The tube bundle of heat exchanger is arranged with an equal space pitch arrangement generally, but using a tube bundle with unequal space pitch one the flow pattern changes and the flow resistance and heat transfer performance may be reduced and improved, respectively. In this study, as a first step the flow resistance of a single raw tube bundle with an unequal spacing is examined experimentally. The equal spacing is the tube pitch of p/d=1.5 (d: tube diameter, =15.0mm), and a unequal spacing is formed by moving only the odd' s number tube.
The experiment showed that using an unequal space pitch the flow resistance was reduced and the heat transfer performance was improved under some conditions. For example, for Reynolds number Re=Ud/ν=5×10³ (U: mean superficial water velocity of coming to tube bundle), p/d=1.33, volumetric flow rate ratio of air to mixture α=0% (single-phase water flow), 10% (air-water two-phase bubbly flow), the flow resistance of the single raw tube bundle with p/d=1.33 decreases about 35, 9%, respectively, and for α=5% the heat transfer performance Nu_m is improved about 10.5%.