review Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to solve and analyze problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of liquids and gases with surfaces defined by boundary conditions. CFD software gives you the power to simulate flows of gases and liquids, heat and mass transfer, moving bodies, multiphase physics, chemical reaction, fluid-structure interaction and acoustics through computer modeling. This software can also build a virtual prototype of the system or device before can be apply to real-world physics and chemistry to the model, and the software will provide with images and data, which predict the performance of that design. Computational fluid dynamics (CFD) is useful in a wide variety of applications and use in industry. The simulation is performed using the FLUENT software. ANSYS Fluent is the most-powerful computational fluid dynamics (CFD) software tool available, empowering you to go further and faster as you optimize your product's performance. Fluent includes well-validated physical modeling capabilities to deliver fast, accurate results across the widest range of CFD and multiphysics applications. As for the shell and tube heat exchangers, they are widely used equipment in various industries such as process, power generation, petroleum refining, chemicals and paper. A shell-and-tube heat exchanger is a type of heat exchanger that consists of a cylinder carrying one fluid, with some smaller cylinders inside it carrying another fluid. Two fluids, of different starting temperatures, flow through the heat exchanger. One flows through the tubes (the tube side) and the other flows outside the tubes but inside the shell (the shell side). Heat is transferred from one fluid to the other through the tube walls, either from tube side to shell side or vice versa. The fluids can be either liquids or gases on either the shell or the tube side. To transfer heat efficiently, a large heat transfer area should be used, leading to the use of many tubes. In this way, waste heat can be used. This is an efficient way to conserve energy. The developments for shell-and-tube exchangers center on better conversion of pressure drop into heat transfer by improving the conventional baffle designs. A good baffle design, while attempting to direct the flowing a plug flow manner, also must fulfill the main function of providing adequate tube support. Heat exchangers transfers heat between a solid object and a fluid, or between two or more fluids. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy and heat between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Heat transfer always occurs from a hot body to a cold one, a result of the second law of thermodynamics.

Numerical Approach and Related Case Study One of the examples of heat exchanger simulation is by using CHEMCAD Steady State together with CC-THERM. CC-THERM is an add-on program and comprises the rigorous simulation of heat exchangers (tubular, plate and twin heat exchangers and air coolers) whereas CHEMCAD Steady State offers the possibility to simulate heat exchangers through a simple energy and mass balance. However, CHEMCAD Steady State does not calculate heat transfer coefficient and the construction parameters are not taken into consideration. For example: Water (1,5 bar, 20 m³/h) is to be heated from 10°C to at least 90°C with hot process water (130°C, 2.7 bar, 50 m³/h). The heat exchanger is to be operated countercurrent. In doing so, the process water that flows in the tubes should not be cooled down by more than 50 K maximum. A tubular heat exchanger is dismounted from on old system and will then be used for this task. The data of the heat exchanger is stated below: Design : TEMA R/BEM Material : Carbon Steel (also C-steel or structural steel) Inner cladding diameter (m) : 0.8 No. of tubes : 670 Length of tubes (m) : 4 Tube alignment : Turned triangular form (60°) Tube spacing : 1,25∙ dtube Tube dimensions : dout = 19 mm; din = 16 mm Number of baffle plates : 11 Spacing of the baffle pieces (m) : 0.32 Free cross section in shell side (%) : 30 Tube nozzle diameter (tube side) (m) : 0.1 Tube nozzle diameter (shell side) (m) : 0.15

The aim of this simulation is to examine by means of a rating whether the heat exchanger delivers the required performance and that the pressure loss (both tube and shell) will not exceed 0.5 bar.

Figure : Design of BEM Heat Exchanger For this simulation, the simplest model, ideal Raoult’s Law is chosen. The hot flow is set to have an outlet temperature in excess of 80°C and the cold flow with outlet temperature of 90°.

Figure : Flow sheet with heat exchanger in

Figure : Settings of HTXR heat exchanger

CHEMCAD

Figure : Results table of the simple heat exchanger

Now, we move to the CC-THERM part. For the rigorous simulation, CC-THERM is now called up at "Sizing: Heat Exchangers".

After selecting the tubular heat exchanger, the module first asks which feed stream is supposed to flow through the heat exchanger in the tubes first. CHEMCAD generates the Q-T diagram. This is generated with 11 data points (pre-setting). It is also possible to choose between concurrent and counter current in the settings window "Heat Curve Parameters".

Figure: Q-T diagram

The Q-T diagram already shows whether a phase change occurs inside the heat exchanger. With a pure component system, it can be expected that the temperature will no longer increase in the case of a phase change, so that the curves will become horizontal. The geometric layout of the heat exchanger is defined in the next step. The layout is stated using the TEMA standard. Then, geometric data of the heat exchanger is defined in more detail in the following. In the case of rating, all entry fields can be edited. In the case of design, the number and length of the tubes are calculated and therefore cannot be edited. CHEMCAD already contains pre-set values for a tubular heat exchanger. The dimension of the tubes is 3/4 inch. However, all values can be overwritten manually. After the simulation is done, here the results that we obtained: Table: Results table after the CC-THERM simulation

Conclusion As a conclusion, CFD enables scientists and engineers to perform ‘numerical experiments’.we can clearly say that CFD method is far more better to gather data compared to experimental way. Through this case study, It becomes evident that the outlet temperature of the hot stream is now cooled down to approximately 85°C (previously: 95°C). The outlet temperature of the cold stream is now 110°C. The heat exchanger thus delivers the required performance. The pressureloss, amongst other parameters,can be derived from the results of the heat exchanger (Figure 21). The pressure loss is less than 0.5 bar, on both the tube and the shell sides. These requirements are therefore fulfilled. References Hamming, R. W. (1962). Numerical methods for scientists and engineers. New York: McGraw-Hill. Othman, K. H. (2009). CFD simulation of heat transfer in shell and tube heat exchanger. Kuantan, Pahang: UMP.

KKEK 2142 Numerical Methods for Engineering II

Simulation of heat transfer process in a Shell and Tube Heat Exchanger by Computational Fluid Dynamics (CFD) Name Tan Hong Ning Nik Faris Faheem bin Nik Lukman Dzuki Mohd Zhariff Azli bin Roziki Piradeepan Ramachandran Athena Hollistini Anak Stanley Hollis Wan Muhd Farizan Wan Ahmad Dahlan Zaim Nor Rashid bin Zainol Nor Rashid Muzammil Iqbal

Matric Number KEK130055 KEK130037 KEK130031 KEK130045 KEK130008 KEK130061 KEK130065