We consider inverse methods for predicting the channel bed topography in experiments of hydraulic falls. Nonlinear solutions and weakly nonlinear approximations from Euler-based models are compared to experimental observations. Accurate predictions are obtained for the maximum height of the topography and its constant horizontal level far downstream using the nonlinear method. The weakly nonlinear approximation is shown only to be a good predictor of the maximum height of the topography. The error in the inverse predictions is examined and discussed.

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Purpose Currently, China is the largest coal producer and consumer in the world. Underground mining is the main practice. In the process of deep mining, large amounts of low-temperature waste heat are available such as in the mine return air (MRA), mine water (MW), bathing waste water (BWW), etc. Without recycling, the low-temperature waste heat is discharged directly into the atmosphere or into the drainage system. The temperature range of the MRA is about 15-25°C, the relative humidity (RH) of the MRA is above 90 per cent, the temperature range of MW is about 18-20°C and the temperature of the BWW is about 30°C. All of the above parameters are relatively stable throughout the year, and thus MRA, MW and BWW are proper low-temperature heat sources for water source heat pump (WSHP) systems. The study aims to introduce the schemes for recycling the different waste heat sources and the relevant key equipment and technology of each waste heat recycle system; analyze the heat recovery performances of the MRA heat recovery technology; and compare the economies between the MRA heat recovery system and the traditional system. Design/methodology/approach Based on the WSHP system, heat and mass transfer efficiencies were calculated and analyzed, the outlet air velocity diffusion of the heat and mass transfer units and the parameters including air flow rate, the MRA’s dry bulb temperatures and wet bulb temperatures at inlet and outlet of MRA heat exchanger were tested. Then, it was assessed whether this system can be applied to an actual construction. An actual reconstructive project of MRA heat recovery system is taken as an example, where the cost-saving effects of heat recovery of mine waste heat sources system are analyzed. Findings Analysis of field test reveals that when heat transfer is stable, heat transfer capacity can be achieved: 957.6 kW in summer, 681 kW in winter and a large amount of heat was recycled. In an economic analysis, by comparing initial investment and 10 years’ operation cost with the traditional boiler and central air conditioning system, the results show that although the MRA system’s initial investment is high, this system can save CNY 6.26m in 10 years. Originality/value MRA has a large amount of air volume and temperature that is constant throughout the year, and hence is a good low-temperature heat source for the WSHP system. It can replace boiler heating in winter and central air conditioning refrigeration in summer. The study reveals that this technology is feasible, and has good prospects for development.

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