Condensation Pressure Drop Research Articles

Experimental investigation on flow condensation pressure drop of R134a in microfin tube at high mass flux

Abstract To clarify the influencing mechanisms of the experimental condition and the tube structure on the pressure drop of heat transfer fluid, the two-phase flow condensation pressure drop of R134a inside the microfin tube was experimentally studied at high mass flux, which is different from other conventional researches. The experimental result shows the pressure drop is proportional to mass flux and fin helical angle, and is inversely proportional to condensation temperature and coolant Reynolds number. Moreover, the experimental data of pressure drop was compared with the predicted value of some existing correlations for the microfin tube. It can be found that the correlations of Cavallini et al., Han et al. and Haraguchi et al. show a good prediction effect with mean relative deviation (MRD) of 13.89, 16.08 and −2.19%, respectively. The correlations of Pierre/0.053, Kedzierski et al. and Choi et al. all underestimate most of the experimental data of the pressure drop inside the tube, and their prediction deviations are >10%. That is, the application effect of the separated flow model is better than that of the homogeneous flow model. Finally, the Kedzierski et al. correlation was improved to realize a high-precision prediction of the fluid flow mechanism inside the tube. Because the prediction deviation of the improved correlation between the experimental value and the predicted value was greatly reduced, its prediction deviation is <10% for R134a and R410A; therefore, it can be said the improved correlation has a good predictive result for the pressure drop.

Performance Evaluation of Split Air Conditioner with Consideration of Pressure Drop in Evaporator and Condenser

In this research, a split air conditioner's performance has been evaluated using exergy analysis on three different low global warming potential (GWP) refrigerants, namely R32, R447A, and R447B, to find a replacement for the GWP-high refrigerant R410A. With regard for pressure loss in the evaporator and condenser, a computational model is built to recreate the operational conditions of a split air conditioner. GENETRON Properties 1.4 software is used to calculate performance metrics such as coefficient of performance (COP), exergy destruction ratio, exergetic efficiency, and efficiency defect. Result shows that pressure drop in evaporator alone has an adverse effect on COP and total exergy destruction and it is higher at higher pressure drop. Effect of pressure drop on exergetic efficiency and exergy destruction ratio is found to be less significant with condenser pressure drop compared to evaporator pressure drop. Exergy efficiency is found to be maximum with R447A followed by R447B, R32, and R410A.

Experimental investigation of condensation pressure drop of zeotropic refrigerant/oil mixtures in plate heat exchanger

The condensation pressure drop characteristics of zeotropic refrigerant/oil mixture and its accurate prediction are fundamental to the design of condensers in ORC systems. This paper presented an experimental study on the condensation frictional pressure drop (FPD) for R245fa/R141b (0.5/0.5 by mass)-lubricant mixtures in a plate heat exchanger (PHE). In addition, the results were compared with its pure compositions. The range of experimental conditions is: vapor quality 0–0.9, polyester oil (POE) concentration 0% to 4%, mass flux 20 to 60 kg·m-2·s-1. The results show that the FPD of R245fa/R141b with an oil concentration of 4% decreases by 25.7% compared to the oil-free refrigerant. In addition, R245fa/POE has the highest FPD, while the FPD of R245fa/R141b POE is between R245fa/POE and R141b/POE. The oil enhancement factor of different refrigerant/POE mixtures is less than 1.0, which can be well predicted by the literature correlation for R22/150-SUS with a maximum mean absolute deviation (MAD) of 17.2%. When the enhancement factor is used to correct the FPD, the FPD predicted by the literature correlation is in good agreement with the experimental data. Its maximum MAD for different refrigerant/POE mixtures is 25.35%, and 98.3% of the predicted results are within ±30% deviation. When the physical properties of refrigerant/POE mixtures are used to predict the FPD, a new correlation is proposed. It can more accurately predict the FPD of refrigerant/oil mixtures in the PHE with a maximum MAD of 5.8%.

Experimental study on condensation heat transfer and pressure drop characteristics of R32 flowing inside an alternating cross-section flattened tube

This work presents the experimental study of two-phase flow inside an alternating cross-section flattened (ACF) tube. The ACF tube was made from a copper circular tube with an inner diameter of 4.31 mm. We conducted the test under the following experimental conditions: a mass flux of 280, 430, and 580 kg/m2s; a saturation temperature of 40, 45, and 50 °C; a heat flux of 10, 15, and 20 kW/m2; and an average vapor quality of 0.1–0.8. Compared to the existing flow pattern maps, most fell into the annular and semi-annular flow regimes. However, the results were found in the transition and intermittent flow regions at low vapor quality. The results from the circular and ACF tubes were examined and discussed. We found that the ACF tube revealed a prominent condensation heat transfer coefficient and a reasonable pressure loss penalty. The heat transfer coefficient and frictional pressure drop of the ACF tube were higher than that of the circular tube by approximately 25.6–111.1% and 4.3–39.9%, respectively. New correlations for the Nusselt number and two-phase friction factor were proposed.

Heat transfer and pressure drop of CO2/R32 mixture in mini-channel

In this study, we investigated the condensation heat transfer characteristics of the CO2/R32 mixture in a mini-channel with a diameter of 2 mm. The experimental conditions were as follows: mass flow rate of 50–400 kg·m−2·s−1, vapor quality of 0–1, and a condensation temperature of 35–45 °C. The experimental data were then compared with the heat transfer correlations. The higher the CO2 content, the smaller the annular flow area. The convective heat transfer coefficient decreases rapidly and then increases slowly with an increase in CO2. The minimum value was obtained when the CO2 content was approximately 55%. In addition, the convective heat transfer coefficient decreased with an increase in the condensation temperature. Higher vapor quality and mass flow rate conditions correspond to higher convective heat transfer coefficients. The prediction correlations applicable to the in-tube condensation heat transfer have low prediction results for CO2/R32, and the model of Shah is recommended as the prediction model. The experimental results of the condensation pressure drop were analyzed, and the results showed that the pressure drop increased linearly with the mass flow rate but decreased with an increase in the condensation temperature. The lower the CO2 content, the more clear the effect of the condensation temperature. The correlation of Kim and Mudawar is recommended for the CO2/R32 two-phase condensation friction pressure drop. This study provides theoretical support for the analysis of the condensation heat transfer mechanism of a CO2/R32 mini-channel.

A New Two-Phase Multiplier for Flow Pressure Drop in Multiport Minichannel Condensers and Evaporators

Due to flow maldistribution, the condensation and evaporation flow patterns in multiport minichannels are considerably different from single minichannels or macrochannels. This article compiled the friction pressure drop data from experimental phase-change investigations in multiport minichannel condensers and evaporators over the past two decades. The data was reduced to friction pressure gradients, and a new two-phase multiplier was proposed for estimating the phase-change pressure drop in multiport condensers and evaporators. Thirteen hundred and forty-four condensation pressure drop and six hundred and twenty-three evaporation pressure drop data from twenty-nine studies were correlated to yield four predictive two-phase multiplier equations in the laminar and turbulent flow regimes. The predictive correlations fit 67% of the laminar condensation and 80% of the turbulent pressure drop data within ±50%. Further, 57% of the laminar evaporation and 100% of the turbulent evaporation pressure drop data were fit within ±50%. The correlations were compared with widely published correlations and were a significant improvement. Meta-analysis revealed that multiport minichannels are most effective for reducing turbulent flow condensation pressure drop and laminar flow evaporation pressure drop. The compiled data and presented correlations and analysis should be helpful to the process, electronics packaging, aviation, and aerospace industries designing compact, lightweight, and high-efficiency condensers, and evaporators.

A Comprehensive Review Regarding Condensation of Low-GWP Refrigerants for Some Major Alternatives of R-134a

In this review, the condensation HTCs (heat transfer coefficients) and pressure drop characteristics of some major low-global-warming-potential (GWP) refrigerants alternative to R-134a such as R-1234ze(E), R-1234ze(Z), R-1234yf, R-513A, and R-450A are reviewed. The thermofluids’ characteristics inside/outside a tube, minichannel, microfin tube, and plate heat exchanger are examined. In addition, several other refrigerants attributed to low GWP are also included in the present review. The experimental/numerical/simulation results’ analysis reveals that condensation HTCs and pressure drop characteristics depend on several parameters such as thermodynamics and transport properties of the working fluid, mass flux of the refrigerants, heat flux, saturation temperature, vapor quality, flow patterns, flow conditions, orientation of the condensing geometry, and condensation geometry (shape, size, and smooth/enhanced).

Experimental study on condensation heat transfer characteristics of steam in rectangular channels rotating about a parallel axis

• Nu in rotating channel increases with Re but decreases with steam temperature. • Pressure drop in rotating channel increases with Re and steam temperature. • Propose a new heat transfer correlation for steam condensation in rotating channel. In the papermaking industry, a kind of new cylinder dryer with multiple small and rectangular channels are employed to enhance the drying efficiency of drying machine. In practical working conditions, the multi-channel cylinder dryer runs under rotating states that could affect the heat transfer characteristics of the inside two-phase flow. However, the fluid heat transfer characteristics in the multi-channel at rotating states have not been well explored. In this study, a set of rotating experimental system is established to investigate the condensation characteristics and pressure drop changes of steam in rotating rectangular channels. Firstly, the experimental apparatus and the data processing method are described in detail. Then the effects of rotation speed, mass flux and steam temperature on the heat transfer coefficients and pressure drop are studied through experiment. The results show that when Re is small, the heat transfer coefficient first increases and then decreases with the increased Re ω ; when Re is large, the heat transfer coefficient increases with the increased Re ω . Moreover, the heat transfer coefficient decreases as the steam temperature increases. In addition, the pressure drop decreases with the increased Re ω while increases with the increased Re and steam temperature. Finally, a heat transfer model of two-phase flow condensation under rotating states is developed to predict the heat transfer coefficient of steam in rotating multiple channels.

In tube condensation heat transfer and pressure drop for R454B and R32—Potential replacements for R410A

The heating, ventilation and air conditioning (HVAC) industry in the United States seeks near-term alternative refrigerants to replace R-410A in unitary equipment. Two potential replacement refrigerants are R-454B and R-32. It is of interest to investigate the capability and accuracy of existing heat exchanger design methods when applied to these replacement refrigerants. To that end, this work presents empirical condensation quasi-local heat transfer coefficient and pressure drop data for R-454B and R-32. These data were obtained in a 38 in. (9.52 mm) outside diameter (OD) smooth copper tube with a wall thickness of 0.032 in. (0.81 mm). The experimental variables and their ranges included refrigerant absolute pressure (1960≤Pabs≤3196 kPa), condensation temperature (35≤Tcond≤50oC), mass flux (100≤G≤200 kg m-2 s-1), vapor quality (0≤x≤1), and heat flux (32.9≤q″≤62.97 kW m-2). It was found that the heat transfer correlation developed by Cavallini et al. Cavallini et al. (2006) predicted the experimental condensation heat transfer data, for both R-454B and R-32, with the greatest accuracy. Using the Cavallini et al. correlation, it was found that the mean absolute percentage error (MAPE) was 10.5% and 15.1% for R-454B and R-32, respectively. Additionally, the pressure drop correlation developed by Friedel Friedel (1979) predicted the experimentally determined pressure gradient with a MAPE of 7.7% and 5.5% for R-454B and R-32, respectively. These results will assist the practicing thermal engineer to choose the most appropriate design correlation for these near-term replacement refrigerants.

Numerical determination of condensation pressure drop of various refrigerants in smooth and micro-fin tubes via ANN method

Abstract In the current work, the pressure drop of the refrigerant flow in smooth and micro-fin pipes has been modeled with artificial neural networks as one of the powerful machine learning algorithms. Experimental analyses have been evaluated in two groups for the numerical model such as operation parameters/physical properties and dimensionless numbers used in two-phase flows. Feed forward back propagation multi-layer perceptron networks have been developed evaluating the practically obtained dataset having 673 data points covering the flow of R22, R134a, R410a, R502, R507a, R32 and R125 in four different pipes. The outputs acquired from the artificial neural network have been evaluated with the target ones, and the performance factors have been estimated and the prediction accuracy of the network models has been resourced comprehensively. The results revealed that the neural networks could predict the pressure drop of the refrigerant flow in smooth and micro-fin pipes between 10% deviation bands.

Experimental research on refrigerant condensation heat transfer and pressure drop characteristics in the horizontal microfin tubes

The condensation heat transfer characteristics and pressure drop for R410A were investigated in the horizontal smooth and microfin tubes. The 6.35-mm-OD, 7-mm-OD and 8-mm-OD tubes with active length 2 m were selected for condensation test cooled by the heat transfer fluid (water) circulated in a surrounding annulus. A refrigerant superheating 2–3 °C was set at the test section inlet and the mass flux range was 300–1100 kg·m−2·s−1. The heat transfer coefficient (HTC) of the microfin tube was about 1.63–2.29 times of that of the smooth one. The microfin one yields ~28.9% higher pressure drop than the smooth one. Large helix angle and fin height were beneficial to enhance heat transfer due to the centrifugal force and surface tension, but increased the pressure drop. 6.35-mm-OD tube produced both the higher HTC and pressure drop than the 7-mm-OD and 8-mm-OD tubes due to the increased effect of the surface tension and the sheer stress at the gas-liquid interface. It was necessary to optimize finned structure to enhance heat transfer. Experimental data were also compared with previous correlations proposed for smooth and microfin tube. It was necessary to collect more data source and make a generally-accepted and accurate correlation in future.

Performance evaluation of a wrapped around condenser for heat pump water heater applications

• A model has been developed to predict the performance of a HPWH condenser in two wrap patterns. • The impact of condenser design on the heat transfer to the storage tank has been established. • Optimization of the spacing for two wrap patterns shows little difference in performance. • Charge amount, as well as subcooled, saturated and super-heated lengths have been determined for the condenser. Accurate performance evaluation of a wrapped-around condenser for heat pump water heaters (WHPWH) is critical since the COP of the system depends heavily on thermal stratification and condenser design. An analytical, quasi-steady state heat balance method has been developed to determine the optimal spacing between adjacent channels, tube diameter, tube shape, and total refrigerant charge amount for the condenser. The heat transfer rate is compared among three approaches: the refrigerant thermodynamic model, the condenser-wrap fin model, and the analytical natural convection model on the inside of the tank for the three regions based on the refrigerant phase (e.g., super-heated, saturated, or subcooled). The heat transfer rate was predicted by a combination of slug-plug and annular flow for a D-shaped helical tube. Experimental data were used as boundary conditions for validating the model. The rate of heat transfer based on tube shape and tank wall temperatures was compared by CFD analysis. Parametric analysis indicates a tradeoff between refrigerant mass, pressure drop, tube diameter, and tube length to maximize the heat transfer rate. The model suggests the saturated region length can be extended by 400%, and the condenser pressure drop can be reduced by 23% with an optimal spacing pattern.

Flow condensation heat transfer and pressure drop of R134a alternative refrigerants R513A and R450A in 0.95-mm diameter minichannels

Due to the Kigali amendment to the Montreal Protocol, refrigerants such as R134a are targeted for phasedown or phaseout due to their global warming potential (GWP) and lower GWP refrigerants are being considered to replace R134a. Since the condenser is typically responsible for 50% of the charge of a refrigeration system, it is vital to have a fundamental understanding of the flow condensation heat transfer performance of low GWP refrigerants such as R513A and R450A. Experimental flow condensation heat transfer coefficient data are reported for R134a, R513A, and R450A in seven parallel 0.95 mm diameter mini-channels for a range of mass fluxes (i.e., 200 – 500 kg/m2s) and qualities (i.e., 0.2 – 0.8) at a saturation temperature of 40 °C. The heat transfer coefficient uncertainties for all experiments were ± 6.3 – 21.2%, with an average of ± 9.8%. Condensation heat transfer coefficients for R134a, R513A, and R450A all increased with increasing mass flux and quality. R513A condensation heat transfer coefficients were 2.6 – 25.6% lower than R134a heat transfer coefficients and pressure drops were 4.5 – 14.0% lower than R134a pressure drops. R450A heat transfer coefficients were 2.4% higher than R134a at higher mass fluxes and qualities and up to 11.7% lower than R134a at lower mass fluxes than R134a heat transfer coefficients; R450A pressure drop were comparable to R134a pressure drop (i.e., 5.0% higher to 9.5% lower). The data were compared to three condensation correlations – Shah (2016), Kim and Mudawar (2013), and Cavallini et al. (2011); the data were predicted with mean average errors of 23.4%, 15.9%, and 23.4%, respectively.

Condensation heat transfer in annuli outside horizontal stainless steel enhanced tubes

The condensation heat transfer of R410A outside several enhanced heat transfer (EHT) tubes [dimple/herringbone (DIM/HB), herringbone (HB), and dimple (DIM)] and smooth tube were evaluated. All tubes are made of stainless steel; the test length is 2 m; the outer diameter is 12.7 mm; the inner diameter is 11.5 mm. Experimental conditions were set at a saturated temperature of 45 °C; condensed vapor mass decreased from 0.8 to 0.2; mass flux ranged between 75 and 225 kg m−2 s−1. As a result, the HB tube effectively improved flow condensation performance outside tubes; while the dimple-only structure is not effective since it produces a lower heat transfer coefficient (HTC) than a smooth tube (at some low flow rate conditions). Substantial enhancement is produced by the DIM/HB composite surface produced from dimple and herringbone microfin patterns, which is due to the combination of the liquid drainage effects by herringbone structure to remove condensate and causing strong turbulence of dimple structure. With the increase of mass flux and average vapor quality, the condensation heat transfer coefficient and pressure drop of each test tube increase as well. Additionally, an improved Nusselt equation for external condensation on a smooth tube was developed to predict the heat transfer coefficient for the experimental conditions considered here. Finally, correlations of enhanced heat transfer (EHT) tubes (microfin – HB, dimple - DIM, and composite surface – DIM/HB) to predict condensation heat transfer coefficient were developed and evaluated.

Two-phase frictional pressure drop of R134a and R410A condensing inside multiport rectangular microchannels with different aspect ratio

ABSTRACT 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.

Condensation heat transfer and pressure drop characteristics of low GWP R-404A alternative refrigerants in a multiport tube having axial microfins

Considering the phase out of the hydrofluorocarbons (HFCs), the search for an alternative refrigerants is of an urgent issue. In this study, four R-404A alternative refrigerants (R-448A, R-449A, R-455A, R-454C) were tested in a microfin multiport tube having 1.30 mm hydraulic diameter. The smooth mutiport tube of 0.8 mm hydraulic diamter was also tested for a comparison purpose. The results showed that, at a low mass flux and low vapour quality, the microfin tube yielded approximately equal heat transfer coefficients to those of the smooth tube. At a high mass flux and high vapour quality, however, the heat transfer coefficient trends were different depending on the refrigerants. For R-404A, which has a negligible temperature glide of 0.31 K (at 45 °C saturation temperature), the heat transfer coefficients of the two tubes were approximately the same. However, for R-454C and R-445A, which have the large temperature glides of 6.59 K and 9.46 K, the heat transfer coefficients of the microfin tube were smaller than those of the smooth tube. Based on the trends of the heat transfer coefficients of this study, three criteria for a possible good correlation are proposed. First, the correlation should predict the heat transfer coefficients of pure (or near azeotropic) refrigerants in a smooth tube adequately. Second, the correlation should predict the heat transfer coefficients of pure (or near-azeotropic) refrigerants in a microfin tube smaller than those in a smooth tube. Third, the underprediction of the microfin data should get weakened as the temperature glide increases. Based on the above criteria, it was found that some micro-channel or conventional channel correlations may be used to predict the condensation heat transfer coefficients in a multiport tube with/without microfins. The pressure drops were generally in the reverse order to the value of vapour density. Furthermore, the pressure drops of the alternative refrigerants were larger than those of R-404A.

임계점 부근의 이산화탄소-메탄 혼합물의 관내 응축 열전달 특성 연구

The condensation heat transfer coefficient and pressure drop for pure CO₂ and CO₂+CH₄ mixture were investigated under the near-critical condition, which simulates the CO₂ transporting conditions under Carbon Capture and Storage (CCS) process. The experimental facility consisted of a test section, heat exchangers, mass flow meters, temperature sensors, a magnetic gear pump, and a differential pressure transducer. The test section made with a copper tube was assembled with Polyvinyl Chloride (PVC) pipe to form a double tube. The condensation temperature and mole fraction of CH₄ in the CO₂ mixture ranged from 20℃ to 30℃, and 1% to 5%, respectively. The mass flux was changed from 500, 600, and 700 kgm-2s-1. The two-phase flow pattern under the set conditions was estimated to be the annular flow. When the mole fraction of methane in the mixture increased from 1% to 5% at 20℃ of condensation temperature, the average condensation heat transfer coefficients and the pressure drop for CO₂+CH₄ decreased from 4.97% to 19.9%, and 30.0% to 54.5%, respectively, compared to those for pure CO₂

Comprehensive performance analysis and optimization of novel SCR-ORC system for condensation heat recovery

• An ORC system based on a novel condenser is proposed for condensation heat recovery. • The comprehensive performance of SCR-ORC system and novel condenser is analyzed. • Genetic algorithm is implemented using optimum combination weights method. • Optimized parameters guarantee excellent comprehensive performance. • Thermodynamic, economic, and environmental performances are improved simultaneously. An organic Rankine cycle (ORC) system with separation, compression, and recycling of exhaust gas (SCR-ORC) based on a novel condenser is proposed. The relationship between volume, temperature, and pressure in fluid mechanics is used to change the internal space structure of condenser, so that a temperature difference is generated between the exhaust gas split in two spaces, which is used to recover the condensation heat. Then, the SCR-ORC system is used to reuse the recovered condensation heat. Further, the comprehensive performance of SCR-ORC system and novel condenser is analyzed and compared with that of ORC system and traditional condenser. Furthermore, multi-objective optimization is conducted by using thermodynamic, economic, and environmental performance as optimization objectives through the genetic algorithm with optimal combination weights method. The results indicate that when the condenser pressure drop (Δ P c ) is 0.12 MPa, the waste condensation heat of traditional condenser reaches 64852.24 kW, while that of novel condenser is 38910.92 kW, the condensation heat recovery and exergy loss of novel condenser are 6114.28 kW and 2408.63 kW respectively. Compared with the ORC system, the net power output ( W net ), thermal efficiency ( η t ), exergy efficiency ( η ex ), and annual emission reduction ( AER ) of equivalent carbon dioxide of SCR-ORC system with R245fa as the working fluid are increased by 6803.17 kW, 2.52%, 6.54%, and 1215.82 × 10 3 kg, respectively, while the payback period ( PBP ) is decreased by 0.59 years. It is also found that the working fluids with lower critical temperature exhibit better comprehensive performance, and the comprehensive performance of R134a is the highest among the considered working fluids.

Flow Condensation Heat Transfer and Pressure Drop of R134a Alternative Refrigerants R513a and R450a in 0.95-Mm Diameter Minichannels

Flow Condensation Heat Transfer and Pressure Drop of R134a Alternative Refrigerants R513a and R450a in 0.95-Mm Diameter Minichannels

Experimental investigation on flow condensation pressure drop of steam in a horizontal tube

The pressure drop characteristics of pure steam condensation are studied in a horizontal tube with an inside diameter of 38 mm and a length of 3.4 m. The mass flux ranges from 3-7.5 kg/(m2s). The saturation temperatures of the inlet steam are 50?, 60?, and 70?. The temperature difference between the inlet steam and the inlet cooling water is from 3-7?. The influences of mass flux, total heat transfer temperature difference and inlet saturation temperature total pressure drop are investigated. The new correlation is proposed to calculate the total pressure drop of pure steam flow in a horizontal tube. The Dukler correlations based on the homogeneous flow model are good predictors for calculating the frictional pressure drop in this work.