![]() Lohse and his colleagues found that the modulation can increase the heat-transfer efficiency by up to 25% compared to a setup with static temperatures. The hot blobs from the bottom plate can efficiently deliver heat upward. The explanation was that the oscillation destabilizes the so-called boundary layer of fluid very close to the plates, allowing blobs of fluid to pinch off from those two regions more easily. They found that the oscillation increased the efficiency of heat transfer between the two plates. In 2020, a team of theorists led by Detlef Lohse of the University of Twente in the Netherlands added an oscillating temperature difference to their numerical simulations of convection. For example, Rayleigh-Bénard convection in the ocean is partly responsible for the melting of ice sheets, and the heat-transfer efficiency of these convective currents determines the melting rate. Understanding how the upward flow of heat-or “heat transfer”-is affected by the temporal variations is critical to accurately modeling the changing climate. So Earth’s atmospheric convection would be better modeled by “temporally modulated Rayleigh-Bénard convection,” where the bottom plate’s temperature oscillates.Īnother important element of such models is the vertical heat flow. On Earth, for example, the temperature of the ground oscillates, warming during the day and cooling at night. Vortices form and arrange themselves to allow the fluid to flow in an alternating pattern of upward and downward drafts, like lanes of oppositely moving highway traffic.įirst analyzed by Lord Rayleigh in 1916, this so-called Rayleigh-Bénard convection has been a classic model of convection because of its relative simplicity and applicability to many kinds of natural phenomena. The warming fluid near the bottom plate rises, and the cooling fluid near the top plate sinks. The bottom plate represents the warm surface of Earth the top plate represents the frigid void of outer space. Weather patterns on Earth can be modeled by a simple setup: a fluid sandwiched between two flat plates, with the bottom plate hotter than the top. A better understanding of these properties could help researchers develop more sophisticated planetary weather models and design more efficient heat exchangers-devices involved in the heating and cooling of many kinds of equipment. The effect was predicted theoretically but was difficult to observe in experiments. The temperature measurements of cold helium gas show that heat flows more efficiently when the temperature is oscillating than when it’s static. ×Īn oscillating temperature difference between two layers of fluid-such as the gases in Earth’s atmosphere-has a strong effect on their thermal properties, according to new experiments. Convection experiments with cryogenic helium demonstrated the thermal effects of an oscillating temperature difference between the top and bottom of a fluid-filled chamber. Blobs repeatedly heat at the bottom, rise, cool at the top, and then sink. A lava lamp undergoes Rayleigh-Bénard convection. ![]()
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