BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

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82 Gelu Coman and Valeriu Damian h ⎧CT T< T s f = ⎨ CT l T ≥ T ⎬ f ⎩ ⎫ , (6) ⎭ h= h + ∫ c dT , (7) ref T Tref p where: T f – solidification temperature, C s ,C l – specific heat for the solid and liquid phases, h – sensitive enthalpy, T ref – reference temperature.h ref – reference enthalpy, c p – specific heat at constant pressure 3. Numerical Results With numerical simulation of ice formation around the pipe submerged in water, a number of 25 210 iterations were made at a time step τ = 10 seconds. The total process running time was 7 hours, considering the process conclusion at the ice free surface temperature of -5,55 0 C. For the pipe is buried in sand a number of 18.000 iterations at a time step of 10 s were carried out . The time taken for solidification process was 5 hours, considering the process complete at an ice free surface temperature of -4,62 0 C. Initialized parameters in the mathematical model were: a) water temperature on the skating track t apa = 10 0 C b) air temperature at the water free surface t aer = 10 0 C c) temperature of the refrigerating agent inside the pipe t agent = -10 0 C d) mass flow fate fo the refrugerating agent m = 0.185 kg/s e) convection coefficient in the pipe α agent = 550 W/m 2 K f) air Convection coefficient on water surface α aer = 15W/m 2 K g) heat flow density o the track foundation board q= 10W/m 2 . Figs. 2 and 3 illustrate the time variation of the water surface temperature in the two cases analyzed: tube submerged in the water and pipe buried in sand. When immersed in water (Fig. 2) there is a sharp decrease in temperature in the nodes above the pipe and a slower decrease in the points located midway between the pipes. Under isothermal 0 0 C after τ = 300min, there is an almost constant distribution in nodes. When the pipe is buried in the sand Fig.3 there is a more rapid decrease in temperature compated with the pipe submerged in water. Isothermal 0 0 C reaches the water surface after approximately 90 minutes. Temperature distribution in the water surface nodes is almost uniform under isothermal 0 0 C, indicating a high quality of the ice.
Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 3, 2012 83 t[ 0 C] x[m] Fig. 2 – Temperature variation on the water surface at pipe submerged in water. t[ 0 C] x[m] Fig.3 – Temperature variation on the water surface at pipe buried in the sand. In Figs.5 and 6 are shown pictures of temperature distribution over time for the water immersed pipe. It can be noticed the different distribution over the 2 axis, due to different boundary conditions and also due to external influences.
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BULETINUL INSTITUTULUI POLITEHNIC D
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BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

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