THE OBJECTIVE OF THE PROPOSED RESEARCH WORK IS TO IMPROVE THE UNDERSTANDING OF ENHANCED HEAT TRANSFER BY DUST LOADING IN HEAT EXCHANGERS FOR BOILER PLANT APPLICATIONS. THE PRINCIPAL AIM IS TO PROVIDE DESIGN CRITERIA TO INCREASE THE POTENTIAL EFFICIENCY OF THESE UNITS.
A closed loop gas particle suspension flow wind tunnel has been designed and constructed to investigate the effect of air Reynolds number, and particle size and concentration on the suspension crossflow heat transfer characteristics of a model triangular tube array with a pitch to diameter ratio of 2.
Instrumentation has been developed to determine local and overall heat transfer coefficients for individual tubes in the array and the variation in suspension heat transfer with location in the array has been investigated.
The results indicate that high concentrations of fine particles are most likely to enhance the overall Nusselt number and go some way towards clarifying the mechanisms of heat transfer modification in gas particle suspension crossflows. In addition, a numerical code has been developed to enable calculations to be performed for 2-phase gas particle flows. The code predicts the particle trajectories and accounts for some interaction between the gas and the particle phase.
IN MANY FLUIDISED BED SYSTEMS, THE SHELL SIDE HEAT TRANSFER ENVIRONMENT OF THE HEAT EXCHANGERS IS GAS MIXED WITH DUST PARTICLES CONVECTED FROM THE COMBUSTION AREA. IT IS GENERALLY ACCEPTED THAT THE PRESENCE OF SUCH PARTICLES ENHANCES THE HEAT TRANSFER CHARACTERISTICS BUT THE MECHANISMS OF ENERGY TRANSFER IN CROSS FLOW HEAT EXCHANGERS HAS NEVER BEEN FULLY INVESTIGATED. AS A CONSEQUENCE, THERE IS A LIMITED UNDERSTANDING OF THE FUNDAMENTALS ASSOCIATED WITH THE PHENOMENON AND THERE IS NO PROCEDURE FOR DESIGNING THESE UNITS FOR OPTIMAL HEAT TRANSFER.
RECENT TESTS AT BABCOCK POWER RESEARCH CENTRE IN SCOTLAND HAVE INDICATED THAT THE INCREASE IN HEAT TRANSFER OBTAINED BY DUST LOADING IS SUFFICIENT TO JUSTIFY A FUNDAMENTAL STUDY TO QUANTIFY THOSE PARAMETERS MOST LIKELY TO INFLUENCE THIS ENHANCEMENT. THIS PROJECT IS A DIRECT CONSEQUENCE OF THESE OBSERVATIONS AND AIMS TO IDENTIFY THOSE PARAMETERS WHICH ARE MOST INFLUENTIAL IN THE PROCESS OF ENHANCEMENT.
AN EXPERIMENTAL RIG SHOULD BE COMPLETED AND THE EXPERIMENTAL PHASE SHOULD BE ACQUIRING RESULTS OF INTEREST USING THE INSTRUMENTATION DEVELOPED AND THE NUMERICAL MODEL ESTABLISHED.
THE PROJECT SHOULD PROVIDE DESIGN GUIDELINES FOR OPTIMISING ENHANCED HEAT TRANSFER AND A COMPUTER ANALYSIS PACKAGE FOR ANALYSIS OF HEAT TRANSFER IN TUBE BUNDLES.