Performance analysis of shell and tube heat exchanger using miscible system

Performance analysis of shell and tube heat exchanger using miscible system


A heat exchanger is a device in which energy is transferred from one fluid to another across a solid surface. Exchanger analysis and design therefore involve both convection and conduction. Two important problems in heat exchanger analysis are (1) rating existing heat exchangers and (ii) sizing heat exchangers for a particular application. Rating involves determination of the rate of heat transfer, the change in temperature of the two fluids and the pressure drop across the heat exchanger. Sizing involves selection of a specific heat exchanger from those currently available or determining the dimensions for the design of a new heat exchanger, given the required rate of heat transfer and allowable pressure drop. The LMTD method can be readily used when the inlet and outlet temperatures of both the hot and cold fluids are known. When the outlet temperatures are not known, the LMTD can only be used in an iterative scheme. In this case the effectiveness-NTU method can be used to simplify the analysis. The choice of heat exchanger type directly affects the process performance and also influences plant size, plant layout, length of pipe runs and the strength and size of supporting structures. The most commonly used type of heat exchanger is the shell-and-tube heat exchanger, the optimal design of which is the main objective of this study. Computer software marketed by companies such as HTRI and HTFS are used extensively in the thermal design and rating of HEs. These packages incorporate various design options for the heat exchangers including the variations in the tube diameter, tube pitch, shell type, number of tube passes, baffle spacing, baffle cut, etc. A primary objective in the Heat Exchanger Design (HED) is the estimation of the minimum heat transfer area required for a given heat duty, as it governs the overall cost of the HE. But there is no concrete objective function that can be expressed explicitly as a function of the design variables and in fact many numbers of discrete combinations of the design variables are possible as is elaborated below. The tube diameter, tube length, shell types etc. are all standardized and are available only in certain sizes and geometry. And so the design of a shell-and-tube heat exchanger usually involves a trial and error procedure where for a certain combination of the design variables the heat transfer area is calculated and then another combination is tried to check if there is any possibility of reducing the heat transfer area. Since several discrete combinations of the design configurations are possible, the designer needs an efficient strategy to quickly locate the design configuration having the minimum heat exchanger cost. Thus the optimal design of heat exchanger can be posed as a large scale, discrete, combinatorial optimization problem (13). Most of the traditional optimization techniques based on gradient methods have the possibility of getting trapped at local optimum depending upon the degree of non-linearity and initial guess. Hence, these traditional optimization techniques do not ensure global optimum and also have limited applications. In the recent past, some experts studied on the design, performance analysis and simulation studies on heat exchangers(12),(13), (15), (16), (18). Modeling and Simulation of Shell and Tube Heat Exchangers Under Milk Fouling was carried out (15). Dynamic Model for Shell and Tube Heat Exchangers was discussed [12). Shell and Tube heat exchangers are applied where high temperature and pressure demands are significant and can be employed for a process requiring large quantities of fluid to be heated or cooled. Due to their design, these exchangers offer a large heat transfer area and provide high heat transfer efficiency in comparison with others. Modeling is a representation of physical or chemical process by a set of mathematical relationships that adequately describe the significant process behavior. Improving or understanding chemical process operation is a major objective for developing a process model. These models are often used for Process design, Safety system analysis and Process control. The simulation of an industrial system on a computer involves mathematical representation of the physical process undergone by the various components of the system, by a set of equations, which are in turn solved. Simulation is much cheaper than setting up big experiments or building prototypes of physical system and variables on the behavior of the system. A steady state model for the outlet temperature of both the cold and hot fluid of a shell and tube heat exchanger will be developed and simulated, which will be verified with the experiments conducted. Based on these observations correlations to find film heat transfer coefficients will be developed.
MATERIALS AND METHODS
Experimental Studies
Experimental Set up: Experiments were conducted on a 1-1 Shell and Tube Heat Exchanger. The Fig. 1 shows the schematic diagram of the heat exchanger