Developments In Heat Transfer

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Successful hyperthermia treatment of tumors requires understanding the attendant thermal processes in both diseased and healthy tissue. Accordingly, it is essential for developers and users of hyperthermia equipment to predict, measure and interpret correctly the tissue thermal and vascular response to heating. Modeling of heat transfer in living tissues is a means towards this end. Due to the complex morphology of living tissues, such modeling is a difficult task and some simplifying assumptions are needed. Some investigators have recently argued that Pennes' interpretation of the vascular contribution to heat transfer in perfused tissues fails to account for the actual thermal equilibration process between the flowing blood and the surrounding tissue and proposed new models, presumably based on a more realistic anatomy of the perfused tissue. The present review compares and contrasts several of the new bio-heat transfer models, emphasizing the problematics of their experimental validation, in the absence of measuring equipment capable of reliable evaluation of tissue properties and their variations that occur in the spatial scale of blood vessels with diameters less than about .2 mm. For the most part, the new models still lack sound experimental grounding, and in view of their inherent complexity, the best practical approach for modeling bio-heat transfer during hyperthermia may still be the Pennes model, providing its use is based on some insights gained from the studies described here. In such cases, these models should yield a more realistic description of tissue locations and/or thermal conditions for which the Pennes' model might not apply.

The new and evolving engineering developments associated with gas turbine and jet engines, nuclear power plants, high-speed and orbital flight, and space travel have all faced significant heat transfer problems. It was the response to these problems that swelled the ranks of heat transfer engineers who then proceeded to elevate heat transfer from an art that relied heavily on empirically correlated data to an engineering science that now embraces a healthy union of analysis and experimentation. This rapid expansion of heat- and mass-transfer engineers prompted M.I.T. to organize an annual two-week intensive course on new developments in heat transfer. This book represents the content of the 1964 version of the course.

The relentless drive to improve manufacturing profitability in developed countries has resulted in greater investment in offshore capacity in lower cost regions. EIL believes that worldwide demand for heat exchangers is expected to increase by at least 5% per annum over the next 5 years, however demand in some developing countries is likely to increase by more than 8% annually. In 2012, the developing world accounted for about 30% of all installed heat exchangers, and within 5 years, this share is projected to increase closer to 40%. Asia Pacific is forecast to emerge as the fastest growing regional market, becoming by far the most important regional market for heat exchangers.

HTRI's research program focuses on industry trends (e.g., lowering carbon footprint or assessing new technologies) and addresses gaps or areas where we need to learn more in process heat transfer (e.g., off-design performance).

You can register for our annual Global Conference as an HTRI member. Join us for the 2021 Virtual Global Conference where we will once again highlight the research we have performed over the last year and share our latest advances in process heat transfer technology through a range of digital experiences, including

Multiphase flow and heat transfer have found a wide range of applications in several engineering and science fields such as mechanical engineering, chemical and petrochemical engineering, nuclear engineering, energy engineering, material engineering, ocean engineering, mineral engineering, electronics and micro-electronics engineering, information technology, space technology, micro- and nano-technologies, biomedical and life sciences. This E-book series presents state-of-the-art review and research topics in all aspects of multiphase flow and heat transfer, which are contributed by renowned scientists and researchers. The topics include multiphase transport phenomena including gas-liquid, liquid-solid, gas-solid and gas-liquid-solid flows, phase change processes, nuclear thermal hydraulics, fluidization, mass transfer, bubble and drop dynamics, particle flow interactions, cavitation phenomena, numerical methods, experimental techniques, multiphase flow equipment, combustion processes, environmental protection and pollution control, phase change materials and their applications, macro-scale and micro-scale transport phenomena, nano-fluidics, micro-gravity multiphase flow and heat transfer, energy engineering, renewable energy, electronic chips cooling, data center cooling, fuel cells, multiphase flow and heat transfer in biomedical engineering and science. The E-book series presents recent advances in both conventional research and interdisciplinary research. This E-book series should prove to be invaluable for scientists and researchers interested in multiphase flows.

This paper summarizes some applications of ultrasonic vibrations regarding heat transfer enhancement techniques. Research literature is reviewed, with special attention to examples for which ultrasonic technology was used alongside a conventional heat transfer process in order to enhance it. In several industrial applications, the use of ultrasound is often a way to increase productivity in the process itself, but also to take advantage of various subsequent phenomena. The relevant example brought forward here concerns heat exchangers, where it was found that ultrasound not only increases heat transfer rates, but might also be a solution to fouling reduction.

In engineering applications, ultrasound is helpfully used to improve systems efficiencies. Intensifying chemical reactions, drying, welding, and cleaning are among the various possible applications of ultrasonic waves [1]. An analogous observation can be made for heat transfer processes, which are omnipresent in the industry: cooling applications, heat exchangers, temperature control, and so forth. It is somewhat logical and natural to wonder what could be the influence of ultrasound upon heat transfer systems. Strangely, it has not been a research topic deeply investigated until recently.

It appears that researches undertaken in the past concerned basic systems, usually with a single fluid, such as heating rods or walls in a volume of water subjected to ultrasonic vibrations. The tendency goes toward systems getting more complicated (e.g., cooling of tiny components, vibrating structures for heat exchangers) and models becoming more accurate with powerful numerical simulations for example.

The objectives of this paper are to provide scientific and historical backgrounds to the future studies concerning heat transfer enhancement by ultrasonic vibrations and to bring forward the evolution of this domain with several examples of applications. The first part describes an overview of ultrasound, induced phenomena, and how they positively influence heat transfer processes. Then, examples drawn from various fields of interest are analysed (thermal engineering, food industry, experimental and numerical simulations). Emphasis is made on the best improvements and results obtained. Finally, recent adaptation of ultrasonic technologies to heat exchanger devices is discussed thoroughly, with examples drawn from new patents and current laboratory work.

Many phenomena may ensue from propagation of an ultrasonic wave into a fluid and more particularly into a liquid medium. Two of them, of major importance for heat transfer enhancement, are acoustic cavitation and acoustic streaming. There exist other subsequent effects such as heating of the medium due to dissipation of the mechanical energy. This phenomenon is used for the determination of the ultrasonic energy supplied to the medium in an ultrasonic reactor, well-known as the calorimetric method [1]. With high-frequency ultrasound, an acoustic fountain at the liquid-gas interface may also appear. Temperatures up to 250°C can be reached precisely at this interface [3]. Laborde et al. [4] provided a general description and mathematical modelling of some phenomena resulting from propagation of ultrasound into a liquid. Figure 2 illustrates some of these important effects that may occur in a liquid.

These phenomena have always been a subject of interest since their discovery, and even though research is still ongoing, some comprehensive descriptions have been made by several authors and are frequently updated [1, 4]. Therefore, this paper focuses only on two significant phenomena: acoustic streaming and acoustic cavitation, tackled from a heat transfer point of view.

Acoustic streaming can be considered as a well-known phenomenon since its comprehensive mathematical description by Lighthill in 1978 [5]. He explained that acoustic streaming ensues from the dissipation of acoustic energy which permits the gradients in momentum, and thereby the fluid currents. Riley [6] also makes the distinction between the quartz wind streaming happening in the fluid bulk, and the Rayleigh streaming located at the boundary layers and solid-liquid interfaces. The speed gained by the fluid allows a better convection heat transfer coefficient near the solid boundaries, sometimes leading to turbulence and promoting heat transfer rate (Figure 3).

Acoustic streaming (forced air current) was created in the air above a vibrating beam [8, 9]. It was sufficient to levitate small objects and make them spin around themselves, and thereby computing the flow velocity. The temperature of the object above the beam was decreased sensitively, and the convection heat transfer coefficient around it was increased proportionally to the stream velocity. This is an interesting first example of how acoustic streaming can modify heat transfer coefficients. 2b1af7f3a8