For vessels operating in the cold climate regions, the ballast water inside or hopper tanks above the waterline may be frozen, starting at the top of the tank and at the side walls. Therefore, countermeasures against freeze-up of the ballast tank such as air-bubbling system, hot steam injecting system, heating coil system and water circulating system are taken to prevent freeze-up phenomenon; however, there are no rigorous investigations of anti-freezing to examine the effectiveness and validity of systems against freeze-up of the ballast tank, in which the temperatures are about -25℃ (ambient air temperature) and 0℃ (sea water), respectively. In this paper, to ensure reasonable specifications for cold regions if the measures from the above-mentioned systems against freeze-up are effective, the phenomenon of ballast tank freeze-up is simulated and discussed in low temperature conditions. With the results using the commercial CFD code, CFX 14, the most cost-effective solution is conducted to prevent being frozen along the outer surface.

/pdf/numerical-investigation-on-freezing-in-ballast-tank-of-ship-5b4szoglbx.pdf

Numerical Investigation on Freezing in Ballast Tank of Ship Navigating in Ice-bound Sea

In this paper, a realizable k-ε turbulence model was used to analyze the mutual heat transfer of a full-scale three-dimensional shell and tube heat exchanger (STHEX) with a heat exchange length of 2,000 ㎜ when the mass flowrate flowing to the shell and the tube is changed into five types. The amount of heat lost from the shell and the amount of heat gained from the tube are almost identical when the mass flowrate of the shell and the tube increases, respectively, and are distributed non-linearly. In addition, the overall heat transfer coefficient increases non-linearly as the mass flowrate of the shell and the tube increases; it shows a value of about 420~670W/㎡·℃ at a given mass flowrate. On the other hand, it is judged that various approximation equations such as heat transfer amount can be important data that provide a lot of information in response to changes in the mass flowrate of the shell and the tube. 

An Estimation on the Heat Transfer Performance of a Full-scale Shell-and-tube Heat Exchanger according to the Change of Mass Flowrate

In this paper, in order to determine the actual heat exchange length suitable for the required heat transfer performance of STHEX by the trial and error method, a complete three-dimensional STHEX model with four heat exchange lengths was subjected to heat transfer numerical analysis as a realizable k-εturbulence model. The pressure drop at the tube bundle and the shell side shows a non-linearly increasing or decreasing distribution when the heat exchange length of STHEX increases, respectively. Its maximum value satisfies both the performance requirements as well. The outlet temperature of the shell side and the tube bundle side decreases or increases as the heat exchange length increases, respectively. Moreover, STHEX with a length of 1300mm is closest to the required performance. On the other hand, the heat transfer amount of STHEX at the shell side and the tube bundle side increases non-linearly as the heat exchange length increases. In addition, for a given STHEX heat exchange length, the overall heat transfer coefficient is about 536-583 W/m²·℃. 

Determination of a Heat Exchange Length Suitable for the Required Heat Transfer Performance of a Full-scale Shell-and-tube Heat Exchanger

In this paper, a full-scale three-dimensional shell-and-tube heat exchanger (STHEX) was analyzed in the steady state with the standard k-ε and realizable k-ε turbulence model, respectively. The pressure drop predicted by the standard k-ε and the realizable k-ε turbulence model has a large deviation from each other, but the outlet temperature prediction shows a very small difference. The hot water temperature at the shell outlet was 9.4°C cooler than the given target value of 40°C, and the temperature of the cooling water at the tube outlet was 4.43°C higher than the target value of 27.6°C indicating that the overall heat transfer area of STHEX was designed excessively. On the other hand, predicting the excessive heat transfer area through numerical analysis of the large STHEX of the full size is judged to have saved a significant amount of time and money in the trial and error design and performance check of the heat exchanger.

Validation of Performance Requirements for Heat Transfer of a Real Full-scale Shell-and-tube Heat Exchanger Through Numerical Analysis

The numerical analysis by using CFX 11.0 commercial code was done for prediction of fluid flow and thermal field in the vertical heat exchanger. The present experimental studies were also conducted to investigate the effects of circulating solid particles on the fluid flow and temperatures in the fluidized bed vertical shell and tube type heat exchanger with counterflow, at which the solid particles of glasses (3 ) were used in the fluidized bed with a smooth tube. The effect of circulation on the distance(L) of tube inlet and baffle plate was also examined. The present experimental and numerical results showed that the particles in the distance (Ds) of 15 mm showed a more efficient circulation without stacked the space and the LMTD(Log Mean Temperature Difference) in the fluidized bed type was much lower than that in the typical type shell and tube heat exchanger.

/pdf/numerical-analysis-of-fluid-flow-and-thermal-fields-in-the-75r097ckc6.pdf

Numerical analysis of fluid flow and thermal fields in the vertical fluidized bed heat exchanger

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Numerical analysis of fluid flow and thermal fields in the vertical fluidized bed heat exchanger