Experimental investigation of mixed convection in a rectangular duct with a heated plate in the middle of cross section
- 161 Downloads
- 7 Citations
Abstract
The flow and heat transfer in an inclined and horizontal rectangular duct with a heated plate longitudinally mounted in the middle of cross section was experimentally investigated. The heated plate and rectangular duct were both made of highly conductive materials, and the heated plate was subjected to a uniform heat flux. The heat transfer processes through the test section were under various operating conditions: Pr ≈ 0.7, inclination angle ϕ = −60° to +60°, Reynolds number Re = 334–1,911, Grashof number Gr = 5.26 × 102–5.78 × 106. The experimental results showed that the average Nusselt number in the entrance region was 1.6–2 times as large as that in the fully developed region. The average Nusselt numbers and pressure drops increased with the Reynolds number. The average Nusselt numbers and pressure drops decreased with an increase in the inclination angle from −60° to +60° when the Reynolds number was less than 1,500. But when the Reynolds number increased to over about 1,800, the heat transfer coefficients and pressure drops were independent of inclination angles.
Keywords
Heat Transfer Reynolds Number Nusselt Number Test Section Inclination AngleList of symbols
- Asum
area sum of the rectangular duct inner surface and heated plate (m2)
- b
thickness of the insulation (m)
- De
equivalent diameter of the test section (m)
- f
friction factor
- Gr
Grashof number
- Gz
Graetz number
- I
current across the heated plate (A)
- k
thermal conductivity [W/(m K)]
- L
length of the test section (m)
- Num
average Nusselt number of the test section
- Pr
Prandtl number
- qcond
conductive heat loss (W/m2)
- qconv
convective heat loss (W/m2)
- qrad
radiant heat loss (W/m2)
- qtot
total heat flux generated by the heated plate (W/m2)
- Re
Reynolds number
- \({\overline{T}_{\rm air}}\)
average air temperature across the test section (K)
- \({\overline{T}_{\rm ins}}\)
average surface temperature of the insulation material (K)
- \({\overline{T}_{\rm p}}\)
average temperature of the heated plate and duct walls (K)
- u
average air velocity (m/s)
- U
voltage drop across heated plate (V)
Greek symbols
- β
thermal expansion coefficient (1/K)
- μ
dynamic viscosity (kg/m s)
- ν
kinematic viscosity (m2/s)
- ρ
density (kg/m3)
- ϕ
inclination angle of the test section (°)
Notes
Acknowledgments
This work was supported by National Natural Science Foundation of China (grant number 50506024)
References
- 1.Lin WL, Lin TF (1996a) Experimental study of unstable mixed convection of air in a bottom heated horizontal rectangular duct. Int J Heat Mass Transf 39:1649–1663CrossRefGoogle Scholar
- 2.Lin WL, Lin TF (1996b) Unstable aiding and opposing mixed convection of air in a bottom-heated rectangular duct slightly inclined from the horizontal. ASME J Heat Transf 118:47–55Google Scholar
- 3.Ozsunar A, Baskaya S, Sivrioglu M (2002) Experimental investigation of mixed convection heat transfer in a horizontal and inclined rectangular channel. Heat Mass Transf 38:271–278CrossRefGoogle Scholar
- 4.Gian LM (2000) Analytical determination of the temperature distribution and Nusselt numbers in rectangular ducts with constant axial heat flux. Int J Heat Mass Transf 43:741–755MATHCrossRefGoogle Scholar
- 5.Barletta A (2002) Fully developed mixed convection and flow reversal in a vertical rectangular duct with uniform wall heat flux. Int J Heat Mass Transf 45:641–654MATHCrossRefGoogle Scholar
- 6.Ramachandran N, Armaly BF, Chen TS (1987) Measurements of laminar mixed convection flow adjacent to an inclined surface. ASME J Heat Transf 109:146–150CrossRefGoogle Scholar
- 7.Abu-Mulaweh HI (2003) Measurements of laminar mixed convection flow adjacent to an inclined surface with uniform wall heat flux. Int J Therm Sci 42:57–62CrossRefGoogle Scholar
- 8.Yang SM, Tao WQ (1998) Heat transfer, 3rd edn. Higher Eduction Press, BeijingGoogle Scholar
- 9.Brown CK, Gauvin WH (1965) Combined free-forced convection, I, II. The Can J Chem Eng 43:306–312, 313–318Google Scholar
- 10.Om Parkash Modi (1972) Application of a hybrid computer technique and variational method to solve the flow in the entrance region of a circular tube with variable physical properties. Ph.D. Thesis, University of Ottawa, CanadaGoogle Scholar
- 11.Jicha M, Ramik Z (1982) Turbulent boundary layer heat transfer in the entrance region of a pipe. Proc Seventh Int Heat Transf Conf 3:45–49Google Scholar
- 12.Zueco J, Alhama F, González Fernández CF (2004) Analysis of laminar forced convection with network simulation in thermal entrance region of ducts. Int J Therm Sci 43:443–451CrossRefGoogle Scholar
- 13.Cheng C-H, Weng C-J, Aung W (2000) Buoyancy-assisted flow reversal and convective heat transfer in entrance region of a vertical rectangular duct. Int J Heat Fluid Flow 21:403–411CrossRefGoogle Scholar
- 14.Shah RK, London AL (1974) Thermal boundary conditions and some solutions for laminar duct flow forced convection. ASME J Heat Transf 96:159–165Google Scholar
- 15.Shah RK, London AL (1978) Supplement 1—laminar flow forced convection in ducts. In: Advances in heat transfer, Academic, New YorkGoogle Scholar
- 16.Moffat RJ (1988) Describing the uncertainties in experimental results. Exp Therm Fluid Sci 1:3–17CrossRefGoogle Scholar
- 17.Holman JP (2002) Heat transfer, 9th edn. McGraw-Hill, New YorkGoogle Scholar
- 18.Metais B, Eckert ERG (1964) Forced, mixed, and free convection regimes. ASME J Heat Transf 86:295–296Google Scholar