Experimental investigation on Heat transfer Performance Comparison for STHXs with Different baffles

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1 Experimental investigation on Heat transfer Performance Comparison for STHXs with Different baffles #1 Sandeep Govind Patil, #2 Shashank S. Chaudhari, #3 S.V. Muthalikdesai 1 Mechanical Department, Savitribai Phule Pune University, Trinity College Of Engineering And Research Pune, State- Maharashtra, India 2 Mechanical Department, Savitribai Phule Pune University, Trinity College Of Engineering And Research Pune, State- Maharashtra, India 3 Mechanical Department, Savitribai Phule Pune University, Trinity College Of Engineering And Research Pune, State- Maharashtra, India Abstract: Heat exchanger is a device that provides the flow of thermal energy between two or more fluids at different temperatures from one medium to another for heating and cooling purpose in industrial and domestic applications. Heat exchanger should be such that which have maximum heat transfer enhancement for minimum power consumptions. A variety of experimental, analytical and computational research work has been carried out on heat transfer enhancement of shell and tube heat exchanger with different baffles such as segmental baffle, helical baffle, disc & doughnut baffle, sector shaped plain baffle, ladder type fold baffle etc. In this paper the proposed horse shoe type baffle and elliptical baffle are place alternate and experimental investigation will be carried out on heat transfer coefficient, overall heat transfer coefficient and compare with segmental baffle.the experimental result show that the and overall heat transfer coefficient and shell side heat transfer coefficient both increases by 3% and 4% respectively. Keywords: Shell and tube heat exchanger, Heat transfer enhancement, Horse Shoe -type baffles, baffle distance, Heat exchanger with Disc and doughnut baffle. I. INTRODUCTION The Shell and tube heat exchangers are the most widely used type of heat exchangers. They are used in the steam generators, process industries, in conventional and nuclear power stations as condensers, feed water heaters and in pressurized water reactor power plant, and they are proposed for many alternative energy applications including ocean, thermal, geothermal and air conditioning and refrigeration systems. Shell and tube heat exchangers provide large ratios of heat transfer area to volume and weight and can be easily cleaned. Shell-and-tube heat exchangers (STHXs) are widely used in environment engineering, chemical engineering, power plant, and waste heat recovery due to their reliable operation, robust geometry construction, possible upgrades and easy maintenance. Baffles are one of the most important parts of STHXs, The baffles are primarily used in shelland-tube heat exchangers for inducing cross flow over the tubes for improving heat transfer performance. Baffles are also used to provide supports for tube bundle. In practice this objective is not quite achieved due to departure from cross flow and bypass stream and due to several leakages. Heat transfer and pressure drop are interdependent and both of them essentially influence the capital and operating costs of any heat exchange system. The optimization and design of shell-and-tube heat exchangers including thermal design and fluid dynamic design, cost estimation, strength calculation represents a complex process containing an integrated whole of design rules. A variety of experimental, analytical and computational research work has been carried out on heat transfer enhancement of shell and tube heat exchanger with different baffles such as segmental baffle, helical baffle, disc & doughnut baffle, sector shaped plain baffle, ladder type fold baffle etc. R. Mukherjee [1], H.D. Li, V. Kottke[2] examined a Segmental baffle in shell and tube heat exchanger. The segmental baffles divided the main stream flow in a zigzag manner, tortuous, across the tube bundle in the shell side as shown in Fig. 1a. This improves the heat transfer by enhancing turbulence and local mixing on shell side of heat exchangers.. (a) 2015, IERJ All Rights Reserved Page 1

2 (b) Fig.1. The main stream flow in zigzag manner in the shell side [12][13] The flow modes in conventional shell-and-tube heat exchangers are demonstrated in Fig. 1b. There are three types of flow modes in the shell side of STHXs. The cross flow of fluid through the tube bundle is A. The flow through the gaps of segmental baffles is B and the shell-baffle leakage flow (short-circuit flow) is C. But there are three major drawbacks in the conventional STHXs with segmental baffles (STHXsSB): (1) It causes a large shell-side pressure drop. (2) It results in leading to an increase of fouling resistance due to dead zone. (3) The zigzag flow pattern causes high risk of vibration failure on tube bundle. To overcome the above-mentioned drawbacks of the conventional segmental baffle, STHXs with helical baffles (STHXsHB) were firstly proposed by Lutcha and Nemcansky[3]. Fig. 2 The main stream flow in an ideal helix manner in the shell side[12] Due to helical baffles the flow patterns generated are much close to plug flow condition which cause reduction in shell-side pressure drop and improves heat transfer performance. The flow patterns induced by the baffles also intensified the shell-side heat transfer remarkably Stehlik et al. [4] and Butterworth[5] have reported that STHXsHB can reduce the flow-induced vibration. Stehlik et al. used experiment methods to compare the STHXsHB with the STHXsSB. Results showed that the performance of STHXsHB was considerably enhanced. Kral et al.[6] compared the performance among five STHXsHB with different helical angles and one STHXsSB. The heat transfer coefficient of STHXsHB was higher than that of the STHXsSB, and the helix angle of 40 0 was the best. Peng et al and Wang et al. [7] carried out experimental and numerical investigation on STHXs with continuous helical baffles. The result of this experiment showed an almost 10% increment in heat transfer coefficient compared with the non-continuous helical baffle schemes and conventional segmental baffles at the same shell-side pressure drop. It is very difficult in manufacture and installation of the above mentioned continuous helical baffles in STHXs, especially with larger shell diameter. Jian-Fei Zhang[8] and S.M. Wang [9] examined noncontinuous helical baffle. In STHXs most of helical baffles used are noncontiguous approximate helicoids due to difficulty in manufacture. These baffles are made by four elliptical sector-shaped plates joined end to end. The triangle zone is said to be an interspace between the two adjacent sector-shaped plates, leads to great fluid leakage. The leakages shunt decrease the medium flow velocity and main spiral medium flow,which in turn degrades the heat transfer performance of STHXsHB. The triangular leakage of STHXsHB could change the flow pattern in the shell-side fluid from a spiral flow to an axial flow, which will weaken the heat transfer. 2015, IERJ All Rights Reserved Page 2

3 Fig. 3. The sector-shaped plain baffle [14] As shown Fig 3, the original elliptical sector-shaped plain baffles is cut off a standard ellipse, symmetrically with respect to the minor axis. The cut off angle of the baffle sector varies with the helix angle β and should be larger than While the projection Angle of the baffle onto the normal cross-section of the heat exchanger is Fig. 4. The structural characteristics sector-shaped plain baffle [6] Fig. 4 demonstrates the installation of the baffles in the tube bundle of heat exchangers. There are two triangular leakage zones are observed forming an X-shape between the two adjacent original plain baffle. Jian Wen, Huizhu Yang [14]A novel ladder-type fold baffle is proposed to block the triangular leakage zones To form a helical pitch in the improved design, there are only two ladder-type fold baffles required and four elliptical sector-shaped plain baffles are required for the original STHXsHB. It was found that the overall heat transfer coefficient and shell side heat transfer coefficient of heat exchanger increased. Also increment in shell side pressure drop leads to penalty in pumping power. Fig. 5. The ladder-type fold baffle [14] 2015, IERJ All Rights Reserved Page 3

4 As shown in Fig 11, the novel ladder-type fold baffle is formed from folding a flat panel twice, which consists of three planes. The plane C and plane A are perpendicular to the axis of the tube bundle. The folding angles between the different planes are the same, denoted as α. The folding ratio ø is the ratio of the distance S to the projection radius R (ø= S/R). The baffle height w is ratio of the baffle height H to the projection diameter D (w= H/D). Fig. 6. The structural characteristics ladder-type fold baffle [14] Fig.13 demonstrates the installation of the baffles in the tube bundle of heat exchangers. The straight edges of the two adjacent ladder-type fold baffles are overlapped to accommodate several rows of tube pitch and two fold planes are made by bending both sides of the baffle, making the two adjacent ladder-type fold baffles connected closely. H. Li. V. kottke [15] investigate the local shell side heat and mass transfer in the shell and tube heat exchanger with disc and doughnut baffle. This baffle provides lower pressure drop as compared to that in single segmental baffle for unsupported tube span and eliminate the tube bundle to shell bypass stream. The disadvantage of this design are that the central tubes are supported by the disk baffle which in turns are supported only by tubes in the overlap of the larger diameter disk over the doughnut hole. Fig. no Horse shoe and elliptical baffle The above fig shows horse shoe and elliptical type baffle used in this experiment for performance comparison of shell and tube heat exchanger with segmental baffle. II. EXPERIMENTAL SETUP 2.1 Test heat exchanger The TEMA E type Heat exchanger is used in this experiment with one shell pass and one tube tube pass. The tube bundle with segmental baffle and improved horse shoe & elliptical baffle are tested on two different shell And tube heat exchanger with same size for comparison under the identical operating conditions. The shell diameter of the STHX is ø203 mm. The Tube Bundle consist of 62 tubes. The tube diameter is ø16mm x 1.65 mm with the length of 800 mm and in a square layout with a tube pitch of 25 mm. The Schematic diagram for the improved STHXs is shown in fig. 7 Fig. 7 Schematic Diagram of experimental system. 2015, IERJ All Rights Reserved Page 4

5 2.2 Experimental Scheme and measurement method The Schematic diagram of the experimental setup is shown in fig. The Experiment were conducted with segmental baffle and improved horse shoe & elliptical baffle alternatively placed in two different shell and tube heat exchanger of same size. It Consist of cold water and hot water loop system and data acquisition system. In the hot water system, hot water is transported from hot water tank by water pump and hot water flows through shell side of STHXs in which hot water is cooled by tube-side cold water before it returns back to the storage tank. In the cold water system, water is transported from water tank by water pump. Then it is heated by shell-side hot water. The Experimental arrangement is shown in fig.8 Fig. 8 The arrangement of experimental table The Data Acquisition unit is adopted to collect operation parameter: temperature, pressure and flow rate. Pt100 thermal resistances are used for temperature measurement of hot and cold water which are installed at the inlet and outlet nozzles of the STHXs with a data measurement accuracy of C. The overall shell side pressure drop (ΔP 12) are recorded by pressure gauge difference. The volume flow meter is measured by water flow meter. The inlet temperature of cold water in the tube side were fixed to 30 0 C and mass flow rate varied from kg/s to 0.41 kg/s. The inlet temperature of cold water in the tube side were fixed to 50 0 C and mass flow rate varied from kg/s to 0.41 kg/s. The energy imbalance between the shell side and tube side was calculated by the flow rate, outlet and inlet temperature on both side. III. Data Reduction 3.1 Heat transfer rate of shell side: 3.2 Shell side heat transfer coeffient: The kern s formula is used for computing shell side heat transfer coefficient ho 3.3 Tube Side Heat Transfer Rate: The heat transfer coefficient of tube side is calculated by using dittus boelter Equation. IV. RESULTS AND DISCUSSIONS 4.1 Effect of horse shoe & elliptical baffle on heat transfer coefficient hs 2015, IERJ All Rights Reserved Page 5

6 Fig no. 9 Shell side heat transfer coefficient verses flow rate Fig no. 9 and fig 10 shows the variation of shell side heat transfer coefficient and Overall heat transfer coefficient u along the water volume flow rate. The shell side heat transfer coefficients & Overall heat transfer coefficient u of the segmental baffle are lower than the horse shoe and elliptical baffle. 4.2 Effect of horse shoe and Elliptical baffle on overall heat transfer coefficient U Fig no. 10 Overall heat transfer coefficient u verses flow rate V. CONCLUSIONS The flow and heat transfer characteristics of shell and tube heat exchanger with segmental baffles and horse shoe & elliptical baffle are experimentally studied. The results are show that: 1) The objective of the present work is to develop proposed horse shoe type and elliptical baffle. The horse shoe and elliptical baffle is made up of alterative horse shoe and elliptical shaped baffles. 2 The shell side heat transfer coefficients and overall heat transfer coefficient horse shoe and elliptical baffle are increased by 4.% and 3% respectively. REFERENCES [1] R. Mukherjee, (1992), use Double-segmental baffles in the shell and tube heat exchangers, Chem. Eng. Prog.88, [2] H.D. Li, V. Kottke, (1998), Visualization and determination of local heat transfer coefficients in shell-and-tube heat exchangers for staggered tube arrangement by mass transfer measurements, Exp. Therm. Fluid Sci. 17, [3] J. Lutcha, J. Nemcansky, (1990), Performance improvement of tubular heat exchangers by helical baffles, Chem. Eng. Res. Des. 68, [4] P. Stehlik, J. Nemcansky, D. Kral, L.W. Swanson, (1994), Comparison of correction factors for shell-and-tube heat exchangers with segmental or helical baffles, Heat Transfer Eng. 15, [5] R. Mukherjee, (1998), Effectively design the shell-and-tube heat exchangers, Chem. Eng. Prog. [6] D. Butterworth, (1992), Developments in shell-and-tube exchangers, Inst. Chem. Eng. Symp. Ser. 1 (129), [7] D. Kral, P. Stelik, H.J. Van Der Ploeg, B.I. Masster, (1996), Helical baffles in shell-andtube heat exchangers, part one: experimental verification, Heat Transfer Eng. 17 (1), [8] B. Peng, Q.W. Wang, C. Zhang, G.N. Xie, L.Q. Luo, Q.Y. Chen, M. Zeng, (2007), An experimental study of shell-and-tube heat exchangers with continuous helical baffles, ASME J. Heat Transfer [9]S. Kakac, H. Hiu, (2000), Heat Exchangers Selection, Rating and Thermal Design, second ed, N.W Croporate Blvd., Boca Raton, Florida 33431,, CRC Press LLC. 2015, IERJ All Rights Reserved Page 6

7 [10] Jian-Fei Zhang, Shao-Long Guo, Zhong-Zhen Li, Jin-Ping Wang, Ya-Ling He, Wen-Quan Tao, (2013), Experimental performance comparison of shell-and-tube oil coolers with overlapped helical baffles and segmental baffles, Applied Thermal Engineering 58, [11] S.M. Wang, J. Wen, H.Z. Yang, Y.L. Xue, H.F. Tuo, (2014), Experimental investigation on heat transfer enhancement of a heat exchanger with helical baffles through blockage of triangular leakage zones, Appl. Therm. Eng. 67, (1 2) [12] Cong Dong, Ya-Ping Chen, Jia-Feng Wu, (2015), Flow and heat transfer performances of helical baffle heat exchangers with different baffle configurations, Appl. Therm. Eng.80, [13] Jian-Feng Yang, Min Zeng, Qiu-Wang Wang, (2014), Effects of sealing strips on shell-side flow and heat transfer performance of a heat exchanger with helical baffles, Applied Thermal Engineering 64, [14] Simin Wang, Jian Wen, Yanzhong Li, (2009), An experimental investigation of heat transfer enhancement for a shell-andtube heat exchanger, Applied Thermal Engineering 29, [15] Jian Wen, Huizhu Yang, Simin Wang, Yulan Xue, Xin Tong, (2015), Experimental investigation on performance comparison for shell-and-tube heat exchangers with different baffles, International Journal of Heat and Mass Transfer 84, [16] H. Li. V. kottke, (1999), Analysis of local shell side heat and mass transfer in the shell and tube heat exchanger with disc and doughnut baffle[j], Int.J. heat mass transfer 42(18), , IERJ All Rights Reserved Page 7