Heat exchange during the movement of a vapor-liquid stream of dissociating nitrogen tetroxide

The results of studies of heat exchange during the flow of a vapor-liquid stream of a dissociating N₂O₄, system in vertical pipes are analyzed and functions are given for calculating the heat-exchange intensity under different flow conditions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 29, No. 2, pp. 251–260, August, 1975.     

Transverse heat transfer coefficient in the dual channel ITER TF CICCs. Part III: Direct method of assessment

The data resulting from the thermal-hydraulic test of the ITER TF CICC are used to determine the flow partition and the overall effective heat transfer coefficient (h_BC) between bundle and central channel in a direct way, i.e. by analysis of the heat transfer between both flow channels, based on the mass and energy balance equations and the readings of thermometers located inside the cable. In cases without a local heat source in the considered cable segment the obtained h_BC values were consistent with those obtained in earlier studies by analysis of experimental data using indirect methods. It was also observed that the transverse heat transfer was strongly enhanced in a cable segment heated from outside. This phenomenon results from the mass transfer from the bundle region to the central channel. The experimental h_BC data obtained for the case without a heat source in the considered segment were also compared with those calculated using various heat transfer correlations.     

Computational Analysis of the Effect of Nano Particle Material Motion on Mixed Convection Flow in the Presence of Heat Generation and Absorption

The present study is concerned with the physical behavior of the combined effect of nano particle material motion and heat generation/absorption due to the effect of different parameters involved in prescribed flow model. The formulation of the flow model is based on basic universal equations of conservation of momentum, energy and mass. The prescribed flow model is converted to non-dimensional form by using suitable scaling. The obtained transformed equations are solved numerically by using finite difference scheme. For the analysis of above said behavior the computed numerical data for fluid velocity, temperature profile, and mass concentration for several constraints that is mixed convection parameter λ_t, modified mixed convection parameter λ_c, Prandtl number Pr, heat generation/absorption parameter δ, Schmidt number Sc, thermophoresis parameter N_t, and thermophoretic coefficient k are sketched in graphical form. Numerical results for skin friction, heat transfer rate and the mass transfer rate are tabulated for various emerging physical parameters. It is reported that in enhancement in heat, generation boosts up the fluid temperature at some positions of the surface of the sphere. As heat absorption parameter is decreased temperature field increases at position X = π/4 on the other hand, no alteration at other considered circumferential positions is noticed.     

Nonlinear thermal instability in a horizontal porous layer with an internal heat source and mass flow

Linear and nonlinear stability analyses of Hadley–Prats flow in a horizontal fluid-saturated porous medium with a heat source are performed. The results indicate that, in the linear case, an increase in the horizontal thermal Rayleigh number is stabilizing for both positive and negative values of mass flow. In the nonlinear case, a destabilizing effect is identified at higher mass flow rates. An increase in the heat source has a destabilizing effect. Qualitative changes appear in R_z as the mass flow moves from negative to positive for different internal heat sources.     

CO2 flow condensation heat transfer and pressure drop in multi-port microchannels at low temperatures

CO₂ flow condensation heat transfer coefficients and pressure drop are investigated for 0.89 mm microchannels at horizontal flow conditions. They were measured at saturation temperatures of −15 and −25 °C, mass fluxes from 200 to 800 kg m⁻² s⁻¹, and wall subcooling temperatures from 2 to 4 °C. Flow patterns for experimental conditions were predicted by two flow pattern maps, and it could be predicted that annular flow patterns could exist in most of flow conditions except low mass flux and low vapor quality conditions. Measured heat transfer coefficients increased with the increase of mass fluxes and vapor qualities, whereas they were almost independent of wall subcooling temperature changes. Several correlations could predict heat transfer coefficients within acceptable error range, and from this comparison, it could be inferred that the flow condensation mechanism in 0.89 mm channels should be similar to that in large tubes. CO₂ two-phase pressure drop, measured in adiabatic conditions, increased with the increase of mass flux and vapor quality, and it decreased with the increase of saturation temperature. By comparing measured pressure drop with calculated values, it was shown that several correlations could predict the measured values relatively well.     

Review of flow condensation of CO2 as a refrigerant

Carbon dioxide (CO₂) has emerged as an excellent substitute natural refrigerant for low temperature refrigeration applications, but a better understanding of its in-tube flow condensation is needed in order to achieve its full potential. From experimental studies in the open literature we review the effects of mass flux, vapour quality and saturation pressure on CO₂ flow condensation heat transfer, frictional pressure drop and flow regime transition inside smooth, micro-fin and microchannel tubes. Successful condensation models which were developed from experiments with other refrigerants are evaluated against the CO₂ flow condensation experimental data. Comparison between the predicted and experimental data shows that the unique thermophysical properties of CO₂ at high reduced pressure conditions lead to these correlations having high prediction errors on the flow condensation heat transfer inside smooth tubes and microchannels, but have less significant effects on the flow condensation heat transfer and two-phase frictional pressure drop under high mass flux conditions inside micro-fin tubes. Recommendations for condensation and pressure drop models to apply to CO₂ flow condensation in different tubes are made. As there is inconsistency between the experimental data in smooth tubes from different sources, and the effects of microchannel and micro-fin tube geometries, on the flow regime transition and condensation heat transfer of CO₂, are unclear, a more extensive range of the experimental data in different tubes is needed for a fully understanding of in-tube CO₂ flow condensation.     

The simulation of turbulent two-phase flow after an abrupt expansion of the pipe in the presence of evaporation of droplets

The results are given of investigation of flow and heat and mass transfer of a gas-droplet flow after an abrupt expansion of the pipe using the Eulerian approach. It is demonstrated that the intensity of heat transfer significantly increases upon addition of evaporating droplets into separated flow (by a factor of more than two compared to single-phase flow at a low value of mass concentration of droplets M _L1 ≤ 0.05). The addition of dispersed phase to a turbulent gas flow leads to an insignificant increase in the length of recirculation zone. Low-inertia droplets (d ₁ ≤ 50 μm) are well entrained into circulation flow and are present in the entire cross section of the pipe. Large particles (d ₁ ≈ 100 μm) pass through the shear layer and do not enter the separated-flow region. Adequate agreement with experimental data is indicative of the adequacy of the developed model for the calculation of gas-droplet separated flow in the case of an abrupt expansion of the pipe.     

Effects of wetted wall on laminar natural convection in vertical annular ducts

Abstract

A detailed numerical analysis is performed to investigate the effects of latent heat exchange, in connection with evaporation of the liquid film on the wall, on the natural convection heat transfer in vertical concentric annuli. Major governing parameters identified are Gr_T, Gr_M, Pr, Sc, and N. Results are specifically presented for an air‐water system under various heating conditions to illustrate the latent heat transport during the evaporation process. The effects of the channel length, ratio of radii N and wetted wall temperature on the momentum, heat and mass transfer are examined in detail. Tremendous enhancement in heat transfer due to the exchange of latent heat was clearly demonstrated.     

Radiative-convective heat transfer for high-temperature two-phase flow around bodies

Some methods for determining the basic parameters of high-temperature two-phase flows and the results of investigation of radiative—convective heat transfer with a flowing body in a flow are presented.Notation x=x/d, x distance from the plasmatron nozzle exit section - d diameter of the plasmatron nozzle - q=q_p/q₀, q_p heat flux in the vicinity of the critical point of the surface in a flow given the gas flow - q₀ neat flux in the absence of particles in the flow - _p mass concentration of particles in the flow - G_p mass flow rate of the condensed phase - G_g mass flow rate of the gas phase Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 3, pp. 300–303, March 1993.     

Convective Heat Transfer at an Annular Jet Impingement on a Flat Blockage

The experimental results on heat transfer of an annular impinging jet have been. The Reynolds numbers Re = (1.2–3.6) × 10⁴, the distance S from the nozzle to a blockage, S/d₀ = 2, 4, 6, and the circular slit height d₂/d₀ = 0.51 and 0.71, where d₀ and d₂ are the internal and external nozzle diameters, have been varied. It is shown that at the same air mass flow rate, replacement of a round nozzle with an annular one results in heat-transfer intensification (up to 70% at the stagnation point). The maximum heat transfer gain occurs at a small nozzle–wall distance (S/d₀ = 2). The heat-transfer increase is accompanied by an increase in the thermal pulsation intensity. The degree of intensification of the heat exchange depends on the height of the circular slit and the nozzle–wall distance.     

Experimental investigation of forced flow boiling of nitrogen in a horizontal corrugated stainless steel tube

Experimental investigation is performed on the heat transfer characteristics of forced flow boiling of saturated liquid nitrogen (LN₂) in a horizontal corrugated stainless steel tube with a 17.6 mm maximum inner diameter. The local heat transfer coefficients (HTCs) are measured at two mass flow rates with a wide range of wall heat fluxes. The effects of the heat flux, mass flow flux and vapor quality on the two-phase heat transfer characteristics are discussed. The results reveal that the local HTCs increase with the heat flux and mass flow flux. The measured local HTCs present a strong dependence on the heat flux. The circumferential averages of the HTCs for the present corrugated tube are compared with the empirical correlations proposed for the smooth tubes, and the results show that the heat transfer is enhanced due to the area augmentation.     

Effects of flow and colony morphology on the thermal boundary layer of corals

The thermal microenvironment of corals and the thermal effects of changing flow and radiation are critical to understanding heat-induced coral bleaching, a stress response resulting from the destruction of the symbiosis between corals and their photosynthetic microalgae. Temperature microsensor measurements at the surface of illuminated stony corals with uneven surface topography (Leptastrea purpurea and Platygyra sinensis) revealed millimetre-scale variations in surface temperature and thermal boundary layer (TBL) that may help understand the patchy nature of coral bleaching within single colonies. The effect of water flow on the thermal microenvironment was investigated in hemispherical and branching corals (Porites lobata and Stylophora pistillata, respectively) in a flow chamber experiment. For both coral types, the thickness of the TBL decreased exponentially from 2.5 mm at quasi-stagnant flow (0.3 cm s⁻¹), to 1 mm at 5 cm s⁻¹, with an exponent approximately 0.5 consistent with predictions from the heat transfer theory for simple geometrical objects and typical of laminar boundary layer processes. Measurements of mass transfer across the diffusive boundary layer using O₂ microelectrodes revealed a greater exponent for mass transfer when compared with heat transfer, indicating that heat and mass transfer at the surface of corals are not exactly analogous processes.     

Investigation on the heat transfer characteristics during flow boiling of liquefied natural gas in a vertical micro-fin tube

This paper presents an experimental investigation on the heat transfer characteristics of liquefied natural gas flow boiling in a vertical micro-fin tube. The effect of heat flux, mass flux and inlet pressure on the flow boiling heat transfer coefficients was analyzed. The Kim, Koyama, and two kinds of Wellsandt correlations with different F_tp coefficients were used to predict the flow boiling heat transfer coefficients. The predicted results showed that the Koyama correlation was the most accurate over the range of experimental conditions.     

Stirring the heat carrier in a heat exchanger by twisting the stream

A theoretical-experimental study was made of the effective diffusion coefficient in longitudinally streamlined helically twisted tubes with an oval profile, using as the basis a homogenized model of flow and applying the method of diffusion from linear heat sources of finite dimensions.Notation D_t effective diffusion coefficient - u stream velocity - d_e equivalent diameter - S pitch of the tube profile - d largest profile dimension - N_Re,b Reynolds number - q_v volume heat emission - density - x and r coordinates - P pressure - N_Pr,t Prandtl number for turbulent flow - hydraulic drag coefficient - c_p specific heat - T temperature - G mass flow rate of heat carrier - m porosity of the bundle of tubes relative to the heat carrier - L length of the bundle of tubes - r_h radius of heated tubes - r_c radius of the bundle of tubes - k dimensionless effective diffusion Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 773–779, May, 1981.     

Ferromagnetism in the RERh4B4 compounds

The magnetic ordering temperatures of the primitive tetragonal rare earth (RE) rhodium boride compounds exhibit a peak at DyRh₄B₄, rather than GdRh₄B₄ as predicted from ordering via the indirect RKKY exchange interaction. This deviation is analyzed in terms of the depression of the superconducting transition temperature of LuRh₄B₄ by dilute amounts of RE impurity ions and the magnetic heat capacities of the RERh₄B₄ compounds for RE = Gd, Tb, Dy, and Ho. The strength of anisotropic crystalline electric field forces, as inferred from magnetic entropy considerations, may be the origin of the anomalous magnetic ordering temperatures. In addition, the depression of the superconducting transition temperatures of ErRh₄B₄ and TmRh₄B₄ from that of LuRh₄B₄ is shown to arise primarily from elastic exchange scattering of the conduction electrons by the magnetic RE ions.This research was supported by the U.S. Department of Energy under Contract EY-76-S-03-0034-PA227-3 (HBM, LDW, MBM) and by the National Science Foundation under Grant NSF/DMR77-08469 (DCJ).     

Thermal dissociation of the complex BF<Subscript>3</Subscript>·D and boron isotope separation in the system BF<Subscript>3</Subscript>-BF<Subscript>3</Subscript>·CH<Subscript>3</Subscript>NO<Subscript>2</Subscript>

Thermal flow reversal and efficiency of interphase isotope exchange in the course of multiplication of the single effect of boron isotope separation in the two-phase system gaseous BF₃-liquid complex of BF₃ with nitromethane in an isotope exchange column at atmospheric pressure and 293 K was studied. The completeness of flow reversal is acceptable for concentrating ¹⁰B. Approximately 19 at. % difference in the concentrations of the isotope ¹⁰B was attained on an experimental installation with a packed mass-exchange column 11 mm in diameter at a packing bed height of 148 cm and spiral-prismatic packing with an element size of 1.25 × 1.25 × 0.2 mm. The degree of separation was K = 3.5, and HETP was in the range from 5.2 ± 0.8 to 8.0 ± 1.0 cm, suggesting high efficiency of the mass exchange.     

Evaporation heat and mass transfer in natural convection pipe flow

Abstract

A numerical analysis has been performed to examine film evaporation on natural convection heat and mass transfer in a vertical pipe. Coupled governing equations for liquid film and induced gas flow were simultaneously solved by the implicit finite difference method. Results for interfacial heat and mass transfer coefficients are specifically presented for ethanol film and water film vaporization. The predicted results indicate that the heat transfer from gas‐liquid interface to the gas flow is predominated by the transport of latent heat in association with film evaporation. The results are also contrasted with those of zero film thickness and show that the assumption of extremely thin film thickness made by Chang et al. [5] and Yan and Lin [19] is only valid for a system with a low liquid Reynolds number Re _l1. But as the liquid Reynolds number is high, the assumption becomes inappropriate.     

Influence of4He impurities on nuclear spin relaxation in solid3He

The NMR properties of solid³He, mainly the ratio of the heat capacities of exchange and Zeeman energies and the exchange-lattice relaxation times are very sensitive to the presence of⁴He impurities, while the transverse relaxation timeT ₂ does not depend on the impurity concentration when the latter remains small. These properties can be explained in two different ways. (1) We assume an enhancement of exchange interactions around⁴He impurities. We derive the consequences of such an assumption and compare them with experimental results. For two molar volumes in the bcc phase, the locally enhanced exchange is equal to approximately7J, withJ being the exchange in pure³He. (2) Guyer and Zane introduce a mass fluctuation wave to explain the excess of heat capacity and the dependence of the longitudinal relaxation time with concentration. Both these models give rise to a four-energy bath system. As in the bcc phase, the exchange-lattice relaxation time in the hcp phase decreases when × increases at low enough⁴He concentrations. ForV=18.48 cm³ we deduce the coefficient for translational diffusion from high-temperature experiments with the help of Torrey's theory for spin-lattice relaxation.This paper is based on a thesis to be submitted in partial fulfillment of the requirements for the degree ofDocteur ès Sciences in Physics at theFaculté des Sciences d'Orsay in 1970. This thesis will be registered at the CNRS under the number AO 3704.     

Investigation on Heat Transfer Properties of Supercritical Water in a Rock Fracture for Enhanced Geothermal Systems

Supercritical water (SCW) has shown promise as a working fluid to extract heat from hot dry rock (HDR); however, fundamental research on its heat transfer characteristics in HDR fractures is still required. A 2D heat transfer model that considers the variable thermophysical properties was updated to numerically investigate the effects of mass flow rate, thermal reservoir temperature, and fracture aperture size on the heat transfer characteristics of SCW flow through a single HDR fracture. The heat transfer performance of SCW and supercritical CO₂ (scCO₂) was compared under the same conditions. The results indicate that the heat transmission performance of SCW is superior to scCO₂ at high temperature and high pressure. It is essential to synthesize the thermal reservoir temperature and pressure, site conditions, and heat transmission fluids during HDR development.     

Heat transfer of oil-contaminated HFC134a in a horizontal evaporator

The introduction of chlorine-free refrigerants to the market requires experimental investigations of their behaviour in heat pumps and refrigerators. One particular area of interest is the effect of the new oils on the heat transfer in evaporators and condensers. Oil can either increase or decrease the heat transfer coefficient. This paper presents the results from an experimental investigation of the effect of three different ester-based oils on the heat transfer of HFC134a in a horizontal evaporator. The tests were carried out at heat fluxes between 2 and 8 kW m⁻² (corresponding to mass fluxes between approximately 40 and 170 kg s⁻¹ m⁻²). The evaporation temperature was varied from−10 to +10°C. The global oil concentration ranged from 0 to 4.5 mass percentage based on the total liquid flow. The heat transfer coefficient decreased in most of the cases. The results indicate that the decrease seems to depend on the viscosity of the oil. The decrease can fairly well be estimated with the correlation for pure refrigerants by Shah if the viscosity of the mixture is used in the calculations. The data for the oil-contaminated refrigerant also agree well with data for pure refrigerants in a plot of α_tp/α_lo^* versus the inverse Martinelli-Lockhart parameter when α_lo^* is calculated with a modified Dittus-Boelter correlation and the mixture viscosity is used in the calculations. The heat transfer is found to increase when introducing oil in the special cases where the flow rate is low and the viscosity is low (oil A, 2 and 4 kW m⁻² oil B, 6kW m⁻² at +10°C). This is most likely due to surface tension effects. It has been suggested that the increased surface tension leads to a better tube wetting and thus an increased heat transfer.