No abstract

Experimental and theoretical studies were performed on flow boiling critical heat flux of R134a in helically coiled tubes. The experiments were carried out at the range of pressure from 0.4MPa to 1.05MPa, with the refrigerant mass flux from 51 to 257kg·m -2 ·s -1 and the vapor quality ranging from 0.18 to 0.43. The experiment results show that the flow boiling critical heat flux in helically-coiled tubes increased with increases in the mass flux and decreased with the increasing of system pressure. Under the experimental conditions it was discovered that the compensation distortion models, such as Merilo model and Katto model, were not suitable to critical heat flux of R134a modeling in helically-coiled horizontal tubes, with error deviations beyond 30%. The centrifugal force and buoyancy force produced during the refrigerant flowing process in helically-coiled horizontal tubes may have strong influences on the critical heat flux fluid to fluid model. A new correlation for flow boiling critical heat flux prediction of R134a in helically-coiled tubes was proposed. It was found that the calculated results from the proposed correlation agreed well with the experimental critical heat flux data in the experimental conditions tested.

In order to enlarge the application scope of the existing criteria for the heat transfer deterioration, the criteria of heat transfer deterioration was assessed by using the method of mechanism analysis and experimental data available in the literature. The obtained results indicated that the criteria based on q = f (G, D) are more useful for practical applications.