International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 07 Issue: 12 | Dec 2020
p-ISSN: 2395-0072
www.irjet.net
Numerical and Theoretical Analysis on Heat Transfer and Flow Characteristics of Helical, Conical, and Inclined Rectangular Coiled Tube in-Tube Heat Exchanger using Nanofluids Chevveti Prasad1, Srinivasa Prasad Katrenipadu2 1P.G.Scholar,
Thermal engineering, JNTUK-University College of Engineering Vizianagaram, A.P, India. Professor, Department of Mechanical engineering, JNTUK-University College of Engineering Vizianagaram, A.P, India. ---------------------------------------------------------------------***---------------------------------------------------------------------2Assistant
Abstract –Recent developments are carried out in the design of heat exchangers to achieve the demand of industries which has led to the evolution of helical coiled heat exchangers for their numerous advantages over a straight tube. In this present study, the CFD analysis is done on various geometrical types of helical, conical, and inclined rectangular coiled tube in- tube heat exchangers using water and three nanofluids such as Al2O3/water, TiO2/water, and MWCNT/water by changing the volume concentrations of nanoparticles percentages in water as 0.2%, 0.4%, and 0.6%. The entire analysis was done in ANSYS Fluent R19.0 in the selected range of Dean number from 1300 to 1700. The results are validated with the theoretical approach by evaluating the flow characteristics of heat exchangers such as heat transfer coefficient, Nusselt number, pressure drop, and friction factor. The MWCNT/water nanofluids in conical coiled tube in-tube heat exchangers, shows better results in overall work. Both theoretical and CFD results are having a good agreement for the inner tube of a coiled tube in tube heat exchangers. Key Words: CFD, Theoretical, Nanofluids Volume Concentrations, Flow Characteristics, Dean number, Helical, conical, and inclined rectangular coiled tube in- tube heat exchangers.
1. INTRODUCTION The design of helical exchangers is considered very important for enhancement of the heat transfer process to acquire the cooling demand in the present industries. However, there is vast research done on curved tubes and helically coiled tubes, because those designs are having a good turbulence due to the presence of good secondary flow which occurs due to centrifugal force which will enhance the flow characteristics of heat exchangers. However, the helical tubes are compact and help in the endurance of large heat removal from thermal systems when compared to straight tubes. Ganesh Kumar et al.[1] work on double pipe heat exchanger by improving the nusselt number. They studied the heat transfer and pressure drop characteristics of activated carbon(AC)- solar glycol (SG) with nanofluid of 0.2%,0.4%, and 0.6% volume concentrations, and their work showed that AC nanomaterials in SG enhance the heat transfer and pressure drop. Wae I.A.Aly [2] worked on coiled tube in tube heat exchanger with Al2O3/water nanofluids of volume concentrations of nanoparticles of 0.5%,1.0%, and 2.0% with different coil diameters. He studied that increasing coil diameter and nanoparticle concentrations will increase the heat transfer coefficient. Y.M.Ferng et al. [3] worked on the effect of changing dean number and pitch size on helically coil tube heat exchangers. They concluded that changing dean number and pitch size are very effective in heat transfer.A.Moktari Andekani, et al.[4] had improve the heat transfer rate in helically coil tubes using Ag-water nanofluids by experimentally and concluded that helically tubes had gives better results than straight tubes under turbulent flow. Vijaya Kumar Reddy K et al.[5] had done a added semicircular plates in annulus region of helically coiled tube in tube heat exchangers. They also studied that with increasing outer flow rate with respect to inner flow rate will causes reduction in LMTD. P.C.Mukesh Kumar et.al [6] worked on helically coiled tube in tube heat exchanger experimentally and numerically. they concluded that increasing of volume concentrations of nanoparticles in water will enhance the heat flow characterstics of nanoparticles of heat exchangers.[7]Gabrieta Humanic [7] studied that increasing of dispersed partricles in water as increases the convective heat transfer coefficients. His results shows 2% CuO, will give 14% of heat transfer for inner and outer by 19% than pure water in double tube helical heat exchangers. B.C.Pak et al.[8] had studied hydrodynamically dispersed particles of Al2O and TiO2 with fluids. They studied that dispersed particle of fluid at 3% was 12% lower than that of pure water by using empirical relation of nusselt number. Yimin Xuan et al.[9] had found concepts for heat transfer correlations for nanofluids, by considering that nanofluids is a mixture of fluid with solid particles. Yang et al.[10] worked on characterstics of convective heat transfer of nanofluids in a helically coiled tube heat exchanger of the working fluid and revealed the nanofluids are superior heat transfer fluids. From the above all, it is concluded that they all investigated the flow characteristics on helically with changing in coil diameters, pitch size and flow patterns. So, in my study I mainly focuses on the different designs of helically coiled tube in tube heat exchangers and to determine which design is best for better heat transfer and flow characteristics of using different nanofluids.
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