Comparative experimental study on heat-up efficiencies during injection of superheated and saturated steam into unsaturated soil. (September 2020) - Janfada, Taraneh Sadat
Highlights: Experiments demonstrate how superheated steam sweeps unsaturated zone over time. Overall heat transfer coefficients and heat losses are evaluated via calculations. Heat-up efficiencies of superheated and saturated steam injections are compared. Higher net differences of inflow enthalpies and heat losses lead to faster heat front. Heat front spread in superheated case can be 12.5% faster compare to saturated case. Abstract: This article presents results from an experimental study on the injection of superheated steam into a quasi-two-dimensional, sand-filled laboratory flume. The main objectives of the study are (I) the evaluation of superheated steam efficiency, as opposed to saturated steam, concerning the heat-up of the sand filling and (II) to observe and understand how the steam in its superheated state sweeps the unsaturated zone over time. Superheated steam was injected at 200 °C, while for comparison, saturated steam was injected at 100 °C. Two different flow rates were applied. The fronts of saturated steam in both injection regimes as well as the dry-out front of the superheated steam were closely monitored and documented here. The effects of the different injection parameters such as temperature and enthalpy as well as other parameters and processes of influence like the heat transfer mechanisms or heat losses and their controlling quantities are discussed in detail. At distinct points, based on measurements, the heat-up efficiencies are calculated locally, and a comparison is made between superheated and saturated steam injection. As expected, in the higher net differences between inflow enthalpy and heat loss, heat transfer in the case of superheated steam injection is faster; for instance, considering 2.4 kg/h steam flow rate, measurements show reaching flume conditions to steady-state after 4 h in the superheated case compared with 4.5 h in the saturated case. Graphical abstract: Image, graphical abstract