Heat transfer and pressure drop characteristics of a single enhanced tube for single phase flow

  • Ming Li

Student thesis: Master's Thesis

Abstract

Heat exchangers have extensive use in almost all major industries worldwide. Enhanced heat transfer performance and operational flexibility are two very important aspects of modern heat exchangers. Effective use of heat exchangers in various industries requires accurate determination of heat transfer and pressure drop data. The main objective of this thesis work is to report thermo-hydraulic performance evaluation of a commercial enhanced tube using experimental and numerical simulation techniques in a heat exchanger. A pipe-in-pipe heat exchanger using a commercial enhanced tube as the inner tube was designed and constructed in house at the Petroleum Institute. The heat exchanger was configured in a counter flow arrangement. Steady state single phase (liquid-to-liquid) experiments were performed to determine Nusselt number and friction factor. Experiments with water were carried out in the Reynolds number range of (500 < Re < 8,000) while this range was reduced to (150 < Re < 2,000) for water-glycol solution based experiments. Flow rates, temperature and pressure drop were measured using calibrated digital instrumentation. Modified Wilson plot method was used to obtain convective heat transfer coefficient. A non-dimensional performance evaluation criterion (PEC) was used to assess the thermal-hydraulic performance of heat transfer enhancement achieved with the enhanced tube. The enhanced tube has shown heat transfer enhancement compared to smooth tube, especially at higher Reynolds number. Conversely, the average friction factor of enhanced tube is also higher than that of smooth tube. In low Reynolds number region, heat transfer enhancement ratio increased faster than higher region where maximum yet stable enhancement was observed. Experimental results were compared with limited previous studies. Based on the experimental data, correlations were proposed for estimation of Nusselt number and friction factor for the enhanced tube. These correlations represent experimental data very well. An attempt was made to simulate the experimental results numerically. The commercial CFD software Fluent was used to obtain temperature distribution, pressure drop and velocity field. The realizable k-ϵ model was employed to find the influence of dimples on the turbulent flow and temperature field. The mechanism of enhancement was revealed that the dimples/ protrusions disturb and mix boundary layers and generate secondary flow that improves turbulence level of flow. The comparison between experimental and numerical simulation results showed good agreement, 15%. The dimples on the tube were found to play leading role on heat transfer enhancement. Numerical simulations were extended to study enhanced tube geometry optimization for improved thermal-hydraulic performance of heat exchangers. Simulations were carried out in Reynolds number range of (2300 < Re < 15,000). The effects of geometrical parameters, such as dimple shape, dimple depth, dimple diameter and pitch on heat transfer and pressure drop of enhanced tube were studied. The enhanced tube with ellipsoidal dimples and in-line configuration showed the best performance.
Date of Award2015
Original languageAmerican English
SupervisorEbrahim Al Hajri (Supervisor)

Keywords

  • Applied sciences
  • Computational fluid dynamics
  • Enhanced tube
  • Sngle phase
  • Thermal-hydraulic
  • Mechanical engineering
  • 0548:Mechanical engineering

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