Pressure drop, local heat transfer coefficient, and critical heat flux of DNB type for flow boiling in a horizontal stra
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ORIGINAL
Pressure drop, local heat transfer coefficient, and critical heat flux of DNB type for flow boiling in a horizontal straight tube with R-123 P. N. Tank 1 & B. K. Hardik 2 & Arunkumar Sridharan 1 & S. V. Prabhu 1 Received: 5 May 2019 / Accepted: 31 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract As far as design safety and operation of heat exchangers with a horizontal flow are concerned, it is necessary to study local heat transfer coefficient, boiling pressure drop, and critical heat flux for flow in a horizontal tube. In the present experimental work, local axial distribution of heat transfer coefficient, two-phase pressure drop, and critical heat flux for the flow boiling in a horizontal straight tube with R-123 as working fluid has been studied. Experiments are performed in horizontal tubes of diameter 11.9 mm and wall thickness 0.4 mm of SS304, having a heated length of 400 mm, 600 mm, and 1000 mm for the mass flux of 180 to 1210 kg/ m2s. The local wall temperature is measured using the Infra-Red thermal imaging technique. The local heat transfer coefficients are compared with six different well-known correlations. Also, the two-phase frictional pressure drop is measured and compared with eight different general correlations. In the present study, a sudden rise in wall temperature at any location of a test section is considered as the occurrence of a boiling crisis. The boiling crisis mechanism observed in the present study is of departure from nucleate boiling (DNB). It takes place in the subcooled, or low quality saturated boiling region and in-between the length of the test sections rather than at exit as in the dry-out type of CHF. The critical heat flux is compared with six different predictive correlations. The mechanism of occurrence of CHF in the present work is found to be a departure from nucleate boiling. Keywords Departure from nucleate boiling . CHF . Local heat transfer coefficient . Two-phase frictional pressure drop . Infra-red thermal imaging technique . Horizontal
* S. V. Prabhu [email protected] P. N. Tank [email protected] B. K. Hardik [email protected] Arunkumar Sridharan [email protected] 1
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, India
2
Department of Mechanical Engineering, Indian Institute of Technology Jodhpur, Jodhpur, India
Nomenclature Symbol Definition Cp Specific heat at constant pressure d Tube diameter f Friction factor G Mass flux g Acceleration due to gravity h Heat transfer coefficient h* Fully developed subcooled heat transfer coefficient hf Enthalpy of sensible heat hfg Enthalpy of latent heat I Current k Thermal conductivity L, l Length LCC Local condition correlation ˙ m, Mass flow rate P Pressure p Perimeter Pr Reduced Pressure (Psys / Pcr)
Unit J/kgK. m Dimensionless kg/m2s m2/s W/m2K W/m2K J/kg J/kg A W/mK m Dimensionless kg/s N/m2 m Dimensionless
Heat Mass Transfer
Q′ r q′′ T UCC V X
Heat supply W Radius m Heat flux W/m2 Temperature °C Upstream condition
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