John R. Thome

Flow Boiling in Horizontal Tubes: Part 1—Development of a Diabatic Two-Phase Flow Pattern Map

An improved two-phase flow pattern map is proposed for evaporation in horizontal tubes. The new map was developed based on flow pattern data for five different refrigerants covering a wide range of mass velocities and vapor qualities. The new map is valid for both adiabatic and diabatic (evaporating) flows and accurately identifies about 96% of the 702 data points. In addition, the new flow pattern map includes the prediciton of the onset of dryout at the top of the tube during evaporation inside horizontal tubes as a function of heat flux and flow parameters.

State of the Art of High Heat Flux Cooling Technologies

The purpose of this literature review is to compare different cooling technologies currently in development in research laboratories that are competing to solve the challenge of cooling the next generation of high heat flux computer chips. Today, most development efforts are focused on three technologies: liquid cooling in copper or silicon micro-geometry heat dissipation elements, impingement of liquid jets directly on the silicon surface of the chip, and two-phase flow boiling in copper heat dissipation elements or plates with numerous microchannels. The principal challenge is to dissipate the high heat fluxes (current objective is 300 W/cm2) while maintaining the chip temperature below the targeted temperature of 85°C, while of second importance is how to predict the heat transfer coefficients and pressure drops of the cooling process. In this study, the state of the art of these three technologies from recent experimental articles (since 2003) is analyzed and a comparison of the respective merits and drawbacks of each technology is presented. The conclusion is that two-phase flow boiling in microchannels is the most promising approach; impingement cooling also has good prospects but single-phase liquid cooling is probably only a short-term solution. As an example of the state of the first technology, the Heat and Mass Transfer Laboratory at Ecole Polytechnique Fédérale de Lausanne has already achieved 200 W/cm2 of cooling in a first prototype, with a low pumping power, good temperature uniformity, and at the required maximal operating temperature.

Flow Boiling in Horizontal Tubes: Part 3—Development of a New Heat Transfer Model Based on Flow Pattern

A new heat transfer model for intube flow boiling in horizontal plain tubes is proposed that incorporates the effects of local two-phase flow patterns, flow stratification and partial dryout in annular flow. Significantly, the local peak in the heat transfer coefficient versus vapor quality can now be determined from the prediction of the location of onset of partial dryout in annular flow. The new method accurately predicts a large, new database of flow boiling data, and is perticularly better than existing mehods at high vapor qualities (x > 85%) and for stratified types of flows.

Condensation in horizontal tubes, part 1: two-phase flow pattern map

Abstract A new flow pattern map and flow pattern based heat transfer model for condensation inside horizontal plain tubes are proposed in this two-part paper. In Part I, a new version of a two-phase flow pattern map, originally developed by Kattan et al. [J. Heat Transfer 120 (1998) 140] for flow boiling, is presented for condensation inside horizontal tubes while a new heat transfer model is presented in Part II. The new flow pattern map incorporates a newly defined logarithmic mean void fraction (LM e ) method for calculation of vapor void fractions spanning from low pressures up to pressures near the critical point. Several other modifications are also made that are appropriate for condensation as opposed to evaporation. In the absence of void fraction data at high reduced pressures for these conditions, the new LM e method has been indirectly validated using the convective condensation model for annular flow and corresponding heat transfer test data at reduced pressures up to 0.8. The new map has also been successfully compared to some recent flow pattern observations for condensation and other existing flow transition criteria and maps.

Boiling of New Refrigerants: a State-of-the-Art Review

The industrial conversion to new alternative refrigerants is now one of the major driving forces in two-phase flow and boiling heat transfer research. A state-of- the-art review is presented here to quantify what has been done so far, assess the strengths and weaknesses in current boiling correlations and two-phase flow pattern maps, and identify future research requirements and objectives.

Heat Transfer Model for Evaporation of Elongated Bubble Flows in Microchannels

Reference LTCM-ARTICLE-2005-032View record in Web of Science Record created on 2005-07-06, modified on 2017-05-10

State-of-the-Art Overview of Boiling and Two-Phase Flows in Microchannels

A state-of-the-art overview of recent work on boiling and two-phase flows in microchannels are reviewed, focusing primarily on the high points of recent developments. The topics covered include critical heat fluxes and their prediction in microchannels, new two-phase flow pattern maps, flow regimes and visualization in microchannels, boiling phenomena and flow instabilities in multi-microchannel cooling elements, flow boiling prediction methods specifically for microchannels and their comparison to data, trends in flow boiling data in microchannels and mechanisms that may be responsible for the seemingly divergent trends, and two-phase pressure drops in microchannels.

Flow Boiling in Horizontal Tubes. Part 2; New Heat Transfer Data for Five Refrigerants

A summary of a comprehensive experimental study on flow boiling heat transfer is presented for five refrigerants (R134a, R123, R402A, R404A and R502) evaporating inside plain horizontal, copper tube test sections. The test data were obtained for both 12.00 mm and 10.92 mm diameters using hot water as the heating source. Besides confirming known trends in flow boiling heat transfer data as a function of test variables, it was also proven that the heat flux level at the dryout point at the top of the tube in annular flow has a very significant downstream effect on heat tranfer coefficients in the annular flow regime with partial dryout.

Two-Phase Flow Patterns and Flow-Pattern Maps: Fundamentals and Applications

Reference EPFL-ARTICLE-147393doi:10.1115/1.2955990View record in Web of Science Record created on 2010-03-19, modified on 2017-05-10

Comprehensive Thermodynamic Approach to Modeling Refrigerant-Lubricating Oil Mixtures

A new Thermodynamic Approach for modelling mixtures of refrigerants and lubricating oils is presented. The model includes generalized methods for predicting the following thermodynamic properties of refrigerant-oil mixtures: bubble point temperatures, local oil concentrations, liquid specific heats release (enthalpy) curves are easily generated and also the effect of oil on the LMTD of evaporators can be modelled. A new definitionof the boiling heat transfer coefficient based on the bubble point temperature is also presented. The new Thermodynamic Approach will allow major advances to be made in two-phase refrigeration heat transfer research and design since now the type of oil and the effects of its physical properties can be included in the analysis.