Effects of a device containing heat pipe sticks on thermal performance of a heat exchanging tube: An experimental study

Applying heat pipes (HP) on heat-exchanging tubes is the main idea of this experimental work. One, two, or three mini copper heat pipes are soldered around a cooper ring to form a new device to passively enhance the performance of a heat-exchanging test tube. The test tube, containing a hot turbulent flow of water-EG solution, is inserted into a cold-water tank. The hot-flow regime is turbulent with Reynolds numbers of 5600 to 10,700. The results for fully developed turbulent flow were compared with existing correlations to validate the experimental setup. The validation showed less than a 10 % difference in both Nusselt number and friction factor. The base fluid in the heat pipes are distilled water and dilute Cu-water nanofluids. The nanofluids with different concentrations (50, 100, 150, and 200 ppm) are applied in HP-sticks. The role of the Cu-nanoparticle's concentration on the performance of the presented device is discussed. The results reveal the notable performance of the device in the target goal. It is reported that the presented device containing HP-sticks filled with water enhances convection rate of the test tube up to 35%. It is also ascertained that applying the Cu-water nanofluid in the HP-sticks lead to about 14 % better thermal performance, compared to water. The outcomes also reveal that dilute Cu-water nanofluids (phi <= 100 ppm) notably improve the device's performance. Conversely, more concentrated nanofluids possibly decrease the device's performance.