Critical heat flux on horizontal tubes in an upward crossflow of Freon-113

Abstract

The critical heat flux (CHF) on horizontal tubes in crossflow of upflowing Freon-113 is obtained under various flow conditions. The effects of the flow field on both the magnitude and the location of the CHF on a horizontal tube are revealed. Data are obtained over a range of mass fluxes (132–560 kg m −2 s −1), subcooling (0–6dgC), and qualities (0 < x Loc < 0.143) at atmospheric pressure. For the case of a tube in a channel, when the mass flux is fixed, the narrower the channel (the smaller the flow area) the lower the CHF. In an in-line bundle the CHF is approximately equal to that of a single tube in an equivalent channel, which has a half width the same as the lateral pitch of the bundle, under the same local mass flux and flow quality. Furthermore, the CHF in this in-line bundle, which has a pitch-to-tube diameter ratio of 1.5, always starts at the upstream stagnation point of the heated tube. This is contrary to the usual situation that occurs on a tube in a channel where the CHF always begins at the downstream portion of the heated tube. This is because, in this in-line bundle, the local quality is highest at the upstream stagnation point of the heated tube due to the presence of the upstream wake. An empirical correlation has been established for the CHF on a horizontal tube in an infinite flow field and in a channel with various channel widths. The correlation also predicts well the CHF on a heated tube in an in-line unheated bundle for the range of conditions examined in this study.