Heat Transfer Coefficients in Falling Film Heater Streamline flow

Bays, G. S.; McAdams, W. H.

doi:10.1021/ie50335a010

Cited by 79 publications

(10 citation statements)

References 6 publications

(7 reference statements)

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“…Accordingly, the q cond values for the studied compositions (especially when comparing the foaming agent emulsion and EA-5 solution with other liquids) differed significantly at identical heating temperatures. The choice of expressions for the calculation of Nu numbers was made in the analysis of the main conclusions [30,[32][33][34][35][36]. Similar to generalization of experimental results in the study [12], possible heat losses are not taken into account in this work when calculating the values of specific heat fluxes.…”

Section: Experimental Setup and Methodsmentioning

confidence: 99%

Rates of High-Temperature Evaporation of Promising Fire-Extinguishing Liquid Droplets

et al. 2019

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Differences in the rates of heating and evaporation of droplets with the component composition are important parameters of heat transfer processes and phase transformations. This paper presents the values of high-temperature (up to 600 °C) evaporation rates of droplets of promising fire-extinguishing compositions (water, bentonite suspension, bischofite solution, EA-5 solution, and foaming agent emulsion) at convective (in the air stream), conductive (on a heated surface), and radiation (in a muffle furnace) heating. A high-speed video recording system and tracking software algorithms are used. At identical initial sizes of droplets of fire-extinguishing suspensions, known as emulsions and solutions, the times of their complete evaporation are shown to differ 3.7 times when heating on the substrate, 1.25 times in the air flow, and 1.9 times in the muffle furnace. A general approximation expression is formulated, and the empirical constants are calculated to predict the evaporation rate of the droplets of extinguishing agents in a wide range of temperatures (up to 600 °C) and heat fluxes (up to 100 kW/m2), which are characteristic of forest fires. With the use of the experimental data obtained, it is possible to predict the completeness of evaporation of promising extinguishing liquids at different schemes of heat supply.

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Section: Experimental Setup and Methodsmentioning

confidence: 99%

Rates of High-Temperature Evaporation of Promising Fire-Extinguishing Liquid Droplets

et al. 2019

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“…In this work, we make the following assumptions: Hot streams supply heat to MR only. No heat transfer between hot streams is allowed. For each data set, the stream compositions, pressures, DPTs, and BPTs are all known constants through the entire bundle. All inlet and outlet temperatures in the data sets are the actual inlet and outlet temperatures of the streams in the MSHE bundle. The film heat‐transfer coefficient $ h_i^n $ for a hot stream i in data set n is given29, 30 by $ h_i^n = \alpha _i \left( {M_i^n } \right)^{0.8} $ , where α i is a parameter that depends on fluid and exchanger properties. The film heat‐transfer coefficient $ h_j^n $ for a cold stream j in data set n is given31, 32 by $ h_j^n = \beta \left( {f_j M_{MR}^n } \right)^{0.25} $ , where β is a parameter that depends on fluid and exchanger properties. Fouling and other thermal resistances are negligible, and the overall heat‐transfer coefficient is given by which is a function of f j only. …”

Section: Minlp Formulationmentioning

confidence: 99%

“…The film heat‐transfer coefficient $ h_j^n $ for a cold stream j in data set n is given31, 32 by $ h_j^n = \beta \left( {f_j M_{MR}^n } \right)^{0.25} $ , where β is a parameter that depends on fluid and exchanger properties.…”

Section: Minlp Formulationmentioning

confidence: 99%

Operational modeling of multistream heat exchangers with phase changes

et al. 2008

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in Wiley InterScience (www.interscience.wiley.com).Multistream heat exchangers (MSHE) enable the simultaneous exchange of heat among multiple streams, and are preferred in cryogenic processes such as air separation and LNG. Most MSHEs are complex; proprietary and involve phase changes of mixtures. Although modeling MSHE is crucial for process optimization, no such work exists to our knowledge. We present a novel approach for deriving an approximate operational (vs. design) model from historic data for an MSHE. Using a superstructure of simple 2-stream exchangers, we propose a mixed-integer nonlinear programming (MINLP) formulation to obtain a HE network that best represents the MSHE operation. We also develop an iterative algorithm to solve the large and nonconvex MINLP model in reasonable time, as existing commercial solvers fail to do so. Finally, we demonstrate the application of our work on an MSHE from an existing LNG plant, and successfully predict its performance over a variety of seasons and feed conditions.

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“…1 [4], a rotameter and a heater [6] (for temperature control) and then through the scraped-film exchanger [8] back to the reservoir. To avoid oxidation of the ferrocyanide solution, nitrogen gas blanketed the storage tanks.…”

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confidence: 99%

Local heat transfer coefficients in scraped-film heat exchanger.

Miyashita

Hoffman

1978

J. Chem. Eng. Japan

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The instantaneous heat transfer coefficientsin a scraped-film heat exchanger have been determined using the electrochemical technique for a two-bladed, 78.7 mmI.D. exchanger. The time-averaged local heat transfer coefficients were found to agree fairly well with previous work of Azoory and Bott, though some variation in liquid flow rate was detected. The timeaveraged local Nusselt number was found to be represented by Nu =0.15(Rer à" Pr)inRel with a=(l-3.74 x 10"W)/9. The variation of heat transfer coefficient with time was observed to be very different from that predicted by the accepted model for the phenomena based upon unsteady state conduction.In a scraped-film heat exchanger, the liquid film is subjected to gravitational and centrifugal forces as the blades rotate and scrape it from the outer heat transfer surface. At the same time, fresh material is exposed to a clean heat transfer surface. The fluid mechanical and heat transfer phenomenaoccurring in such a system are very complex and hence any analysis of the heat transfer mechanisms must be based on a simplified model for these phenomena. The object of this study was to measure indirectly the instantaneous heat transfer rate at points in the exchanger in order to elucidate the actual behavior in such systems. This was done using the electrochemical method developed for such studies10\ The main advantage of such a system is that it provides an instantaneous mass transfer rate uncomplicated by thermal or mass capacity effects.The analogy between heat and mass transfer allows translation of the mass transfer rate to a heat transfer rate (or coefficient).Many investigators have studied the scraped-film heat exchanger. For instance, Kern and Karakas7) and Lustenader et al.9) have postulated that heat is transferred through the film by steady-state molecular conduction. Kool8) and Harriot5) suggest that the rate of heat transfer depends more on the rate of transient conduction in a frequently renewed layer than on the rate of steady-state conduction through Received February 16, 1978. Correspondence concerning this article should be addressed to H. Miyashita.

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Heat Transfer Coefficients in Falling Film Heater Streamline flow

Cited by 79 publications

References 6 publications

Rates of High-Temperature Evaporation of Promising Fire-Extinguishing Liquid Droplets

Rates of High-Temperature Evaporation of Promising Fire-Extinguishing Liquid Droplets

Operational modeling of multistream heat exchangers with phase changes

Local heat transfer coefficients in scraped-film heat exchanger.

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