Providing a comprehensive introduction to the fundamentals and applications of flow and heat transfer in conventional and miniature systems, this fully enhanced and updated edition covers all the topics essential for graduate courses on two-phase flow, boiling, and condensation. Beginning with a concise review of single-phase flow fundamentals and interfacial phenomena, detailed and clear discussion is provided on a range of topics, including two-phase hydrodynamics and flow regimes, mathematical modeling of gas-liquid two-phase flows, pool and flow boiling, flow and boiling in mini and microchannels, external and internal-flow condensation with and without noncondensables, condensation in small flow passages, and two-phase choked flow. Numerous solved examples and end-of-chapter problems that include many common design problems likely to be encountered by students, make this an essential text for graduate students. With up-to-date detail on the most recent research trends and practical applications, it is also an ideal reference for professionals and researchers in mechanical, nuclear, and chemical engineering.

/pdf/two-phase-flow-boiling-and-condensation-in-conventional-and-5aink3qfmk.pdf

Two-phase flow, boiling and condensation in conventional and miniature systems

Halogenated hydrocarbons with high ozone depletion potential (ODP) were banned under Montreal Protocol (1987) due to their detrimental effects on ozone layer that shields the planet against ultraviolet radiations. The greenhouse gases (GHG) used in modern refrigeration, air conditioning, and heat pumping systems, are under Kyoto Protocol (1997)’s time-barred permission period. In order to reduce the depletion of ozone and reverse the climate change effects, the European Union legislation (2014) and Paris Accord (2016) are strongly emphasizing the phasing out of the use of harmful synthetic refrigerants. Choice of natural refrigerants makes no net addition of the greenhouse gases (GHG) in the environment. To retrofit and modify existing cooling and heating systems using natural refrigerants, extensive investigations are in progress worldwide. This work reviews timeworn, current and the next-generation refrigerants using Refrigerant Qualitative Parametric (RQP) quantification model to assist the refrigerant choice decision process. It is based on the ratio of arithmetic sums of actual parametric values of refrigerants normalized to equivalent ideal values. This model can help in choosing alternative refrigerants to replace CFCs by HCFCs or HFCs provisionally and finally replacing HCFCs or HFC to low GWP and ODP synthetic and natural refrigerants. A set of 16 refrigerants, both natural and synthetic, as an example, is computed for the standard Vapour Compression Cycle (VCC) based on the proposed model using REFPROP (NIST- 23 standard). The techno-economic parametric values of chosen refrigerants are taken from cited literature, ASHREA safety standards and international environmental legislations, laws and protocols. This paper reports the environment benign natural (CO2, NH3, HCs) and a few synthetic (R-152a, R-1234yf) refrigerants to be the optimal options.

Natural and synthetic refrigerants, global warming: A review

Boiling phenomena with surfactants and polymeric additives: A state-of-the-art review

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1131&context=coolingpubs

Bubble nucleation characteristics in pool boiling of a wetting liquid on smooth and rough surfaces

Pool boiling is of interest in high heat flux applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is not adequate to match the cooling ability provided by enhanced microchannels operating under single-phase conditions. The objective of this work is to evaluate the pool boiling performance of structured surface features etched on a silicon chip. The performance is normalized with respect to a plain chip. This investigation also focuses on the bubble dynamics on plain and structured microchannel surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism. It was determined that surface modifications to silicon chips can improve the heat transfer coefficient by a factor up to 3.4 times the performance of a plain chip. Surfaces with microchannels have shown to be efficient for boiling heat transfer by allowing liquid to flow through the open channels and wet the heat transfer surface while vapor is generated. This work is expected to lead to improved enhancement features for extending the pool boiling option to meet the high heat flux removal demands in electronic cooling applications.

Pool Boiling Heat Transfer and Bubble Dynamics Over Plain and Enhanced Microchannels

The correct prediction of the heat transfer performance of the boiling liquid within the evaporator of a refrigeration unit is one of the essential features for the successful operation of the whole unit. A theoretically consistent calculation method for the heat transfer coefficient α in nucleate boiling, which should be based on the physical phenomena connected with vapour bubbles growing, departing and sliding on the wall and with the interactions of bubbles and of neighbouring nucleation sites within the microstructure of the heating surface, does not yet exist, despite the increasing number of papers on the subject in the recent past. Instead, the predictive methods for α available at present are empirical or semiempirical, especially for heat transfer conditions relevant in practice. Many of these correlations have been established in the form of power laws in which the relative influences of the main groups of variables on α are treated by separate factors. One of these may stand for the influence of the thermophysical properties of the boiling liquid or these properties will be included in several of the factors. New experimental results are presented for pool boiling heat transfer from a single horizontal copper tube (8 mm OD) to HFC-refrigerants (R32, 125, 134a, 143a, 152a, 227ea) and hydrocarbons (propane, i -butane). The results are compared to experimental data from the literature, and methods are discussed, how to incorporate the data in semiempirical correlations to describe the influence of the thermophysical properties of the fluids on the heat transfer performance.

Influence of thermophysical properties on pool boiling heat transfer of refrigerants

Bubble formation with pool boiling on tubes with or without basic surface modifications for enhancement

Within the frame of a German Joint Research Project on fundamentals of boiling heat transfer, institutes of six universities recently started collaboration for the development of a general theory for pool boiling. The subproject to be discussed in this paper aims at understanding of the fundamental processes promoting heat transfer enhancement in nucleate pool boiling. Surface modifications with comparatively simple geometries are applied to a plain horizontal copper tube (25.4 mm O.D.) with uniform surface roughness. The reduced saturation pressure is varied within 0.8 ≤ p s /p crit ≤ 0.007 with R134a and 2-Propanol as boiling liquids. First measurements without surface modifications show that the local superheat of the tube wall can be measured very accurately along the whole circumference of the tube, thus demonstrating the variation of convective effects with heat flux, pressure, and azimuthal position. It can be expected that the comparison of these data with future measurements after modifying the surface structure will provide further insight in the basic processes connected with heat transfer enhancement.

Pool boiling heat transfer from tubes with basic surface modifications for enhancement: Design of the test tubes and first measurements

On a commence des etudes sur l'influence de la convection et de la formation de bulles sur le transfert thermique local en ebullition libre d'un tube de cuivre (25 mm O) a Propane pour un grand domaine de pression et flux thermique. Les premiers resultats montrent que les variations des temperatures locales du tube peuvent etre mesurees tres exactement.

Untung Chandra

Papers

Influence of thermophysical properties on pool boiling heat transfer of refrigerants

Bubble formation with pool boiling on tubes with or without basic surface modifications for enhancement

Pool boiling heat transfer from tubes with basic surface modifications for enhancement: Design of the test tubes and first measurements

Pool boiling heat transfer and bubble formation of natural refrigerants on horizontal tubes.

Pool Boiling Heat Transfer from Tubes with and without Basic Surface Modification for Enhancement