Measurements of Heat Transfer Coefficients to Cylinders in Shallow Bubble Columns

Tow, Emily W.; Lienhard, John H.

doi:10.1615/ihtc15.tbf.008857

Cited by 4 publications

(12 citation statements)

References 20 publications

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“…We have found no correlation developed for tall columns that satisfacto-rily predicts the heat transfer coefficient in a shallow column, but we have demonstrated agreement with several correlations with respect to the dependence on superficial velocity [15]. One of these correlations is Deckwer's [18], which is straightforward and widely-used.…”

Section: Theoretical Backgroundmentioning

confidence: 77%

“…We have previously shown that the heat transfer coefficient in a shallow column depends on the distance, H, from the sparger plate [15], and we wish to quantify this effect with a correlation that utilizes the vast amount of existing knowledge about heat transfer in tall bubble columns. Of the two correlations mentioned, Deckwer's is more straightforward.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…Little is known, however, about the effect of geometry on the heat transfer coefficient in shallow bubble columns with internals. Tow and Lienhard [15] found that cylinder diameter does not significantly affect the heat transfer coefficient outside cylinders in a shallow columns. The influence of additional geometric parameters relevant to shallow columns has not been studied extensively.…”

Section: Introductionmentioning

confidence: 97%

“…The influence of additional geometric parameters relevant to shallow columns has not been studied extensively. The heat transfer coefficient has been shown to vary with radial [13] and vertical [16,13] position in a tall column, and with vertical position in a short column [15]. Narayan et al [1] proposed that horizontal position of internals with respect to the gas sparger orifices could affect heat transfer coefficients.…”

Section: Introductionmentioning

confidence: 99%

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Heat transfer to a horizontal cylinder in a shallow bubble column

Tow¹,

Lienhard²

2014

International Journal of Heat and Mass Transfer

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Heat transfer coefficient correlations for tall bubble columns are unable to predict heat transfer in shallow bubble columns, which have unique geometry and fluid dynamics. In this work, the heat transfer coefficient is measured on the surface of a horizontal cylinder immersed in a shallow air-water bubble column. Superficial velocity, liquid depth, and cylinder height and horizontal position with respect to the sparger orifices are varied. The heat transfer coefficient is found to increase with height until reaching a critical height, and a dimensionless, semi-theoretical correlation is developed that incorporates superficial velocity, liquid properties, and height. Additionally, the more minor effects of flow regime, column region, and bubble impact are discussed with the aim of informing design. Notably, the heat transfer coefficient can be as high in the region of bubble coalescence as in the bulk of the column, but only if the probe is placed so that bubbles impact the cylinder. The correlation and discussion provide a framework for modeling and designing * Address all correspondence to lienhard@mit.edu Greek

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Section: Theoretical Backgroundmentioning

confidence: 77%

Section: Theoretical Backgroundmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Heat transfer to a horizontal cylinder in a shallow bubble column

Tow¹,

Lienhard²

2014

International Journal of Heat and Mass Transfer

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“…Tow and Lienhard [11,12] also measured heat transfer rates up to more than 8,000 W/m 2 -K in shallow bubble columns, further justifying their use in the dehumidification side of an HDH system.…”

Section: Bubble Column Dehumidifiers In Hdhmentioning

confidence: 92%

Thermodynamic balancing of a fixed-size two-stage humidification dehumidification desalination system

Chehayeb

Narayan²,

Zubair

et al. 2015

Desalination

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Humidification dehumidification (HDH) is a desalination technology that has shown promise in small scale, decentralized applications. Previous studies on the multi-staging of HDH have used fixed-effectiveness models which do not explicitly account for transport processes in the components. However, to fully understand the effect of the variation of the mass flow rate ratio, it is necessary to implement heat and mass transfer models of the HDH system. In this paper, we model an HDH system consisting of a packed-bed humidifier and a multi-tray bubble column dehumidifier. We study the effect of the mass flow rate ratio on the performance of a fixed-size system, and we consider its effect on the entropy generation and the driving forces for heat and mass transfer. In addition, we define a generalized energy effectiveness for heat and mass exchangers. We also implement an air extraction/injection and simulate a wide range of operating conditions. We define criteria for the best system performance, and we study the effect of the distribution of available area between separate stages. We also present a thorough explanation of why the direction of extraction should always be from the humidifier to the dehumidifier.

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Energy Savings in Desalination Technologies: Reducing Entropy Generation by Transport Processes

Lienhard

2019

Journal of Heat Transfer

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Desalination systems can be conceptualized as power cycles in which the useful work output is the work of separation of fresh water from saline water. In this framing, thermodynamic analysis provides powerful tools for raising energy efficiency. This paper discusses the use of entropy generation minimization for a spectrum of desalination technologies, including those based on reverse osmosis (RO), humidification–dehumidification (HDH), membrane distillation (MD), electrodialysis (ED), and forward osmosis (FO). Heat and mass transfer are the primary causes of entropy production in these systems. The energy efficiency of desalination is shown to be maximized when entropy generation is minimized. Equipartitioning of entropy generation is considered and applied. The mechanisms of entropy generation are characterized, including the identification of major causes of irreversibility. Methods to limit discarded exergy are also identified. Prospects and technology development needs for further improvement are mentioned briefly.

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Measurements of Heat Transfer Coefficients to Cylinders in Shallow Bubble Columns

Cited by 4 publications

References 20 publications

Heat transfer to a horizontal cylinder in a shallow bubble column

Heat transfer to a horizontal cylinder in a shallow bubble column

Thermodynamic balancing of a fixed-size two-stage humidification dehumidification desalination system

Energy Savings in Desalination Technologies: Reducing Entropy Generation by Transport Processes

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