Cryonics is one extreme of cryopreservation where the whole body is frozen in the hope that one day it will be possible to revive it.

On a smaller scale in day-to-day medicine, freezing is an extremely useful technique for storing living cells, such as blood cells, bone marrow, sperm and embryos, at ultra-low temperatures.

But scientists agree that preserving and reawakening the complete human body is a remote possibility which would take massive breakthroughs in technology.

How unlikely?

Prof John Armitage, director of tissue banking at the University of Bristol, believes you can never say never in science but there was little chance of it happening based on current knowledge.

He said taking tissues from healthy people to be stored for future use was one thing but taking a diseased body, freezing it safely – including the complex structure of the brain – and reactivating it was a far, far more difficult task.

“What are the chances there wouldn’t be some damage?” Prof Armitage says.

“We are not even at the stage of cryopreserving organs yet, so doing it with a whole body would be a huge challenge.”

Organs themselves are very complicated, containing different types of cells, blood vessels and an inter-cellular structure – which would all need to be preserved.

Barry Fuller, professor in surgical science and low temperature medicine at University College London, said the first step was to demonstrate that human organs could be cryopreserved for transplantation.

But at the moment the equipment to make that happen is not available, he said.

“This is why we have to say that at the moment we have no objective evidence that a whole human body can survive cryopreservation with cells which will function after rearming,” he said.

What happens to the body?

After death, patients have to be acted on quickly.

In the UK, a group of volunteers trained in cryonics takes care of the body, starts the process of freezing and arranges for it to be shipped to the country where it is to be stored.

At this stage, dry ice is used to keep the body at a low temperature.

Once at the storage facility, patients are infused with cryoprotectants (like antifreeze) to prevent ice crystal formation – which would kill cells – before the temperature is slowly lowered and they are preserved in liquid nitrogen at extremely low temperatures of below -130C.

The low temperatures are needed to allow the cells to survive dehydration after death – but uncontrolled dehydration and freezing is also lethal to living cells, so it has to be done carefully.

The eventual aim is that one day they will be rewarmed and revived, but there is no evidence or guarantee that they can be.

Several hundred people have already paid to have their bodies cryogenically preserved in three existing facilities in the US and Russia, and there are as many as 1,250 on waiting lists.

Cryonics UK, a non-profit organisation which provides assistance to people in the UK who want their body to be frozen on death, said it has helped 10 people so far.

Source: https://www.bbc.com/news/health-38019392

Controlling the placement and hydration temperature of concrete is important to concrete durability. Thermal gradients and delayed ettringite formation (DEF) result in cracking when concrete in the plastic state becomes too hot. Cooler placement temperatures slow hydration reaction, increase working time, reduce the maximum temperature in the concrete member, and reduce thermal gradients. Furthermore, cooler concrete achieves better long-term strength and microstructural development. Concrete producers have been using multiple methods of reducing the placement temperature of concrete, such as cooling mixtures with ice or chilled water, shading aggregate piles, placing concrete at night, and using evaporative cooling of aggregate piles. More recently, concrete producers have turned to liquid nitrogen for cooling fresh concrete.

The objective of this research was to determine the effects of liquid nitrogen on concrete hydration, microstructural development, and performance. The following concrete mixture properties and methods were investigated: cement type, the effects of selected supplementary cementing materials and chemical admixtures, placement temperature, and the time at which liquid nitrogen dosing occurs (delayed dosing). Concrete performance was tested in terms of slump, setting time, yield, compressive and splitting tensile strength, elastic modulus, rapid chloride permeability, and hardened and fresh air void analysis. Hydration and microstructural development were monitored by isothermal calorimetry, semi-adiabatic calorimetry, x-ray diffractometry, inductively coupled plasma, and environmental scanning electron microscopy.

Additional testing was performed on concrete mixing drums to determine the effects of liquid nitrogen on the durability of steel mixing drums. The results indicate that performance, hydration, and microstructural development of fresh concrete are relatively unaffected when cooled with liquid nitrogen to room temperatures. Significant findings show that the slump of liquid nitrogen cooled concrete is similar to hot concrete mixtures and not room temperature mixtures. Additionally, setting time results show that liquid nitrogen dosing of hot concrete can be delayed for up to 1 hour and setting times will still be similar to room temperature mixtures. Based on findings from this research study, liquid nitrogen is recommended as a primary cooling option to reduce the placement temperature of fresh concrete.

Source: https://repositories.lib.utexas.edu/handle/2152/3591

by Dr. Mohammad Kassemi, NASA Glenn Research Center, [email protected]

Long-duration cryogenic storage of propellant and life support liquids is an enabling technology within the critical path of nearly all envisioned human planetary missions [1]. The pressurization and pressure control of such propellant tanks will be governed by complicated dynamic interactions amongst forced mixing, the various gravity-dependent transport mechanisms in the vapor and liquid phases, and the condensation-evaporation process at the interface. The effective implementation and optimization of a dynamic pressure control system for space applications can consequently be extremely difficult to achieve, especially without collected and relevant microgravity experimental data.

Current zero boiloff tank (ZBOT) experiments represent a series of small scale tank pressurization and pressure control experiments aboard the International Space Station (ISS). The researchers use a transparent volatile simulant fluid in a transparent sealed tank to delineate various fluid flow, heat and mass transport and phase change phenomena that control storage tank pressurization and pressure control in microgravity [2].

The hardware and experimental setup of ZBOT-1, the first of three envisioned hierarchical experiments, detailed in Cold Facts Vol. 33, No. 3. NASA transported the unit to ISS in 2017, where astronaut Joe Acaba handled installation within the microgravity science glovebox (MSG), as shown in Figure 1.

Close to 100 tests were then conducted over a period of roughly three months. Each test studied and quantified fluid flow and thermal stratification during self-pressurization; and mixing, thermal destratification, depressurization and jet ullage penetration during the pressure control intervals.

Hand-in-hand with the experiments, a comprehensive two-phase computational fluid dynamics (CFD) model has also been developed for simulation and prediction of storage tank pressurization and pressure control [3]. The model uses a VOF (volume of fluid) scheme to capture the fluid phases and tracks velocity, temperature and multi-component species concentrations in both domains under tight coupling with the evaporative/condensing mass transfer and energy and force balances at the phase front. The NASA team has extensively verified and validated the CFD model against both ZBOT ground-based and microgravity data, though a validation process against microgravity data continues.

Hardware and Experimental Setup

Figure 2 shows a schematic of the main components of the ZBOT-1 hardware in MSG and a cross-sectional view of the test cell made of polished optical quality cast acrylic. The test cell consists of a cylindrical midsection capped at two ends by hemispherical domes, both four inches in diameter by eight inches in height. And the device is equipped with a strip heater mounted on the outer surface of the cylindrical acrylic wall; a jet flow nozzle at the bottom that is activated during the pressure control tests; and a screened Liquid Acquisition Device (LAD) that ensures only liquid is extracted, thermally conditioned and pumped in through the nozzle during the jet flow mixing cycles.

To provide proper containment and definable and controllable thermal boundary conditions for model validation, the test cell is isolated from the MSG environment via a temperature-controlled vacuum jacket (VJ) that is also enclosed within another cooling jacket. The tank fluid temperature prior to each test and the jet flow temperatures during the mixing cycles are maintained by careful conditioning of the fluid via a counter-flow shell and tube heat exchanger in the fluid supply unit (FSU) located just below the MSG test cell.

The simulant phase change fluid used in the experiment is Perfluoro-n-Pentane (PnP, or C5F12), a non-polar volatile refrigerant with a boiling point of 29°C at 1 atm and a near zero contact angle with the test tank. NASA toxicology and ECLSS groups have approved a high purity (99.7 percent straight-chained n-isomer) version of PnP as safe for use within the ISS. A bellowed reservoir stores the fluid that is degassed on orbit initially and before each fill level change. A radial flow membrane contactor performs degassing to a high degree of purity (less than 5 torr residual gases). This process ensures that any noncondensable effects are eliminated during the ZBOT-1 tests.

Temperature-controlled windows on the VJ accommodate the camera and white light/laser sheet illumination packages included for image-capture of the ullage. This diagnostic setup also accommodates particle streaking flow visualization and particle imaging velocimetry (PIV) in the liquid region. Tank pressure and jet flow rate are measured using a high accuracy pressure transducer and a Coriolis flow meter, respectively. There are 43 RTDs embedded on a rack in the fluid, on the inside and outside surfaces of the tank wall, on the VJ and in the jet flow line and nozzle. These RTDs measure fluid and wall temperatures with a precision and accuracy that is conducive to detailed computational model validation.

Microgravity Tests and Procedures

Self-pressurization tests were conducted under three modes: VJ heating, strip heating and simultaneous VJ and strip heating; therein creating an attempt to simulate heat leaks from the environment, the support structure and both. The pressure control studies were performed either from an elevated uniform temperature condition or from thermally stratified conditions following a self-pressurization run.

Liquid was drawn from the tank, passed through the heat exchanger in the FSU and then injected into the tank at a given flow rate. This was conducted either at the average tank fluid temperature for mixing only destratification and ullage penetration studies or at a prescribed subcooled level for active cooling pressure control tests.

Jet flow rates were varied from 2 to 25 cm/s and spanned a range of jet Reynolds numbers in laminar, transitional and turbulent regimes; and a range of Weber numbers covering no ullage penetration, partial penetration and complete ullage penetration and breakup.

Particle image velocimetry (PIV) test runs were also performed to both visualize and quantify the flow fields, especially during the jet mixing operations. Since particle injection and PIV was carried out for the first time with this class of nonpolar fluids in microgravity, ZBOT tests were performed with and without particle injection to ensure both the integrity of the primary temperature and that pressure data was not compromised.

Overview of Microgravity Results

Interesting quantitative results were obtained with regard to the altered and sometimes non-intuitive microgravity behavior of fluid flow, heat and mass transfer and ullage dynamics in the storage tank, providing important implications for several aspects of storage tank design.

ZBOT pressurization data indicates that classic tank self-pressurization trends in microgravity, due to either localized or global heating, are quite similar to their 1g counterparts. However, it is also shown that both the rate and magnitude of pressurization in microgravity are lower than in 1g under otherwise similar conditions. Thus, ground-based results may be used as conservative estimates for designing the storage tank for space applications.

Such pressurization results further indicate that deviations from the classic self-pressurization trends can more readily occur in weightlessness due to microgravity thermal stratification. In microgravity, nucleate boiling of localized hot spots on the vessel wall can occur at much lower wall heat fluxes, a condition due to the weaker natural convection and thermal stratification compared to their 1g counterparts—especially if the wall also provides suitable nucleation sites.

Thus, it is envisioned that a propellant tank with a perforated internal wall structure may be subject to low intensity nucleate wall boiling, even under relatively moderate heat fluxes. Herein, a simultaneous combination of global and local heating provides the most conducive condition for microgravity nucleate boiling.

Microgravity results indicate that jet mixing during tank thermal destratification and pressure control follows a surprisingly non-intuitive trend compared to its 1g behavior. At low jet speeds (low Weber numbers) the ullage will move towards the jet nozzle inlet if the jet is not perfectly aligned with the ullage central axis. Of course, such alignment is quite difficult to arrange due to the existence of a varying 3D residual gravitational field.

At higher jet speeds (high Weber number), the ullage can be kept in the upper portions of the tank opposite the jet nozzle inlet, but will tend to move to accommodate the passage of the jet with minimal penetration. Thus, a stable ullage that can be punctured and penetrated centrally and split by the jet will be elusive, particularly at higher fill levels.

Pressure control through thermal destratification—provided by an uncooled jet entering the tank at the average tank temperature—was seen to be minimal and ineffective. However, results showed that subcooled jet mixing can serve as an effective means of tank pressure control by providing a very rapid and drastic initial tank pressure drop followed by further depressurization at a continuously decreasing rate until a steady pressure level is achieved.

A very non-intuitive and surprising phenomenon involved an immense phase change at the screened LAD. It occurred during subcooled jet mixing, where the entire test cell was filled initially with small, but subsequently growing and coalescing bubbles. It was shown that during subcooled jet mixing, the sudden drop in tank pressure—as the cold jet surrounds and isolates the ullage from the rest of the tank—causes a similar sudden decline in the saturation temperature.

It is postulated that massive nucleate boiling can be instigated at the numerous nucleation sites on the LAD screen as the saturation temperature drops below the LAD temperature. If this hypothesis is true, it implies that a liquid jet (one that selectively isolates the ullage from other hotspots in the tank to provide an effective and rapid pressure control) may still not be a suitable means of tank pressure control in microgravity due to the possibility of instigating intense boiling/phase change at other locations in the tank.

CFD model validation against ZBOT microgravity data is continuing with good success. The useful and pertinent results of the experiment have underscored the value of such subscale simulant fluid ISS-class experiments for model validation. It has also demonstrated its effectiveness for gaining a better understanding of the intricate transport and phase change interactions that control tank pressurization and pressure control while pointing out serious practical implications that may prove important to future large cryogenic storage tank design for space applications.

References
[1] J. Salzman, “Fluid management in space-based systems,” Proceedings of the Engineering, Construction, and Operations in Space, 5th International Conference on Space, Vol. 1, 1996.
[2] S. Barsi and M. Kassemi, “Investigation of Tank Pressurization and Pressure Control—Part I: Experimental Study,” ASME Journal of Thermal Science & Engineering Applications, Vol. 5, No 2, December 2013.
[3] M. Kassemi, O. Kartuzova, S. Hylton, “Validation of Two-Phase CFD Models for Propellant Tank Self-Pressurization: Crossing Fluid Types, Scales, and Gravity Levels,” Cryogenics Vol. 89, January 2018.

Acknowledgement
Funding from the ISS Microgravity Physical Sciences Program, NASA HQ, tireless efforts by William Sheredy, ZBOT Project Manager, and Dr. R. Balasubramaniam, ZBOT Project Scientist, and CFD work by ZBOT Science Team, Sonya Hylton and Dr. Olga Kartuzova, are gratefully acknowledged.