Journal of Thermal Science and Technology Vol. 11(2016) No. 2

This paper investigates the CHF in saturated pool boiling of ethanol, R141b, and water on a 7 mm diameter vertical copper surface at high pressures. The pressures are from 0.1 to 3 MPa for ethanol, 0.1 to 1.5 MPa for R141b, and 0.1 to 0.8 MPa for water. The results show that the occurrence of CHF is accompanied by the formation of large vapor masses covering most of the heating surface with all three liquids over the whole range of pressures investigated here. The well-known Kutateladze-type CHF correlation explains the variations in the CHF with pressure well for ethanol and R141b, and underestimates the pressure dependence of the CHF for water. A correlation considering the effect of surface wettability on the CHF agrees fairly well with the CHF for water in the whole range of pressures here, when the temperature dependence of the contact angle determined from available data is incorporated into the correlation. This suggests that it is necessary to consider changes in surface wettability with pressure to be able to predict the CHF of water at high pressures.

The effect of ferric oxide concentration on particulate fouling in two-dimensional repeated rib tubes is investigated. Three repeated rib tubes with the range of roughness configuration 0.015≤e/D_i≤0.030 and 10≤p/e≤20 are tested. The fouling curves show an asymptotic behavior. The fouling resistances of repeated rib tubes are higher than that of the plain tube. At low concentration of 750 ppm, however, they are approximately the same. The repeated rib tubes show stronger concentration dependencies compared with the plain tube. Within the test range, the repeated rib tube fouling resistance increases as p/e increases and e/D_i decreases. The deposit inspection supports this trend. The effect of the deposit non-uniformity on fouling resistance and the effect of deposit on heat transfer performance are additionally examined.

In this study, experiments on a pulse detonation turbine engine (PDTE) were conducted. The final goal of this work is the self-sustained operation of a PDTE system in which all of the air used for its operation is supplied by a turbine-compressor driven by pulsed detonations in the system itself. Currently, air used for PDTE operation is supplied by using an external device because the air flow rate for PDTE operation is too high. That is, air is used not only for combustion but also for purge of the residual hot burned gas in a pulse-detonation combustor (PDC), and sometimes for the control of the turbine-inlet temperature by blowing secondary air into a PDTE system downstream of the PDC. In this work, for reducing the air flow rate for PDTE operation, the water-droplet-injection technique was introduced in two ways. First, water droplets were injected into the PDC for purging the residual hot burned gas. Second, water droplets were injected into the PDTE system downstream of the PDC for controlling the turbine-inlet temperature. In particular, the effect of the latter was analyzed by using simple model calculations. As a result, the turbine-inlet temperature was precisely controlled by the water-droplet injection, and the air flow rate for PDTE operation was drastically reduced.