Showing papers in "Heat Transfer Engineering in 1981"

The Evolution of Enhanced Surface Geometries for Nucleate Boiling

Abstract: This paper surveys the evolution of special surface geometries that promote high-performance nucleate boiling. Early work by Jakob and Fritz in 1931 showed that emery paper roughening or machined grooves provided only temporary performance increase. However, this improvement dissipated after a few days to the flat surface value. There was little sustained interest in this unique, but apparently unuseful, phenomenon until the mid-1950s. During the period 1955-1965, supporting fundamental studies of the character and stability of nucleation sites provided a basis for renewed efforts to develop a high area density of stable, artificially formed nucleation sites whose performance does not deteriorate with time. Beginning in 1968 industrial research produced patented technology that achieved the long-sought goal. In 1980 at least six high-performance nucleate boiling surfaces were commercially available. The technology reported in this paper represents a dramatic advance in the field of heat transfer.

Influence of Fouling Biofilms on Heat Transfer

Abstract: In heat exchange equipment, fouling biofilm formation causes a significant energy loss by increasing heat transfer resistance. This paper describes experiments which quantify the influence of fouling biofilms on heat transfer resistance under controlled laboratory conditions. Experimental results compare well with a rather simple mathematical model employing friction factor, biofilm thickness, wall temperature, bulk temperature, and fluid properties as inputs. Limitations of the experimental apparatus and mathematical model are discussed

Heat Transfer Coefficients and Pressure Drops for Air Coolers with Different Numbers of Rows Under Induced and Forced Draft

Abstract: Tests are described on a pilot plant simulating an air-cooled heat exchanger that can be operated in both the induced-draft and forced-draft modes. Heat transfer coefficients in the induced-draft mode were well correlated, for greater than six rows, by the Briggs and Young correlation; for smaller numbers of rows, a new correlation is presented. In the forced-draft mode, however, none of the literature correlations fit the data and two new correlations (for more than six rows and for less than six rows, respectively) are presented. Data were also obtained for pressure drop and these are compared with existing correlations. Two new pressure-drop correlations are presented for the forced-draft mode.

Heat Transfer and Pressure Drop Characteristics of Finned Tubes in Cross Flow

Abstract: Finned tubes in various configurations with the same fin geometry (height, thickness, and pitch) were tested in five row tube banks in staggered and aligned arrangements. Measurements on heat and flow characteristics and flow pattern observation have shown that the semicircular finned tube has excellent characteristics as an evaporator tube for waste heat boilers because of its low pressure drop, high heat transfer coefficient, and reduction in dryout risk.

The Influence of Improved Physical Property Data on Calculated Heat Transfer Coefficients

Abstract: Heat transfer coefficients calculated from accepted correlations, but using physical properties derived from different sources, are compared with experimentally determined local heat transfer coefficients. In all cases, consistent, accurate property data yield more accurate estimates of the heat transfer coefficients.

Thermal Energy Storage for Solar Power Generation: State of the Art

Abstract: High temperature storage for applications in solar-thermal electric systems is considered. Noting that thermal storage is in either the form of latent, sensible or chemically stored heat, sensible heat storage is stressed as the most developed of the thermal storage technologies, spanning direct heating of a storage medium from 120-1250 C. Current methods involve solids, packed beds, fluidized beds, liquids, hot water, organic liquids, and inorganic liquids and molten salts. Latent heat storage comprises phase-change materials that move from solid to liquid with addition of heat and liquid to solid with the removal of heat. Metals or inorganic salts are candidates, and the energy balances are outlined. Finally, chemical heat storage is examined, showing possible high energy densities through catalytic, thermal dissociation reactions.

Research needs in low Reynolds number flow heat exchangers

Abstract: Low Reynolds number flows prevail in some process, power, automotive, aircraft, and other industrial heat exchangers such as shell-and-tube, plate, and compact heat exchangers. Laminar or low Reynolds number turbulent flows are the results of either high viscosity fluids, compact flow passages (i.e., small hydraulic diameter), or low fluid velocities. Significant advancements have been made in the past 100 years in understanding and predicting flow and heat transfer in such internal flows. This paper summarizes the research needs to further advance the science of low Reynolds number flow heat exchangers. Emphasis is primarily given to the thermal design aspects; research needs related to mechanical design, manufacturing, material selection, and other nonthermal design aspects are not covered. Also the coverage is restricted primarily to single-phase applications. The outlined research needs are based on the input from invited lecturers and some participants, experts in the field, at the Fourth NATO Advanc...

Multizone Condensers: Desuperheating, Condensing, Subcooling

Abstract: This article examines the design of multizone condensers. It also marks the first published discussion of the existence of a “wet desuperheating zon” in every multizone condenser with a “dry desuperheating zone. ’Considered in this discussion are only single component vapors in shell-and-tube heat exchangers with single shell-side pass

A Comparative Assessment of RODbaffle Shell-and-Tube Heat Exchangers

Abstract: The shell-and-tube heat exchanger (SBE), with its tubes held in plate baffles to produce cross flow of the shell-side fluid, has recently been modified to produce a RODbaffle heat exchanger (RBE) free from tube failure due to vibration. The results showed slightly enhanced heat transfer coefficients with significant reductions in pressure loss, leading to reduced cost of exchangers and in some instances smaller exchangers.

The Potential for Development in Heat Exchanger Plants

Abstract: The potential for the overall optimization of heat exchanger systems for process plants is considered. By using a more systematic approach, considerable savings in energy and capital may be possible. The next section of the paper deals with the scope for improvement of existing heat exchanger designs with particular reference to shell-and-tube heat exchangers and tube-in-plate heat exchangers. In the future, there is likely to be an increasing trend toward modularization and examples cited here are those of the plate exchanger and the heat pipe heat exchanger. Perhaps the most important unsolved problem is that of heat exchanger fouling and this area is discussed next. Costs of fouling in the U.K. are likely to be in the range of £300M to £500M☆ per annum. A number of research tools are becoming available for the study of heat exchange systems and two of these (namely electrochemical analogue techniques and numerical flow modeling) are reviewed in the final section of the paper.

On the Necessary Criteria for Stream-Symmetric Tubular Heat Exchanger Geometries

Abstract: The basic criteria are derived in determining whether the heat transfer relationship for a given heat exchanger geometry is invariant to the interchanging of shell-side and tube-side fluids. It is shown that the total heat duty, LMTD correction factor, and other indices of exchanger performance remain unchanged for a stream-symmetric exchanger when the two flow streams are switched, provided the overall heat transfer coefficient is not changed.

The Cartridge Heat Exchanger: A New Concept for Difficult Services

Abstract: A new concept in the design of heat exchangers has been developed and is now in production. This paper outlines the generic design concept of the cartridge heat exchanger.

Large-scale Heat Transfer Research and Testing

Abstract: Large-scale research and testing in the area of energy conversion become a fundamental necessity during the current national effort to commercialize proven processes that have been dormant for many years. A recent example of such necessity is the on-site use of a 1-MWe ocean thermal energy conversion (OTEC) system where ocean temperatures are suitable for energy extraction. Other experimental examples are the coal liquefaction plants currently under construction, as well as many first-of-their-kind syngas systems and “combined cycle“power-generating loops. The large investment in such research design and development projects is further extended by the cost of operation, where budget limitation may force the preclusion of certain test objectives or the premature termination of ongoing test programs. To reduce the probability of such happenings, optimal test programs need to be devised and implemented. This article deals with various aspects of such testing optimization. It is hoped that some of the stated ...

A New Look at the Old Problem of Altitude Derating of Air-cooled High-Power Broadcast Tubes

Abstract: An analysis is presented of the effect of altitude on heat transfer from an RCA 8807 power tube. Results of this analysis are included along with a comparison with existing data. A generalization of the results is presented as is a method that allows the design engineer to make use of the results in new and existing transmitter designs.

Application of a Honeycomb Insulator Design in a Variable High-Temperature, High-Pressure Environment

Abstract: Structural heat transfer problems (heat addition and loss) encountered in small-scale experimental facilities used in the nuclear safety research industry are reviewed. The influence of excess structural heating or cooling on small-scale facility test results relative to expected reactor performance during loss-of-coolant accidents or off-normal transient response is addressed. The design and construction of an evacuated honeycomb canister insulator and its thermal performance during steady state and transient reactor safety related experiments are discussed.