Thermal Design and Performance Prediction of a Shell Condenser for Closed-Cycle Underwater Vehicles

2018 ◽  
Author(s):  
Peiyu Chen ◽  
Hongbin Yan ◽  
Gongnan Xie ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Computational Model ◽  
Performance Prediction ◽  
Mass Velocity ◽  
Underwater Vehicles ◽  
Thermal Design ◽  
Condensation Process ◽  
Inlet Temperature ◽  
Straight Channel ◽  
Helical Channel

The shell condenser is a key component for the underwater vehicles. To study its heat transfer performance and flow characteristics and to design a more efficient structure, a mathematical model is generated to simulate condensation inside the straight and helical channels. The model combines empirical correlations and MATLAB based on an iterative algorithm. Here, quality is used as a sign of the degree of condensation. The computational model is verified by comparison of simulations and experiments. Several cases are designed to reveal the effects of the initial condition. The inlet temperature varies from 160 to 220°C and the inlet mass velocity ranges between 133 and 200 kg/m2·s. The results show that the inlet temperature and mass velocity significantly affect flow and heat transfer in the condensation process. In addition, comparisons of the straight channel and helical channel with different Dh/R indicate that the heat transfer capability of the helical channel is obviously better than that of the straight channel, and the heat transfer coefficient and total pressure drop increase with the decrease of Dh/R. This study may provide useful information for performance prediction and structure design of shell condensers, and provide a relatively universal computational model for condensation in channels.

Prediction and Comparison of Shell Condensers With Straight or Helical Channels for Underwater Vehicles

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
Peiyu Chen ◽  
Gongnan Xie ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Underwater Vehicles ◽  
Condensation Process ◽  
Inlet Temperature ◽  
Mass Rate ◽  
R Ratio ◽  
Universal Prediction ◽  
Inlet Conditions ◽  
Degree Of Condensation ◽  
Helical Channels

The shell condenser is one of the key components of underwater vehicles. To study its thermal performance and to design a more efficient structure, a computational model is generated to simulate condensation inside straight and helical channels. The model combines empirical correlations and a MATLAB-based iterative algorithm. The vapor quality is used as a sign of the degree of condensation. Three calculation models are compared, and the optimal model is verified by a comparison of simulated results and available experimental data. Several cases are designed to reveal the effects of various inlet conditions and the diameter-over-radius (Dh/R) ratio. The results show that the inlet temperature and mass rate significantly affect the flow and heat transfer in the condensation process, the heat transfer capabilities of the helical channels are much better than that of the straight channel, and both the heat transfer coefficient and total pressure drop increase with the decrease of Dh/R. This study may provide a useful reference for performance prediction and structural design of shell condensers used for underwater vehicles and may provide a relatively universal prediction model for condensation in channels.

scholarly journals Numerical Analysis of Laminar Convective Condensation with the Presence of Noncondensable Gas Flowing Downward in a Vertical Channel

2019 ◽  
Vol 2019 ◽  
pp. 1-15
Author(s):  
Mustapha Ait Hssain ◽  
Youness El Hammami ◽  
Rachid Mir ◽  
Sara Armou ◽  
Kaoutar Zine-Dine
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Relative Humidity ◽  
Liquid Film ◽  
Vertical Channel ◽  
Dimensionless Temperature ◽  
Condensation Process ◽  
Inlet Temperature ◽  
Mixture Flow ◽  
Noncondensable Gas

The purpose of this paper is to study and perform a numerical analysis of the simultaneous processes of mass and heat transfer during the condensation process of a steam in the existence of noncondensable gas (NCG) inside a descending vertical channel. In this study, the flow of the vapor-air mixture is laminar and the saturation conditions are prevailing at the inlet of the channel. The coupled control equations for liquid film, interfacial conditions, and mixture flow are solved together using the approach of finite volume. Detailed and valuable results are presented both in the liquid condensate film and in the mixing regions. These detailed results contain the dimensionless velocity and dimensionless temperature profiles in both phases, the dimensionless mass fraction of vapor, the axial variation of the dimensionless thickness of the film liquid δ⁎, and the accumulated condensate rate Mr as well the local Nusselt number Nuy. The relative humidity at the inlet varies from 60% to 100% and the inlet temperature from 40°C to 80°C. The results confirm that a decrease in the mass concentration of NCG by the increasing the inlet relative humidity has a direct influence on the liquid film layer, the local number of Nusselt, and the variation of condensation rate accumulated through the channel. The results also designate that an increase of the inlet relative humidity and the inlet temperature ameliorates the condensation process. The comparison made for the coefficient of heat transfer due to condensation process and the condensate liquid film thickness with the literature results is in good concordance which gives more credibility to our calculation model.

Conjugate Heat Transfer Enhancement of an Internal Blade Pin-Finned Tip-Wall

2009 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Conjugate Heat Transfer ◽  
Gas Flow ◽  
Turbine Blades ◽  
Thermal Design ◽  
Inlet Temperature ◽  
Computational Domain ◽  
Pin Fins ◽  
Blade Tip

To improve gas turbine performance, the operating temperature has been increased continuously. However, the heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Cooling methods are therefore needed for the turbine blades to ensure a long durability and safe operation. The blade tip region is exposed to the hot gas flow and is difficult to cool. A common way to cool the tip is to use serpentine passages with 180-deg turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement. Increasing internal convective cooling is therefore required to increase the blade tip life. In this paper, augmented heat transfer of a blade tip with internal pin-fins has been investigated numerically using a conjugate heat transfer approach. The computational model consists of a two-pass channel with 180-deg turn and an array of pin-fins mounted on the tip-cap. The computational domain includes the fluid region and the solid pins as well as the solid tip regions. Turbulent convective heat transfer between the fluid and pins, and heat conduction within pins and tip are simultaneously computed. The inlet Reynolds numbers are ranging from 100,000 to 600,000. Details of the 3D fluid flow and heat transfer over the tip surface are presented. A comparison of the overall performance of the two models is presented. It is found that due to the combination of turning impingement and pin-fin cross flow, the heat transfer coefficient of the pin-finned tip is a factor of about 3.0 higher than that of a smooth tip. This augmentation is achieved at the cost of a pressure drop penalty of about 7%. With the conjugate heat transfer method, not only the simulated model is close to the experimental model, but also the distribution of the external tip heat transfer can be relevant for thermal design of turbine blade tips.

scholarly journals Experimental and Numerical Study of Double-Pipe Evaporators Designed for CO2 Transcritical Systems

Processes ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 547 ◽  
Author(s):  
Junlan Yang ◽  
Shuying Ning
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Velocity ◽  
Numerical Study ◽  
Parameter Method ◽  
Inlet Temperature ◽  
Pump System ◽  
Heat Pump System ◽  
Evaporation Temperature ◽  
Double Pipe

The performance of a CO2 double-pipe evaporator was studied through experiments and a simulation model that was established by the steady-state distribution parameter method and experimentally verified while using a CO2 transcritical water‒water heat pump system. The effects of different operating parameters on heat transfer performance were studied over a range of evaporation temperatures (−5 to 5 °C), mass velocity (100‒600 kg/m2s), and heat flux (5000‒15,000 W/m2). It was found that the dryout quality increased at a small evaporation temperature, a large mass velocity, and a small heat flux. The simulation yield means relative error (RE) of heat transfer for the evaporation temperature and that of the CO2 pressure drop for the chilled water inlet temperature were 5.21% and 3.78%, respectively. The effect of tube diameter on the performance of CO2 double-pipe evaporator is probed through simulations. At the same time, this paper defines a parameter α , which is the proportion of the pre-dryout region to the whole heat transfer region. A larger α value is desirable. A further theoretical basis is provided for designing an efficient and compact CO2 evaporator.

scholarly journals A MCDM Methodology to Determine the Most Critical Variables in the Pressure Drop and Heat Transfer in Minichannels

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2069
Author(s):  
Eloy Hontoria ◽  
Alejandro López-Belchí ◽  
Nolberto Munier ◽  
Francisco Vera-García
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Saturation Pressure ◽  
Computational Cost ◽  
Urban Systems ◽  
Condensation Process ◽  
Geometrical Parameters ◽  
Maximum Heat ◽  
Maximum Heat Transfer

This paper proposes a methodology aiming at determining the most influent working variables and geometrical parameters over the pressure drop and heat transfer during the condensation process of several refrigerant gases using heat exchangers with pipes mini channels technology. A multi-criteria decision making (MCDM) methodology was used; this MCDM includes a mathematical method called SIMUS (Sequential Interactive Modelling for Urban Systems) that was applied to the results of 2543 tests obtained by using a designed refrigeration rig in which five different refrigerants (R32, R134a, R290, R410A and R1234yf) and two different tube geometries were tested. This methodology allows us to reduce the computational cost compared to the use of neural networks or other model development systems. This research shows six variables out of 39 that better define simultaneously the minimum pressure drop, as well as the maximum heat transfer, saturation pressure fluid entering the condenser being the most important one. Another aim of this research was to highlight a new methodology based on operation research for their application to improve the heat transfer energy efficiency and reduce the CO2 footprint derived of the use of heat exchangers with minichannels.

scholarly journals Energy and Exergy Efficiency Analysis of Fluid Flow and Heat Transfer in Sinter Vertical Cooler

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4522
Author(s):  
Zude Cheng ◽  
Haitao Wang ◽  
Junsheng Feng ◽  
Yongfang Xia ◽  
Hui Dong
Keyword(s):  
Heat Transfer ◽  
Energy Efficiency ◽  
Fluid Flow ◽  
Waste Heat ◽  
Exergy Efficiency ◽  
Inlet Temperature ◽  
Operational Parameters ◽  
Flow And Heat Transfer ◽  
Maximum Value ◽  
Energy And Exergy

In order to fully understand the energy and exergy transfer processes in sinter vertical coolers, a simulation model of the fluid flow and heat transfer in a vertical cooler was established, and energy and exergy efficiency analyses of the gas–solid heat transfer in a vertical cooler were conducted in detail. Based on the calculation method of the whole working condition, the suitable operational parameters of the vertical cooler were obtained by setting the net exergy efficiency in the vertical cooler as the indicator function. The results show that both the quantity of sinter waste heat recovery (SWHR) and energy efficiency increased as the air flow rate (AFR) increased, and they decreased as the air inlet temperature (AIT) increased. The increase in the sinter inlet temperature (SIT) resulted in an increase in the quantity of SWHR and a decrease in energy efficiency. The air net exergy had the maximum value as the AFR increased, and it only increased monotonically as the SIT and AIT increased. The net exergy efficiency reached the maximum value as the AFR and AIT increased, and the increase in the SIT only resulted in a decrease in the net exergy efficiency. When the sinter annual production of a 360 m2 sintering machine was taken as the processing capacity of the vertical cooler, the suitable operational parameters of the vertical cooler were 190 kg/s for the AFR, and 353 K for the AIT.

scholarly journals Study on the Convective Heat Transfer and Fluid Flow of Mini-Channel with High Aspect Ratio of Neutron Production Target

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 4020
Author(s):  
Peng Sun ◽  
Yiping Lu ◽  
Jianfei Tong ◽  
Youlian Lu ◽  
Tianjiao Liang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Aspect Ratio ◽  
Optimization Design ◽  
Heat Dissipation ◽  
Neutron Production ◽  
Thermal Design ◽  
Maximum Deviation ◽  
Test Channel ◽  
Production Target

In order to provide a theoretical basis for the thermal design of the neutron production target, flow and heat transfer characteristics are studied by using numerical simulations and experiments. A rectangular mini-channel experimental model consistent with the geometric shape of the heat dissipation structure of neutron production target was established, in which the aspect ratio and gap thickness of the test channel were 53.8:1 and 1.3 mm, respectively. The experimental results indicate that the critical Re of the mini-channel is between 3500 and 4000, and when Re reaches 21,000, Nu can reach 160. The simulation results are in good agreement with the experimental data, and the numerical simulation method can be used for the variable structure optimization design of the target in the later stage. The relationship between the flow pressure drop of the target mini-channel and the aspect ratio and Re is obtained by numerical simulation. The maximum deviation between the correlation and the experimental value is 6%.

scholarly journals Effects of Temperature on the Flow and Heat Transfer in Gel Fuels: A Numerical Study

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 821
Author(s):  
Qin-Liu Cao ◽  
Wei-Tao Wu ◽  
Wen-He Liao ◽  
Feng Feng ◽  
Mehrdad Massoudi
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Transport System ◽  
Apparent Viscosity ◽  
Thermal Design ◽  
Straight Pipe ◽  
Heating Wall ◽  
Supply Pressure ◽  
Flow And Heat Transfer ◽  
The Mean

In general, rheological properties of gelled fuels change dramatically when temperature changes. In this work, we investigate flow and heat transfer of water-gel in a straight pipe and a tapered injector for non-isothermal conditions, which mimic the situations when gelled fuels are used in propulsion systems. The gel-fluid is modeled as a non-Newtonian fluid, where the viscosity depends on the shear rate and the temperature; a correlation fitted with experimental data is used. For the fully developed flow in a straight pipe with heating, the mean apparent viscosity at the cross section when the temperature is high is only 44% of the case with low temperature; this indicates that it is feasible to control the viscosity of gel fuel by proper thermal design of pipes. For the flow in the typical tapered injector, larger temperature gradients along the radial direction results in a more obvious plug flow; that is, when the fuel is heated the viscosity near the wall is significantly reduced, but the effect is not obvious in the area far away from the wall. Therefore, for the case of the tapered injector, as the temperature of the heating wall increases, the mean apparent viscosity at the outlet decreases first and increases then due to the high viscosity plug formed near the channel center, which encourages further proper design of the injector in future. Furthermore, the layer of low viscosity near the walls plays a role similar to lubrication, thus the supply pressure of the transport system is significantly reduced; the pressure drop for high temperature is only 62% of that of low temperature. It should be noticed that for a propellent system the heating source is almost free; therefore, by introducing a proper thermal design of the transport system, the viscosity of the gelled fuel can be greatly reduced, thus reducing the power input to the supply pressure at a lower cost.

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