An experimental study of heat transfer enhancement in an air channel with broken multi type V-baffles

Abstract

This work aims at studying the effect of broken multi type V-baffles on heat transfer, pressure drop, and thermal hydraulic performance characteristics in an air channel is experimentally investigated. The air channel had aspect ratio of 10.0 and the Reynolds number (Re) based upon the mass flow rate of air (m _a ) at entrance of the channel varied from 3000 to 8000. The discrete baffle distance (D _d /L _v ) varied from 0.27 to 0.77, relative baffle gap width (G _w /H _B ) varied from 0.50 to 1.5, relative baffle height (H _B /H _D ) varied from 0.25 to 1.0, relative baffle pitch (P _B /H _B ) varied from 8.0 to 12, relative baffle width (W _D /H _D ) varied from 1.0 to 6.0, and flow attack angle (α _a )varied from 30^° to 70^°. It has been found that performance of broken multi type V-baffles air channel is better than the performance of smooth surface air channel for the range of geometrical parameters investigated. Experimental results observed that maximum enhancement in overall thermal performance have been found at D_d/L_v value of 0.67, G_w/H_B value of 1.0, H_B/H_D value of 0.50, P _B /H _B value of 10, and α_avalue of 60°.

Appendix: uncertainty analysis calculation

Uncertainty is the possible numerical value of the error encountered during experimentation. The experimental value may differ from its true value due to presence of lot of factors which come into play during investigation. This deviation in the data of measured parameters from actual data is the uncertainty in measurement. The important parameters considered for the calculation of uncertainty are: mass flow rate, heat transfer coefficient, Nusselt number and friction factor etc. Uncertainty associated with instruments used in various measurements of parameters in the experiment is given in Table 6.

Table 6 Uncertainty intervals of various measurements

• 1. Mass flow rate

  $$ \dot{m}={C}_d\times {A}_o\times {\left[\frac{2.\rho .{\left(\Delta P\right)}_o}{1-{\psi}^4}\right]}^{0.5} $$
  $$ \dot{m}={C}_d\times {A}_o\times {\rho}^{0.5}\times {\left(\Delta P\right)}_o^{0.5}\times {\left[\frac{2}{1-{\psi}^4}\right]}^{0.5} $$
  $$ {\left[\frac{2}{1-{\beta}^4}\right]}^{0.5}= X= Cons \tan t $$
  $$ Then,\kern0.6em \dot{m}={XC}_d\;{A}_o{\rho}^{0.5}{\left(\Delta P\right)}_0^{0.5} $$
  $$ \frac{\delta\;\dot{m}}{\delta\;{C}_d}={XA}_o{\rho}^{0.5}{\left(\Delta P\right)}_o^{0.5} $$
  $$ \frac{\delta \dot{m}}{\delta {A}_o}={XC}_d{\rho}^{0.5}{\left(\Delta P\right)}_o^{0.5} $$
  $$ \frac{\delta \dot{m}}{{\delta \rho}_o}={XA}_o{C}_d0.5{\rho}^{-0.5}{\left(\Delta P\right)}_o^{0.5} $$
  $$ \frac{\delta \dot{m}}{\delta \left({\left(\Delta P\right)}_o\right)}={XA}_o{C}_d\rho 0.5{\left(\Delta P\right)}_o^{-0.5} $$
  $$ \delta \dot{m}={\left[{\left(\frac{\delta \dot{m}}{\delta {C}_d}\times \delta {C}_d\right)}^2+{\left(\frac{\delta \dot{m}}{\delta {A}_o}\times \delta {A}_o\right)}^2+{\left(\frac{\delta \dot{m}}{\delta \rho}\times \delta \rho \right)}^2+{\left(\frac{\delta \dot{m}}{\delta {\left(\Delta P\right)}_o}\times \delta {\left(\Delta P\right)}_o\right)}^2\right]}^{0.5} $$
  $$ \frac{\delta \dot{m}}{\dot{m}}={\left[{\left(\frac{\delta {C}_d}{C_d}\right)}^2+{\left(\frac{\delta {A}_o}{A_o}\right)}^2+{\left(\frac{\delta \rho}{\rho}\right)}^2+{\left(\frac{\delta {\left(\Delta P\right)}_o}{{\left(\Delta P\right)}_o}\right)}^2\right]}^{0.5} $$

  From calibration chart of orifice meter, the value of $\frac{\delta {C}_d}{C_d}$= 1.5%, the uncertainty in (ΔP)_o, for U-tube manometer is 1 mm ΔP _o  = Δh _o  sin 90 = 100 × sin 90 = 100mm

  $$ \frac{\delta\;\dot{m}}{\dot{m}}=1.73\% $$

• 2. Heat transfer coefficient

  $$ h=\frac{Q_u}{A_P.\left({T}_P-{T}_f\right)}\kern0.24em or\kern0.24em h=\frac{Q_u}{A_p.\Delta {T}_f} $$
  $$ \frac{\delta\;h}{h}={\left[{\left(\frac{\delta\;{Q}_u}{Q}\right)}^2+{\left(\frac{\delta {A}_p}{A_P}\right)}^2+{\left(\frac{\delta \left(\Delta {T}_f\right)}{\Delta {T}_f}\right)}^2\right]}^{0.5} $$
  $$ \frac{\delta\;h}{h}=3.014\% $$

• 3. Nusselt number

  $$ Nu=\frac{hD}{K} $$
  $$ \frac{\delta Nu}{Nu}={\left[{\left(\frac{\delta h}{h}\right)}^2+{\left(\frac{\delta D}{D}\right)}^2+{\left(\frac{\delta K}{K}\right)}^2\right]}^{0.5} $$
  $$ \frac{\delta Nu}{Nu}=3.2\% $$

• 4. Friction factor

  $$ {f}_r=\frac{2.{\left(\Delta P\right)}_d. D}{4.\rho . L.{V}^2} $$
  $$ \frac{\delta\;{f}_r}{f_r}={\left[{\left(\frac{\delta V}{V}\right)}^2+{\left(\frac{\delta \rho}{\rho}\right)}^2+{\left(\frac{\delta D}{D}\right)}^2+{\left(\frac{\delta L}{L}\right)}^2+{\left(\frac{\delta {\left(\Delta P\right)}_d}{{\left(\Delta P\right)}_d}\right)}^2\right]}^{0.5} $$
  $$ \frac{\delta\;{f}_r}{f_r}=3.45\% $$