Experimental determination of the heat exchange coefficient of industrial steam pipelines
Abstract
The article discusses and analyses the factors related to the use of a thermal imaging camera to determine heat loss in industrial steam pipelines at factories from chemical and metallurgical industry, by measuring their surface temperature. The generally accepted enthalpy method for determination of the loss has serious drawback it gives accurate results, but in averaged units in which it is impossible to take account of the contribution of the different parts and components of the pipeline in the total heat loss. The unavailability of information on where, how and in what way along the route this loss is formed does not allow prompt and specific measures to be taken for its reduction. An attempt has been made to structure empirically a reliable analytic dependence for determination of the heat exchange coefficient, bringing together the various factors influencing the heat exchange. By the method of the least squares the free coefficient and the exponent have been determined of criterion equation satisfying initial and boundary conditions of the experiment. Based on the obtained results for determining the heat losses by measuring the surface temperature of steam pipelines with a thermal imaging system, a reliable and acceptable method is proposed, which has a place in engineering practice. For this purpose, an industrial experiment has been carried out at three actually operating steam pipelines of different diameters and steam parameters. A criterion equation has been derived that can be used as a mathematical model for software products with a practical orientation for regular assessment of heat losses of steam pipelines. Values of heat losses determined through energy balance of heat carrier and heat flux from the outer surface of the steam pipelines have been compared. Results for the heat exchange coefficient, obtained through a balance have been compared with the analytically determined values based on current standards. A new method has been developed for express evaluations of the current heat losses of the steam pipeline in real time, as the sum of the losses through its individual components gives as average values 9÷12 % increased results for the losses compared to the enthalpy method. Its great advantage is that it can be used selectively to determine the losses through individual sections of the steam pipeline.
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