New concept for magnetocaloric heat pumps based on thermal diodes and latent heat transfer

Since the beginning of the last decade, several dozens of magnetocaloric heat pump systems have been built by different groups. Basically all of these systems are based on the Active Magnetic Regenerator (AMR) concept, where a heat transfer fluid is actively pumped through a bed of magnetocaloric material in order to transfer thermal energy to hot and cold side heat exchangers. Hereby several powerful systems were built, generating large temperature spans of more than 50 K while others provided large cooling capacities of several kW. However, up to now no system has been built which provides large temperature span and cooling capacity while having a coefficient-of-performance (COP) better than standard compressor-based cooling systems [1]. In this work a new concept and first experimental data of a magnetocaloric heat pump will be presented. In this concept, the heat transfer is realized by the combination of magnetocaloric material with thermal diodes which are based on latent heat transfer. Similar to thermosyphons, thermal energy is efficiently transported by condensation and evaporation processes leading to heat transfer rates which are several orders of magnitude larger than in conventional systems. At the same time, no additional pumps are required for transporting the heat exchange fluids, enabling systems which large temperature spans and competitive COPs

Flat-Plate PHP with Gravity-Independent Performance and High Maximum Thermal Load

In many energy-related applications, components with high heat loads, such as power electronics, play an important role. Pulsating heat pipes (PHPs) are an effective solution to deal with the increasing heat load of these components. In many real-life applications, the PHP must work against gravity and still be able to operate efficiently. However, the majority of present flat-plate PHP designs do not perform well under this condition. Therefore, this paper presents a flat-plate PHP with a conventional channel design optimized for gravity-independent operation. The PHP was capable of transmitting a heat output of 754 watts in all orientations, while the testing heater in use never exceeded a temperature of 100 °C. No indications of dryout were observed, implying that the maximum thermal load the PHP can handle is even higher. Additionally, three different condenser zone sizes were tested with the PHP. Previously published results indicated that there is a specific range of suitable condenser zone sizes, and performance problems will occur if the condenser zone size falls outside of this range. The findings from this work point in the same direction

Comparing temperature and water vapor pressure for days with different frequencies of ATAAD events.

Comparing temperature and water vapor pressure for days with different frequencies of ATAAD events.</p

Small-Sized Pulsating Heat Pipes/Oscillating Heat Pipes with Low Thermal Resistance and High Heat Transport Capability

Electronics (particularly power electronics) are the core element in many energy-related applications. Due to the increasing power density of electronic parts, the demands on thermal management solutions have risen considerably. As a novel passive and highly efficient cooling technology, pulsating heat pipes (PHPs) can transfer heat away from critical hotspots. In this work, we present two types of small and compact PHPs with footprints of 50 × 100 mm2, thicknesses of 2 and 2.5 mm and with high fluid channel density, optimized for cooling electronic parts with high power densities. The characterization of these PHPs was carried out with a strong relation to practical applications, revealing excellent thermal properties. The thermal resistance was found to be up to 90% lower than that of a comparable solid copper plate. Thus, a hot part with defined heating power would remain at a much lower temperature level and, for the same heater temperature, a much larger heating power could be applied. Moreover, the dependence of PHP operation and thermal properties on water and air cooling, condenser area size and orientation is examined. Under some test configurations, dryout conditions are observed which could be avoided by choosing an appropriate size for the fluid channels, heater and condenser

Comparing ATAAD events by months.

Box plots for ATAAD events recorded in Germany, 2005 to 2015, per month. The warm months (May to August) exhibit less events.</p

ATAAD events by months.

Time series of monthly numbers of ATAAD events in Germany and linear trend line (red). The data points were weighted by the length of each month. There is a significant upward trend (signal-to-noise ratio = 2.62, p = 0.009, data are approximately normally distributed).</p

Comparing ATAAD events by seasons.

Box plots for ATAAD events recorded in Germany, 2005 to 2015, per meteorological seasons (spring = March/April/May, summer = June/July/August, etc). The summer exhibits less events.</p

Bio-synop classes (see subsection Bio-synop classes in Materials and methods) at which significantly more or less ATAAD events occur.

Bio-synop classes (see subsection Bio-synop classes in Materials and methods) at which significantly more or less ATAAD events occur.</p