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Showing papers in "Heat Transfer Engineering in 1999"


Journal ArticleDOI
TL;DR: In this article, the validity of 20 nonboiling heat transfer correlations obtained from a comprehensive literature review are assessed and compared with seven extensive sets of two-phase flow experimental data available from the literature, for vertical and horizontal tubes and different flow patterns and fluids.
Abstract: In this study, the validity of 20 nonboiling heat transfer correlations obtained from a comprehensive literature review are assessed. These correlations were tested against seven extensive sets of two-phase flow experimental data available from the literature, for vertical and horizontal tubes and different flow patterns and fluids. A total of 524 data points from five available experimental studies (which included the seven sets of data) were used for these comparisons. Based on the tabulated and graphical results of the comparisons with and without considering author-specified ranges of applicability, appropriate correlations for different flow patterns and tube orientations are recommended.

61 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of modified surfaces on deposition of calcium sulfate on heat transfer surfaces was studied and the results showed that these modifications of the heat transfer surface mitigated fouling significantly.
Abstract: The formation of scale on heat transfer surfaces during pool boiling is a frequent engineering problem where aqueous solutions are involved. In this investigation the effect of modified surfaces on deposition of calcium sulfate on heat transfer surfaces was studied. The surfaces were either implanted with ions such as F, Si, and H using range-matched implants, or sputtered with diamond-like carbon, TaC, and TaC-F using a closed-field magnetron ion sputtering system. Fouling runs during pool boiling of CaSO4 were carried out with varied heat fluxes and two different salt concentrations. The results showed that these modifications of the heat transfer surfaces mitigated fouling significantly.

56 citations


Journal ArticleDOI
TL;DR: In this article, an experimental study was carried out to examine the effects of the waffle height on the heat transfer and friction characteristics of typical fin-and-tube heat exchangers having wavy fins.
Abstract: An experimental study was carried out to examine the effects of the waffle height, including three different values of waffle height-1.18, 1.32, and 1.58 mm-on the heat transfer and friction characteristics of typical fin-and-tube heat exchangers having wavy fins. A total of 13 samples of heat exchangers, nine of them having wavy fins and the other four having plain fin configurations, were tested. The test results indicated that the effect of waffle height on the heat transfer enhancement ratio, compared to the plain-fin counterpart, is pronounced only for smaller fin pitch and larger waffle height, while its effect on the pressure drop is considerably significant throughout the test range.

53 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe particulate fouling experiments performed on small-scale and full-scale plate heat exchangers for three different corrugation angles (30 deg, 45 deg and 60 deg).
Abstract: This article describes particulate fouling experiments performed on small-scale and full-scale plate heat exchangers for three different corrugation angles (30 deg, 45 deg and 60 deg). The velocity effect has been studied as well as the particle type and concentration effects. The test duration ranges between 20 and 1,500 h in order to reach asymptotic behavior. The results clearly indicate that the corrugation angle has a major influence on the asymptotic fouling resistance. Increasing the corrugation angle leads to lower values for the fouling resistance. Furthermore, for a given corrugation angle, the asymptotic fouling resistance is inversely proportional to the velocity squared. Finally, the asymptotic fouling resistance is proportional to the particle concentration. Fouling mitigation can be obtained by taking into account at the design stage the heat exchanger geometry and fluid velocity.

41 citations


Journal ArticleDOI
TL;DR: In this article, a steam condensation test rig of a plate heat exchanger (PHE) was set up and the heat transfer and pressure drop characteristics of two kinds of typical operation condition in a PHE were obtained.
Abstract: In cooperation with Alfa Laval Thermal AB Company in Sweden, a steam condensation test rig of a plate heat exchanger (PHE) was set up. The heat transfer and pressure drop characteristics of two kinds of typical operation condition in a PHE were obtained: complete condensation and partial condensation. This article introduces the test rig, various sensors, and the data acquisition system used in the measurements. The process of steam condensation in a PHE is analyzed in detail. The two-phase frictional pressure drop along this wavy channel was obtained from the measured steam condensation pressure drop. The Lockhart-Martinelli model was extended to predict the pressure drop of steam condensation in a PHE and was verified by the experimental results. Based on the data processing of 109 experimental points, a correlation of frictional pressure drop of steam condensation in a PHE is suggested. This correlation is recommended for calculation of the steam condensation pressure drop in a PHE.

41 citations


Journal ArticleDOI
TL;DR: In this paper, a mathematical model is developed to analyze a single-effect thermal vapor-compression (TVC) desalination process, considering the effect of various thermodynamic losses on the system preformance ratio, the specific heat transfer area, and the specific flow rate of cooling water.
Abstract: A mathematical model is developed to analyze a single-effect thermal vapor-compression (TVC) desalination process. The model considers the effect of various thermodynamic losses on the system preformance ratio, the specific heat transfer area, and the specific flow rate of cooling water. The losses contemplated are the boiling-point elevation, the nonequilibrium allowance, and the temperature depression corresponding to the pressure drop in the demister and during the vapor-condensation process. The model takes into consideration the dependence of the physical properties of the seawater on temperature and salt concentration. In addition, the model considers the effects of the fouling factors and the presence of noncondensable gases on the heat transfer coefficients in the evaporator and the condenser. The system performance is analyzed in terms of parameters controlling the cost of product water, which include the performance ratio, the specific heat transfer area, and the specific flow rate of cooling wa...

38 citations


Journal ArticleDOI
TL;DR: In this paper, a mathematical model was developed to study the performance of a counterflow heat exchanger in which both fluid streams are exposed to external heating, and it was found that under the external heat transfer condition, the effectiveness of the heat exchange was drastically reduced, and the hot fluid temperature increased as the external thermal conductance ratios, Rh and Rc, decreased.
Abstract: A mathematical model was developed to study the performance of a counterflow heat exchanger in which both fluid streams are exposed to external heating. It was found that under the external heat transfer condition, the effectiveness of the heat exchanger was drastically reduced. The hot fluid temperature effectiveness increased as the external thermal conductance ratios, Rh and Rc, decreased. For effective operation and to avoid temperature cross, there exist a maximum possible NTU for a given Rh and Rc.

32 citations


Journal ArticleDOI
TL;DR: In this article, horizontal two-phase flow patterns were observed in a transparent circular channel (1.90 cm I.D.) using adiabatic mixtures of air and water.
Abstract: Horizontal two-phase flow patterns were observed in a transparent circular channel (1.90 cm I.D.) using adiabatic mixtures of air and water. Visual identification of the flow regimes was supplemented with photographic data and the results were plotted on the flow regime map which has been proposed by Breber et al. for condensation applications. The results indicate general consistency between the observations and the predictions of the map, and, by providing data for different fluids and conditions from which the map was developed, support its general applicability.

28 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a cross-flow plate-type heat exchanger that has been studied and manufactured in laboratory conditions because of its effective use in waste heat recovery systems.
Abstract: This article presents a cross-flow plate-type heat exchanger that has been studied and manufactured in laboratory conditions because of its effective use in waste heat recovery systems. This new heat exchanger was tested with an applicable experimental setup, considering temperatures, velocity of the air, and the pressure losses occurring in the system. These variables were measured and the efficiency of the system was determined. The irreversibility of the heat exchanger was taken into consideration, while the design of the heat exchanger was such that the minimum entropy generation number was analyzed with respect to the second law of thermodynamics in the cross-flow heat exchanger. The minimum entropy generation number depends on the parameters called the optimum flow path length and dimensionless mass velocity. Variations of the entropy generation number with these parameters are analyzed.

26 citations


Journal ArticleDOI
TL;DR: In this article, the thermal radiative effects are taken into account in modified Nusselt and Rayleigh numbers for inclined channels with uniform symmetric or asymmetric heat flux.
Abstract: Design and thermal control of tilted channels in air natural convection requires knowledge of relations between process parameters. Composite correlations of average Nusselt number in terms of channel Rayleigh number (10 Ra 9.0 104) are proposed for inclined channels with uniform symmetric or asymmetric heat flux. The thermal radiative effects are taken into account in modified Nusselt and Rayleigh numbers. The surface emissivities considered are 0.05 and 0.8. Experimental data employed to obtain the proposed correlations are in good agreement with the correlations for a vertical channel from published literature. Composite correlations between Nu and Ra cos theta valid in the whole range 0-85 of the inclination angle are given. Moreover, a general composite correlation is proposed for all heating modes, in which the inclination angle is in the range 0-85 and for surface emissivity not greater than 0.8. Recommendations for the thermal design of single or multiple channels are given.

23 citations


Journal ArticleDOI
TL;DR: In this article, the principle of superposition and the method of separation of variables are used to obtain analytical transient solutions when the fin base is subjected to a step change in base temperature for a two-dimensional cylindrical pin fin with tip convection.
Abstract: The principle of superposition and the method of separation of variables are used to obtain analytical transient solutions when the fin base is subjected to a step change in base temperature for a two-dimensional cylindrical pin fin with tip convection. Analytical solutions for two other boundaries of the tip in which the temperature is equal to that of the sourroundings and the tip is insulated are also obtained. The effects of tip convections on the temperature distributions along the entire fin and the heat flow rates at the fin base are examined. For short fins, the effects of tip convections on heat transfer can be more significant for small transversal Biot number and large time.

Journal ArticleDOI
TL;DR: In this article, a mathematical model is presented to describe the dynamic thermal behavior of counterflow cooling towers that contain packing materials, taking into account both the sensible and latent heat cooling effects on the tower performance.
Abstract: In this study, a mathematical model is presented to describe the dynamic thermal behavior of counterflow cooling towers that contain packing materials. The proposed model takes into account both the sensible and latent heat cooling effects on the tower performance. Closed-form solutions are obtained for the transient and steady temperature distribution within the cooling tower. Under steady-state conditions, a mathematical criterion is derived to obtain the proper length of the cooling tower that is sufficient to ensure complete cooling for the hot water stream.

Journal ArticleDOI
TL;DR: In this article, a numerical simulation of two-dimensional laminar natural convection in a fully open tilted square cavity with an isothermally heated back wall is conducted, where the remaining two walls of the cavity are adiabatic.
Abstract: A numerical simulation of two-dimensional laminar natural convection in a fully open tilted square cavity with an isothermally heated back wall is conducted. The remaining two walls of the cavity are adiabatic. Steady-state solutions are presented for Grashof numbers between 102 and 105 and for tilt angles ranging from 60 to 90 (where 90 represents a cavity with the opening facing down). The fluid properties are assumed to be constant except for the density variation with temperature that gives rise to the buoyancy forces, which is treated by the Boussinesq approximation. The fluid concerned is air with Prandtl number fixed at 0.71. The governing equations are expressed in a normalized primitive variables formulation. Numerical predictions of the velocity and temperature fields are obtained using the finite-volume-based power law (SIMPLER: Semi-Implicit Method for Pressure-Linked Equations Revised) algorithm. For a vertical open cavity (alpha = 0 deg), the algorithm generated results that were in good agr...

Journal ArticleDOI
TL;DR: In this article, a simple and accurate thermodynamic model for a four-heat-reservoir, absorption chiller is presented, which is expressed in terms of the dominant external and internal losses that stem from the finite-rate heat transfer and internal entropy generation.
Abstract: A simple and accurate thermodynamic model is presented for a four-heat-reservoir, absorption chiller. The performance of chillers, as described by 1/COP , is expressed in terms of the dominant external and internal losses that stem from the finite-rate heat transfer and internal entropy generation in the absorber, condenser, generator, and evaporator. It is found that the relative contributions from these losses of absorption chillers govern their behavior over a wide range of cooling capacities. The successful formulation of the thermodynamic model, as presented in this article, implies that all previous endoreversible approaches are inadequate because they cannot portray the real behavior of absorption chillers accurately. At best, these models give only the upper bounds of experimental realities and thus they can be viewed only as subsets of the generic thermodynamic approach described here. To this end, we present evidence from an experimental facility to show that true absorption chiller behavior is ...

Journal ArticleDOI
TL;DR: In this paper, a comparison of three-dimensional computational fluid dynamics simulation, HEATX, for E-type shell-and-tube heat exchangers with experimental data and other existing calculation methods is presented.
Abstract: A comparison is presented of a three-dimensional computational fluid dynamics simulation, HEATX, for E-type shell-and-tube heat exchangers with experimental data and other existing calculation methods. The comparison reveals that HEATX simulations perform consistently well across different geometries and operating conditions, with values for overall pressure drop within 10% of the measured ones. HEATX is more accurate than the other prediction methods but at a higher computational cost.

Journal ArticleDOI
TL;DR: In this paper, the transient temperature response of a convective-radiative rectangular profile annular fin under a step temperature change occurring in its base is considered, and the nonlinear transient heat transfer and boundary conditions are solved by using the hybrid method of Taylor transformation and finite difference approximation.
Abstract: This article presents the transient temperature response of a convective-radiative rectangular profile annular fin under a step temperature change occurring in its base. A convection-radiation fin tip is considered. The nonlinear transient heat transfer and boundary conditions are solved by using the hybrid method of Taylor transformation and finite-difference approximation. Also, time domain is controlled by Taylor transformation, and the spatial coordinates are handled by finite-difference approximation. Temperature distribution is implemented by employing natural cubic spline fitting.

Journal ArticleDOI
TL;DR: In this paper, an empirical correlation for the local peripheral average heat transfer coefficient with an absolute average deviation of 9.9% was developed for laminar flow with the presence of a U-bend.
Abstract: For horizontal flow in the laminar flow regime, the interaction between natural and forced convection and the effect of the secondary flow induced by an unheated U-bend were considered in developing an empirical correlation for the nearly uniform heat flux condition. The correlation predicts the local peripheral average heat transfer coefficient with an absolute average deviation of 9.9%. In this article the mechanisms involved in laminar flow with the presence of a U-bend are explained. The realistic behavior of the correlation is illustrated. Also, a brief discussion of some of the existing correlations for laminar flow is presented. Four cases showing the practicality of using the correlation in the design of horizontal double-pipe heat exchangers are demonstrated.

Journal ArticleDOI
TL;DR: In this article, the average heat transfer coefficient inside the cyclone separator of a circulating fluidized bed (CFB) for different operating parameters, viz., solid circulation rate, gas superficial velocity, and pressure drop, was investigated.
Abstract: Effect of fins on the average heat transfer coefficient inside the cyclone separator of a circulating fluidized bed (CFB) for different operating parameters, viz., solid circulation rate, gas superficial velocity, and pressure drop, has been investigated. The cyclone separator is an integral part of a CFB and is specially fabricated according to the high-efficiency Lapple design [1] to accommodate two identical heat transfer probes in series. For the same operating conditions, the incorporation of fins results in a drop of heat transfer coefficient, but the total heat transfer increases with the increased surface area, more than compensating for this drop. It is also observed that the heat transfer coefficient increases linearly with the increase of solid circulation rate, gas superficial velocity as well as pressure drop. The collection efficiency of the cyclone separator is found to decrease with increase in solid circulation rate as well as with the pressure drop. It is also noted that the collection e...

Journal ArticleDOI
TL;DR: Explicit approximations for determining the roots of the transcendental equations arising in the series solutions for one-dimensional transient conduction with one convection and one adiabatic boundary condition are presented for rectangular, spherical, and cylindrical coordinate systems as discussed by the authors.
Abstract: Explicit approximations for determining the roots of the transcendental equations that arise in the series solutions for one-dimensional transient conduction with one convection and one adiabatic boundary condition are presented for rectangular, spherical, and cylindrical coordinate systems The method is described for the case of rectangular coordinates so that it can be applied to other coordinate systems, or other combinations of boundary conditions The error in the root from using the explicit approximations is examined, along with the resulting error in the calculated dimensionless temperature

Journal ArticleDOI
TL;DR: In this article, the authors present the results of the application of a quite simple method for analyzing shell-side fouling in shell-and-tube exchangers, capable of taking into account the formation of irregular fouling deposits with variable thermal conductivity.
Abstract: This article presents the results of the application of a quite simple method for analyzing shell-side fouling in shell-and-tube exchangers, capable of taking into account the formation of irregular fouling deposits with variable thermal conductivity. This method, based on the utilization of elementary heat exchangers, has been implemented for E-shell TEMA-type heat exchangers with two tube passes. Several fouling deposit distributions have been simulated so as to ascertain their effects on the heat transfer rate. These distributions consider that fouling is concentrated in zones where the temperature of the fluids is maximum or minimum.

Journal ArticleDOI
TL;DR: In this article, a model describing the transient thermal behavior of an insulated electric wire is presented, where the transient temperatures in both conductor and insulator result from the energy generated in the conductor by means of an alternating electric current that fluctuates in any specified manner.
Abstract: A model describing the transient thermal behavior of an insulated electric wire is presented. The transient temperatures in both conductor and insulator result from the energy generated in the conductor by means of an alternating electric current that fluctuates in any specified manner. The mathematical model is solved analytically using Green's function method. The effect of many parameters on the transient thermal behavior of the insulated wire is described. The cooling rate from the wire is evaluated at different values of the insulation thickness, and then the effect of different parameters on the critical thickness of insulation is investigated.

Journal ArticleDOI
TL;DR: In this article, a method of arriving at an optimum design of the plate heat exchanger and the corresponding terminal heat radiators in a geothermal heating system is proposed, and a comparison is made between the results of the optimized design and those by the conventional design.
Abstract: Plate heat exchangers and terminal heat radiators usually take a major initial capital investment in a low-temperature geothermal heating project. In this article, a method of arriving at an optimum design of the plate heat exchanger and the corresponding terminal heat radiators in a geothermal heating system is proposed. A comparison is made between the results of the optimized design and those by the conventional design. The effects of the configuration and some parameters of plate heat exchangers on the design results are discussed. Emphasis is also given to how to obtain the best operation status while a geothermal well is producing at constant flow rate and wellhead temperature.

Journal ArticleDOI
TL;DR: In this article, a multiplicator of heat flux was introduced to calculate the total heat flux of finned tube banks in a tubular fired heater convective section, based on radiative coefficients.
Abstract: For more exact calculation of combined heat transfer in the case of finned tube banks (e.g., in the convective section of a furnace), the radiative heat transfer cannot be neglected. A new method for relatively simple calculation of total heat flux (convection + radiation + conduction in fins) is fully compatible with that for bare tube banks/bundles developed earlier. It is based on the method of radiative coefficients. However, the resulting value of heat flux must be corrected due to fin thickness and especially due to the fin radiative influence. For this purpose the so-called multiplicator of heat flux was introduced. The applicability of this method has been demonstrated on a tubular fired heater convective section. A developed computer program based on the method has also been used for an analysis of the influence of selected parameters to show the share of radiation on the total heat flux.

Journal ArticleDOI
TL;DR: In this paper, an algorithm is presented for the design and simulation of multieffect evaporators, with forward or backward feed, based on the elimination of an unknown, namely the product stream flow rate, for simulation in the balances set by assuming a given product concentration and the reduction of the heat transfer rate equations set by elimination of the corresponding equation.
Abstract: An algorithm is presented for the design and simulation of multieffect evaporators, with forward or backward feed. The mass and enthalpy balances and the heat transfer rate equations poses around each effect are linearized as suggested by Lambert et al., but a new iterative scheme is proposed to ensure convergence and stability when the solution boiling-point rise is considered. Boiling-point rise can reduce the thermal driving force significantly, leading to important errors in the calculation. The algorithm is based on the elimination of an unknown, namely, the product stream flow rate, for simulation in the balances set by assuming a given product concentration and the reduction of the heat transfer rate equations set by elimination of the corresponding equation. The simulation problem is thus converted into a design that can be solved by known numerical methods rendering the required area. If that is not available, the calculation is repeated assuming a new product composition, selected by a criterion presented here, until convergence on the actual area is attained.

Journal ArticleDOI
TL;DR: In this article, the authors discuss the various correlations that are available for predicting the thermal-hydraulic performance of turbulent flows in enhanced tubes, including pressure drop and heat transfer correlations.
Abstract: A number of investigators have carried out studies on enhanced tubes, leading to better understanding of their thermal hydraulic characteristics. The variables considered in these investigations include the ''design'' parameters, namely, height, pitch, and helix angle of the rib, and the tube diameter, and ''flow'' variables such as the Reynolds number and the Prandtl number. The pressure drop and heat transfer correlations needed for prediction of the performance of ribbed tubes can be developed using either an analogy approach or an empirical technique. These two methods are explained, along with the many correlations that have been developed based on them. The numerous studies pose a dilemma for the designer in selecting the most appropriate correlation. This article outlines the various correlations that are available for predicting the thermal-hydraulic performance of turbulent flows in enhanced tubes. Specific correlations that are valid for particular enhancement types as well as general correlatio...

Journal ArticleDOI
TL;DR: In this article, the optimum design of a radiating radial fin of trapezoidal profile is presented in the form of simple correlations and the base thickness and the length of the fin can be easily determined from the given data of heat dissipation, thermal conductivity, emittance, base radius, base temperature, and environment temperature.
Abstract: This article presents the optimum design of a radiating radial fin of trapezoidal profile. Optimum parameters for rectangular and triangular profiles are given in the form of simple correlations. Using these, the base thickness and the length of the fin can be easily determined from the given data of heat dissipation, thermal conductivity, emittance, base radius, base temperature, and environment temperature.

Journal ArticleDOI
TL;DR: In this article, a novel method for analyzing the heating of coal particles in a coal powder-laden jet in the near-burner region is proposed, taking into account both the time delay due to coal particle unsteady heating and the induction period needed for the coal particle to ignite from the practical engineering point of view.
Abstract: A novel method for analyzing the heating of coal particles in a coal powder-laden jet in the near-burner region is proposed. This method takes into account both the time delay due to coal particle unsteady heating and the induction period needed for the coal particle to ignite from the practical engineering point of view. A review of the flow and heating of coal particles is presented. The principle and analysis procedures for estimating the ignition heat and the heat balance are outlined. The advantage of the proposed method over the previous analyzing method which is based on the steady-state heat balance is also discussed. The influencing trends of various factors on the results are calculated and drawn in a group of diagrams. The calculating procedure is demonstrated by using an industrial swirl burner as data source. The predicted hot gases recirculating ratio is in general agreement with the measurements on the physical model. This study offers a useful reference in engineering practice for improving burner design and performance.

Journal ArticleDOI
TL;DR: In this article, the authors compare the early theoretical solutions for the condensation of multicomponent vapors with recent, as well as older, experimental data and propose possible modifications to the theories to obtain a better approximation method to handle more complex mixtures.
Abstract: The prupose of this article is to compare the early theoretical solutions for the condensation of multicomponent vapors with recent, as well as older, experimental data and to propose possible modifications to the theories to obtain a better approximation method to handle more complex mixtures. To understand the complex process for condensing multicomponent vapors, we will describe the process starting with the simplest case

Journal ArticleDOI
TL;DR: In this paper, the effects of the power transient on critical heat flux (CHF) and maximum heat flux correlations in transient boiling systems with a countercurrent flow between the liquid and vapor flow were investigated.
Abstract: The objectives of this study are to investigate the effects of the power transient on critical heat flux (CHF), and to develop CHF and maximum heat flux (MHF) correlations in transient boiling systems with a countercurrent flow between the liquid and vapor flow. The test section consists of narrow, vertical, rectangular channels between parallel plates. Rate of change of wall temperature at the CHF point, (dTw/dt)CHF, and a nondimensional transient parameter, kappao =(L2/alphafTsat) (dTw/dt) CHF are introduced to evaluate the effects of power transients on CHF and MHF. Experimental ranges were 738.0-1,968.0 kg/m2s for mass flux, 7.0-17.5 C for inlet subcooling, and 3.0-8.0 mm for channel gap distance. The system pressure was kept constant at 1.0 atm. The experimental results show that CHF and MHF values increase with an increasing rate of change of wall temperature, and the increasing rate of CHF is higher in a wider channel gap distance. CHF and MHF increase linearly with increasing mass flux at the top ...