Showing papers in "Heat Transfer Engineering in 1983"

Thinking about Heat Transfer Fouling: A 5 × 5 Matrix

Abstract: Fouling of heat transfer surfaces, which leads to high economic penalties and is still dealt with by heat exchanger designers by the crude TEMA approach, is classified into five principal categories. The measurement of thermal fouling is considered critically, and this is followed by a discussion of the successive events, up to five in number, that characterize most fouling situations. The resulting 5×5 matrix of fouling categories and sequential events illustrates the fact that the fundamental fouling problem has now been mainly resolved, at least for liquid-solid interfaces, although it still remains largely unsolved.

Nucleate Boiling on Porous Coated Surfaces

Abstract: Boiling test results and theoretical evaluations related to predictive models for the boiling coefficient with porous coatings are critically surveyed. Consideration is limited to boiling pure fluids and coatings made of spherical particles of uniform diameter. The data for seven different porous coatings suggest that particle diameter has very little effect on performance. The preferred coating thickness is in the range of three to four particle diameters. Detailed consideration of cavity stability requirements suggests that a dynamic model is needed to rationally predict the boiling coefficient. A modified pore classification is proposed for use in the development of a dynamic model. The assumption and derivation of O'Neill's static boiling model is presented. Its ability to predict the boiling coefficient is evaluated by a comparison with the values predicted by an empirical correlation developed by Nishikawa and Ito.

Costs of Irreversibilities in Heat Exchanger Design

Abstract: An operationally convenient methodology is presented for relating economic costs to entropy generation. This methodology, in the hands of the heat exchanger designer, allows an interaction with the...

Generalized Prediction of Heat Transfer during Subcooled Boiling in Annuli

Abstract: A general correlation for heat transfer during subcooled boiling in tubes was compared with a large amount of varied data for boiling in cylindrical annuli. The data include the fluids water, R-113, and methanol; mass fluxes from 2 78 to 7774 kg/m1 s; heat fluxes from 0.03 to 4.4 MW/m2; liquid subcooling from 2 to 109°C; and reduced pressures from 0.009 to 0.89. The inner tube diameter varied from 4.5 to 42.2 mm and the annular gap from 1 to 6.6 mm. The data include heating of the inner, outer, and both tubes of the annuli. The 450 representative data points from all studies are correlated with a mean deviation of 8.9%.

Thermal Design of Immersion Cooling Modules for Electronic Components

Abstract: Direct immersion of electronic components in low-boiling point, dielectric fluids can provide a benign local ambience and accommodate substantial spatial and temporal power variations while minimizing component temperature excursions and failure rates. Following a review of possible immersion cooling configurations and the thermal mechanisms active in vapor-space and submerged condenser modules, attention is focused on the operational limits and relations for predicting submerged condenser performance. Finally, descriptions of three likely applications of submerged condenser technology are presented.

Time-Dependent Heat Exchanger Modeling

Abstract: A quasi-finite-element model of a multipass shell-and-tube heat exchanger is developed after the method of Gaddis and SchlUnder. The present model includes time-dependent inlet conditions and heat exchange. It is therefore applicable as a tool in system modeling for dynamic processes involving this type of heat exchanger. Under steady-state conditions, the present model reduces to that of Gaddis and SchlUnder.

Application of Gas-Dynamic Functions for Steam Ejector Design

Abstract: The paper outlines application of gas dynamic functions (GDF) for practical design of steam ejectors. Some experimental results on designed ejectors are presented. An extensive table of GDF for saturated steam (k = 1.135) is also included.

Heat Transfer Performance of Metal Fiber Sintered Surfaces

Abstract: Boiling heat transfer performance on stainless steel metal fiber sintered surfaces is experimentally investigated with Freon 11 (Rll) as the working fluid. The boiling heat transfer coefficient for the optimum surface structure gives a tenfold improvement over a smooth surface. The nondimensional specific parameter including all design parameters is introduced to explain the trend of the performance of various kinds of metal fiber sintered surfaces. Moreover, the metal fiber sintered surface clad with titanium film is suggested to be appropriate to an evaporator for Ocean Thermal Energy Conversion (OTEC)system.

Two-phase flow and its applications: Past, present, and future

Abstract: This article presents the three main alternative approaches to the prediction of two-phase flow systems (empirical, analytical, and phenomenological) and explores their advantages and disadvantages. Empirical correlations are the most widely used but have considerable error whereas full analytical treatments are rarely applicable. By understanding the phenomena involved and representing them by simple models, better prediction methods are feasible. This approach is exemplified in its application to the prediction of annular two-phase flow and to the prediction of two-phase flow in equipment, for example a kettle reboiler. The article closes by indicating the possible lines that future development may follow in this area.

Reliability Problems of Heat Transfer Equipment

Abstract: In its simplest form, a heat exchanger consists of a bundle of tubes arranged between two thick perforated tube plates and enclosed by an outer shell Covers over the tube plates allow one fluid to pass inside the tubes while a second hotter or cooler fluid is introduced via openings in the shell Since they contain no moving parts it might be expected that heat exchangers would be highly reliable pieces of equipment However, everyday experience with small domestic and automotive heaters and coolers suggests this is not always the case In the case of mass-produced items such as these, replacement of a defective component is usually relatively straightforward and inexpensive However, for the much larger heat exchangers used in the process chemical and power industries, a single failure may result in significant financial losses

Generalized Prediction of Maximum Heat Transfer to Single Cylinders and Spheres in Gas-Fluidized Bed

Abstract: A simple dimensionless correlation is presented and compared with data from 35 experimental studies. Data include spheres, horizontal and vertical cylinders, cylinder diameters from 0.13 to 220 mm, particle diameters from 104 to 15,000 ..mu..m, bed temperatures up to 900/sup 0/C, and bed pressures up to 9.25 bars. Fluidizing gases include air, helium, CO/sub 2/, H/sub 2/, and R-12. Particle densities range from 1986 to 11,340 kg/m/sup 3/ and p /SUB s/ C /SUB s/ from 1474 to 4173 kJ/m/sup 30/C. A total of 142 data points are correlated with a mean deviation of 17%. Complete tabulations are provided for all data analyzed. Application to tube bundles is discussed briefly.

A Metho of Comparing Performance of Extended-Surface Heat Exchangers

Abstract: The expression for the performance of a gas-cooled heat exchanger per unit of power expended to the flowing gas provides a useful figure of merit for extended-surface heat exchangers. As developed here, the expression accounts for the effects of both increased heat transfer coefficient and increased effective temperature difference with higher power expended. Previous expressions accounted for only the increase in heat transfer coefficient. The convenience of comparing different heat exchanger configurations, as well as different tube spacing in the same configuration, is shown.

Hybrid Evaporative – Condenser Cooling Tower

Abstract: The need to save energy in power producing and power consuming systems and the fact that evaporative cooling is the most efficient method for heat rejection led to the design and testing of a model of a special cooling tower, fn this hybrid system an evaporative condenser is being built into the cooling tower and the advantages of evaporative cooling are combined with those of a wet cooling tower, causing a lower condensing temperature or saving heat transfer area or both The present work not only deals with the development of a practical model of a cooling tower module but also further develops, modifies and consolidates a computer program originally designed for horizontal finned or bare tube condensers These modifications are associated with the vertical tube condenser in the hybrid tower considered in this work It is shown that the performance of the model tower can be predicted by use of this computer program, as previously shown by Leidenfrost and Korenic for a different geometry It is

Transient Response of Heat Exchangers with One Infinite Capacitance Fluid

Abstract: Information on the transient response of heat exchangers is essential to produce the optimum heat exchanger operation for the required function. A transient response analysis is presented for a heat exchanger with an infinite capacitance fluid on the shell side. The inlet temperature of the finite capacity fluid is stepped, and the heat exchanger response is represented by the change in the temperature of this fluid at the outlet of the tubes. The results cover all practical combinations of the dependent parameters and are presented as a set of charts. Results of previous workers in this field are discussed. Their charts cover a very restricted range of heat transfer conditions and are therefore of limited use. In addition, assumptions have been incorporated into their analyses which result in major discrepancies.

Design of Packed Bed Regenerator with By-pass

Abstract: An explicit procedure for the design of a system containing a regenerator with bypass has been developed. Bypass of the regenerator during the energy retrieval process is controlled so that the temperature of the recombined fluid stream is held at a selected value. The procedure involves two sets of curves. The design curves relate the specific characteristics of the storage matrix and the mass rate of flow of the fluid through the regenerator. The performance curves relate the nondimensional length and period to the thermal ratio, maximum pressure drop, duration of hot period, and temperature of the combined fluid stream during the retrieval process. The mass of the storage material and dimensions of the regenerator are determined for the specified operating conditions.

Heat Transfer Characteristics of One-and Two-Tube-Pass Split-Flow Heat Exchangers

Abstract: The heat transfer process in a split-flow heat exchanger designated as G type by TEMA standards is analyzed for two cases: with one tube pass and with two tube passes. Equations are presented for the shell fluid temperature distribution as a function of exchanger length or surface area. The thermal performance of the two-tube-pass exchanger is compared with those of a 1:1 counterflow exchanger and a one-pass split-flow exchanger. Results are presented in terms of temperature efficiency, reduced thermal flux (NTU), and thermal flow rate ratio.

Tube Entrance Heat Transfer with Deposit Formation

Abstract: While flowing a kerosene-type gas turbine fuel through a direct-resistance heated tube, a condition was found which resulted in a tube wall temperature profile with two peaks near the tube entrance. The downstream peak gradually diminished as deposits formed inside the tube and only one peak remained after seven hours. On the basis of existing analytical studies and experimental data pertaining to heat transfer in the entrance region of tubes, it was concluded that the temperature profile can be divided into five regions: development of the thermal boundary layer, appearance of secondary flows, fully developed thermal boundary layer, transition to turbulent flow and turbulent flow. Deposits increased the tube roughness and reduced the length required for laminar-turbulent transition.

On-line Information Resources in Heat Transfer Engineering

Abstract: The computerized information retrieval techniques available to those involved in heat transfer engineering are reviewed. The various types of information contained in on-line data bases, the means of accessing it, and the potential benefits to be gained from its use are discussed.

Method for Quantifying Heat Duty Derating Due to Interpass Leakage in Bolted Flat Cover Heat Exchanger

Abstract: Functional relations are derived to determine the reduction in the heat duty of a multipass heat exchanger due to tube-side fluid bypass. A simplified structural model of the channel cover is constructed to determine the interpass leakage due to cover deflection under pressurized (operating) conditions. A numerical example shows that design rules based on stress limits are adequate to keep interpass leakage within tolerable limits.