Hybrid PCM\u2014aluminium foams\u2019 thermal storages: an experimental study

The latent heat absorption phenomenon associated with melting of a suitable Phase Change Material can be an effective way to improve the Thermal Energy Storage behaviour in many applications. However, the most suitable materials to be used in heating and refrigeration systems find intrinsic limitations due to their poor heat transfer capabilities. This work experimentally studies the use of aluminum foams as heat transfer medium to improve the overall heat transfer of paraffin waxes that can be possible phase change materials to be implemented in hybrid sensible-latent water thermal energy storages. The experimental tests were run in a dedicated setup designed, developed, and built at the Department of Management and Engineering of the University of Padova. The effects of the use of aluminum foams as enhancing heat transfer medium were studied by comparing the loading and unloading processes of a paraffin wax with melting temperature around 40 \ub0C, with and without metal foams, in a water thermal storage unit. The effects of three different foams with 5, 20, and 40 Pores Per Inch (PPI) were investigated

Experimental Analysis of R134a and R1234ze(E) Flow Boiling Inside a Roll Bond Evaporator

Roll bond type evaporator is one of the most widely used technology in household refrigerators. Despite that, only few works that analyze the performance of this component are available in literature. Furthermore, no evidence is given to the impact on the heat transfer performance when substituting the original HFC refrigerant with an HFO inside the same evaporator. This paper presents an experimental study of R134a and R1234ze(E) inside an off the shelf roll bond evaporator, commonly used for small size domestic refrigerators. The evaporator was mounted inside a climate dark chamber where ambient temperature and humidity were maintained stable during the tests. To control the inlet conditions (evaporation temperature, inlet quality, refrigerant mass flow rate) it was used a water cooled miniature scale vapor cycle system with R134a and R1234ze(E) as working fluids. By means of an IR-thermo-camera, the whole roll bond temperature field was investigated under different working conditions. 15 thermocouples were collocated on the back of the evaporator to verify the temperatures reported in the images collected by the IR thermo-camera. From these pictures it was possible to delineate the super heating region and to point out the areas of the evaporator in which heat transfer is less efficient depending on the fluid and on the working conditions. During the experimental tests the refrigerant mass flow rate was varied by regulating the compressor speed, while ambient temperature and evaporation temperature were kept as constant. The data acquired from the vapor cycle system (i.e. condensation and evaporation pressure, evaporator inlet quality, vapour superheating, refrigerant mass flow rate) coupled with the IR thermo-camera images allowed to evaluate the behavior and the efficiency of the roll bond. Since the data were collected maintaining the same operating conditions in term of ambient temperature and humidity, heat flow rate and evaporation temperature, it was possible to highlight differences among the two refrigerants in term of mass flux. Furthermore, on the basis of the IR images and of the thermocouples measurements, an average heat transfer coefficient was defined and determined both on the air and the refrigerant side. The average heat transfer coefficients of the two refrigerants are compared and outlined in the paper

Up the nose of the beholder? Aesthetic perception in olfaction as a decision-making process

Is the sense of smell a source of aesthetic perception? Traditional philosophical aesthetics has centered on vision and audition but eliminated smell for its subjective and inherently affective character. This article dismantles the myth that olfaction is an unsophisticated sense. It makes a case for olfactory aesthetics by integrating recent insights in neuroscience with traditional expertise about flavor and fragrance assessment in perfumery and wine tasting. My analysis concerns the importance of observational refinement in aesthetic experience. I argue that the active engagement with stimulus features in perceptual processing shapes the phenomenological content, so much so that the perceptual structure of trained smelling varies significantly from naive smelling. In a second step, I interpret the processes that determine such perceptual refinement in the context of neural decision-making processes, and I end with a positive outlook on how research in neuroscience can be used to benefit philosophical aesthetics

R134a And Its Low GWP Substitutes R1234yf And R1234ze(E) Flow Boiling Inside A 4mm Horizontal Smooth Tube

The substitution of HFC134a with low GWP refrigerants is one of the most important challenge for refrigeration and air conditioning. The possible substitutes include natural refrigerants, such as HC600 (Butane) and HC600a (Isobutane), and also synthetic refrigerants, such as HFO1234yf and HFO1234ze(E). The HC refrigerants exhibit very low GWP, 3 and 4 HC600a and HC600 respectively, good thermodynamic and transport properties, and pressure and volumetric performance very similar to HFC134a. The major drawback of HC refrigerants is their high flammability, being classified in class A3 according to ASHRAE classification. Also the HFO refrigerants present a mild flammability, being classified in class A2L. In fact, it is very difficult to found low GWP substitutes for traditional HFC refrigerants with no flammability, as a weak chemical stability and / or a big chemical reactivity are presuppositions for low GWP. Both HFO1234yf and HFO1234ze(E) seem to be very promising as substitute for HFC134a, showing a GWP lower than 1 together with pressure and volumetric properties closely near to those of HFC134a. This paper presents the comparative analysis of HFC134a HFO1234yf and HFO1234ze(E) during saturated flow boiling inside a 4 mm horizontal smooth tube: the effects of heat flux, refrigerant mass flux, mean vapour quality and saturation temperature (pressure) are investigated separately to rank the superposed effects of different heat transfer regimes (nucleate boiling or/and forced convection boiling). The experimental tests were carried out at three different saturation temperatures (10, 15, and 20 °C) at increasing vapour quality up to incipient dryout to evaluate the specific contribution of heat flux, refrigerant mass flux, mean vapour quality, and saturation temperature (pressure). The refrigerant mass flux ranges from 200 to 600 kg m-2s-1 and the heat flux from 15 to 30 kW m-2. The experimental measurements were reported in term of boiling heat transfer coefficients and frictional pressure drops. Heat transfer coefficients have a positive slope versus vapour quality and the slope increases with refrigerant mass flux and decreases with heat flux. Saturation temperature (pressure), refrigerant mass flux and mean vapour quality have a remarkable impact on the frictional pressure drop, whereas the effect of heat flux appears marginal or negligible. Convective boiling seems to be the prevailing heat transfer regime in present experimental tests. HFO1234ze(E) and HFO1234yf exhibit heat transfer coefficients and pressure drops similar to HFC134a. Present heat transfer coefficients and pressure drops were also compared against different correlations for refrigerant boiling inside tube. The universal correlation proposed by Kim and Mudawar (2014) and the Friedel (1979) correlation show the best performance in predicting heat transfer coefficients and pressure drops, respectively

HFO1234ze(E) And HFC134a Flow Boiling Inside a 4mm Horizontal Smooth Tube

Nowadays, the substitution of HFC134a with low GWP refrigerants is one of the most important challenge for refrigeration and air conditioning. The possible substitutes include natural refrigerants, such as HC600 (Butane) and HC600a (Isobutane), and also synthetic refrigerants, such as HFO1234yf and HFO1234ze(E). The HC refrigerants exhibit very low GWP, 3 and 4 HC600a and HC600 respectively, good thermodynamic and transport properties, and pressure and volumetric performance very similar to HFC134a. The major drawback of HC refrigerants is their high flammability, being classified in class A3 according to ASHRAE classification. Also the HFO refrigerants present a mild flammability, being classified in class A2L. In fact it is very difficult to found low GWP substitutes for traditional HFC refrigerants with no flammability, as a weak chemical stability and / or a big chemical reactivity are presuppositions for low GWP. In particular HFO1234ze(E) seems to be very promising as substitute for HFC134a, showing a GWP lower than 1 together with pressure and volumetric properties closely near to those of HFC134a. This paper presents the comparative analysis of HFC134a and HFO1234ze(E) during saturated flow boiling inside a 4 mm horizontal smooth tube: the effects of heat flux, refrigerant mass flux, mean vapour quality and saturation temperature (pressure) are investigated separately to rank the superposed effects of different heat transfer regimes (nucleate boiling or/and forced convection boiling). The experimental tests were carried out at three different saturation temperatures (10, 15, and 20 °C) at increasing vapour quality up to incipient dryout to evaluate the specific contribution of heat flux, refrigerant mass flux, mean vapour quality, and saturation temperature (pressure). The refrigerant mass flux ranges from 200 to 600 kg m-2s-1 and the heat flux from 15 to 30 kW m-2. The experimental measurements were reported in term of boiling heat transfer coefficients and frictional pressure drops. The heat transfer coefficients have a positive slope versus vapour quality and the slope increases with refrigerant mass flux and decreases with heat flux. Saturation temperature (pressure), refrigerant mass flux and mean vapour quality have a remarkable impact on the frictional pressure drop of both HFO1234ze(E) and HFC134a whereas the effect of heat flux appear marginal or negligible. Convective boiling seems to be the prevailing heat transfer regime in present experimental tests. HFO1234ze(E) exhibits heat transfer coefficients similar to HFC134a and slightly higher frictional pressure drops. Present heat transfer coefficients were compared against different heat transfer correlations for refrigerant boiling inside tube. The universal correlation proposed by Kim and Mudawar (2014) shows the best performance with a mean absolute percentage deviation of 6.1% both for HFO1234ze(E) and HFC134a data, respectively. Present frictional pressure drops were compared against different correlation for two-phase pressure drop inside tube: Friedel (1979) correlation shows the best performance with a mean absolute percentage deviation of 11.7% and 12.6% for HFO1234ze(E) and HFC134a respectively

HFO1234ze(E) Boiling Inside a Brazed Plate Heat Exchanger

HFC134a has been probably the most important refrigerant of the two past decades as it dominated the application in domestic refrigeration, mobile air conditioning and large chillers and it took part as component in several refrigerant mixtures such as HFC404A, and HFC407C. Unfortunately HFC134a exhibits a relatively large Global Warming Potential (GWP), and it will be subjected to a gradual reduce in the use up to a complete phase out in the next future according to the different national and international regulations. The HydroFluoroOlefins (HFO) refrigerants HFO1234yf and HFO1234ze(E) seem to be the most promising substitutes for HFC134a as they exhibit very low GWP values (1 or less) together with pressure and volumetric properties closely near to those of HFC134a. The unique drawback of HFO refrigerants seems to be their mild flammability. The Brazed Plate Heat Exchangers (BPHE), which involve a reduction of the refrigerant charge of one order of magnitude as compared to the traditional tubular heat exchangers, are particularly interesting for limiting the risk of flammable or mildly flammable refrigerants such as HFO1234ze(E). In fact the first attempt to reduce the risk of flammable refrigerants is to decrease the refrigerant charge. This paper presents the experimental heat transfer coefficients and pressure drop measured during HFO1234ze(E) boiling inside a small BPHE: the effects of heat flux, refrigerant mass flux, saturation temperature (pressure) and outlet conditions are investigated. The evaporator tested is a BPHE consisting of 10 plates, 72 mm in width and 310 mm in length, which present a macro-scale herringbone corrugation with an inclination angle of 65° and a corrugation amplitude of 2 mm. The experimental tests have been carried out at three different saturation temperatures (10, 15 and 20°C) and four different evaporator outlet conditions (vapour quality around 0.80 and 1.00, vapour super-heating around 5 and 10°C), whereas the inlet vapour quality ranges between 0.2 and 0.3. The refrigerant mass flux ranges from 11 to 31 kg/m2s and the heat flux from 4 to 17 kW/m2. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show great sensitivity to heat flux, outlet conditions and fluid properties and weak sensitivity to saturation temperature (pressure). The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on refrigerant mass flux. The heat transfer and pressure drop measurements are complemented with an IR thermography analysis carried out during the vaporisation tests. The saturated boiling heat transfer coefficients were compared with a new model for refrigerant boiling inside BPHE (Longo et al., 2015): the mean absolute percentage deviation between calculated and experimental data is 7.2%. The present data points were also compared with those of HFC134a and HFO1234yf previously measured inside the same BPHE under the same operating conditions: HFO1234ze(E) exhibits heat transfer coefficients very similar to HFC134a and HFO1234yf and frictional pressure drops slightly higher than HFC134a and HFO1234yf

R1233zd(E) and R245fa Flow Boiling Heat Transfer and Pressure Drop inside a 4.2 mm ID Microfin Tube

This paper presents R1233d(E) and R245fa flow boiling heat transfer and pressure drop measurements inside a mini microfin tube having internal diameter at the fin tip equal to 4.2 mm, 40 fins 0.15 mm high, and a helix angle of 18°. The tube was brazed inside a copper plate and electrically heated from the bottom. Sixteen T-type thermocouples were located in the copper plate to monitor the wall temperature. The experimental measurements were carried out at a constant mean saturation temperature of 30 °C, by varying the refrigerant mass velocity between 100 kg m-2 s-1 and 300 kg m-2 s-1, the vapour quality, and the heat flux from 15 to 90 kW m-2. The experimental results are here presented in terms of two-phase heat transfer coefficient, onset dryout vapour quality, and frictional pressure drop. Moreover, R1233zd(E) has been proposed as low GWP alternative to R245fa. In this paper, the two fluids performance is compare under the same working conditions and commented. Finally, the experimental measurements were used to assess a few selected models for boiling heat transfer coefficient and frictional pressure drop estimations available in the open literature for microfin tubes

R134a and its low GWP substitutes R1234yf and R1234ze(E) condensation inside a 4mm horizontal smooth tube

The substitution of HFC134a with low GWP refrigerants is one of the most important challenge for refrigeration and air conditioning. The possible substitutes include natural refrigerants, such as HC600 (Butane) and HC600a (Isobutane), and also synthetic refrigerants, such as HFO1234yf and HFO1234ze(E). The HC refrigerants exhibit very low GWP, 3 and 4 HC600a and HC600 respectively, good thermodynamic and transport properties, and pressure and volumetric performance very similar to HFC134a. The major drawback of HC refrigerants is their high flammability, being classified in class A3 according to ASHRAE classification. Also the HFO refrigerants present a mild flammability, being classified in class A2L. In fact it is very difficult to found low GWP substitutes for traditional HFC refrigerants with no flammability, as a weak chemical stability and / or a big chemical reactivity are presuppositions for low GWP. Both HFO1234yf and HFO1234ze(E) seem to be very promising as substitute for HFC134a, showing a GWP lower than 1 together with pressure and volumetric properties closely near to those of HFC134a. This paper presents the comparative analysis of HFC134a HFO1234yf and HFO1234ze(E)during saturated condensation inside a 4 mm horizontal smooth tube. The experimental tests were carried out at three different saturation temperatures (30, 35, and 40 °C) at decreasing vapour quality up to sub-cooled liquid condition, to evaluate the specific contribution of refrigerant mass flux, mean vapour quality, and saturation temperature. The refrigerant mass flux ranges from 100 to 600 kg m-2 s-1. The experimental measurements were reported in term of condensation heat transfer coefficients and frictional pressure drops and plotted in non-dimensional co-ordinates showing the heat transfer factor and the friction factor against the equivalent Reynolds number. A transition point from gravity dominated and forced convection condensation was found for an equivalent Reynolds number around 10000-20000. HFO1234yf and HFO1234ze(E) exhibit heat transfer coefficients and pressure drops similar to HFC134a and they seem to be valuable long term low GWP substitutes for HFC134a. The experimental heat transfer coefficients in the forced convection condensation regime were very well predicted by the Akers et al. (1959) model, whereas the Friedel (1979) correlation was able to reproduce the frictional pressure drop data both in gravity dominated and forced convection condensation regimes