Condensation Heat Transfer Correlations Research Articles

Condensation heat transfer correlation for smooth tubes in annular flow regime

Condensation heat transfer coefficients in a 7.92 mm inside diameter copper smooth tube were obtained experimentally for R22, R134a, and R410A. Working conditions were in the range of 30–40°C condensation temperature, 95–410 kg/m2s mass flux, and 0.15–0.85 vapor quality. The experimental data were compared with the eight existing correlations for an annular flow regime. Based on the heat-momentum analogy, a condensation heat transfer coefficients correlation for the annular flow regime was developed. The Breber et al. flow regime map was used to discern flow pattern and the Muller-Steinhagen & Heck pressure drop correlation was used for the term of the proposed correlation. The proposed correlation provided the best predicted performance compared to the eight existing correlations and its root mean square deviation was less than 8.7%.

Experimental study of R134A condensation heat transfer inside the horizontal micro-fin tubes

The Investigation of the two-phase flow patterns and their transitions during the condensation has gained increasing interest and importance from the well-known phenomenon that the heat transfer characteristics are strongly dependent on the flow patterns. Therefore, it is very important to study on which heat transfer enhancement approach is suitable for an individual flow pattern inside a condenser, so that an accurate heat transfer mechanism can be understood that is consistent with the flow patterns. The condensation heat transfer for R134a in the two kinds of in-tube three-dimensional (3-D) micro-fin tubes with different geometries is experimentally investigated. Based on the flow pattern observations, the flow patterns in the Soliman flow regime map are divided into two-flow regimes; one with the vapor-shear-dominant annular regime and the other with the gravitational-force-dominant stratified-wavy regime. The flow regime transition criterion between the annular regime and the stratified-wavy regime is at Fr equal to 2. In the annular regime, the heat transfer coefficients h of the two kinds of in-tube 3-D micro-fin tubes decreases as the vapor quality x decreases. The regressed condensation heat transfer correlation from the experimental data of the annular flow region is obtained. The dispersibility of the experimental data is inside the limits of ±25%. In the stratified-wavy regime, the average heat transfer coefficient h of the two kinds of in-tube 3-D micro-fin tubes increases as the mass flux increases and the number of micro fins in the 3-D micro-fin tube is not the controlling factor for the performance of a condensation heat transfer. The regressed condensation heat transfer correlation of the stratified-wavy flow regime is experimentally obtained. The dispersibility of the experimental data is inside the limits of ±22%. Combined with the criteria of flow pattern transitions, the correlations can be used for the design of a condenser with 3-D micro-fin tubes.

Evaluation of existing condensation heat transfer models in horizontal micro-fin tubes

Three condensation heat transfer correlations for micro-fin tubes are reviewed in this paper. These heat transfer models were developed by using different approaches to account for the heat transfer enhancement effect in micro-fin tubes. The heat transfer coefficients predicted by the three models are compared to 414 experimental data points for pure refrigerant. The Yu and Koyama [Proceedings of the International Refrigeration Conference at Purdue, 1998, pp. 325–330] model displayed poor prediction on most of the R22 pure refrigerant data used for its validation. In addition, this model does not clearly describe the effects of the tube geometries on the heat transfer coefficient in micro-fin tubes. In general, the other two models, Cavallini et al. [Enhanced Heat Transfer 6 (1999) 441] and Kedzierski and Goncalves [Enhanced Heat Transfer 6 (1999) 161], are capable of predicting most of the pure refrigerant experimental data sets within the mean absolute deviation range of ±30%. However, Cavallini et al. [Enhanced Heat Transfer 6 (1999) 441] achieves better predictions for most of the pure refrigerant data sets if compared with the other model.

Review of In-Tube Condensation Heat Transfer Correlations for Smooth and Microfin Tubes

This article provides a comprehensive review of the published literature on inside-tube condensation heat transfer correlations for smooth and microfin tubes with an emphasis on correlations used in air conditioning and refrigeration. The correlations presented are discussed and evaluated with experimental data from different authors for different fluids and flow conditions. This review is divided in two main parts: condensation inside smooth tubes and condensation inside microfin tubes. According to the comparison between empirical correlation and experimental data for smooth tubes, correlations proposed by Dobson et al., Dobson and Chato, and Cavallini et al. appear to be the most accurate ones to be used for different fluids and boundary conditions. In the case of microfin tubes, much additional work is needed to develop more general and accurate correlations.

A new set of correlations for EHD enhanced condensation heat transfer of tubular systems

An improved set of correlations for evaluating the heat transfer coefficient of EHD assisted condensation heat transfer for tubular systems is presented in this paper. The correlations were developed by curve fitting a wide range of experimental data and then optimising the empirical constants so that the percentage deviation is less than ±30%. The experimental data was classified in four categories: (I) condensation outside horizontal smooth tubes, (II) condensation inside horizontal smooth tubes, (III) condensation outside vertical tubes and (IV) condensation inside vertical tubes. The experimental data in each category included results obtained using various refrigerants and various electrode systems. The improved correlations were used to predict a total of 166 experimental data points. A comprehensive literature review of all available correlations for EHD assisted condensation heat transfer is also described in this paper. Two correlations that were identified to be simple were used to predict the above-mentioned data bank. These are the correlations of Choi and Reynolds and Didkovesky and Bologa. The Choi and Reynolds correlation was found to successfully predict heat transfer rates of condensation outside horizontal and vertical tubes and of condensation inside vertical tubes when high intensity electric field is applied. However, the Didkovesky and Bologa correlation was found to successfully predict only the results of condensation heat transfer outside vertical surfaces.

A condensation heat transfer correlation for millimeter-scale tubing with flow regime transition

This study documents local convection heat transfer and flow regime measurements for HFC-134a condensing inside a horizontal rectangular multi-port aluminum condenser tube of 1.46 mm hydraulic diameter. The data is compared with condensation heat transfer correlations and flow regime maps from the literature. Existing correlations are found to overpredict both heat transfer and the stratified-to-annular flow regime transition velocity. Results of the experiments suggest that liquid drawn into the corners of the tube alter the phase distribution in the annular flow regime as well as stabilizing the annular flow regime at lower vapor velocities. To predict the heat transfer data, two correlations, each representing the physics of the specific phase distributions, are developed. A boundary layer analysis is applied for annular flow, in which the friction multiplier and dimensionless boundary layer temperature are evaluated specifically for this tube configuration. For stratified flow, documented film condensation and single-phase forced convection correlations are combined with straightforward void fraction weighting. Finally, a weighting correlation is successfully proposed to account for the all data regardless of the mix of flow regimes experienced. This weighting applies the result of a modified flow regime map developed from the flow visualizations. The final result is a practical correlation for the design of a condenser with millimeter-scale tubes.

Two-phase heat transfer coefficients of three HFC refrigerants inside a horizontal smooth tube, part II: condensation

This paper presents local heat transfer results obtained during the condensation of Isceon 59, R407C and R404A in a smooth horizontal tube. The results have been compared with existing correlations for condensation heat transfer to assess the validity of these models for refrigerant mixtures. Two correlations (Dobson MK, Chato JC. Condensation in smooth horizontal tubes. Journal of Heat Transfer, Transactions of ASME 1998; 120: 193–213, Shah MM. A general correlation for heat transfer during film condensation inside pipes. Int J Heat & Mass Transfer 1979; 22: 547–56) have been considered because they deal with refrigerant blends and their range of applicability suited the experimental test conditions. The Dobson and Chato correlation provided the best prediction for these refrigerant mixtures. The Shah correlation fitted the measurements of the local heat transfer coefficients well and seem to cope well with refrigerant mixtures.

A heat exchanger model for mixtures and pure refrigerant cycle simulations

This paper describes a heat exchanger simulation developed for transient and steady state cycle simulations of mixtures and pure components. The simulation focuses on air to refrigerant condensers and evaporators found in residential heat pumps. The refrigerant differential momentum, continuity, species and energy equations are solved for these components and the steady state results are verified experimentally. Ten different heat transfer correlations for condensation and evaporation are evaluated to determine which best reproduces experimental data. Of those tested Jung and Radermacher's (1989, Int. J. Heat Mass Transfer 32 2435–2446) heat transfer correlation worked the best for evaporation while Dobson et al.'s (1994, ACRC Project 37) correlation worked the best for condensation. The experimentally determined capacity of four cross flow heat exchangers operating as condensers and evaporators with four different refrigerants is compared to the simulation results. The capacities predicted by the simulation agreed with the experimental results within ±8.0%. Furthermore, the simulation is used to quantify the effects of using a zeotropic mixture, R-407C, with cross, parallel and counter flow heat exchangers. As compared to a typical cross flow heat exchanger at typical heat pump operating conditions, the simulation predits that a pure parallel flow heat exchanger can decrease capacity by as much as 8.3% while a pure counter flow heat exchanger can increase performance by up to 4.4%.

Separate effects tests for gothic condensation and evaporative heat transfer models

The gothic computer program, under development at NAI for EPRI, is a general purpose thermal hydraulics computer program for design, licensing, safety and operating analysis of nuclear containments and other confinement buildings. The code solves a nine-equation model for three-dimensional multiphase flow with separate mass, momentum and energy equations for vapor, liquid and drop phases. The vapor phase can be a gas mixture of steam and non-condensing gases. The phase balance equations are coupled by mechanistic and empirical models for interface mass, energy and momentum transfer that cover the entire flow regime from bubbly flow to film-drop flow. A variety of heat transfer correlations are available to model the fluid coupling to active and passive solid conductors. This paper focuses on the application of gothic to two separate effects tests: condensation heat transfer on a vertical flat plate with varying bulk velocity, steam concentration and temperature, and evaporative heat transfer from a hot pool to a dry (superheated) atmosphere. Comparisons with experimental data are included for both tests. Results show the validity of two condensation heat transfer correlations as incorporated into GOTHIC and the interfacial heat and mass transfer models for the range of the experimental test conditions. Comparisons are also made for lumped vs. multidimensional modeling for buoyancy-controlled flow with evaporative heat transfer.

A heat transfer correlation for condensation inside horizontal smooth tubes using the population balance approach

Population balance model with homogeneous flow assumption is applied for forced convective condensation inside smooth horizontal tubes. The purpose of the paper is to examine the applicability of the homogeneous flow assumption for in-tube condensation although the common observation is that annular flow is physically more realistic [Soliman and Azer, ASHRAE Trans. 77(1), 210–224 (1971); Stoecker and DeGrush, Oak Ridge National Laboratory 81-7762/6 and 01 (1987); Taitel and Dukler, A.I.Ch.E.J. 22, 47–55 (1976)]. Lin's model [Lin, Ph.D. Dissertation (1979)] is applied suitably for the smooth tube conditions. Differences between Lin's model [Lin, Ph.D. Dissertation (1979)] and the present approach are clearly stated in the text. A correlation for the local heat transfer coefficient is obtained involving fewer parameters but with an additional constant and is applicable for oil-refrigerant mixtures also. Experimental data over a wide range of mass flux rates and condensing temperatures are used in obtaining the correlation. The predicted values of local Nu, compared with the experimental data indicate that 90% of the predictions are within ±20% of the experimental data, with a mean deviation of 13.2%.

Numerical approach for cocurrent stratified steam water flow in a horizontal configuration

The present study deals with the one-dimensional numerical approach in predicting the local flow properties for cocurrent stratified steam-water flow in a horizontal configuration. The turbulence-centered model, developed principally for gas absorption, has been modified and introduced for the condensation heat transfer coefficient using interfacial parameters, such as turbulent velocity and length scales. The calculated condensation rates, pressures and mean water layer thicknesses are in good agreement with Lim’s experimental data obtained from cocurrent stratified steam flow on a fairly thick layer of water. In addition, the approach was applied to the case of relatively thin liquid films, and the results were compared with Linehan’s experimental data. The comparison indicates that the one-dimensional numerical approach with the present condensation heat transfer correlation developed from the thick liquid data can be applicable to the prediction of the flow properties for thin liquid films.

GENERAL FILM CONDENSATION CORRELATIONS

A comprehensive film condensation heat transfer correlation, established on the basis of analytical and empirical results from the literature, is in excellent agreement with all existing data. It incorporates the effects of interfacial shear stress, interfacial waviness, and turbulent transport in the condensate film. The usefulness of this correlation is demonstrated for annular-film condensation inside tubes. This correlation can easily be incorporated into condensing models once the interfacial shear stress is known. Two cases, cocurrent annular-film condensation inside vertical and horizontal tubes and countercurrent annular-film reflux condensation such as occurs inside the two-phase closed thermosyphon, are used to demonstrate this procedure.

An empirical correlation for condensation heat transfer under one‐component stratified flow conditions

An empirical correlation for condensation heat transfer under one‐component stratified flow conditions

A General Heat Transfer Correlation for Annular Flow Condensation

The interaction between friction, momentum, and gravity, as they affect the heat transfer process during annular flow condensation inside tubes, is studied. Analytical forms for each of these forces are derived and incorporated in a correlation that predicts the local heat transfer coefficient. The predictions agree well with the available experimental data over a wide range of vapor velocities and over a range of Prandtl numbers from 1 to 10. The analysis also yields a means for predicting the onset of liquid run-back in the presence of an adverse gravitational field.

Closure to “Discussion of ‘A General Heat Transfer Correlation for Annular Flow Condensation’” (1968, ASME J. Heat Transfer, 90, p. 274)

Closure to “Discussion of ‘A General Heat Transfer Correlation for Annular Flow Condensation’” (1968, ASME J. Heat Transfer, 90, p. 274)

Heat transfer at low temperatures

The non-condensable gas at the top of the main condenser of the distillation section, such as helium or neon, would lower the heat transfer efficiency and the productivity of the air separation plant. Current research mainly focuses on the study of the water vapor condensation mechanism with non-condensable gases, while those on cryogenic fluids are rare. In this work, an experimental setup was designed to study the condensation mechanism of pure nitrogen vapor and nitrogen vapor mixed with helium on the vertical plate. The experimental data of pure nitrogen vapor is in good agreement with the results calculated by the classical Nusselt model, which demonstrates that the experimental system has high reliability. The influences of the mass fraction of helium and system pressure on the condensation heat transfer coefficient are analyzed. Results show that even a very low mass fraction of helium can cause the condensation heat transfer coefficient of nitrogen vapor to decrease obviously. The deviation between the heat transfer coefficient of the nitrogen-helium mixture and pure nitrogen increases with the increases of the helium mass fraction and the decrease of system pressure. A new condensation heat transfer correlation for nitrogen with helium is developed that the deviations of most of its predictions are within 20% compared to the experimental data.