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Ammonia has been used as a refrigerant since the beginning of the refrigeration industry and it continues to be an important industrial refrigerant. However, there is no well-verified method for predicting heat transfer during condensation in tubes and annuli. Available information is often contradictory, especially about the effect of oil. In this paper, available test data and predictive methods are reviewed. Reliable test data are identified and compared to well-known general correlations. The effect of oil on heat transfer is investigated. The results of this research are presented, and recommendations are made for design calculations. [ABSTRACT FROM AUTHOR]

Boiling with downflow in vertical channels is involved in many applications such as boilers, nuclear reactors, chemical processing, etc. Accurate prediction of CHF (Critical Heat Flux) is important to ensure their safe design. While numerous experimental studies have been done on CHF during upflow and reliable methods for predicting it have been developed, there have been only a few experimental studies on CHF during downflow. Some researchers have reported no difference in CHF between up- and downflow, while some have reported that CHF in downflow is lower or higher than that in upflow. Only a few correlations have been published that are stated to be applicable to CHF during downflow. No comprehensive comparison of correlations with test data has been published. In the present research, literature on CHF during downflow in fully heated channels was reviewed. A database for CHF in downflow was compiled. The data included round tubes and rectangular channels, hydraulic diameters 2.4 mm to 15.9 mm, reduced pressure 0.0045 to 0.6251, flow rates from 15 to 21,761 kg/m2s, and several fluids with diverse properties (water, nitrogen, refrigerants). This database was compared to a number of correlations for upflow and downflow CHF. The results of this comparison are presented and discussed. Design recommendations are provided. [ABSTRACT FROM AUTHOR]

The author's model for evaporation from water pools is further developed and verified. Further development includes the determination of wind velocity in application to outdoor pools. A value for this height at which wind velocity is to be determined is proposed and verified through analysis of test data. Furthermore, a method for calculating the velocity at this height from measurements at other heights is proposed and verified by analysis of test data. The air velocity above indoor pools is discussed and recommendations are made for the velocity to be used in calculations. The model is further verified with new data that include those for an outdoor swimming pool (there were none before) and data for air at temperatures up to 269 °C, with the maximum temperature in previous data analysis being 200 °C. All data were also compared to 20 other prediction methods. The Shah model had a mean absolute deviation of 15.9% for 537 data points from 29 sources. All others had much larger deviations. [ABSTRACT FROM AUTHOR]

Calculation of evaporation is needed in many applications including swimming pools, water reservoirs, nuclear fuel pools, pools for rejection of heat from refrigeration systems, process tanks, etc. Hence accurate methods for prediction of evaporation are needed. Many prediction methods have been published including analytical models and empirical correlations. In the present study, 18 published prediction methods are compared to a very wide-ranging database which includes data from laboratory scale studies, swimming pools, and fuel pools in nuclear power plants. The data are from 25 sources. The range of data includes air temperatures from 6°C to 200°C, water temperatures from 7.1°C to 94.2°C, relative humidity from 0.21% to 98%, and air velocity from 0 to 8.5 m/s. The accuracy of prediction methods is examined for conditions in which natural convection dominates, that in which forced convection dominates, and that in which natural convection is absent. The results are reported and discussed. Recommendations are made for application. [ABSTRACT FROM AUTHOR]

There is presently great interest in use of mini/micro channels with boiling in heat exchangers and for heat dissipation from microelectronic systems. Design of such devices requires the ability to predict critical heat flux (CHF). It is therefore desirable to know the applicability of general correlations for CHF in conventional tubes to minichannels. The most verified general correlations are those of Katto and Ohno and of Shah. In this study, these correlations were compared to an extensive database with 55 data sets from 30 sources, which included single tubes and multichannels with diameters from 0.13 mm to 3.0 mm, 15 diverse fluids (water, halocarbon refrigerants, hydrocarbons, and cryogens), reduced pressures from 0.009 to 0.887, and flow rates from 10 to 41810 kg/m2-s. The correlations of Shah and of Katto and Ohno gave mean absolute deviations of 18.9 and 33.2%, respectively. To put the performance of these general correlations in perspective, the same database was also compared to two of the best correlations specifically developed for minichannels. [ABSTRACT FROM AUTHOR]