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Showing papers on "Heat transfer coefficient published in 1990"


Journal ArticleDOI
TL;DR: In this article, a simple correlation was developed earlier by Kandlikar (1983) for predicting saturated flow boiling heat transfer coefficients inside horizontal and vertical tubes, which was further refined by expanding the data base to 5,246 data points from 24 experimental investigations with ten fluids.
Abstract: A simple correlation was developed earlier by Kandlikar (1983) for predicting saturated flow boiling heat transfer coefficients inside horizontal and vertical tubes. It was based on a model utilizing the contributions due to nucleate boiling and convective mechanisms. It incorporated a fluid-dependent parameter F{sub fl} in the nucleate boiling term. The predictive ability of the correlation for different refrigerants was confirmed by comparing it with the recent data on R-113 by Jensen and Bensler (1986) and Khanpara et al. (1986). In the present work, the earlier correlation is further refined by expanding the data base to 5,246 data points from 24 experimental investigations with ten fluids. The proposed correlation gives a mean deviation of 15.9 percent with water data, and 18.8 percent with all refrigerant data, and it also predicts the correct h{sub TP} versus x trend as verified with water and R-113 data yielded the lowest mean deviations among correlations tested. The proposed correlation can be extended to other fluids by evaluating the fluid-dependent parameter F{sub fl} for that fluid from its flow boiling or pool boiling data.

1,003 citations


Journal ArticleDOI
TL;DR: In this paper, the physical meaning of the constant τ in Cattaneo and Vernotte's equation for materials with a nonhomogeneous inner structure has been considered and some values for selected products have been given.
Abstract: The physical meaning of the constant {tau} in Cattaneo and Vernotte's equation for materials with a nonhomogeneous inner structure has been considered. An experimental determination of the constant {tau} has been proposed and some values for selected products have been given. The range of differences in the description of heat transfer by parabolic and hyperbolic heat conduction equations has been discussed. Penetration time, heat flux, and temperature profiles have been taken into account using data from the literature and the experimental and calculated results.

459 citations


Proceedings ArticleDOI
TL;DR: In this article, the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages were investigated with a large scale, multi-pass, smooth-wall heat transfer model with both radially inward and outward flow.
Abstract: Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multi-pass, smooth-wall heat transfer model with both radially inward and outward flow. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages (coolant-to-wall temperature ratio, Rossby number, Reynolds number and radius-to-passage hydraulic diameter ratio). These four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. It was found that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs and that the effect of rotation on the heat transfer coefficients was markedly different depending on the flow direction. Local heat transfer coefficients were found to decrease by as much as 60 percent and increase by 250 percent from no rotation levels. Comparisons with a pioneering stationary vertical tube buoyancy experiment showed reasonably good agreement. Correlation of the data is achieved employing dimensionless parameters derived from the governing flow equations.

234 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of a centered, square, heat-conducting body on natural convection in a vertical square enclosure was examined numerically and the analysis revealed that the fluid flow and heat transfer processes are governed by the Rayleigh and Prandtl numbers, the dimensionless body size, and the ratio of the thermal conductivity of the body to that of the fluid.
Abstract: The effect of a centered, square, heat-conducting body on natural convection in a vertical square enclosure was examined numerically. The analysis reveals that the fluid flow and heat transfer processes are governed by the Rayleigh and Prandtl numbers, the dimensionless body size, and the ratio of the thermal conductivity of the body to that of the fluid. For Pr = 0.71 and relatively wide ranges of the other parameters, results are reported in terms of streamlines, isotherms, and the overall heat transfer across the enclosure as described by the Nusselt number. Heat transfer across the enclosure, in comparison to that in the absence of a body, may be enhanced (reduced) by a body with a thermal conductivity ratio less (greater) than unity. Furthermore, the heat transfer may attain a minimum as the body size is increased. These and other findings are justified through a careful examination of the local heat and fluid flow phenomena.

226 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the heat transfer coefficients on interior building surfaces (such as vertical walls, ceilings and glazing) using a real-sized indoor test cell which measures 2.95 × 2.08 m (length × width × height) and a total of 142 tests, each one lasting about 24 hours, were conducted under controlled steady-state conditions to cover nine of the most widely used heating configurations in buildings.

195 citations



Journal ArticleDOI
TL;DR: In this article, experimental membrane distillation fluxes were increased by up to 50% by deaeration and a new theoretical model showed that under these conditions, membrane permeability increased by around seven-fold, but temperature polarisation decreased the thermal driving force by five-fold.

177 citations


Journal ArticleDOI
TL;DR: In this article, an analytical model is presented that can be used to predict the heat-transfer characteristics of film evaporation on a microgroove surface, assuming that the liquid flow along a "V"-shaped groove channel is driven primarily by the capillary pressure difference due to receding of the meniscus toward the apex of the groove, and the flow up the groove side wall is driven by the disjoining pressure difference.
Abstract: An analytical model is presented that can be used to predict the heat-transfer characteristics of film evaporation on a microgroove surface. The model assumes that the liquid flow along a "V"-shaped groove channel is driven primarily by the capillary pressure difference due to the receding of the meniscus toward the apex of the groove, and the flow up the groove side wall is driven by the disjoining pressure difference. It also assumes that conduction across the thin liquid film is the dominant mechanism of heat transfer. A correlation between the Nusselt number and a nondimensional parameter ¥ is developed from this model which relates the heat transfer for the microgroove surface to the fluid properties, groove geometry, and the constants for the disjoining pressure relation. The results of a limited experimental study of the heat transfer during vaporization of a liquid coolant on a microgroove surface are also reported. Film-evaporation transfer coefficients inferred from these experiments are found to correlate fairly well in terms of Nusselt number and ¥ parameter format developed in the model. The results of this study suggest that disjoining pressure differences may play a central role in evaporation processes in microgroove channels.

175 citations


Journal Article
TL;DR: In this paper, the authors investigated the flow pattern in the shell side space of tubular heat exchangers and revealed a potential for improvement of the heat transfer performance in at least two respects: a proper arrangement of circle sector shaped plates into a pseudo-helical baffle causes near plug flow conditions within the shell space with increased heat exchanger effectiveness.
Abstract: An investigation into the flow pattern in the shell side space of tubular heat exchangers has revealed a potential for improvement of the heat transfer performance in at least two respects. First of all, a proper arrangement of circle-sector shaped plates into a pseudo-helical baffle causes near plug flow conditions within the shell space with increased heat exchanger effectiveness. Secondly, the rotational flow induced by helical baffles creates a vortex which interacts with the boundary layer on the tube surface and favourable affects the film heat transfer coefficient. These effects are achieved with little increase in pressure head. (author).

169 citations



Journal ArticleDOI
TL;DR: In this article, the authors presented evaporation and boiling heat transfer coefficients for thin, distilled water films flowing over the outside of horizontal, electrically heated brass tubes for thin-slot water distribution system for 2.54 and 5.08-cm-dia smooth tubes.
Abstract: Evaporation and boiling heat transfer coefficients are presented for thin, distilled water films flowing over the outside of horizontal, electrically heated brass tubes. Tests were conducted with a thin-slot water distribution system for 2.54- and 5.08-cm-dia smooth tubes. Both local and average heat transfer data were obtained for nonboiling and boiling conditions corresponding to feedwater temperatures ranging from 49 to 127C and heat-flux values ranging from 30 to 80 kW/m{sup 2}. Feedwater flow rates ranged from 0.135 to 0.366 kg/s per meter length per side of the tube. Both nonboiling and boiling correlations of the average heat transfer coefficients were developed and compared.

Journal ArticleDOI
TL;DR: In this paper, a heuristic approach to improving current automatic heat exchanger network synthesis (HENS) methods is presented, where the various sets of matches that all achieve the minimum or a specified number of units are rated according to their potential for being able to transfer heat vertically between the composite curves, and thus give minimum total area in the corresponding network.

Journal ArticleDOI
TL;DR: In this article, the effects of array configuration and pin-endwall fillet on the heat transfer and pressure drop of short pin-fin arrays are investigated experimentally, including an in-line and a staggered array, each having seven rows of five pins.
Abstract: The effects of array configuration and pin-endwall fillet on the heat transfer and pressure drop of short pin-fin arrays are investigated experimentally. The pin-fin element with endwall fillet, typical in actual turbine cooling applications, is modeled by a spool-like cylinder. The arrays studied include an in-line and a staggered array, each having seven rows of five pins

Journal ArticleDOI
TL;DR: In this paper, it was shown that for small values of the molecular Peclet number no resistance at the rigid wall exists, and that the effect of lateral maldistribution of fluid velocity and/or thermal conductivity, of axial dispersion of heat, and of small, systematic errors in measurement is investigated.

Journal ArticleDOI
TL;DR: In this article, an experimental investigation is described that characterizes the convective heat transfer of a heated circular air jet impinging on a flat surface and the radial distributions of the recovery factor, the effectiveness, and the local heat transfer coefficient are presented.
Abstract: An experimental investigation is described that characterizes the convective heat transfer of a heated circular air jet impinging on a flat surface. The radial distributions of the recovery factor, the effectiveness, and the local heat transfer coefficient are presented. The recovery factor and the effectiveness depend on the spacing from jet exit to the impingement plate, but do not depend on jet Reynolds number. The effectiveness does not depend on the temperature difference between the jet and the ambient. A correlation is obtained for the effectiveness. The heat transfer coefficient is independent of the temperature difference between the jet and the ambient if it is defined with the difference between the heated wall temperature and the adiabatic wall temperature.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated single-phase heat transfer from a smooth 12.7 mm-sup 2 -simulated chip to a two-dimensional jet of dielectric Fluorinert FC-72 liquid issuing from a thin rectangular slot into a channel confined between the chip surface and nozzle plate.
Abstract: Experiments were performed to investigate single-phase heat transfer froma smooth 12.7 {times} 12.7 mm{sup 2} simulated chip to a two-dimensional jet of dielectric Fluorinert FC-72 liquid issuing from a thin rectangular slot into a channel confined between the chip surface and nozzle plate. The effects of jet width, confined channel height, and impingement velocity have been examined. Channel height had a negligible effect ont eh theat transfer performance of the jet for the conditions of the present study. A correlation for the convective heat transfer coefficient is presented as a function of jet, width, heat length, flow velocity, and fluid properties. A self-contained multichip cooling module consisting of a 3 {times} 3 array of heat sources confirmed the uniformity and predictability of cooling for each of the nine chips, and proved the cooling module is well suited for packaging large arrays of high-power density chips.

Journal ArticleDOI
TL;DR: In this article, the heat transfer from a stretching sheet to a micropolar fluid is analyzed using the theory of Eringen, and the governing equations for momentum, angular momentum and energy have been solved numerically.
Abstract: The heat transfer from a stretching sheet to a micropolar fluid is analyzed using the theory of micropolar fluids formulated by Eringen. The governing equations for momentum, angular momentum and energy have been solved numerically. Numerical data for the friction factor and Nusselt number has been tabulated for a range of Prandtl numbers. Surface mass transfer rate and the power law constant for the wall temperature have considerable influence on the heat transfer mechanism.

Journal ArticleDOI
TL;DR: In this paper, heat and mass transfer in a metal hydride bed is modeled and the effect of augmenting heat conduction and hydrogen flow governed by Darcy's law modified for the transitional flow regime is demonstrated.


Journal ArticleDOI
TL;DR: In this article, a high-purity copper sphere was plunged into cooling baths without boiling and the sphere was instrumented with several interior thermocouples for measuring the transient temperature response during quenching.
Abstract: Methodological and experimental aspects of the estimation of transient heat transfer coefficients in quenching experiments, using inverse heat transfer methods, were addressed and investigated. Beck's method was used for the estimation of the transient heat transfer coefficient history from interior transient temperature measurements during quenching. Experiments involved plunging a high-purity copper sphere into cooling baths without boiling. The sphere was instrumented with several interior thermocouples for measuring the transient temperature response during quenching. Water and ethylene glycol were investigated. The early transient values of the heat transfer coefficient history were found to be about 100-120% higher than the values predicted using well-known empirical correlations for free convection. The later time values were in good agreement with those predicted with empirical correlations. The transient inverse technique has the capability of estimating early transients and subsequent quasi-steady-state values of heat transfer coefficient in a single transient experiment.

Journal ArticleDOI
TL;DR: In this paper, a numerical analysis of the overall performance of a heat pipe with single or multiple heat sources is presented, which includes the heat conduction in the wall and liquid-wick regions as well as the compressibility effect of the vapor inside the heat pipe.

Journal ArticleDOI
TL;DR: In this paper, a model satisfying the near-wall balance between viscous diffusion, viscous dissipation and pressure diffusion, and also having the characteristics of approaching their respective conventional high-Reynolds-number models far away from the wall is proposed.

Proceedings ArticleDOI
TL;DR: In this article, the influence of high mainstream turbulence on leading edge film effectiveness and heat transfer coefficient was studied using a blunt body with a semicylinder leading edge with a flat afterbody.
Abstract: The influence of high mainstream turbulence on leading edge film effectiveness and heat transfer coefficient was studied. High mainstream turbulence was produced by a passive grid and a jet grid. Experiments were performed using a blunt body with a semicylinder leading edge with a flat afterbody. The mainstream Reynolds number based on leading edge diameter was about 100,000. Spanwise and streamwise distributions of film effectiveness and heat transfer coefficient in the leading edge and on the flat sidewall were obtained for three blowing ratios, through rows of holes located at ± 15 and ± 40 deg from stagnation

Proceedings ArticleDOI
TL;DR: In this article, the effect of rotation, aspect ratio, and turbulator roughness on heat transfer in rib-roughened passages was investigated in an orthogonally rotating setup to simulate the actual rotation of the cooling passages.
Abstract: Turbine blade cooling is imperative in advanced aircraft engines. The extremely hot gases that operate within the turbine section require turbine blades to be cooled by a complex cooling circuit. This cooling arrangement increases engine efficiency and ensures blade materials a longer creep life. One principle aspect of the circuit involves serpentine internal cooling passes throughout the core of the blade. Roughening the inside surfaces of these cooling passages with turbulence promoters provides enhanced heat transfer rates from the surface. The purpose of this investigation was to study the effect of rotation, aspect ratio, and turbulator roughness on heat transfer in these rib-roughened passages. The investigation was performed in an orthogonally rotating setup to simulate the actual rotation of the cooling passages. Single-pass channels, roughened on two opposite walls, with turbulators positioned at 45 deg angle to the flow, in a criss-cross arrangement, were studied throughout this experiment. The ribs were arranged such that their pitch-to-height ratio remained at a constant value of 10. An aspect ratio of unity was investigated under three different rib blockage ratios (turbulator height/channel hydraulic diameter) of 0.1333, 0.25, and 0.3333. A channel with an aspect ratio of 2 was also investigated for a blockage ratio of 0.25. Air was flown radially outward over a Reynolds number range of 15,000 to 50,000. The rotation number was varied from 0 to 0.3. Stationary and rotating cases of identical geometries were compared. Results indicated that rotational effects are more pronounced in turbulated passages of high aspect and low blockage ratios for which a steady increase in heat transfer coefficient is observed on the trailing side as rotation number increases while the heat transfer coefficient on the leading side shows a steady decrease with rotation number. However, the all-smooth-wall classical pattern of heat transfer coefficient variation on the leading and trailing sides is not followed for smaller aspect ratios and high blockage ratios when the relative artificial roughness is high.

Journal ArticleDOI
TL;DR: In this paper, the behavior of a general class of cyclic endoreversible heat engines at maximum power point is considered and the functional temperature dependence of heat transfer is considered as a variable.
Abstract: The behavior of the efficiency of a general class of cyclic endoreversible heat engines at maximum power point is considered. The functional temperature dependence of heat transfer is considered as a variable, and its physical significance is addressed. It is shown that a broader spectrum of solutions emerges for efficiency at maximum power, as a function of the relevant system parameters, than originally realized. Specifically, it is proved that efficiency at maximum power is in general not independent of the heat‐transfer coefficients, and that a type of ‘‘symmetry’’ exists relative to the functional temperature dependence of Newtonian heat conduction. The ‘‘Curzon–Ahlborn efficiency’’ of finite‐time thermodynamics is shown not to be a fundamental upper limit on the efficiency of an endoreversible engine at maximum power point. Rather, this upper limit depends both on the functional temperature dependence of the heat transfer and on the relative value of the hot‐ and cold‐side heat‐transfer coefficients.

Journal ArticleDOI
01 Nov 1990
TL;DR: In this article, the effects of the induced magnetic field and sources or sinks have been included in the analysis of flow and heat transfer over a stretching sheet with a magnetic field in an electrically conducting ambient fluid.
Abstract: The flow and heat transfer over a stretching sheet with a magnetic field in an electrically conducting ambient fluid have been studied. The effects of the induced magnetic field and sources or sinks have been included in the analysis. Both non-isothermal wall and constant heat flux conditions have been considered. The governing equations have been solved numerically using a shooting method. It is observed that for the prescribed wall temperature the skin friction, induced magnetic field at the wall and heat transfer are enhanced due to the magnetic field, but in general, they reduce as the reciprocal of the magnetic Prandtl number increases. For constant heat flux case, the temperature at the wall reduces as the magnetic field increases, but it increases with the reciprocal of the magnetic Prandtl number. The heat transfer is strongly affected by the Prandtl number, wall temperature and sink. Whenm 2.5 the unrealistic temperature distributions are encountered. The present analysis is more general than any previous investigation.

Journal ArticleDOI
TL;DR: In this paper, the effect of surface roughness on spray cooling was studied, and the results showed that the roughness variation influences the flowfield, altering the maximum liquid film thickness, the bubble diameter, vapor entrapment, bubble departure characteristics and the ability of the surface to transfer heat.
Abstract: In the spray cooling of a heated surface, Variations in the surface contact angle cause a change in nucleation characteristics and, thereby, influence the heat transfer process; a higher contact angle shows an enhanced heat transfer due to the ease in nucleation caused by the lowered free energy associated with bubble formation. Results are presented for different surface coatings and spray configurations. The surface roughness variation influences the flowfield, altering the maximum liquid film thickness, the bubble diameter, vapor entrapment, bubble departure characteristics, and, thereby, the ability of the surface to transfer heat. The effect of surface roughness on spray cooling is also studied.

Journal ArticleDOI
TL;DR: In this article, the most important geometric parameter influencing the heat transfer from pin fin arrays is the ratio of the fin diameter to the center-to-center spacing, and the experimental results indicate that a pin fin array performs better than a plate fin array under the same conditions.

Journal ArticleDOI
TL;DR: In this paper, a numerical analysis is carried out to investigate the effects of latent heat transfer, in association with the evaporation of a finite liquid film on the channel wall, on the natural convection heat and mass transfer.

Proceedings ArticleDOI
TL;DR: In this paper, heat transfer and leakage loss measurements were obtained for compressible flows in typical straight-through labyrinth seals with high rotational speeds, and the experiments were an extension of earlier measurements in a stationary test facility.
Abstract: Heat transfer and leakage loss measurements were obtained for compressible flows in typical straight-through labyrinth seals with high rotational speeds. The experiments are an extension of our earlier measurements in a stationary test facility. In order to ensure direct comparisons to the original experiments, the principal dimensions of the test facility and gas dynamic parameters of the hot gas were kept similar. The new study encompasses a wide range of Taylor numbers, Reynolds numbers, and clearances between the rotating annular fins and the stationary shroud