Experimental Study On The Effects Of Mechanical Vibration On Heat Transfer Characteristics Of Tubular Laminar Flow

The instable problems exist commonly in the flow and heat transfer process,such as the flow field instability caused by fluid pulsation,the deviation of heat transfer induced by solid wall vibration,and the instability of bubble motion caused by ultrasonic vibration in two phase flow.Thereinto,the instability caused by a coupling effect between mechanical vibration and heat transfer is a more common phenomenon.The indistinct of their relationship will affect the fluid flow and heat transfer process,influence the design accuracy and quality of heat exchangers,and cause economic losses and security issues.In a separate discipline,heat transfer and mechanical vibration have been both studied extensively,and abundant valuable results were obtained.However,the combination studies are few and needed to be further explored In this thesis,the effect of flutter of aircraft on heat transfer characteristics is taken as a point of penetration,and the laminar convective heat transfer in three different types of tubes is studied.A wide frequency vibration investigation of heat transfer characterisitics is carried out experimentally.The specific research work was concluded as shown in the following 4 points:1)Design and build a wide frequency vibration experiment platform.The heat transfer model under a wide frequency vibration was estabilished,and the fluid flow and mechanical vibration parameters were determined such as the temperature,fluid flow velocity and vibration acceleration..The system fluid flow Re number,heat flux Q,heat transfer coefficient h and the Nu number uncertainties were analyzed and uncertainty errors were obtained.2)Determine the mechanical transient dynamic characteristics in three types of tubes under a sweep frequency condition.The time domain signal of acceleration was measured by an accelerometer.A Matlab program coupling with the fast Fourier transform(FFT)method was used to transfer the time domain acceleration signal to a frequency domain acceleration signal.The frequency domain signal was then captured and analyzed.Finally,the resonance frequency of each tube was obtained.3)Mechanical vibration on laminar convective heat transfer in a smooth circular tube was investigated experimentally.The effects of vibration acceleration,vibration frequency and fluid Reynolds number on the heat transfer coefficient and the enhancement percentage were studied.A relational expression of the vibration frequency,vibration acceleration and fluid flow Reynolds number were fitted on the vibration heat transfer coefficient.4)The effect of mechanical vibration on laminar heat transfer in microfinned tube and corrugated tube were investigated,which considered the vibration acceleration,vibration frequency and fluid flow Reynolds number.The cause for the heat transfer enhancement was analyzed and the influence of different Rayleigh number(or different power input)was considered.Finally,the influence of mechanical vibration on heat transfer in different tubes was compared,and the general law of vibration effects on heat transfer was summarized.