Comparative investigations of the condensation of R134a and R404A refrigerants in pipe minichannels
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New methods and experimental techniques were developed in this research to quantify the incident heat flux, absorbed (net) heat flux into a sample, and heat transfer coefficient for samples exposed to mixed mode (radiation and convection) heat transfer typical in fires. Net heat flux into the material was measured at elevated temperatures using a recently developed Hybrid heat flux gage, which is both a thermopile type gage as well as a slug calorimeter with an operating temperature >1000°C without cooling. The heat transfer coefficient was determined as a function of time using the Hybrid gage output only through a reference state approach. The net heat flux and heat transfer coefficient were then used to calculate a cold surface heat flux and the adiabatic surface temperature. Experiments were performed in the cone calorimeter at different heat fluxes to quantify the incident heat flux, net heat flux, heat transfer coefficient, cold surface heat flux, and adiabatic surface temperature as a function of time. Measured heat transfer coefficients were 9-18% different than values calculated using idealized natural convection correlations. The cold surface heat fluxes determined with the Hybrid gage were within 5% of cold surface heat fluxes measured using a water-cooled Schmidt-Boelter heat flux gage.
Calorimeter (particle physics)
Film temperature
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The characteristics of two-phase flow boiling of R-290 are required for replacing R-22 that has been phased-out. The present study focuses on experimental pressure drop for R-22 and R-290. The experiment was run with heat flux of 5.09 kW/m 2 to 19.03 kW/m 2 , mass flux of 114.91 kg/m 2 s to 751.74 kg/m 2 s and saturation temperature of 4.77°C to 18.12°C. The present result showed that pressure drop was affected by heat flux, mass flux and saturation temperature. Lower mass flux, heat flux and saturation temperature results in lower pressure drop. The pressure drop of R-290 is lower than that of R-22. Among the existing pressure drop prediction methods, Lokhart-Martinelli (1949) gives the best prediction for the present pressure drop data.
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Boiling point
Saturation (graph theory)
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Vapor quality
Saturation (graph theory)
Hydraulic diameter
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This study experimentally investigated two-phase flow pressure drop of propane as refrigerant in horizontal small tube. Inner diameter and length of the tube were 7.6 mm and 1.07 m, respectively. In order to get pressure drop data, the experiment was conducted in various conditions of 10 to 25 kW m -2 heat flux, 200 to 628 kg m -2 s -1 mass flux, and 4.0 to 11.7°C saturation temperature. This study clearly showed the effect of heat flux, mass flux, and saturation temperature on the pressure drop of propane. This study also investigated which fluid properties gave higher effect on the frictional pressure drop due to its change over the process based on the recent experiment data. The existing pressure drop correlations were evaluated against the experimental result.
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Propane
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Pressure gradient
Boiling point
Saturation (graph theory)
Hydraulic diameter
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Hydraulic diameter
Pressure gradient
Vapor quality
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Differential pressure
Vapor quality
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Hydraulic diameter
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Microchannel
Vapor quality
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This paper deals with an experimental investigation of two-phase frictional pressure drop behavior of 1,1-difluoroethane in an 8 mm inside-diameter smooth horizontal tube. Pressure drop characteristics are measured in a pressure range of 0.19—0.41 MPa, heat flux range of 14—62 kW/m2, and mass flux range of 128—200 kg/m2s. The effects of experimental parameters on pressure drop are analyzed. It is found that with the increases of mass flow and vapor quality, the frictional pressure drop increases. The proportion of momentum pressure drop in the total pressure drop increases slightly as heat flux increases, and accordingly the proportion of the frictional pressure drop decreases. The frictional pressure drop increases with saturation pressure decreasing. Experimental results are compared with the calculations from the two extensively used correlation formulae. Our investigations show that the Friedel model has a relatively large deviation, and the Müller-Steinhagen-Heck model accords well with the experimental results.
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This paper presents the experimental result of R134a and R410A (without lubricating oil) pressure drop condensing along three parallel, rectangular microchannels with the aspect ratio varying from 0.5 to 1 and Dh from 0.66 to 1 mm, while maintaining the constant channel depth (1 mm), base area (63 cm2), and channel length (30 cm). All the factors accountable for change in pressure through microchannels were determined for all the configurations separately, i.e. contraction, expansion, frictional, and deceleration. Two distinct saturation temperatures were used in the present experimental study, with vapor quality 0.05 < x < 0.83 and mass flux 200 < G < 600 kg/m2s. Frictional pressure drop estimations were found to be greater than 90% of overall pressure drop. Condensation pressure drop for both the refrigerants increases directly with increasing mass flux and vapor quality, whereas it decreases with the channel aspect ratio and saturation temperature increase. At constant mass flux, R134a has a higher condensation pressure drop than R410A, and the highest value of condensation pressure drop was obtained in MC-1 having an aspect ratio of 0.5, followed by MC-2 and MC-3 having aspect ratios of 0.7 and 1, respectively.
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Vapor quality
Aspect ratio (aeronautics)
Overall pressure ratio
Hydraulic diameter
Boiling point
Saturation (graph theory)
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