A Numerical Simulation of Rapid Depressurization in Pressure Vessels Incorporating Nucleate Boiling of Hydrocarbon Mixture

2017 ◽  
Author(s):  
Ahmin Park ◽  
Yoonae Ko ◽  
Youngsub Lim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Material Selection ◽  
Convective Heat Transfer Coefficient ◽  
Nucleate Boiling ◽  
Pressure Vessels ◽  
Hydrocarbon Mixture ◽  
Liquid Wall ◽  
The Heat Transfer Coefficient

In offshore operations, overpressure of pressure vessels can arise in case of emergencies like fire or malfunction of valves. This situation can cause physical damages of the vessel and, operation break. Thus, managing overpressure is important in terms of safety of offshore facilities. To handle the overpressure problems, the rapid depressurization, so-called ‘Blowdown’, is used. During depressurization, temperature of internal fluids in a vessel get decreases by the expansion of the fluids. Predicting decrease of the temperature is critical to choose the material of a pressure vessel. Overdesign without the prediction leads to the rapidly decreasing profit margins. For these reasons, the analyzing dynamic behavior of thermodynamics properties like temperature is required for material selection and design verification during depressurization. In this study, a dynamic model for depressurization was developed to simulate thermodynamics behavior in a vessel during depressurization including low temperature phenomena. The model contains non-equilibrium zone between phases, heat transfer between walls and fluids in the vessels. The heat transfer coefficient between internal vapor and wall was calculated from a combined convection that includes the both natural and forced convection. This study includes the calculation of liquid/wall heat transfer coefficient. During depressurization, liquid in the vessel becomes boiling closed to surface of the wall because the temperature of the wall is higher than the boiling point of the liquid. This phenomenon can be described as ‘nucleate boiling’, causes decreasing convective heat transfer coefficient from inner wall to the liquid in the vessel. Using the proper correlations about this phenomenon, the calculated coefficient made this study get closer to reality. The results were compared to experimental and simulation data from literature and it shows this model can properly estimate the thermodynamic property change in a vessel.

Study on Flow Boiling Heat Transfer of Carbon Dioxide With PAG-Type Lubricating Oil in Pre-Dryout Region Inside Horizontal Tube

2010 ◽  
Author(s):  
Chaobin Dang ◽  
Minxia Li ◽  
Eiji Hihara
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this study, the boiling heat transfer coefficients of carbon dioxide with a PAG-type lubricating oil entrained from 0 to 5 wt% in a horizontally placed smooth tube with an inner diameter of 2 mm were experimentally investigated under the following operating conditions: mass fluxes from 170 to 320 kg/m2s, heat fluxes from 4.5 to 36 kW/m2, and a saturation temperature of 15 °C. The results show that for a low oil concentration of approximately 0.5% to 1%, no further deterioration of the heat transfer coefficient was observed at higher oil concentrations in spite of a significant decrement of the heat transfer coefficient compared to that under an oil-free condition. The heat flux still had a positive influence on the heat transfer coefficient in low quality regions. However, no obvious influence was observed in high quality regions, which implies that nucleate boiling dominates in the low quality region whereas it is suppressed in the high quality regions. Unlike the mass flux under an oil-free condition, mass flux has a significant influence on the heat transfer coefficient, with a maximum increase of 50% in the heat transfer. On the basis of our experimental measurements of the flow boiling heat transfer of carbon dioxide under wide experimental conditions, a flow boiling heat transfer model for horizontal tubes has been proposed for a mixture of CO2 and polyalkylene glycol (PAG oil) in the pre-dryout region, with consideration of the thermodynamic properties of the mixture. The surface tension and viscosity of the mixture were particularly taken into account. New factors were introduced into the correlation to reflect the suppressive effects of the mass flux and the oil on both the nucleate boiling. It is shown that the calculated results can depict the influence of the mass flux and the heat flux on both nucleate boiling and convection boiling.

Prediction of the Heat Transfer Coefficient in a Small Channel with the Superposition and Asymptotic Correlations

2018 ◽  
Vol 26 (01) ◽  
pp. 1850001
Author(s):  
Yushazaziah Mohd-Yunos ◽  
Normah Mohd-Ghazali ◽  
Maziah Mohamad ◽  
Agus Sunjarianto Pamitran ◽  
Jong-Taek Oh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Experimental Work ◽  
Nucleate Boiling ◽  
Vapor Quality ◽  
Two Phase ◽  
Forced Convective Heat Transfer ◽  
Small Channel ◽  
The Heat Transfer Coefficient

Heat transfer coefficient as an important characteristic in heat exchanger design is determined by the correlation developed from previous experimental work or accumulation of published data. Although discrepancies still exist between the existing correlations and practical data, several researchers claimed theirs as a generalized heat transfer correlation. Through optimization method, this study predicts the heat transfer coefficient of two-phase flow of propane in a small channel at the saturation temperature of 10[Formula: see text]C using two categories of correlation — superposition and asymptotic. Both methods consist of the contribution of nucleate boiling and forced convective heat transfer, the mechanisms that contribute to the total two-phase heat transfer coefficient, which become as two objective functions to be maximized. The optimization of experimental parameters of heat flux, mass flux, channel diameter and vapor quality is done by using genetic algorithm within a range of 5–20[Formula: see text]kW/m2, 100–250[Formula: see text]kg/m2[Formula: see text]s, 1.5–3[Formula: see text]mm and 0.009–0.99, respectively. In the result, the selected correlations under optimized condition agreed on the dominant mechanism at low and high vapor qualities are caused by the nucleate boiling and forced convective heat transfer, respectively. The optimization work served as an alternative approach in identifying optimized parameters from different correlations to achieve high heat transfer coefficient by giving a fast prediction of parameter range, particularly for the investigation of any new refrigerant. In parallel with some experimental works, a quick prediction is possible to reduce time and cost. From the four selected generalized correlations, Bertsch et al. show the closer trend with the reference experimental work until vapor quality of 0.6.

Nucleate Boiling Performance of Refrigerants and Refrigerant-Oil Mixtures

1980 ◽  
Vol 102 (4) ◽  
pp. 701-705 ◽  
Author(s):  
S. Chongrungreong ◽  
H. J. Sauer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Significant Influence ◽  
Correlation Equation ◽  
Nucleate Boiling ◽  
Experimental Results ◽  
General Correlation ◽  
Oil Mixtures ◽  
The Heat Transfer Coefficient

Current and previous studies by the authors and others have shown shown that the carryover of oil in refrigeration systems can have a significant influence on the boiling performance in the evaporator of refrigeration systems. This investigation was conducted primarily to develop a general correlation equation for predicting the heat transfer coefficient for refrigerants and refrigerant-oil mixtures under pool boiling conditions. Experimental results were obtained to establish the validity of the correlation equation.

Wind-Related Heat Transfer Coefficient for Flat-Plate Solar Collectors

1987 ◽  
Vol 109 (2) ◽  
pp. 108-110 ◽  
Author(s):  
S. Shakerin
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Separation Bubble ◽  
Convective Heat Transfer Coefficient ◽  
Leading Edge ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

Experiments were performed to evaluate the convective heat transfer coefficient for a flat plate mounted in a wooden model of a roof of a building. The experiments were carried out in a closed-circuit wind tunnel and included parametric adjustments of the roof tilt and Reynolds number, based on the length of the plate. The roof tilt was set at 0, 30, 45, 60, and 90 degrees and the Reynolds number ranged from 58,000 to 250,000. A transient, one lump, thermal approach was used for heat transfer calculations. Due to a separation bubble at the leading edge of the model, i.e., the roof, at angles of attack of less than 40 degrees, the flow became turbulent after reattachment. This resulted in a higher heat transfer than previously reported in the literature. At higher angles of attack, the flow was not separated at the leading edge and remained laminar. The heat transfer coefficient for higher angles of attack, i.e., α > 40 deg, was found to be approximately independent of the angle of attack and in good agreement with the previously published results.

Effects of Non-Condensable Gas on Characteristics of Natural Circulation Flow of Isolation Condenser

2021 ◽  
Author(s):  
Tetsuya Takada ◽  
Yasunori Yamamoto ◽  
Kosuke Ono
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Natural Circulation ◽  
Nucleate Boiling ◽  
Hydrogen Effect ◽  
Heat Transfer Tube ◽  
System Pressure ◽  
Transfer Tube ◽  
The Heat Transfer Coefficient

Abstract An isolation condenser (IC) is a passive core cooling system in boiling water reactors. The cooling performance of IC is deteriorated when hydrogen generated in the core flows into the IC pipes. In this study, we conducted high pressure experiments using natural circulation loop with non-condensable gas injection, where helium was used to simulate hydrogen effect on the IC. The reaching distance of steam in the heat transfer tube was estimated by observing the region where nucleate boiling occurred on the outer surface of the heat transfer tube, and the heat transfer coefficient was estimated. The heat transfer coefficient hardly changed when helium was injected to the loop that indicates injected helium was not accumulated in the heat transfer tube. The system pressure at quasi-steady state increased with increasing amount of the injected helium. Since the differential pressure at the down comer section increased by helium injection, the injected helium may be accumulated in the section, leading to increment of the system pressure.

On Selection of Reference Temperature of Heat Transfer Coefficient for Complicated Flows

2007 ◽  
Author(s):  
X. C. Li ◽  
J. Zhou ◽  
K. Aung
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Convective Heat Transfer Coefficient ◽  
Internal Heat ◽  
Reference Temperature ◽  
The Heat Transfer Coefficient

One of the most fundamental concepts in heat transfer is the convective heat transfer coefficient, which is closely related with the flow Reynolds number, flow geometry and the thermal conditions on the heat transfer surface. To define the heat transfer coefficient, a reference temperature is needed besides the surface temperature and heat flux. The reference temperature can be chosen differently, such as the fluid bulk mean temperature (for internal flows) and the temperature at the far field (for external flows). For complicated flows, the adiabatic wall temperature, defined as the wall temperature when the surface heat flux is zero, is commonly adopted as the reference temperature. Other options can also be applied to complicated flows. This paper analyzed some of the potential selections of the reference temperature for different flow settings, including film cooling, jet impingement with cross flows and a mixing flow in a straight duct with or without internal heat source. Both laminar and turbulent flows are considered with different boundary conditions. Dramatic changes of heat transfer coefficient are observed with different reference temperatures. In some special conditions the heat transfer coefficient becomes negative, which means the heat flux has a different direction with the driving temperature difference defined. An innovative method is proposed to calculate the heat transfer coefficient of complicated flows with constant surface temperature.

Estimation of the Heat Transfer Coefficient of a Microchannel Heat Sink Using an Optimal Control Technique

2006 ◽  
Author(s):  
Florentina Simionescu ◽  
Daniel K. Harris
Keyword(s):  
Heat Transfer ◽  
Optimal Control ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Convective Heat Transfer Coefficient ◽  
Control Technique ◽  
Microchannel Heat Sink ◽  
Convective Boundary ◽  
The Heat Transfer Coefficient

Cooling of electronic devices requires the use of heat spreaders whose function is to allow the spreading of the heat flux lines in the 3-D space and to increase the exchange area with the coolant. The objective of this analysis is to estimate the convective heat transfer coefficient of a microchannel heat sink that corresponds to a maximum amount of heat removed from heat source placed on the top surface of the sink. This problem is solved using an optimal control technique in which we control the solution of the heat equation with the convective boundary condition, taking the heat transfer coefficient as the control. A conjugate gradient method is used to solve the optimal control problem. The results show that the temperature distributions corresponding to the controlled solution are lower than those corresponding to the uncontrolled solution. This study can provide guidance in designing micro heat pipe sinks, which have emerged as an effective technique for cooling electronic components.

Experimental Study on Flow Boiling of HFE-7100 in Wavy Copper Microchannels

2020 ◽  
Author(s):  
Peilin Cui ◽  
Zhenyu Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Thin Liquid Film ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

Abstract This study experimentally investigated the flow boiling of HFE-7100 in wavy copper microchannel heat sink (20 mm × 10 mm), which was fabricated with the ultrafast laser micromachining approach, consisting of 20 wavy microchannels with wavelength of 2000 μm and wave amplitude of 100 μm with triangular cross section (200 μm × 573 μm). The experiment was conducted with the mass fluxes of 330.07–550.11 kg/(m2·s) and heat flux of 14.5–411.3 kW/m2 at an inlet temperature of 15°C. Four flow patterns including bubbly flow, slug flow, churn flow and annular flow were captured with the visualization technique. Several confined bubbles with irregular shape were observed. In the low heat flux region, the dominant flow regime of heat transfer in the microchannels is the nucleate boiling and the heat transfer coefficient increases with increasing heat flux. With the nucleate boiling suppressed gradually, the evaporation of thin liquid film begins to dominate and the heat transfer coefficient decreases with the increase of heat flux. The heat flux has a significant effect on heat transfer coefficient compared with the mass flux and vapor quality.

scholarly journals Convective Bubbly Flow of Water in an Annular Pipe: Role of Total Dissolved Solids on Heat Transfer Characteristics and Bubble Formation

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1566 ◽  
Author(s):  
M. M. Sarafraz ◽  
M. S. Shadloo ◽  
Zhe Tian ◽  
Iskander Tlili ◽  
Tawfeeq Abdullah Alkanhal ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Heat Transfer Characteristics ◽  
The Heat Transfer Coefficient

Formation of bubbles in water inside an annulus pipe in a flow boiling regime was experimentally investigated. The effect of various variables, such as total dissolved solid materials (TDS) in terms of mass fraction, flow rate of water, and applied heat flux (HF) on the heat transfer coefficient (HTC) and bubble behavior of water, was experimentally investigated. A regression formula was fitted to estimate the average bubble diameter at various TDS values, with accuracy of <4.1% up to heat flux of 90 kW/m2. Results show that the presence of TDS materials can increase the contact angle of bubble and bubble diameter, and also promotes the HTC value of the system. However, flow rate of water suppressed bubble generation, and increased the heat transfer coefficient due to the renewal of the thermal boundary layer around the boiling surface. Likewise, it was identified that forced convective and nucleate boiling heat transfer mechanisms contribute to the flow of boiling water, and heat flux is a key parameter in determining the mechanism of heat transfer. In the present study, heat flux of 15 kW/m2 at 50 °C was the heat flux in which onset of nucleate boiling was identified inside the annulus pipe. The contact angle of water at TDS values of 300 mg/L and 1200 mg/L was 74° and 124°, respectively, showing the improvement in heat transfer characteristics of water due to the presence of TDS materials.

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