Showing papers in "Heat Transfer Engineering in 1994"
TL;DR: In this paper, the authors compared heat transfer and pressure drop correction factors based on the Bell-Delaware method for an optimized segmental baffle heat exchanger and a helical baffle.
Abstract: Heat transfer and pressure drop correction factors based on the Bell-Delaware method have been compared for an optimized segmental baffle heat exchanger and a helical baffle heat exchanger. In general, the results showed that properly designed helical baffles offer a significant improvement in heat transfer while providing a reduced exchanger pressure drop. The enhancement in heat transfer for helical baffles was reflected by the so-called turbulence enhancement correction factor, which accounted for the increase in heat transfer observed at a critical baffle inclination angle of 25°. As the baffle inclination angle was increased beyond this critical angle, the turbulence enhancement factor continued to increase and eventually produced a maximum heal transfer enhancement of 1.39 times that for ideal cross-flow conditions. The reduction in pressure drop due to the helical baffles was found to vary from 0.26 to 0.60 depending on the helical inclination angle.
156 citations
TL;DR: In this paper, the authors provided a correlation for convective vaporization on banks of plain tubes, based on three data sets: the present data, the R-113 data of Comwell and Scoones, and that of Jensen and Hsu.
Abstract: This article provides a correlation for convective vaporization on banks of plain tubes. New data are provided for R-113 and R‐123 vaporization on 16.8‐mm‐O.D. tubes over a wide range of vapor qualities (0.1 to 0.9) with low mass velocities (8 kg / m2 s to 40 kg / m2 s) for a wide range of heat flux. The correlation is based on three data sets: the present data, the R-113 data of Comwell and Scoones, and that of Jensen and Hsu. The asymptotic model (exponent of 3) provided the best correlation, having a mean square error of 14.6%. The asymptotictype correlation provided better results than the superposition model. A disturbing anomaly was noted in the lack of agreement between pool boiling on a single tube and pool boiling on one heated tube in a bundle for the Comwell and Scoones data. More work is required to understand this situation. The data were analyzed to interpret whether convection causes boiling suppression. Assuming that the pool boiling data are correct, it appears that the higher-mass-veloci...
19 citations
TL;DR: In this article, an extensive survey of the shell-side pressure field within the tube bundle of an E-type segmented-baffle shell-and-tube heat exchanger is presented.
Abstract: Representatkie pressure distributions from an extensive survey of the shell-side pressure field within the tube bundle of an E-type segmented-baffle shell-and-tube heat exchanger are presented. Reynolds numbers based on minimum intertubc flow area were varied within the range 270-2,200. Strategically placed tubes forming part of the bundle were fitted with pressure tappings and were used to measure (1) axial distributions of cross-flow pressure drop, symmetric about the pass partition lane and in the central vertical plane of the bundle, and also at the edge of the bundle near the bypass lane; (2) flow pressure drops between adjacent baffle compartments; and (3) circumferential pressure distributions on selected tubes in the center and at the periphery of the bundle. Comparison of the results with those obtained in a previous study with no pass partition lane reveal the effect of the removal of the central row of tubes on the shell-side flow distribution.
17 citations
TL;DR: In this paper, the effective pore radius in screen-wick heat pipes was investigated, which is very important for the prediction of maximum heat transfer rates due to capillary limitation, based on the model of the screen geometry.
Abstract: The effective pore radius in screen-wick heat pipes was investigated, which is very important for the prediction of maximum heat transfer rates due to capillary limitation. An equation for the effective pore radius of the screen wicks was derived based on the model of the screen geometry. The capillary height for stainless steel and phosphor bronze screens was measured using water, ethyl alcohol, and Freon 113 as the test liquids. The effect of surface treatment (acid cleaning and oxidation) on the capillary height was also examined. From the comparison of the experimental data for water and ethyl alcohol with those for Freon 113, it was indicated that the contact angle was 24.2{degree} for water and 16.9{degree} for ethyl alcohol. Consequently, it was found that the effective pore radius of the screen wicks could be predicted fairly well from the expression presented in this study, and that the contact angle should be taken into consideration to evaluate the maximum capillary pressure accurately.
16 citations
TL;DR: In this article, a dynamic model of a tunnel kiln is developed in detail, based on the transient heat conduction occurring in the products and in the lining bricks of kiln cars (LBKC), as well as on the gas continuity, heat balance, and material balance equations.
Abstract: In this article the dynamic model of a tunnel kiln is developed in detail, based on the transient heat conduction occurring in the products (or wares) and in the lining bricks of kiln cars (LBKC), as well as on the gas continuity, heat balance, and material balance equations. The computational method used to solve the present model is discussed briefly. Numerical simulations associated with a 72-m-long tunnel kiln that is used for firing clay bricks were performed. Transient heat conduction in two dimensions in wares and in LBKC were computed. Two oxygen schedules under one firing schedule and three lining brick structures were simulated. The fuel consumption and flow rates of primary air, cooling air, and exhaust flow were investigated under different atmosphere (i.e., oxygen concentration) schedules. The relationship between the fuel consumption and heat storage rate in wares and in LBKC was also studied. The results of the present numerical simulations show that, using the present model, we can predict...
14 citations
TL;DR: In this paper, the authors present the solutions to two fundamental problems in the design of the insulation for a refrigerator: the first problem is how to incorporate the new generation of non-CFC materials in a composite layer that also contains polyurethane foam.
Abstract: This article presents the solutions to two fundamental problems in the design of the insulation for a refrigerator. The first problem is how to incorporate the new generation of non-CFC materials in a composite layer that also contains polyurethane foam. The article shows how to select the thickness of each sublayer in the composite so that the total cost is minimized over the lifetime of the refrigerator. The second problem addresses the distribution of a given amount of insulation material around the refrigerator, for example, over the freezer and cooler sections. The article reports the optimal insulation thicknesses for the freezer and cooler sections so that the overall heat leak into the cold space is minimum.
13 citations
TL;DR: In this paper, the design and construction of a novel heat pipe apparatus is described, and results from experiments that employed the apparatus are presented, and the apparatus is designed to permit visual and photographic study of liquid flow and vapor formation within the heat pipe wick structure, artery, and vapor flow channel.
Abstract: The design and construction of a novel heat pipe apparatus is described, and results from experiments that employed the apparatus are presented. The apparatus is designed to permit visual and photographic study of liquid flow and vapor formation within the heat pipe wick structure, artery, and vapor flow channel. The vapor temperature field in the vapor flow channel is displayed by use of thermochromic liquid crystal material. Liquid and vapor flow phenomena observed during normal and the approach to boiling-limited heat pipe operation are described.
13 citations
TL;DR: An analysis of the errors due to the length of arc idealization in convective extended surfaces is presented in this article, where longitudinal fin, spines, and annular fin of triangular profile are considered.
Abstract: An analysis of the errors due to the length of arc idealization in convective extended surfaces is presented. Longitudinal fins, spines, and annular fins of triangular profile are considered. It is shown that in fins that are designed according to the criteria established by Razelos and Georgiou [7], the resulting errors are negligibly small. These criteria suggest that fins should be designed with order of magnitude of aspect and Biot numbers of u = O(1) and Bi = O(0.01). It is also shown that for spines and annular fins only the Biot number restriction suffices to warrant negligible errors.
11 citations
TL;DR: In this article, a quasi-three-dimensional approach is used to predict the fluid flow and heat transfer in the steam surface condenser, and the governing equations are solved in primitive variable form using a semi-implicit consistent control volume formulation in which a segregated pressure correction-linked algorithm is employed.
Abstract: The present study reports on an analysis of the sensitivity of condensation heat transfer coefficient correlations on the simulations of the performance of steam surface condensers. Five correlations of heat transfer coefficient for filmwise condensation are tested against the experimental data for a steam surface condenser. A quasi-three-dimensional approach is used to predict the fluid flow and heat transfer in the steam surface condenser. The governing equations are solved in primitive variable form using a semiimplicit consistent control-volume formulation in which a segregated pressure correction-linked algorithm is employed. The modeling of the geometries of condensers, including tube bundles and baffle plates, is carried out based on the porous media concept using flow, heat, and mass transfer resistances.
10 citations
TL;DR: In this paper, an expression for optimum aspect ratio is derived mathematically from a correlation that includes both aspect ratio and bend curvature parameters for curved rectangular ducts, and enhancement factors are developed that show optimal, near-optimal, and nonoptimal aspect ratios for curved rectilinear ducts.
Abstract: Enhanced heal transfer in curved rectangular channels depends on at least two geometric factors, the radius of curvature of the duct and the aspect ratio, which is the width / depth ratio of the duct. In this work, an expression for optimum aspect ratio is derived mathematically from a correlation that includes both aspect ratio and bend curvature parameters. Enhancement factors are developed that show optimal, near-optimal, and nonoptimal aspect ratios for curved rectangular ducts. Predicted enhancements are within 25% of published literature results for individual designs, two of which show heat transfer enhancement of 200% over that of a straight duct with turbulent flow. The theoretical maximum enhancement is shown to be about 480% over a straight-duct, turbulent-flow situation. This is not achievable in practice, but near-optimal solutions are achievable, yielding enhancements on the order of 200-300%
8 citations
TL;DR: In this paper, the absorption process in a smooth-tube heat exchanger with a porous medium is analyzed and a countercurrent model for GAX absorber that includes an absorption process within the porous medium was proposed.
Abstract: In this article the absorption process in a smooth-tube heat exchanger (GAX absorber) with a porous medium is analyzed and a countercurrent model for GAX absorber that includes an absorption process within the porous medium is proposed. The absorption process is separated into three regions, a vapor region without a porous medium (region 1), a vapor region within a porous medium (region 2), and a liquid region within a porous medium (region 3). The effects of thermal conductivities and porosities of the porous medium on the absorption rate and the required tube length are investigated, and the Nusselt number within each region is also predicted. The results show that the absorption rate increases with an increase of the thermal conductivity and with a decrease in porosity of the porous medium. The optimum value of the ratio of thermal conductivities (k{sub p} / k{sub 1}) was found to be 5.0, and the optimum value of the porosity was found to be larger than 0.2.
TL;DR: In this paper, a profile of the least-weight longitudinal cooling fin is obtained considering temperature dependence of thermophysical properties, where a power-law-type wall heat flux is assumed on the lateral and lip surfaces of the fin.
Abstract: The profile of the least-weight longitudinal cooling fin is obtained considering temperature dependence of thermophysical properties. A power-law-type wall heat flux is assumed on the lateral and lip surfaces of the fin. Uniform temperature is imposed at the fin base, whereas two kinds of boundary conditions at the fin tip are considered. First, a specified heat transfer rate is prescribed at the free end. Second, the outer edge of the fin is also subject to a power-law-type surface heat flux and dissipates energy to the ambient fluid. Special cases of negligible heat transfer from the fin tip and zero tip temperature are investigated. The temperature distributions and profiles of the optimum fins are calculated for various single heat transfer modes. In addition, it is shown that the fin length plays an important role in the determination of the optimum fin with minimum volume.
TL;DR: An analytical study of transient heat conduction process with moving heat source/sink was considered in this article, where a closed-form solution for the heat-conduction equation is obtained, the spatial temperature distribution and the temperature time history could be obtained.
Abstract: An analytical study of transient heat conduction process with moving heat source/sink was considered. In this study a closed-form solution for the heat conduction equation is obtained. Using the obtained solution, the spatial temperature distribution and the temperature time history could be obtained. The obtained results are compared with numerical and experimental data in the literature. The comparison shows that the present solution can be used do determine the effect of different heat flow parameters on the temperature pattern and history in any similar heat conduction problem.
TL;DR: In this article, the average heat transfer coefficients for a slot jet, a single row of round jets, and a triple row of rounds jets impinging onto a concave semicylindrical surface were obtained.
Abstract: Experimental results for average heat transfer coefficients have been obtained for a slot jet, a single row of round jets, and a triple row of round jets impinging onto a concave semicylindrical surface. Average Nusselt numbers have been expressed as functions of Reynolds number, Prandtl number, and non-dimensional geometric parameters of jet-target configuration. One of the major applications of jet impingement cooling is in gas turbines. Gas turbine cooling systems need to be designed for turbine blades, vanes, end walls, shrouds, and other components to meet metallurgical temperature limits. A few of the important research publications in this field are mentioned here.
TL;DR: In this article, the authors presented the solutions of die developing temperature field as well as the heat transfer coefficient are presented as functions of axial distance for different opening angles of sector.
Abstract: Hydrodynamically developed and thermally developing laminar incompressible forced-connective flow in ducts containing twisted-tape inserts is analyzed. The flow is subjected to either uniform temperature or uniform heat flux on the curved duct surface, and the straight duct surfaces are insulated. The heat input into the fluid is only from the curved duel surface and is uniform axially. The thermal properties are assumed constant; the axial conduction and viscous dissipation are negligibly small. Numerical calculations of the temperature field and Nusselt number march forward axially in the thermal entrance region. The solutions of die developing temperature field as well as the heat transfer coefficient are presented as functions of axial distance for different opening angles of sector. Comparisons are made between computed results and some analytical and numerical findings reported in the literature. In all cases, satisfactory comparisons are attained.
TL;DR: In this article, a correlation was developed for laminar film condensation on vertical fluted surfaces based on the theoretical analysis of Panchal and Bell for defining important physical property groups.
Abstract: A correlation was developed for laminar film condensation on vertical fluted surfaces. The theoretical analysis of Panchal and Bell was used for defining important physical property groups. The experimental data of Combs et al. were used to validate the proposed correlation. The experimental database used in the present study included four flute geometries that could be approximated to cosine-type flutes and seven fluids. The resulting correlation can predict the average condensate heat transfer coefficient within {+-}20%.
TL;DR: In this article, the radiation heat transfer between rectangular electronic components on a printed circuit board and the walls of its enclosure is studied analytically using a Monte Carlo method, and it is shown that radiation can serve as an effective heat transfer mechanism for the cooling of electronic components in sealed enclosures cooled externally.
Abstract: Radiation heat transfer between rectangular electronic components on a printed circuit board and the walls of its enclosure is studied analytically using a Monte Carlo method. The radiation heat transfer between the electronic components and the cover is determined for the cases of diffuse and specular surfaces with constant properties, and for diffuse and specular surfaces with variable temperature and direction-dependent properties. The radiation interchange between the components and the cover of the enclosure are determined and presented for various dimensionless parameters and surface emissivities in tabular and graphical forms. The radiation heat transfer, in general, is found to be comparable in magnitude to natural-convection heat transfer at operating conditions encountered in practice. It is shown that radiation can serve as an effective heat transfer mechanism for the cooling of electronic components in sealed enclosures cooled externally.
TL;DR: In this article, the authors present the view factors between the surfaces of a long duct, in which a long cylinder is located at its center, in terms of two dimensionless parameters: D % S, the ratio of the cylinder diameter to the length of the short side, and S % L, the proportion of the long side length to the long one.
Abstract: Radiation view factors between opposed rectangular surfaces, between normal rectangular surfaces, and between cylinders and parallel rectangular surfaces are readily found in the literature. However, when the cylinder is located at the center of a rectangular duct, the view factors between the surfaces of the duct are obviously influenced by the presence of the cylinder; these uiew factors do not appear to be auailablc in the literature. This article presents the uiew factors between the surfaces of a long duct, in which a long cylinder is located at its center, in terms of two dimensionless parameters: D % S, the ratio of the cylinder diameter to the length of the short side, and S % L, the ratio of the length of the short side to the length of the long side.
TL;DR: In this paper, a mathematical model for the time-dependent heat conduction process in a region of arbitrary geometry was developed and an alternating direction implicit (ADI) scheme was worked out for the computer solution of the problem in three space dimensions.
Abstract: A mathematical model has been developed for the time-dependent heat conduction process in a region of arbitrary geometry. An alternating direction implicit (ADI) scheme has been worked out for the computer solution of the problem in three space dimensions. The time and nodal propagation of the errors are depicted graphically. Also included in the computer software is a subroutine for plotting the isotherms in various geometries.
TL;DR: In this article, the authors take care to determine whether measuring the pipe wall temperature will give a reasonable approximation of the bulk temperature of a process stream, and further calculations must be performed.
Abstract: When trying to determine the bulk temperature of a process stream, engineers must take care to determine whether measuring the pipe wall temperature will give a reasonable approximation of the bulk temperature. If the pipe wall temperature will not give a reasonable approximation of the bulk fluid temperature, further calculations must be performed.
TL;DR: In this paper, two heat-recovery heat exchangers were designed using a simplified computer model and tested at a flooded abandoned mine vein at Scranton, Pennsyluania.
Abstract: The temperature of water in large water reservoirs remains essentially constant at approximately 60° F throughout the year and therefore is attractive for space-conditioning applications. The energy exchange with the water reservoir is accomplished through a heat exchanger. In the present work, two heat-recovery heat exchangers were designed using a simplified computer model. Design-1, which used smooth tubes, was tested at a flooded abandoned mine vein at Scranton, Pennsyluania. The subsequent design, which used the spirally fluted tubes, was tested at the Ohio State University ( OSU) and at a lake in Lackawanna Stale Park in Pennsylvania. A more detailed thermal hydraulic model was developed for the analysis of these heat-recovery heat exchangers. The data obtained at OSU and Lackawanna were analyzed using the thermal hydraulic model to develop a correlation for natural convection. Finally, using this correlation, it was found that the design with spirally fluted tube clearly offers advantages in terms ...