Experimental study on heat and mass transfer of falling liquid films in converging-diverging tubes with water

Abstract

To improve the heat and mass transfer performances of falling films and develop a new type of falling film evaporator, the characteristics of falling film evaporation and sensible heat and mass transfer in four different sizes of converging-diverging (CD) tubes were experimentally explored in this study. By analyzing the relationship between the heat transfer coefficient and the falling film flow rate, it was found that the CD tube is suitable for falling film evaporation and sensible heating with a large Reynolds number. For different sizes of tubes, the key factor affecting the heat transfer in falling film evaporation and sensible heating is the height of the ribs. At the same rib height and rib pitch, the longer the converging segment of the CD tube, the better the heat transfer performance. According to the comparative analysis of the evaporation and sensible heating heat transfer performances inside the four CD tubes, the CD tube 3# is best. The evaporation heat transfer coefficient (at Reynolds number of liquid films of 2356), evaporation mass transfer rate (at the perimeter flow rate of liquid films is 0.173 kgm-1 s-1), and sensible heating heat transfer coefficient (at Reynolds number of liquid films of 1635) of CD tube 3# are 62%, 38% and 63% higher than that of the smooth tube, respectively. For the same CD tube, the evaporation heat transfer coefficient is larger than the sensible heating heat transfer coefficient, but both increases as the flow rate increases. The heat transfer correlations of falling film evaporation and sensible heating in the experimental range were obtained through data fitting. It will provide a useful reference for future engineering design and industrial applications.

Study of the Mechanical Properties of Highly Efficient Heat Exchange Tubes

“…Equations (6) and (7) were verified by experimental measurements. Tables 7 and 8 list the results respectively for SG tubes and CD tubes, where K E f is the stiffness equivalent factors obtained by experiments and K S f and K C f are the stiffness equivalent factors respectively obtained by Equations (6) or (7), where the error is defined as (K S f or K C f -K E f )/K E f . It is seen that the errors are less than 10%, implying that the accuracy of Equations (6) and 7is acceptable in engineering.…”

“…Kareem et al [6] presented an extensive review of numerical and experimental studies on the heat transfer enhancement of corrugated tubes, which cover laminar and turbulent flow. In order to improve the heat and mass transfer performance of falling film and develop a new type of falling film evaporator, Huang et al [7] studied the heat and mass transfer characteristics of falling film evaporation and sensible heat in four different sizes of converging-diverging tubes. Rashid et al [8] presented a novel model of a parabolic trough-based solar thermal and natural gas hybrid power plant.…”

Comparison and evaluation of supercritical CO 2 cooling performance in horizontal tubes with variable cross‐section by field synergy theory

“…Besides, varying cross-section tube such as the converging-diverging tube is also a representative and feasible method to improve and enhance the heat transfer performance. 38 For example, Wang et al 39 considered the effects of heat flux, thermal acceleration, geometric orientation, corner effect, and secondary flow on heat transfer of sCO 2 in a semicircular tube of the printed circuit heat exchanger. Some researchers have also conducted investigations in the converging-diverging tube about the heat transfer performance through experimental and numerical methods and indicated that the converging-diverging tube could improve the heat transfer efficiency effectively.…”

“…Chai et al 37 examined some influences of various cross‐sectional geometries on the thermohydraulic properties of sCO 2 . Besides, varying cross‐section tube such as the converging‐diverging tube is also a representative and feasible method to improve and enhance the heat transfer performance 38 . For example, Wang et al 39 considered the effects of heat flux, thermal acceleration, geometric orientation, corner effect, and secondary flow on heat transfer of sCO 2 in a semicircular tube of the printed circuit heat exchanger.…”

“…For example, Wang et al 39 considered the effects of heat flux, thermal acceleration, geometric orientation, corner effect, and secondary flow on heat transfer of sCO 2 in a semicircular tube of the printed circuit heat exchanger. Some researchers have also conducted investigations in the converging–diverging tube about the heat transfer performance through experimental and numerical methods and indicated that the converging–diverging tube could improve the heat transfer efficiency effectively 38,40 . For example, Duryodhan et al 40 developed the investigation on the heating of single‐phase fluid flow and heat transfer in some varying cross‐section microchannels by the experimental and numerical approaches.…”