Modelica.Fluid.Dissipation.Utilities.SharedDocumentation.HeatTransfer.HelicalPipe

Package Content

Name	Description
kc_laminar
kc_overall
kc_turbulent

Modelica.Fluid.Dissipation.Utilities.SharedDocumentation.HeatTransfer.HelicalPipe.kc_laminar

Calculation of the mean convective heat transfer coefficient kc for a helical pipe in the laminar flow regime.

Functions kc_laminar and kc_laminar_KC

There are basically three differences:

• The function kc_laminar is using kc_laminar_KC but offers additional output variables like e.g. Reynolds number or Nusselt number and failure status (an output of 1 means that the function is not valid for the inputs).
• Generally the function kc_laminar_KC is numerically best used for the calculation of the mean convective heat transfer coefficient kc at known mass flow rate.
• You can perform an inverse calculation from kc_laminar_KC, where an unknown mass flow rate is calculated out of a given mean convective heat transfer coefficient kc

Restriction

• laminar regime (Reynolds number ≤ critical Reynolds number Re_crit)
• neglect influence of heat transfer direction (heating/cooling) according to Sieder and Tate

The critical Reynolds number Re_crit in a helical pipe depends on its mean curvature diameter d_coil . The smaller the mean curvature diameter of the helical pipe, the earlier the turbulent regime will start due to vortexes out of higher centrifugal forces.

Geometry

Calculation

The mean convective heat transfer coefficient kc for helical pipes is calculated through the corresponding Nusselt number Nu according to [VDI 2002, p. Gc 2, eq. 5] :

    Nu = 3.66 + 0.08*[1 + 0.8*(d_hyd/d_coil)^0.9]*Re^m*Pr^(1/3)

with the exponent m for the Reynolds number

    m = 0.5 + 0.2903*(d_hyd/d_coil)^0.194

and the resulting mean convective heat transfer coefficient kc

    kc =  Nu * lambda / d_hyd

with

Verification

The mean Nusselt number Nu representing the mean convective heat transfer coefficient kc is shown below for different numbers of turns n_nt at constant total length of the helical pipe.

The convective heat transfer of a helical pipe is enhanced compared to a straight pipe due to occurring turbulences resulting out of centrifugal forces. The higher the number of turns, the better is the convective heat transfer for the same length of a pipe.

Note that the ratio of hydraulic diameter to total length of helical pipe d_hyd/L has no remarkable influence on the coefficient of heat transfer kc .

References

GNIELINSKI, V.:

Heat transfer and pressure drop in helically coiled tubes.. In 8th International Heat Transfer Conference, volume 6, pages 2847-2854, Washington,1986. Hemisphere.

Modelica.Fluid.Dissipation.Utilities.SharedDocumentation.HeatTransfer.HelicalPipe.kc_overall

Calculation of the mean convective heat transfer coefficient kc of a helical pipe in a hydrodynamically developed laminar and turbulent flow regime.

Functions kc_overall and kc_overall_KC

There are basically three differences:

• The function kc_overall is using kc_overall_KC but offers additional output variables like e.g. Reynolds number or Nusselt number and failure status (an output of 1 means that the function is not valid for the inputs).
• Generally the function kc_overall_KC is numerically best used for the calculation of the mean convective heat transfer coefficient kc at known mass flow rate.
• You can perform an inverse calculation from kc_overall_KC, where an unknown mass flow rate is calculated out of a given mean convective heat transfer coefficient kc

Geometry and Calculation

This heat transfer function enables a calculation of heat transfer coefficient for laminar and turbulent flow regime. The geometry, constant and fluid parameters of the function are the same as for kc_laminar and kc_turbulent.

The calculation conditions for laminar and turbulent flow is equal to the calculation in kc_laminar and kc_turbulent. A smooth transition between both functions is carried out between 2200 ≤ Re ≤ 30000 (see figure below).

Verification

The mean Nusselt number Nu representing the mean convective heat transfer coefficient kc is shown below for different numbers of turns n_nt at constant total length of the helical pipe.

The convective heat transfer of a helical pipe is enhanced compared to a straight pipe due to occurring turbulences resulting out of centrifugal forces. The higher the number of turns, the better is the convective heat transfer for the same length of a pipe.

Note that the ratio of hydraulic diameter to total length of helical pipe d_hyd/L has no remarkable influence on the coefficient of heat transfer kc .

References

GNIELINSKI, V.:

Heat transfer and pressure drop in helically coiled tubes.. In 8th International Heat Transfer Conference, volume 6, pages 2847?2854, Washington,1986. Hemisphere.

Modelica.Fluid.Dissipation.Utilities.SharedDocumentation.HeatTransfer.HelicalPipe.kc_turbulent

Calculation of the mean convective heat transfer coefficient kc of a helical pipe for turbulent flow regime.

Functions kc_turbulent and kc_turbulent_KC

There are basically three differences:

• The function kc_turbulent is using kc_turbulent_KC but offers additional output variables like e.g. Reynolds number or Nusselt number and failure status (an output of 1 means that the function is not valid for the inputs).
• Generally the function kc_turbulent_KC is numerically best used for the calculation of the mean convective heat transfer coefficient kc at known mass flow rate.
• You can perform an inverse calculation from kc_turbulent_KC, where an unknown mass flow rate is calculated out of a given mean convective heat transfer coefficient kc

The critical Reynolds number Re_crit in a helical pipe depends on its mean curvature diameter. The smaller the mean curvature diameter of the helical pipe d_mean , the earlier the turbulent regime will start due to vortexes out of higher centrifugal forces.

Geometry

Calculation

The mean convective heat transfer coefficient kc for helical pipes is calculated through the corresponding Nusselt number Nu according to [VDI 2002, p. Ga 2, eq. 6]:

    Nu = (zeta_TOT/8)*Re*Pr/{1 + 12.7*(zeta_TOT/8)^0.5*[Pr^(2/3)-1]},

where the influence of the pressure loss on the heat transfer calculation is considered through

    zeta_TOT = 0.3164*Re^(-0.25) + 0.03*(d_hyd/d_coil)^(0.5) and

and the resulting mean convective heat transfer coefficient kc

    kc =  Nu * lambda / d_hyd

with

Verification

The mean Nusselt number Nu representing the mean convective heat transfer coefficient kc is shown below for different numbers of turns n_nt at constant total length of the helical pipe.

The convective heat transfer of a helical pipe is enhanced compared to a straight pipe due to occurring turbulences resulting out of centrifugal forces. The higher the number of turns, the better is the convective heat transfer for the same length of a pipe.

Note that the ratio of hydraulic diameter to total length of helical pipe d_hyd/L has no remarkable influence on the coefficient of heat transfer kc .

References

GNIELINSKI, V.:

Heat transfer and pressure drop in helically coiled tubes.. In 8th International Heat Transfer Conference, volume 6, pages 2847?2854, Washington,1986. Hemisphere.