Study the Effect of Single Segmental Baffle cut on Overall Heat Transfer Coefficient in Shell and Tube Heat Exchanger

Transcription

1 GRD Journals- Global Research and Development Journal for Engineering Volume 3 Issue 6 May 2018 ISSN: Study the Effect of Single Segmental Baffle cut on Overall Heat Transfer Coefficient in Shell and Tube Heat Exchanger Er. Satvirpal Singh Grewal M.Tech Scholar Er. Didar Singh Assistant Professor Er. Kulwinder Singh Brar Assistant Professor Er. Karanjeet Singh M.Tech Scholar Abstract To figure out the best baffle cut to obtain the maximum overall heat transfer coefficient for the better performance of shell and tube heat exchanger. Methods: To identify the best relation between the baffle cut and overall heat transfer coefficient, six different baffle cut varies from 15% to 40% were taken at the same mass of fluid. To analyze thermal design and overall heat transfer coefficient HTRI was used. To find out the relation between the baffle cut to overall heat transfer coefficient, we generated 2d profile corresponding to length and 3d profile for local heat transfer coefficient. We compared all six design variations to analyze the variation in overall heat transfer coefficient. After comparison of all six variations we figured out optimum relationship between Baffle cut and Overall Heat Transfer Coefficient. Result shows that at a particular cut the rate of heat transfer is the maximum. We found that 25% baffle cut is the optimum cut for single segmental baffle, this provides best combination of shell side velocity and B stream and generate enough turbulence for better heat transfer coefficient. It is also demonstrating good distribution of heat transfer in all localities of heat exchanger. If we decrease the baffle cut, it may increase turbulence but leads to decrease the shell side velocity and B stream, this results the less heat transfer coefficient. Similarly, by increasing the baffle cut there is increase in shell side velocity and B stream, but due to less turbulence less heat transferred. So there is less heat transfer coefficient. Thus for beat the performance of heat exchanger and optimum heat transfer coefficient, there should be best combination of all effective variables. Keywords- Shell and Tube Heat Exchanger, Baffle, Segmental Baffle, Helical Baffle, Overall Performance I. INTRODUCTION In this modern world, heat exchangers are indispensible part of oil refining, electric power generation, environmental protection, chemical industry and many others. Although, there is much type of types of heat exchangers, but shell and tube heat exchanger is the most suitable type, because of its suitability at high pressure, robust construction and easy maintenance. Heat exchangers can be classified in many different ways like: i). Recuperates and Regenerators. ii). Transfer process: Direct contact and Indirect contact. iii) Geometry of construction: tubes, plates and extended surfaces. iv) Heat transfer mechanisms: single phase and two phase. V) Flow arrangements: parallel, counter and cross flows. In this paper we will majorly focus on shell and tube heat exchanger and its performance. Although there are many factors on which the performance of shell and tube depends, but we will majorly discuss about the baffle cut and its effect on the overall heat transfer coefficient. II. LITERATURE SURVEY H. Reza Tasouji Azar, Shahram Khalilarya, Samad (2016) calculated data pressure drop and overall average heat transfer coefficient of shell side in helix baffles and segmental baffles and concluded for the common rete of mass flow and code and EXPRESS was used to compare this data. Results show that to improve the performance of heat transfer in helix baffles over segmental baffles, helix bundle achieved up to three times longer operational time. All rights reserved by 1

2 Fig. 1: Operating and maintenance costs; Bundle replacement From the above results we can calculate that initial and installation cost of helix baffles is higher than segmental baffles but the maintenance and operating cost is low. Yonghua You, Aiwu Fan, Suyi Huang, Wei Liu (2016) solved the numerical method of Reynolds numbers ranging from 6813 to 22,326 at shell side for a shell and tube heat exchanger with flower baffles and to demonstrate the reasonable accuracy comparison is done by test data. After all results we calculated that after the installation of flower baffles the velocity magnitude of fluid and coefficient of connective heat transfer vary in periodical way. Fig. 2: Overall performance index hs,m /Dp on the shell side between CFD results and test data for the heat exchanger with flower baffles B. Mayank Vishwakarma, K. K. Jain (2013) develop the arrangement of tilt baffle angle to increase the heat transfer and to reduce the pressure drop in shell and tube heat exchangers. Fig. 3: Graph plot between shell-side mass flux and helical angle Using the Kern s method, the thermal analysis provides the clear results that ratio of coefficient of heat transfer is the maximum in helical baffles sell and tube heat exchanger as compared to segmental baffles shell and tube heat exchanger. All rights reserved by 2

3 III. METHODOLOGY A. Development of a General Design Problem A problem was developed as per industrial practical conditions. We took water as hot and cold fluid on the both sides of heat exchanger. Hot water was on shell side and cold fluid was on tube side. Problem is detailed in result section. B. Add values in HTRI For thermal designing of heat exchanger, we put all geometrical and conditional values in HTRI software. C. Change in Baffle Cut We changed baffle cut from 15% to 40% and analyze the variation in results. D. Generation of 2D & 3D Profiles for Every Baffle Cut Value To find out the relation between the baffle cut to overall heat transfer coefficient, we generated 2d profile corresponding to length and 3d profile for local heat transfer coefficient. E. Analyze the Variation in Overall Heat Transfer Coefficient We compared all six design variations to analyze the variation in overall heat transfer coefficient. F. Figure Out the Optimum Relationship between Baffle Cut and Overall Heat Transfer Coefficient After comparison of all six variations we figured out optimum relationship between Baffle cut and Overall Heat Transfer Coefficient. Result shows that at a particular cut the rate of heat transfer is the maximum. IV. RESULTS A. General Design Problem From the literature review we identified that water is the standard fluid to study such kind to heat exchanger problems. We developed a design problem detailed below for our study. We took atmospheric pressure with suitable flow rate. Geometric values that we selected also most common values used in manufacturing of shell and tube heat exchanger. B. Problem Fluid = Water Flow Rate = kg/hour Hot Fluid Temperature (inlet/outlet) = (42/38) Degree Celsius Cold Fluid Temperature (inlet/outlet) = (32/36) Degree Celsius 1) Geometry of Heat Exchanger Shell ID = 254 mm Tube OD = 12.7 mm Tube Length = 1000 mm Tube Thickness = mm Tube material = Carbon Steel Fig. 4: Profile of Local Overall U with 15% baffle cut All rights reserved by 3

4 Fig. 5: Profile of Local Overall U with 20% baffle cut Fig. 6: Profile of Local Overall U with 25% baffle cut Fig. 7: Profile of Local Overall U with 30% baffle cut All rights reserved by 4

5 Fig. 8: Profile of Local Overall U with 35% baffle cut Fig. 9: Profile of Local Overall U with 40% baffle cut Fig. 10: Final Results All rights reserved by 5

6 The final results are showing that exchanger with 15% baffle may provide good turbulence but due to low shell side velocity and low B stream, the value of overall heat transfer coefficient is only kcal/m^2-hr-c. By increasing the baffle cut with 5%, there is a small increase in shell side velocity and B stream. This further leads to increase the overall heat transfer coefficient. 25% baffle cut is best solution. It gives the optimum efficiency and best combination of shell side turbulence, shell side velocity and B stream. The overall heat transfer coefficient is maximum with 25% baffle cut i.e kcal/m^2-hr-c. If we increase baffle cut further due to less turbulence less heat transferred by the fluid. So there is decrease in overall heat transfer coefficient with increment in baffle cut. V. CONCLUSION The objective of the thesis is to figure out the optimum relation between baffle cut and overall heat transfer coefficient. We developed a practical design problem of shell and tube heat exchanger. We put problem values in HTRI to figure out the solution. We developed six cases with six variations of baffle cut. After the comparison of all six cases results we found that 25% baffle cut is the optimum cut for single segmental baffle, this provides best combination of shell side velocity and B stream and generate enough turbulence for better heat transfer coefficient. It is also demonstrating good distribution of heat transfer in all localities of heat exchanger. If we decrease the baffle cut, it may increase turbulence but leads to decrease the shell side velocity and B stream, this results the less heat transfer coefficient. Similarly, by increasing the baffle cut there is increase in shell side velocity and B stream, but due to less turbulence less heat transferred. So there is less heat transfer coefficient. 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