【正文】 4 , A. VenuVinod/Chemical Engineering and Processing 102(2021)1–8 where,d isinnerdiameterofthecoiltube,R iscurvatureradiusof i c the coil and v velocity of the ?uid through the coil. Viscosity (m) and density (r)ofthe?uid havebeen evaluated atthe average of the inlet and outlet temperatures of the coilside ?u。 240。 222。 helical coil was set at using rotameter. . Dean number and Reynolds number v. Shell side temperature was maintained constant using temperature controller and the experiment was allowed to run in steady state (as indicated by constant shellside ?uid temperature). vi. At steady state, outlet temperature of coilside ?uid (water) was noted. vii. The ?ow rate of the water through the coil was increased to 1lpm and steps (v)and (vi) wererepeated upto5lpm inthe increments of . viii. Nowthesteps from (ii)to(vii) wererepeated with nano?uid of different concentrations on shellside. Dean number was calculated using the following equation: 05 d 2R : i 4 5 De188。 240。2222。Tci222。m_Cp240。1222。2021Elsevier . All rights reserved. Chemical Engineering and Processing: Process Intensi?cation journal homepage: Contents lists available at ScienceDirect Chemical Engineering and Processing 102(2021)1–8 2 , A. VenuVinod/Chemical Engineering and Processing 102(2021)1–8 continuous ?ow of nano?uid on the shellside. In the present Nomenclature study,therewasnocontinuous ?owofshellside ?uid(waterand subsequently nano?uid).Further,stirrerwasusedtopromoteheat transfer to coilside ?uid. Heat transfer intensi?cation was determined in terms of enhancement in heat transfer rate and effectiveness of heat exchanger involving nano?uids. Al O , CuO Cp Speci?c heat (kJ/kg C) d Diameter of the coil tube (m) De Dean number 2 3 m Q Mass ?owrate (kg/s) Heat transfer rate (W) and TiO /water nano?uids were used on shellside and water on 2 the coilside. The effect of Dean number and shellside tempera ture(40,45and50C)atstirrer speeds (500,1000 and1500rpm) ontheforced convection heat transfer fromtheshellside ?uidto coilside ?uid was investigated. Rc Curvature radius of the coil Re Reynolds number T Temperature (K) v Velocity of the ?uid through the coil (m/s) wt Weight 2. Materials and methods Greek symbols preparation e Effectiveness of heat exchanger m Viscosity (kg/ms) Density (kg/m3) Preparation ofnanoparticle suspension inwateristhe?rststep inapplying nano?uidforheattransferenhancement. Inthisstudy, Al O ,CuOandTiO /waternano?uidswerepreparedseparatelyby r 2 3 2 Subscript dispersing nanoparticles into the base liquid, water. Details of Al O ,CuOandTiO nanoparticles of BF ci co i Base?uid 2 3 2 Coilside ?uid inlet Coilside ?uid outlet Inner nano?uid was increased by adding surfactant (Cetyltrimethyl ammonium bromide (CTAB) 1% wt. of nanoparticle). Addition of surfactant did not affect the properties of nano?uid. A similar observation wasmadebyAguiaretal.[33].Inordertobreakdown the large agglomerates, ultrasonic processer (Hielscher, UP200H) was used at 200Wand 24kHz for 3h to mix a preset amount of nanoparticles withwatertogiverequired nanoparticle concentra tion. Nano?uids with ?ve different nanoparticle concentrations (%, %, 1%, % and 2% wt.) were prepared to measure the thermal conductivity of nano?uids. The thermal conductivity of Al O ,CuOandTiO /waternano?uidswasmeasured withKD2Pro max Maximum NF o Nano?uid Outer s Shellside ?uid intensi?cation due to different types of nanoparticles such as metallic particles (Ag, Au, Cu, and Fe) [17–20]. nonmetallic particles (Al O , CuO, Fe O , SiO , TiO2 and ZrO ) [21–27]. 2 3 2 thermal property analyzer. 2 3 3 4 2 2 Kannadasan et al. [28] experimentally investigated the effect of CuO/water nano?uidinahelicallycoiledtubeheatexchangerwith horizontal and vertical positions under turbulent condition. The experimental results showed thattheheattransfer intensi?cation wasmoreinverticalpositionthaninhorizontal. Theyalsoreported that the friction factor of nano?uid increased while increasing particle volume concentration in turbulent ?ow conditions. JamalAbad et al. [29] have experimentally investigated the performance ofaspiralcoilheatexchanger usingCu/waterandAl/ water nano?uids. It was found that the maximum thermal performance factor % vol. ofCu/water nano?uid. Thethermal performance factoristheratiooftheNusseltnumber ratio (NuNF/NuBF) to the friction factor ratio (fNF/fBF) at the same . Experimental setup diagram oftheexperimental setup usedinthepresent work[34]. Dimensions ofhelical coiltubeand withglasswooland shellside ?uid temperature was maintained constant using a temperature controller. Two 5kWelectrical heaters were used to heat the shellside ?uid, and temperature measurements were made using PT100typeRTDsensors. Anaxialturbine typestirrer (Make: RemiLaboratory Instruments, model: RQ121/D)wasused to(i)promoteheattransferfromtheshellside ?uidtothecoilside ?uid (water) by forced convection and (ii) maintain uniform temperature in the shell. Flow rate of the water through the coil wasmeasured usingrotameter (–5lpm).Thesetupisprovided withadataacquisition systemtorecordalltemperatures. Aswater ?owsthrough thecoil,heatistransferred fromtheshellside ?uid towater in the coil. pumping power. Jamshidi et al. [30] have experimentally investigated the performance of shell and helical tube heat exchangers by changing the coil diameter and pitch. Their experimental results indicated that heat transfer rate increased withincreaseincoildiameter, et al. [31] have experimentally investigated the heat transfer behavior between metal oxide nano?uid (Al O /water and TiO2/ . Experimental