T.K. Nandi

Issues on the Testing of Small Cryogenic Recuperators and Experimental Studies on Perforated Plate Heat Exchangers

ABSTRACT This paper deals with various issues on testing heat exchangers at cryogenic temperatures, the test setup and experimental studies on perforated plate heat exchangers. A number of fluid flow circuits are used in practice for testing a heat exchanger at cryogenic temperatures. These circuits are reviewed and a simplified fluid circuit is proposed with justifications. Effects of the fluid inlet/outlet tubes on the performance evaluation of the heat exchanger were investigated numerically. It is found that convection heat transfer between fluid and the tube as well as conduction heat transfer through the tube walls can cause significant errors in the evaluation. These errors are considered while designing the inlet/outlet tubes for the test setup. Details of the test setup including mounting of temperature sensors, instrumentation and data acquisition are discussed. Some selected data from our experimental studies on perforated plate heat exchangers are presented. Transient study on the heat exchanger by using the setup is also demonstrated. For pressure drop studies, a separate test setup is used.

Heat transfer and flow friction correlations for perforated plate matrix heat exchangers

Perforated plate matrix heat exchangers (MHE) are constructed of high conductivity perforated plates stacked alternately with low conductivity spacers. They are being increasingly used in many cryogenic applications including Claude cycle or Reversed Brayton cycle cryo-refrigerators and liquefiers. Design of high NTU (number of (heat) transfer unit) cryogenic MHEs requires accurate heat transfer coefficient and flow friction factor. Thermo-hydraulic behaviour of perforated plates strongly depends on the geometrical parameters. Existing correlations, however, are mostly expressed as functions of Reynolds number only. This causes, for a given configuration, significant variations in coefficients from one correlation to the other. In this paper we present heat transfer and flow friction correlations as functions of all geometrical and other controlling variables. A FluentTM based numerical model has been developed for heat transfer and pressure drop studies over a stack of alternately arranged perforated plates and spacers. The model is validated with the data from literature. Generalized correlations are obtained through regression analysis over a large number of computed data.

Experimental studies on cu-ss diffusion bonded Perforated plate heat exchangers

In this paper experimental studies on Cu-SS diffusion bonded perforated plate heat exchangers (PPHEs) are reported. A test set up has been developed for testing the heat exchangers at cryogenic temperatures. The paper presents the details of the test setup, instrumentation and the test results. Due attention is given to the accuracy of the experiment. Data on frictional pressure drop have been obtained under isothermal conditions. These data are useful for observing the behavior of the heat exchangers. Besides, these will also be useful for validation of numerical models of PPHEs.