Advances in Heat Transfer (eBook)

James P. Hartnett (Autor)

Young I. Cho, George A. Greene (Herausgeber)

eBook Download: PDF

2003 | 1. Auflage
478 Seiten
Elsevier Science (Verlag)
978-0-08-049355-8 (ISBN)

Infos

This series presents review articles on topics of current interest. Each contribution starts from widely understood principles and brings the reader up to the forefront of the topic being addressed.

The favourable response by the international scientific and engineering community to the 37 volumes published to date is an indication of the success of our authors in fulfilling this purpose. This is recommended reading for all mechanical engineers and researchers.

Provides an overview of review articles on topics of current interest
Bridges the gap between academic researchers and practitioners in industry
A Long running and prestigious series

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Advances in Heat Transfer presents review articles on topics of current interest. Each contribution starts from widely understood principles and brings the reader up to the forefront of the topic being addressed. The favorable response by the international scientific and engineering community to the 37 volumes published to date is an indication of the success of our authors in fulfilling this purpose. This is recommended reading for all mechanical engineers and researchers. - Provides an overview of review articles on topics of current interest- Bridges the gap between academic researchers and practitioners in industry- A long-running and prestigious series

Inhalt

Front Cover 1
Advances in: HEAT TRANSFER 4
Copyright Page 5
Contents 6
Contributors 10
Preface 12
Chapter 1. Microgravity Heat Transfer in Flow Boiling 14
I. Introduction 14
II. Development of Transparent Heated Tube 17
III. Experimental Apparatus and Procedure 23
IV. Effect of Gravity on Flow Boiling Heat Transfer in Circular Tubes 28
V. Mechanisms of Gravity-dependent Heat Transfer due to Two-phase Forced Convection in Annular Flow Regime 36
VI. Experiments on Dryout Phenomena under Microgravity Conditions 52
VII. Experiments on Flow Boiling Heat Transfer in Narrow Channels 73
VIII. Future Investigations for Microgravity Flow Boiling 84
Nomenclature 86
References 87
Chapter 2. Fluid Mechanics and Heat Transfer with Non-Newtonian Liquids in Mechanically Agitated Vessels 90
I. Introduction 90
II. Scope 94
III. Rheological and Thermo-physical Properties 94
IV. Non-Newtonian Effects in Agitated Vessels 99
V. Mechanisms of Mixing 100
VI. Fluid Mechanics 104
VII. Heat Transfer 154
VIII. Mixing Equipment and its Selection 163
IX. Concluding Summary 169
Nomenclature 173
References 173
Chapter 3. Optical and Thermal Radiative Properties of Semiconductors Related to Micro/Nanotechnology 192
I. Introduction 192
II. Fundamentals of Optical Properties of Semiconductors 195
III. Radiative Properties of Layered Structures 239
IV. Radiative Properties of Rough and Microstructured Surfaces 259
V. Quantum Confinement and Photonic Crystals 282
VI. Concluding Remarks 288
Nomenclature 290
References 291
Chapter 4. Microchannel Heat Exchanger Design for Evaporator and Condenser Applications 310
I. Introduction 310
II. Single- and Two-phase Flows in Microchannels 311
III. Two-phase Flow Mal-distribution in Microchannel Headers and Heat Exchangers 351
IV. Air-side Performance 362
V. Heat Exchanger Applications 414
VI. Conclusion 424
Nomenclature 425
References 427
Author Index 444
Subject Index 470

Textauszug

Microgravity Heat Transfer in Flow Boiling

Haruhiko Ohta    Department of Aeronautics and Astronautics, Kyushu University, Fukuoka, Japan

Abstract

To investigate flow boiling in microgravity, test sections of transparent heated tube and transparent heating surface were developed, and heat transfer characteristics were directly related to the liquid–vapor behaviors observed. The experiments were performed on board aircraft where the boiling system was exposed in series to normal, hyper and reduced gravity fields along a parabolic trajectory. In the experiments using a round tube and an analytical model, an important gravity effect on two-phase forced convective heat transfer where heat transfer is deteriorated in microgravity at low mass velocity was clarified. As regards the dryout phenomenon, measurement of critical heat flux was attempted in a short microgravity duration and the process of dryout was investigated for a moderate quality region based on the measured temperature fluctuation and corresponding liquid–vapor behaviors. Flow boiling in narrow channels was also investigated as one of the systems to be applied to space heat exchangers, and a few important characteristics were clarified concerning the gravity effect. Because of the limited opportunity for experiments and the short microgravity duration created by aircraft, the results obtained here could not cover all aspects of the phenomenon for the gravity effects on flow boiling for different systems and parameters, but the results are intended to become a powerful aid for further investigation in the present discipline utilizing longer microgravity periods in a new space platform to be realized soon.

1 Introduction

Recent increases in spacecraft size and power requirements for advanced satellites and other orbiting platforms have increased the demands for more effective thermal management and thermal control systems. Thermal systems utilizing boiling and two-phase flow are effective means for the development of high-performance, reliable and safe heat transport systems for future space missions. Boiling heat transfer offers high heat transfer rates associated with the transport of latent heat of vaporization and has the potential to significantly reduce the required size and weight of heat exchangers. The latent heat transport in two-phase flow reduces the flow rate of liquid circulated in the loop for the same amount of heat transport and, in turn, reduces the pump power requirement. Furthermore, two-phase fluids allow for precise adjustment of the fluid's temperature responding to the thermal load by simply pressurizing the system using an accumulator.

Despite their acknowledged importance, boiling and two-phase flow systems have not yet been fully implemented in new spacecraft except for small-scale heat pipes and a thermal transport loop planned in the Russian module of the International Space Station. This is partially attributed to the lack of a reliable database for the operation of such systems in microgravity. In addition, the uncertainty in the critical heat flux (CHF) conditions discourages space system designers from introducing such systems. Single-phase liquid cooling systems are favored despite the large mass penalty. But even with single-phase systems, boiling and two-phase flow would inevitably occur as a result of, for example, accidental increase in the heat generation rate, or a sudden system depressurization caused by valve operation.

It is safe to say that, to date, there is no cohesive database for microgravity boiling and two-phase flow (reduced gravity is referred to as microgravity or μg here). There is also a prevailing misconception that few differences actually exist between normal and microgravity heat transfer coefficients in flow boiling in the existence of bulk flow. But this is not true, as is shown in the following section when bulk flow is not so large. In addition to the clarification of phenomena in microgravity, the establishment of a coherent database for microgravity flow boiling and two-phase flow provides fundamental information for the development of large-scale two-phase thermal management systems for possible implementation in future spacecraft and earth orbiting satellites.

Research on microgravity boiling has a history of more than 40 years with a short pause in the 1970s and has been advanced with the development of various microgravity facilities and with increased experimental opportunities, especially in the last 15 years. Most boiling experiments in microgravity, however, have been conducted for pool boiling, while the data on flow boiling experiments are very limited except those for isothermal two-phase flow concerning the gravity-dependent flow pattern change and pressure drop. This is partially due to the practical difficulties in adapting the flow boiling apparatus with its various components to the microgravity facilities such as drop towers, aircraft, ballistic rockets and space shuttles with limited capacities in both integration volume and power supply.

Misawa and Anghaie [1] introduced two different test sections for boiling experiments, i.e. a transparent square channel of pyrex glass with a coating of transparent heating films for flow pattern observation and a copper tube with a nichrome coil on the outer surface for the pressure drop measurements. Drop experiments were conducted for Fron113 flowing in vertical test sections. It was clarified that the slip ratio under microgravity is less than unity and the pressure drop is larger than the values predicted by the homogeneous model because of the increased contribution of acceleration resulting from the increase of void fraction. Kawaji et al. [2] investigated on board KC-135 aircraft the behavior of two-phase flow and heat transfer during the quenching of a preheated quartz tube. The tube, heated externally by a spiral nichrome tape, was initially empty and Fron113 was pumped into it. In microgravity, a thicker vapor film is formed on the tube wall making the rewetting of the wall more difficult and resulting in the reduction of the heat transfer rate. They observed flow patterns for flow boiling of subcooled Fron113 and saturated LN2 both on the ground and in microgravity, and reported marked differences in the shapes of liquid droplets in the dispersed flow region [3]. Saito et al. [4], using Caravelle aircraft, performed flow boiling experiments for water under subcooled and saturated conditions in a horizontal transparent duct with a concentric heater rod. In microgravity, generated bubbles move along the heating rod without detachment and grow and coalesce to become large bubbles, while the local heat transfer coefficients along the periphery of the heater rod, however, are quite insensitive to gravity levels. Lui et al. [5] presented experimental results on subcooled flow boiling in a horizontal tube, where the heat transfer coefficients due to nucleate boiling in microgravity increase up to 20% from those in normal gravity if subcooling is low. Rite and Rezkallah [6,7] investigated heat transfer in bubbly to annular flow regimes of air–water two-phase flow. The method is useful for the investigation of heat transfer mechanisms for two-phase forced convection under various flow rate combinations of both phases, involving those not easily realized by the single-component system, if the differences between the single-component and binary systems in the interaction of liquid and vapor phases are taken into consideration.

To improve the approach for the clarification of phenomena in microgravity, the present author developed the observation technique, i.e. transparent heated tubes and transparent heating surfaces employed in the flow boiling using round tubes and narrow channels, respectively. In the experiments for flow boiling in a tube, the effect of gravity on the heat transfer was clarified by making reference to the observed liquid–vapor behaviors in a wide quality range covering the bubble to the annular flow regime. Gravity effects on heat transfer due to two-phase forced convection in the annular flow regime were analytically investigated to clarify the mechanisms relating to the gravity-dependent behaviors of annular liquid film. Acquisition of CHF data was attempted in microgravity and one of the major dryout mechanisms was investigated based on the temperature fluctuations obtained at heat fluxes just lower and higher than the critical value. For flow boiling in a narrow gap, a transparent flat heating surface was developed and integrated in a narrow channel, and some heat transfer characteristics inherent in microgravity conditions were clarified.

2 Development of Transparent Heated Tube

2.1 Structure of Transparent Heated Tube

The heated tube is made from a pyrex tube of I.D. 8 mm with a wall thickness of 1 mm to minimize the heat capacity for the effective use of short microgravity duration. The heated length is varied from 17 mm to 260 mm depending on the purposes of individual experiments. The heater is made of a thin gold film and the heating is conducted by the application of DC electric current directly thorough it. The film has a thickness of the order of 0.01 μm and it is transparent to allow the observation of liquid–vapor behavior through the glass tube wall. At the same time the film is utilized as a resistance thermometer to evaluate directly the inner wall temperature averaged over the entire heated length. The gold film is coated uniformly along the heated length by the pulse magnetron spattering technique and therefore...

Produkt-Details

• Erscheint lt. Verlag: 9.10.2003
• Sprache: englisch
• Themenwelt: Sachbuch/Ratgeber
• Themenwelt: Naturwissenschaften ► Chemie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Thermodynamik
• Themenwelt: Technik ► Bauwesen
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 0-08-049355-6 / 0080493556
• ISBN-13: 978-0-08-049355-8 / 9780080493558