• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.2
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• pp.70-78
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• 2004

An experimental study on the pressure drop during flow boiling for pure refrigerants Rl34a and R123, and their mixture was carried out in a uniformly heated horizontal tube. Tests were run at a pressure of 0.6㎫ and in the ranges of heat flux 5-50㎾/$m^2$, vapor quality 0-100 percent and mass velocity of 150-600 kg/$m^2$s. Generally, the two-phase frictional multiplier is used to predict the frictional pressure drop during the two-phase flow boiling. The obtained results have been compared to the existing various correlations for the two-phase multiplier. Also, the frictional pressure drop was compared to a few available correlations; The Lockhart-Martinelli correlation considerally overpredicted the frictional pressure drop data for mixture as well as pure components in the entire mass velocity ranges employed in the present study, while the Chisholm correlation underpredicted the present data. The Friedel correlation was found to satisfactorily correlate the frictional pressure drop data except for a low quality region.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.5
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• pp.1273-1279
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• 2016

Flow boiling pressure drop in multi channels was experimently investigated. The multi channel has a width and depth of 0.45 and 0.2mm respectively, and comprises 15 parallel channels. The measured total pressure drop is expressed by the sum of the frictional pressure drop and acceleration pressure drop. In order to predict the total pressure drop, it is required to obtain the correct frictional pressure drop. The existing correlations to predict the frictional pressure were compared with measured frictional pressure drop. The new correlation was developed in the form of the Chisholm correlation. It was related to Chisholm Constant B as a function of Martinelli parameter. The new correlation predicted the experimental data within a mean absolute error of 5.5%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.6
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• pp.510-517
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• 2003

An experimental study on the pressure drop during flow boiling for pure refrigerants R134a and Rl23, and their mixture was carried out in a uniformly heated horizontal tube. Tests were run at a pressure of 0.6 MPa and in the ranges of heat flux 5~50 kW/m$^2$, vapor quality 0~100 percent and mass velocity of 150~600 kg/m$^2$s. Generally, the two-phase frictional multiplier is used to predict the frictional pressure drop during the two-phase flow boiling. The obtained results have been compared to the existing various correlations for the two-phase multiplier. Also, the frictional pressure drop was compared to a few available correlations; The Lockhart-Martinelli correlation considerally overpredicted the frictional pressure drop data for mixture as well as pure components in the entire mass velocity ranges employed in the present study, while the Chisholm correlation underpredicted the present data. The Friedel correlation was found to satisfactorily correlate the frictional pressure drop data except for a low quality region.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.119-125
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• 2003

An experiment study on pressure drop was carried out for both an adiabatic and a diabatic two-phase flow with pure refrigerants R134a and Rl23 and their mixtures as test fluids in a uniformly heated horizontal tube. The frictional pressure drop during flow boiling is predicted by using two models; the homogeneous model that assumes equal phase velocity and the separate flow model that allows a slip velocity between two phases. The measured frictional pressure drop was compared to a few available correlations. Homogeneous model considerally underpredicted the present data for mixture as well as pure component in the entire mass velocity ranges employed in the present study, while Friedel correlation was found to satisfactorily correlate the frictional pressure drop data as compared to other correlation.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.2
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• pp.338-346
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• 2004

Experimental data on the effect of the variable gravity magnitude, namely microgravity, normal gravity and hyper-gravity, on flow pattern and frictional pressure drop were obtained during co-current air-water flow in a horizontal tube, The flow patterns were found to depend strongly on the gravity magnitude and certain flow pattern were found to depend on the gas superficial velocity. The effect of the gravity magnitude had an effect on the frictional pressure drop only at low flow rates. The present data are used to evaluate some of existing flow pattern transition and pressure drop models and correlations.

• Journal of Mechanical Science and Technology
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• v.17 no.5
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• pp.758-765
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• 2003

An experimental investigation on the flow pattern and pressure drop was carried out for both an adiabatic and a diabatic two-phase flow in a horizontal tube with pure refrigerants R134a and R123 and their mixtures as test fluids. The observed flow patterns were compared to the flow pattern map of Kattan et al., which predicted well the present data over the entire regions of mass velocity in this study. The measured frictional pressure drop in the adiabatic experiments increased with an increase in vapor quality and mass velocity These data were compared to various correlations proposed in the past for the frictional pressure drop. The Chisholm correlation underpredicted the present data both for pure fluids and their mixtures in the entire mass velocity range of 150 to 600 kg/m$^2$s covered in the measurements, white the Friedel correlation was found to overpredict the present data in the stratified and stratified-wavy flow region, and to underpredict in the annular flow region.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.4
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• pp.169-174
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• 2007

The characteristics of nine existing condensation frictional pressure drop correlations for microfin tubes were evaluated with geometries, vapor quality, mass flux, and refrigerants. The $M\ddot{u}ller-Steinhagen$ and Heck [17] smooth tube frictional pressure drop correlation was utilized to evaluate the pressure drop penalty factor (PF). Except the Nozu et al. [2], the Kedzierski and Goncalves [3], the Choi et al. [10], and the Cavallini et al. [7], other pressure drop correlations did not consider the effect of tube geometry. The prediction values for R407C by pressure drop correlations show discrepancy with previous researcher's experimental trend. Additional efforts on the development of reliable condensation pressure drop correlation for microfin tubes are still required with the systematic investigation of various effects like geometries and working conditions.

• Journal of Mechanical Science and Technology
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• v.19 no.12
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• pp.2289-2295
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• 2005

Two-Phase flow pattern and pressure drop data were obtained for pure refrigerants R134a and R123 and their mixtures as test fluids in a horizontal tube. The flow pattern is observed through tubular sight glasses located at inlet and outlet of the test section. The flow map of Baker developed for air-water two-phase flow at atmospheric pressure failed to predict the observed flow patterns at the higher value of the mass velocity used in the present study. The map of Kattan et al. predicted the data well over the entire region of mass velocity selected in the present study. The measured pressure drop increased with an increase in vapor quality and mass velocity. A new two-phase multiplier was developed from a dimensional analysis of the frictional pressure drop data measured in the present experiment. This new multiplier was found successfully to correlate the frictional pressure drop.

• Journal of Fisheries and Marine Sciences Education
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• v.14 no.2
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• pp.177-190
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• 2002

An experimental study was carried out to make clear heat transfer characteristics in flow boiling of binary mixtures of refrigerants R134a and R123 in a uniformly heated horizontal tube. Experiments were run at a pressure of 0.6 MPa both for pure fluids and mixtures in the ranges of heat flux $10{\sim}50{kW/m}^2$, vapor quality 0~100% and mass flux 150-600 $kg/m^2s$. Heat transfer coefficients of mixtures were reduced compared to the interpolated values between pure fluids both in the low quality region where the nucleate boiling is dominant and in the high quality region where the convective evaporation is dominant. Total pressure drop during two-phase flow boiling in a horizontal tube consists of the sum of two components, that is, the frictional pressure drop and pressure drop due to acceleration. The frictional pressure drop is the most difficult component to predict, and makes the most important contribution to the total pressure drop. On the other hand, the acceleration pressure drop resulting from the variation of the momentum flux caused by phase change is generally small as compared to the frictional pressure drop. There is no significant difference in measured pressure drop between mixtures and pure fluids. The correlation of Martinelli and Nelson predicted most of the present data both for pure and mixed refrigerants within 30%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1035-1042
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• 2006

An experimental investigation was performed to study two-phase pressure drop of deionized water in a microchannel. Measurement and evaluation of two-phase frictional pressure gradient were carried out using a single horizontal rectangular microchanne1 having a hydraulic diameter of $100{\mu}m$. Tests were performed for mass fluxes of 90, 169, and 267 $kg/m^2$s and heat fluxes of 200-700 $kW/m^2$. Test results showed that the measured two-phase frictional pressure gradient increased with the mass flux and vapor quality. Most macro-channel correlations of two-phase frictional pressure gradient did not provide reliable predictions except under certain limited conditions.