An experimental heat-transfer study for a heat-recovery unit made of corrugated tubesPoredoš, Primož (Avtor) Šuklje, Tomaž (Avtor) Medved, Sašo (Avtor) Arkar, Ciril (Avtor) convective heat-transfer coefficientcorrugated tubesWilson-plot methodheat exchangerThis paper presents a study of the thermal characteristics of a concentric-tube heat exchanger that is a key element in local ventilation device. The inner tube of the concentric-tube heat exchanger has a sinusoidal, wavy surface in the longitudinal direction, which enables heat-transfer enhancement. The tube can be stretched to a certain extent and thus change the corrugation of the heat-transfer surface area. We designed an experiment in which we used the Wilson-plot method to separately determine the convective heat-transfer coefficient on the inside and outside of the inner tube of the concentric-tube heat exchanger with different corrugation ratios. Based on the measurements correlation equations were developed to calculate the convective heat-transfer coefficient for any corrugation ratio, which allows us to simplify the design of local ventilation devices. Performed studies showed that, compared to a smooth tube, the convective heat-transfer coefficient increased only in the case of corrugated tubes with a corrugation ratio of less than 1.648, but the heat transfer was more intense for all considered corrugated tubes by 65-90% due to the increased heat-transfer surface area. The highest heat-transfer rate was observed for the case of the maximum-stretched tube with a corrugation ratio of 1.401, which is advantageous also in terms of material consumption.20132021-04-02 11:10:01Članek v reviji125698UDK: 697:628.8ISSN pri članku: 1359-4311DOI: 10.1016/j.applthermaleng.2013.01.004COBISS_ID: 12647963OceCobissID: 1861910sl