A formulation of the fin efficiency based on New- ton＇s law of cooling is compared with a formulation based on a ratio of heat transferred from the fin surface to the sur- rounding fluid to the heat conducted through...A formulation of the fin efficiency based on New- ton＇s law of cooling is compared with a formulation based on a ratio of heat transferred from the fin surface to the sur- rounding fluid to the heat conducted through the base. The first formulation requires that the solution of the nonlinear fin equations for constant heat transfer coefficient and constant thermal conductivity is known, whilst the second formulation of the fin efficiency requires only that a first integral of the model equation is known. This paper shows the first for- mulation of the fin efficiency contains approximation errors as only power series and approximate solutions to the non- linear fin equations have been determined. The second for- mulation of the fin efficiency is exact when the first integrals can be determined.展开更多
Numerical simulation is investigated to disclose how propeller boss cap fins （PBCF） operate utilizing Reynolds-averaged Navier-Stokes （RANS） method. In addition, exploration of the influencing mechanism of PBCF on...Numerical simulation is investigated to disclose how propeller boss cap fins （PBCF） operate utilizing Reynolds-averaged Navier-Stokes （RANS） method. In addition, exploration of the influencing mechanism of PBCF on the open water efficiency of one controllable-pitch propeller is analyzed through the open water characteristic curves, blade surface pressure distribution and hub streamline distribution. On this basis, the influence of parameters including airfoil profile, diameter, axial position of installation and circumferential installation angle on the open water efficiency of the controllable-pitch propeller is investigated. Numerical results show： for the controllable-pitch propeller, the thrust generated is at the optimum when the radius of boss cap fins is 1.5 times of propeller hub with an optimal installation position in the axial direction, and its optimal circumferential installation position is the midpoint of the extension line of the front and back ends of two adjacent propeller roots in the front of fin root. Under these optimal parameters, the gain of open water efficiency of the controllable-pitch propeller with different advance velocity coefficients is greater than 0.01, which accounts for approximately an increase of 1%-5% of open water efficiency.展开更多
Pin fins are widely used in applications where effective heat transfer is crucial.Their compact design,high surface area,and efficient heat transfer characteristics make them a practical choice for many thermal manage...Pin fins are widely used in applications where effective heat transfer is crucial.Their compact design,high surface area,and efficient heat transfer characteristics make them a practical choice for many thermal management applications.But for a high heat transfer rate and lightweight application,aerofoil shape pin fins are a good option.This work focuses on an experimental model analysis of pin-fins with aerofoil shapes.The results were evaluated between perforation,no perforation,inline,and staggered fin configurations.Aluminum is used to make the pin fins array.The experiment is carried out inside a wind tunnel,and the heat supply varies between 500 to 3000 W.An electric heater,fan,anemometer,thermocouple,pressure transmitter,data logger,and computer system were used for this experiment.The friction factor,thermal efficiency,performance efficacy,and pressure drop of a pin fin aerofoil shape have been assessed.A comparison study was carried out with and without perforations and inline and staggered arrangements.In terms of overall efficacy,different aerofoil shape pin fin arrays achieve values varying between 1.8 and 14.7.The acquired data demonstrate that perforated staggered configurations perform 10%better than inline.Furthermore,the pressure drop is reduced by 50%in staggered setups.The empirical correlation of Dittus-Bolter and Blasius correlations was used to validate the experimental heat dissipation enhancement factor requirements of Nusselt number and friction factor.The validation of the experiment using correlation has been completed satisfactorily.Hence,experimental results prove that aerofoil pin-fin arrays can be used successfully for applications like the electronics industry,heat exchangers and gas turbine blade cooling.展开更多
The entransy theory developed in recent years is used to optimize the aspect ratio of a plate fin in heat convection.Based on a two-dimensional model,the theoretical analysis shows that the minimum thermal resistance ...The entransy theory developed in recent years is used to optimize the aspect ratio of a plate fin in heat convection.Based on a two-dimensional model,the theoretical analysis shows that the minimum thermal resistance defined with the concept of entransy dissipation corresponds to the maximum heat transfer rate when the temperature of the heating surface is fixed.On the other hand,when the heat flux of the heating surface is fixed,the minimum thermal resistance corresponds to the minimum average temperature of the heating surface.The entropy optimization is also given for the heat transfer processes.It is observed that the minimum entropy generation,the minimum entropy generation number,and the minimum revised entropy generation number do not always correspond to the best heat transfer performance.In addition,the influence factors on the optimized aspect ratio of the plate fin are also discussed.The optimized ratio decreases with the enhancement of heat convection,while it increases with fin thermal conductivity increasing.展开更多
In this paper,differential transform method(DTM)is used to solve the nonlinear heat transfer equation of a fin with the power-law temperature-dependent both thermal conductivity and heat transfer coefficient.Using DTM...In this paper,differential transform method(DTM)is used to solve the nonlinear heat transfer equation of a fin with the power-law temperature-dependent both thermal conductivity and heat transfer coefficient.Using DTM,the differential equation and the related boundary conditions transformed into a recurrence set of equations and finally,the coefficients of power series are obtained based on the solution of this set of equations.DTM overcame on nonlinearity without using restrictive assumptions or linearization.Results are presented for the dimensionless temperature distribution and fin efficiency for different values of the problem parameters.DTM results are compared with special case of the problem that has an exact closed-form solution,and an excellent accuracy is observed.展开更多
文摘A formulation of the fin efficiency based on New- ton＇s law of cooling is compared with a formulation based on a ratio of heat transferred from the fin surface to the sur- rounding fluid to the heat conducted through the base. The first formulation requires that the solution of the nonlinear fin equations for constant heat transfer coefficient and constant thermal conductivity is known, whilst the second formulation of the fin efficiency requires only that a first integral of the model equation is known. This paper shows the first for- mulation of the fin efficiency contains approximation errors as only power series and approximate solutions to the non- linear fin equations have been determined. The second for- mulation of the fin efficiency is exact when the first integrals can be determined.
基金Supported by the National Natural Science Foundation of China under Grant No.51079157
文摘Numerical simulation is investigated to disclose how propeller boss cap fins （PBCF） operate utilizing Reynolds-averaged Navier-Stokes （RANS） method. In addition, exploration of the influencing mechanism of PBCF on the open water efficiency of one controllable-pitch propeller is analyzed through the open water characteristic curves, blade surface pressure distribution and hub streamline distribution. On this basis, the influence of parameters including airfoil profile, diameter, axial position of installation and circumferential installation angle on the open water efficiency of the controllable-pitch propeller is investigated. Numerical results show： for the controllable-pitch propeller, the thrust generated is at the optimum when the radius of boss cap fins is 1.5 times of propeller hub with an optimal installation position in the axial direction, and its optimal circumferential installation position is the midpoint of the extension line of the front and back ends of two adjacent propeller roots in the front of fin root. Under these optimal parameters, the gain of open water efficiency of the controllable-pitch propeller with different advance velocity coefficients is greater than 0.01, which accounts for approximately an increase of 1%-5% of open water efficiency.
文摘Pin fins are widely used in applications where effective heat transfer is crucial.Their compact design,high surface area,and efficient heat transfer characteristics make them a practical choice for many thermal management applications.But for a high heat transfer rate and lightweight application,aerofoil shape pin fins are a good option.This work focuses on an experimental model analysis of pin-fins with aerofoil shapes.The results were evaluated between perforation,no perforation,inline,and staggered fin configurations.Aluminum is used to make the pin fins array.The experiment is carried out inside a wind tunnel,and the heat supply varies between 500 to 3000 W.An electric heater,fan,anemometer,thermocouple,pressure transmitter,data logger,and computer system were used for this experiment.The friction factor,thermal efficiency,performance efficacy,and pressure drop of a pin fin aerofoil shape have been assessed.A comparison study was carried out with and without perforations and inline and staggered arrangements.In terms of overall efficacy,different aerofoil shape pin fin arrays achieve values varying between 1.8 and 14.7.The acquired data demonstrate that perforated staggered configurations perform 10%better than inline.Furthermore,the pressure drop is reduced by 50%in staggered setups.The empirical correlation of Dittus-Bolter and Blasius correlations was used to validate the experimental heat dissipation enhancement factor requirements of Nusselt number and friction factor.The validation of the experiment using correlation has been completed satisfactorily.Hence,experimental results prove that aerofoil pin-fin arrays can be used successfully for applications like the electronics industry,heat exchangers and gas turbine blade cooling.
基金Project supported by the National Natural Science Foundation of China (Grant No. 51106082)the Tsinghua University Initiative Scientific Research Program
文摘The entransy theory developed in recent years is used to optimize the aspect ratio of a plate fin in heat convection.Based on a two-dimensional model,the theoretical analysis shows that the minimum thermal resistance defined with the concept of entransy dissipation corresponds to the maximum heat transfer rate when the temperature of the heating surface is fixed.On the other hand,when the heat flux of the heating surface is fixed,the minimum thermal resistance corresponds to the minimum average temperature of the heating surface.The entropy optimization is also given for the heat transfer processes.It is observed that the minimum entropy generation,the minimum entropy generation number,and the minimum revised entropy generation number do not always correspond to the best heat transfer performance.In addition,the influence factors on the optimized aspect ratio of the plate fin are also discussed.The optimized ratio decreases with the enhancement of heat convection,while it increases with fin thermal conductivity increasing.
文摘In this paper,differential transform method(DTM)is used to solve the nonlinear heat transfer equation of a fin with the power-law temperature-dependent both thermal conductivity and heat transfer coefficient.Using DTM,the differential equation and the related boundary conditions transformed into a recurrence set of equations and finally,the coefficients of power series are obtained based on the solution of this set of equations.DTM overcame on nonlinearity without using restrictive assumptions or linearization.Results are presented for the dimensionless temperature distribution and fin efficiency for different values of the problem parameters.DTM results are compared with special case of the problem that has an exact closed-form solution,and an excellent accuracy is observed.
