Spin-and-chills are household examples of heat transfer technology. They can be analyzed to understand engineering processes that are widely studied and applied in industry. Spin-and-chills cool soft drinks much faster than refrigerators or ice chests. They operate by rotating soda cans within a reservoir of ice at speeds of hundreds of revolutions per minute. The spin-and-chill utilizes convective heat transfer to cool the soda cans. By measuring the cooling rate under different conditions, the convective behavior can be determined. Which can be used to improve the cooling efficiency as well as model and understand related heat transfer situations. This video illustrates the operating principles of the spin-and-chill, demonstrates experiments that evaluate convective heat transfer, and discusses related applications.
The spin-and-chill is modeled as consisting of a warm soda can submerged in a large, cold environment. The can has thin walls and is filled with fluid. The fluid is hottest at the center and coldest at the rim. And the temperature distribution is symmetric around the can's axis of rotation. As the can spins, the fluid inside is cooled. The surroundings are assumed to be so large that they do not appreciably warm up. This visualization can be divided into several zones, each characterized by its unique temperature distribution and heat transfer mechanism. The wall is modeled as a thin membrane. Its dominant mechanism of heat transfer is conduction. The spread of heat without macroscopic motion of the medium. The can wall is so thin, however, that conduction in the wall is negligible. On either side are boundary layers, regions of fluid with strong temperature gradients. Here the dominant mechanism of heat transfer is convection. Heat transfer aided by the motion of fluids. During rapid spinning, conduction is negligible inside the can, because the contents are well-mixed. Finally, in the bulk regions, conduction once again predominates. However, because the volume of ice is large compared to the fluid in the can, the temperature in the bulk ice phase does not change appreciably. And conduction is negligible. Because conduction within the can is negligible and convection is the determinant factor in cooling the fluid in the can, lumped parameter analysis can be used to model the cooling behavior. The lumped parameter analysis reduces a thermal system to a single discrete lumped resistance. Where the temperature difference of each individual resistance is considered unknown. The lumped parameter model assumes the greatest resistance to heat transfer occurs in the boundary layers. As the can cools over time, the temperature of the bulk decreases uniformly over its volume. Using the equation shown, one can calculate the lumped heat transfer coefficient, h, for a can being cooled using a spin-and-chill. The heat transfer coefficient takes into account all of the resistances to convective heat transfer, and lumps them into one constant. That constant is a ratio of heat flux to the driving force for heat flow. In this case, the difference between the temperature of the fluid in the can and the temperature of the ice. Those are the principles. Now let's demonstrate how to study convective heat transfer using a spin-and-chill.
The procedure requires a spin-and-chill, ice, and a sealable aluminum sample can. Record the dimensions of the can. Fill it with water and record its mass and temperature. Then seal the can with a plastic sealing lid. Weigh the ice that will be used in the setup. Load it into the apparatus, and finally, insert the aluminum can. Set the spin-and-chill to perform a single two-minute cycle at 300 RPM, and switch it on. After the spin completes, withdraw the can, remove the lid, and measure the temperature of the water. Lastly, use a graduated cylinder to measure the amount of ice that has melted. Use sequential cycles to assess the effects of longer run times on cooling the fluid in the can. In sequential cycles, a two-minute cycle is performed as before, and the temperature is recorded. Then the can is replaced in the spin-and-chill, and another two-minute cycle is started. In addition to spin time, study the effect of modifying other parameters. Such as rotational speed on cooling performance. Perform two-minute cycles at multiple speeds, ranging from a few RPM to over 500 RPM.
Data for the lumped parameter model was averaged over 10 single-run trials. Each lasting two minutes at 300 RPM. On average, a two-minute run decreased the temperature of the can from 82.12 degrees Fahrenheit to 55.88 degrees Fahrenheit. Substituting in the relevant physical and geometric characteristics of the can, the heat transfer coefficient can be calculated. The thermodynamic efficiency was estimated by dividing the heat lost by the can to the heat required to melt the ice during the run. Using sequential runs at a constant RPM, it was shown that cooling performance was enhanced with longer cycle times. However, the sequential cycles show that cooling efficiency decreases with time. This decrease in efficiency is common in heat transfer, when the temperature differential driving the heat transfer becomes smaller. Varying the RPMs at a fixed run time shows the effect of speed on cooling performance. A faster spin time led to a larger temperature drop within the can. The heat transfer efficiency was greatest when the spin-and-chill was operated at the highest RPM.
The heat transfer process observed in the spin-and-chill is seen in many laboratory and industrial settings. High pressure freezing is used to preserve tissue samples for transmission electron spectroscopy. In a process analogous to the spin-and-chill, samples are exposed to pressurized liquid nitrogen jets. Permitting quick, non-destructive cryofixation. This is particularly useful for plant tissues, which must be rapidly frozen to prevent cellular damage through the formation of ice. Similar procedures are used to preserve human muscle cells or stem cells. Nuclear reactors also operate on the principles of convective heat transfer. They contain a core within which a highly-controlled fission reaction occurs. The core is submerged in a stream of pressurized water, which absorbs the heat generated by the fission reaction and vaporizes. The vaporized water is then used to drive generators. The safety of these reactors, regardless of scale, largely depends on the control of the convective heat transfer process that occurs at its core.
You've just watched JOVE's introduction to the heat transfer in the spin-and-chill. You should now be familiar with convective heat transfer, a procedure for measuring parameters affecting convective heat transfer, and some applications. As always, thanks for watching.