Experimental Study on Enhanced Heat Transfer Capability of the Array of Microtubes

The micro-tubes with inner diameter 0.8 mm are arrayed to serve as the heat transfer unit in the mini heat exchanger we developed and the investigation on the heat transfer capability of the array of micro-tubes are carried out experimentally. To perform the experiments conveniently and economically, six plates with nozzles and sealing grooves are used to construct a hexahedral shell of the mini heat exchanger based on bolted connections, and the units are easily to be disassembled so that the heat transfer array can be replaced if necessary. The arrangement of micro-tubes is similar to that in the conventional micro shell-and-tube heat exchanger. The experiments are carried out under atmospheric pressure condition, so the inlet temperatures and mass flow rates for both shell-side and tube-side fluids can be adjusted. The heat transfer coefficient is calculated to evaluate the heat transfer efficiency of the array of micro-tubes, and the influences of some parameters, such as tube inner diameter, tube spacing distance, inlet temperature difference, inlet mass flow rates, etc., on the heat transfer coefficient are investigated. By comparing the heat transfer coefficient of the mini heat exchanger with that of the conventional shell-and-tube heat exchanger, it is revealed that the heat transfer enhancement is realized by using the array of micro-tubes. The enhancement profits from the large heat transfer area per unit volume and small thermal resistance in boundary layer.