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Design of a heat recovery system of a mining truck using Flow Network Modeling (FNM)
This study involved the design of an innovative heat recovery system used in a mining truck. The large mining trucks use
a very high-capacity engine for fulfilling the large power requirement at the mining site. It is therefore desirable to recover the waste heat from the large amount of hot exhaust generated by the
engine. The heat recovery mechanism involves directing the flow through the beams supporting the dump platform. The objective of the design was to minimize the back-pressure at the engine exhaust while
recovering as much heat as possible.
The flow system involved a number of hollow beams of various cross-sections joined to each other, creating a complex system for the flow to travel from the
engine exhaust to the atmosphere. The Flow Network Modeling (FNM) program MacroFlowTM was used to represent the flow system as a network of ducts, bends, orifices (formed at the joint of two beams), and tee and cross junctions. Most parts of the system were standard and correlations for pressure loss and heat tranfer were readily available. In parts of the system where these correlations were not available, COMPACTTM-based CFD analysis was used to
determine the performance characteristics. MacroFlow-based analysis allowed prediction of the flow rates and pressure drops in all parts of the system and back-pressure at the engine exhaust. This
enabled identification of the parts of the system in which the pressure drops are large and localized. Modifications, such as rounding of the bends and incorporation of ducts to provide parallel paths,
were incorporated and their effect on the heat recovery and back-pressure was analyzed. After several interactive modifications, an optimum design of the flow/structural system was determined. The final
design was validated on a prototype and then deployed in practice. Note that a conventional design method would have involved an iterative testing on a prototype - a procedure that would be very
expensive and time consuming given the scale of the physical system involved. Use of MacroFlow-based analysis significantly shortened the design cycle and enabled determination of an effective design at
substantially reduced cost.
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