The back-and-forth movement of flow in oscillatory flow condition that can be found in blood flow, thermoacoustic energy system and ocean wave can be categorized as bi-directional flow condition and heat transfer in this flow condition is not well understood. This paper reports an experimental investigation that compares temperature and velocity values between the onedirectional (the usual flow condition) and the bi-directional flow conditions. The experiment was done using thermoacoustic's standing wave rig with two different drivers to drive the one-directional flow and bi-directional flow conditions in the test rig. Results, that were recorded using piezoresistive pressure sensor, type-K thermocouple and hotwire anemometer, indicate that care should be exercised when calculating heat transfer in bi-directional flow conditions as the temperature and velocity changes are different compared to the one-directional flow condition. Differences were recorded to be within the range of 77% for temperature and 59.5% for velocity, presumably due to the different behavior of forced and natural convection effect as flow conditions changed.

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The one-directional flow condition and the bi-directional flow condition are two flow conditions that can be found in many energy systems depending on the nature of the flow and the working mechanism of the system. This paper reports the differences in heat transfer performance for an in-line tube banks heat exchanger that is placed in the one-directional and the bi-directional flow conditions. The experiments involve the use of a blower as a flow inducer for one-directional flow while a loudspeaker with a constant frequency of 14.2 Hz is used as a flow inducer for bi-directional flow condition. A quarter wavelength resonator with 4 mm wall thickness and a length of 6600 mm was used in the investigation. The results of velocity and temperature were recorded using a hotwire anemometer and a type-K thermocouple, respectively. Results show that the behaviour of velocity and temperature in one-directional and the bi-directional flow conditions over an in-line heated tube banks are different with a maximum difference of 52 % for velocity and 79 % for temperature.

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