Cryogen Spray Research Articles

Development of test rig for optical diagnostics of cryogenic spray

Spray cooling is the primary method for conducting chilldown and fill of cryogenic propellant tanks. In a typical spray injection process, a liquid sheet/jet that exits the spray nozzle undergoes primary breakup by the development of surface instabilities. Droplets and ligaments generated after the primary breakup undergo secondary breakup to create a dispersion of droplets, which extract heat on impact with the tank walls. In the existing literature, there is limited data on the primary breakup of cryogenic sprays and their detailed visualization. Moreover, an insight into the spray characteristics such as primary breakup length and cone angle is vital to the development of computational models. In this investigation, optical diagnostics of cryogenic spray breakup and measurements of cryogenic spray characteristics have been conducted. Liquid nitrogen is the selected cryogen for the present analysis. To capture the transient nature of spray breakup after the injection, a novel shadowgraph technique is developed to photographically freeze the spray motion. Cryogenic spray characteristics such as cone angle and primary breakup length are obtained from the shadowgraph. In addition, droplet velocity measurement using Particle Image Velocimetry is explored. The comprehensive experimental dataset obtained herein not only provides insights into the mechanism of spray formation for cryogenic fluids but also helps in designing of spray cooling system for tank chilldown.

Improving fluid flow and heat transfer of cryogen spray cooling using sweeping cold air jet

Industrial growth has led to increased electronic component integration, resulting in higher working temperatures and technological failures. Cryogen spray cooling (CSC) could reach cryogenic temperatures with fast-responding, but its heat transfer limitation due to liquid film deposition is potentially challenging. In this study, CSC cooling is incorporated with either a cold air jet (CAJ) or a sweeping jet (SWJ) to enhance heat and fluid flow. A K-type thermocouple is used for measuring the surface temperature, while the improved Duhamel theorem is used to estimate the heat flux. The spray and film intensities are recorded through the Mie-scattering methodology via high-speed camera. The results demonstrated that the CAJ/SWJ exhibited a significant reduction in surface temperature and film intensity, enhanced heat dissipation and spray efficiency compared to CSC cooling. More precisely, it demonstrated a 26%–36% heat transfer coefficient improvement, along with a 52% increase in the corresponding time of the critical heat flux. Meanwhile, the CAJ/SWJ intensifies heat transfer during film and transition boiling, inspired by the fast liquid film evaporations. In contrast, the SWJ is much preferred due to its wider and stable coolant coverage throughout film evaporation, as seen by its greater heat transfer coefficient. The combined results demonstrated the need to promptly eliminate the deposited film, as it holds the potential to serve as a pivotal resolution for the advancement of thermal management technology.

Intermittent cryogen spray cooling coupled with cold air jet for heat transfer enhancement and cryogen saving of laser dermatology

Laser dermatology has become a convenient technique for medical treatment. However, the epidermal temperature could be increased, leading to intolerable side effects. Cryogen spray cooling (CSC) is implemented to decrease epidermal damage, but the current CSC could increase cryogen wastage. In this study, the CSC is coupled with a cold air jet (CAJ) and is further subjected to intermittent strategy (ICSC) to mitigate film deposition, enhance heat transfer, and save cryogen consumption, through CAJ-to-spray interaction. The surface temperature is measured by a thin film type-T thermocouple, while the heat transfer is estimated by enhanced Duhamel theorem. The film intensity is captured by a digital single-lens reflex camera through the scattering-illumination technique. The results affirmed the benefits of using ICSC/ICSC-CAJ for laser dermatology. It demonstrated lower surface temperature, film intensity, and film resistance as well as higher convection and efficiency compared with CSC. ICSC-CAJ showed the lowest minimum temperature (1.8%–4.9% decrement) and film resistance (3.8%–17.5% decrement), the highest average convective coefficient (84%–92% increment) and efficiency (7%–9% increment) compared with ICSC. Lower frequency and moderate duties would be preferable for ICSC, while higher frequency and lower duties would be preferable for ICSC-CAJ. The efficiency increased with the saving (110% increment), which insights into our understanding of alternative enhancement toward cryogen saving strategy.

Transient behavior of liquid film deposition and surface heat transfer upon cryogen-spray cooling coupled with cold air jet

Cryogen spray cooling (CSC) has become a promising auxiliary-cooling technique for laser dermatology, which recently enhanced by cold air jet (CSC-CAJ). However, the CAJ-to-spray interactions could worsen the CSC performance and associated liquid film behavior. In this study, the transient behavior of liquid film deposition and surface heat transfer of CSC-CAJ was investigated. A high-speed camera was used to capture the film intensity through Mie-scattering technique. Fast-response TFTC thermocouple was used to measure the transient surface temperature. The large eddy simulation (LES) was used to extract the vortical structure, while the discrete-phase model (DPM) and Eulerian wall film (EWF) were coupled for the spray process and the transient film modeling. The results showed that the CAJ significantly enhanced CAJ-to-spray mixing and mitigated the film thickness (i.e., 32 % reduction). The CSC-CAJ had asymmetric film coverage due to induced counter-rotating vortex-pairs (CRVP) from the CAJ-to-spray interaction, which laterally clustered the spray. It permitted fast evaporation with dominant CAJ at the spray-periphery while permitting fast evaporation with dominant spray at the spray-core. Consequently, the CSC-CAJ showed 75 % temperature increment at the windward side and 15 % temperature reduction with 60 % heat transfer coefficient enhancement at the impingement point. The experimental film intensity and simulated film thickness were linearly correlated and significantly influenced the surface temperature. The combined results affirmed the significant impact of the CAJ on the transient film deposition, which potentially helps promote advanced cooling technology.

Unstable spray pattern and cooling performance of cryogen spray coupled with cold air jet: An experimental study

This study focuses on the interactions between cryogen spray cooling (CSC) and cold air jet (CAJ), as well as the heat transfer performance upon CAJ-CSC impingement assisted for laser dermatology. CAJ is found to collapse downstream spray on the windward side, enhancing fluctuations of R1234yf spray width. Standard deviation (SD) distribution identifies that fluctuations at nozzle exit are attributed to ambient-to-spray interactions, which is also confirmed by the proper orthogonal decomposition (POD) analysis. The third POD mode highlights jet-to-spray interactions on the windward side of spray, yielding an enhanced instability by 1.72 times when CAJ flow rate (Q) increases from 4 to 8 m3/h. The closer location to the spray center on the same radial side corresponds to a faster thermal response and a lower temperature drop (ΔT). ΔT on the windward side decreases due to the considerable CAJ-induced droplet swarm drift. The heat transfer degrades on the leeward side due to the thermal gas boundary layer originating from the inclined CAJ sweep. Nevertheless, the CAJ with a small flow rate (4 m3/h) enhances the heat transfer at spray center, yielding a minimum surface temperature of −32.3 °C. Comparative investigation indicates R134a has superior cooling performance but more significant instabilities inside spray plume. R1234yf serves a relatively stable sub-cooling region within a radial distance of ±1 mm from spray center characterized by low spray fluctuations and high temperature drops at Q = 4 m3/h. Substitution of R1234yf for R134a still needs heat transfer enhancement for clinical considerations.

350. FUNCTIONAL RESPONSES OF SWINE ESOPHAGUS TO FOCAL CRYOTHERAPY

Abstract Barrett’s esophagus is a premalignant condition where the squamous epithelium of the distal esophagus is replaced by columnar epithelium. Treatment involves endoscopic resection followed by ablation for complete eradication. Various ablative techniques exist including cryotherapy which utilizes a cryogen spray or balloon catheter. While efficacious, complications such as dysphagia have been reported. To better understand the underlying mechanism of how cryotherapy might damage the muscularis, isolated muscle strips were ablated and their function studied. Isolated muscle strips with the mucosa layers removed were prepared from freshly isolated swine esophagus and placed in tissue baths where they were electrically stimulated, and contractile forces were recorded. Contractile responses were allowed to stabilize before a given muscle strip was removed for focal ablation. Cryoablation was performed with a focal cardiac ablation catheter (Freezor, Medtronic). Following ablation, the given muscle strip was returned to the tissue baths. Regression analyses were performed using temperature data from a thermocouple integrated into the tip of the ablation catheter and contractile forces after the esophageal muscle strips had recovered for 3 hours. Ablations lasting less than 60 seconds were applied to 135 esophageal muscle strips: with an average mass of 94 mg. From the experimental data, a multiple linear regression model was generated: 71.93 + 0.4770x—0.5530y = z, where x is the minimum temperature (C), y is the time below 0 C, and z is the contractile force (normalized to preablative force, %). Our model has an adjusted R-squared value of 0.508. As expected, lower minimum temperatures and longer treatment times were associated with greater losses in stimulated muscle forces. We were able to reproducible ablate isolated swine esophageal strips that elicited contractile responses in vitro. Lower temperatures and longer treatment times were associated with greater losses in stimulated muscle forces. Yet, the adjusted R-squared value indicates that temperature and time only partially explain the response. Future studies could be improved by accounting for variabilities in sample sizes and additionally, regression diagnostics need to be performed to check for outliers and validate model assumptions.

Investigation of unsteady flow behavior of cryogen-spray coupled with cold air jet

Cryogen spray cooling (CSC) coupled with cold air jet (CAJ) was used to mitigate Cryogen consumption. However, the CAJ interaction could affect the flow structure and spray's unsteadiness, permitting coolant intermittency. In this study, the unsteady behavior and flow structure of CSC coupled with CAJ have been qualified. During the experiment, CAJ at an inclined angle of 30°, temperature of 266 K, flowrate of 0.0, 3.0, 6.0 m3/h, and axial distance of 20 mm from the spray-nozzle was injected into a typical R-134a spray system. A high-speed camera was used to capture the unsteady spray through the Mie-scattering technique, while large-eddy simulation (LES) coupled with discrete-phase model (DPM) was used to predict the vortical structure. The spatial correlation was used to identify the coherent structures, while the proper orthogonal decomposition (POD) was used to demonstrate their unsteady signatures. The results showed a significant impact of the CAJ on the spray-pattern and associated unsteadiness, providing an asymmetric spray-plume at the CAJ windward side. The CAJ increased the fluctuating energies of the unsteady coherent structures by 32 % through CAJ-to-spray interactions. It contributed to the unsteady spray through the counter-rotating vortex-pairs (CRVP) at the lateral sides and hairpin vortices along the injection line. The CRVP clustered the spray in recirculating regions, introducing unsteady CAJ entrainment at the leeward and thermal field at the windward. This work could insight into our understanding of unsteady multiphase flow, promoting advanced cooling technology by uncovering their causes and effects.

Comparison of Surface Morphology and Tool Wear in the Machining of Ti-6Al-4V Alloys with Uncoated and TiAlN Tools under Dry, Minimum Quantity Lubrication, Flood Cooling, and Low-Temperature Spray Jet Cooling Conditions.

TiAlN-coated carbide tools have been used to machine Ti-6Al-4V alloys in aviation workshops. However, the effect of TiAlN coating on surface morphology and tool wear in the processing of Ti-6Al-4V alloys under various cooling conditions has not been reported in the public published literature. In our current research, turning experiments of Ti-6Al-4V with uncoated and TiAlN tools under dry, MQL, flood cooling, and cryogenic spray jet cooling conditions were carried out. The machined surface roughness and tool life were selected as the two main quantitative indexes for estimating the effects of TiAlN coating on the cutting performance of Ti-6Al-4V under various cooling conditions. The results showed that TiAlN coating makes it hard to improve the machined surface roughness and tool wear of a cutting titanium alloy at a low speed of 75 m/min compared to that achieved by uncoated tools. The TiAlN tools presented excellent tool life in turning Ti-6Al-4V at a high speed of 150 m/min compared to that achieved by uncoated tools. From the perspective of obtaining finished surface roughness and superior tool life in high-speed turning Ti-6Al-4V, the selection of TiAlN tools is feasible and reasonable under the cryogenic spray jet cooling condition. The dedicative results and conclusions of this research could guide the optimized selection of cutting tools in machining Ti-6Al-4V for the aviation industry.

Study of Operating Modes of a Cryogenic Spray Mixing Gasifier with Adjustable Capacity

Study of Operating Modes of a Cryogenic Spray Mixing Gasifier with Adjustable Capacity

Parametric investigation of multi-pulsed cryogen spray cooling for skin protection during hyperthermal laser lipolysis through in vitro experiment and numerical simulation

Nowadays laser lipolysis has been a widely accepted modality to remove fat. Transcutaneous hyperthermal laser lipolysis has attracted researchers’ interest because of its non-invasive nature and high efficiency. However, the possible thermal damage of skin tissue owing to the competitive absorption of laser energy between water and adipose tissue limits its application, which necessitates the development of efficient skin cooling technology. An in vitro laser experiment of streaky pork under 1210 nm laser irradiation with different power (E) and irradiation (t) proved that the epidermis temperature will exceed the safety threshold of 47 °C when E = 6W and t ≥ 5s, or E ≥ 9W and t ≥ 3s. To protect skin from thermal injury, the multi-pulsed cryogen spraying cooling (MP-CSC) by using R134a was introduced and numerical simulation was conducted to optimize cooling and laser parameters by simplifying the skin tissue to a multi-layered model. The simulation results suggest that hyperthermal laser lipolysis with a power of 6W∼9W and an irradiation duration of 7s can be realized for an area as large as 3 × 7.2 mm2, by coupling MP-CSC with a pulse duration of 10 ms, a pulse delay of 2000 ms and a pulse number of 5. In this sense, the MP-CSC has great potential to prompt transcutaneous hyperthermal laser lipolysis.

Lunar dust removal and material degradation from liquid nitrogen sprays

Lunar regolith degrades human health and equipment making mitigation paramount for lunar missions. Cryogenic liquid sprays are a recently developed, simple, and convenient concept for dust mitigation in a lunar environment. However, removal efficacy and material degradation under the extreme cryogenic vacuum environment are unknown. Traditional space suit dust mitigation technologies used on the Apollo missions, such as brushing and vacuuming, introduced suit fabric abrasion which must be addressed for all dust mitigation methods considered for lunar implementation. This publication reports the efficacy of dust removal in a simulated airlock vacuum environment and the associated impact of repeated dusting-washing cycles on spacesuit materials. Specimens were impinged with measured liquid nitrogen sprays at different spray angles within a vacuum chamber. Mean mass removal of 98.4% was achieved in a vacuum environment at optimal conditions, correlating to 95.9% removal of particles below 10 μm. To investigate material degradation, a total of 26 samples were cycled a cumulative 233 times through cryogen spray washings under ambient conditions. A degradation scale was created to classify optical microscopy observations. Degradation results indicate minimal spacesuit material abrasion from liquid nitrogen removal. Results additionally show an average of 2.66% increased removal with each subsequent washing cycle for fabric washed twice, possibly due to clogging and occupancy of specific sites. The conclusion is that liquid nitrogen sprays cause relatively less damage than conventional dust mitigation techniques, even under the extremes of cryogenic temperatures and vacuum.

Tissue harvest with a laser microbiopsy.

Traditional pathology workflow suffers from limitations including biopsy invasiveness, small fraction of large tissue samples being analyzed, and complex and time-consuming processing. We address limitations of conventional pathology workflow through development of a laser microbiopsy device for minimally invasive harvest of sub-microliter tissue volumes. Laser microbiopsy combined with rapid diagnostic methods, such as virtual hematoxylin and eosin (H&E) imaging has potential to provide rapid minimally invasive tissue diagnosis. Laser microbiopsies were harvested using an annular shaped Ho:YAG laser beam focused onto the tissue surface. As the annulus was ablated, the tissue section in the center of the annulus was ejected and collected directly onto a glass slide for analysis. Cryogen spray cooling was used before and after laser harvest to limit thermal damage. Microbiopsies were collected from porcine skin and kidney. Harvested microbiopsies were imaged with confocal microscopy and digitally false colored to provide virtual H&E images. Microbiopsies were successfully harvested from porcine skin and kidney. Computational and experimental results show the benefit of cryogen pre- and post-cooling to limit thermal damage. Virtual H&E images of microbiopsies retained observable cellular features including cell nuclei. Laser microbiopsy with virtual H&E imaging shows promise as a potential rapid and minimally invasive tool for biopsy and diagnosis.

Histopathological evaluation of the R134a multipulsed spray cooling assisted 1210 nm laser lipolysis by the murine model in vivo.

Owing to the greater absorption affinity for lipo-rich tissue than water, the 1210 nm laser is a promising candidate for transcutaneous lipolysis in the near-infrared band. However, fat reduction is limited because laser therapy may yield thermal injury of normal tissue. A new protocol to incorporate multipulsed cryogen spray cooling is beneficial to improve the lipolysis effect, and the parameters of laser and cooling can be optimized via skin histopathological analysis. A murine in vivo model of inguinal tissue of SD rats was established to test the effectivity of transcutaneous lipolysis protocol by R134a multipulsed spray cooling assisted 1210 nm laser irradiation. Tissue response of lipolysis with/without cooling 10 days post the treatment was evaluated by histopathological analysis of skin samples stained with hematoxylin-eosin (HE), through which safe and effective parameters for lipolysis were determined. From histopathological analysis of the inguinal tissue of SD rats irradiated by the 1210 nm laser alone, the optimal durations are respectively 7 and 3 s (seconds) for low-dosage (6 W) and high-dosage (9 W) therapy, with pronounced lipolysis effect and minimum injury of skin tissue. The multipulsed spray cooling by R134a with a pulse duration of 10ms (milliseconds), a pulse delay of 2000ms, and a pulse number of 5 can be introduced to assist the 1210 nm laser therapy with a power of 9 W and a duration of 7 s to achieve desirable fat liquefaction while keeping the complete structure of skin tissueas well as esthetic-related beneficial effects of hair removal and skin rejuvenation. Excellent lipolysis effect can be achieved via R134a multipulsed spray cooling assisted high-dosage 1210 nm laser irradiation with reasonably matched laser and cooling parameters. The protocol is as follows: Start MP-CSC for one cycle, and then fire the laser with specific power and duration, while keeping MP-CSC accordingly. This new protocol may promote the safe and effective clinical implement of transcutaneous laser lipolysis in body contouring.

Transient cooling performance of R134a flash-evaporation spray enhanced by cold air jet: A novel heat transfer enhancement method in laser dermatology

Nevus of Ota is a dermal hyperplastic pigmented disease with a morbidity rate of 0.1–0.6% in the Asian population. Laser surgery with the assistance of cryogen spray cooling (CSC) is a potential clinical treatment for nevus of Ota. However, for Asians with high melanin content, it is necessary to enhance cooling capability without the increment of refrigerant amount. In this study, a R134a flash-evaporation cryogen spray cooling coupled with cold air jet (CSC-CAJ) was developed to improve the cooling capacity. Epoxy resin was employed as a skin phantom to investigate the heat transfer characteristics of CSC-CAJ with different air jet parameters. Air jet parameters of CSC-CAJ are recommended to be Ta = -7 ℃, Va = 3 m3/h Za = 10 mm and Φa = 30°. Compared to CSC, CSC-CAJ could reduce the minimum surface temperature from -39 to -42.1 ℃, and the average value of convective heat transfer coefficient (h) of CSC-CAJ could increase from 8 to 12.9 W/(m2·k) or 61.3% for the recommended parameters. The liquid film residence time (τ) decreases from 301 to 234 ms or 23.3%. In addition, based on the visualization observation and surface heat transfer measurement, the frost formation phenomenon on the surface and the heat transfer enhancement mechanisms are well understood. Four modes, including Leidonfrost mode, no runoff mode, runoff mode and evaporation mode, are proposed to describe the four stages of CSC-CAJ. A non-dimensional correlation of normalized Nusselt number (Nu*) and time (t*) is summarized. The primary heat transfer enhancement mechanism of CSC-CAJ is found to be the increase in cryogen evaporation rate and the ratio of heat removal from the phantom surface to phase change latent heat.

Mechanism of crescent-shaped and ring-shaped epidermal damage from laser hair removal with cryogen spray cooling.

The safety and efficacy of laser hair removal have been well established through many clinical studies and through clinical use over the past 25years. A laser hair removal device that protects the epidermis by utilizing cryogen spray cooling (CSC) is widely used internationally. In darker skin types, post-inflammatory hyperpigmentation (PIH) can occur after laser hair removal. In particular, laser hair removal with CSC is known to cause crescent-shaped or ring-shaped PIH. In this experiment, we report a visualization of this PIH mechanism. The laser used in this experiment is a 755-nm-long-pulsed alexandrite laser. Graph paper was treated with this laser to assess for thermal damage. We investigated changes in thermal damage due to differences in laser spot size, fluence output, and laser beam angle in relation to the graph paper. When using a spot size of 18mm, we observed that higher fluences caused crescent-shaped thermal damage on the margins of the treated graph paper. It was also confirmed that when the hand piece is not held perpendicular to the skin, the laser-treated area is expanded and the CSC range is narrowed. These factors caused the area of thermal damage to widen. This widening causes ring-shaped thermal injury, leading to PIH. We treated graph paper using a hair removal laser with CSC to investigate the mechanism of crescent or ring-shaped thermal damage. Laser treatment on graph paper is effective as a test for defects in the CSC device. Factors that cause inadequate cooling, which leads to PIH, are large spot size, high fluence, not holding the laser hand piece perpendicular to the skin, and malfunctioning of CSC device.

CRYOTHERAPY IN MANAGEMENT OF ORAL LESIONS USING LIQUID NITROGEN –A CASE STUDY

Aim of the study to Evaluation of the efcacy of cryotherapy as a treatment modality for Oral lesions Objectives: to evaluate the post- operative clinical outcome of oral lesions after treatment with cryotherapy, with respect to Ÿ Post- operative wound healing. Ÿ Recurrence of the lesion Results: There was no slough formation in 46. 7 %( 7) of the patients on 1 stweek post treatment and 53. 3%(8) of the patients had slough formation. After 2 weeks post treatment 46. 7% ( 7)of the patients had fair amount of granulation tissue formation and 53. 3%(8)of the patients had a good amount of granulation One month after treatment there was fair epithelization in 53.3% (8)of patients and 46 .7%(7) of patients had good epithelization. There was recurrence of the lesion in 13.3%( 2) after 2months and 86.7 %(13 ) of them had no recurrence. , Low complication rate, minimal volume of tissue destruction, Particularly suited to extensive supercial lesions. Conclusion: Cryosurgery is the use liquid nitrogen were extreme cold is produced to destroy abnormal tissue. Cryosurgery is very safe, easy to perform and relatively inexpensive technique for treating various oral lesions in out-patient clinic it is very useful for oral lesion as the oral mucosa. . In this study the open method used to treat lesion with cryogen spray using liquid nitrogen has shown signicantly good results in achieving complete regression of the benign and premalignant lesion of oral cavity .

Effects of microgravity on cryogenic spray quenching of a simulated propellant storage tank with enhancement by surface coating and flow pulsing

In-space cryogenic propulsion will play a vital role in space exploration mission to the Moon and future mission to the Mars. The enabling of in-space cryogenic rocket engines and the Lower-Earth-Orbit (LEO) cryogenic fuel depots for these future manned and robotic space exploration missions begins with the technology development of advanced cryogenic thermal-fluid management systems for the propellant transfer line and storage tank system.One of the key thermal-fluid management operations is the chilldown of the propellant storage tank. As a result, highly energy efficient, breakthrough concepts for quenching heat transfer to conserve and minimize the cryogen consumption during chilldown have become the focus of engineering research and development, especially for the deep-space mission to Mars. In this paper, we introduce such thermal transport concepts and demonstrate their feasibility in space for cryogenic propellant storage tank chilldown in a simulated space microgravity condition on board an aircraft flying a parabolic trajectory. In order to maximize the storage tank chilldown thermal efficiency for the least amount of required cryogen consumption, the breakthrough quenching heat transfer concepts developed include the combination of cryogenic spray quenching cooling, Teflon thin-film coating on the simulated tank surface, and spray flow pulsing. The boiling heat transfer physics that supports the concepts is clearly explained. The completed flight experiments successfully demonstrated the feasibility of the concepts and discovered that spray cooling is the most efficient cooling method for the tank chilldown in microgravity. In microgravity, the data shows that the chilldown thermal efficiency can reach 30% with Teflon coating alone. However, Teflon coating together with flow pulsing was found to substantially enhance the chilldown efficiency further to reach the 50% goal.

Cryogenic spray quenching of simulated propellant tank wall using coating and flow pulsing in microgravity

In-space cryogenic propulsion will play a vital role in NASA’s return to the Moon mission and future mission to Mars. The enabling of in-space cryogenic engines and cryogenic fuel depots for these future manned and robotic space exploration missions begins with the technology development of advanced cryogenic thermal-fluid management systems for the propellant transfer lines and storage system. Before single-phase liquid can flow to the engine or spacecraft receiver tank, the connecting transfer line and storage tank must first be chilled down to cryogenic temperatures. The most direct and simplest method to quench the line and the tank is to use the cold propellant itself that results in the requirement of minimizing propellant consumption during chilldown. In view of the needs stated above, a highly efficient thermal-fluid management technology must be developed to consume the minimum amount of cryogen during chilldown of a transfer line and a storage tank. In this paper, we suggest the use of the cryogenic spray for storage tank chilldown. We have successfully demonstrated its feasibility and high efficiency in a simulated space microgravity condition. In order to maximize the storage tank chilldown efficiency for the least amount of cryogen consumption, the technology adopted included cryogenic spray cooling, Teflon thin-film coating of the simulated tank surface, and spray flow pulsing. The completed flight experiments successfully demonstrated that spray cooling is the most efficient cooling method for the tank chilldown in microgravity. In microgravity, Teflon coating alone can improve the efficiency up to 72% and the efficiency can be improved up to 59% by flow pulsing alone. However, Teflon coating together with flow pulsing was found to substantially enhance the chilldown efficiency in microgravity for up to 113%.

Impact of geometrical surface modification on spray cooling heat transfer performance with liquid nitrogen: An experimental investigation

In this study, an experimental study on the spray cooling using liquid nitrogen (LN2) as the coolant was studied. Accordingly, an open-cycle experimental setup for cryogenic spray cooling was built. Investigation of spray cooling heat transfer performance on both plain and straight-grooved surfaces was carried out. The spray morphology was captured using the visual technique in the cryogenic system and the spray angles under different injection pressures were obtained. Additionally, a parametric study of heat transfer characteristics on the straight-grooved surfaces was carried out. The results have shown that the spray angle, at first, increases as with the inlet pressure, which is followed by a decrease. The straight-grooved surface significantly improved the spray cooling heat transfer compared to its plain counterpart by the maximum improvement rate of 64.2%. However, temperature uniformity was poorer. As the groove depth increases, the heat flux experiences increases at first, followed by a decrease. Finally, it was observed that the increase in groove width reduces the heat flux.

New protocol for the R134acryogen spray cooling assisted 1064-nmlaser lipolysis.

Laser lipolysis is a promising body contouring technology. However, the skin tissue could be thermally damaged owing to the laser energy absorption by water, which limits the lipolysis efficiency. To protect skin tissue and improve the lipolysis effect, cryogen spray cooling is introduced and synergized with the pulsed laser irradiation aiming to propose a new therapy protocol. By simulating heat conduction in the skin after spray cooling assisted laser lipolysis, the temperature distribution in the skin tissue was obtained to analyze the tissue damage by the Arrhenius integral. After parameter optimization according to the damage threshold of skin and adipose tissue, a new protocol with high laser intensity and short time was proposed including 150-ms R134a spray cooling with spray distance of 30mm, and 100ms 1064nm laser irradiation with energy density of 20J/cm2, with a relaxation for 9.75s. This cycle of 10s can be repeated 90 to 150 times for a total of 15 to 25min. Compared with previous treatment procedure, new protocol can increase the fat dissolution depth from 2 to 4.5mm beneath the dermis with same order laser fluence.