HEAT TRANSFER ENHANCEMENT IN SHELL AND TUBE HEAT EXCHANGERS USING INSERTS

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 10, October 2017, pp , Article ID: IJMET_08_10_022 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed HEAT TRANSFER ENHANCEMENT IN SHELL AND TUBE HEAT EXCHANGERS USING INSERTS K. Shanmuganandam, V. Velmurugan, V. Jayakumar Department of Mechanical Engineering, Saveetha School of Engineering, Saveetha University, Chennai, Tamilnadu, India S. Madhu and P. Kumaran Department of Automobile Engineering, Saveetha School of Engineering, Saveetha University, Chennai, Tamilnadu, India ABSTRACT Heat exchangers are widely used in thermal applications. The effective performances of heat exchangers depend on their heat transfer rate. In this work an attempt is made to study the effect of inserts viz., twisted tape inserts, glass sphere packing and pebble packing in increasing the heat transfer rate in a shell and tube heat exchanger. The water to water system is considered with hot water on shell side and cold water on tube side. Furthermore the results obtained were compared with performance of the heat exchanger without using inserts. It was inferred that the heat transfer rate increased with usage of inserts. The twisted tape inserts exhibited better performance than glass sphere packing and pebble packing. Keywords: Heat exchangers, Shell and tube, Inserts, Twisted tape, Glass sphere packing and Pebble packing. Cite this Article: K. Shanmuganandam, V. Velmurugan, V. Jayakumar, S. Madhu and P. Kumaran, Heat Transfer Enhancement in Shell and Tube Heat Exchangers Using Inserts, International Journal of Mechanical Engineering and Technology 8(10), 2017, pp INTRODUCTION The heat exchangers have found wide applications in various industries [1,2]. Of late, the emphasis is on improving the heat transfer rate of heat exchangers. Research was conducted across the globe to enhance the performance of heat exchangers. From published literatures it was evident that usage of inserts increases the overall heat transfer rate of heat exchangers [3,4]. Different types of inserts Viz., motionless mixers, twisted tapes, baffles and fins have been employed as inserts to increase the heat transfer rate. Among the inserts used, the twisted tapes finds wide application for its capability to enhance the heat transfer rate [5-8]. A twisted editor@iaeme.com

2 K. Shanmuganandam, V. Velmurugan, V. Jayakumar, S. Madhu and P. Kumaran tape is a metal strip twisted about its longitudinal axis, the width being equal to the internal diameter of the tube in which it is inserted. The tape has a sliding fit in the tube and produces two identical, intertwined channels of the semi-circular cross-section. Thus the tape causes a helical type flow with a strong secondary motion which leads to an enhancement of heat transfer [9-12]. An additional factor leading to enhancement is that the tape itself acts as a fin and provides additional heat transfer surface [13-15]. The objective of this work is to study the influence of inserts viz., twisted tapes, glass spheres and pebbles in enhancing the heat transfer rate in a shell and tube heat exchanger. 2. EXPERIMENTAL AND INSTRUMENTATION SETUP A shell and tube heat exchanger, of length 1m, shell diameter 6 inches and tube diameter 1 inch was chosen for the study. The heat exchanger was fabricated using mild steel material. The hot water which was heated by the heating coil fitted in the tank is pumped through the tube side of the heat exchanger using centrifugal pump of 0.5 HP capacities. Hot water flow is controlled by a globe valve. The cold water was stored in a separate tank and pumped using another centrifugal pump. The cold water was pumped across the shell side of the heat exchanger. A bypass is provided in the discharge line of pumps to avoid damages caused to the pump by the variation in flow rates of fluids. For efficient heating the hot fluid is recirculate. Cold water flow rate is controlled by a valve fitted in the inlet side. The twisted tapes were fabricated using mild steel of 1 inch diameter and 1 m in length. The glass spheres were placed in mild steel mesh at regular pitch of 1 inch. Totally 10 identical glass spheres were employed. The glass spheres with the above mentioned pitch was placed inside mild steel mesh and twisted, to avoid relative movement. The glass spheres are made of glass material and are inert. These glass spheres are employed only to create turbulence. These glass spheres don t chemically react with the heat exchanger fluid nor do they absorb heat from the heat exchanger. Furthermore these glass spheres don t exhibit relative motion, so they are termed as motionless mixers. The pebbles of size less than 1 inch are selected and are placed at equal pitch distance of 1 inch, inside the mild steel mesh. Similar to the glass sphere packing, the pebbles doesn t chemically react with the heat exchanger fluid. The pebbles create turbulence in the heat exchanger. The pebbles don t exhibit relative motion and are termed as motion less mixers. The temperatures were measured using K-thermocouples at 4 locations ie at hot water and cold water inlet and outlet points. The temperatures were noted at steady state conditions. First experiments were conducted without using twisted tapes. The experiments were conducted for a fixed flow rate of hot water and cold water in shell and tube sides. The flow rates of the fluid were determined using rotometers. The four terminal temperatures T 1,T 2,T 3,T 4 were noted at steady state conditions. The same procedure was repeated after usage of inserts at identical flow rates of hot and cold water. 3. RESULTS AND DISCUSSION The experiments were initially conducted in the heat exchanger without using the inserts to fix the baseline values. The hot water flow rate is maintained as kg/s in the tube side, while the cold water flow rate in the shell side is varied from kg/s to 0.05 kg/s. The experimental results are tabulated in Table editor@iaeme.com

3 Heat Transfer Enhancement in Shell and Tube Heat Exchangers Using Inserts Mass flow rate (kg/s) Table 1 Experimental results without using tapes Shell Side Tube side Shell side Tube side Thi Tho Tci Tco Overall heat transfer coefficient (W/m 2 K) It is inferred that the overall heat transfer coefficient (U) and heat transfer rate (Q) increases as the flow rate is increased in shell side. As the flow rate increased from kg/s to 0.05 kg/s in the shell side the overall heat transfer coefficient (U) increased from 194 to 225 W/m 2 K. From published literatures it is evident that the heat transfer coefficient for water to water system is less. This may be due to less heat transfer occurring in the shell and tube heat exchanger. The experimental results indicate the scope for further improvement. Of late various methods are exhibited by researchers to increase the heat transfer rate. From published literature it is inferred that inserts Viz., twisted tapes, glass spheres and pebbles are employed to increase the heat transfer rate. Initially experiments were conducted using twisted tape inserts to enhance the heat transfer rate. The Table 2 represents the experimental results after using the twisted tapes. The identical flow rates for cold water and hot water were maintained in the shell side and tube side of the heat exchanger. Initially the temperatures increased with respect to time after which steady state was identified. The experimental readings were recorded after the system reached the steady state condition. Mass flow rate (kg/s) Shell side Table 2 Experimental results using twisted tape inserts Tube side Shell Side Tube side Thi Tho Tci Tco Overall heat transfer Coefficient (W/m 2 K) From the experimentation results it is inferred that the heat transfer rate after using twisted tapes increased when compared against baseline values. The increment in heat transfer due to usage of twisted tape is due to creation of turbulence inside the heat exchangers. The twisted tapes continuously interchange the fluid elements between the wall and center of conduit, thereby providing enhanced heat transfer. Additional power is not required for the twisted tape as they utilize the power of the fluid as such and diverts them to the walls. The twisted tape successfully divides and recombines the portions of the fluid stream. Due to the above mentioned reasons the twisted tape inserts enhances the heat transfer rate. Similar experimentation was conducted using glass sphere packing and the experimental results are tabulated in Table editor@iaeme.com

4 K. Shanmuganandam, V. Velmurugan, V. Jayakumar, S. Madhu and P. Kumaran Table 3 Experimental results using glass sphere packing Mass flow rate (kg/s) Shell Side Tube side Overall heat transfer Shell side Tube side Thi Tho Tci Tco coefficient w/m 2 K From the experimental results it is inferred that the heat transfer rate increases when glass sphere packing was employed. The usage of glass spheres increases the turbulence in the tubes, thereby splitting the water flow. This turbulence facilitates the increment in heat transfer rate. Furthermore, the experiments were conducted using pebble packing and the experimental results are tabulated in Table 4. Table 4 Experimental results using pebble packing Mass flow rate (kg/s) Shell Side Tube side Overall heat transfer Shell side Tube side Thi Tho Tci Tco coefficient w/m 2 K From the experimentation it is inferred that the heat transfer rate increases when pebbles were employed. The usage of pebbles induces turbulence thereby splitting the water from center of the pipe to the surface of the pipe. This increases the heat transfer rate. Among the twisted tape inserts, glass sphere packing and pebbles, the twisted tape inserts performed better than glass sphere packing and pebbles. The glass sphere packing exhibited the lowest heat transfer rate when compared with other inserts. The twisted tape inserts and pebbles possess larger surface area than other inserts which facilitated more turbulence than other inserts. Due to the higher turbulence generated by the twisted tapes and pebbles, more heat transfer was facilitated, than glass spheres. 4. CONCLUSIONS From the experimentation, the following conclusions were drawn: 1. A shell and tube heat exchanger with necessary instrumentation was fabricated. 2. Experiments conducted without using inserts indicates the scope for enhancing the heat transfer rate. 3. The effect of usage of twisted tape inserts, glass sphere packing and pebbles in enhancing the overall heat transfer rate has been studied. 4. From the experimental study it is inferred that it is possible to increase the overall heat transfer rate by usage of twisted tapes, glass sphere packing and pebbles. 5. The twisted tape inserts performed better than pebbles and glass sphere packing. 6. The glass sphere packing exhibited lowest performance than pebbles and twisted tape inserts editor@iaeme.com

5 Heat Transfer Enhancement in Shell and Tube Heat Exchangers Using Inserts REFERENCES [1] S.P. Sukathame. Laminar convective heat transfer to a thermic fluid in a tube with a twisted tape, Journal of energy, heat and mass transfer , [2] K. Ramakrishna, Correlations of horizontal in tube condensation with twisted tape inserts Journal of energy, heat and mass transfer, 10,4, ,1988. [3] K. Ramananda Rao, Study of the structure of feasible designs of shell and tube heat exchanger, Journal of energy, Heat and mass transfer, 14, 87-93, [4] A. krueger, Heat exchanger performance enhancement through using of tube inserts, Proceedings of International conference on heat exchanger fouling and cleaning. June 1419, [5] Nilesh C Kanojiya, Dr. V. M. Kriplani, Dr. P. V. Walke, Heat Transfer Enhancement in Heat Exchangers With Inserts: A Review, International Journal of Engineering research and technology,3,10,2014. [6] Francois Pouponnot, Heat exchanger tube inserts an update in new applications with trouble shooting aspects in crude units, residue service, reboilers and u-tubes, Proceedings of 6th International Conference on Heat Exchanger Fouling and Cleaning - Challenges and Opportunities,2, June 5-10,2005. [7] R. Surendran & P. Suresh, insert of passive techniques in double pipe heat exchanger for heat transfer enhancement International Journal of Mechanical and Production Engineering Research and Development (IJMPERD), 4,2, ,2014. [8] Tabatabaeikia, Heat Transfer Enhancement by Using Different Types of Inserts, Advances in mechanical Engineering, [9] Humair A. Ansari, Sanjay U. Bokade, Chandrakant C. Jadav, Optimizing Physical Dimension of Heat Exchanger Using Insert to Improve Its Portability, International Journal of Science and Research (IJSR),5,2,2013. [10] M. J. Patel, K. S. Parmar, Umang R. Soni, Enhance the Performance of Heat Exchanger with Twisted Tape Insert: A Review, International Journal on Recent and Innovation Trends in Computing and Communication ISSN: , 2, 2,2015. [11] Maheshkumar J. Patel, K. S. Parmar, U. R. Soni, Improve the Performance of Heat Exchanger: Twisted Tape Insert With Metallic Wiry Sponge, International Journal on Recent and Innovation Trends in Computing and Communication ISSN: ,2,4,2015. [12] Kiran, A Review on Effect of Various Types of Tube Inserts on Performance Parameters of Heat Exchanger, International Journal of research in Advent Technology,2.6,2014. [13] Sunil Kulkarani, Heat Transfer Enhancement in Tube in Tube Heat Exchanger with Helical Wire Coil Insert sand CuONanofluid, International Journal of Mechanical Engineering, 3.5,2015. [14] ArezuoGhadi, Roja ParviziMoghaddam, MajidTaghizadehMazandarani, CFD Modelling of Increase Heat Transfer in Tubes by Wire Coil Inserts, 18 (10): , [15] A. KirsanovR. A. Nazipov E. I. Ivanova, A technique for thermal design of a heat exchanger with porous inserts, 56, Issue 1, pp 73 82, [16] Uttam Roy and Mrinmoy Majumder. Estimation and Analysis of Cycle Efficiency for Shell and Tube Heat Exchanger by Genetic Algorithm. International Journal of Mechanical Engineering and Technology, 8(2), 2017, pp [17] K. Shanmuganandam, Heat Transfer Enhancement in Shell and Tube Heat Exchangers Using Twisted Tapes, International Journal of Mechanical Engineering and Technology 8(8), 2017, pp [18] M. P. S. Bharadwaj and S. Sudhakar Babu, Heat transfer Enhancement in 2S-2T Shell and Tube Heat Exchanger with Wire Coil and Twisted Tape Turbulators using TIO 2 Nanofluid. International Journal of Mechanical Engineering and Technology, 8(7), 2017, pp editor@iaeme.com