CHAPTER-3METHODOLOGY – Twisted Tape Fabrication of Fins:Fins were also

CHAPTER-3METHODOLOGY    METHOD OF FABRICATION OF TUBE WALL INSERTS:    Fabrication of Twisted Tapes:Twist tapes were made from Aluminium sheet of length 120 cm and width 20 mm. A twist ratio of 5 was maintained constant. Twist ratio is defined as the ratio of length between two consecutive points on a twist to the width of the tape. At first, the CAD model was made which is shown in the fig. 3 below. Then, the strip from aluminium sheet was cut in the required dimensions.

Twists were made by holding one end and rotating the other while maintaining the twist ratio constant and the final image is as shown in the fig. 4. Fig.

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3 – CAD model of Twisted Tape Fig. 4 – Twisted Tape    Fabrication of Fins:Fins were also made from Aluminium sheet of 120 cm length and 90 mm width. Triangular Fins of 10 mm height and 10 mm base with a 30 mm longitudinal pitch and 20 mm transverse pitch in a staggered arrangement were made. The CAD model was made first as shown in the fig. 5 and then the fins were cut at two sides and were raised perpendicularly upright. Then the sheet containing fins was wound on the inner pipe.

Gas Metal Arc Welding was done longitudinally for Aluminium-Aluminium material and brazing was done circumferentially at the two ends for Aluminium-MS material. Fig. 5 and 6 show the actual image and the drafting image of the fins respectively.            Fig.

7 – Drafting of CAD model    EXPERIMENTAL SETUP:The experimental setup consists of a double pipe heat exchanger, water tank with heater, thermocouples, data logger, rotameter, pressure transducer and a pump. The internal diameter of the inner pipe is 28 mm and for outer pipe, it is 66 mm, both are of mild steel and 4 mm thick. The inner tube is having two passive enhancements, the first is the twisted tape inserts on the inner side and the fins on the outer side of the tube. The test section is 1.2 m long and is insulated with asbestos and glass tape.

Another pipe of 20 mm inner diameter and 80 cm length is attached at the entrance of the inner tube to eliminate the entrance effects or for getting a fully developed flow at the entrance. Hot fluid flows through the inner pipe, whereas the cold fluid flows through the annular space. Hot fluid flows in a closed loop and is heated in the tank by autotransformer controlled heater whose temperature is controlled using a Selec TC303A thermostat. The outer walls of the tank are also perfectly insulated in order to prevent heat losses. Six K-type thermocouples are used for temperature measurements. One thermocouple is mounted at the entrance and the other at the exit of the inner tube. Four thermocouples are mounted on the outer tube at different longitudinal positions with equal spacing. All the thermocouples are calibrated using standard procedure and are connected to Masibus 85XX+ Data Acquisition unit.

The flow rate of the hot fluid is controlled by adjusting the valves. Cold water is directly taken from the constant temperature water tank, and the flow rate is measured by a rotameter. Two ABB 2600T series pressure transmitters are used to measure the pressure of the hot fluid at inlet and outlet so that the pressure drop can be calculated. At first, the CAD model of the experimental setup was developed which is as shown in the fig.

8. The photographic view of the setup is shown in the fig. 9.

     Two set of the experiments were conducted by varying the flow rate in inner tube and annular space, they are    The tube side flow rate is constant and annular region flow rate is varied: The flow rate of annular region is varied as 4, 6, 9, 12, and 15 LPM (Re 900 to 4500), while the tube side flow is kept constant at 9 LPM (Re 10500). The inlet temperature of the hot fluid is kept constant at 70?C.Initially, the experiments are conducted using DI water and Ethylene Glycol in the volume proportion of 60:40 as hot fluid, and then by using 0.05, 0.1 and 0.2% concentrations by volume of iron oxide nanofluids.

    The tube side flow rate is varied and annular region flow rate is constant: Annular region flow rate is maintained at 12 LPM and tube side flow rate is varied as 4, 6, 9, 12, and 15 LPM (Re 4600 to 18000). Again, the inlet temperature of the hot fluid is kept constant at 70?C. Initially, DI water and Ethylene Glycol in the volume proportion of 60:40 is used as the hot fluid. After this, 0.05, 0.

1 and 0.2% concentrations by volume of iron oxide nanofluids are used as the hot fluid. Fig. 9 – Experimental Setup    Nanofluids:Nanofluid is the mixture of fluid, called base fluid, which is in larger quantity and nanoparticles, which are dispersed in the base fluid. The two-step method is followed for the nanofluid preparation.

Nanoparticles are procured from Nano Research Labs, India. ?- type iron oxide (20-30nm, 99.5% purity) is used as a nanoparticle in the experiment.

  Figure 10 show SEM analysis of Iron oxide. The nanofluid is prepared by dispersing these nanoparticles in DI water and Ethylene Glycol in the volume proportion of 60:40, which is the base fluid. In order to obtain stable nanofluid against sedimentation, Ultrasonication is used. The volume concentration (?) and mass of nanoparticle can be related to the following equation.?(%)=w_np/?_np /{w_np/?_np +w_bf/?_bf } Fig. 10 – FESEM image of iron oxide nanoparticleNanofluid preparation The required amount of nanoparticles to form a particular concentration is weighed using a high accuracy (resolution of 0.1mg) electronic weighing machine.

Then, the nanoparticles and DI water and Ethylene Glycol in the volume proportion of 60:40 are mixed using a magnetic stirrer (REMI) in order to form a homogeneous mixture. After 30 minutes of magnetic stirring, nanofluid is sonicated for one-hour duration using Ultrasonicator (Oscar). There is no sedimentation observed in the prepared nanofluid for more than 2 days, which is sufficient to carry on the experiment.    Pump:Centrifugal pump was used to circulate hot fluid through the tube side. The specifications of the pump are given in the following Table 1:Pump    SpecificationsPower    0.5 HPRated Speed    2800 rpmRated Head    20 mRated Discharge    30 LPMType    CentrifugalTable – 1: Specifications of Pump                               Data Acquisition System:Masibus 85XX+ Data Acquisition Unit as shown in fig. 15 is used for measuring temperatures.

The detailed specifications are given in Table-2.    Pressure Transmitter:ABB 2600T series 266 model pressure transmitters were used for measuring the pressures at inlet and outlet. The range of pressure transmitter is 0-250 mBar. The power supply to the transmitter is 24V.