Multistable autonomous motion of fruit on a smooth hotplate

Origin of scale coupling may be clarified by the understanding of multistability, or shifts between stable points via unstable equilibrium points due to a stimulus. When placed on a glasstop hotplate, cobs of corn underwent multistable autonomous oscillation, with unsteady viscous lubrication below and transitional plumes above, where the buoyancy to inertia force ratio is close to ≥ 1.0. Subsequently, viscous wall-frictional multistability occurred in six more types of smooth fruit with nominal symmetry. Autonomous motion observed are: cobs roll, pitch and yaw; but green chillies, blueberries, tropical berries, red grapes, oblong grapes and grape tomatoes roll and yaw. The cross products of the orthogonal angular momentum produce the observed motion. The prevalence of roll and yaw motion are the most common. Lubricant film thickness h$$\propto$$ ∝ U/(TF), for cob mass F, tangential velocity U and temperature T. In heavier cobs, the film thins, breaking frequently, changing stability. Lighter cobs have high h, favoring positive feedback and more spinning: more T rises, more viscosity of water drops, increasing U and h more, until cooling onsets. Infrequent popping of the tender corn kernel has the same mean sound pressure level as in hard popcorn. The plume vortex jets lock-in to the autonomous rolling cob oscillation. Away from any solid surface, the hot-cold side boundary produces plumes slanted at ± 45°. Surface fencing (13–26 μm high) appears to control motion drift.

Study on Performance of the Thermoelectric Cooling Device with Novel Subchannel Finned Heat Sink

The thermoelectric refrigeration system is an application of the Peltier effect, and good refrigeration performance is dependent on effective heat dissipation performance. To enhance the cooling performance of the thermoelectric system, this paper designs a new type of finned heat sink, which does not change the overall size of the thermoelectric system. The performance of the refrigeration system under the new fin is tested by experiments under various conditions. During the experiment, the cooling wind speed, the temperature of the hot and cold side of the TEC, the power consumption of the fan, and other parameters were directly recorded through the measuring instrument. The results show that the use of new finned heat sinks can improve the COP of the thermoelectric refrigeration system. Within the scope of the study, the thermal resistance of the new fins can be reduced by , and the system COP value can be increased by . In addition, increasing the cooling wind speed can further reduce the cold side temperature. Within the research range, the lowest temperature can reach , but the power consumed by the fan is of that of the conventional fin heat sink refrigeration device.

Experimentation of a Wearable Self-Powered Jacket Harvesting Body Heat for Wearable Device Applications

The development of special wearable/portable electronic devices for health monitoring is rapidly growing to cope with different health parameters. The emergence of wearable devices and its growing demand has widened the scope of self-powered wearable devices with the possibility to eliminate batteries. For instance, the wearable thermoelectric energy harvester (TEEH) is an alternate to batteries, which has been used in this study to develop four different self-powered wearable jacket prototypes and experimentally validated. It is observed that the thermal resistance of the cold side without a heat sink of prototype 4 is much greater than the rest of the proposed prototypes. Besides that, the thermal resistance of prototype 4 heat sinks is even lower among all proposed prototypes. Therefore, prototype 4 would have a relatively higher heat transfer coefficient which results in improved power generation. Moreover, an increase in heat transfer coefficient is observed with an increase in the temperature difference of the cold and hot sides of a TEEH. Thus, on the cold side, a heat flow increases which benefits heat dissipation and in turn reduces the thermal resistance of the heat sink. Besides that, the developed prototypes on people show that power generation is also affected by factors like ambient temperature, person’s activity, and wind breeze and does not depend on the metabolism. A different mechanism has been explored to maximize the power output within a 16.0 cm2 area, in order to justify the wearability of the energy harvester. Furthermore, it is observed that during the sunlight, any material covering the TEEH would improve the performance of prototypes. Prototypes are integrated into jacket and studied extensively. The TEEH system was designed to produce a maximum delivering power and power density of 699.71 μW and 43.73 μW/cm2, respectively. Moreover, the maximum voltage produced is 62.6 mV at an optimal load of 5.6 Ω. Furthermore, the TEEH (prototype 4) is connected to a power management circuit of ECT310 and LTC3108 and has been able to power 18 LEDs.

Evaluation of Thermoelectric Generators under Mismatching Conditions

Due to the wide usability of thermoelectric generators (TEG) in the industry and research fields, it is plausible that mismatching conditions are present on the thermal surfaces of a TEG device, which induces negative-performance effects due to uneven surface temperature distributions. For this reason, the objective of this study is to characterize numerically the open-circuit electric output voltage of a TEG device when a mismatching condition is applied to both the cold and hot sides of the selected N and P-type semiconductor material Bi0.4Sb1.6Te3. A validated numerical simulation paired with a parametric study is conducted using the Thermal-Electric module of ANSYS 2020 R1, for which different thermal boundary and mismatching conditions are applied while considering the temperature-dependent thermoelectrical properties of the N and P-type material. The results show an inverse relationship between the open-circuit voltage and the mismatching temperature difference. When a mismatching condition is applied on the hot side of the TEG device, the temperature-dependent electrical resistance has lower values, deriving in higher voltage results (linear tendency) compared to a mismatching condition applied to the cold side (non-linear tendency).

The investigation of natural-rubber for improving self-powered heat detector based on thermoelectric generators

Fire hazard has destroyed humanity creations. Fire detectors have been developed by using different techniques. Thermoelectric generator (TEG) is a part of energy harvesting which is able to convert heat into electricity because of temperature difference between hot and cold side of thermoelectric device (TE). Different materials are used for thermoelectric generators which depend on the characteristics of the heat source, heat sink and the design of the thermoelectric generator. Many thermoelectric generator materials are currently undergoing research. This paper presented an investigation of seeking an alternative way of detecting fire hazard by developing architecture prototype of a fire detection technique using natural rubber. The thermoelectric prototype used self-powered device which improved the temperature difference gap and stabilized the cold side of TE alongside natural rubber as the cooling material. The technique is relatively simple system realization based on three viable components, i.e. a heat sensor, a low-power RF-transmitter and a RF-receiver. The heat sensor is designed and fabricated by thermoelectric and heat sink with natural rubber (NR) coating. The NR coating is heat absorption reduction. Therefore, the temperature difference is wildly resulting in the higher TE output voltage. The voltage is also supplied to the low-power RF transmitter module. In case of fire hazard, the temperature increases from 26 to 100 °C , the prototype can operate successfully. This technique will solve potentially the power supply issue in fluctuated situations. The rubber coating from rubber trees in Thailand would be a value chain added for bio-economy, supporting a sustainable development goal of the country

Pitched unventilated wood frame roof with smart vapour barrier – field measurements

Unventilated wood-frame roofs may provide smaller roof thickness and less material use compared to conventional unventilated roofs with all the thermal insulation above the load bearing structure. Unventilated roofs are, however, normally built without wooden materials between the vapour barrier and roof membrane due to moisture safety. Field measurements on the pitched unventilated wood-frame roof of an office building in Norway is performed to demonstrate and document the performance of this type of roof construction. Through monitoring of moisture and temperature, the study aims to contribute to verification of simulations and laboratory measurements showing that unventilated wood-frame roofs may be built with wooden materials if a smart vapour barrier is used. The results show moisture levels below 15 weight-% on the warm side of the rafters throughout the first 15 months of measurements. On the cold side of the rafters, the moisture content increased during winter due to built-in moisture in the construction and reached levels close to 25 weight-%. The moisture content decreased to around 15 weight-% when summer arrived, which shows an expected redistribution of moisture and indicates possible drying of the construction. The measurements underline the importance of limiting built-in moisture to reduce the risk of mould growth, but the study also implies that for some given premises an unventilated pitched wood-frame roof may have acceptable moisture risk.

The Soret coefficients of the ternary system water/ethanol/triethylene glycol and its corresponding binary mixtures

Thermodiffusion in ternary mixtures is considered prototypic for the Soret effect of truly multicomponent systems. We discuss ground-based measurements of the Soret coefficient along the binary borders of the Gibbs triangle of the highly polar and hydrogen bonding ternary DCMIX3-system water/ethanol/triethylene glycol. All three Soret coefficients decay with increasing concentration, irrespective of the choice of the independent component, and show a characteristic sign change as a function of temperature and/or composition. With the exception of triethylene glycol/ethanol at high temperatures, the minority component always migrates toward the cold side. All three binaries exhibit temperature-independent fixed points of the Soret coefficient. The decay of the Soret coefficient with concentration can be related to negative excess volumes of mixing. The sign changes of the Soret coefficients of the binaries allow to draw far-reaching conclusions about the signs of the Soret coefficients of the corresponding ternary mixtures. In particular, we show that at least one ternary composition must exist, where all three Soret coefficients vanish simultaneously and no steady-state separation is observable. Graphic abstract

Experimental Investigation for a Novel Prototype of a Thermoelectric Power Generator With Heat Pipes

In order to obtain the power generation of the thermoelectric power generator (TEG) group, a similar structure of the disc sandwich structure and an experimental system are built to analyze the power generation performance and temperature characteristics. To improve heat transfer and move heat from the hot side to the cold side, heat pipes with high thermal conductivity are arranged on the adjacent cold and hot plates of the TEG. The similar sandwich structure has 17 cold plates and 17 hot plates for the TEG pieces, which are connected in series on the circuit. Working conditions are hot air flow and cold water flow; hot air temperature and cold water temperature are set to a fixed temperature. The power generation of a single TEG is tested for verifying linear changes in the power generation performance with temperature differences (Td). Experimental results are that the power generation is improved by the air flow and water flow increasing. The water flow has a smaller effect on the power generation than the air flow. In the cold side of TEG pieces, the temperature of the cold side showed a gradual upward trend, the temperature of the hot side showed a wave trough phenomenon, and the Td showed a wave trough phenomenon. The hot air flow and the cold water changing cannot weaken the temperature trend of the hot side and the cold side. The hot air flow can more significantly increase the Td than the cold water.

Thermoelectric Generator with Passive Biphasic Thermosyphon Heat Exchanger for Waste Heat Recovery: Design and Experimentation

One of the measures to fight against the current energy situation and reduce the energy consumption at an industrial process is to recover waste heat and transform it into electric power. Thermoelectric generators can be used for that purpose but there is a lack of experimental studies that can bring this technology closer to reality. This work presents the design, optimizations and development of two devices that are experimented and compared under the same working conditions. The hot side heat exchanger of both generators has been designed using a computational fluid dynamics software and for the cold side of the generators two technologies have been analysed: a finned dissipater that uses a fan and free convection biphasic thermosyphon. The results obtained show a maximum net generation of 6.9W in the thermoelectric generator with the finned dissipater; and 10.6W of power output in the generator with the biphasic thermosyphon. These results remark the importance of a proper design of the heat exchangers, trying to get low thermal resistances at both sides of the thermoelectric modules, as well as, the necessity of considering the auxiliary consumption of the equipment employed.

Performance Improvement of Thermoelectric Air Cooler System by Using Variable-Pulse Current for Building Applications

The thermoelectric air conditioning system (TE-AC) is a small, noiseless alternative to standard vapor compression refrigeration (VCR) systems. The cooling characteristics of a TE-AC system operating under two conditions, i.e., steady current and current pulses, are investigated in this study. This system consists of three thermoelectric modules, a heat sink, and an air circulation fan. The result shows that maximum temperature reduction in cooling side of TE-AC system was achieved at 6 A input current under steady state operation. The optimum performance of the TE-AC system under steady state operation depends upon the combined effect of the cooling load, Joule, Fourier, and Peltier heat. In TE-AC pulse operation, both current width and cooling load applied on the cold side of the thermoelectric module (TEMs) play an important role in achieving optimum cooling performance of the system. When normal input current operation (i.e., no current pulse) was compared to pulse-operated TE-AC system operation, it was found that pulse operation provides an additional average temperature reduction of 3–4 °C on the cold side of TEMs. Although on the hot side, it maintains a temperature in the range of 18 °C to 24 °C to reduce overshoot heat flux. The duration of operation is also important in determining pulse width and pulse amplitude. Minimum and overshoot peak temperature rises during each cycle for longer run operation. In the TE-AC system, the accumulated Joule heat during a current pulse frequently causes a temperature overshoot, which lasts much longer. As a result, the next current pulse was not released until the temperature of TE was restored to its initial value.