Validation of in-tube condensation performance (original) (raw)
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Flow pattern-based heat transfer correlation for condensing R-22 in a smooth tube.
This paper presents a study of probabilistic flow regime-based heat transfer coefficients during refrigerant condensation inside a smooth tube. Experimental work was conducted using refrigerant R-22, at an average saturation temperature of 40 o C, with mass fluxes ranging from 250-650 kg/m 2 s, and with test section inlet vapor qualities ranging from 0.65 down to 0.10. These tests conditions represent mostly Intermittent flow, with some data points in the Annular and Stratified-wavy flow regimes. Utilizing time fraction data gathered in this experimental setup, a new time fraction-corrected flow regime-based heat transfer correlation, heavily based on the Thome et al. (J.R. Thome, J. El Hajal and A. Cavallini, Condensation in horizontal tubes, part 2: New heat transfer model based on flow regimes, International Journal of Heat and Mass Transfer, 46:3365-3387, 2003) correlation was developed for use in the Intermittent flow regime. The modified correlation predicted the experimental data with a mean absolute deviation of 10%.
2018
In the phase change process, latent heat is transferred and the amount of heat transferred will be excessive high compared to the amount of sensible heat transfer. For that reason, condensation and evaporation processes are the main steps in the refrigeration cycle in order to increase the amount of heat transferred. The main objective of this study is to experimentally and analytically examine overall heat transfer coefficient and to present the effect of water flow and refrigerant pressure on condensation process. For this purpose, a refrigeration system where a water cooled condenser with a heat transfer surface area of 0.075 m 2 was installed. R134a was used as a refrigerant and condenses on the outer surface of the pipe that water circulates through. In this study, experiments were repeated for water mass flow rates of 15, 20, 25, 30 and 35 g/s at constant 7.0 bar condensation pressure. Then, condensation pressures were changed to 6.5, 6.75, 7.0, 7.25 and 7.5 bar at constant wa...
An Improved and Extended General Correlation for Heat Transfer During Condensation in Plain Tubes
HVAC&R Research, 2009
An improved version of the author's published correlation , extended to a wider range of parameters, is presented. The new correlation has been shown to be in good agreement with data ranging from highly turbulent flows to the laminar flow conditions of Nusselt's analytical solutions. The data used for the correlation's validation includes 22 fluids (water, halocarbon refrigerants, hydrocarbon refrigerants, and organics) condensing in horizontal, vertical, and downward-inclined tubes. The range of parameters includes tube diameters from 2 to 49 mm, reduced pressure from 0.0008 to 0.9, flow rates from 4 to 820 kg/m 2 ·s, all liquid Reynolds numbers from 68 to 85,000, and liquid Prandtl numbers from 1 to 18. A total of 1189 data points from 39 sources are predicted with a mean deviation of 14.4%. Comparisons are also made with some other well-known correlations.
Volume 2: Heat Transfer Enhancement for Practical Applications; Heat and Mass Transfer in Fire and Combustion; Heat Transfer in Multiphase Systems; Heat and Mass Transfer in Biotechnology, 2013
Heat exchangers using in-tube condensation have great significance in the refrigeration, automotive and process industries. Effective heat exchangers have been rapidly developed due to the demand for more compact systems, higher energy efficiency, lower material costs and other economic incentives. Enhanced surfaces, displaced enhancement devices, swirl-flow devices and surface tension devices improve the heat transfer coefficients in these heat exchangers. This study is a critical review on the determination of the condensation heat transfer coefficient of pure refrigerants flowing in vertical and horizontal tubes. The authors' previous publications on this issue, including the experimental, theoretical and numerical analyses are summarized here. The lengths of the vertical and horizontal test sections varied between 0.5 m and 4 m countercurrent flow double-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The measured data are compared to theoretical and numerical predictions based on the solution of the artificial intelligence methods and CFD analyses for the condensation process in the smooth and enhanced tubes. The theoretical
The applicability of an existing fluted tube condenser model when used with refrigerant R-407C
International Journal of Refrigeration, 2013
Fluted tube-in-tube condensers are key components in energy efficient water heating heat pumps. Rousseau et al. (2003) developed a model that incorporates all the essential features of these heat exchangers. A feature of the model was that it allowed for the extension to simulate heat exchangers for cycles employing zeotropic refrigerant mixtures. This paper investigates the applicability of the model for R-407C condensation inside fluted tube annuli. To evaluate the model experimental data was gathered using a test facility. Comparisons between the experimental results and the model showed an average model accuracy of 48% when predicting the pressure drop and 56% for the log mean temperature difference (LMTD) for the tubes sizes used. Based on these accuracies new enhancement factors were derived and implemented in the model. This resulted in an average difference between the simulated and measured pressure drops of 9.5% and an average difference for the LMTD of 3.3%.
Determination of condensation heat transfer inside a horizontal smooth tube
International Journal of Heat and Mass Transfer, 2018
A mathematical model has been developed with the open source toolbox OpenFOAM to simulate the heat transfer process during flow condensation inside a smooth horizontal tube. The proposed model borrows some of the ideas of a recent boiling model, already developed in OpenFOAM 4.0. Modifications have been brought to this model to take into account the specific nature of flow condensation. A new coefficient called the ''condensation area fraction" is introduced and a new library is added to the solver to simulate the wall heat flux during the condensation process. In order to assess the performance of the new model, numerical simulations are conducted for mass fluxes ranging from 100 to 750 kg/m 2 s, with a nominal saturation temperature of 40°C and a hydraulic diameter between 7 and 12 mm. The numerical predictions are compared to the results of two experimental works and good agreement has been found between measurements and model's predictions. It shows the validity of the suggested numerical solution for modeling of flow condensation inside of a horizontal smooth tube. Moreover, the effect of some parameters such as mass flux, tube hydraulic diameter, vapor quality and difference between the wall and saturation temperature on the heat transfer coefficient are investigated. Finally, a new relationship for the prediction of the total heat transfer coefficient of flow condensation is proposed.
Applied Thermal Engineering, 2005
The determination of apparent heat transfer coefficient by condensation in a fined-tube heat exchanger is presented numerically in this paper. The film method is used in order to predict the partial or total condensation of the water vapour, contained in the humid air over the smooth or finned tubes-heat recuperators. This method is incorporated in a computer code developed here. The determination of the fin portion, which functions in wet regime, is carried out by the calculation of temperature field over a circular fin. The computer code predicts the heat flux exchanged in a range of 20-5%, in wet and dry regime, respectively. The apparent heat transfer coefficient by condensation can exceed 10 times the value of the heat transfer coefficient.
Heat Transfer Engineering, 2008
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C-2006 An Experimental Study of Condensation Heat Transfer and Pressure Drop.pdf
Only recently, experimental data is available in open literature in condensation of various refrigerants in small hydraulic diameter microchannels. The phenomenon of twophase flow and heat transfer mechanism in small diameter microchannels (< 1 mm) may be different than that in conventional tube sizes due to increasing dominance of several influencing parameters like surface tension, viscosity etc. This paper presents an on-going experimental study of condensation heat transfer and pressure drop of refrigerant R134a is a single high aspect ratio rectangular microchannel of hydraulic diameter 0.7 mm and aspect ratio 7:1. This data will help explore the condensation phenomenon in microchannels that is necessary in the design and development of small-scale heat exchangers and other compact cooling systems. The inlet vapor qualities between 20% and 80% and mass fluxes of 1 30 and 200 kg/m 2 s have been studied at present. The microchannel outlet conditions are maintained at close to thermodynamic saturated l iquid state through a careful experimental procedure. A unique process for fabrication of the microchannel involving milling and electroplating steps has been adopted to maintain the channel geometry close to design values. Measurement instruments are well-calibrated to ensure low system energy balance error, uncertainty and good repeatability of test data. The trends of data recorded are comparable to that found in recent literature on similar dimension tubes.
Fluid Dynamics & Materials Processing, 2023
A theoretical study based on the Penalty factor (PF) method by Cavallini et al. is conducted to show that the pressure drop occurring in a wire-on-tube heat exchanger can be converted into a temperature difference for two types of refrigerants R-134a and R-600a typically used for charging refrigerators and freezers. The following conditions are considered: stratified or stratified-wavy flow condensation occurring inside the smooth tube of a wire-on-tube condenser with diameter 3.25, 4.83, and 6.299 mm, condensation temperatures 35°C, 45°C, and 54.4°C and cover refrigerant mass flow rate spanning the interval from 1 to 7 kg/hr. The results show that the PF variation is not linear with vapor quality and attains a maximum when the vapor quality is 0.2 and 0.18 for the R-134a and R-600a refrigerants, respectively. The PF increases with the refrigerant mass flow rate if the inner diameter and saturation temperature constant, and it decreases on increasing the inner diameter to 6.299 mm for constant refrigerant mass flow rate and saturation temperature. The PF for R-600a is higher than that for R-134a due to the lower saturation pressure in the first case. Furthermore, a stratified flow produces higher PF in comparison to the annular flow due to the effect of the surface tension.