[en] In development of an SCWR concept, the heat transfer at supercritical pressures is one of the most demanding research areas. Despite the numerous supercritical heat transfer correlations have been suggested in the past several decades, a search for a reliable and accurate correlation is still required, since the predictions from those correlations showed wide discrepancy each other. Especially in the deteriorated heat transfer regime, no correlation is able to produce accurate predictions. Under a strong buoyancy influence, the boundary layer structure is known to deform significantly, as the wall temperature approaches to the pseudocritical temperature. The deterioration may be a function not only of local flow properties but also possibly of flow history as well. Some of currently available SCWR concepts introduce a multi-pass core design instead of single pass like the conventional LWR, in order to reduce hot channel factor. In the multi-pass design, coolant in at least one pass flows vertically upward. The flow direction is known to greatly affect a flow structure and results in completely different thermal characteristics between upward and downward flows. This paper addresses three main subjects: 1) difference of thermal characteristics between upward and downward flows; 2) effect of simulating flow passage shape; 3) evaluation of existing supercritical heat transfer correlations. To achieve the objectives, a series of experiment were carried out with carbon dioxide flowing upward and downward in a circular tube with an inner diameter of 4.57mm and in an annular channel created between a tube with inner diameter of 10 mm and a heater rod with outer diameter of 8 mm. The hydraulic diameter of the annular channel based on a heated perimeter was 4.5 mm. The working fluid was CO2, which has been regarded as an appropriate modeling fluid to water, primarily because of their mutual resemblance in property variations against normalized temperatures. The mass flux ranged from 400 to 1200 kg/m2s and the heat flux was varied between 30 and 140 kW/m2 so that the pseudocritical point located in the middle of the heated section at a give pressure. The measurements were made at a pressure of 8.12 MPa. The pressure effect is known to be negligible and its effect, if any, is reflected through the property variation with pressure. The difference between the upward and downward flows was observed clearly. A heat transfer deterioration occurred over the wide range of enthalpy in the downward flow through the annular subchannel; however, the exact cause of that phenomenon is not clearly known and subject to further analysis. New heat transfer correlations were proposed. Several well known correlations were evaluated against the experimental data, and new correlations were suggested for both tube and annular channel. (author)