Abstract
In the present study numerical analysis of enhancement in heat transfer characteristics in a double pipe heat exchanger is studied using a holed twisted tape.The twisted tape with a constant twist ratio is inserted in a double pipe heat exchanger. Holes of diameter 1mm, 3 mm and 5 mm were drilled at regular pitch throughout the length of the tape. Numerical modeling of a double pipe heat exchanger with the holed twisted tape was constructed considering hot fluid flowing in the inner pipe and cold fluid through the annulus.Simulation was done for varied mass flow rates of hot fluid in the turbulent condition keeping the mass flow rate of cold fluid being constant. Thermal properties like Outlet temperatures, Nusselt number, overall heat transfer coefficient, heat transfer rate and pressure drop were determined for all the cases. Results indicated that normaltwisted tape without holes performed better than the bare tube. In the tested range of mass flow rates the average Nusselt number and heat transfer rate were increased by 85% and 34% respectively. Performance of Twisted tape with holes was slightly reduced than the normal twisted tape and it deteriorated further for higher values hole diameter. Pressure drop was found to be higher for the holed twisted tape than the normal tape.
Highlights
Double pipe heat exchangers are considered to be the simple heat exchangers with the fact that they are simple in construction and easy to manufacture
Numerical simulation reveals that average Cold water outlet temperature is found to be increasing with mass flow rates and is higher for twisted tape than the bare tube
The velocity plot and turbulence plot for the normal twisted tape are shown in Fig. 6 and 7 respectively
Summary
Double pipe heat exchangers are considered to be the simple heat exchangers with the fact that they are simple in construction and easy to manufacture. Passive methods include modifications in geometry and surface to the flow channel by incorporating inserts or additional devices They promote higher heat transfer by disturbing or altering the existing fluid flow behavior. Examples of this type includes rough surfaces, extended surfaces inserts, addition of additives etc. They analyzed heat transfer rate and friction factor for different conditions of tapes in the turbulent regime. The experiments were conducted using HTTs (Helical twisted tapes) with three twist ratios (y/W) of 2, 2.5 and 3, three helical pitch ratios (p/D) of 1, 1.5 and 2 They concluded that heat transfer rate and friction factor increase as the tape twist ratio and helical pitch ratio decrease, while the thermal performance shows opposite trend. The results so obtained were compared with the results obtained by the simulation of bare tube and the tube with normal twisted tape
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