Showing papers in "Heat Transfer Engineering in 1989"
TL;DR: In this article, the authors summarized some of the insights and experience discussed during a recent symposium on this subject and concluded that maldistribution of flow should not normally be a problem in single-phase heat exchangers where good engineering practice is pursued.
Abstract: Maldistribution of flow in heat exchangers may have dramatic consequences on thermal and mechanical performance. This article summarizes some of the insights and experience discussed during a recent symposium on this subject. The paper concludes that maldistribution of flow should not normally be a problem in single-phase heat exchangers where good engineering practice is pursued. However, two-phase flow heat exchangers still pose a formidable challenge if poor performance resulting from maldistribution of flow is to be avoided.
57 citations
TL;DR: In this paper, the authors investigated the effect of mixtures on the nucleate boiling contribution to flow boiling inside vertical tubes at low vapor qualities, operating conditions typical of vertical thermosyphon reboilers.
Abstract: The present study has investigated the effect of mixtures on the nucleate boiling contribution to flow boiling inside vertical tubes at low vapor qualities, operating conditions typical of vertical thermosyphon reboilers. The mass diffusion process created by the composition difference between the vapor and liquid phases was found to impede the boiling process and substantially reduce the nucleate boiling heat transfer contribution to flow boiling in mixtures. Two widely quoted flow boiling mixture correction factors were tested against a published set of experimental data for ethanol/cyclohexane mixtures and were determined to be only partially reliable. Instead, several theoretically based nucleate pool boiling mixture correlations were shown to be accurate for flow boiling conditions and are recommended for design use.
33 citations
TL;DR: In this article, the influence of the above parameters on the asymptotic fouling resistance is discussed, and measured values of fouling resistances are compared with results for a double-pipe heat exchanger and with the prediction of a fouling model from the literature.
Abstract: Particulate fouling in an Alfa-Laval P20 plate heat exchanger was investigated using a suspension of aluminum oxide particles in heptane. Process parameters such as flow velocity, heat flux, and particle concentration were varied over a considerable range. In this paper, the influence of the above parameters on the asymptotic fouling resistance is discussed. Measured values of fouling resistance are compared with results for a double-pipe heat exchanger and with the prediction of a fouling model from the literature.
21 citations
TL;DR: In this article, high-speed cinephotography was used to measure drop size and velocity, and the velocity values used in the correlation of heat transfer data were averaged over the time traveled by individual droplet.
Abstract: The rates of heat transfer to individual droplets of liquid nitrogen falling freely in air were measured under different air temperatures similar to the conditions in a cryogenic freezing system. High-speed cinephotography was used to measure drop size and velocity. Experimental results of heat transfer rates to individual droplets were analyzed and the data were compared to those obtainable using other types of dimensionless correlations. Droplets of initial size range investigated ( 2.5-0.72 mm diameter) attained terminal velocities at distances of 4-6 cm freefall away from the drop generator tip. The velocity values used in the correlation of heat transfer data were averaged over the time traveled by individual droplet.
15 citations
TL;DR: In this article, the authors deal with effectiveness-NTU relations for crossflow heat exchangers and propose algebraic relations for two limiting cases: unmixed and mixed flows, which will yield performance between the above limiting cases.
Abstract: This paper deals with effectiveness-NTU relations for crossflow heat exchangers. The literature contains algebraic relations for two limiting cases: “unmixed” and “mixed” flows. These are simply thermodynamically defined limiting cases. The authors argue that many practical flow situations may not satisfy either of the above cases. Rather, conditions of “partial mixedness” may exist, which will yield performance between the above limiting cases. Algebraic relations are provided to calculate the effectiveness-NTU relationship for arbitrary values of partial mixedness. Graphs are provided for 25, 50, and 75 % mixedness. It is argued that inadequate knowledge of the actual flow structure exists to define the actual mixedness that will occur in various actual heat exchanger-surface geometries. Definition of the actual mixedness would require measurement of the spatial temperature distribution leaving the heat exchanger. The problem addressed is of particular importance for high effectiveness designs....
14 citations
TL;DR: In this paper, heat transfer coefficients were measured for the cooling of water or a nonvolatile oil by direct contacting in a packed column, which contained random packing, and separate measurements were made on a number of different types of packing elements.
Abstract: Heat transfer coefficients were measured for the cooling of water or a nonvolatile oil by direct contacting in a packed column. The column contained random packing, and separate measurements were made on a number of different types of packing elements. Volumetric coefficients were correlated by empirical equations as well as by relationships based on a heat transfer/mass transfer analogy. The latter approach proved effective, and it is concluded that the large body of information on packed column mass transfer rates can be directly useful for predicting heat transfer coefficients for direct-contact exchangers.
13 citations
TL;DR: In this paper, heat transfer data and correlations for hydrodynamically developed but thermally developing buoyancy-assisted and -opposed flows of water in vertical annuli at low Reynolds numbers are presented.
Abstract: This paper presents heat transfer data and correlations for hydrodynamically developed but thermally developing buoyancy-assisted and -opposed flows of water in vertical annuli at low Reynolds numbers (Re < 104). Data are for forced and mixed laminar flows, forced transitional and turbulent flows, and natural laminar and turbulent flows. A general correlation of the forced upflow data (Re < 104) is obtained by superimposing the correlations developed for forced laminar and transitional flows: NuF = (Nu9 F.L + Nu9 F.Tr)1/9. Similarly, the data for both the laminar and the mixed laminar flows as well as those for natural laminar flow are correlated by superimposing the correlations developed for forced laminar and natural laminar flows: NuL = (Nu3 F.L + Nu3 N.L)1/3. This correlation is in good agreement with the laminar and mixed downflow data, but with a negative sign for NuN.L Although Nu values for natural laminar flow increased proportionally to Ra0.2 q and those for natural turbulent flow incr...
12 citations
TL;DR: In this paper, the influence of recirculating warm plume air on the performance of mechanical-draft cooling towers is investigated analytically, numerically, and experimentally.
Abstract: The influence of recirculating warm plume air on the performance of mechanical-draft cooling towers is investigated analytically, numerically, and experimentally. It is shown that the amount of recirculation that occurs is a function of the flow and the thermal and geometric characteristics of the tower. The presence of a wind wall tends to reduce the amount of recirculation. An equation is presented with which the performance effectiveness due to recirculation can be evaluated approximately for a mechanical-draft cooling tower.
9 citations
TL;DR: Based on a simplified model, a fully generalized chart has been developed that can readily be applied by users of wet cooling towers, and the predicted values obtained by the presented simplified method are in acceptable agreement both with field tests and with the predictions of far more sophisticated and complex models as mentioned in this paper.
Abstract: Environmental and economic incentives demand an accurate prediction of the behavior of wet cooling towers, including the prediction of evaporation loss as a function of ambient conditions and operational mode. Based on a simplified model, a fully generalized chart has been developed that can readily be applied by users of wet cooling towers. The predicted values obtained by the presented simplified method are in acceptable agreement both with field tests and with the predictions of far more sophisticated and complex models.
9 citations
TL;DR: The Gewa-TX enhanced boiling tube as mentioned in this paper is an improved version of the widely studied GewA-T tube, which was observed to have a boiling performance ranging from about four to ten times that of an ordinary smooth tube operating at the same heat flux and up to 44 times when when compared at different wall superheat.
Abstract: This experimental study reports nucleate pool boiling results for two hydrocarbon mixtures boiling on the new Gewa-TX enhanced boiling tube. This tube is an improved version of the widely studied Gewa-T tube. The new tube was observed to have a boiling performance ranging from about four to ten times that of an ordinary smooth tube operating at the same heat flux and up to 44 times when when compared at the same wall superheat. An example design application shows that the overall heat transfer coefficient for a reboiler evaporating a wide boiling range mixture can be increased to five times that of a conventional plain tube reboiler by use of the Gewa-TX tube.
7 citations
TL;DR: In this article, it was shown that the thermal performance of a particular in-line finned tube bank decreases with row number and reaches about 0.25 to 0.35 of the staggered value with seven tube rows.
Abstract: In-line finned tube banks are preferred for waste heat recovery applications because they can be cleaned with commercially available on-line soot-blowing methods. However, there is some uncertainty about the heat transfer effectiveness of in-line finned tube banks. It is first demonstrated that the outside heat transfer coefficients of in-line finned tube banks are about 0.7 to 0.8 of those of similar staggered banks if the banks are deep and the Reynolds number is large. It is then shown that the thermal performance of a particular in-line finned tube bank decreases with row number and reaches about 0.25 to 0.35 of the staggered value with seven tube rows. Herein lies the uncertainty. New data are also presented, which show that stagnation regions develop in the wakes behind the tubes in the front rows but do not develop deeper in the bundle. The number of tube rows with the stagnation region decreases with increasing Reynolds number. It is apparent, then, that the heat transfer performance of a...
DSM1
TL;DR: In this article, a table of guide values for the fouling resistance has been drawn up based on experiments with cooling water treated by different methods in a semi-iechnical test rig, as well as in a laboratory test rig.
Abstract: On the basis of experiments with cooling water treated by different methods in a semiiechnical test rig, as well as in a laboratory test rig, and from plant operation measurements and literature data, a table of guide values for the fouling resistance has been drawn up.
TL;DR: In this article, the thermal hydraulic characteristics of a double-walled tube steam generator designed for nuclear reactors are presented, along with double-barrier welds for tube-to-tubesheet joints, virtually eliminating the probability of heat transfer tube failure.
Abstract: The thermal hydraulic characteristics of a double-walled tube steam generator designed for sodium-cooled nuclear reactors are presented. The double-walled tube construction, along with double-barrier welds for tube-to-tubesheet joints, virtually eliminates the probability of heat transfer tube failure. Considerations are given to the use of the internal core tube, helical vane swirl generator, external protector tube, and variably perforated flow baffles to improve thermal and hydraulic performance of the steam generator. These thermal hydraulic design features with a particular reference to a 432 MW PRISM steam generator are discussed.
TL;DR: In this article, the authors investigated fluidized beds of dielectric particles as a heat transfer medium for cooling electronic equipment and found that the heat dissipation from a simulated 20-pin flat pack in this fluidized environment was a factor of eight greater than forced convection without particles.
Abstract: We are investigating fluidized beds of particles as a heat transfer medium for cooling electronic equipment. These fluidized beds share several of the attractive qualities of dielectric liquids but employ air rather than liquids in their operation. Experiments in cooling electronic circuit boards by directly immersing them in fluidized beds of dielectric particles have been performed. Heat dissipation from a simulated 20-pin flat pack in this fluidized environment was a factor of eight greater than forced convection without particles. In designs where heat conduction from the component to the circuit board is severely limited, enhancements approaching a factor of 50 are expected.
ALFA1
TL;DR: In this paper, the authors demonstrate that a failure to recognize this difference and thus to select an inappropriate condenser geometry can lead to the catastrophic failure of the unit to perform the anticipated duty.
Abstract: The heat and mass transfer processes taking place within a condenser for a mixture of vapors (total or partial condensation) will differ very significantly depending on whether integral or differential condensation is involved. It will be demonstrated that a failure to recognize this difference and thus to select an inappropriate condenser geometry can lead to the catastrophic failure of the unit to perform the anticipated duty.
TL;DR: In this paper, the effect of heat transfer from a robotic hand to a robotic arm was analyzed using a lumped-capacitance model to find the transient temperature response of the robotic hand.
Abstract: Thermal modeling of a robotic arm equipped with a multifingered robotic hand (end effector) is considered in this paper. The robotic arm is assumed to move its multifingered hand into and out of a high-temperature medium while gripping an object for a pick and place assembly and heat treatment process. If the rate of heat transfer from robotic hand to robotic arm is small, a lumped-capacitance model can be used to find the transient temperature response of the robotic hand. Different models to approximate the effect of thermal coupling between the robotic hand and robotic arm are discussed. To analyze the effect of heat transfer from robotic hand to robotic arm, transient temperature distribution in one dimension of a rod periodically moving into a hot medium is found numerically. The rod is divided into two parts; the first part simulates the robotic hand and second part simulates the robotic arm. Using different thermal parameters and environmental conditions, transient and quasi-steady state t...
TL;DR: To obtain more efficient system designs, it is necessary to accommodate additional integration while preventing system failures, and the first step in achieving this is to identify the failure modes of the system.
Abstract: Heat integration of multiple processes is currently limited by concern over maintaining operability should a change in one or more process streams affect the heat recovery and operation of subsequent units. To obtain more efficient system designs, it is necessary to accommodate additional integration while preventing system failures. The first step in achieving this is to identify the failure modes of the system. This is followed by incorporating measures to prevent the individual failures leading to the failure of the system. Failure modes of a heat recovery system are discussed and suggestions to contain them are presented. Design considerations are also discussed along with factors that increase or decrease heat recovery system reliability.
TL;DR: In this article, future trends in heat transfer for the nuclear industry in Japan are presented, with particular emphasis on the energy problems, contribution of nuclear energy to the primary energy supply, the situation of heat transfer research in relation to nuclear energy, and research subjects in Heat Transfer and fluid flow that are important to the nuclear energy industry in relation with the development of LMFBR, HTGR, and fusion rectors.
Abstract: Future trends in heat transfer for the nuclear industry in Japan are presented. Particular emphasis is given to the energy problems, the contribution of nuclear energy to the primary energy supply, the situation of heat transfer research in relation to nuclear energy, and research subjects in heat transfer and fluid flow that are important to the nuclear industry in relation to the development of LMFBR, HTGR, and fusion rectors as well as the improvement of light water reactors and treatment of radioactive wastes. In conclusion, heat transfer will continue to be important in various fields of the nuclear industry. Since the research subjects summarized here are not limited to the nuclear industry in Japan, this article will be informative to both the industrial and academic communities of heat transfer in the world.
TL;DR: In this article, an equation for the core volume of two-fluid, flat plate, plate fin heat exchangers is put into closed form by using empirical relationships between j Re and f Re3.
Abstract: An equation for the core volume of two-fluid, flat plate, plate fin heat exchangers is put into closed form by using empirical relationships between j Re and f Re3. Fin effectiveness is included, and different core types may be used on the two sides of the exchanger. Although the equation cannot be solved explicitly, the results of an implicit solution for cross-flow cores may be plotted as volume/UA, with pumping power/UA on each side as independent variables. Using an additional fit of) versus Re, face area/flow for each side can be mapped on the same cross-flow plot, and plots for counterflow made. Such plots are useful for quickly indicating the relative volumes and shape of different core types for a given application and for system trade-off studies.