Modeling of condensation heat transfer coefficients and flow regimes in flattened channels

2021 ◽  
Vol 126 ◽  
pp. 105391
Author(s):  
M. Mehrabi ◽  
S.M.A. Noori Rahim Abadi
Keyword(s):  
Heat Transfer ◽  
Flow Regimes ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Measurement and Modeling of Condensation Heat Transfer Coefficients in Circular Microchannels

2006 ◽  
Vol 128 (10) ◽  
pp. 1050-1059 ◽  
Author(s):  
Todd M. Bandhauer ◽  
Akhil Agarwal ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Transfer Model ◽  
Condensation Heat Transfer ◽  
Low Flow ◽  
Transfer Model ◽  
Shear Stresses ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Circular Microchannels

A model for predicting heat transfer during condensation of refrigerant R134a in horizontal microchannels is presented. The thermal amplification technique is used to measure condensation heat transfer coefficients accurately over small increments of refrigerant quality across the vapor-liquid dome (0<x<1). A combination of a high flow rate closed loop primary coolant and a low flow rate open loop secondary coolant ensures the accurate measurement of the small heat duties in these microchannels and the deduction of condensation heat transfer coefficients from measured UA values. Measurements were conducted for three circular microchannels (0.506<Dh<1.524mm) over the mass flux range 150<G<750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The heat transfer model is based on the approach originally developed by Traviss, D. P., Rohsenow, W. M., and Baron, A. B., 1973, “Forced-Convection Condensation Inside Tubes: A Heat Transfer Equation For Condenser Design,” ASHRAE Trans., 79(1), pp. 157–165 and Moser, K. W., Webb, R. L., and Na, B., 1998, “A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes,” ASME, J. Heat Transfer, 120(2), pp. 410–417. The multiple-flow-regime model of Garimella, S., Agarwal, A., and Killion, J. D., 2005, “Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3), pp. 1–8 for predicting condensation pressure drops in microchannels is used to predict the pertinent interfacial shear stresses required in this heat transfer model. The resulting heat transfer model predicts 86% of the data within ±20%.

The Impact of Fin Deformation on Condensation Heat Transfer Coefficients in Internally Grooved Tubes

2013 ◽  
Author(s):  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Thermal Contact ◽  
Heat Pumps ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Condensing Heat Transfer ◽  
The Impact ◽  
Tube Expansion

In HVACR equipment, internally enhanced round tube (microfin) designs such as axial, cross-grooved, helical, and herringbone are commonly used to enhance the boiling and condensing performance of evaporators, condensers, and heat pumps. Typically, such tubes are mechanically expanded by a mandrel into a fin pack to create an interference fit between the tube outside surface and the fin collar to minimize the thermal contact resistance between tube and fin. However, during this expansion process, the internal enhancements undergo varying amounts of deformation, which degrades the in-tube thermal performance. Extensive data on condensing heat transfer coefficients in microfin tubes have been reported in the open literature. However, researchers have seldom used expanded tubes to acquire and report such data. Hence, it is always questionable to use such pristine tube data for designing heat exchangers and HVACR systems. Furthermore, the HVACR industry has been experiencing steeply rising copper costs, and this trend is expected to continue in coming years. So, many equipment manufacturers and suppliers are actively converting tubes from copper to aluminum. However, because of appreciable differences between the material properties of aluminum and copper, as well as other manufacturing variables, such as mandrel dimensions, lubricant used, etc., tube expansion typically deforms aluminum fins more than copper fins. Based on an analysis of the surface area changes arising from tube expansion, and an assessment of the best extant in-tube condensation heat transfer correlations, this work proposes a method of estimating the impact of tube expansion on in-tube condensation heat transfer. The analysis leads to certain interesting and useful findings correlating fin geometry and in-tube condensation thermal resistance. This method can then be applied to more realistically design HVACR heat exchangers and systems.

scholarly journals Experimental Study on the Evaporation and Condensation Heat Transfer Characteristics of a Vapor Chamber

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 11
Author(s):  
Yanfei Liu ◽  
Xiaotian Han ◽  
Chaoqun Shen ◽  
Feng Yao ◽  
Mengchen Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Transfer Performance ◽  
Condensation Heat Transfer ◽  
Transfer Performance ◽  
Vapor Chamber ◽  
Filling Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Evaporation And Condensation

A vapor chamber can meet the cooling requirements of high heat flux electronic equipment. In this paper, based on a proposed vapor chamber with a side window, a vapor chamber experimental system was designed to visually study its evaporation and condensation heat transfer performance. Using infrared thermal imaging technology, the temperature distribution and the vapor–liquid two-phase interface evolution inside the cavity were experimentally observed. Furthermore, the evaporation and condensation heat transfer coefficients were obtained according to the measured temperature of the liquid near the evaporator surface and the vapor near the condenser surface. The effects of heat load and filling rate on the thermal resistance and the evaporation and condensation heat transfer coefficients are analyzed and discussed. The results indicate that the liquid filling rate that maximized the evaporation heat transfer coefficient was different from the liquid filling rate that maximized the condensation heat transfer coefficient. The vapor chamber showed good heat transfer performance with a liquid filling rate of 33%. According to the infrared thermal images, it was observed that the evaporation/boiling heat transfer could be strengthened by the interference of easily broken bubbles and boiling liquid. When the heat input increased, the uniformity of temperature distribution was improved due to the intensified heat transfer on the evaporator surface.

PURE NH3 AND CO2 HEAT TRANSFER AND PRESSURE DROP IN HORIZONTAL SMOOTH TUBES FOR NH3 TWO-STAGE AND NH3/CO2 CASCADE REFRIGERATION SYSTEMS: A REVIEW

2010 ◽  
Vol 18 (02) ◽  
pp. 85-100 ◽  
Author(s):  
C. Y. PARK ◽  
P. S. HRNJAK
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Boiling ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Two Stage ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Predicted Values ◽  
Cascade Refrigeration

This paper presents a review of differences and similarities of in-tube heat transfer and pressure drop between ammonia (NH3) and carbon dioxide (CO2) from the perspective of the design of heat exchangers for NH3 two-stage and CO2/NH3 cascade refrigeration systems. The focus is on differences in thermophysical properties and thus different characteristics of heat transfer and pressure drop. A brief summary of published literatures about CO2/NH3 cascade refrigeration systems is provided and literature review of available correlations and developed correlations are presented for flow boiling and condensation heat transfer and pressure drop. Because of large deviation of calculated values with exiting correlations from measured results, a new correlation to predict flow condensation heat transfer coefficients was developed based on experimental results for CO2 at -15°C. From comparison of measured and predicted values, it is shown that some correlations, previously published in open literature, can be used to calculate flow boiling heat transfer coefficients for NH3 at -20°C, if a flow pattern can be appropriately determined for a flow condition. Also, it is presented that existing correlations can predict well the heat transfer coefficients for CO2 flow boiling at -15 and -30°C. It is shown that some correlations can predict pressure drop relatively well for NH3 and CO2 two-phase flow. The NH3 and CO2 flow evaporation heat transfer and pressure drop characteristics at -40°C are compared with predicted values.

Experimental Apparatus for Measuring in Tube Condensation Heat Transfer Coefficient and Pressure Drop Using Smooth and Micro-Fin Tubes for HFC Refrigerants

2008 ◽  
Author(s):  
Pradeep A. Patil ◽  
S. N. Sapali
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Condensation Heat Transfer ◽  
Test Facility ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Fin Tube ◽  
Condensation Heat Transfer Coefficient

An experimental test facility is designed and built to calculate condensation heat transfer coefficients and pressure drops for HFC-134a, R-404A, R-407C, R-507A in a smooth and micro-fin tube. The main objective of the experimentation is to investigate the enhancement in condensation heat transfer coefficient and increase in pressure drop using micro-fin tube for different condensing temperatures and further to develop an empirical correlation for heat transfer coefficient and pressure drop, which takes into account the micro-fin tube geometry, variation of condensing temperature and temperature difference (difference between condensing temperature and average temperature of cooling medium). The experimental setup has a facility to vary the different operating parameters such as condensing temperature, cooling water temperature, flow rate of refrigerant and cooling water etc and study their effect on heat transfer coefficients and pressure drops. The hermetically sealed reciprocating compressor is used in the system, thus the effect of lubricating oil on the heat transfer coefficient is taken in to account. This paper reports the detailed description of design and development of the test apparatus, control devices, instrumentation, and the experimental procedure. It also covers the comparative study of experimental apparatus with the existing one from the available literature survey. The condensation and pressure drop of HFC-134a in a smooth tube are measured and obtained the values of condensation heat transfer coefficients for different mass flux and condensing temperatures using modified Wilson plot technique with correlation coefficient above 0.9. The condensation heat transfer coefficient and pressure drop increases with increasing mass flux and decreases with increasing condensing temperature. The results are compared with existing available correlations for validation of test facility. The experimental data points have good association with available correlations except Cavallini-Zecchin Correlation.

Prediction of Horizontal Tubeside Condensation of Pure Components Using Flow Regime Criteria

1980 ◽  
Vol 102 (3) ◽  
pp. 471-476 ◽  
Author(s):  
G. Breber ◽  
J. W. Palen ◽  
J. Taborek
Keyword(s):  
Heat Transfer ◽  
Prediction Method ◽  
Local Heat Transfer ◽  
Flow Regimes ◽  
Local Heat ◽  
Pure Component ◽  
Liquid Volume ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

In order to select the appropriate correlations for prediction of horizontal tubeside condensation heat transfer coefficients, it is necessary to estimate what types of flow patterns exist at various points along the tube. The main criteria required are shown to be the ratio of shear to gravity forces on the condensate film and the ratio of vapor volume to liquid volume. A recently proposed prediction method by Taitel and Dukler is compared with observed flow regimes for condensation in horizontal tubes. The theoretically obtained parameters are shown to characterize the flow regimes well. Based on these parameters, a simplified procedure for prediction of local heat transfer coefficients for pure component condensation in horizontal tubes is proposed.

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