Prediction and Control of Internal Condensing Flows in the Experimental Context of their Inlet Condition Sensitivities

The reported experimental results are for annular zones of fully condensing flows of pure FC-72 vapor. The flow condenses on the bottom surface (316 Stainless Steel) of a horizontal, rectangular cross-section duct. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) values of mass flow rate, inlet (or exit) pressure, and wall cooling conditions. It has been reported elsewhere that, with the condenser mean (time averaged) inlet mass flow rate, mean inlet (or exit) pressure, and wall cooling condition held at quasi-steady values, there is a very strong sensitivity to certain impositions of pressure fluctuations and accompanying flow rate pulsations at the condenser inlet. For these impositions, it was found that the mean exit (or inlet) pressure changes to significantly affect mean test-section pressure difference, local heat-flux variations over the annular portion of the flow, and the nature of the annular flow regime. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of pressure fluctuations imposed on the inlet of the condenser from the vapor line. It has been found that, for various frequencies of interest, there are typically two classes of responses to inlet pressure fluctuations. These are termed supercritical (for the larger amplitudes for which a strong sensitivity exists) and subcritical (for the smaller amplitudes for which a weak sensitivity exists).

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“…The uniqueness and repeatability of these realizations have been shown elsewhere (see Kivisalu et al[1]) by a slightly different procedure.…”

mentioning

confidence: 55%

Shear/Pressure Driven Internal Condensing Flows and Their Sensitivity to Inlet Pressure Fluctuations

Kivisalu

Gorgitrattanagul

Mitra

et al. 2011

Volume 10: Heat and Mass Transport Processes, Parts a and B

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“…), are needed for these critical applications. Although some experimental and computational works have been done, and their results reported [1][2][3][4][5][6][7][8][9][10], further experimental and computational evaluations are needed to enable these critical applications.…”

Section: Introductionmentioning

confidence: 99%

“…Past studies [1][2][3][4][5][6][7][8][9][10] focused on consideration of different flow regimes, flow control methods, and estimating heat transfer coefficient related to the particular flow regimes. Various methods of flow regime control have been proposed, such as actively controlled vapor re-circulation in flow condensers and vapor and liquid re-circulation in flow boilers.…”

Section: Introductionmentioning

confidence: 99%

“…For micro-scale flow boilers and condensers operating at a given mean mass flow rate, it is found that portions of the test section experiencing quasi-steady or transient nonannular (plug/slug, bubbly, etc.) flow regimes require much larger pressure drops [1,2,7,31] than portions where the liquid and vapor phases are mostly separated as in annular flows-with or without micro-bubbles. The experiments reported here involve all-annular boiling flows implemented with the novel method in which re-circulating vapor is used to stabilize the annular flow regime over the entire length of the flow channel while interacting with the rest of the system like a conventional flow boiler (receiving all-liquid flow from the system and sourcing all-vapor flow to the system).…”

Section: Introductionmentioning

confidence: 99%

“…In the system design proposed by Narain et al [7,8,10] and Kivisalu et al [1][2][3][4], to resolve the aforementioned issues, both liquid and vapor are present at the inlet of the boiler as shown in Fig. 1b.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Heat-flux enhancement response for novel flow-boiler operations under resonant, sub-harmonic, and superharmonic imposition of vapor pulsation frequencies relative to a liquid flow-rate pulsation frequency

Koca

Kivisalu

2019

J Braz. Soc. Mech. Sci. Eng.

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This paper presents fundamental results from experimental investigations of shear/pressure-driven internal flow boiling of FC-72 in a horizontal test section of total flow channel length 1000 mm, gap height 2 mm, and width 15 mm. It compares effects of the frequencies of vapor and liquid pressure fluctuations (pulsations) on the experimentally measured heat-flux rates and heat transfer coefficients at a representative location within the flow boiler under a flow operation method in which re-circulating vapor maintains an annular flow regime over the entire length of the device. For liquid flow/pressure pulsations at 3.8-3.9 Hz, four externally imposed inlet vapor pressure fluctuation conditions were considered: (1) no externally imposed vapor pulsations and (2)-(4): high-amplitude externally imposed vapor pulsations at (2) the same, (3) half, and (4) double the inlet liquid pulsation frequency. Representative pressure differences within the flow boiler are also examined. Local time-averaged heat-flux and heat transfer coefficient responses of these flows are compared with previously published data at the same liquid pulsation frequency, but at a different inlet liquid flow rate, vapor quality, and pressure. The reported measurements, and the discussions and conclusions in this paper, enable better understanding of an established pulsationinduced heat-flux enhancement phenomenon which may be used in future cooling systems to significantly enhance average heat-flux values over the entire length of an annular flow boiler. The main conclusion is that, for the flow conditions investigated, optimal heat transfer efficiency occurs when vapor and liquid pulsations are imposed at the same frequency on the flow-boiler inlet.

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Sensitivity of shear-driven internal condensing flows to pressure fluctuations and its utilization for heat flux enhancements

Kivisalu

Gorgitrattanagul

Narain

et al. 2013

International Journal of Heat and Mass Transfer

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Prediction and Control of Internal Condensing Flows in the Experimental Context of their Inlet Condition Sensitivities

Cited by 10 publications

References 10 publications

Shear/Pressure Driven Internal Condensing Flows and Their Sensitivity to Inlet Pressure Fluctuations

Shear/Pressure Driven Internal Condensing Flows and Their Sensitivity to Inlet Pressure Fluctuations

Heat-flux enhancement response for novel flow-boiler operations under resonant, sub-harmonic, and superharmonic imposition of vapor pulsation frequencies relative to a liquid flow-rate pulsation frequency

Sensitivity of shear-driven internal condensing flows to pressure fluctuations and its utilization for heat flux enhancements

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