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 can be generated. The biggest limitation of this technique is the mixing and dilution of the brine. The brine volume will keep rising as the process continues. Therefore, when making ice this way, it is important to be aware of the rising brine volume and dropping brine salinity. In addition, it was observed that if the generated ice is not collected, it will melt. This may be because the brine is not at its melting temperature, allowing both heat and mass transfer between the formed ice and the bulk fluid. The mode of heat and mass transfer is by diffusion only, and the rate of melting is slow. However, since ice floats on the brine surface, additional heat ingress from the ambient environment boosts the rate of ice melting. For this reason, the generated ice should be collected promptly once it is produced to avoid a further increase in the volume of the brine.
Reducing dilution or separating the water and salt is currently being studied in our lab. One of the many ideas is to reintroduce the injected water to another tube that is larger in diameter so that water will only be exposed to the bulk fluid for a short period of time, minimizing the change in volume of the secondary refrigerant. Ice nucleation will occur when water is exposed to the brine, followed by the completion of the ice growth in the bigger tube. By adding this solid surface, the bulk salinity of the generated ice is controllable. For example, if lower salt content in the ice is required, one can add more "sweet water" to the fluid in the secondary tube. The submerged length of this secondary tube can be easily changed, depending on the required ice fraction of the product.
The flow rheology has a significant impact on the surface area of contact and on the area-to-volume ratio of the flow in the bulk fluid. Our observations indicate that a larger area of contact is more favorable for encouraging more ice to form. An increased area of contact should also enhance mass transfer, but has not yet been observed in the studied brine temperature and concentration range. It seems that before the flow enters the transition zone, where turbulences and separation of flow start to occur, ice will always be created. If the flow separates and large turbulences exist, each cluster of water molecules needs its own nucleation point, and ice may not form in these situations.
The relationship between the brine temperature and the water-to-ice conversion ratio is linear while at a constant brine concentration. The shifts of the conversion ratio versus the brine temperature best-fit lines indicate that brine concentration also plays an important role in the ice formation/water dilution process. Due to the phase transformation, the boundary conditions are very different in conventional heat- and mass-transfer analogy studies, and hence, those analogies are not sufficient for describing this situation.
This study also revealed that, since the freezing frontier can be fixed to a relative stable distance from the exit of the tube, the flow can reach a steady-state condition. This indicates that this phenomenon can be used as a reliable new mechanism for ice production in industry, since a much higher evaporator temperature and COP are expected in comparison to the existing ice-making techniques.

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.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>DMA 4500 M</td>
			<td>Anton Paar</td>
			<td>81546022</td>
			<td>Density Metre</td>
		</tr>
		<tr>
			<td>GELATO Chef 2200</td>
			<td>magimix</td>
			<td>0036500504R13</td>
			<td>Ice Cream Maker</td>
		</tr>
		<tr>
			<td>280D</td>
			<td>FREEZE MASTER</td>
			<td>241-1441</td>
			<td>Pipe Freezer</td>
		</tr>
		<tr>
			<td>M17.5X2</td>
			<td>BLUE ICE MACHINES</td>
			<td>GK924</td>
			<td>Slushy Puppy Machine</td>
		</tr>
		<tr>
			<td>HH68K</td>
			<td>OMEGA</td>
			<td>140045</td>
			<td>Thermometer</td>
		</tr>
		<tr>
			<td>OHAUS</td>
			<td>TS4KW</td>
			<td>1324</td>
			<td>Scale</td>
		</tr>
		<tr>
			<td>ZFC321WA/BNI225</td>
			<td>ZANUSSI</td>
			<td>920672574-00</td>
			<td>Freezer</td>
		</tr>
		<tr>
			<td>EIS Heater Matrix</td>
			<td>Vauxhall</td>
			<td>214720041</td>
			<td>Heat Exchanger</td>
		</tr>
		<tr>
			<td>2500LPH</td>
			<td>JBA</td>
			<td>AP-2500</td>
			<td>Pump</td>
		</tr>
		<tr>
			<td>Glass syringe</td>
			<td>FORTUNA Optima</td>
			<td></td>
			<td>100 mL</td>
		</tr>
		<tr>
			<td>OAT concentrated coolant</td>
			<td>wilko</td>
			<td>P30409014</td>
			<td>Ethylene Glycol</td>
		</tr>
		<tr>
			<td>pure dried vacuum salt</td>
			<td>INEOS Enterprise</td>
			<td>1433324</td>
			<td>NaCl Salt</td>
		</tr>
		<tr>
			<td>Methylated Spirits</td>
			<td>Barrettine</td>
			<td>1170</td>
			<td>Methanol&#160;</td>
		</tr>
	</tbody>
</table>

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; 10, and Le &#8776; 50), so ice can form easily. There is neither formation of a mushy layer nor salt rejection in this experiment. Once the ice grows thicker, it will hinder the rate of heat transfer due to its low thermal conductivity and affect the rate of ice formation. At this point, it can be clearly observed that the introduced &#34;sweet water&#34; can no longer promptly freeze into a solid. In addition, without convection, the low thermal conductivity of the brine itself also hinders the transportation of the latent heat from the cold sink. The rate of ice formation is directly associated with and very sensitive to the brine temperature. For example, water in -15 &#176;C brine freezes much faster than in -13 &#176;C brine. In the water injection case, the shape and size of the ice is related to the flow rheology. The rod of ice shown in Figure 1 has two distinctive parts: a straight head followed by a curly tail. The curly section is formed much closer to the brine surface, where the flow has more turbulence to it. The curly tail is usually much thinner than the straight head because of the onset of turbulence, which minimizes the difference between heat and mass transfer rates, especially at the outer layer of the stream, where the heat and mass transfers are the same. Therefore, only the inner core can freeze into ice. If the tube exit is kept horizontal rather than vertically up, a sheet of ice will be generated. The generation of ice becomes more stable and the results are reproducible. Lastly, it was found that lowering the flow rate is not an effective way of eliminating mixing. Instead, it significantly increases the chances of blocking the tube.
The water injection angle is kept at 0&#176; to the horizontal axis when performing water-to-ice conversion ratio measurements. The influence of brine temperatures and concentrations are illustrated in Figure 2. The conversion ratios usually sit between 0.4 to 0.9 for the studied brine temperatures and concentrations. It is important to keep the flow rheology and position of ice formation frontier constant throughout the experiment. The large volume of brine in Tank B helps to reduce the effects of local thermal gradients on the measurements. The relation between the brine temperature and the conversion ratio is first order for the studied temperature range. Coefficients for the best-fit lines are listed in Table 1. If a different injection angle is used, the water-to-ice conversion ratios will no longer follow these relationships because the area of contact and hence, the rates of heat and mass transfer, are different. When collecting the ice, it is important to keep the force applied to shake off the brine/washing water consistent and to try to minimize the amount of water left in the sieve. Similar amounts of water used to wash off the brine should be applied to avoid inconsistent results. It was found that if more than 500 mL of water is used to wash the ice, any further salinity reduction is unlikely to occur. When the volume is below 200 mL, the salinity can be as high as 4 wt%.
Since the evaporator temperature is much higher than a scraped-surface ice maker, which usually uses -40 &#176;C, if this method is used to produce ice, a higher COP is expected according to our calculation in Figure 3. If for example, the evaporator temperature is elevated to -20 &#176;C, the COP can almost reach 3 for refrigerant R134A.
<img alt="Figure 1" src="/files/ftp_upload/55014/55014fig1.jpg" /> 
Figure 1: Water introduction position. An &#34;ice cap&#34; can form when water is introduced at the brine surface. A rod of ice forms when the tube exit is kept upright. When water is injected in the brine, the shape of the ice depends on the flow rheology. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55014/55014fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55014/55014fig2.jpg" /> 
Figure 2: Conversion ratio comparison at different brine concentrations with a best-fit line. Both brine temperature and concentration influence how much water can be frozen into ice (conversion ratio) when the flow rate and rheology are kept the same. The conversion ratio increases linearly with a drop in brine temperature. Lower brine concentrations at lower bath temperatures generate more ice. The washing method collects more ice than the dry-collection method. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55014/55014fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55014/55014fig3.jpg" /> 
Figure 3: Coefficient of performance at different evaporator temperatures for a range of coolants. Higher evaporator temperatures favor the coefficient of performance (COP) of the cooling systems. The two transitional refrigerants (R22 and R134A) have better COPs than the already-banned R502 and the blends (R404A and R507A). <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55014/55014fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Salt concentration (wt%)</td>
			<td colspan="2">Dry collection</td>
			<td colspan="2">Wet collection</td>
		</tr>
		<tr>
			<td></td>
			<td>p1</td>
			<td>p2</td>
			<td>p1</td>
			<td>p2</td>
		</tr>
		<tr>
			<td>23.3</td>
			<td>&#8722;0.09909</td>
			<td>&#8722;1.34</td>
			<td>&#8722;0.1196</td>
			<td>&#8722;1.439</td>
		</tr>
		<tr>
			<td>22</td>
			<td>&#8722;0.1204</td>
			<td>&#8722;1.633</td>
			<td>&#8722;0.1439</td>
			<td>&#8722;1.839</td>
		</tr>
		<tr>
			<td>21</td>
			<td>&#8722;0.1261</td>
			<td>&#8722;1.682</td>
			<td>&#8722;0.1545</td>
			<td>&#8722;1.98</td>
		</tr>
	</tbody>
</table>
Table 1: Coefficients for the best-fit lines for the conversion ratio versus brine temperature diagram. The conversion ratio linearly correlates with the brine temperature according to the formula: <img alt="Equation" src="/files/ftp_upload/55014/55014eq5.jpg" />. Both dry- and wet-collection methods are listed here.

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 ...

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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

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do so is highly important in view of a number of applications in functional soft matter including electronics, biomedical engineering, and sensors. In the past, successful strategies to control the size and shape of supramolecular polymers typically focused on the use of templates2,3, end cappers4 or selective solvent techniques5. 
Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing electrostatic repulsive interactions on the hydrophilic rim and attractive non-covalent forces within the hydrophobic core of the polymerizing building block, we manage to create small and discrete spherical objects6,7. Increasing the salt concentration to screen the charges induces a sphere-to-rod transition. Intriguingly, this transition is expressed in an increase of cooperativity in the temperature-dependent self-assembly mechanism, and more stable aggregates are obtained. 
For our study we select a benzene-1,3,5-tricarboxamide (BTA) core connected to a hydrophilic metal chelate via a hydrophobic, fluorinated L-phenylalanine based spacer (Scheme 1). The metal chelate selected is a Gd(III)-DTPA complex that contains two overall remaining charges per complex and necessarily two counter ions. The one-dimensional growth of the aggregate is directed by &pi;-&pi; stacking and intermolecular hydrogen bonding. However, the electrostatic, repulsive forces that arise from the charges on the Gd(III)-DTPA complex start limiting the one-dimensional growth of the BTA-based discotic once a certain size is reached. At millimolar concentrations the formed aggregate has a spherical shape and a diameter of around 5 nm as inferred from 1H-NMR spectroscopy, small angle X-ray scattering, and cryogenic transmission electron microscopy (cryo-TEM). The strength of the electrostatic repulsive interactions between molecules can be reduced by increasing the salt concentration of the buffered solutions. This screening of the charges induces a transition from spherical aggregates into elongated rods with a length &gt; 25 nm. Cryo-TEM allows to visualise the changes in shape and size. In addition, CD spectroscopy permits to derive the mechanistic details of the self-assembly processes before and after the addition of salt. Importantly, the cooperativity -a key feature that dictates the physical properties of the produced supramolecular polymers- increases dramatically upon screening the electrostatic interactions. This increase in cooperativity results in a significant increase in the molecular weight of the formed supramolecular polymers in water.

The goal of this experiment is to determine and control the size, shape and stability of self-assembled discotic amphiphiles in water. For aqueous based supramolecular polymers such level of control is very difficult. We apply a strategy using both repulsive and attractive interactions. The experimental techniques applied to characterize this system are broadly applicable.

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do ...

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical electrohydrodynamic liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields and polar dielectric liquids. The construction of basic apparatus and operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and ...

A Robotic Platform to Study the Foreflipper of the California Sea Lion

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most of their thrust with their large foreflippers. This protocol describes a robotic platform designed to study the hydrodynamic performance of the swimming California sea lion (Zalophus californianus). The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;). The kinematics of the sea lion&#39;s propulsive stroke are extracted from video data of unmarked, non-research sea lions at the Smithsonian Zoological Park (SNZ). Those data form the basis of the actuation motion of the robotic flipper presented here. The geometry of the robotic flipper is based a on high-resolution laser scan of a foreflipper of an adult female sea lion, scaled to about 60% of the full-scale flipper. The articulated model has three joints, mimicking the elbow, wrist and knuckle joint of the sea lion foreflipper. The robotic platform matches dynamics properties&#8212;Reynolds number and tip speed&#8212;of the animal when accelerating from rest. The robotic flipper can be used to determine the performance (forces and torques) and resulting flowfields.

A robotic platform is described that will be used to study the hydrodynamic performance&#8212;forces and flowfields&#8212;of the swimming California sea lion. The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;).

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most ...

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 ...

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer coefficient as a function of the liquid flow rate in a transparent pipe. With certain amendments, the approach is extended to gas-liquid flows, with a particular emphasis on the effect of a single elongated (Taylor) air bubble on heat transfer enhancement. A non-invasive thermography technique is applied to measure the instantaneous temperature of a thin metal foil heated electrically. The foil is glued to cover a narrow slot cut in the pipe. The thermal inertia of the foil is small enough to detect the variation in the instantaneous foil temperature. The test section can be moved along the pipe and is long enough to cover a considerable part of the growing thermal boundary layer.
At the beginning of each experimental run, a steady state with a constant water flow rate and heat flux to the foil is attained and serves as the reference. The Taylor bubble is then injected into the pipe. The heat transfer coefficient variations due to the passage of a Taylor bubble propagating in a vertical pipe is measured as function of the distance of the measuring point from the bottom of the moving Taylor bubble. Thus, the results represent the local heat transfer coefficients. Multiple independent runs preformed under identical conditions allow accumulating sufficient data to calculate reliable ensemble-averaged results on the transient convective heat transfer. In order to perform this in a frame of reference moving with the bubble, the location of the bubble along the pipe has to be known at all times. Detailed description of measurements of the length and of the translational velocity of the Taylor bubbles by optical probes is presented.

This manuscript describes methods aimed at measuring the local instantaneous convective heat transfer coefficients in a single or two-phase pipe flow. A simple optical method to determine the length and the propagation velocity of an elongated (Taylor) air bubble moving at a constant velocity is also presented.

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer ...

Uncoupling Coriolis Force and Rotating Buoyancy Effects on Full-Field Heat Transfer Properties of a Rotating Channel

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that characterize the transport phenomena in a rotating channel are identified via the parametric analysis of the momentum and energy equations referring to a rotating frame of reference. Based on these dimensionless flow equations, an experimental strategy that links the design of the test module, the experimental program and the data analysis is formulated with the attempt to reveal the isolated Coriolis-force and buoyancy effects on heat transfer performances. The effects of Coriolis force and rotating buoyancy are illustrated using the selective results measured from rotating channels with various geometries. While the Coriolis-force and rotating-buoyancy impacts share several common features among the various rotating channels, the unique heat transfer signatures are found in association with the flow direction, the channel shape and the arrangement of heat transfer enhancement devices. Regardless of the flow configurations of the rotating channels, the presented experimental method enables the development of physically consistent heat transfer correlations that permit the evaluation of isolated and interdependent Coriolis-force and rotating-buoyancy effects on the heat transfer properties of rotating channels.

Here, we present an experimental method for decoupling the interdependent Coriolis-force and rotating-buoyancy effects on full-field heat transfer distributions of a rotating channel.

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that ...

Design and Fabrication of an Optical Fiber Made of Water

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with solid-cladding devices, capillary oscillations are not restricted, allowing the fiber walls to move and vibrate. The fiber is constructed by a high direct current (DC) voltage of several thousand volts (kV) between two water reservoirs that creates a floating water thread, known as a water bridge. Through the choice of micropipettes, it is possible to control the maximal diameter and length of the fiber. Optical fiber couplers, at both sides of the bridge, activate it as an optical waveguide, allowing researchers to monitor the water fiber capillary body waves through transmission modulation and, therefore, deducing changes in surface tension.
Co-confining two important wave types, capillary and electromagnetic, opens a new path of research in the interactions between light and liquid-wall devices. Water-walled microdevices are a million times softer than their solid counterparts, accordingly improving the response to minute forces.

This protocol describes the design and manufacture of a water bridge and its activation as a water fiber. The experiment demonstrates that capillary resonances of the water fiber modulate its optical transmission.

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with ...

Nerve Stem Cell Differentiation by a One-step Cold Atmospheric Plasma Treatment In Vitro

As the development of physical plasma technology, cold atmospheric plasmas (CAPs) have been widely investigated in decontamination, cancer treatment, wound healing, root canal treatment, etc., forming a new research field named plasma medicine. Being a mixture of electrical, chemical, and biological reactive species, CAPs have shown their abilities to enhance nerve stem cells differentiation both in vitro and in vivo and are becoming a promising way for neurological disease treatment in the future. The much more exciting news is that using CAPs may realize one-step, and safely directed, differentiation of neural stem cells (NSCs) for tissue transportation. We demonstrate here the detailed experimental protocol of using a self-made CAP jet device to enhance NSC differentiation in C17.2-NSCs and primary rat neural stem cells, as well as observing the cell fate by inverted and fluorescence microscopy. With the help of immunofluorescence staining technology, we found both the NSCs showed an accelerated differential rate than the untreated group, and ~75% of the NSCs selectively differentiated into neurons, which are mainly mature, cholinergic, and motor neurons.

Nerve Stem Cell Differentiation by a One-step Cold Atmospheric Plasma Treatment In Vitro

This protocol aims to provide detailed experimental steps of a cold atmospheric plasma treatment on neural stem cells and immunofluorescence detection for differentiation enhancement.

As the development of physical plasma technology, cold atmospheric plasmas (CAPs) have been widely investigated in decontamination, cancer treatment, ...

Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support substrates. Accomplishing this transfer in a highly controlled, mechanized, and reproducible manner can eliminate the creation of macroscale defect structures (e.g., tears, cracks, and wrinkles) within the thin film that compromise device performance and the usable area per sample. Here, we describe a general protocol for the highly controlled and mechanized transfer of a polymeric thin film onto an arbitrary porous support substrate for eventual use as a water filtration membrane device. Specifically, we fabricate a block copolymer (BCP) thin film on top of a sacrificial, water-soluble poly(acrylic acid) (PAA) layer and silicon wafer substrate. We then utilize a custom-designed, 3D-printed transfer tool and drain chamber system to deposit, lift-off, and transfer the BCP thin film onto the center of a porous anodized aluminum oxide (AAO) support disc. The transferred BCP thin film is shown to be consistently placed onto the center of the support surface due to the guidance of the meniscus formed between the water and the 3D-printed plastic drain chamber. We also compare our mechanized transfer-processed thin films to those that have been transferred by hand with the use of tweezers. Optical inspection and image analysis of the transferred thin films from the mechanized process confirm that little-to-no macroscale inhomogeneities or plastic deformations are produced, as compared to the multitude of tears and wrinkles produced from manual transfer by hand. Our results suggest that the proposed strategy for thin film transfer can reduce defects when compared to other methods across many systems and applications.

We present a procedure for highly controlled and wrinkle-free transfer of block copolymer thin films onto porous support substrates using a 3D-printed drain chamber. The drain chamber design is of general relevance to all procedures involving transfer of macromolecular films onto porous substrates, which is normally done by hand in an irreproducible fashion.

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support ...