Micro channel technology is touted as means for process intensification, which in simple terms means shrinking the size of process equipment (heat ex-changers, chemical reactors, chemical separation processes, etc.) to do the same job that a larger piece of equipment would do. In processes that require convective heat transfer (usually all of the above), process intensification basically comes down to increasing the convective heat-transfer coefficient.
Consider a single tube of 1-cm inner diameter. Micro channel fabrication technology offers a means to make a parallel array of tiny tubes or “micro channels” to serve in place of a single tube. For example, a single 1-cm-inner-diameter tube could be broken up into 1000 micro channels, each of 316 micron (μm) inner diameter, all imbedded within a single block of thermally conducting material. Metal is often the preferred material but is difficult to work with. For small-scale applications, silicon is also commonly used, where micro channels are etched into silicon using technologies originally developed by the microelectronic device fabrication industry.
a. Compare the total surface area for heat transfer of the single tube and the parallel array of micro channels described above.
Now consider that the total mass flow rate of liquid water into the process is 60 g/m, and that the physical properties of water are constant over the temperature range of interest with v = 1.0 × 10^-6  m²/s, α = 1.4 × 10^-7 m²/s, ρ = 1000 kg/m³, and k = 0.6 W/m · K. The walls of the tube are maintained at constant temperature.
b. What is the heat-transfer coefficient associated with the single 1-cm-diameter tube 10 cm in length?
c. What the heat-transfer coefficient associated with a single micro channel of the same length? What level of process intensification does the micro channel system offer over the single tube?
d. Assume the solid surface temperature is maintained constant at 100°C. Compare the temperatures of the fluid exiting the tube for both the single tube and the micro channel array when the inlet temperature is 20°C. Assume also as a first estimate that the fluid properties given above are constant with temperature.