Development of the New Comprehensive Performance Evaluation Equipment for Enhanced Convective Heat Transfer Techniques
Based on the new performance evaluation criterion system (PECS) for enhanced convective heat transfer techniques, an evaluation equipment of enhanced heat exchange tube was developed. The equipment structure and functions, parameters measurement and control of auxiliary system were introduced in detail. The monitoring and control software was programmed with the Delphi 7.0, and be used to realize the data acquisition and processing, database operation and management, and many other functions. A kind of new type enhanced heat exchange tube was tested. The experience result shows that apparatus is feasible to evaluate the performance of enhanced convection techniques.
Survey and evaluation of techniques to augment convective heat transfer
Abstract : The report presents a survey and evaluation of the numerous techniques which have been shown to augment convective heat transfer. These techniques are: surface promoters, including roughness and treatment; displaced promoters, such as flow disturbers located away from the heat-transfer surface; vortex flows, including twisted-tape swirl generators; vibration of the heated surface or the fluid near the surface; electrostatic fields; and various types of fluid additives. Natural and forced convection situations for nonboiling, boiling, and condensation heat transfer are included. The conditions under which heat transfer is improved are summarized, and the efficiency of each technique is presented in terms of a performance criterion where possible. (Author)
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.