An experimental study on the spray and thermal characteristics of R134a two-phase flashing spray

Zhou, Zhifu; Wu, Wei‐Tao; Chen, Bin; Wang, Guoxiang; Guo, Liejin

doi:10.1016/j.ijheatmasstransfer.2012.04.021

Cited by 75 publications

(19 citation statements)

References 20 publications

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“…They also proposed a simple two-phase flow model inside straight-tube nozzle to explain the acceleration of droplet velocity near nozzle field that the higher velocity airflow accelerated the lower velocity droplet. Zhou et al [25] obtained droplet density, diameter, and velocity evolution along both radial and axial directions within flow field. A sharp decrease in droplet diameter and an increase in droplet velocity near nozzle field were found, while their variation became more gradual in the far field of spray.…”

Section: Spray and Thermal Characteristics Of Flashing Spraymentioning

confidence: 99%

“…They also reported a dimensionless minimum temperature distance ranging from 150 to 170 (normalized by nozzle diameter) for R134a and propane flashing spray. Later, Zhou et al [25] conducted a much more comprehensive study on the global thermal characteristics of R134a flashing spray with an inserted thermocouple of 0.1 mm. It was found that a warm core existed near nozzle field where droplet radial distribution showed "W" shape, while it transited to a "U" shape in the far field of spray as shown in Figure 6.…”

Section: Spray and Thermal Characteristics Of Flashing Spraymentioning

confidence: 99%

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The Fundamental and Application of Transient Flashing Spray Cooling in Laser Dermatology

Zhou¹,

Chen²

2019

Advanced Cooling Technologies and Applications

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Cryogen spray cooling (CSC) has been successfully implemented in laser dermatology such as the treatment of port wine stain. It can protect epidermis from irreversible thermal injuries and increase laser energy, leading to the improvement in therapeutic outcomes. Different from traditional steady spray cooling, CSC is highly transient with short spurt duration (several tens of milliseconds). Besides, CSC can achieve flashing atomization and fine droplets with simple structure nozzles by rapid release of superheat. In this chapter, the mechanism of CSC flashing spray, spray and thermal characteristics of droplets, the measurement method of transient temperature and algorithms for heat flux estimation, and the dynamic surface heat transfer and its relation with spray characteristics are fully discussed. Finally, the heat transfer enhancement of CSC is introduced including alternative cryogens, new nozzles, and hypobaric pressure method to increase the cooling ability, which is essential to improve therapeutic outcome, especially for darkly pigmented human skin.

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Section: Spray and Thermal Characteristics Of Flashing Spraymentioning

confidence: 99%

Section: Spray and Thermal Characteristics Of Flashing Spraymentioning

confidence: 99%

The Fundamental and Application of Transient Flashing Spray Cooling in Laser Dermatology

Zhou¹,

Chen²

2019

Advanced Cooling Technologies and Applications

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“…• were 295 reported with water (Du et al, 2013;Park and Lee, 1994) as well as R134a (Zhifu et al, 2012). Luo…”

mentioning

confidence: 97%

“…Also, non-common organic solvents such as Dimethyl ether (DME), an isomer of EtOH, have been tested (Ju et al,255 2016a). Due to their high volatility, refrigerants such as liquid nitrogen (Luo and Haidn, 2016), Freon-11 , PFnH (Kurschat et al, 1992), R134a (Ju et al, 2015;Zhifu et al, 2012;Ju et al, 2016b;Wang et al, 2017) have been 260 investigated as well. Organic compounds with high vapor pressures can be included in this category, such as Acetaldehyde (Lecourt et al, 2009).…”

mentioning

confidence: 99%

“…One reason might be that these angles have been reported using different imaging methods. Some of them used high-speed photography (Du et al, 2013;Ju et al, 2015;Lamanna 310 et al, 2014;Pavlenko et al, 2013;Vetrano et al, 2013;Zhifu et al, 2012;Zhang et al, 2015;Guo et al, 2017;Ju et al, 2016b,a;Thompson and Heister, 2016;Wang et al, 2017), while others took photographs with short light pulses or short expo-315 sure times (Park and Lee, 1994;Kurschat et al, 1992;Guo et al, 2018). Alternatively, pulsed lasers have been used to illuminate since they emit light during very short times (Xu et al, 2013;Lecourt et al, 2009;Günther and Wirth, 2013;Sinha 320 et al, 2018).…”

mentioning

confidence: 99%

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Ultra-high speed visualization of a flash-boiling jet in a low-pressure environment

Alghamdi

Thoroddsen

Hernández-Sánchez

2019

International Journal of Multiphase Flow

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Highlights• We visualized flash-boiling jets at an unprecedented frame rate of 5 Million frames per second. At such high frame rate we observed for the first time the evolution of the bubble expansion and the burst mechanisms, responsible for the jet atomization.• For developed flash-boiling conditions, minimum pixel intensity profiles revealed that droplets are ejected in all directions from the nozzle. This crucial fact was translated into spray angles larger than 300• .• The detailed close up to the nozzle revealed that the droplet size distribution of the spray is wide, contrary to the common belief. Using a simple argument we infer that the smallest droplets are on the hundreds of nanometer range. This means that the drop size distribution extends trough almost four orders of magnitude.• We measured velocities up to 140 m/s during the expansion of bubbles from the core of the jet. Such velocity is a bit less than half of the speed of a 0.22 bullet, an unprecedented velocity for expanding bubbles. AbstractWe visualize the flash-boiling atomization of liquid jets released into a low-pressure environment at frame rates of up to five million frames per second using a long distance microscope. Such temporal resolution allowed us to capture the details of the bubble expansion mechanism, responsible for the jet atomization, for the first time. We document an abrupt transition from a laminar to a fully external flashing jet by systematically reducing the ambient pressure. We perform experiments with different volatile liquids, ejected through micro-nozzles with different inner diameters. Surprisingly, minimum pixel intensity projections revealed spray angles close to θ s ∼ 360• and speeds of bubble expansion up to 140 m/s. Particle tracking shows that ejected droplets achieve speeds much larger than the jet velocity and drop sizes order of magnitude smaller than the diameter of the nozzle. Furthermore, hole growth speeds measured on the bubbles film in combination with to Taylor-Culick predictions suggests that the smallest droplet sizes are on the hundreds of nanometer or submicron range, which contravenes the general belief that flash-boiling atomization results in uniform drop sizes.

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Droplet Entrainment Analysis in a Flash Evaporator with an Image‐Based Measurement Technique

Jasch

Schulz

Bart

et al. 2021

Chemie Ingenieur Technik

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Local droplet sizes and volumes of entrained liquid are captured with an image-based measurement technique for comparison with a conventional, integral method for entrainment analysis. Experiments in a forced circulation flash evaporation were performed for different operating conditions and with two different chemical systems. Droplet size and frequency rise with an increase in thermal energy input. The local readings confirm the trends found by the integral measurement method. The modification of the image-based probe enables the detection of small ( 10 mm) and at the same time fast droplets under challenging operating conditions, such as vacuum and superheated feed similar to industrial process conditions.

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An experimental study on the spray and thermal characteristics of R134a two-phase flashing spray

Cited by 75 publications

References 20 publications

The Fundamental and Application of Transient Flashing Spray Cooling in Laser Dermatology

The Fundamental and Application of Transient Flashing Spray Cooling in Laser Dermatology

Ultra-high speed visualization of a flash-boiling jet in a low-pressure environment

Droplet Entrainment Analysis in a Flash Evaporator with an Image‐Based Measurement Technique

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