The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Giovanni A Longo - One of the best experts on this subject based on the ideXlab platform.
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Saturated flow boiling of HFC134a and its low GWP substitute HFO1234ze(E) inside a 4 mm horizontal smooth tube
International Journal of Refrigeration, 2016Co-Authors: Giovanni A Longo, Giulia Righetti, Simone Mancin, Claudio ZilioAbstract:This paper presents the comparative analysis of HFO1234ze(E) and HFC134a during vaporisation inside a 4 mm smooth tube. 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 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 appears marginal or negligible. Convective boiling seems to be the prevailing heat transfer regime in the present experimental tests. HFO1234ze(E) exhibits heat transfer coefficients similar to HFC134a and slightly higher frictional pressure drops.
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HFC32 and HFC410A flow boiling inside a 4 mm horizontal smooth tube
International Journal of Refrigeration-revue Internationale Du Froid, 2015Co-Authors: Giovanni A Longo, Giulia Righetti, Simone Mancin, Claudio ZilioAbstract:Abstract This paper presents the comparative analysis of HFC32 and HFC410A during vaporisation inside a 4 mm smooth tube. The experimental tests were carried out at three different Saturation Temperatures (5, 10, 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). HFC32 and HFC410A heat transfer coefficients exhibit great sensitivity to heat flux and weak sensitivity to refrigerant mass flux and mean vapour quality and this tendency is particularly evident for increasing Saturation Temperature (pressure) and is more relevant for HFC410A refrigerant. HFC32 and HFC410A frictional pressure drops show great sensitivity to Saturation Temperature (pressure), refrigerant mass flux and mean vapour quality and weak or null sensitivity to heat flux. HFC32 exhibits heat transfer coefficients and frictional pressure drops higher than those of HFC410A under the same operating conditions.
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hfo1234ze z saturated vapour condensation inside a brazed plate heat exchanger
2014 Purdue Conferences. 15th International Refrigeration and Air-Conditioning Conference at Purdue., 2014Co-Authors: Giovanni A Longo, Claudio Zilio, Giulia Righetti, Steven J BrownAbstract:This paper presents the experimental heat transfer coefficients and pressure drop measured during HFO1234ze(Z) saturated vapour condensation inside a small commercial BPHE: the effects of refrigerant mass flux and Saturation Temperature were investigated. The heat transfer coefficients show weak sensitivity to Saturation Temperature and great sensitivity to refrigerant mass flux. At low refrigerant mass flux ( 15 kg m-2s-1) the heat transfer coefficients depend on mass flux and forced convection condensation occurs. 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 the refrigerant mass flux. HFO1234ze(Z) shows heat transfer coefficients and frictional pressure drop higher than HFC236fa. The experimental results were compared against theoretical models for condensation heat transfer coefficients (Nusselt, 1916 and Akers et al., 1959) and a new linear correlation for two-phase frictional pressure drop was presented.
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Vaporisation of the low GWP refrigerant HFO1234yf inside a brazed plate heat exchanger
International Journal of Refrigeration, 2012Co-Authors: Giovanni A LongoAbstract:This paper presents the experimental heat transfer coefficients and pressure drop measured during vaporisation of the new low Global Warming Potential (GWP) refrigerant HFO1234yf inside a Brazed Plate Heat Exchanger (BPHE): the effects of heat flux, mass flux, Saturation Temperature (pressure) and outlet conditions are investigated. The heat transfer coefficients show great sensitivity to heat flux and outlet conditions 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 saturated boiling experimental heat transfer coefficients are reproduced by two well-known equations for nucleate boiling, Cooper (1984) and Gorenflo (1993), with reasonable agreement. The heat transfer and pressure drop measurements are complemented with IR thermography analysis in order to quantify the portion of the heat transfer surface affected by vapour super-heating. ?? 2012 Elsevier Ltd and IIR. All rights reserved.
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Refrigerant R410A vaporisation inside a small brazed plate heat exchanger
2011Co-Authors: Giovanni A Longo, Andrea GasparellaAbstract:This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant R410A vaporisation inside a small brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, Saturation Temperature and outlet conditions are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show high sensitivity both to heat flux and outlet conditions and weak sensitivity to Saturation Temperature. The frictional pressure drop shows high sensitivity to refrigerant mass flux and weak sensitivity both to Saturation Temperature and outlet conditions. The experimental heat transfer coefficients are also compared with two well-known correlations for nucleate pool boiling: a fair agreement is found.
Andrea Gasparella - One of the best experts on this subject based on the ideXlab platform.
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Refrigerant R410A vaporisation inside a small brazed plate heat exchanger
2011Co-Authors: Giovanni A Longo, Andrea GasparellaAbstract:This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant R410A vaporisation inside a small brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, Saturation Temperature and outlet conditions are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show high sensitivity both to heat flux and outlet conditions and weak sensitivity to Saturation Temperature. The frictional pressure drop shows high sensitivity to refrigerant mass flux and weak sensitivity both to Saturation Temperature and outlet conditions. The experimental heat transfer coefficients are also compared with two well-known correlations for nucleate pool boiling: a fair agreement is found.
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Refrigerant R134a vaporisation heat transfer and pressure drop inside a small brazed plate heat exchanger
International Journal of Refrigeration, 2007Co-Authors: Giovanni A Longo, Andrea GasparellaAbstract:This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant R134a vaporisation inside a small brazed plate heat exchanger (BPHE): the effects of heat flux, refrigerant mass flux, Saturation Temperature and outlet conditions are investigated. The BPHE tested consists 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 corrugation amplitude of 2 mm. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show great sensitivity both to heat flux and outlet conditions and weak sensitivity to Saturation Temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. The experimental heat transfer coefficients are also compared with two well-known correlations for nucleate pool boiling and a correlation for frictional pressure drop is proposed. ?? 2006 Elsevier Ltd and IIR.
Vipin Kumar - One of the best experts on this subject based on the ideXlab platform.
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effect of glass transition Temperature and Saturation Temperature on the solid state microcellular foaming of cyclic olefin copolymer
Journal of Applied Polymer Science, 2015Co-Authors: Vipin KumarAbstract:Effect of glass transition Temperature and Saturation Temperature on the solid-state microcellular foaming of cyclic olefin copolymer (COC)—including CO2 solubility, diffusivity, cell nucleation, and foam morphology—were investigated in this article. COCs of low Tg (78°C) and high Tg (158°C) were studied. Solubilities are 20–50% higher in high Tg COC than in the low Tg COC across the Saturation Temperature range. Diffusivities are about 15% higher on average in high Tg COC for Temperatures up to 50°C. A much faster increase of diffusivity beyond 50°C is observed in low Tg COC due to it being in the rubbery state. Under similar gas concentration, high Tg COC starts foaming at a higher Temperature. And the foam density decreases faster in low Tg COC with foaming Temperature. Also, high Tg COC foams show about two orders of magnitude higher cell nucleation density than the low Tg COC foams. The effect of Saturation Temperature on microcellular foaming can be viewed as the effect of CO2 concentration. Nucleation density increases and cell size decreases exponentially with increasing CO2 concentration. Uniform ultramicrocellular structure with an average cell size of 380 nm was created in high-Tg COC. A novel hierarchical structure composed of microcells (2.5 μm) and nanocells (cell size 80 nm) on the cell wall was discovered in the very low-density high-Tg COC foams. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42226.
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Effect of glass transition Temperature and Saturation Temperature on the solid‐state microcellular foaming of cyclic olefin copolymer
Journal of Applied Polymer Science, 2015Co-Authors: Vipin KumarAbstract:Effect of glass transition Temperature and Saturation Temperature on the solid-state microcellular foaming of cyclic olefin copolymer (COC)—including CO2 solubility, diffusivity, cell nucleation, and foam morphology—were investigated in this article. COCs of low Tg (78°C) and high Tg (158°C) were studied. Solubilities are 20–50% higher in high Tg COC than in the low Tg COC across the Saturation Temperature range. Diffusivities are about 15% higher on average in high Tg COC for Temperatures up to 50°C. A much faster increase of diffusivity beyond 50°C is observed in low Tg COC due to it being in the rubbery state. Under similar gas concentration, high Tg COC starts foaming at a higher Temperature. And the foam density decreases faster in low Tg COC with foaming Temperature. Also, high Tg COC foams show about two orders of magnitude higher cell nucleation density than the low Tg COC foams. The effect of Saturation Temperature on microcellular foaming can be viewed as the effect of CO2 concentration. Nucleation density increases and cell size decreases exponentially with increasing CO2 concentration. Uniform ultramicrocellular structure with an average cell size of 380 nm was created in high-Tg COC. A novel hierarchical structure composed of microcells (2.5 μm) and nanocells (cell size 80 nm) on the cell wall was discovered in the very low-density high-Tg COC foams. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42226.
N V Vasilev - One of the best experts on this subject based on the ideXlab platform.
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boiling of liquid subcooled to Saturation Temperature in channels as a method for removal of ultimate heat fluxes
Thermal Engineering, 2019Co-Authors: N V Vasilev, Yu A Zeigarnik, K A Khodakov, I V MaslakovaAbstract:The results of a comprehensive experimental study of the boiling of water subcooled to the Saturation Temperature in a channel are presented. This technology is used to remove extreme heat fluxes in modern equipment. An emphasis is placed on the study of the characteristics of vapor bubbles, their changes under the effect of various regime factors, and characteristics of the heating surface. For the realization of the goals, a high-speed video of the process was used. Experiments were carried out with distilled deaerated water at atmospheric pressure, heat flux densities of up to q = 8 MW/m2, subcooling of the liquid to the Saturation Temperature of Δts = 30–80°C, and the flow velocity of the liquid of up to w = 0.7 m/s. Smooth and structured surfaces with coatings, most of which were produced by microarc oxidation, were used in the experiments. Significant subcooling of the liquid to the Saturation Temperature is shown to cause a deep deactivation of the active nucleation cites after the collapse of the vapor bubble and spatial and temporal randomness of the distribution of the nucleation cites over the heating surface. The bubble size distribution, the density of nucleation cites that is approximately proportional to the heat flux density, the bubble lifetime, and the duration of individual stages of its life cycle are determined. A picture of the bubble collapse is clarified. The subcooling of the coolant to the Saturation Temperature is shown to be the strongest among the parameters that determine the boiling of the subcooled liquid. The phenomenological Snyder–Bergles model of the boiling process was established to agree best with the measurement results. Such engineering aspects of the problem as the choice of limiting design parameters of the cooling system and the use of coatings for boiling enhancement of a subcooled coolant are considered.
Bilal Zemher - One of the best experts on this subject based on the ideXlab platform.
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Effect of Saturation‐Temperature on the performance of a vapour‐compression refrigeration‐cycle working on different refrigerants using exergy method
International Journal of Energy Research, 2020Co-Authors: Mehmet Kopac, Bilal ZemherAbstract:In this study, the behaviour of a vapour-compression refrigeration cycle, for different refrigerants such as NH3, R-12, R-22 and HFC-134a was investigated using the exergy method. The cooling load of the plant and the Saturation-Temperature of the cold chamber were held constant, whereas the Saturation-Temperatures of the evaporator and the condenser were varied from 303 to 313 K and 258 to 248 K, respectively. The irreversibility rates (or exergy destruction rates) of sub-regions for the whole cycle, using energy and exergy analysis, were determined for each refrigerant. The effects of changes in the Saturation-Temperature in the condenser and evaporator on the irreversibility rate of the cycle were obtained for each refrigerant. The relations between the total irreversibility rate of the plant and the irreversibility rate of the condenser and the evaporator were determined for different values of Saturation Temperatures of the condenser and the evaporator. The COP of the cycle and the rational efficiency were determined for each of the refrigerants and compared with each other. Among the refrigerants used, R-12 was found to be the most economical refrigerant as compared with the others. Copyright © 2005 John Wiley & Sons, Ltd.
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effect of Saturation Temperature on the performance of a vapour compression refrigeration cycle working on different refrigerants using exergy method
International Journal of Energy Research, 2006Co-Authors: Mehmet Kopac, Bilal ZemherAbstract:In this study, the behaviour of a vapour-compression refrigeration cycle, for different refrigerants such as NH3, R-12, R-22 and HFC-134a was investigated using the exergy method. The cooling load of the plant and the Saturation-Temperature of the cold chamber were held constant, whereas the Saturation-Temperatures of the evaporator and the condenser were varied from 303 to 313 K and 258 to 248 K, respectively. The irreversibility rates (or exergy destruction rates) of sub-regions for the whole cycle, using energy and exergy analysis, were determined for each refrigerant. The effects of changes in the Saturation-Temperature in the condenser and evaporator on the irreversibility rate of the cycle were obtained for each refrigerant. The relations between the total irreversibility rate of the plant and the irreversibility rate of the condenser and the evaporator were determined for different values of Saturation Temperatures of the condenser and the evaporator. The COP of the cycle and the rational efficiency were determined for each of the refrigerants and compared with each other. Among the refrigerants used, R-12 was found to be the most economical refrigerant as compared with the others. Copyright © 2005 John Wiley & Sons, Ltd.
