Analysis of the heat transfer coefficient for liquid nitrogen droplets in cryogenic freezing of foods

Awonorin, S. O.

doi:10.1016/0140-7007(93)90071-f

Cited by 6 publications

(5 citation statements)

References 16 publications

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“…Such models have been developed for gravity spread of liquefied natural gas on flat surfaces [10–12], as well as spread of liquid hydrogen [13], and for the flow of hot gases under a ceiling [14–16]. Data on physical parameters for liquid nitrogen have been reported in the literature [17, 18].…”

Section: Experimental Results and Analysissupporting

confidence: 67%

Cryogenic extinguishment of liquid pool fires

Levendis

Ergut

Delichatsios

2009

Process Safety Progress

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Results on fire extinguishment using direct application of liquid nitrogen are presented in this article. This technique targets challenging fires, such as burning hazardous chemicals or fuels, in which cases prompt suppression or extinguishment is paramount to prevent explosions, avoid release of toxic fumes and avert environmental catastrophes. Liquid nitrogen is a rather environmentally benign extinguishing agent that does not cause property damage or groundwater contamination. Application of this cryogen onto a hot pyrolyzing/burning surface induces abrupt vaporization, spread and expansion. The pyrolyzing gases are inerted, the surface is cooled and hence its pyrolysis rate is reduced, air is separated from the fuel, and the fire extinguishes. To demonstrate this technique, experiments were conducted with pool fires of ethanol, propanol, and diesel fuel. To examine the underlying principles, analysis of the results was conducted based on simplified calculations. Sufficient quantities of the cryogen extinguished the fires nearly instantaneously. Half-liter quantities were sufficient to extinguish 1 m 2 pool fires. The method of dispensing and distributing the cryogen on the pool fires proved to be of considerable importance. The existence of wind, which disturbed the flame, was not found to prevent extinguishment.

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Section: Experimental Results and Analysissupporting

confidence: 67%

Cryogenic extinguishment of liquid pool fires

Levendis

Ergut

Delichatsios

2009

Process Safety Progress

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“…The maximum droplet diameter, d,, and the average droplet diameter, d32 (Sauter mean diameter) can be predicted for a given spray using the nomograph if the spray pressure, physical properties of the liquid and nozzle diameter are known. The nomograph gives good agreement with the results of Lee (1932) and is also satisfactory when applied to sprays of liquid nitrogen (Awonorin, 1982). It was applied in the present work.…”

Section: Introductionsupporting

confidence: 80%

“…Figure 1 shows a section of the experimental equipment when assembled. The gelatine slab (15 cm0x5.04 cm thick) was prepared in a perspex ring containing six chromel-alumel thermocouples connected in a grid form to different points in the slab at approximately 1 mm deep from its external surface in order to measure the average slab surface temperature, Tp (Awonorin, 1982). The temperature differences, AT, i.e.…”

Section: Methodsmentioning

confidence: 99%

“…Schoessow, Chmielewski and Baumeister (1978) concluded that contamination of nitrogen by ice at the early stages of droplets' formation, and convection effects account for approximately 20% of the vaporization times. Hassan (1981), Awonorin (1982), and Awonorin and Lamb (1988) measured vaporization times and heat transfer to liquid nitrogen droplets on a food surface and showed decreased vaporization times, and hence, high heat transfer coefficients. The heat transfer coefficient to individual droplets contacting a solid surface (metal or food) varies with droplet diameter (d-1'4) (Baumeister etal., 1966;Awonorin & Lamb, 1988).…”

Section: Introductionmentioning

confidence: 99%

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A model for heat transfer in cryogenic food freezing

Awonorin

1989

Int J of Food Sci Tech

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An experimcntal study of the heat transfer between liquid nitrogen sprays and a model food (a gelatine slab) was carried out under conditions similar to those in a cryogenic freezer. Measurements of heat flux and local mass flow rates of the spray were made at various liquid N2 pressures and various temperature differences between the spray and the food surface.At higher spray pressures, the heat transfer doefficient increases with the mass flux density of the liquid available at the food surface. The quantity of liquid nitrogen sprayed onto the solid surface, the mean droplet size, spray velocity, surface coverage and the mean temperature difference between the boiling nitrogen and the food surface are major factors influencing the rate of heat transfer during the freezing process. Although the heat transfer coefficients at the food surface are much less than those obtained for individual droplets, the model provides useful data.The results are critically discussed in relation to cryogenic freezing of foods.

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“…The construction and final arrangement of the drop generator, heat exchanger, Dewar flask, positioning of flood lighting unit, camera, gelatine slab and temperature recorders are as used by Hassan (1981) and modified by Awonorin (1982).…”

Section: Methodsmentioning

confidence: 99%

Heat transfer coefficient for nitrogen droplets film‐boiling on a food surface

Awonorin

Lamb

1988

Int J of Food Sci Tech

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A method of measuring heat transfer rates from a solid food surface to liquid nitrogen droplets on it has been developed using 0.5 sec repeat-shot photography. Droplet diameters were varied from 0.1 to 2.5 mm and food surface temperatures from +30 to -100°C. All measurements were carried out at atmospheric pressure.The mean heat transfer coefficients were determined using an energy balance for the droplets. An empirical dimensionless correlation equation was established, and the significance of the results for food freezing by liquid nitrogen sprays is critically discussed. KeywordsHeat transfer rates, liquid nitrogen food freezing, nitrogen droplets.

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Analysis of the heat transfer coefficient for liquid nitrogen droplets in cryogenic freezing of foods

Cited by 6 publications

References 16 publications

Cryogenic extinguishment of liquid pool fires

Cryogenic extinguishment of liquid pool fires

A model for heat transfer in cryogenic food freezing

Heat transfer coefficient for nitrogen droplets film‐boiling on a food surface

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