Abstract
Though convective heat transfer is one of the main factors that dominate the thermal characteristics of stratospheric airships, there is no specific correlation equations for the calculation of convective heat transfer of airships. The equations based on flat plate and sphere models are all in use. To ameliorate the confusing situation of diverse convective heat transfer equations and to end the misuse of them in the thermal characteristic analysis of stratospheric airships, a multinode steady-state model for ellipsoid airships is built. The accuracy of the five widely accepted equations for natural convective heat transfer is compared and analysed on the proposed large-scale airship model by numerical simulation, so does that of the five equations for external forced convective heat transfer. The simulation method is verified by the available experimental data. Simulation results show that the difference of the five natural convection equations is negligible, while that of the five external forced convection equations must be considered in engineering. Forced convection equations with high precision and wide application should be further investigated.
Highlights
Stratospheric airships are the airships conducting missions at altitudes of 20–30 km, which have a wide range of applications in military, scientific, and commercial areas, such as surveillance, intelligence and reconnaissance, aerial transportation, environmental monitoring, telecommunication relay, and emergency rescue [1,2,3]
Affected by the diurnal variation of solar radiation, the temperature distribution of airship envelope changes during a period of one day. Both external and internal surfaces of the envelope experience convective heat transfer, which accounts for a large proportion of the overall heat transfer of a stratospheric airship, thereby being the most important factors affecting the thermal characteristics of stratospheric airships
Since it seems intractable to obtain the convection heat transfer coefficient of the airship h (h = Nu λ/L ) via theoretical analysis, the coefficient is usually acquired in engineering by diverse empirical and semiempirical Nu correlation equations based on experiments
Summary
Stratospheric airships are the airships conducting missions at altitudes of 20–30 km, which have a wide range of applications in military, scientific, and commercial areas, such as surveillance, intelligence and reconnaissance, aerial transportation, environmental monitoring, telecommunication relay, and emergency rescue [1,2,3]. Rohsenow [12] provided an equation regarding Nu to the spatial position of airship envelope by using the concept of grid discretisation Some scholars, such as Carlson and Horn [13] and Morris [14], introduced the correlation equations for natural convection in the shell. To ameliorate the confusing situation of diverse convective heat transfer equations and to end the misuse of them in the thermal characteristic analysis of stratospheric airships, an ellipsoid airship model is built and the accuracy of ten widely accepted equations for convective heat transfer is compared and analysed on the proposed large-scale airship model by numerical simulation. This study provides reference for the selection and correction of convective heat transfer equations
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