High-efficiency boilers: Condensation and transient behavior
Abstract
A high efficiency, condensing, hydronic boiler is described, and previous research is reviewed. Research undertaken to develop a transient model of the boiler, and studies conducted to advance the understanding of the condensation process are presented. Mode and retention behavior are examined, and it is demonstrated, experimentally and theoretically, that the mode of condensation of water on copper heat exchangers is dropwise at 23$\sp\circ$C (73$\sp\circ$F). Further visual studies with other surfaces are presented. A theoretical study of transient, filmwise condensation on a cylinder is presented. Experiments demonstrate that real condensation behaves according to this theory as steady state is approached. However, departure at low time is observed, and an ad hoc model is developed. Additional studies of the condensation process are also presented. The studies of condensation were partially motivated by the application, and play a role in modeling the condensing boiler. Before the transient modeling is presented, improvements to existing steady state simulations are discussed. Wind tunnel studies of the low Reynolds number behavior of condensing heat exchangers are presented. Trends in observed sensible Colburn J-factor are explained through visual studies. The impact of these studies on the steady state modeling is assessed. The transient model of the condensing boiler is undertaken through standard lumped parameter, and numerical techniques. An experiment designed to subject the boiler to transients in firing rate, water mass flow rate, and inlet water temperature is described. Results of these transient tests are compared to the computer simulation, and agree closely. The computer simulation is useful as a design and development tool, and as a means of investigating alternate boiler control schemes. Examples of simulation application to conventional boilers, and to the study of alternate control algorithms are given.
Degree
Ph.D.
Advisors
Goldschmidt, Purdue University.
Subject Area
Mechanical engineering
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