A study on the heat transfer performance of a sintered CNT/Cu composite coated inside pipe surface

The heat transfer performance effects of CNT/Cu composite coated inside pipe surface was investigated. It was compared with other pipes used in some heat transfer equipment used today particularly pipes used in present heat exchangers. The powder composite used in this experiment was created through ball milling at 900 rpm in 4 hours using an attrition ball mill. After creating the powder it is sprayed on the inside pipe surface of a Cu pipe through electrostatic spraying then sintered at 600 °C for 8 hrs. The CNT and Cu powder are used as received and did not undergo any chemical processes. The composite coating consists of copper as the base powder and different volume percent of CNT's namely 5, 10, 15, 20 and 30 vol. % respectively. Another type of pipe used also is the plain Cu pipe as a standard reference and basis for analysis interpretation of the results. The heat transfer performance was obtained and compared with each other. Based on the result the CNT composite coating having a 20 vol. % CNT gives the highest heat transfer performance. Too much CNT or a composition of 30 vol. % in the composite affects the heat transfer performance of the pipe making it less effective due to the powder being too small and the coagulation of the powders during powder making and sintering process. The spiral pipe used also on this test gives a good result but lower when compared to the 20 vol. % CNT/Cu composite coating. Surface characterization is done by SEM imaging and EDX to identify whether a presence of CNT is observed in the composite coating. The surface roughness was acquired by the use of Mitutoyo Surftest SJ-400 which immediately gives a direct average of the surface roughness being measured.