Name: ice generation and the heat and mass transfer phenomena of introducing water to a cold bath of brine
Uploaded: 2017-03-13T12:30:00.000+00:00
Duration: 8 min 16 s
Description: Watch this Scientific Journal Video about Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine at JoVE.com

The authors have no acknowledgements.

Caution: There are two poisonous chemicals, methanol and ethylene glycol, used in these experiments. Methanol can be metabolized in the human body to generate formaldehyde and then to formic acid or formate salt. These substances are poisonous to the central nervous system and may even cause death. Ethylene glycol can be oxidized to glycolic acid, which can then turn into oxalic acid. This can cause kidney failure and death. Do not drink these chemicals. Consult a doctor immediately if an accident occurs.
1. The Cooling System
NOTE: It is very difficult to keep the brine at -18 &#176;C or so when the ambient temperature is roughly at room temperature. It is important that the tanks storing the ethylene glycol and brine are well-insulated and of a reasonable size to avoid excess electricity consumption and to ensure optimal system performance. It is recommended that the tank size does not exceed 30 L.
<ol>
	<li>Prepare the secondary cooling fluid
	<ol>
		<li>Pour 1 L of ethylene glycol into the secondary cooling tank, Tank A (Base: 400 mm &#215; 200 mm, Height: 350 mm). Add roughly 0.6-0.65 L (600-650 g) of water to Tank A.</li>
		<li>Repeat step 1.1.1 several times until there is enough fluid in Tank A (25 L).</li>
		<li>Stir the fluid so that the fluid is homogeneous.</li>
		<li>Switch on the two pumps in Tank A to the full-capacity setting (2,500 L/h). Make sure that all bubbles trapped in the heat exchangers and pipes are released.</li>
		<li>Switch off the pump to observe if all the bubbles are released. If not, repeat step 1.1.4.</li>
	</ol>
	</li>
	<li>Preparation of the brine 
	NOTE: In this example, 22 wt% brine is prepared. If other concentrations are needed, the mass of salt added should also be changed accordingly. The reference brine concentration and density values can be found on Page D-257 of the 64th Edition (1983) of the CRC Handbook of Chemistry and Physics46.
	<ol>
		<li>Add 4 kg of water into a 5-L plastic beaker.</li>
		<li>Measure 1 kg of NaCl salt on an electronic scale and pour this salt into the beaker with the water.</li>
		<li>Stir the mixture until the solution is clear (i.e., there are no salt particles or water bubbles visible in the solution).</li>
		<li>Take a sample, ~10 mL, of the solution using a 10-mL syringe.</li>
		<li>Inject the fluid into the U-tube density meter.</li>
		<li>Check for air bubbles in the tube. If there are any, inject more fluid to push them out.</li>
		<li>Press &#34;Quick Settings&#34; and select &#34;Density Temperature.&#34; Type in 20 &#176;C and press &#34;OK.&#34; The density meter will now measure the fluid density at this temperature.</li>
		<li>Press start and wait for the result.</li>
		<li>Compare the density reading with 1164.00 kg/m3.</li>
		<li>Add more salt if the reading is below the comparison density. Add water if otherwise.</li>
		<li>Repeat steps 1.2.3-1.2.10 until the fluid density is correct (1164.00 kg/m3).</li>
		<li>Pour this solution into a larger container, Container A.</li>
		<li>Use steps 1.2.1-1.2.12 to make 35-40 L of brine and put Container A into a chest freezer at -40 &#176;C. Keep the brine there for 48-72 h, until its temperature reaches -19.18 &#176;C (freezing point of this 22 wt% brine).</li>
	</ol>
	</li>
</ol>
2. Preparation of the Ice for the Injecting and Washing Water
<ol>
	<li>Prepare ice for the injecting water
	<ol>
		<li>Pour 1 L of water into a small container (200 &#215; 200 &#215; 50 mm).</li>
		<li>Repeat step 2.1.1 with another container and place the two containers in the chest freezer at -40 &#176;C.</li>
		<li>Keep them in the freezer for 10 h or more to ensure that all of the water is frozen.</li>
	</ol>
	</li>
	<li>Prepare the washing water&#39;s ice shell
	<ol>
		<li>Fill a 5-L beaker with 5 L of water.</li>
		<li>Fill a 2-L beaker with 2 L of water.</li>
		<li>Place both beakers into the chest freezer at -40 &#176;C for 8-10 h so that there is a thick shell of ice wrapping around unfrozen water.</li>
		<li>Use a high-velocity water jet at a speed of 3-5 m/s from the tap to open up a 3-cm diameter hole at the top of the ice shell.</li>
		<li>Drain the water inside the ice shell.</li>
		<li>Put the two beakers back in the freezer.</li>
		<li>If the mass of the ice shell does not reach 3 kg and 1 kg for the two beakers, respectively, repeat steps 2.2.1-2.2.5, but keep the beakers in the freezer longer in step 2.2.3. The two beakers should now be able to contain 2 L and 1 L of water, respectively.</li>
	</ol>
	</li>
</ol>
3. Water Introduction Position and the Rheology Control Experiment
<ol>
	<li>Introduce water at the brine surface
	<ol>
		<li>Decant 2 L of 22 wt% cold brine from Container A into the aluminum bucket of the ice cream maker and switch on the cooling unit.</li>
		<li>Measure the temperature of the brine with a thermometer/thermocouple (either K-Type or T-type are suitable). Carry on the experiment if the brine is -15 &#176;C or lower.</li>
		<li>Fill up the 100-mL glass syringe with tap water at room temperature. Attach a 2-mm internal diameter, 1-mm thick, and 1-m long silicone tube to the tip of the syringe.</li>
		<li>Place the syringe at a specific position such that there is a head between the water in the syringe and the exit of the silicone tube. The hydrostatic pressure will squeeze the water out of the tube.</li>
		<li>Submerge a certain length of the silicone tube, typically 70 cm, into the brine.</li>
		<li>Adjust the relative position between the syringe and the tube exit so that the hydrostatic pressure is great enough to allow water to leave the syringe. If the tube is blocked, increase the head by elevating the syringe to a higher vertical position, until the hydrostatic pressure can overcome the shear stress within the tube.</li>
		<li>Keep the tube exit roughly 1 cm or less above the brine surface.</li>
		<li>Adjust the length of submerged tube and the syringe height to control the water&#39;s outlet let temperature and flow rate in order to determine how much ice can be made or how much mixing occurs at the brine surface. The freezing phenomenon should now be observed at the brine surface. See Reference 45 for further direction.</li>
	</ol>
	</li>
	<li>Introduce water through the brine
	<ol>
		<li>Repeat steps 3.1.1-3.1.6.</li>
		<li>Keep the tube exit inside the brine, preferably at the bottom of the container.</li>
		<li>Adjust the length of the submerged tube and the syringe height.</li>
		<li>Adjust the angle of the tube exit to control the rheology of the flow.</li>
		<li>Repeat steps 3.2.3-3.2.4 to find the best coupled flow rheology and flow rate that can produce the most ice.</li>
	</ol>
	</li>
</ol>
4. Ice Production, Collection, and Measurement
<ol>
	<li>Make ice
	<ol>
		<li>If there are bubbles in the pipes, switch on the two pumps inside Tank A to release the bubbles out of the glycol circulation system, and then switch off the pumps.</li>
		<li>Switch on the three refrigeration units and let them run for 10-16 h to cool down the ethylene glycol solutions.</li>
		<li>Measure the ethylene glycol solution with a thermometer/thermocouple. The glycol temperature should be at about -25 &#176;C.</li>
		<li>Measure the temperature of the brine in Container A to make sure it is at -19 &#176;C before proceeding to step 4.1.5.</li>
		<li>Fill the brine tank, Tank B, with roughly 30 L of brine from Container A and switch on the two pumps in Tank A.</li>
		<li>Measure the temperature of the glycol in Tank A. If it is colder than -19 &#176;C, switch off one or more cooling units to prevent the precipitation of ice particles outside the heat exchangers in Tank B. If the temperature is warmer than the expected brine temperature, turn on all three cooling units. Carry out the experiment at -17 &#176;C to -19 &#176;C.</li>
		<li>Place the two premade blocks of ice from step 2.1 into the insulated 5-L beaker, Container B, and pour roughly 3 L of water into the beaker.</li>
		<li>Measure the water temperature and keep it at 2 &#176;C by stirring the mixture between experiments if the temperature rises.</li>
		<li>Fill the glass syringe with 100 mL of the 2 &#176;C water.</li>
		<li>Apply 5-10 mL of methanol to the glass window of Tank B to stop condensation and the formation of ice.</li>
		<li>Inject the water into the brine by adjusting the relative position between the syringe and the tube&#39;s exit so that there is a constant hydrostatic pressure and thus a constant flow rate. About 70 cm of the silicone tube should be submerged in the brine. Adjust the angle of injection to 0&#176; so that the initial water velocity in the upward direction is 0 m/s. 
		NOTE: The syringe can be either hand-held or clamped to a stand. Hand-held is more appropriate when the brine temperature is colder, because it takes more time to adjust a stand, and ice may block the tube. Keep the flow rheology consistent throughout the experiment by ensuring a constant flow rate and injection angle (0&#176;) and by keeping the freezing frontier roughly 3 cm above the tube exit. Do not let the flow enter the region where it starts to turn turbulent47. See Reference 45 for further direction.</li>
		<li>Collect the ice as described in steps 4.2 and 4.3. Repeat steps 4.1.8 - 4.1.11 at different brine temperatures.</li>
	</ol>
	</li>
	<li>Collect the produced ice and estimate how much ice is produced (dry collection)
	<ol>
		<li>Put a container (200 &#215; 200 &#215; 50 mm) on the scale and zero the reading by pressing the &#34;Turn On&#34; button.</li>
		<li>Use the sieve to scoop out the ice and shake off the brine.</li>
		<li>Put this ice in the container. Measure the mass of the ice using the scale.</li>
		<li>After the ice is melted, use the 10-mL syringe to take a sample. Inject this sample of liquid into the density meter.</li>
		<li>Perform steps 1.2.6-1.2.9.</li>
		<li>Record the density reading.</li>
		<li>Calculate the net water mass from its density (i.e., the mass of water converted into ice) using the following formula: 
		<img alt="Equation" src="/files/ftp_upload/55014/55014eq1.jpg" /> 
		where <img alt="Equation" src="/files/ftp_upload/55014/55014eq2.jpg" /> is the brine concentration by wt% and <img alt="Equation" src="/files/ftp_upload/55014/55014eq3.jpg" /> and <img alt="Equation" src="/files/ftp_upload/55014/55014eq4.jpg" /> are the masses of salt and water, respectively.</li>
	</ol>
	</li>
	<li>Collect the produced ice and estimate how much ice is produced (wet collection)
	<ol>
		<li>Fill the 5-L beaker with an ice shell (step 2.2) and room-temperature tap water. Put it back into the freezer at -40 &#176;C.</li>
		<li>Decant the water with the ice shell from the 5-L beaker into a 2-L beaker when its temperature is at 0 &#176;C. Fill up the 5-L beaker. Keep both beakers in the freezer.</li>
		<li>Scoop out the ice produced in steps 4.1.8 and 4.1.9 and pour 200-500 mL of water from the 2-L beaker onto the ice to wash it. Do not shake the sieve before applying the 0 &#176;C water.</li>
		<li>Shake off the fluid in the sieve.</li>
		<li>Repeat steps 4.2.2-4.2.7.</li>
	</ol>
	</li>
</ol>

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Res. 75, 583-597 (1970).</li><li>Wettlaufer, J. S., Worster, M. G., Huppert, H. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Natural+convection+during+solidification+of+an+alloy+from+above+with+application+to+the+evolution+of+sea+ice.">Natural convection during solidification of an alloy from above with application to the evolution of sea ice.</a> J. Fluid Mech. 344, 291-316 (1997).</li><li>Paige, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stalactite+Growth+beneath+Sea+Ice.">Stalactite Growth beneath Sea Ice.</a> Science. 167, 171-172 (1970).</li><li>Dayton, P. K., Martin, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observations+of+ice+stalactites+in+McMurdo+Sound,+Antarctica.">Observations of ice stalactites in McMurdo Sound, Antarctica.</a> J. Geophys. Res. 76, 1595-1599 (1971).</li><li>Eide, L. I., Martin, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+formation+of+brine+drainage+features+in+young+sea+ice.">The formation of brine drainage features in young sea ice.</a> J. Glaciol. 14, 137-154 (1975).</li><li>Martin, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ice+stalactites:+comparison+of+a+laminar+flow+theory+with+experiment.">Ice stalactites: comparison of a laminar flow theory with experiment.</a> J. Fluid Mech. 63, 51-79 (1974).</li><li>Jeffs, K., Attenborough, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Frozen Planet: Episode 5 'Winter'. , (2011).</li><li>Fothergill, A., Berlowitz, V., Attenborough, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ch.+Winter:+Life+closes+down.">Ch. Winter: Life closes down.</a> in Frozen Planet: A World Beyond Imagination. , (2011).</li><li>Yun, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ice+formation+in+the+subcooled+brine+environment.">Ice formation in the subcooled brine environment.</a> Int. J. Heat Mass Transfer. 95, 198-205 (2016).</li><li>Weast, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> CRC Handbook of Chemistry and Physics. 64, 257-258 (1983).</li><li>Bejan, A., Lage, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Prandtl+Number+Effect+on+the+Transition+in+Natural+Convection+Along+a+Vertical+Surface.">The Prandtl Number Effect on the Transition in Natural Convection Along a Vertical Surface.</a> J. Heat Transfer. 112, 787-790 (1990).</li></ol>

The authors have nothing to disclose.

The process of ice generation using brine as a secondary refrigerant involves the combination of heat and mass transfer. If the heat transfer is greater, then ice forms before the water has the chance to mix with the bulk fluid. It was observed that when there is a relative movement between the introduced water and the quiescent bulk brine (i.e., injecting water within the brine), the flow helps the heat transfer and encourages ice to form rapidly. However, when there is too much turbulence in the flow, no ice c...

Ice slurries are extensively used in industry, and one particularly successful application is the ice-pigging technology1,2. In comparison to the conventional foam and solid pig, the ice pig can travel through complex topologies over a long distance because of the lubrication effect of the liquid phase and the elevation of its freezing point as some of the ice crystals melt3,4,5. Even if the pig gets stuck, one can simply wait for the ice slurries to melt and resume the cleaning process later. This method of pipe cleaning is cheap and easy to use.
The ice fraction plays a key role in the performance of the ice pig. To measure the ice fraction, one can use a cafeti&#232;re (French press) to determine if the ice slurry is thick enough6,7. A high cafeti&#232;re ice fraction, typically 80%, is required when carrying out ice pigging. Recent research on online ice fraction detection showed that both electromagnetic and ultrasonic waves are suitable for the job8,9,10,11.
The ice pig is usually made by a scraped-surface ice maker from a 5 wt% NaCl solution (brine). It is also the primary way of making ice slurries in industry. This type of ice maker freezes water or brine onto a cold metallic surface, typically a smooth 316 steel surface and then cyclically shears the ice particles off. The liquid-to-metal interfaces are very complex and are affected by a broad range of factors that are essential to ice making12. The interface between non-metal and water can be very different, and one especially interesting example is Kaolinite. The Kaolinite-water interface is special because there is not a favorable ice structure adjacent to the solid&#39;s surface, but rather a layer of amphoteric substrate fluid that encourages the ice-like hydrogen-bonded clusters to form on top of it13,14. Another way of producing the ice pig requires crushing the premade ice blocks while high-concentration brine is added simultaneously. For this method, the refrigeration system can run at a much higher evaporating temperature because no freezing point depressant (FPD) is added prior to the formation of ice; it is hence considered more efficient due to the lowered compression ratio and lessened power for a given cooling duty15,16,17.
There are two other ice production methods: producing ice from supercooled water and putting refrigerant and water in direct contact18,19. The supercooling method involves disturbing the metastable supercooled water to generate ice nucleation and growth. The biggest problem for this method is the unwanted ice formation that can block the system. The direct contact method is considered not suitable for ice pigging because neither refrigerant nor lubrication oil are wanted in the final ice product.
The formation of ice requires heat and mass transfer due to the latent heat of fusion generated in the process. It was first discovered by Osborn Reynolds in 1874 that the transportation of heat and mass in gases are strongly coupled and can be expressed in similar mathematical formulae20. This work formed the pioneering paper on the subject of momentum, heat, and mass transfer in fluids and was reprinted several times21,22. This subject was then studied by a number of others, from both analytical and empirical approaches, for gases, liquids, and molten metal23,24,25,26,27,28,29,30,31,32,33. Aside from the heat and mass transfer, the fluid needs nucleation sites where dendritic ice growth can develop. A modern insight into the growth of ice crystals uses Constructal Law, developed by Adrian Bejan, to explain why ice grows in this way34,35,36.
The ice formation in brine is very different from that in pure water due to the existence of salt. First of all, salt changes the thermodynamics of the fluid and depresses its freezing point. Secondly, salt cannot dissolve in the ice matrix (except for hydrohalite, which can only form when the temperature reaches the eutectic point), and it is rejected to the bulk fluid when ice starts to grow. The rejection of salt was discovered in both sea ice and ice studied in the lab37,38. Since the rejected high-concentration brine is at a temperature well below the freezing point of sea water, as it descends, ice grows at the interface between the flowing brine and the quiescent bulk fluid. These ice stalactites, also named brinicles, were first discovered in McMurdo Sound, Antarctica and were studied experimentally39,40,41,42. In 2011, BBC filmed the formation of brinicles in its Frozen Planet series43,44.
In our lab, it was discovered that by reversing the flowing and quiescent fluids when water is introduced to a bath of cold brine, the water may transform into ice under the correct conditions45. It was found that the location where the water is introduced, flow rheology, and brine temperature and concentration are all key factors influencing how much ice can be produced. The overall goal of this study is to investigate if an ice maker can be developed through this mechanism to generate ice slurries, considering that the elevated evaporator temperature and the high rate of liquid-to-liquid heat transfer can enhance the efficiency of energy usage. This article shares key aspects of the experiment.

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ice generation and the heat and mass transfer phenomena of introducing water to a cold bath of brine

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed that, under the proper conditions, ice can be produced when water is introduced to a bath of cold brine. To make ice form, in addition to having the brine and water mix, the rate of heat transfer must bypass that of mass transfer. When water is introduced in the form of tiny droplets to the brine surface, the mode of heat and mass transfer is by diffusion. The buoyancy stops water from mixing with the brine underneath, but as the ice grows thicker, it slows down the rate of heat transfer, making ice more difficult to grow as a result. When water is introduced inside the brine in the form of a flow, a number of factors are found to influence how much ice can form. Brine temperature and concentration, which are the driving forces of heat and mass transfer, respectively, can affect the water-to-ice conversion ratio; lower bath temperatures and brine concentrations encourage more ice to form. The flow rheology, which can directly affect both the heat and mass transfer coefficients, is also a key factor. In addition, the flow rheology changes the area of contact of the flow with the bulk fluid.

Figure 1 compares the effects of water introduced at the brine surface to water injected through the brine. In the &#34;ice-cap&#34; scenario, the formed ice is solid because the water did not mix much with the bulk fluid. The temperature and density difference between the two fluids generates buoyancy force on the water and prevents them from mixing. Both fluids are static (i.e., the heat transfer is much greater than that of the mass; Sc &#8776; 500, Pr &#8776;...

Watch this Scientific Journal Video about Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine at JoVE.com

Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine

Here, we present a protocol to demonstrate the generation of ice when water is introduced to a cold bath of brine, as a secondary refrigerant, at a range of temperatures well below the freezing point of water. It can be used as an alternative way of producing ice for industry.

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed ...

ice-generation-heat-mass-transfer-phenomena-introducing-water-to-cold

Universidad San Sebastian

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Physics

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Unit 1

Temperature and Heat

SCIENTISTS IN ACTION

13.8K Views.  University of Bristol. Here, we present a protocol to demonstrate the generation of ice when water is introduced to a cold bath of brine, as a secondary refrigerant, at a range of temperatures well below the freezing point of water. It can be used as an alternative way of producing ice for industry.

Video: Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine

Reservoir Condition Pore-scale Imaging of Multiple Fluid Phases Using X-ray Microtomography

X-ray microtomography was used to image, at a resolution of 6.6 &#181;m, the pore-scale arrangement of residual carbon dioxide ganglia in the pore-space of a carbonate rock at pressures and temperatures representative of typical formations used for CO2 storage. Chemical equilibrium between the CO2, brine and rock phases was maintained using a high pressure high temperature reactor, replicating conditions far away from the injection site. Fluid flow was controlled using high pressure high temperature syringe pumps. To maintain representative in-situ conditions within the micro-CT scanner a carbon fiber high pressure micro-CT coreholder was used. Diffusive CO2 exchange across the confining sleeve from the pore-space of the rock to the confining fluid was prevented by surrounding the core with a triple wrap of aluminum foil. Reconstructed brine contrast was modeled using a polychromatic x-ray source, and brine composition was chosen to maximize the three phase contrast between the two fluids and the rock. Flexible flow lines were used to reduce forces on the sample during image acquisition, potentially causing unwanted sample motion, a major shortcoming in previous techniques. An internal thermocouple, placed directly adjacent to the rock core, coupled with an external flexible heating wrap and a PID controller was used to maintain a constant temperature within the flow cell. Substantial amounts of CO2 were trapped, with a residual saturation of 0.203 &#177; 0.013, and the sizes of larger volume ganglia obey power law distributions, consistent with percolation theory.

We present a methodology for the imaging of multiple fluid phases at reservoir conditions by the use of x-ray microtomography. We show some representative results of capillary trapping in a carbonate rock sample.

X-ray microtomography was used to image, at a resolution of 6.6 &#181;m, the pore-scale arrangement of residual carbon dioxide ganglia in the pore-space ...

Evolution of Staircase Structures in Diffusive Convection

Diffusive convection (DC) occurs when the vertical stratified density is controlled by two opposing scalar gradients that have distinctly different molecular diffusivities, and the larger- and smaller- diffusivity scalar gradients have negative and positive contributions for the density distribution, respectively. The DC occurs in many natural processes and engineering applications, for example, oceanography, astrophysics and metallurgy. In oceans, one of the most remarkable features of DC is that the vertical temperature and salinity profiles are staircase-like structure, composed of consecutive steps with thick homogeneous convecting layers and relatively thin and high-gradient interfaces. The DC staircases have been observed in many oceans, especially in the Arctic and Antarctic Oceans, and play an important role on the ocean circulation and climatic change. In the Arctic Ocean, there exist basin-wide and persistent DC staircases in the upper and deep oceans. The DC process has an important effect on diapycnal mixing in the upper ocean and may significantly influence the surface ice-melting. Compared to the limitations of field observations, laboratory experiment shows its unique advantage to effectively examine the dynamic and thermodynamic processes in DC, because the boundary conditions and the controlled parameters can be strictly adjusted. Here, a detailed protocol is described to simulate the evolution process of DC staircase structure, including its generation, development and disappearance, in a rectangular tank filled with stratified saline water. The experimental setup, evolution process, data analysis, and discussion of results are described in detail.

Diffusive convection (DC) widely occurs in natural processes and engineering applications, characterized by a series of staircases with homogeneous convecting layers and stratified interfaces. An experimental procedure is described to simulate the evolution process of the DC staircase structure, including the generation, development and disappearance, in a rectangular tank.

Diffusive convection (DC) occurs when the vertical stratified density is controlled by two opposing scalar gradients that have distinctly different ...

Environment

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This technique utilizes wavelengths of 1150 and 1412 nm, at which the absorption coefficient of water is dependent on temperature. Water or a non-turbid aqueous gel containing a 2.0-mm- or 0.5-mm-diameter magnetic sphere is irradiated with 1150 nm or 1412 nm incident light, as selected using a narrow bandpass filter; additionally, two-dimensional absorbance images, which are the transverse projections of the absorption coefficient, are acquired via a near-infrared camera. When the three-dimensional distributions of temperature can be assumed to be spherically symmetric, they are estimated by applying inverse Abel transforms to the absorbance profiles. The temperatures were observed to consistently change according to time and the induction heating power.

A technique utilizing wavelengths of 1150 and 1412 nm to measure the temperature of water surrounding an induction-heated small magnetic sphere is presented.

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This ...

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and salty seawater from cold and pure water, thus allowing only pure water vapor to pass through. To achieve this feat, commercial DCMD membranes are derived from or coated with water-repellent perfluorocarbons such as polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF). However, the use of perfluorocarbons is limiting due to their high cost, non-biodegradability, and vulnerability to harsh operational conditions. Unveiled here is a new class of membranes referred to as gas-entrapping membranes (GEMs) that can robustly entrap air upon immersion in water. GEMs achieve this function by their microstructure rather than their chemical make-up. This work demonstrates a proof-of-concept for GEMs using intrinsically wetting SiO2/Si/SiO2 wafers as the model system; the contact angle of water on SiO2 is &#952;o &#8776; 40&#176;. Silica-GEMs had 300 &#956;m-long cylindrical pores whose diameters at the (2 &#956;m-long) inlet and outlet regions were significantly smaller; this geometrically discontinuous structure, with 90&#176; turns at the inlets and outlets, is known as the &#34;reentrant microtexture&#34;. The microfabrication protocol for silica-GEMs entails designing, photolithography, chrome sputtering, and isotropic and anisotropic etching. Despite the water loving nature of silica, water does not intrude silica-GEMs on submersion. In fact, they robustly entrap air underwater and keep it intact even after six weeks (&#62;106 seconds). On the other hand, silica membranes with simple cylindrical pores spontaneously imbibe water (&#60; 1 s). These findings highlight the potential of the GEMs architecture for separation processes. While the choice of SiO2/Si/SiO2 wafers for GEMs is limited to demonstrating the proof-of-concept, it is expected that the protocols and concepts presented here will advance the rational design of scalable GEMs using inexpensive common materials for desalination and beyond.

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Presented here is a stepwise protocol for realizing gas-entrapping membranes (GEMs) from SiO2/Si wafers using integrated circuit microfabrication technology. When silica-GEMs are immersed in water, the intrusion of water is prevented, despite the water-loving composition of silica.

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and ...

Measuring Electrical Conductivity to Study the Formation of Brines Under Martian Conditions

This paper describes a protocol to design experiments to study the formation of brines under Martian conditions and monitor the process with electrical conductivity measurements. We used the Engineering Qualification Model (EQM) of Habitability: Brines, Irradiation, and Temperature (HABIT)/ExoMars 2022 instrument for the experiment setup but we provide a brief account of constructing a simple and inexpensive electrical conductivity measurement setup. The protocol serves to calibrate the electrical conductivity measurements of the salt deliquescence into brine in a simulated Martian environment. The Martian conditions of temperature (-70 &#176;C to 20 &#176;C), relative humidity (0% to 100%) and pressure (7 - 8 mbar) with carbon-dioxide atmosphere were simulated in the SpaceQ Mars simulation chamber, a facility at the Lule&#229; University of Technology, Sweden. The hydrate form of the known amount of salt accommodated between a pair of electrodes and thus the electrical conductivity measured depends predominantly on its water content and the temperature and relative humidity of the system. Electrical conductivity measurements were carried out at 1 Hz while exposing salts to a continuously increasing relative humidity (to force transitioning through various hydrates) at different Martian temperatures. For demonstration, a day-night cycle at Oxia Planum, Mars (the landing site of ExoMars 2022 mission) was recreated.

The objective of the protocol is to monitor the hydration of salts and the brine formation process. Electrical conductivity is used as the measurement technique. The experiments are performed in a simulated Martian environment of temperature, relative humidity and carbon-dioxide atmosphere.

This paper describes a protocol to design experiments to study the formation of brines under Martian conditions and monitor the process with electrical ...

Chemistry

Experimental Multiscale Methodology for Predicting Material Fouling Resistance

The buildup of fouling deposits in energy systems degrades their ability to transfer heat, reducing efficiency and causing operational issues such as localized corrosion. Each application presents its own challenges. In nuclear power generation, the buildup of CRUD (Chalk River Unidentified Deposits) induces unique, negative effects ranging from reduced heat transfer, to axial power shifting, to CRUD-induced localized corrosion (CILC), the last of which can cause sudden fuel failure. Knowledge of why CRUD forms and how to prevent its adhesion to nuclear fuel rods represents a major step towards eliminating it. This paper demonstrates a methodology to ascertain which materials may resist CRUD adhesion, thereby preventing its initiation and growth. It presents experiments targeted at multiple length scales: pool boiling (macroscale), which simulates CRUD initiation processes in a nuclear reactor, and atomic force microscope (AFM) force spectroscopy (microscale), which yields quantitative measurements of the adhesion between CRUD constituents and candidate CRUD-resistant materials. Early data from both sets of experiments show some correlation, suggesting that AFM force spectroscopy (AFM-FS) may be used to pre-screen materials for fouling resistance. So far, it appears that CRUD constituents adhere well to oxides, while carbides show both greatly reduced adhesion and no adherent CRUD in pool boiling experiments. The relationship between the AFM-FS measurements and the growth of CRUD in the pool boiling experiments may provide insight into the possible factors affecting fouling in nuclear reactors, eventually leading to its elimination.

Fouling, or corrosion product deposition, plagues numerous fields of energy production. At its core is adhesion between dissimilar materials. Understanding and controlling adhesion could reduce or eliminate fouling. This paper demonstrates pool boiling experiments (macroscale) and atomic force microscope force-spectroscopy measurements (microscale), which when in agreement, indicate fouling-resistance.

The buildup of fouling deposits in energy systems degrades their ability to transfer heat, reducing efficiency and causing operational issues such as ...

Biology

Conducting Reactions Below Room Temperature

Source: Laboratory of Dr. Dana Lashley - College of William and Mary
Demonstration by: Matt Smith
When new bonds are formed in the course of a chemical reaction, it requires that the involved species (atoms or molecules) come in very close proximity and collide into one another. The collisions between these species are more frequent and effective the higher the speed at which these molecules are moving. A widely used rule of thumb, which has its roots in the Arrhenius equation1, states that raising the temperature by 10 K will approximately double the rate of a reaction, and raising the temperature by 20 K will quadruple the rate:
(1) <img alt="Equation 1" src="/files/ftp_upload/10224/10224eq1.jpg" />
Equation (1) is often found in its logarithmic form:
(2) <img alt="Equation 2" src="/files/ftp_upload/10224/10224eq2.jpg" />
where k is the rate of the chemical reaction, A is the frequency factor (relating to frequency of molecular collisions), Ea is the activation energy required for the reaction, R is the ideal gas constant, and T is the temperature at which the reaction is taking place.
A higher temperature therefore means a reaction is completed much faster. Nonetheless, in some cases it is desirable to carry out reactions at low temperatures, in spite of the lowering effect on the rate of the reaction. A few scenarios in this regard are elaborated upon further below.
When it is useful to run a reaction below room temperature, chemists use cooling baths to maintain a certain temperature or temperature range. Reactions are cooled down to a desired temperature by placing the reaction flask inside an appropriate cooling bath. The reagents in the reaction never come in direct contact with the chemicals in the cooling bath. The cooling bath may consist of a single cryogenic (cooling) component (such as ice, dry ice, or liquid nitrogen) or may be a mixture of the cryogenic component with a certain solvent and/or an additive salt. The purpose of the solvent is to effectively transfer temperature of the cooling agent to the reaction flask, and the purpose of the additive is to lower (or depress) the freezing point of the mixture. (Note that it is possible for a substance to be both a solvent and an additive.)

Source: Laboratory of Dr. Dana Lashley - College of William and Mary
Demonstration by: Matt Smith
When new bonds are formed in the course of a chemical ...

JoVE Science Education

Organic Chemistry

Quenching and Boiling

Source: Alexander S Rattner, Sanjay Adhikari, and Mahdi Nabil; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Controlled heating followed by rapid cooling is an important element of many materials processing applications. This heat-treating procedure can increase material hardness, which is important for cutting tools or surfaces in high wear environments. The rapid cooling stage is called quenching, and is often performed by immersing materials in a fluid bath (often water or oil). Quenching heat transfer can occur due to forced convection - when the action of rapidly moving material through coolant drives the heat transfer process, and due to free convection - when the reduced density of hot fluid near the material surface causes buoyancy-driven circulation and heat transfer. At high material temperatures, the coolant can boil, leading to increased heat transfer effectiveness. However, when extremely hot materials are quenched, they can be blanketed in relatively low thermal conductivity coolant vapor, leading to poor heat transfer.
In this experiment, quenching heat transfer will be measured for a heated copper cylinder, which is representative of small heat-treated parts. The transient sample temperature profile will be measured during quenching and compared with theoretical results for free convection heat transfer. Boiling phenomena will also be investigated qualitatively.

Quenching, Boiling, Convection and Nusselt Number

Source: Alexander S Rattner, Sanjay Adhikari, and Mahdi Nabil; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, ...

Mechanical Engineering

Evaluating the Heat Transfer of a Spin-and-Chill

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
The Spin-and-Chill uses heat transfer and fluid flow fundamentals to chill beverages from room temperature to 38 &#176;F in as little as 2 min. It would take a refrigerator approximately 240 min and an ice chest approximately 40 min to achieve an equivalent temperature change. This is accomplished Spin and Chill by spinning a can or bottle at up to 500 rpm, which creates little or no foaming.
In this experiment, the efficacy of spinning a cylinder (i.e., soda can) at high speeds to cool a soft drink will be evaluated. Operational parameters, such as rpm and spin time, will be varied to assess their effect on heat transfer, and the heat transfer coefficient will be calculated using a lumped parameter model.

Convective Spin-and-Chill Heat Transfer: Lumped Parameter Model

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
The Spin-and-Chill uses ...