Furthermore, an understanding of the effects that varying wall superheat values have on the ratio of sensible to evaporative heat transfer is critical to optimizing the falling film heat exchanger.
Also, this investigation defines tube wall superheat as the difference between the inlet heating fluid temperature and saturation temperature of the system.
This is ideal because, due to the counter-flow design of the heating and solution fluid lines, the bottommost row always has the highest wall superheat and therefore produces the greatest evaporative heat transfer.
The tube wall superheat also contributes to the overall ratio of evaporative-to-sensible heat transfer in the falling-film heat exchanger.
Since evaporation is enhanced as wall superheat is increased and as the thickness of the solution film decreases (due to less thermal resistance), it would seem that rather than constant heat duty for the whole solution flow regime, the heat duty would decrease with increased solution Reynolds number due to the thicker liquid film on the evaporator tubes.
This is because thin liquid films facilitated at these low flow rates combined with the high wall superheat prove to be ideal for evaporation heat transfer.
Because the liquid is saturated at toe vapor-liquid interface, a low effective thermal conductivity requires a large amount of wall superheat
which, in turn, causes the liquid to boil.
Upward facing surface of this wafer has been immersed in deionised water at atmospheric pressure and uniformly heated maintaining constant wall superheat by circulating fluid on its lower side (Fig.
Onset of nucleate boiling process occurs as wall superheat reaches the value of 19 [degrees]C.
Results that present the stages of ebullition cycle have been acquired at wall superheat value of [[DELTA]T.