Current and Recent Research Topics

Current and Recent Projects

• Two-Phase Flow Experimental Studies in Pipes with Different Orientations 
  Gas-liquid two phase flow being a sub category of multiphase flow phenomenon is extensively incorporated in chemical, nuclear, refrigeration and petroleum industry. Flow patterns, void fraction, pressure drop and heat transfer are essential components of gas-liquid two phase flow and of special interest for industrial operations. The pressure drop and heat transfer in two phase flow is altogether different from its single phase counter part due to the complex nature of the flow patterns and compressibility nature of the gas phase and hence making it difficult to model the gas-liquid two phase phenomenon mathematically. Research on void fraction, pressure drop and heat transfer in two phase flow dates back to 1960’s reporting various models proposed by different investigators. However, till date there exist no single model for the accurate prediction of void fraction, pressure drop and heat transfer independent of the flow patterns, pipe geometry and orientation and the fluid thermo physical properties. The ultimate objective of the present research work is to develop unified models to accurately predict void fraction, pressure drop and heat transfer in two phase flow independent of the aforementioned experimental variables. The existing two-phase flow experimental facility is capable of flow pattern visualization and experimental measurements of the void fraction, pressure drop and heat transfer for any given pipe orientation. So far our research has contributed in the experimental analysis of the two phase flow and development of improved empirical correlations for void fraction and heat transfer in different pipe orientations.  Three video clips (Annular Flow-different inclination Angles, Slug Flow–Different Inclination Angles, and Different Flow Patterns–Horizontal Flow) based on this study appear in Chapter 1 (Video Gallery of Flow Phenomena) under Section 1.2 (Two-Phase Flow Patterns in Horizontal Tubes, see pages 1-5 to 1-6 and videos 1.2.14, 1.2.15, and 1.2.16) of the Wolverine Engineering Data Book III. 
• Heat Transfer/Pressure Drop in Mini/Micro Tubes 
  The quest for smaller, faster, and cheaper electronics has surpassed the current air cooled technologies ability to dissipate the heat generated.  Forced convection, direct contact, single (liquid) and two-phase flow cooling is investigated using mini/micro tubes. Recent experimentation indicates there is a deviation from classical theory of heat transfer and pressure drop due to scaling and roughness effects from mini to the micro scale. The objectives of this study are to perform systematic pressure drop and heat transfer experiments for different flow rates (laminar-transition-turbulent), heat fluxes and inclination angles in mini and micro tubes with different roughness to gain a fundamental understanding of the important parameters influencing fluid flow and heat transfer in these systems. This is a joint project with Dr. L. M. Tam, Department of Electromechnical Engineering, University of Macau, China and Institute for the Development and Quality, Macau, China. Some of the experiments on this project are being conducted at the University of Macau.
• Heat Transfer/Pressure Drop in the Transition Region (Plain and Enhanced Tubes)
  An important design problem in industrial heat exchangers arises when flow inside the tubes falls in the transition region, typically for Reynolds numbers as low as 200 to as high as 10,000 depending on the type of inlet configuration. Under these conditions the usually cited correlations for heat transfer and friction factor do not give reliable predictions. The aim of this study is to obtain accurate design correlations for heat transfer and pressure drop (isothermal and non-isothermal) in plain tubes in the transition region for various entry configurations. Both experimental and analytical approaches were used. The results of this study have been summarized and appear in Chapter 5 (Enhanced Single-Phase Turbulent Tube-Side Flows and Heat Transfer) under Section 5.2 (Turbulent and Transition Flows and Heat Transfer in Plain Tubes, see pages 5-4 to 5-13) of the Wolverine Engineering Data Book III. The study of single-phase heat transfer and pressure drop (isothermal and non-isothermal) in the transition region inside plain tubeswith different inlet configurations has now been extended to includeenhanced tubes(helically ribbed tubes) with different rib height, rib pitch, and rib helix angle. This is a joint project with Dr. L. M. Tam, Department of Electromechnical Engineering, University of Macau, China and Institute for the Development and Quality, Macau, China. The experimental facility for this project is located at the University of Macau and experiments are underway for both plain and enhanced tubes. The goal of this project is to quantify the tube-side heat transfer and pressure drop characteristics of enhanced tubes in the transition region for single-phase flow and to study the effect of fin geometry and inlet flow configuration on transition Reynolds number. This study is designed to increase fundamental understanding of transition flows inside commercially available enhanced tubes. The ultimate goal of the project is to develop fundamentally based correlations for predicting single-phase heat transfer and pressure drop inside enhanced tubes for the laminar and transition regions. The results of this study would be of great interest to HVAC industry which uses enhanced tube bundles in flooded evaporators and shell side condensers to increase heat transfer.
• Bubble Phenomena in a Vibrating Fluid Column
  Bubble column reactors are widely used in chemical industry for carrying out a variety of liquid phase reactions. For relatively fast reactions, there is often a need to improve the mass transfer between the gas and liquid phases. The mass transfer performance is dictated by both the bubble size and bubble rise velocity. One method of influencing both the bubble size and the bubble rise velocity is to subject the liquid phase to vibrations.  An experimental setup has been built to test bubble motion in a controlled vibration environment. The experimental apparatus is a liquid-filled column into which bubbles can be injected, then the entire apparatus shaken and the bubble response measured. The influence of liquid properties, column diameter, liquid height, vibration characteristics (frequency and amplitude), and overall system pressure on the bubble motion and size are being systematically studied.

Laboratories

• Single/Two-Phase Heat Transfer Laboratory

  The 1-inch tube experimental setup for near horizontal measurements is equipped for measuring heat transfer, pressure drop, void fraction, and also conducting flow visualization in air-water flow at pipe inclinations from - 20° to + 20°.

   

  PHOTOS 

   

  
  Setup at Max Inclination Angle

  
  Flow Visualization Setup

   

  VIDEOS (tested only in the versions listed:  WMV – Windows XP Media Player versions 6 & 10; AVI – Windows 7 Media Player 12 and RealPlayer SP 1.1.4)

   

  WMV     AVI
  Annular Flow-Different Inclination Angles

  WMV     AVI
  Different Flow Patterns-Horizontal Flow

  WMV     AVI
  Slug Flow-Different Inclination Angles

• Mini/Micro Channel Heat Transfer Laboratory

  PHOTOS 

   

  
  Sample of Mini/Micro Tubes

  
  Test Apparatus

  
  Mini/Micro Channel Heat Transfer Lab

  
  Low Flow Rate Coriolis Flow Meter

   

  FRICTION FACTOR IN THE TRANSITION REGION FOR STAINLESS STEEL TUBES (JPG files – best viewed at 125% zoom, or higher, in your browser)

  • Results for D = 2083 to 1372 µm 
  • Results for D = 838 to 337 µm