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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 5, May 2017, pp. 420–424, Article ID: IJMET_08_05_045 Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=5 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed

HEAT TRANSFER ENHANCEMENT OF DOUBLE PIPE HEAT EXCHANGER USING

TWISTED TAPE INSERTS Kalapala Lokesh

Assistant Professor; Department of Mechanical Engineering; KL University, Andhra Pradesh, India

N. Somasankar, Sk. Azharuddin, K. Uma Maheswara Rao, M. Hari Krishna, M. Siva Sankar Mani Kumar

U.G Student, Department of Mechanical Engineering; KL University, Andhra Pradesh, India

ABSTRACT The heat transfer rate determines the performance of heat exchangers. There is a

need to look after the new techniques to enhance the heat transfer rate. There are several heat transfer enhancement techniques exist, out of which passive heat transfer enhancement techniques are preferred as they do not affect the overall performance of the system. Heat transfer technique with twisted tape inserts are broadly used in several industries for their cost savings, lower maintenance requires and the fact is that they can be easily setup. In this work, a double pipe heat exchanger system is considered for studying the variation of effectiveness of the heat exchanger by inserting twisted tape. The analysis is done for different mass flow rates, different inlet temperatures for parallel and counter flow arrangements. It is observed that the effectiveness of heat exchanger in parallel flow arrangement with twisted plate is higher than the effectiveness in counter flow arrangement without twisted tapes. Hence twisted tape inserts in counter flow arrangement enhance heat transfer rate considerably there by increases effectiveness of the system at a marginal increase in pressure drop. Key words: heat transfer enhancement, double pipe heat exchanger, twisted tape

Cite this Article: Kalapala Lokesh, N. Somasankar, Sk. Azharuddin, K. Uma Maheswara Rao, M. Hari Krishna, M. Siva Sankar Mani Kumar, Heat Transfer Enhancement of Double Pipe Heat Exchanger using Twisted Tape Inserts. International Journal of Mechanical Engineering and Technology, 8(5), 2017, pp. 420–424. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=5

Kalapala Lokesh, N. Somasankar, Sk. Azharuddin, K. Uma Maheswara Rao, M. Hari krishna, M. Siva Sankar Mani Kumar

http://www.iaeme.com/IJMET/index.asp 421 editor@iaeme.com

1. INTRODUCTION Heat transfer enhancement means to improve thermal performance of heat exchanger. To improve thermal performance of heat exchangers lot of methods are introduced such as treated surfaces, rough surfaces, coiled tubes etc.., at present scenario there is a need to improve the heat transfer rate in heat exchangers. We can improve heat transfer rate by creating turbulence in the fluid flow. There are two types of heat transfer enhancement techniques. They are active techniques and the passive techniques. In the design point of view because of the need of some external power input to cause the desired flow modifications active techniques are complex. Various active techniques are surface vibration, fluid vibration, mechanical aids, injection and suction. Passive techniques generally use geometrical modifications to the flow channel by placing additional devices. Passive techniques are far more used because no external power supply is needed. Various passive techniques are swirl flow, coiled tubes, extended surfaces etc

2. LITERATURE REVIEW Mukesh P Mangtani [1] has suggested that heat transfer rate can be increased by creating turbulence by inserting a twisted tape in the flow. Sudhakat et al. [2] has done analysis on shell and tube heat exchanger with twisted plate and concluded that twisted tapes enhance the heat transfer rate. Kolepaka Sridhar [3] has done analysis on flow arrangements and concluded that counter flow is the best method suitable for more heat transfer rate. In the literature lot of works are concentrated on quantifying the heat transfer enhancement, however there is a need to know the enhancement in effectiveness of the system. In this work, an attempt is made to study the effect of twisted tape inserts on effectiveness of the heat exchanger

3. METHODOLOGY Double pipe component is modelled in solidworks. The dimensions of the inner pipe are: diameter of 20mm, thickness 5mm. the dimensions of outer pipe: diameter=50mm.Length of the pipe is 450mm.

Figure 1 Geometry of double pipe with twisted tape

A plain rod of 450mm length is created with 10 mm diameter. With the help of helix and spiral curves make a curve throughout the length of the pipe. And with the help of sweep cut a helical grove is made at 25mm diameter and 1800 pitch angle. These two models are to be imported into Ansys workbench.

Heat Transfer Enhancement of Double Pipe Heat Exchanger using Twisted Tape Inserts

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Figure 2 Geometry of twisted tape

The necessary geometry and mesh were exported to Fluent and given names for hot inlet, hot outlet, cold inlet, and cold outlet faces. steady state pressure based and absolute velocity formulation. Since we deal with temperatures we make the energy equation, and viscous model as standard k- epsilon model and standard wall function condition. the fluid that considered is water with fluid Density of 998.2 Kg/m3, Specific heat of 4182 J/Kg-K, Thermal Conductivity of 0.6 W/m-K, viscosity of 0.001003Kg/m-sec. And for the pipe copper material was considered with Density 8979 Kg/m3, Specific heat of 381 J/Kg-K, and Thermal conductivity of 387.6W/m-k. Hot inlet temperature is 330,380 0C and cold inlet temperature is kept constant throughout the analysis. We solved the problem by considering mass flow rate condition, at 0.0002, 0.0004, 0.0006, 0.0008 and at 0.001 and with the different hot inlet temperatures the analysis is carried out and hot outlet temperatures and cold outlet are seen at the end. This procedure was repeated in counter flow for plain pipe, and in twisted pipe insert in parallel flow and also in counter flow. And the results are compared. Pressure- velocity scheme simple, Gradient as least squares cell based, pressure as standard, momentum as first order upwind, turbulent kinetic energy as second order upwind and turbulent dissipation rate an second order upwind. And change all the residual monitors such as continuity, x-velocity, y-velocity, z-velocity to 10-7

Data Reduction Equations Mass flow rate . = ∗ ∗

Where is the density of the fluid, A is the cross-sectional area and v is the velocity of the fluid So velocity = ./( ∗ ) Reynolds number Re = ( ∗ ∗ )/ Where D is the hydraulic diameter, is the dynamic viscosity of the fluid. And Nu = 0.023* Re0.8 * pr0.3.

Where Nu is the Nusselt number and pr is the Prandtl number.

4. RESULTS AND DISCUSSIONS At different hot inlet temperatures say 3300C and 3800C temperatures graph is plotted between Reynolds number and effectiveness. Four lines in each graph shows normal pipe with parallel flow, normal pipe with counter flow, pipe with twisted tape inset and parallel flow, pipe with twisted tape insert and counter flow respectively. At 3300C and 3800C with increase in mass flow rate Reynolds number also increases.

Kalapala Lokesh, N. Somasankar, Sk. Azharuddin, K. Uma Maheswara Rao, M. Hari krishna, M. Siva Sankar Mani Kumar

http://www.iaeme.com/IJMET/index.asp 423 editor@iaeme.com

Figure 3 At 3300C and 3800C hot inlet temperature plot shows Reynolds number vs effectiveness

The effectiveness order goes like this at constant mass flow rate Effectiveness of normal pipe with parallel flow < effectiveness of normal pipe with

counter flow < effectiveness of pipe with twisted tape inset and parallel flow < effectiveness of pipe with twisted tape inset and counter flow.

At different hot inlet temperatures say 3300C and 3800C temperatures graph is plotted between mass flow rate and cold outlet temperatures. Four lines in each graph shows normal pipe with parallel flow, normal pipe with counter flow, pipe with twisted tape inset and parallel flow, pipe with twisted tape insert and counter flow respectively. At 3300C and 3800C with increase in mass flow rate there is a decrease in cold outlet temperature.

Figure 4 At 3300C and at 3800C hot inlet temperature plot shows mass flow rate vs cold outlet temperature

The cold outlet temperature order goes like this at constant mass flow rate The cold outlet temperature order goes like this at constant mass flow rate Cold outlet temperature of normal pipe with parallel flow < cold outlet temperature of

normal pipe with counter flow < cold outlet temperature of pipe with twisted tape inset and parallel flow < cold outlet temperature of pipe with twisted tape inset and counter flow. At different hot inlet temperatures say 3300C and 3800C temperatures graph is plotted between mass flow rate and effectiveness. Four lines in each graph shows normal pipe with parallel

Heat Transfer Enhancement of Double Pipe Heat Exchanger using Twisted Tape Inserts

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flow, normal pipe with counter flow, pipe with twisted tape inset and parallel flow, pipe with twisted tape insert and counter flow respectively. From plots with increase in mass flow rate

there is a decrease in effectiveness.

Figure 5 At 3300C and at 3800C hot inlet temperature plot shows mass flow rate vs effectiveness

The effectiveness order goes like this at constant mass flow rate Effectiveness of normal pipe with parallel flow < effectiveness of normal pipe with counter flow < effectiveness of pipe with twisted tape inset and parallel flow effectiveness of pipe with twisted tape inset and counter flow.

5. CONCLUSION In this paper we concluded that effectiveness in counter flow is greater than parallel flow because temperature difference is constant throughout the cross section in counter flow but in parallel flow temperature difference get decreases. And effectiveness is more in twisted tape insert setup this is because a twisted tape creates turbulence in the hot fluid flowing region. Approximately 30% increase in effectiveness is observed at low mass flow rates by inserting twisted tapes.

REFERENCES [1] Mukesh P Mangtani and k.m.watt “effect of twisted tape inserts on heat transfer in a

tube”, International journal of mechanical engineering and robotics research. Issn 2278-0149, vol 4, no-2, april 2015.

[2] Sudhakar uppalapati, ”CFD analysis of double pipe parallel flow heat exchanger” IJSRD || National Conference on Recent Trends & Innovations in Mechanical Engineering, ISSN(online): 2321-0613,april 2016.

[3] Kolepaka Sridhar, K.Bicha, ”Comparative analysis of parallel and counter flow heat exchangers”, International journal of scientific engineering and technology research, ISSN 2319-8885,vol.06Issue.04,February-2017.

[4] Dr. Zena K. Kadhim, Dr. Muna S. Kassim and Adel Y. Abdul Hassan, Effect of (MGO) Nanofluid on Heat Transfer Characteristics For Integral Finned Tube Heat Exchanger International Journal of Mechanical Engineering and Technology, 7(2), 2016, pp. 11-24.

[5] V. Murali Krishna, Experimental Investigation of Heat Transfer Enhancement by Using Al2o3-Water Nanofluid in a Concentric Tube Heat Exchanger. International Journal of Mechanical Engineering and Technology, 7(6), 2016, pp. 449–458.

[6] Kankan Kishore Pathak, Asis Giri and Pradip Lingfa, Evaluation of Heat Transfer Coefficient of A Shrouded Vertical Array of Heat Sinks (Fins): A Computational Approach, International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 319-326