Abstract
The study examined heat transfer of two dilute viscoelastic solutions in helical exchangers of circular cross-section. Ten helical coil heat exchangers with diameter ratios ranging from 4 to 50 were constructed. Results showed doubling the concentrations of polymer increased heat transfer performance by 12 %. The results were expressed in forms of some existing equations and were found to be in fair agreement to previous results.
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Abbreviations
- cp :
-
Specific heat
- d:
-
Tube diameter
- D:
-
Helix diameter of curvature
- Dn:
-
Dean number (Re(di/D)0.5)
- Gz:
-
Graetz number (mcp/kL)
- h:
-
Heat transfer coefficient
- hs :
-
Heat transfer coefficient, straight tube
- hc :
-
Heat transfer coefficient, curved tube
- k:
-
Thermal conductivity
- L:
-
Length
- m:
-
Mass
- Nu:
-
Nusselt number (hd/k)
- q:
-
Heat flux
- Q:
-
Volumetric flow rate (m3/s)
- Re:
-
Reynolds number (dvρ/μ)
- Pr:
-
Prandtl number (cpμ/k)
- T1 :
-
Inlet temp (°C)
- T2 :
-
Outlet temp (°C)
- Tw :
-
Average wall temp (°C)
- U:
-
Overall heat transfer coefficient
- v:
-
Velocity
- W:
-
Watt
- ρ:
-
Density
- μ:
-
Viscosity
- s:
-
Straight
- c:
-
Curved
- w:
-
Wall
- 1:
-
Inlet
- 2:
-
Outlet
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Appendix: Error estimates
Appendix: Error estimates
Density of water at 20 °C = 0.9982 g/l
Density of water at 40 °C = 0.9922 g/l
Error in assuming constant density = 0.006/0.9952 approximately = 0.5 %
Average flowrate = 10 ml/s
The gear pump was calibrated to read up to an accuracy of 0.2 ml/s
Average error in measuring volumetric flowrate = 0.2/10 approximately = 2 %
Error in obtaining mass flowrate = (0.5 + 2)% = 2.5 %
Error in assuming constant specific heat = 0.004/1.000 approximately = 0.5 %
Thermal conductivity at 285 K = 0.5818 w/(mK)
Thermal conductivity at 300 K = 0.6096 w/(mK)
Error in assuming constant thermal conductivity = 0.0278/0.5957 approximately = 5 %
Average length of exchanger tubes = 74.81 cm
Estimated error in length = 0.5/74.81 approximately = 0.5 %
Average error in Graetz Number (mcp/kL) = (2.5 + 0.5 + 5 + 0.5) % = 8.5 %
Average internal diameter is obtained by back-calculating from internal volumes and length of tubes. This gives an error of less than 2 %.
Velocity is proportional to Flowrate/(diameter)2
Error in velocity = (2.5 + 4) % = 6.5 %
Variations of viscosities and temperature for the solutions were experimentally determined.
Estimated error in reading from the calibration curves is about 1 %
Estimated error in Reynolds Number = (2 + 6.5 + 1) % = 9.5 %
Average diameter of curvature = 141.4 mm
Error in diameter of curvature = 0.5/141.4 approximately = 0.4 %
Error in Dean Number [Re(di/D)0.5] = [9.5 + (2 + 0.4)/2] % = 10.7 %
Overall error in Prandtl Number (cpμ/k) = (0.5 + 1 + 5) % = 6.5 %.
Error associated with using the Mori and Nakayama form = [(8.5/3) + (10.7/2)] % = 8.18 %
Error associated with using the Dravid form = [(10.7/2) + (6.5 × 0.175)] % = 6.5 %
Error associated with using the Cengiz form = [(10.7 × 0.864) + (6.5 × 0.4)] % = 11.8 %
Error associated with using the Kalb and Seader form = [(10.7*0.5) + (6.5*0.1)] % = 6 %.
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Ismail, Z., Karim, R. Heat transfer of dilute viscoelastic solutions in helical exchangers. Heat Mass Transfer 49, 711–721 (2013). https://doi.org/10.1007/s00231-013-1113-3
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DOI: https://doi.org/10.1007/s00231-013-1113-3