Performance Enhancement Theory And Optimal Design Of Helically Coiled Tube Heat Exchanger

Low energy efficiency,rising energy costs,and rising pollution have all become major global issues in recent years.To address the aforementioned issues,improving the energy transfer process and lowering energy transfer usage are crucial.Heat exchanger design and optimization are critical to energy and environmental projects since they are the most frequently utilized energy transfer equipment in the energyconsuming sector.This dissertation examines the performance enhancement mechanism of a helically coiled tube heat exchanger using theoretical innovation based on entropy dissipation theory,field synergy theory,and irreversible loss theory,with the objective function of optimizing the structure.After that,the heat exchanger’s performance improvement process is investigated using tests and numerical simulation techniques,and lastly,the overall topology optimization issues of the helically coiled tube heat exchanger are investigated and solved.The heat exchanger thermodynamic model and application of the entransy loss theory in the heat exchanger are enhanced using the useful energy loss theory.The temperature structure of the heat exchanger’s thermodynamic system is rectified,and the heat exchanger’s temperature connection is constructed by analogy with the irreversible Carnot heat engine system model.The equivalent average temperature is used to represent the temperature in the equivalent finite-time thermodynamics of the heat exchanger.Then,based on the actual working state of the counterflow heat exchanger,the useful energy loss and overall entransy dissipation of each stage in heat transfer are calculated,and finally,the corrected "entransy loss number NgHE" is obtained to characterize the heat exchanger’s overall degree of useful energy loss.The findings indicate that the revised model and theory can more accurately account for the impact of each heat transfer process,and they offer objective functions and theoretical advice for optimizing the tube and shell sides of a heat exchanger at the same time.A two-layer cyclic model for simultaneous optimization of structural parameters and flow conditions as well as separate layer modeling of helically coiled tube heat exchanger(HCT HE)was developed.The Multi-Objective Genetic Algorithm is utilized to accomplish the multi-layer structure,multi-layer loop,and multi-objective function optimization.The entransy loss number,performance evaluation criteria,and field synergy numbers are employed as optimization criteria.First,the helically coiled plain tube(HCPT)heat exchanger’s hydraulic performance,thermal performance,comprehensive performance,field synergy performance,and useful energy loss analysis are examined.A helically coiled-twisted trilobal tube(HCTTT)heat exchanger is suggested and its better performance is shown to enhance the low flow zone and low heat exchange zone between the HCPT heat exchanger tubes.The sensitivity analysis obtains the priority factors in the optimization under different objectives,the single factor analysis obtains the changes of different performance parameters with a single factor,and the 3D response surface analysis obtains the effect of design parameters on each performance under pairwise coordination in the optimization of the two types of heat exchangers.Finally,it is demonstrated that the entransy loss number can effectively optimize the heat exchange process and increase the overall heat exchange of the heat exchanger,and the correlation equations of flow and heat transfer in the tube and shell sides are obtained under the conditions of 4000≤Res≥80000,2800 ≤Ret≤40000,with a maximum error of 9.17 percent between the experimental data and the theoretical data.The experimental platform was developed and constructed,and the HCPT and HCTTT heat exchangers were tested in the lab.The two heat exchangers’ original size models were created,and then numerical simulations were run to compare and evaluate the flow performance,thermal performance,and overall performance of the two heat exchangers.The findings indicate that the measurement error is less than 4%,with the shell side pressure drop error being 3.72 percent to 9.13 percent and the tube side pressure drop error being 14.78 percent to 16.09 percent in contrast to the numerical simulation.The thermal performance of the tube and shell sides of HCTTT has been improved,according to the experimental comparison of the two heat exchangers;the comprehensive evaluation criteria and field synergy number of HCTTT are higher than those of HCPT,the performance evaluation criteria of the tube is 12 percent to 18 percent higher,and that of the shell side is 6 percent to 10%higher,the field synergy numbers of the tube side and the shell side can be increased by 19%and 22.6%at the maximum,and the entransy loss number can be reduced by 10.64%at the maximum.The velocity and temperature fields are used to investigate the strengthening process.Using the criteria of optimum structural molding,various modeling techniques are suggested and chosen,with the numerical method validated by experiment coupled with MO-SHERPA being utilized to carry out the shape optimization using 120,000 sets of different cross-sections under the same heat exchange region.For MO-SHERPA optimization,a model for this chapter is created,the heat exchanger’s thermodynamic model is simplified,and the modified entransy loss number NgHE is coupled with PEC and Fc.The findings indicate that using the suggested modeling approach in combination with MO-SHERPA may successfully prevent sharp phenomena in the structure,with clear benefits in terms of optimized structure search and optimal structure search time.Multi-objective optimization yields optimum solutions for a variety of goals,allowing for greater flexibility in selecting optimization outcomes under various working circumstances.The performance evaluation criteria of the tube side are increased by 22 percent,and the entransy loss number can be reduced by up to 66 percent,according to a comparative analysis of different heat exchangers in the same heat exchange area;the performance evaluation criteria of the shell side are increased by 4 percent to 20%,and the advantages of OPT in comprehensive performance ar increased by 4 percent to 20%,and the advantages of OPT in comprehensive performance ar increased by 4 percent to 20%with the increase of mass flow.Moreover,the creation of the internal secondary flow is discovered to be strongly linked to the increase of the tube and shell sides of the heat exchanger.The topology optimization of the helically coiled tube heat exchanger(Bi-fluid heat exchanger)is achieved utilizing the "multi-material" model and various values of a single design variable to describe distinct fluid-solid states using the FEM framework linked MM A algorithm.The exploration process reveals that the method of selecting design variables,the superposition of the two-fluid flow field,which is then solved separately,and finally the heat-fluid coupling is the key to two-fluid separation;increasing the coefficient q*of RAMP interpolation and decreasing the order p of SIMP interpolation within a certain range will inhibit fluid interaction.Under the condition of no wall penetration,the 2D optimum design indicates that raising the allowed pressure drop of the flow channel,increasing the ratio of convective heat transfer and heat conduction,and decreasing fluid viscosity may improve heat transfer.The topology optimization structure is in the shape of a "tree" in the 3D optimum design,and the overall performance may be improved by raising the intake pressure or velocity within the allowed range.The flow resistance of the TO structure is 22.7 percent 30.5 percent higher than that of an ordinary tube heat exchanger,but the heat transfer performance increases by 65.8 percent 78.1 percent,and the comprehensive performance increases by 42.46 percent 75 percent,according to the performance comparison.The discrete method’s verification reveals that the FEM technique’s objective function value is 2.24 percent higher than the finite volume method(FVM)and 4.26 percent higher than the Boltzmann approach for the identical standard scenario(LBM).