CFD Simulation of Helical Shell and Tube Heat Exchanger Using Optimization Techniques

The objective of this study is to simulate the performance of helical tube shell and tube heat exchanger with several optimization techniques using computational fluid dynamics CFD. To check the performance of a designed model of heat exchanger various techniques are available. In this study, the various possible model of the heat exchanger to enhance the performance of the device have been designed. Firstly, the straight tube is replaced by helical tube in the heat exchanger and used 10, 12, 14 number of helical baffles with 50% baffle cut. Total ten models have been developed. These models are model-I 4-turns without baffle, model-II 4-turns with 10 number baffles, model-III 5-turns without baffle, model-IV 5-turns with 12 number baffles, model-V 6-turns without baffle, model-VI 6-turns with 10 number baffles 0.083m baffle space, model-VII 6-turns with 12 number 0.083m baffle space, model-VIII 6-turns with 14 number baffles 0.064m baffle space, model-IX 7-turns without baffle, model-X 7-turns with 14 number baffles, different number of baffles and baffle space with 50% baffle cut and used CUO nanofluid model-XI 6-turns with 14 number baffle CUO fluid 0.083m baffle space CFD analysis simulation done on ANSYS FLUENT 18. The simulated result shows that the model XI is approximately 40% more optimized as compared to model-I and approximately 24% than model-VIII. It also found that the high heat transfer obtains with increased number of baffles.

Influence of Coiling Direction of Helical Tube Bundles on the Thermal-Hydraulics of the HTGR Steam Generator

Helical tube bundles were usually adopted in the steam generators (SGs) or intermediate heat exchangers (IHXs) of high temperature gas-cooled reactors (HTGRs). Heat transfer tubes in neighboring tube layers can be coiled in the same direction or in the opposite direction. The coiling direction has influences on the thermal-hydraulic performances of the SGs or IHXs. The cross flow convection over helical tube bundles with neighboring tube layers having the same coiled direction and opposite coiled direction were numerically investigated. Reynolds stress model with standard wall functions was used for the turbulence modeling. For a helical tube bundle with neighboring layers coiled in the same direction (parallel tube layers), the tangential velocity along the coiled circumferential direction could be observed obviously. For a helical tube bundle with neighboring layers coiled in the opposite direction (crossed tube layers), there is no average tangential velocity of the whole flow filed. And the streamlines of the fluid are very complex. The flow resistances and heat transfer coefficients over helical tube bundle with parallel tube layers and crossed tube layers were compared. Although the heat transfer over helical tube bundles with crossed tube layers was 9.39% smaller than that with parallel tube layers, the pressure drop over tube bundle with crossed tube layers was much smaller compared with those with parallel tube layers.

Experimental investigation on thermal behavior of non-boiling slug and bubbly two phase-flow in helical tube with spiral

The present study provides experimental results of the flow pattern and thermal behavior of a none-boiling air-water two-phase flow in a helical tube with a turbulator. In order to evaluate the thermal behavior, a glass tube was put under constant heat flux. The inlet, outlet, and surface temperature of the helical tube were measured to calculate the heat transfer coefficient. The results showed that the addition of the turbulator in the helical tube leads to a rapid conversion from bubble flow to slug flow. Also, the formed bubbles are much smaller and spread radially throughout the pipe. Findings showed that the turbulator significantly improved the heat transfer of the two-phase flow, in which ratios of heat transfer enhancement with and without turbulator is 28% and 19%, respectively. Finally, cost-to-benefit ratio (C.B.R) analysis confirmed that when air-water two-phase flow transits through the helical tube are not affected by the presence or absence of turbulator.