Showing papers in "Heat Transfer Engineering in 1980"

Heat Transfer Performance of Internally Finned Tubes in Turbulent Flow

Abstract: The heat transfer performance for heating water in turbulent flow was experimentally determined for II tubes having integral internal spiral and longitudinal fins. Eight of these tubes were previously tested with air and results have previously been reported. Individual tube performance is presented and compared with a smooth tube datum at constant pumping power. A longitudinal and spiral fin tube from within the II tubes and a smooth tube were also tested heating a 50% w/w ethylene glycol-water solution, and these data are included. These data are compared with relevant data available in the literature. Correlating equations are presented for heat transfer and Fanning friction factor that describe the air, water, and ethylene glycol-water data within ± 10%

Air-Side Heat Transfer in Finned Tube Heat Exchangers

Abstract: Because of the low heat transfer coefficient of gases, it is necessary to use extended surfaces on the gas side when exchanging heat with liquids or two-phase fluids. Such finned tube exchangers are a very important basic class of heat exchangers. Although finned tube exchangers have been in existence for 50 yr, there have been numerous developments in the technology. This paper attempts to survey the recent developments related to the air-side aspects of heat exchanger design. Nearly all of the recent developments have been empirical because of the complicated gas-side flow structure. Among the developments discussed are the use of special surface geometries for enhanced heat transfer, row effects, local heat transfer coefficient distribution, and correlations for heat transfer coefficient and pressure drop. Two important design configurations—circular finned tubes and plate fin designs—are considered separately.

Critical Review of Correlations for Predicting Two-Phase Flow Pressure Drop across Tube Banks

Abstract: Published correlations for predicting the two-phase flow pressure drop across ideal tube banks are reviewed and compared with experimental data. No presently available methods can be considered general enough for use under all conditions. The Martinelli-type method used for tube-side pressure drop correlation appears to be a basically usable approach if correspondingly modified. All available data are reasonably well represented in terms of the Martinelli parameters at low liquid loading (Xtt small). At high liquid loading ( Xtt large) there is increasing scatter and additional parameters are needed. Substantial improvement is believed to be possible by adjustment of the Martinelli model through recognition of the different flow regimes.

Tube-Side Heat Transfer and Pressure Drop for Tubes Having Helical Internal Ridging with Turbulent/Transitional Flow of Single-Phase Fluid. Part 2. Multiple-Helix Ridging

Abstract: An experimental investigation was conducted of the tube-side behavior of various internal configurations with turbulent/transitional flow of water in the Reynolds number range 10,000-120,000 and Prandtl number range 2-11. By using a heat-momentum transfer analogy, correlations were obtained that enable practical designs with standard products or optimization of tube geometry for specific conditions.

The Accident at Three Mile Island

Abstract: On March 28, 1979, what has been called the worst accident in the history of commercial nuclear power generation occurred at the Three Mile Island no 2 reactor unit in Pennsylvania The sequence of events that occurred during the first 16 h of the incident are described There was extensive damage to the core of the reactor as well as some release of gaseous fission products from the station However, the radiation doses received by the general public as a result of exposure to this released radioactivity were so small that there will be no detectable adverse health effects Nevertheless, the accident at Three Mile Island will have a profound effect on commercial nuclear power in the United States and throughout the world

Cooling Water Fouling in Plate Heat Exchangers

Abstract: Heat exchangers using cooling water are designed with fouling resistance applicable to tubular equipment, in most cases TEMA recommended values. Plant experiences indicate that plate heat exchangers produce substantially lower fouling rates due to turbulence induced by the plate corrugations. Furthermore, plate exchangers are more severely penalized by fouling resistance than tubular exchangers because of the high heat transfer coefficients typical of plate exchangers. To supply reliable folding data to the designer, APV Company. Ltd. sponsored a research project to study fouling in plate exchangers with Heat Transfer Research. Inc. (HTRI). The test fluid was a typical, treated cooling-tower water. Results of these experiments, described in this paper, show that at typical operating conditions the fouling resistances for plate exchangers are substantially lower than those used for tubular equipment.

Fundamental mechanisms that influence the estimate of heat transfer to gas turbine blades

Abstract: The quest for improved efficiency has motivated the elevation of turbine inlet temperatures in all types of advanced aircraft gas turbines. The accommodation of higher gas temperatures necessitates complex blade cooling schemes so as not to sacrifice structural integrity and operational life in advanced engine designs. Estimates of the heat transfer from the gas to stationary (vanes) or rotating blades poses a major uncertainty because of the complexity of the heat transfer processes. The gas flow through these blade rows is three-dimensional with complex secondary viscous flow patterns that interact with the end walls and blade surfaces. In addition, upstream disturbances, stagnation flow, curvature effects, and flow acceleration complicate the thermal transport mechanisms in the boundary layers. Some of these fundamental heat transfer effects will be discussed. The chief purpose of this paper is to acquaint those in the heat transfer community, who are not directly involved in gas turbines, with the ser...

Flow Patterns for Isothermal Condensation in One-Pass Air-Cooled Heat Exchangers

Abstract: An analytic method is developed to describe the flow in each row of tubes of an air-cooled one-pass isothermal condenser. This leads to a better understanding of some common steam condenser problems, including freezing of condensate, rapid tube-side corrosion, and worse performance than predicted by any reasonable condensing coefficient. The NTU approach is used to derive expressions for pressure drop in each row in terms of exchanger effectiveness. The resulting simultaneous equations are solved numerically, and the solutions, presented graphically, show the flow pattern to be solely a function of effectiveness. For steam condensers contaminated by traces of air, it is found that air pockets will develop inside the tubes of the lower rows, blanketing the surface and preventing condensation. Several designs are described that attack the problem of noncondensable accumulation, including the most recent developments in the air-cooled condenser field.

Performance of Counterflow, Parallel Plate Heat Exchangers under Laminar Flow Conditions

Abstract: Multilayered heat exchangers were analyzed theoretically and their heat transfer characteristics were clarified. The problem was treated as a two-dimensional, conjugated one with three phases-two fully developed laminar flows and the exchanger wall. From numerical results, the exchanger effectiveness was found to be definitely influenced by the following parameters: Graetz number, heat capacity flow rate ratio, dimensionless wall thickness, and conductance ratios between fluid and wall and between both fluids. Examination of mixed-mean temperature distributions in the exchanger showed that longitudinal wall conduction significantly reduces exchanger effectiveness in the low-Graetz-number region. Experimental results were in fairly good agreement with theoretical predictions.

A General Predictive Technique for Heat Transfer during Saturated Film Boiling in Tubes

Abstract: A simple predictive technique for heat transfer during film boiling in tubes is presented. This technique is based on the two-step model and consists of a graphic correlation for nonequilibrium quality and an equation for liquid droplet cooling at high pressures. It has been developed from and verified with data for water, nitrogen, para-hydrogen, R-113, methane, and propane. The range of data includes equilibrium qualities from 0.1 to 2.9, pressures from 1.4 to 215 bar, reduced pressures from 0.01 to 0.97, mass flux from 30 to 3442 kg/m2 s, tube diameters from 2.5 to 14.9 mm, heat flux from 0.012 to 2.1 [Macute]W/m2, and wall temperatures from 81 to 1112 K. For all 722 data points analyzed, heat transfer coefficients based on actual vapor temperatures are correlated with a root-mean-square error of 15%.

The Energy-saving NESTS Concept

Abstract: The NESTS concept (an acronym for Neoteric Endo-Stratiformed Tube Supports) consists of a device and a method for supporting heat exchanger tubes. The device is particularly suited, but not necessarily limited, to triangular pitch tube patterns having maximum TEMA-allowed densities. Because the basic device offers minimal interference to a heat exchanger's shell-side fluid flow, significant energy savings are possible.

Heat Transfer in a Scraped-Wall, Continuous Unit

Abstract: The effect of the use of scrapers on the film heat transfer coefficient was investigated. Experimental runs were conducted in liquid-full, continuous-flow heat exchangers of commercial size, with a 6-in. ID and 6-ft length. Three test fluids were used: two petroleum lube fractions and corn syrup. Flow rates were varied from 0.8 to 5.8 gpm and the scraper speed from 0.5 to 25 rpm. The data collected were utilized in developing a design correlation in the laminar regime (Rer < 150). The correlation obtained for heating and cooling was Nu = 57 Ref 0.059 Rer 0.113 Pr0.063 Visr−0.018, for 0.0016 < Ref < 9.23 and 0.0164 < Rer < 68.65. A possible flow pattern in the heater was suggested to explain the relative ineffectiveness of scraping for improving the film coefficient for heating very viscous fluids in liquid-full heat exchangers. Comparison of the experimentally obtained film coefficient with those predicted by the penetration theory model indicate that this model is unsuitable for predicting the coefficien...

Free convection heat transfer from the outside of radial fin tubes

Abstract: Heat transfer rates for a variety of finned tubes in water and asphalt-water emulsion were determined experimentally. From these data, free convection heat transfer coefficients on the outside of the tube were calculated as a function of the Rayleigh number. A correlation of the form Nu = C1(Ra)C2 was then determined by a least-squares fit of the data.

Flow-induced Tube Vibration Data Banks for Shell-and-Tube Heat Exchangers

Abstract: Flow-induced tube vibration in shell-and-tube heat exchangers has resulted in tube failure that has caused industrial plants and power stations to be shut down for costly repairs. As a result, possible flow-induced tube vibration problems have joined thermal, hydraulic, and mechanical design considerations. There have been few vibration research studies made with actual shell-and-tube heat exchangers. Most tests have been made with ideal tube banks, and there is a serious question as to whether the methods developed from these tests apply to the complex geometry in a shell-and-tube heat exchanger. Although not providing the best solution, data banks of field experience offer a practical way of evaluating proposed methods for predicting vibration problems. This paper follows the evolution of various data banks, discusses the essential need for vibration data banks, notes the difficulties in collecting and using their content, and describes the latest project to develop the new DOE/ANL/HTRI Heat Ex...

Three Mile Island: A Call for Fundamentals and Real-Time Analysis

Abstract: The fundamental heat transfer processes that occurred during the Three Mile Island unit 2 accident are reviewed. Emphasis is placed on the elements that might have been overlooked during the design and operation of the power plant.

An Engineering View of Wind Chill

Abstract: The hazard of frostbite when low air temperatures are combined with high winds is made quantitative by the wind chill concept. The original treatment of the experimental data used a one-film model with a constant surface temperature. A two-film model is more satisfactory because a critical surface temperature at which frostbite might occur can be predicted.

A History of Steam Surface Condensers for the Electric Utility Industry

Abstract: At the session entitled History and Evolution of Heat Exchanger Equipment and Standards at the ASME/AIChE 18th National Heat Transfer Conference, San Diego, California, August 6-8, 1979, various segments of the history of heat transfer devices were discussed by engineers who had themselves played significant roles in that history. Because of time, topics were limited to those involving shell-and-tube exchangers. One of these historical studies, Joe Sebald's history of the surface condenser, is presented in this issue. It provides an excellent record of the evolution of the modern surface condenser, which is in fact a spectacularly large, fixed, tube sheet shell-and-tube unit. The history of other types of heat transfer apparatus, as well as shell-and-tube exchangers, will appear in this column in future issues.