Numerical and experimental investigations of heat transfer enhancement in circular tubes with transverse twisted-baffles

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• 作者：K. Nanan ; N. Piriyarungrod ; C. Thianpong ; K. Wongcharee…
• 刊名：Heat and Mass Transfer
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：52
• 期：10
• 页码：2177-2192
• 全文大小：3,713 KB
• 刊物类别：Engineering
• 刊物主题：Engineering Thermodynamics and Transport Phenomena
  Industrial Chemistry and Chemical Engineering
  Thermodynamics
  Physics and Applied Physics in Engineering
  Theoretical and Applied Mechanics
  Engineering Fluid Dynamics
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1432-1181
• 卷排序：52

文摘

Transverse twisted-baffles (T-TBs) and transverse baffles (TBs) were employed for heat transfer enhancement in circular tubes. The experimental and numerical studies were carried out to investigate heat transfer, friction loss and thermal performance factor associated with the use of the baffles (T-TBs/TBs). The studies encompass three different baffle width ratios (w/D = 0.1, 0.2 and 0.3, for TBs and T-TBs), three baffle twist ratios (y/w = 2.0, 3.0 and 4.0, for T-TBs) and Reynolds numbers from 6000 to 20,000. The experimental results reveal that at similar conditions, thermal performance factors of the tubes with the T-TBs are consistently higher than those of the ones with the TBs. This is attributed to the superior heat transfer enhancement with lower pressure drop penalty as the beneficial effects given by the T-TBs, as compared to those given by the TBs. For T-TBs, thermal performance factor increases as baffle width ratio (w/D) increases and twist ratio (y/w) decreases. The T-TBs with the smallest twist ratio (y/w = 2.0) give higher thermal performance factors than the ones with 3.0 and 4.0 by around 4.7–6.1 and 10.2–15 %, respectively. For the studied range, the T-TBs with the optimal geometric parameters, (y/w = 2.0 and w/D = 0.3), give the thermal performance factors in a range of 1.46–1.69.List of symbolsAHeat transfer surface area (m2)C_pSpecific heat capacity of air (J kg−1 K−1)DInside diameter of test tube (m)D_oOutside diameter of test tube (m)fFriction factorhConvective heat transfer coefficient (W m−2 K−1)kTurbulent kinetic energy (\( k = \frac{1}{2}\overline{{u_{i}^{\prime } u_{j}^{\prime } }} \))k_aThermal conductivity of air (W m−1 K−1)LLength of test tube (m)lLength of twisted baffle (m)\( \dot{m} \)Mass flow rate (kg s−1)NuNusselt numberpPitch length (m)PPressure of flow in test tube (Pa)ΔPPressure drop in the test sextion (Pa)PrPrandtl number (μC_p/k)QHeat transfer rate (W)q′′Heat flux (W m−2)RResistance (Ω)ReReynolds number (ρuD/μ)TTemperature (°C)\( \tilde{T} \)Mean temperature (°C)tThickness of twisted baffle (m)u′Fluctuating component of velocity (m s−1)uMean or uniform velocity (m s−1)u_iVelocity component in x_i-direction (m s−1)u_jVelocity component in x_j-direction (m s−1)VVoltage (V)wWidth of twisted baffle (m)xCoordinate directionyTwist length of twisted baffle (m)