There has been strong demand for enhancement techniques of single-phase forced convection heat transfer because of its wide area of application on the one side and because of inferior heat-transfer capability, when compared with phase change heat transfer such as boiling and condensation, on the other side. The enhancement techniques are indispensable when gases are used as heat-transfer media. In this article the basic principles of enhancement of single-phase forced convection heat transfer are described in the first place. Three principal techniques currently employed, i.e.,(a) interrupted fins, (b) twisted tapes, and (c) turbulence promoters, are introduced. Mechanisms of heat-tansfer enhancement and the state-of-the art review on the R&D are presented for these techniques. In addition to these, supplementary remarks are given on techniques utilizing multiphase flow and electrostatic field.

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The absorption machines of the lithium bromide-water type have recently been established as heat source equipments for residential and industrial use, which include refrigerating machines, heat pumps, and heat transformers. Several advanced cycle machines have also been proposed and tested. All of the absorption machines consist fundamentally of four kinds of heat exchangers, i.e. evaporator, absorber, generator, and condenser. The horizontal or vertical falling film system is usually applied to these heat exchangers, since the pressure drop which causes an undesirable change in the fluid temperature is relatively small in either system. The horizontal system is popular for the present, while the vertical system is going to be developed promisingly. This may save an installation space and also fit a plan for the Lorentz cycle. The purpose of this paper is to survey the available information for increasing heat and mass transfer rates in the heat exchangers of absorption machines. Emphasis is placed on the hydrodynamic characteristics of falling liquid films in absorbers and generators. The following topics are covered in this paper: 1. Characteristics of thin liquid films over horizontal tubes 2. Characteristics of wavy thin liquid films flowing down the vertical or inclined wall surface 3. Effect of the artificial surface roughness on the heat and mass transfer rates 4. Enhancement in the heat and mass transfer rates by the Marangoni convection 5. Conditions of film breakdown and the minimum wetting rates.

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An equationon the formation rate of R11 hydrate in water and aqueous alcohol solutions is derived on basis of a dispersed liquid interface reaction model. From the equation, the relation between percent conversion(β) of R11 and elapse time (θ) is obtained by; −(1⁄m)ln(1-β)=kAΔTⁿθ where, m is conversion coefficient (R11 in hydrate⁄hydrate = 0.3095), k is over-all coefficient of mass trnsfer [kg⁄m²h°C], A is surface area of dispersed liquid (R11) [m²⁄kg], and ΔT is supercooling degree [°C]. Using above equation, the experimental date of the previous paper are analyzed, and it is found that these date are well applied to the equation. From these results, it can be considered that the formation rate of R11 hydrate in water and the aqueous solutions of ethanol (3.6% and 10%), n-propanol(0.9%) and n-butanol(1.9%) is principally governed by the dispersed liquid interface reaction, not by the crystal growth of R11 hydrate.

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Superheated steam drying and highly humid air drying have been applied in many industrial drying fields, such as drying of by-products of food industry. The most significant reason for this wide range of applications of superheated steam is that more water evaporates in this steam or highly humid air than in dry air above the inversion point temperature. As compared with these wide practical applications, fundamental research for determining controlled operating conditions or optimum design conditions for a superheated steam drying system have not been sufficiently performed. From this viewpoint, in experimenting for drying water in the closed circuit dryer, by changing drying variables, such as the mass velocity of heat transfer of the steam,the existance of the inversion point temperature was confirmed and the locus of the temperature were found. The behavior of the locus enables one to specify the drying variables for a controlled drying system. The difference of the evaporation phenomenon between superheated steam drying and conventional air drying was examined from the heat convection standpoint. The reliability of the data obtained from the experiment was too checked by comparing the data with another reported data.

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This paper describcs electronic control technologies for a variable capacity heat pump air conditioner. ln this paper, we discuss how the following control items should be realizd. The first is the improvement in heating seasonal performance factor. The question as to whatneeds to be done about the control of the electronic expansion valve so as to keep the superheated amount of the refrigerant at the compressor inlet at the optimum level not only during continuous operation but also during start-up, remains to be answerd. The second is the reduction of start-up time. The frequency is rapidly accelerated in order to reduce the start-up time. The way in which the frequency is to be accelerated must be below the upper current limit allowed by the inverter by establishing a correlation with the time constant of the refrigeration cycle response.

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Experiments on evaporation for lithium bromide aqueous solution (0–55 wt% LiBr) were made in Summary a externally heated wetted–wall column under reduced pressures. The evaporation rates of 5 and 8 wt% LiBr–water solutions were similar to those of water. The evaporation rates, however, owered with further increase of the concentration of LiBr, and at low feed rates the evaporation rates lowered with decrease of the feed rate because the temperature of the falling film rose. On the other hand, at high feed rates the evaporation rates lowered with increase of feed rates because the heat transfer coefficients of the falling film decreased. Therefore, a maximum evaporation rate existed and it was supposed that there is the optimum feed rate. The experimental data agreed with the values that were calculated numerically based on the unidirectional model that lithium bromide didn't move through falling film.

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A two-phase loop thermosyphon transports thermal energy by natural convective circulation without any external power supply. Therefore, it has been paid attention as a heat transfer equipment for saving energy. A basic investigation of flow and heat transfer characteristics in the thermosyphon was performed both experimentally and theoretically. The circulation flow rate, pressure and temperature distributions along the loop, and heat transfer coefficients in the heated section were measured using water, ethanol and Freon 113 as the working liquids. And, the effects of the heat input and liquid physical properties on the flow and heat transfer characteristics were examined. In the theoretical study, the circulation flow rate was calculated from the force balance between the driving force arising from density differences and the pressure drop in the loop. The comparison of the calculated with experimental results was made concerning the circulation flow rate and pressure and temperature distributions. For water and ethanol, the comparison presented the considerably close agreement. But, for Freon 113, the agreement was insufficient and further detailed investigation is needed.

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Heat transfer from tubes has been numerically simulated in a fan coil unit for an airconditioning equipment. The array of tubes has parallel louver continuous fins, perpendicular to staggered round tubes. Quite a few of slits divide plates into many strips, which are offsetted, so that the heat transfer will be augmented from the plate to the air flow. On the other hand, the conduction of heat in the platemight be prevented with these slits. The conduction retardation due to slit is estimated, and the simulation shows that the retardation is not serious for present fins.

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An exprimental study on heat transfer of upward impinging circular water jet system shows the influence of the height of supplementary water with a view to improving heat transfer at the stagnation point. Optimum heights of supplementary water which brings about the augmentation of heat transfer are S⁄D=2 for H⁄D=10, and S⁄D=1 for H⁄D=20—50. For the single phase forced convection heat transfer, generalized correlations that include the effects of nozzle—to—heated surface distance and the height of supplementary water were found by using modified Nusselt number, Reynolds number at each nozzle diameter. Nu⁄Pr^0.4=C•Re^m•ε, ε=1.0+α(S⁄D)^β And for H=24cm, dimensionless correlation was found to be NUH/⁄Pr^0.4=C•Re_H^1.27 (D⁄H)ⁿ for 0≤S⁄D≤3, V_o=3.5−8.29m⁄s and D=4−8mm^φ.

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In vapor compression refrigeration system using oil-lubricated compressors, some amount of oil is always circulated through the system. Oil circulation can have a significant influence on the evaporator performance of automotive air conditioner which is especially required to cool quickly the car interior after a period standing in the sun. An experimental investigation was carried out an electrically heated horizontal tube to measure local heat transfer coefficients for various flow rates and heat fluxes during forced convection boiling of pure refrigerant R12 and refrigerant-oil mixtures (0-11% oil concentration by weight) and the results were compared with oil free performance. Local heat transfer coefficients increased at the region of low vapor quality by the addition of oil. On the other hand, because the oil-rich liquid film was formed on the heat transfer surface, heat transfer coefficients gradually decreased as the vapor quality became higher. Average heat transfer coefficient reached a maximum at about 4% oil concentration and this trend agreed well with the results of Green and Furse. Previous correlations, using the properties of the refrigerant-oil mixture, could not predict satisfactorily the local heat transfer coefficients data. New correlation modified by oil concentration factor was developed for predicting the corresponding heat transfer coefficient for refrigerant-oil mixture convection boiling. The maximum percent deviation between predicted and measured heat transfer coefficient was within ±30%.

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Measurements of the vapor-liquid coexistence curve in the critical region for the refrigerant mixture of R152a (CH₃CHF₂: 1, l-difluoroethane) +R 114 (CCIF₂CCIF₂ :1, 2-dichloro-1, 1, 2, 2-tetrafluoroethane) system were made by visual observation of the disappearance of the meniscus at the vapor-liquid interface within an optical cell. Forty-eight saturated densities along the vapor-liquid coexistence curve between 204 and 861 kg·m^-3 for five different compositions of 10, 20, 50, 80 and 90 wt% R 152a were obtained in the temperature range 370 to 409 K. The experimental errors of temperature, density, and mass fraction were estimated within ±10mK, ±0.5% and +0.05 %, respectively. On the basis of these measurements, the critical parameters of five different compositions for the R 152a +R 114 system were determined in consideration of the meniscus disappearance level as well as intensity of the critical opalescence. In accordance with the previous results of three other refrigerant mixtures, i.e., R 12 +R 22 system, R 22 +R 114 system and R 13B1 + R 114 system, the coexistence curve and critical curve on the temperature-density diagram for binary refrigerant mixtures were discussed. In addition, correlations of its composition dependence for this system were proposed.

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This paper reports measurements of the PVTx properties of the R152a + R114 system for 10, 20, 50, 80, 90 and 100 wt% R152a mixtures. The PVTx measurements of this work were made by the constant volume method coupled with isothermal expansion procedures for a certain fixed composition of a mixture. The measurements were conducted in the range of temperatures from 303 to 443K, pressures from 0.4 to 9.7 MPa and of densities from 160 to 1330 kg/m³ along 46 different isochores. The experimental uncertainty in the determination of the composition was estimated to be less than 0.1 % for eachcomposition. And the experimental uncertainties in the temperature, density and pressure measurements were estimated ±8mK, ±0.16% and ±3kPa, respectively. Comparing our vapor pressure data for pure R152a with other reported data and correlation, it was found that the present measurements were consistentand reliable. Analyzing the present experimental results graphically and referring to the measured data of coexistence curves, the dew and bubble points for measured isochores were determined and the composition dependence of the critical points were examined. We have also discussed the general behavior of the critical curve for the present binary refrigerant mixtures with those of other mixtures reported previously by the present authors.

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The objectives of this report are to propose a new method of the high performance cold energy storage using ice as a phase change material and to clarify the heat transfer characteristics of the apparatus of ice cold energy storage based on the proposed principle. A working medium vapor layer a water layer and a working medium liquid layer stratified in this order from the top were kept in an enclosure composed of a condenser, an evaporator and a condensate receiver-and-return tube. The direct contact heat transfers between water or ice and a working medium in an enclosure were applied for realizing the high performance cold energy storage and release. In the storage and release processes, water changes the phase between the liquid and the solid, and the working medium cnanges between the vapor and the liquid with a natural circulation. Experimental apparatus was manufactured and R12 and R114 were selected as working media in the thermal energy storage enclosure. It was confirmed by the measurements that the efficient formation and melting of ice were achieved. Then, th e heat transfer characteristics were clarified for the effects of the initial water height, the initial height of woking medium liquid layer and the inlet coolant temperature.

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Numerical analyses were performed on the heat transfer characteristics of a latent heat TES apparatus, in which a row of horizontal plate fins were attached to the heat transfer surface to increase the heat flux through the heat storage process. The transient melting process of the phase change material was treated, including the melting phenomena by heat conduction or natural convection heat transferin the liquid phase, and the direct contact melting phenomena between the solid phase and fin surfaces. In the calculations, nondimensional parameters, composed of the various dimensions of the TES space, the physical properties of the materials and the heat transfer surface temperature, were changed systematically to clarify the effects of the parameters on the average heat flux.

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