HEAT TRANSFER CHARACTERISTICS OF A CIRCULAR CHANNEL INSERTED METALLIC WIRE WITH HIGH POROSITY

摘要

There are several methods for heat transfer enhancement. For example, there are attaching various fins on the heat transfer surface, processing the surface roughly, inserting twisted tape, and so on. These methods increase heat transfer coefficient or area by manufacturing of the heat transfer surface. However, it has to take into consideration the deterioration of the structure strength by attaching the fins on the tube surface with the design of the heat exchanger.The objective of this study is to clarify characteristics of heat transfer and pressure drop in the channel inserted metallic wire with high porosity. A heat transfer experiment has been performed using a horizontal circular tube to obtain the heat transfer characteristics in the channel inserted copper wire.This paper describes the heat transfer and flow characteristics of a heat exchanger tube filled with a high porous material. Fine copper wire (diameter : 0.5 mm) was inserted in a circular tube dominated by thermal conduction and forced convection. Working fluid was air. Hydraulic equivalent diameter was cited as the characteristic length in Nusselt number and Reynolds number.From the results obtained in this experiment, it was found that an amount of heat transfer in the tube with the copper wire was larger than that without one. An effectiveness of heat transfer enhancement increased with the temperature of the heated wall. The amount of heat transfer in the circular tube inserted copper wire, which has 0.993~0.998 of porosity, increased about 15% comparing with the tube having a smooth wall surface under the condition of the constant heat flux and lower than 170°C of the wall temperature.