SOME TEST RESULTS OF EXPERIMENTAL AND PILOT SNOW-MELTING INSTALLATIONS

N. A. POPOV, A. I. KLEMAITIS

(Presented by the Department of Industrial Heat Power Engineering)

To solve a number of problems connected with the development of designs for industrial snow-melting units and the adjustment of their operation, some experimental studies were carried out.

Figure 1 presents a diagram of the experimental installation. In conducting experiments on it, the following tasks were set:

a) testing of the direct-flow nozzle P-3 after a certain modernization;

Fig. 1. Experimental snow-melting installation

b) determination of the maximum permissible value of the thermal loading of the snow-melter casing area.

The direct-flow nozzle P-3 produces water spraying mainly in the shape of a torch. A considerable part of the space inside the torch is not filled with particles of sprayed water. In order to eliminate this shortcoming, a cylindrical hole was drilled in the screw insert of the nozzle for the passage of an additional quantity of water going to spraying (Fig. 2).

As the tests showed, water spraying in the presence of an opening in the screw insert became more uniform over the transverse section of the jet. In this configuration the nozzles could be used for spraying water in snow melters. However, during subsequent testing of the nozzles on the pilot-plant installation, clogging was observed of the screw passages for water in the nozzle insert by suspended particles present in the meltwater circulating there. It is therefore necessary either to employ more advanced purification of the water from suspended matter, or to create a nozzle that would not become clogged and would provide the required spray.

Fig. 2. Nozzles for spraying water

Solving the second test problem, i.e., determining the maximum permissible heat flux over the area of the snow-melter body, makes it possible to determine the dimensions of the snow-melter body when designing the installation.

Fig. 3. Schematic diagram of an experimental pilot-plant installation for melting snow

The maximum permissible heat flux is understood as the amount of heat supplied by the sprayed water to \(1\ \text{m}^2\) of the body area. In this case, the discharge of meltwater must be carried out at a temperature not higher than \(1^\circ\text{C}\).

Thus, the value of the maximum permissible heat flux will depend on the thickness of the snow layer in the body, the irrigation density, and the temperature of the sprayed water.

Experiments to determine the maximum permissible heat flux—

tests were carried out with a snow-layer thickness of 1.0, 1.25, and 1.5 m, at different irrigation densities and temperatures of the sprayed water. As a result of the experiments it was established that, with a snow-layer thickness of 1.25–1.5 m, the maximum permissible heat flux should not exceed 300,000 kcal/m² h.

If possible (according to the conditions for discharge of meltwater into the sewer system), the height of the snow layer should be taken as large as possible. This makes it possible to increase the heat flux, the capacity of the body, and to improve the economy of operation of the installation.

Figure 3 shows the schematic diagram of the experimental pilot installation.

As can be seen from the diagram, meltwater from the receiving sump of the body is directed by circulation pump 1 for heating into heat exchanger 2, after which it goes for spraying through nozzles 3. The excess meltwater is drained into the sewer system. The circulating water is heated by the heat of the return water from the heating system. Pump 4 is installed to pump the heating water through the heat exchanger.

In testing this installation, the coefficient of utilization of the heat supplied for snow melting, \(\eta_{\mathrm{st}}\), was determined. On the basis of the experiment performed, its value in preliminary calculations in the design of snow melters may be taken as \(\eta_{\mathrm{st}} = 0.9\).

During the experiments, a number of shortcomings in the design of the pilot snow melter were also revealed. First of all, it was established that the body width, equal to one meter, is insufficient, since when wetted the snow forms an arch that prevents it from sliding down to the bottom of the body. In addition, the small angle of inclination of the nozzles to the vertical wall (23°) created a small irrigation area. All this, taken together, led to a decrease in the operating efficiency of the snow melter. For better sliding of the snow, the side walls must be made at an angle, i.e., with widening of the transverse section of the body as the snow moves downward. The transfer pump should be installed so that it can pump the heating water not only from the return pipeline but also from the supply pipelines.

In view of the small number of hours of use per year of the installed capacity of the snow-melting installation and the insignificant share of costs for pumping the heating and circulating water, the water velocities in the heat exchangers of the installation should be taken as the maximum possible, in order to increase the heat-transfer coefficient, i.e., to reduce the heating surface of the heat exchangers.

Conclusion

The experimental work carried out showed that, in adjusting the operation of snow melters, the main attention should be directed toward creating spraying devices that not only would not become clogged, but would also ensure uniform spraying of water.

Those wishing to become acquainted in more detail with the question of snow melting on the basis of district heating are referred to [2], [3].

References

1. A. V. Nikitin. Snow Melters. Moscow, Publishing House of the Ministry of Municipal Economy of the RSFSR, 1952.

2. N. A. Popov. Increasing the load of extraction points of district-heating turbines on the basis of snow melting. Proceedings of TPI, vol. 205, 1972.

3. N. A. Popov. Technical-and-economic comparison of snow melting on the basis of district heating with hauling it to dumps. Proceedings of TPI, vol. 205, 1972.