1,721,245 research outputs found
An assesment on forced convection in metal foams
Full text linkMetal foams are a class of cellular structured materials with open cells randomly
oriented and mostly homogeneous in size and shape. In the last decade, several authors have
discussed the interesting heat transfer capabilities of these materials as enhanced surfaces for
air conditioning, refrigeration, and electronic cooling applications. This paper reports an
assessment on the forced convection through metal foams presenting experimental and
analytical results carried out during air heat transfer through twelve aluminum foam samples
and nine copper foam samples. The metal foam samples present different numbers of pores per
linear inch (PPI), which vary between 5 and 40 with a porosity ranging between 0.896-0.956;
samples of different heights have been studied. From the experimental measurements two
correlations for the heat transfer coefficient and pressure drop calculations have been
developed. These models can be successfully used to optimize different foam heat exchangers
for any given application
Vaporization inside a mini microfin tube: Experimental results and modeling
No full textThis paper proposes a comparison among the common R134a and the extremely low GWP refrigerant R1234yf during vaporization inside a mini microfin tube. This microfin tube has an internal diameter of 2.4 mm, it has 40 fins, with a fin height of 0.12 mm. Due to the high heat transfer coefficients shown by this tube, this technology can lead to a refrigerant charge reduction. Tests were run in the Heat Transfer in Micro Geometries Lab of the Dipartimento di Ingegneria Industriale of the Universita di Padova. Mass velocities range between 375 and 940 kg m(-2) s(-1), heat fluxes from 10 to 50 kW m(-2), vapour qualities from 0.10 to 0.99, at a saturation temperature of 30 degrees C. The comparison among the two fluids is proposed at the same operating conditions, in order to highlight the heat transfer and pressure drop differences among the two refrigerants. In addition, two correlations are proposed to estimate the heat transfer coefficient and frictional pressure drop during refrigerant flow boiling inside mini microfin tubes. These correlations well predict the experimental values, and thus they can be used as a useful tool to design evaporators based on these mini microfin tubes
Flow boiling heat transfer of R1234yf inside a 3.4mm ID microfin tube
No full textThis paper presents experimental results about the flow boiling of R1234yf inside a mini microfin tube. R1234yf is a Hydro Fluoro Olefin with a GWP<1, and thus it has recently been proposed as one of the possible substitutes of the common R134a. This study was carried out in a facility located at the Dipartimento di Ingegneria Industriale of University of Padova. The microfin tube has an inner diameter at the fin tip of 3.4mm, an outer diameter of 4.0mm, it has 40 fins and each fin is 0.12mm high. From the experimental measurements, it was possible to calculate the heat transfer coefficients, frictional pressure drops, and vapour qualities at the onset of the dryout phenomenon. The mass velocity was varied from 190 to 940kgm-2s-1, the heat flux from 10 to 50kWm-2, the vapour quality from 0.10 to 0.99, and the saturation temperature at the inlet of the test section was kept constant and equal to 30°C. The experimental results were also compared against the values predicted by empirical correlations available in the open literature
Experimental evaluation of a mini-VCS for electronic cooling applications: R1234yf vs R134a
No full textThis paper compares the performance of R1234yf and R134a used as working fluids in a mini Vapour Cycle System (VCS) for electronic thermal management of aeronautical packaging. The water cooled miniature scale refrigeration system implements a new concept oil-free linear compressor prototype. The compressor operates at constant speed whileits capacity can be varied by controlling the piston stroke. The experimental measurements were carried out at constant evaporation temperature of 15°C and varying the condensation levels permitted to compare the performance of the mini VCS, operating with R134a and R1234yf, in terms of cooling capacity and COP. Furthermore, particular attention was dedicated to the cold plate design, which had to meet the requirements established by the aeronautical standards. The cold plate was equipped with 15 thermocouples in order to analyze the wall temperatures distribution. In this way, it was possible to directly compare the flow boiling heat transfer behaviors of the two fluids under the same operating conditions
R1234ze(E) flow boiling inside a 3.4 mm ID microfin tube
No full textR1234ze(E) has a GWP<1 and a normal boiling temperature approximately 7.3 °C lower than that of R134a; it represents an interesting candidate for its replacement as working fluid in refrigerating machines. The refrigerant charge minimization in refrigerating and air conditioning equipment is a key issue for the new environmental challenges. Mini microfin tubes represent an optimal solution for both heat transfer enhancement and charge minimization tasks. This paper presents an experimental study of R1234ze(E) flow boiling inside a mini microfin tube with internal diameter at the fin tip of 3.4 mm. The experimental measurements were carried out at constant saturation temperature of 30 °C, by varying the refrigerant mass velocity between 190 kg m-2 s-1 and 940 kg m-2 s-1, the vapour quality from 0.2 to 0.99 at three different heat fluxes: 10, 25, and 50 kW m-2
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