HEAT TRANSFER IN TWO-PHASE VERTICAL CO-FLOW IN THE PRESENCE OF A MESH-TYPE BUBBLE BREAKER

摘要

Bubble breakers have been shown to be effective at reducing bubble size and delaying transition from bubbly to slug and churn flow regimes in the two-phase vertical pipe flow. If used in bubble column reactors, bubble breakers can increase the surface area-volume ratio of the gas-liquid interface allowing for an enhanced mass transfer or chemical reaction rate. Studies have been done showing the effect of bubble breakers on bubbles size and flow regime but none exist to showthe effect of a bubble breaker on heat transferfor a two-phase pipe flow. Anew method of measuring the heat transfer for a two-phase vertical pipe flow is proposed in the current study. The method uses thermocouples inserted directly into the flow for bulk fluid temperature measurements and a thermal camera for surface temperature measurements of a thin walled stainless steel pipe. Heat transfer measurements, expressed as a Nusseltnumber, for a single phase laminar liquid flow are compared to accepted values to showthe validity of the experimental method. Preliminary results of two-phase gas-liquid heat transfer rates with and without a bubble breaker present in the vertical pipe are compared. The liquid flowrates used in the experiment represented superficial Reynolds numbers of Re_1＜2000 and the gas flowrates used in the experiment represented superficial Reynolds numbers of Re_g＜100. Without a bubble breaker, the convective heat transfer coefficient, represented as Nusselt number, was found to decrease with increasing gas flowrate. When a bubble breaker was added, the effect on the heat transfer was dependent on the flow regime. For most cases, the bubble breaker had very little effect on the measured heat transfer rate. In a case where the bubble breaker was able to generate slug flow rather than churn flow that was generated when no bubble breaker was present, the measured Nusselt number was increased.