Hideaki Mori

Steady state heat transfer in transition boiling of helium on copper surfaces

Abstract Using a heated copper block partially coated with a thin resin film, the block temperatures at which transition boiling is commonly considered to occur on copper surfaces are observed in the steady state. The thickness of the coating ranged from 3.5 to 17 μm and the coating area ratio was 71–88%. Assuming that no interference exists between the coated and uncoated parts and that the copper block is isothermal, the heat flux for transition boiling on the copper surface is calculated from the measured heat fluxes of the fully and partially coated surfaces. These results are consistent with data from the literature obtained by the transient technique and present slightly higher heat flux values than those obtained using the conventional estimation method of graphical interpolation.

Cooling characteristics of an impinging spray jet which forms an ellipsoidal liquid film

The cooling characteristics of an impinging spray jet which forms an ellipsoidal liquid film were experimentally investigated in order to estimate the cooling performance of a rotating roll in a hot mill system

Measurement of liquid helium heat transfer in a high-speed rotational field and consideration of effect of obstacles blocking channels on the heat transfer

Abstract The heat transfer of liquid helium is measured in a high-speed rotating field. The centrifugal acceleration is in the range of 900–4600 g . Vertical test surfaces with channel are used, as well as horizontal surfaces. Moreover, for the vertical surfaces with channels, heat transfer is investigated with a blocked inlet and outlet. We examine blocking at the orifice channel outlet and the cover channel inlet for the heat transfer. Results show that heat transfer on vertical surfaces and the upward facing horizontal surface can be approximately represented by correlation equations for constant property fluids. Channel gap size and coriolis force do not affect heat transfer. The heat transfer of a horizontal surface facing downward is 1 6 – 1 7 of the upward facing surface. The orifices and covers for simulating channel blocking have almost no effect on heat transfer. Thus, obstacles blocking the channels do not affect cooling with helium unless blocking is complete.

Heat Transfer Characteristics of Cable-in-Conduit Type Forced Flow Cooled Superconductor.

Heat transfer characteristics of a cable-in-conduit conductor are measured for the Reynolds numbers of 1000-6000. Heat transfer coefficients were estimated by the transient temperatures at the inlet and outlet of the conduit, and these measured values were used as boundary conditions in a heat transfer simulation. In this way, the heat transition simulations were used to estimate the heat transfer coefficients. The Reynolds numbers of our experiments spanned the laminar and turbulent flow regimes. Our estimated heat transfer coefficients indicate, however, that heat transfer over this flow range is similar to heat transfer in te turbulent flow regime, as expressed by the Dittus-Boelter correlation. Our estimated heat transfer coefficients were about 25% higher than those determined using the Dittus-Boelter correlation.

Natural Convection Heat Transfer to Liquid Helium in a High Centrifugal Acceleration Field.

This paper reports the experimental results on the natural convection heat transfer to liquid helium in a rotating field in the range 1600-3700rpm. Test surfaces are vertical plates (10mm width, 5mm height) with rectangular channels in a radial direction and upward and downward horizontal plates (8mm diameter) at radial distances of 0.3m. The results show that the heat transfer for vertical plates is approximately the same as that for horizontal ones facing upward, independent of the channel gap sizes ranging from 0.4-5mm and directions of the Coriolis force. The heat transfer can be predicted from the conventional correlation: Nu=0.13Ra1/3 in the Ra ranges of 1011-1013, if the film temperature for evaluating properties is substituted for the pseudocritical temperature only when it is above the pseudocritical temperature. The heat transfer for the horizontal plate facing downward is 1/6-1/7 of that for the one facing upward and the Ra exponent of its correlation is 0.2 in the Ra ranges of 1012-1014, which is the same as that for laminar free convection.

Natural Convection Heat Transfer of Supercritical Helium in a Channel.

Natural convection heat transfer of supercritical helium in laminar flow are measured on a vertical surface with and without the channel, which has the sizes of 10mm width, 0.4mm gap and 130mm length. The experimental pressures are from 0.25 to 0.8MPa and fluid temperatures are about 4.2K. The results show that the channel effects on heat transfer coefficients are in the range of about ±20%. The conventional non-dimensional equation for laminar flows with constant properties is successfully applied to correlate, the results by using film temperature in the case when it is below the pseudocritical temperature, and pseudocritical temperature in the opposite case, as the reference temperature in evaluating the properties of helium. Another convection source in the channel increases the heat transfer further when the temperature difference between wall and fluid is less than 10K, but not above it.

Effect of counterflow on heat transfer to He II in a channel

Abstract The effect of internal counterflow on heat transfer to superfluid helium (He II) is measured in the rectangular channel (1 × 10 × 120 mm) with an open upper end and a closed lower end. A heater at the lower end induces upward normal fluid component flow and downward superfluid component flow. The test section is located at a distance of 50 mm from the open end of the channel. The results show that normal fluid component flow does not influence heat transfer. Heat transfer coefficients in the mode of single phase flow are equal to the Kapitza conductance.