322,993 research outputs found
Atti del 1° Simposio AISAL : La sperimentazione animale in Italia e in Europa : verso un futuro comune
No full textComparison between miniature periodic two-phase thermosyphons and miniature LHP applied to electronic cooling equipment
No full textSeveral tests have been carried out with two miniature periodic two-phase thermosyphons (PTPTs), which have been developed for thermal control applications. A PTPT is a wickless device which can operates even against gravity. The two PTPTs have the same condenser and accumulator and different evaporators: the evaporator Type A, which can contain a large amount of liquid (20 × 10−6 m3) and which can be tilted up to 90°, and the evaporator Type B, which has an internal volume of 5 × 10−6 m3 and can operate just in horizontal orientation. Their unsteady and their periodic steady state performances have been studied and compared with those of several miniature loop heat pipes quoted in the references. The paper shows that the PTPT thermal resistances are similar to those of miniature LHPs, even those of PTPTs are less influenced by the arrangement of the condenser and the evaporator with respect to the gravity. The thermal resistance, as the PTPT steadily operates, is about 0.55 K/W with a heat load of 110 W. The main experimental observation on the PTPT unsteady behaviour is that their start-ups are rather smooth in the most cases. However the start-up performances does not depend on any configuration and orientation of the loop element
Performance of High Frequency Periodic Two-Phase Thermosyphons for Electronic Cooling Applications
No full textThis paper deals with a particular miniature two-phase loop named Periodic Two-Phase Thermosyphon (PTPT), whose operation is periodic. A Periodic two-phase thermosyphon allows remote condensation and broad flexibility in the mutual displacement of the evaporator with respect to the condenser. In addition, a PTPT allows the overall dimensions of the evaporator to be drastically reduced, and allows it to be placed close to the electronic equipment; it is suitable for high density packaging thermal control applications.
In this paper the authors have experimentally compared the performance of two mini-PTPT prototypes which operate at high frequency (0.016 Hz) with those obtained by 4 high performance commercial devices which are designed to be implemented on the surface of a Pentium© IV processor.
The PTPT device shows a specific thermal resistance of 5.1 K cm2/W, about twice those measured with commercial devices, but similar to other capillary thermal loops (LHP). These devices show that their performance is not influenced by the tilt angle of the heating surface. The dynamic response of these devices is influenced by the operational frequency. In the case of compact high frequency operating PTPT, the dynamic response is quicker than with other capillary loops such as LHP and CPL, and similar to that of heat pipe cooling devices, which do not allow remote condensation. The PTPT device can really be a low cost solution for compact thermal control application
An Infrared Experimental Approach to Visualize Thermal Irregularities in Historical Building Mansonry Walls
No full textFeasibility of periodic thermosyphons for environmentally friendly ground source cooling applications
No full textThis paper presents a feasibility study of a low-energy consumption ground source cooling system based on a periodic two-phase thermosyphon (PTPT) device in which a condensate is periodically transferred back to the evaporator. Operation of the PTPT is passive with the ground condenser positioned 1–11 m below the evaporator. The ground condenser may be at the condensing temperatures of 12–20°C depending on the ground depth. A semi-analytical approach is used to simulate the transient behaviour of the PTPT device. The simulation aims to study the effect of several parameters on the cooling rate of the device, including the length of condensing coil, the ground depth, the temperatures of the soil and the indoor air. The preliminary simulation results indicate that the PTPT device may be promising for ground source cooling applications
Experimental analysis of the melting process in a pcm/aluminum foam composite material in hypergravity conditions
No full textPhase change materials [(PCMs), e.g., paraffin waxes, fused silica salts, and polyethylene glycol] can be successfully used for thermal management and heat storage in ground and space applications. Open-cell metal foams embedded in the PCM material increase the overall thermal conductivity and accelerate the melting process. The literature shows that the pore size and relative density strongly affect the melting process performance. Most studies have shown that the high thermal conductivity of the open-cell metal foam dominates the melting process. The natural convection effect usually is attenuated; however, it can be relevant if it occurs. An experimental activity has been designed and carried out under the framework of the European Space Agency student program Spin Your Thesis 2017 to analyze the effect of different hypergravity levels and configurations on the melting performance of a composite aluminum foam (10 pores per inch)/paraffin wax material at two different heat fluxes. The gravity level ranges from 5g up to 20g using a large diameter centrifuge facility. The effect of gravity on the melting process has been investigated by measuring the melting time and the dynamic evolution of the melted area. The experiments show that the hypergravity condition accelerates the melting process: it is 12% faster ranging from 5g to 10 g. Infrared visualization allowed us to define the melting front dynamic evolution. A natural convection regime was observed in all of the experiments. The natural convection incipience accelerates the melting process. A critical analysis of the scaling criterion in the literature has been qualitatively done and a modified Rayleigh number is proposed to characterize the melting process
Heat transfer delay method for the fluid velocity evaluation in a multi-turn pulsating heat pipe
No full textA multi-turn closed loop pulsating heat pipe made of aluminium is tested in vertical bottom heated mode and
different condenser temperatures with the aim of providing quantitative information regarding its flow dynamics
through a novel post-processing technique on the local wall-to-fluid heat flux, evaluated within the adiabatic
section. The studied device is made of an annealed aluminium tube (inner/outer diameter: 3/5 mm), folded in 14
turns and partially filled with methanol (volumetric filling ratio: 50%). The aluminium channels are coated with
a high-emissivity opaque paint, thus allowing thermographic measurements on the outer wall by means of a
high-resolution medium wave infrared camera. The proposed method, named Heat Transfer Delay Method, is
validated by means of a dedicated experimental approach. Then, the acquired time-space temperature maps are
used as input data for the inverse heat conduction problem resolution approach to estimate the local convective
heat flux locally exchanged at the inner wall-fluid interface. The resulting wall-to-fluid heat fluxes are then post-
processed by applying the Heat Transfer Delay Method to the oscillatory and circulatory flow modes. The average
fluid velocity is assessed at varying working conditions during the circulatory flow, finding values up to 0.77 m/s
and 0.3 m/s for condenser temperature equal to 20 ◦C and 10 ◦ C, respectivel
Preliminary design of a self-deployable Pulsating Heat Pipe by means of a Shape Memory Alloy actuator
No full textThe preliminary design of thermally driven self-deployable pulsating heat pipe with
Shape Memory Alloy (SMA) actuator is presented. The use of SMA wire allows the passive
folding of the heat transfer device: the hot side of the heat exchanger acts as hot source for the
SMA deformation. The system consists of a torsion-spring shaped Pulsating Heat Pipe tube
portion (Al6063, 1.8 and 2.6 mm inner and outer diameter) and a SMA wire (0.5 mm diameter,
closed and open configuration length 165 mm and 172 mm respectively). When the SMA wire
is heated up by the hot source, it shortens inducing a moment on the PHP torsion spring that
allows the PHP panel to rotate 90 deg
Periodic thermosyphons for environmentally friendly ground source cooling applications
No full textThis paper presents a feasibility study of a low-energy consumption ground source cooling systems based on a Periodic Two-Phase Thermosyphon (PTPT) device in which the condensate is periodically transferred back to the evaporator. Operation of this PTPT is passive with the ground condenser positioned 1-11 m below the evaporator. The ground condenser may at the condensing temperatures of 12-20 °C depending on the ground depth. A semi-analytical approach has been used to simulate the behaviour of the PTPT device over time. The model has been used to study the effect of several parameters on the cooling rate of the device, including the length of condensing coil, the ground depth, the temperatures of the soil and the indoor air. The preliminary results looks promising
- …
