The drying process of a macrolayer on a 15 mm diameter boiling surface was observed with high speed video in the region of nucleate and of transition boiling close to the critical heat flux (CHF). It was found that the macrolayer rests beneath a large vapor mass. It partially dries in nucleate boiling and completely dries in transition boiling at the detachment of the vapor mass. The macrolayer thickness at CHF and in transition boiling was determined on the basis of the energy balance relation proposed by Katto and Yokoya. The macrolayer thickness at low heat flux was obtained by decreasing CHF with downward-facing heating surfaces and agreed well with the correlation proposed previously by the present authors. The macrolayer thickness in transition boiling with a vertical surface also agrees fairly well with the correlation, when the heat flux at macrolayer formation, given on the nucleate boiling curve, is extrapolated to surface superheat of transition boiling and when the surface temperature at macrolayer formation is equal to a time-averaged value. © 1998 Scripta Technical, Heat Trans Jpn Res, 27(2): 155–168, 1998
To visualize heat transfer distributions in systems with complex internal geometries, an experimental technique using a combination of the transient method and the hysteresis effect of thermopaint was developed. A mercury compound based thermopaint was used as a temperature indicator. Features of the paint are its reusability and its hysteresis nature. Isothermal lines visualized by the thermopaint are preserved after the experiment by utilizing the hysteresis nature. Also heat transfer on those parts that are hidden behind other parts can be visualized. Effects of initial and air temperature on the measurement uncertainty were evaluated. With this method, local heat transfer coefficients were obtained on the model scroll of a single can type combustor. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(3): 229–242, 1998
Experiments were carried out to determine the effect of flow separation on freezing heat transfer characteristics along a horizontal cooled flat plate immersed within a rectangular duct. The flow separation was induced by a vertically situated thin plate placed against the flow at the leading edge of a uniformly cooled plate. The degree of flow separation was altered by employing vertical plates of various heights. The Reynolds number and the cooling temperature ratio ranged from 5.6 x 102 to 8.4 x 104 and from 3.0 to 10.0, respectively. The measurements showed that the flow separation exerts a marked influence on the local ice formation characteristics. Two kinds of ice formation of convex and concave profiles were observed to occur as a function of the Reynolds number, as well as of the cooling temperature ratio. © 1998 Scripta Technica. Heat Trans Jpn Res, 27(1): 43–56, 1998
In order to clarify the daily effects of increasing carbon dioxide level on the regional thermal environment, a two-dimensional numerical analysis was carried out on unsteady heat and mass-transfer. The results indicate a large surface temperature change in the nighttime and in the summer. The nighttime change is proportional to the change in infrared radiation flux from the atmosphere. An interaction between the effects of water vapor and those of carbon dioxide is found only in the daytime. When carbon dioxide is released from an urban surface, the vertical distributions of the air temperature and the pollutant concentration are affected in urban areas. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(4): 299–311, 1998
In the present report, first, heat transfer coefficients of oscillatory flow at inner surfaces of the heating and cooling regions of oscillation controlled heat transport tubes (OCHTs) are investigated numerically. The numerical simulation is conducted under the following three conditions for the tube walls at the heating and cooling regions : isothermal, extremely thin and actual wall systems. Based on the numerical results and Hausen's correlating equation for laminar flow heat transfer in tubes, a correlating equation of the heat transfer coefficient is developed which can be generally applied to these three conditions. Next, using this correlating equation and the author's simplified model of overall thermal resistance in OCHTs, heat transport rates are predicted, and it is found that the predicted results are in good agreement with the numerical results. Finally, numerical simulation is conducted also to compare the heat transport rates of OCHTs with those of the conventional forced circulation type under the same pumping power. The results indicate that there exist oscillatory flow regions in which the heat transport rate of the phase shifted OCHTs is larger than that of the conventional circulation type.
A heat transfer and flow visualization experiment was conducted with a one-fifth scale model simulating a dry shielded canister (DSC) with 24 PWR spent fuel assemblies in order to elucidate the heat transfer characteristics and the velocity distribution for natural convection inside a DSC filled with air or water at atmospheric pressure. It was found that the average heat transfer coefficients were proportional to the one-fourth power of the Rayleigh number despite the complicated geometry inside the DSC. Flow patterns inside the DSC were visualized clearly through a digital image processing system. The velocity distributions inside the DSC were obtained quantitatively from the Particle Tracking Velocimetry. In comparison with the results of a two-dimentional thermal hydraulic analysis, computed flow patterns were similar to the experimental results and the computational temperature distributions on the sleeve surfaces agreed well. with the experiments within 8%, except at the top point of the center gap. It was also found that the difference in the heat transfer coefficient was within 25% for air as the working fluid, while a satisfactory agreement was not obtained when water was the working fluid.
A simulation model for predicting air quality along urban main roads is being studied. The objective of the model is to predict the effects on air quality of various road-related parameters such as configurations of roads and surrounding buildings as well as traffic flow, chemical reactions, and other related phenomena. In this paper, the development of an atmospheric diffusion model, which will be the platform of the whole simulation model, is reported. A new concentration diffusion coefficient model is proposed, in which the effect of vehicle wind is taken into account. By comparing with field experiments in which the diffusing tracer gas concentration was measured in a real street canyon, the validity of the simulation model is verified. Also, the new diffusion coefficient model is found to be capable of improving predictive accuracy of air quality around a street canyon. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(7): 483–496, 1998
The drag reduction and heat transfer characteristics of water solutions with two kinds of surfactants (cetyltrimethylammonium bromide and dodecyltrimethylammonium chloride) in a straight pipe were investigated experimentally. The flow resistance and heat transfer of water solution flow with the two kinds of surfactants were markedly reduced as compared with those of pure water flow. Useful nondimensional correlative equations for flow resistance and heat transfer were derived in terms of various nondimensional parameters. © 1998 Scripta Technica. Heat Trans Jpn Res, 27(1): 1–15, 1998
In order to elucidate boiling heat transfer characteristics for each tube and the critical heat flux (CHF) for tube bundles, an experimental investigation of pool and flow boiling of Freon-113 at 0.1 MPa was performed using two typical tube arrangements. A total of fifty heating tubes of 14 mm diameter, equipped with thermocouples and cartridge heaters, were arrayed at pitches of 18.2 and 21.0 mm to simulate both square in-line and equilateral staggered bundles. For the flow boiling tests the same bundles as were used in pool boiling were installed in a vertical rectangular channel, to which the fluid was supplied with an approach velocity varying from 0.022 to 0.22 m/s. It was found in this study that the boiling heat transfer coefficient of each tube in a bundle was higher than that for an isolated single tube in pool boiling. This enhancement increases for tubes at higher locations, but decreases as heat flux is increased. At heat fluxes exceeding certain values, the heat transfer coefficient becomes the same as that for an isolated tube. As the heat flux approaches the CHF, flow pulsations occurred in the pool boiling experiments although the heat transfer coefficient was invariant even under this situation. The approach velocity has an appreciable effect on heat transfer up to a certain level of heat flux. In this range of heat flux, the heat transfer coefficient exceeds the values observed for pool boiling. An additive method with two contributions, i.e., single phase convection and boiling, was used to predict the heat transfer coefficient for bundles. The predicted results showed reasonable agreement with the measured results. The critical heat flux in tube bundles tended to increase as more bubbles were rising through the tube clearance. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(4): 312–325, 1998
Heat transfer characteristics and flow patterns were measured over a plate for various separation distances between the nozzle exit and target plate when air issues from a sharp-edged cross-shaped nozzle and impinges on a plate. The local heat transfer coefficients in the radial direction for different circumferential positions were calculated using the wall temperatures measured by means of thermocouples, and flow patterns were observed using an oil-titanium IV oxide method. The isotherms of the infrared images were also measured using an infrared radiometer with a two-dimensional array of indium-antimony (InSb) sensors. The geometric axes were switched as a result of the self-induced velocity of a vortex filament; the convex corners became flat and the concave corners generated outward ejection. The distributions of the iso-heat transfer coefficient contours correspond well to the flow pattern and the isotherm contours. These contours extended diagonally and demonstrated the St. Andrew's cross pattern for short separations, subsequently changing to an octagonal pattern, and then becoming circular at large separations. The correspondence of the heat transfer characteristics to the flow behavior, as well as the heat transfer mechanism are also described. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(3): 192–204, 1998
In the process of crystal growth from solution under normal gravity, double diffusive convection occurs due to thermal and solute gradients. This natural convection disturbs the pure thermal and solutal diffusion field around a crystal, and phase change phenomena during the diffusion process cannot be seen directly. Microgravity environments, generated by parabolic flight, were used during experiments in order to suppress the double diffusive convection. In-situ measurements of the diffusion fields were carried out using a real-time phase-shift interferometer. The saturated solution around a seed crystal of NaClO3 was subjected to rapid cooling during the duration of microgravity by Peltier elements in the test cell. A number of temperature profiles were applied during the microgravity experiments. In particular, the diffusion phenomena measured for a system subjected to rapid cooling to −17 °C cannot be explained in terms of a conventional diffusion process nor by the kinetics of crystal growth. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(2): 114–129, 1998
This paper deals with a continuous ice making method which could be used to provide an ice storage system using off-peak electricity during nighttime. The critical condition for an ice blockage to occur in the cooling tube has been examined in terms of the concentration of water-propylene glycol solution and thermo-hydraulic operating parameters. The results obtained show that nondimensional correlation equations for the critical condition have been derived as a function of thermo-hydraulic parameters in the laminar and the turbulent flow regions. The equations can be used to predict whether an ice making system is operating in a continuous ice making condition or is in the ice blocking phase. © 1998 Scripta Technica. Heat Trans Jpn Res, 27(1): 74–83, 1998
The characteristics of critical heat flux (CHF) in existing experiments under high subcooling and high velocity in short heated channels were, for the first time, systematically and quantitatively investigated to provide a CHF correlation which could properly predict the effect of channel length, especially when the channel length-to-channel diameter ratio L/D is less than about 20. Major test conditions of existing CHF experiments investigated in this study were 1 to 4 mm of channel diameter, 1 to 25 of L/D, 0.1 to 1.2 MPa of pressure, 34 to 117°C of inlet water subcooling and 500 to 40 700 kg/(m2·s) of mass flux in circular channels, and 3 to 20 mm of gap size, 6 to 40 of L/De, 0.1 to 3.1 MPa of pressure, 4 to 166°C of inlet water subcooling and 940 to 27000 kg/(m2·s) of mass flux in rectangular channels. The effect of L/D on CHF was evaluated referring to the analytical solution of CHF, which was previously derived by the author for the channel flow at high subcooling and high velocity. As a result, the effect of L/D was quantitatively clarified as an effect of magnitude in heat trnasfer of the single-phase forced-convection flow, giving a larger CHF with a smaller L/D in the case of L/D less than about 20. The proposed correlation could predict CHF within a ±35 percent error margin.
Void fractions of liquid fluidized beds were measured using water as the fluidizing liquid. Particles of glass, ceramics and chromium were tested, and their diameter range was from 1.87mm to 8.34mm. Fluidization columns having a diameter of 51, 34, 21 and 8mm were used. A void fraction measurement was performed for each particle column combination. Based on the experimental data, a new correlation was derived which enabled over 95% of the data to be predicted within ±7%. Existing correlations were also reviewed and compared with the results.
Microcapsulated liquid-crystal particles are widely used as temperature sensors in the field of heat transfer engineering. Conventionally, these particles are painted on a surface of a heated plate for temperature measurements. The temperature is measured by tracing the color changes of the microcapsulated liquid-crystal particle through the color digital image processing technique. Recently, these particles are often suspended in thermal fluid flows as temperature tracers of the flows. For the use of a microcapsulated liquid-crystal particle itself as a temperature sensor in the suspending method, the heat capacity of the capsule covering the liquid crystal should be regarded as an important factor in predicting the time response of the microcapsulated liquid-crystal particle which is directly injected into a thermal fluid flow. The heat capacity of the liquid crystal and the capsule can produce a delayed time response for the temperature change of the outside fluids and eventually produce erroneous measurement data. Without a new temperature sensor smaller than the particle, it is very difficult to measure the time response of the microcapsulated liquid-crystal particle since the particles move with the working thermal fluid in different flow conditions. Therefore, a numerical simulation for the time response of the particle is made and its usable limit is discussed in detail for the measurement of turbulent thermal flows. Responses for a temperature step change, fluctuating temperature changes, and the thermal inertia of the working fluid temperature are considered. The response time of the microcapsulated liquid-crystal particle has been evaluated to be as much as 150 ms time delay for a step change of the working fluid temperature, which means the physical properties of the particle itself must be considered for outside temperature changes. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(5): 390–398, 1998
To control the flow around a flat plate, a small rod was set upstream of the plate. The chord length of the plate, D, was 50 mm. The diameter of the rod, d, and the distance between the axes of the rod and plate, L, were varied. The Reynolds number ranged from 1.3 × 104 to 7.7 × 104. For the cases without vortex shedding from the rod, the shear layer from the rod reattaches to the front face of the plate. Consequently, quasi-stationary vortices are formed between the rod and the plate. In this case, at d/D = 0.4 and L/D = 1.4 to 2.0, the maximum reduction of total drag coefficient is 20 to 30%. The average heat transfer on each face increases and the overall heat transfer increases by about 40 to 50% compared with values obtained without the rod in place. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(2): 99–113, 1998
Thermophoresis of small particles, like mist, fumes, dust, and so on, floating in a gas, particularly in the vicinity of a solid surface, is of practical interest in aerosol technology and related fields of treating gas molecule-surface interactions. This paper deals with thermal creep flow of a gas around a spherical particle suspended near a plane plate; temperature and flow fields are analyzed by counting the discontinuous rarefaction effects of the gas. In a consequence, the thermal force, as well as the drift velocity of the particle at an arbitrary distance from the plate, but limited to lower Knudsen numbers, are clarified, with thermal and flow fields in the gas being presented for some selected schemes. The thermal force is enlarged by the temperature jump decreased by the momentum slip. It increases as the particle approaches the plate; this increase is very sharp when the particle is closer to the plate. The drift velocity, on the other hand, remains nearly the same as that far away from the plate, but shows a slight decrease in the very vicinity of the plate. © 1998 Scripta Technica. Heat Trans Jpn Res, 27(1): 57–73, 1998
This paper presents the results of an experimental investigation relating to heat transfer during evaporation of thin liquid films falling over horizontal tubes. Experiments were conducted using 25 mm o.d. copper tubes heated by internal electrical cartridge heaters so that a uniform heat flux was generated on the outside tube surface. Five heated tubes were arrayed on a vertical plane with a pitch of 50 mm. Freon R-11 preheated to the saturation temperature at 0.2 MPa was supplied to the topmost heated tube through feeding tubes. Heat transfer characteristics on each heated tube were clarified in a range of film Reynolds number from 10 to 2000 and the measured data are presented in the form of correlations. Deterioration of heat transfer due to film break down was also considered. © 1999 Scripta Technica, Inc. Heat Trans Jpn Res, 27(8): 609–618, 1998
Heat Transfer - Japanese ResearchVolume 27, Issue 2 p. 142-154 Evaluating the performance of forced convection heat transfer enhancement Koichi Ichimiya, Corresponding Author Koichi Ichimiya Department of Mechanical Engineering System, Yamanashi University, Yamanashi, JapanDepartment of Mechanical Engineering System, Yamanashi University, Yamanashi, JapanSearch for more papers by this authorShunichi Morimoto, Shunichi Morimoto Clarion Ltd., Saitama, JapanSearch for more papers by this authorToshiyoshi Miyazawa, Toshiyoshi Miyazawa Department of Mechanical Engineering System, Yamanashi University, Yamanashi, JapanSearch for more papers by this author Koichi Ichimiya, Corresponding Author Koichi Ichimiya Department of Mechanical Engineering System, Yamanashi University, Yamanashi, JapanDepartment of Mechanical Engineering System, Yamanashi University, Yamanashi, JapanSearch for more papers by this authorShunichi Morimoto, Shunichi Morimoto Clarion Ltd., Saitama, JapanSearch for more papers by this authorToshiyoshi Miyazawa, Toshiyoshi Miyazawa Department of Mechanical Engineering System, Yamanashi University, Yamanashi, JapanSearch for more papers by this author First published: 07 December 1998 https://doi.org/10.1002/(SICI)1520-6556(1998)27:2<142::AID-HTJ4>3.0.CO;2-VCitations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Abstract Two methods for assessing thermal performance were evaluated for four kinds of forced convective heat transfer augmentations. On method uses the first law of thermodynamics, i.e., the heat transfer improvement at (1) constant Reynolds number, (2) constant pressure loss, and (3) constant pumping power. The other method uses the second law of thermodynamics, i.e., the entropy generation. The first method restricts the effective region and the second method supplies the condition for achieving the minimum entropy generation rate. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(2): 142–154, 1998 Citing Literature Volume27, Issue21998Pages 142-154 RelatedInformation
Thin-layer electrodepositions at a single trench on a substrate are investigated using a Monte Carlo simulation. The Monte Carlo simulation method is obtained by extending the simulation method of the diffusion-limited aggregation (DLA) fractal. The method is applied to the coverage problem of a small trench on a substrate. Transport phenomena (diffusion and migration) and the surface reaction are taken into account as is Brownian motion with drift and sticking probability. It is shown that the transport of metal ions and the surface reaction have an important effect on the morphology of electrodeposits. It is found that a well-covered electrodeposit is formed when the sticking probability is low. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(5): 365–375, 1998
