Micro-channel heat exchangers offer potential for a highly compact solution in heat transfer applications that have space limitations. Mobile applications such as automotive vehicles are one such area. This work presents the design, modeling, simulation and testing of a two-region micro-channel heat exchanger, employing both engine coolant and R134a, for use in an engine that compresses natural gas for on-board refueling at pressures up to 250 bar. The novel design of the micro-channel heat exchanger is presented. Numerical simulations were performed using ANSYS Fluent utilizing extrapolation techniques to estimate the pressure drop as a function of flow rate and symmetry methods to investigate heat transfer. Pressure drop was determined experimentally, and heat transfer was investigated through system tests employing the novel engine. Experimental results showed good comparison with corresponding numerical simulations which demonstrated the validity of the applied extrapolation and symmetry methods, enabling considerable reduction in computational cost. The pressure drop, flow distribution, and heat transfer characteristics of the heat exchanger are discussed.
An internal combustion engine which is primarily designed for producing power can be utilized as a chemical reactor for a range of chemical processes given its inherent advantages including high throughput, high chemical conversion efficiency, and reactant/product handling benefits. For gas-phase processes requiring a catalyst, the ability to develop a fluidized bed reactor within the engine cylinder would greatly enhance gas/solid mixing, reducing mass transfer barriers and allowing the reactor to efficiently process large volumes of fluid. In addition, use of an engine could facilitate vibration and pulsed flow which may enhance fluidization quality. This work examines the fluidization behavior of particles within a cylinder of an internal combustion engine at various engine speeds using analytical and experimental methods. First, calculations were carried out to determine the maximum fluidization velocity and the corresponding engine speeds below which fluidization of a particle bed is possible given the properties of the particles and engine dimensions. Fluidization depends on particle properties as well as the engine used. For 40–63 micron diameter silica gel particles placed inside a modified Megatech Mark III transparent combustion engine (with a bore of 4.1 cm, stroke length of 5.1 cm and compression ratio of 2.4), calculations indicate that engine speeds of approximately 1.1 to 60.8 RPM would result in fluidization of the particles. For higher engine speeds, the fluidization behavior is expected to deteriorate as the maximum fluidization velocity is surpassed. Next, experiments were conducted using the transparent engine and video recording to obtain qualitative confirmation of the analytical predictions. Simulations were then performed using ANSYS Fluent to investigate pressure drop across the bed. Consistent with the calculations, for an engine speed of 48 RPM, fluidized behavior was observed. In contrast for an engine speed of 171 RPM, the fluidization was observed to deteriorate and result in a “cake” of particles that moved in a lumped manner. Overall, the investigation shows that a fluidized bed can be obtained within the cylinder of a reciprocating piston engine if the engine speed is within the range predicted by the maximum fluidization velocity.
Micro-channel heat exchangers offer potential for a highly compact solution in heat transfer applications that have space limitations. Mobile applications such as automotive vehicles are one such area. This work presents the design, modeling, simulation and testing of a two-region micro-channel heat exchanger, employing both engine coolant and R134a, for use in an engine that compresses natural gas for on-board refueling at pressures up to 250 bar. The novel design of the micro-channel heat exchanger is presented. Numerical simulations were performed using ANSYS Fluent utilizing extrapolation techniques to estimate the pressure drop as a function of flow rate and symmetry methods to investigate heat transfer. Pressure drop was determined experimentally, and heat transfer was investigated through system tests employing the novel engine. Experimental results showed good comparison with corresponding numerical simulations which demonstrated the validity of the applied extrapolation and symmetry methods, enabling considerable reduction in computational cost. The pressure drop, flow distribution, and heat transfer characteristics of the heat exchanger are discussed.
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