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Fermilab Vertical Test Stand-1 (VTS-1) has been in operation since 2007 for testing superconducting radio frequency (SCRF) cavities at 2K. This test stand includes a heat exchanger consisting of a single layer; helically wound finned tube, upstream of the J-T valve. A finite difference thermal model has been developed in Engineering Equation Solver (EES) to study the thermal performance of this heat exchanger during refilling of the test stand. The model can predict heat exchanger performance under various other operating conditions and is therefore useful as a design tool for similar heat exchangers in other facilities. The present paper discusses the different operational modes of this heat exchanger and its thermal characteristics under these operational modes. Results of this model have been compared with experimental data gathered from the VTS-1 heat exchanger, and they are in good agreement with the present model. [ABSTRACT FROM AUTHOR]

Abstract: Cross-counter flow coiled finned tube heat exchangers used in medium capacity helium liquefiers/refrigerators were developed in our lab. These heat exchangers were developed using integrated low finned tubes. Experimental studies have been performed to know the pressure drop characteristics of tube side and shell side flow of these heat exchangers. All experiments were performed at room temperature in the Reynolds number range of 3000–30,000 for tube side and 25–155 for shell side. The results of present experiments indicate that available correlations for tube side can not be used for prediction of tube side pressure drop data due to complex surface formation at inner side of tube during formation of fins over the outer surface. Results also indicate that surface roughness effect becomes more pronounced as the value of di/Dm increases. New correlations based on present experimental data are proposed for predicting the friction factors for tube side and shell side. [Copyright &y& Elsevier]

Abstract: The aim of present experimental research is to find out the suitable correlations for designing the coiled finned-tube heat exchangers used in cryogenic applications. In order to conduct above experimental study, cross-counter-flow coiled finned-tube heat exchangers were developed in our lab and used in actual refrigeration cycle. The experiments were conducted in the range of effective Reynolds number 500–1900. The effect of diametrical clearance on the prediction of overall heat transfer coefficient is also investigated experimentally. The results from present study were compared in the form of overall heat transfer coefficient. Results of present experimental research indicate that different correlations selected in the study can be used with reasonable accuracy for designing the coiled finned-tube heat exchangers, if they are applied with suitable method of calculation of free-flow cross-sectional area. A more accurate new correlation has also been proposed that fitted experimental data within ±10% error band. [Copyright &y& Elsevier]

Abstract: Performance of highly effective heat exchangers is governed by the various internal and external irreversibilities. In low temperature applications, the performance of these heat exchangers strongly depends on the irreversibilities such as ambient heat-in-leaks, longitudinal heat conduction through separating wall of heat exchanger and conduction through high temperature connecting tubes when they are integrated to the system. The special focus of present analysis is the study of effect of these irreversibilities on the performance of heat exchangers through second law analysis. It is observed that the effect of ambient heat-in-leak is different for the balanced and imbalanced counter flow high NTU heat exchangers. Study also makes it possible to compare the different irreversibilities for varying range of NTU and analyze the influence of external irreversibilities on the performance of heat exchangers when either hot fluid or cold fluid is minimum capacity fluid. [Copyright &y& Elsevier]

Abstract: Coiled finned-tube heat exchangers have been used in small and medium helium refrigerators/liquefiers, miniature J–T refrigeration systems for many years. The efficiency of these cryogenic systems strongly depends on the thermal and pressure drop performance of these heat exchangers. A considerable improvement in the performance of heat exchanger is possible by choosing an appropriate geometrical configuration for a given process requirement. In the present study, geometry of heat exchanger has been derived taking into consideration the clearance provided for manufacturing of the heat exchangers and an optimized geometrical configurations have been find out. The results show the possibility of adjusting the thermal and pressure drop performance by varying the clearance. The predictions of four end temperatures from present design method have been compared with the actual experimental results of one of the prototypes fabricated in our lab. [Copyright &y& Elsevier]

This paper presents seasonal variation of surface ozone monitored continuously at site of the meteorological observatory at Port Blair, a maritime site of the Bay of Bengal for the period of August, 2005–March, 2007. Present observation depicts the characteristics of surface ozone at the remote marine site and the long range transport of pollutants from three different sides i.e., Indian Subcontinent, South East Asia and Indian Ocean. Very high ozone mixing ratio (~70–80 ppbv) is occasionally observed during March and November at this site. A campaign mode of observation of trace gases (surface ozone, CO, NO x , CO 2 ), aerosol concentration and its size, UV radiation at Port Blair was made to understand the role of transport on pollutants during March 16–26, 2002. During this period of observation, a near zero surface ozone of different time scales (~few hours) has been observed several times during the period of midnight to early morning. Simultaneously NO x (NO+NO 2 ) (~40 ppbv) and carbon monoxide was observed very high (300–600 ppbv) during this period. Source of this high pollutant are not expected at this remote marine sites although wind patterns, 7-days isentropic back Trajectory analysis and MATCH Model output suggest that polluted air mass has come from eastern side of Indian subcontinent. [ABSTRACT FROM AUTHOR]