Showing papers in "Heat Transfer Engineering in 1985"
TL;DR: In this article, a technique of optimization of bank geometries is suggested on the basis of the authors' experiments and the other published data and the suggested efficiency factor Eu Re3 may be useful for the interpretation of the available vast experimental data and for the evaluation of efficiency of heat transfer surfaces in further improvements of heat exchanger construction.
Abstract: Correlations for heat transfer and pressure drop for in-line and staggered banks of tubes dre suggested. They apply to Re from 1 to 2 × 106 and Pr from 0.7 to 104, and a wide range of relative transverse and longitudinal pitches. A technique of optimization of bank geometries is suggested on the basis of the authors’ experiments and the other published data. The suggested efficiency factor Eu Re3 may be useful for the interpretation of the available vast experimental data and for the evaluation of efficiency of heat transfer surfaces in further improvements of heat exchanger construction.
107 citations
TL;DR: In this paper, the theoretical basis for the least material optimization of convectively cooled arrays of longitudinal, rectangular fin is presented, and the aspect ratio (fin thickness divided by fin width J of the array-optimum fin is found to be only marginally thinner than implied by the conventional single fin optimization.
Abstract: The theoretical basis for the least material optimization of convectively cooled arrays of longitudinal, rectangular fins is presented. The aspect ratio (fin thickness divided by fin width J of the array-optimum fin is found to be only marginally thinner than implied by the. conventional single fin optimization. Using this result, it is possible to define the geometry and thermal performance of least material, air-cooled natural convection arrays and to identify the array geometry yielding the maximum heat dissipation capability. Alternately, the added mass of a forced convection-cooled fin array is shown to be inversely related to the available pumping power and, as a consequence, no single optimum geometry could be defined. This paper includes several illustrative examples that serve to demonstrate the optimization pro cedure and to quantify the theoretical thermal performance of specific natural and forced convection air-cooled fin arrays.
57 citations
TL;DR: In this article, the authors discuss procedures for the prediction of pressure gradients, flow patterns, entrainment, and void fraction on the shell side of heat exchangers and in pipes during horizontal flow.
Abstract: This paper discusses procedures for the prediction of pressure gradients, flow patterns, entrainment, and void fraction on the shell side of heat exchangers and in pipes during horizontal flow.
56 citations
TL;DR: In this paper, a two-size model is proposed to predict the overall effectiveness of the heat exchanger in most cases of practical interest. But, in practice, an improper entrance configuration or imperfect flow passages create a flow maldistribution.
Abstract: Multipassage heat exchangers are normally designed with the assumption that the fluid stream is uniformly divided among all the parallel channels. But, in practice, an improper entrance configuration or imperfect flow passages create a flow maldistribution. Paired-channel exchangers in which the channels are continuously distributed as a function of flow rate have been investigated. Two cases of continuous maldistribution have been considered: (1) “one-side” nonuniformity, the other side having a uniform flow distribution, and (2) “both-sides” nonuniformity, where each channel pair serves as a balanced counterflow exchanger. Comparison with discrete distribution models investigated by other authors shows that a two-size model is adequate to predict the overall effectiveness of the heat exchangers in most cases of practical interest.
23 citations
TL;DR: In this paper, an extremely compact cross-flow heat exchanger is described, which is constructed by furnace-brazing together a stack of hundreds of stainless-steel sheets, but fluid channels as small as 51 μm (0.002 in) are not plugged by excess brazing material.
Abstract: An extremely compact cross-flow heat exchanger is described. The exchanger is constructed by furnace-brazing together a stack of hundreds of stainless-steel sheets. The resulting structure is leak-tight and very strong, but fluid channels as small as 51 μm (0.002 in) are not plugged by excess brazing material. Measurements of heat transfer between water and liquid propylene flowing through the heat exchanger are in excellent agreement with calculations based on exchanger geometry and fluid properties.
17 citations
TL;DR: In this paper, a three-dimensional mathematical model was developed for calculating Joule heat release, glass flow, and heat transfer in electric glass furnaces, which allows for multiple electrodes, multiphase firing, and the feeding and withdrawal of molten glass.
Abstract: A three-dimensional mathematical model was developed for calculating Joule heat release, glass flow, and heat transfer in electric glass furnaces. The model developed here allows for multiple electrodes, multiphase firing, and the feeding and withdrawal of molten glass. The model is fairly general with respect to the arrangement of the electrodes, the firing pattern, and the choice of boundary conditions, and it allows for the temperature dependence of the glass properties. The model was used to calculate electric potential, rate of heat release, flow pattern, and temperature distribution in the melting of flint and amber glasses in an all-electric melter with side-entering electrodes. Calculations were performed for the industrial conditions of pull, power, and electric firing scheme. The bulk glass temperature was found to be very uniform with large temperature gradients near the boundaries. The calculated flow pattern was in general quite complex, with several circulation loops. The temperature and max...
14 citations
TL;DR: In this paper, the effect of twisted tapes on the heat duty in fluid-to-fluid once-through vapor generators was investigated and the results showed that significant area, pressure drop, and pumping power reductions are possible using twisted-tape swirl generators; almost the entire area reduction is attributable to the suppression of the critical heat flux condition.
Abstract: Correlations covering all modes of single- and two-phase heat transfer with twisted-tape swirl generators have been incorporated into a computer program that predicts the effect of twisted tapes on the heat duty in fluid-to-fluid once-through vapor generators. These Results are compared with those from axial flow once-through vapor generators operating at the same inlet conditions. Pumping power and pressure drop with and without swirl generators are compared. The correlations used satisfactorily predict the performance of both types of heat exchangers. Significant area, pressure drop, and pumping power reductions are possible using twisted-tape swirl generators; almost the entire area reduction is attributable to the suppression of the critical heat flux condition.
12 citations
TL;DR: In this article, mass transfer coefficients for shell-and-tube heat exchanger were determined from mass transfer measurements using the naphthalene sublimation technique, where the external surface of the tubes is coated with a film of naphalene, which sublimes when exposed to an air flow.
Abstract: Experiments are described in which shell-side heat transfer coefficients for a shell-and-tube heat exchanger were determined from mass transfer measurements. The mass transfer experiments were carried out using the naphthalene sublimation technique. In utilizing the technique, the external surface of the tubes is coated with a film of naphthalene, which sublimes when exposed to an air flow. Mass transfer coefficients were measured for fully developed flow conditions at each of the tubes in the cross section. These coefficients were transformed to heat transfer coefficients by employing the analogy between heat and mass transfer. Detailed pressure drop measurements were made internal to the heat exchanger, and the axial pressure distribution indicated that the fluid flow was fully developed downstream of the first compartment. The cross-sectionally averaged mass (heat) transfer coefficients and the pressure drop were compared with the predictions from two well-established methods for the thermal-h...
10 citations
TL;DR: In this paper, the authors present a description of three computer algorithms developed to perform rating calculations of commercially available cooling towers, evaporative fluid coolers, and evaporative condensers.
Abstract: This paper presents a description of three computer algorithms developed to perform rating calculations of commercially available cooling towers, evaporative fluid coolers, and evaporative condensers. The paper illustrates the various simulations that are possible, including varying wet-bulb, inlet and exit temperatures, different fluid flow rates, altitude, or combinations of the above. The heat and mass transfer “characteristic equations, ”as a function of the fluid flow rates for a given evaporative heat exchanger, are derived from the manufacturer's rating data on one operating point, e.g., at the rating point. Or, one may use independently developed “characteristic equations” for any packing or tube bundle geometry of interest. The algorithms provide capability to predict the heat exchange capacity at any weather or process condition. They also allow the plant engineer to assess the effect of varying the air flow rate on the fan power for specified operating conditions. Example cases are ana...
9 citations
TL;DR: In this paper, the problem of heat transfer in a four-channel plate heat exchanger involving the effect of unsymmetrical heat transfer on the outer two channels is studied analytically and experimentally.
Abstract: The problem of heat transfer in a four channel plate heat exchanger involving the effect of unsymmetrical heat transfer in the outer two channels is studied analytically and experimentally. An energy balance over a control volume yields the governing system of differential equations that has been solved exactly for the cases of parallel flow and counterflow to give the temperature distribution in the channels. The results show that zero or even reversed heat flow may be obtained at the middle plate of the heat exchanger. Expressions for the heat exchanger efficiency and the log-mean temperature difference correction factor in terms of the heat capacity rate ratio and the number of transfer units are presented. Experiments carried out with a counterflow plate heat exchanger show reasonable agreement between the experimentally observed and the theoretically calculated efficiencies and mean driving temperature differences.
8 citations
TL;DR: In this paper, the results for air undergoing laminar forced-convective heat transfer in the entrance region of a flat rectangular duct with uniform wall temperature were obtained for Uniform inlet velocity and temperature profiles.
Abstract: Numerical results for air undergoing laminar forced-convective heat transfer in the entrance region of a flat rectangular duct with uniform wall temperature are obtained for Uniform inlet velocity and temperature profiles. The coupled governing partial differential equal ions are solved in discretized form with property variations being updated through physical property relations. This enables the physical property and thermofluid solutions to converge simultaneously, resulting in a realistic solution to the governing equations. Constant-property results are also obtained, and Nusselt numbers of both the constant-and variable-property models are compared with those of other numerical computations. The results of the variable-property model are also compared with available experimental data. The variable-property results exhibit excellent correlation with the available experimental data. A sensitivity analysis is performed to determine the effects of individual property variations on local Nusselt numbers.
TL;DR: In this paper, a highly effective method for heat transfer enhancement in tube and plate-finned heat exchangers through artificial flow turbulization is proposed, which allows a 1.5-to 2-fold decrease in the heat exchanger volume, a 3-to 8-fold increase in film boiling heat transfer, and a 2-to 3.4-fold increased in condensation heat transfer on the outer surfaces of annular grooved tubes as well as a decrease in salt deposition on the inner surfaces of tubes.
Abstract: A highly effective method for heat transfer enhancement in tube and plate-finned heat exchangers through artificial flow turbulization is proposed. Heat transfer surfaces of different design and their production are developed. A correlation for the increase in heat transfer is found as a function of increasing hydraulic resistance for channels of various cross sections. Results are compared with similar smooth channels with discrete wall flow turbulization. The use of the proposed surfaces allows a 1.5- to 2-fold decrease in the heat exchanger volume, a 3- to 8-fold increase in film boiling heat transfer, a 1.4-fold increase in surface boiling heat transfer, and a 2- to 3.4-fold increase in condensation heat transfer on the outer surfaces of annular grooved tubes as well as a decrease in the salt deposition on the outer and inner surfaces of tubes.
TL;DR: In this article, the results of a study of nonuniform irregularities due to tube diameter and wall thickness deviations, inaccurate bores in tube sheets, initial deflection of bundle tubes, and their deformation accumulating during heat exchanger operation are presented.
Abstract: Thermohydraulic irregularities may exert considerable effect on thermal performance of high-efficiency heat exchangers. There are two general types of such irregularities: uniform and nonuniform. The present paper presents the results of a study of nonuniform irregularities due to tube diameter and wall thickness deviations, inaccurate bores in tube sheets, initial deflection of bundle tubes, and their deformation accumulating during heat exchanger operation. The total effect on the effectiveness of heat exchanger operation is expressed in a single value referred to as the irregularity parameter ∊.
TL;DR: In this article, computer analyses were used to predict thermal-hydraulics, flow-induced vibration, and fretting-wear damage in shell-and-tube heat exchangers.
Abstract: This paper outlines computer analyses to predict thermal-hydraulics, flow-induced vibration, and fretting-wear damage in shell-and-tube heat exchangers. The analytical techniques are briefly described and the results arc illustrated by example. It is concluded that computer techniques can do much to improve the reliability and performance of heat exchangers.
TL;DR: This paper presents the results on the development of methods, algorithms, and computer programs for calculation and optimization parameters of heat exchangers at the design stage.
Abstract: This paper presents the results on the development of methods, algorithms, and computer programs for calculation and optimization parameters of heat exchangers at the design stage. Three classes of mathematical models are considered: one-dimensional models for engineering calculation of real heat exchangers and two- and three-dimensional models, and solutions of conjugated differential equation systems in the approximation of the boundary layer theory. The choice of optimization parameters, control criteria, and restriction functions is discussed in optimization models.
TL;DR: The early history of undergraduate education in heat transfer and of the textbooks intended for use in these lectures is treated up to the year 1945 in Central Europe and from 1945 to the early 1960s in the United States as mentioned in this paper.
Abstract: The early history of undergraduate education in heat transfer and of the textbooks intended for use in these lectures is treated up to the year 1945 in Central Europe and from 1945 to the early 1960s in the United States. Topics which might be considered for inclusion in future undergraduate courses in heat transfer are also suggested.
TL;DR: In this paper, a detailed three-dimensional local interaction model for spray units is used to predict the cooling performance of both a pass of sprays coaxially aligned with the wind, and a multipass spray system.
Abstract: The detailed three-dimensional local interaction model developed previously for spray units is used here to predict the cooling performance of both a pass of sprays coaxially aligned with the wind, and a multipass spray system. Since the model predicts the local changes in temperature and humidity of the air-vapor phase as well as droplet trajectories and temperatures, it is capable of determining the degree of interference between adjacent spray units as a function of upwind conditions and spray spacing without recourse to empirical interference factors. Model predictions are compared with droplet cooling and wet-bulb temperature data for spray passes consisting of units of the Power Spray Module. The thermal efficiency of a pass of sprays is examined by use of a theoretically generated dimensionless performance chart.. Such charts are utilized in a computer model of a multipass spray canal system. The model shows excellent agreement with system data. System design and performance charts are presented fo...
TL;DR: In this paper, reasonable goals of a first course in heat transfer are identified and prioritized. Highest priority is assigned to those goals which enhance the student's understanding of basic principles and the skill to apply these principles in thermal system design and evaluation.
Abstract: During the past three decades, many new technologies have enhanced the application of heat transfer, while other technologies (computational and measurement) have strongly influenced its practice. These developments present the heat transfer instructor with many options, and compromises must be made in deciding what balance should be reached in presenting heat transfer principles, establishing their relationship to thermal system behavior, and introducing modern tools of heat transfer analysis and measurement. In this paper, reasonable goals of a first course in heat transfer are identified and prioritized. Highest priority is assigned to those goals which enhance the student's understanding of basic principles and the skill to apply these principles in thermal system design and evaluation.
TL;DR: In this article, a laboratory test project was conducted to determine the effectiveness of using a four-ribbed tube on improving the tube metal temperature conditions of a 300MW power boiler operating at subcritical pressures.
Abstract: In subcritical pressure, once-through boilers, suppressing the DNB phenomenon is one of the key problems in ensuring safe operation of boiler water wall tubes. A laboratory test project was conducted to determine the effectiveness of using a four-ribbed tube on improving the tube metal temperature conditions of a 300-MW power boiler operating at subcritical pressures. For the heating test section, a specially engineered heating apparatus was used to simulate a one-sided healing condition in the boiler furnace. In the pressure range 165-200 kg/cm2 (160-194 atm), the test results showed that nucleate boiling could be maintained to much higher steam qualities with a four-ribbed tube than with a smooth-bore tube. Field test data proved that this type of tube has satisfactory effectiveness and showed that the experimental correlation recommended in this paper provides a sufficient safety margin for boiler design.
TL;DR: In this paper, an analytical method for predicting pressure drop in a heat exchanger with partially smooth and roughened surfaces was developed using the annulus flow model, which is based on the test results.
Abstract: The pressure drop on the gas-side of an experimental shell-and-tube heat exchanger consisting of a bundle of seven tubes with roughened outer walls inside a smooth hexagonal shell is described. Based on the test results, an analytical method for predicting pressure drop in a heat exchanger with partially smooth and roughened surfaces was developed using the annulus flow model.
TL;DR: In this paper, the I2R effect from impedance heating is further increased by heat from the proximity effect, eddy currents, and hysteresis, and the electrical circuit is completed by a return conductor that closely parallels the pipe.
Abstract: Impedance heating, to maintain fluid temperature in transfer piping or to increase temperature in process-heating applications, is advantageous because the pipe itself is used as the heating element. In contrast to simple resistance heating, heat attributable to the I2R effect from impedance heating is further increased by heat from the proximity effect, eddy currents, and hysteresis. Heating from these effects is induced in pipes connected to the terminal of a step-down transformer. The electrical circuit is completed by a return conductor that closely parallels the pipe. Principles, advantages, and applications of impedance heating are discussed.
TL;DR: In this paper, the authors presented arguments to prove identical results in determining the most thermohydraulically efficient surface in three comparison studies: the heat flux (at equal pumping powers for the coolant and equal heat transfer surface areas); the pumping power for the cooledant (at the equal heat fluxes and surface areas), and the heat transfer area (at a constant heat flux and surface area).
Abstract: This paper presents arguments to prove identical results in determining the most thermohydraulically efficient surface in three comparison studies: the heat flux (at equal pumping powers for the coolant and equal heat transfer surface areas); the pumping power for the coolant (at equal heat fluxes and surface areas); and the heat transfer surface area (at equal heat fluxes and coolant pumping powers). General parameters, St Re/d and ξ(Re3/d3),have been derived. The relationship between these parameters uniquely determines the thermohydraulic efficiency of the convective heat transfer surface. Analysis of equations of the type St Re/d = f( ξ Re3 / d3) helped to identify types of surfaces showing promise for compact viscous-fluid (Re ≤ 2000) heat exchangers. These surfaces are helical ducts, surfaces with short strip fins (StF), wavy fins (WF), and staggered bundles of smooth pipes (St). Heat transfer and friction in laminar flow (Re ≤ 2000) in helical ducts of rectangular cross section with an aspect ratio...