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ABSTRACT
The influence of serrated circular rings with rectangular winglets (SCRWRW) on the thermal performance of circular tube heat exchanger has been studied experimentally and computationally. The geometrical parameters considered are diameter ratio (DR = 0.8, 0.85), pitch ratio (PR = 3, 4), attack angle (ϴ = 15°, 30°, 45°), and blockage ratio (0.05). The test section is a circular tube of length 1.5 m and diameter 68.1 mm, in which uniform heat flux of 1000 W/m2 has been applied. Air is the working fluid flowing in the range of Reynolds number between 6000 and 24000. The results obtained showed that SCRWRW enhances heat transfer rate 5.54 times of smooth tube while the maximum thermal performance obtained is 3.2 at DR = 0.85, PR = 3, and ϴ = 15°. The computational investigation has also been carried out using Ansys fluent and presented the effect of SCRWRW on temperature distribution and fluid flow.
Abbreviations
SCR: Serrated Circular Ring; SCRWRW: Serrated Circular Ring with Rectangular Winglets; DR: Diameter Ratio (d/D); PR: Pitch Ratio (l/D); BR: Blockage Ratio (H/D)
Nomenclature
| Re | = | Reynolds number |
| v | = | Velocity of air (ms−1) |
| D | = | Test section diameter (m) |
| Nu | = | Nusselt number |
| k | = | Thermal conductivity of air (Wm−1 k−1) |
| h | = | Average convective heat transfer coefficient (W m−2 K−1) |
| Pr | = | Prandtl number |
| cp | = | Specific heat of air (Jkg−1 K−1) |
| m | = | Air flow rate (kgs−1) |
| Cd | = | Coefficient of discharge |
| Ao | = | Area of orifice plate (m2) |
| ΔP | = | Pressure difference (Pa) |
| Twm | = | Wall mean temperature (K) |
| Tfm | = | Fluid mean temperature (K) |
| Ti | = | Inlet air temperature (K) |
| To | = | Outlet air temperature (K) |
| Qair | = | Heat carried by air (W) |
| Qconv | = | Heat transfer by convection (W) |
| A | = | Surface area of the pipe (m2) |
| f | = | Friction factor |
| L | = | Test section length (m) |
| l | = | Distance between two consecutive inserts (m) |
| Nus | = | Nusselt number for smooth tube |
| fs | = | Friction factor for smooth tube |
| d | = | Inner diameter of circular insert (m) |
| ϴ | = | Attack Angle (°) |
| H | = | Width of rectangular wing (m) |