THEORETICAL AND EXPERIMENTAL STUDY OF HEAT TRANSFER CHARACTERISTICS OF CABINET CALORIMETER SYSTEM

摘要

The purpose of this work was to develop a cabinet calorimeter which can accurately measure the cabinet heat leakage rate in a short time while simulating the normal operating conditions of the cabinet. Several calorimeter schemes were proposed. Based on the simple analyses, the final scheme was selected for further analyses and tests.;By approximating the flow in the testing coil as that in a straight tube, the influences of the viscous dissipation in the fluid on the system performances were examined analytically. The Eigenfunction series expansion technique was employed to solve the governing energy equation. The effects of the Brinkman number on the wall heat transfer rate were studied in detail. Under the flow conditions in this study, viscous heating was found to be negligible.;To predict the transient system performances theoretically, a fully implicit upwind finite-difference numerical scheme was proposed to investigate the characteristics of thermal entrance heat transfer in the laminar pipe flows subject to a step change in the ambient temperature. Then the unsteady thermal entrance heat transfer in the laminar pipe flows resulting from both a step change in the pressure gradient and a step change in the pipe inlet temperature was studied numerically. The problem was solved by the exponential scheme. The special features of the transient heat transfer against the corresponding steady ones were discussed in great detail. Finally in the modeling of the whole system, the lumped-system method was used to model the unsteady heat transfer for the air in the cabinet and the heat transfer for the fluid in the testing coil was modeled by that in a straight tube.;The proposed system was built and tested. It was shown in the experiment that the gross features of the system such as the transient time and the time variations of the cabinet temperature were in good agreement with the theoretical predictions.