Design, Fabrication and Testing of helical tube in tube coil heat exachanger

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1 Design, Fabrication and Testing of helical tube in tube coil heat exachanger #1 Sachin Meshram, #2 Prof.P.T.Nitnaware, #3 M.R.Jagdale ABSTRACT Helical coil heat exchangers are one of the most common equipment found in many industrial applications. Helical coil heat exchanger is one of the devices which are used for the recovery system. The helical coil heat exchangers can be made in the form of a shell and tube heat exchangers and can be used for industrial applications such as power generation, nuclear industry, process plants, heat recovery systems, refrigeration, food industry etc. In our work we had designed, fabricated and experimentally analysed a helical coil heat exchanger and a straight tube heat exchanger. From the observations and calculations, the results of the helical coil heat exchanger and straight tube heat exchanger are obtained and are compared. From our obtained results, the helical coil heat exchanger showed increase in the heat transfer rate, effectiveness and overall heat transfer coefficient over the straight tube heat exchanger on all mass flow rates and operating conditions. The centrifugal force due to the curvature of the tube results in the secondary flow development which enhances the heat transfer rate. Comparative study shows that helical coil heat exchanger is having better performance that straight tube heat exchanger. KEYWORDS: - Helical coil heat exchanger, straight tube heat exchanger, effectiveness, overall heat transfer coefficient. I. INTRODUCTION Heat exchange between flowing fluids is one of the most important physical process of concern, and a variety of heat exchangers are used in different type of installations, as in process industries, compact heat exchangers nuclear power plant, HVACs, food processing, refrigeration, etc. The purpose of constructing a heat exchanger is to get an efficient method of heat transfer from one fluid to another, by direct contact or by indirect contact. The heat transfer occurs by three principles: conduction, convection and radiation. In a heat exchanger the heat transfer through radiation is not taken into account as it is negligible in comparison to conduction and convection. Conduction takes place when the heat from the high temperature fluid flows through the surrounding solid wall. The conductive heat transfer can be maximised by selecting a minimum thickness of wall of a highly conductive material. But convection is plays the major role in the performance of a heat exchanger. Heat exchangers are the important engineering systems with wide variety of applications including power plants, nuclear reactors, refrigeration and air-conditioning systems, heat recovery systems, chemical processing and food industries. Helical coil configuration is very effective for heat exchangers and chemical reactors because they can accommodate a large heat transfer area in a small space, with high heat transfer coefficients. The flow through a curved pipe has been attracting much attention because helical coiled pipes are widely used in practice as heat exchangers and chemical reactors. The fluid flowing through curved tubes induces secondary flow in the tubes. This secondary flow in the tube has significant ability to enhance the heat transfer due to mixing of fluid. Forced convection in a heat exchanger transfers the heat from one moving stream to another stream through the wall of the pipe. The cooler fluid removes heat from the hotter fluid as it flows along or across it. Mainly trasfer of heat depend upon the three ways 1 Parallelflow 2Counter flow 3Cross flow 1.Parallel Flow Figure1.1 shows a fluid flowing through a pipe and exchanges heat with another fluid through an annulus surrounding the pipe. In a parallel-flow heat exchanger fluids flow in the same direction. If the specific heat capacity of fluids are constant, it can be shown that dq/dt=ua T where, dq/dt=rateofheattransferbetweentwofluids U=Overallheattransfercoefficient A=Areaofthetube T= Logarithmic mean temperature difference defined by T = ( T1 - T2)/In ( T1 / T2) 2015, IERJ All Rights Reserved Page 1

2 2.Counter Flow Figure 1.2 shows a fluid flowing through a pipe and exchanges heat with another fluid through an annulus surrounding the pipe. In a counter-flow heat exchanger fluids flow in the opposite direction. If the specific heat capacity of fluids are constant, it can be shown that dq/dt=ua T where, dq/dt=rateofheattransferbetweentwofluids U=Overallheattransfercoefficient A=Areaofthetube T= Logarithmic mean temperature difference defined by T = ( T1 - T2)/In ( T1 / T2) 3.Cross Flow In a cross-flow heat exchanger the direction of fluids are perpendicular to each other. The required surface area, Across for this heat exchanger is usually calculated by using tables. It is between the required surface area for counter-flow, Acounter and parallel-flow, Aparallel i.e. Acounter<Across <Aparallel II. METHODOLOGY Here I will design the Helical Tube in Tube Coil Heat Exchanger For the Given Input Data. 2.1Input Data :- 2.2Schematic Cut way of Heat Exchanger: , IERJ All Rights Reserved Page 2

3 r = Mean Coil Radius (m) p = Pitch (m) d o = Diameter of Inner Tube (m) D = Diameter of outer Tube (Annulus) (m) De = Equivalent Outside Diameter of Coil (m) C = Outside Wetted diameter of Annulus (m) B = Inside wetted diameter of Annulus (m) DH 2 = Outside diameter of Helix of Inner Coil (m) DH 1 = Inside diameter of Helix of Inner Coil (m) N = No. of turns of coil L = Length of tube to make N turns (m) Gs = Mass flow velocity of fluid ( Kg/m 2 h) M = Mass flow rate of fluid (Kg/h) A = Area of Coil (m 2 ) N Re = Reynolds Number Q = Heat Load ( Kcal / h) U = Overall Heat Transfer Coefficient ( Kcal /h m 2 C) Fig. Schematic Cut Way of Heat Exchanger Where, III.FABICATION AND EXPERIMENTAL SET UP 3.1 Fabrication Of Coil The heat exchangers coil is manufactured from copper material. The inner tube having dia. 6.4 mm and outer tube of dia mm. Pitch is of 30 mm. The curvature radius of the coil is 62.5 mm and the stretched length of the coil is 2000 mm. While the bending of tubes very fine sand filled in tube to maintain smoothness on inner surface and this washed with compressed air. The care is taken to preserve the circular cross section of the coil during the bending process. The end connections soldered at tube ends and two ends drawn from coiled tube at one position To maintain the pitch (p) 30 mm we take the rope of diameter 20 mm and maintain the pitch as shown in photo. Below are some photos while manufacturing the coil. 3.2Proposed Experimental Set Up : Fig 4.2 Proposed Experimental Set Up 2015, IERJ All Rights Reserved Page 3

4 3.3Apparatus Required For Set Up: o Helical Coil: This is the main component in our Set Up. The helical coil is the focus of the heat exchanger. Simple Drawing Actual Coil o Tank : This tank is fabricated from MS material and given a small hole at the bottom of tank. Fig 4.4 Fabricated Tank o Pump We are going to use the submersible pump of following specification Make: SUTEX Specification: V 50 Hz 1 Ph. 12 W Maximum Lifting Height: 1.30 m Output : 800 Ltr/h o o Water Heater Measurement Flask: 4.4 Actual Experimental Set Up : We fitted the coil on a Stand for the purpose of mobility and ease of storage. We connected helical coil to Storage Tank through Rubber Pipe. We will heat the fluid in storage tank by the water heater. Hot fluid is flowing through the inner tube while cold fluid will flow through the annulus. As we arranged the storage tank on the top side, hot fluid will flow through the gravity. To circulate the cold fluid we will use the submersible water pump, necessary electrical connection are arranged as per requirement. To control the flow, valves are given at necessary location. 2015, IERJ All Rights Reserved Page 4

5 Fig 4.8 Fabricated Experimental Set Up III. TESTING OF HEAT EXCHANGER 5.1Input Data For Testing :- o Hot Fluid through Inner Tube - SAE 20 W 40 Oil o Cold Fluid through Outer Tube (Annulus) - Water o Properties Of SAE 20 W 40 Oil - SPECIFIC GRAVITY = SPECIFIC HEAT = Btu / lb-f =1.7 KJ/KGK Note: 1 kj/(kg K) = kcal/(kg o C) = Btu/(lb o m F) - Hence specific heat of SAE20W40 = x1/ = = 1.7 kj/kg-k o Properties Of Water - Specific Heat of water at (25 to 30 0 C) = kj/kg-k 5.1 Procedure For Testing:- We will Test the Heat Exchanger in two Configurations 1. Parallel Flow Configuration 2. Counter Flow Configuration PROCEDURE FOR TESTING IN PARALLEL FLOW CONFIGURATION 1. Heat oil in the top tank up to desired temperature by heater 2. Start flow of oil in downward direction 3. Start cooling water pump, and send water top to bottom 4. Take mass flow readings for hot oil: Collect the Hot oil in measuring flask up to desired level and note down the time required to fill the hot oil up to desired level. It will give you the reading ml/sec. Convert that reading into Kg/Hr 5. Also note down the temperature of Hot Oil at Inlet and Outlet 6. Take mass flow readings for cold water: Collect the Watero in measuring flask up to desired level and note down the time required to fill the hot oil up to desired level. It will give you the reading in Ltr/Sec. Convert that reading into Kg/Hr 7. Also Note down the Temperature Of water at Inlet and Outlet o Set Up Arrangement In Parallel Flow Configuration: - Fig 5.1 Set Up Arrangement For Parallel Flow Testing o Procedure For Testing In Counter Flow Configuration:- 1. Heat oil in the top tank up to desired temperature by heater 2. Start flow of oil in downward direction 2015, IERJ All Rights Reserved Page 5

6 3. Start cooling water pump, and send water bottom to top 4. Take mass flow readings for hot oil: Collect the Hot oil in measuring flask up to desired level and note down the time required to fill the hot oil up to desired level. It will give you the reading ml/sec. Convert that reading into Kg/Hr 5. Also note down the temperature of Hot Oil at Inlet and Outlet 6. Take mass flow readings for cold water: Collect the Water in measuring flask up to desired level and note down the time required to fill the hot oil up to desired level. It will give you the reading in Ltr/Sec. Convert that reading into Kg/Hr 7. Also Note down the Temperature Of water at Inlet and Outlet o Set Up For Counter Flow Configuration Fig. 5.2 Set Up Arrangement For Counter Flow Configuration 6.1 Parallel Flow Configuration :- Sample Calculation LMTD (θm) = (θ1- θ2) / ln (θ1/ θ2) Overall Heat Transfer Coefficient (U) We know, Q = U A θm Q = m Cp T Equating 1 and 2 we get following equation U A θm = m Cp T U = m Cp T / A θm Capacity Ratio ( C ) : C = (m Cp) min /(m Cp) max Effectiveness ε =Thi The / Thi Tci IV. RESULTS& DISCUSSION 6.2Counter Flow Configuration : Sample Calculation LMTD Calculation LMTD (θm) = (θ1- θ2) / ln (θ1/ θ2) Overall Heat Transfer Coefficient (U) We know, Q = U A θm Q = m Cp T Equating 1 and 2 we get following equation U A θm = m Cp T U = m Cp T / A θm Capacity Ratio ( C ) : C = (m Cp) min /(m Cp) max Effectiveness ε =Thi The / Thi Tci 6.3Graph For the Trends Of Results In Parallel Flow and Counter Flow Configuration Trends Of Results In Parallel Flow Configuration 2015, IERJ All Rights Reserved Page 6

7 HelicalCoil HE Shell Tube Mass Flow Rate Oil Vs Overall Heat Transfer Coefficient As seen above overall heat transfer coefficient increases with increase in mass flow rate of oil in both helical coil and shell and tube heat exchanger up to certain level. But from the graph it is clear that Overall heat transfer coefficient is always less in Shell and tube heat exchanger as compared to helical tube heat exchanger. Helical Coil HE Shell Tube Mass Flow Rate Oil Vs Effectiveness In above graph effectiveness increases with increase in mass flow rate of oil in both helical coil and shell and tube heat exchanger up to certain level. But from the graph it is clear that effectiveness is always less in Shell and tube heat exchanger as compared to helical tube heat exchanger Mass Flow Rate Oil Vs Nu As seen above Nusseltnumber increases with increase in mass flow rate of oil in both helical coil and shell and tube heat exchanger up to certain level. But from the graph it is clear that Nusselt Number is always less in Shell and tube heat exchanger as compared to helical tube heat exchanger. 2015, IERJ All Rights Reserved Page 7

8 Helical Coil Mass Flow Rate Water Vs Overall Heat Transfer Coefficient Above graph indicate that Overall Heat Transfer Coefficient increases with increase in mass flow rate of water in helical coil heat exchanger, but in shell and tube heat exchanger overall heat transfer coefficient increases with increase in mass flow rate of water up to certain level. But from the graph it is clear that Overall heat transfer coefficient is always less in Shell and tube heat exchanger as compared to helical tube heat exchanger Mass Flow Rate Water Vs Effectiveness As seen above overall heat transfer coefficient increases with increase in mass flow rate of oil in both helical coil and shell and tube heat exchanger up to certain level. But from the graph it is clear that Overall heat transfer coefficient is always less in Shell and tube heat exchanger as compared to helical tube heat exchanger Mass Flow Rate Water Vs Nu As seen above Nusseltnumber increases with increase in mass flow rate of water in both helical coil and shell and tube heat exchanger up to certain level. But from the graph it is clear that Nusselt Number is always less in Shell and tube heat exchanger as compared to helical tube heat exchanger Graph In Counter Flow Configuration 2015, IERJ All Rights Reserved Page 8

9 Mass Flow Rate Oil Vs Overall Heat Transfer Coefficient As seen above the overall heat transfer coefficient in helical tube heat exchanger is remaining approximately same over different mass flow rate of oil. In shell and tube heat exchanger overall heat transfer coefficient increases as mass flow rate of oil increases but overall heat transfer coefficient is always less in shell and tube heat exchanger than in helical coil heat exchanger Mass Flow Rate Oil Vs Effectiveness From the above graph effectiveness of Helical coil heat exchanger is decreasing but if we seen it very closely we can understand that it is approximately same over different mass flow rate of oil.in shell and tube heat exchanger effectiveness is always less than helical coil heat exchanger Mass Flow Rate Oil Vs Nu As seen above Nusselt Number in helical tube heat exchanger is remaining approximately same over different mass flow rate of oil. In shell and tube heat exchanger NusseltNumber increases as mass flow rate of oil increases but Nusselt Number is always less in shell and tube heat exchanger than in helical coil heat exchanger. 2015, IERJ All Rights Reserved Page 9

10 Mass Flow Rate Water Vs Overall Heat Transfer Coefficient From the graph we can see that overall heat transfer coefficient increases with increase in mass flow rate of water in both helical coil and shell and tube heat exchanger but overall heat transfer coefficient is always less in shell and tube heat exchanger than in helical coil heat exchanger Mass Flow Rate Water Vs Effectiveness From the graph we can see that effectiveness increases with increase in mass flow rate of water in both helical coil and shell and tube heat exchanger but effectiveness is always less in shell and tube heat exchanger than in helical coil heat exchanger Mass Flow Rate Water Vs Nu As seen above Nusselt number increases with increase in mass flow rate of water in both helical coil and shell and tube heat exchanger but Nusselt number is less in shell and tube heat exchanger than in helical coil heat exchanger. IV. CONCLUSION 1. Capacity ratio of designed heat exchanger in counter flow configuration increases with increase in mass flow rate with maximum capacity ratio of Capacity ratio of designed heat exchanger in parallel flow configuration increases with increase in mass flow rate with maximum capacity ratio of Designed Helical coil in coil heat exchanger in counter flow configuration is 1.27 (ie, 0.66/0.52) times effective than the Helical coil in coil heat exchanger in parallel flow configuration 4. From the graph we can conclude that our designed helical coil in coil heat exchanger is always better option than shell and tube heat exchanger. 2015, IERJ All Rights Reserved Page 10

11 REFERENCES 1.Experimental investigation of helical coil heat cxchanger Srijith K, t.r. SreesataRam,JaivanAvarghese, Manoj Francis 2.Thermal Analysis of a helical coil Heat exchanger AmolAndhare RCOEM Nagpur, V.M.KulkarniGHRCE,Nagpur 3.Fabrication Analysis of Tube-in-Tube Helical coil heat Exchanger Researcher Scholar,SinhgadInstiyude of technology. Mrunalkshrisager, Trupti J. Kansara, SwapnilAher, 4.helical coil heat exchangers J.S. Jayakumar, prof.mechanicalengg.kollam India. 5.Experimentalevalution of helical coil tube in heat exchanger GavaePravin p, Prof. Kulkarni P.R.,DME,J j Magdum college of engineering, JaysingpurMaharastra, India 6. Parametric Analysis of Helical Coil Heat Exchanger -Pramod S. Purandarea, Mandar M. Leleb, RajkumarGuptac, International Journal of Engineering Research & Technology (IJERT) Vol. 1 Issue 8, October Ramchandra K Patil,Rathi Industrial Equipment Co,. B W Shende, Polychem Ltd and Prasanta K Ghosh, Hindustan Antibiotics Ltd presented simple design procedure for Helical Coil Heat Exchanger Review on Comparative Study between Helical Coil and Straight Tube Heat Exchange 8.N. D. Shirgire1, P. Vishwanath Kumar 2,IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-issn: ,p-ISSN: X, Volume 8, Issue 2 (Jul. - Aug. 2013), PP Timothy J. Rennie, Vijaya G.S. Raghavan, 2005 Experimental studies of a double-pipe helical heat exchanger. 2015, IERJ All Rights Reserved Page 11