Technological innovations in optics in the form of a spiral mask system and in electronics in the form of on-line gate scanning of Fabry-Pérot fringes and critical balancing of gate widths for complete background rejection have allowed unambiguous detection of faint dayglow emission features of multiple wavelengths buried in the bright daytime background continuum. The technical details of this unique multiwavelength daytime photometer (MWDPM) and its performance characteristics together with its potential application for the investigation of several geophysical phenomena are presented and discussed.

A unique photometer capable of measuring line intensities of <0.1% of the bright background continuum (5 x 10(6)/A) has been developed and successfully commissioned for the measurement of daytime OI 630.0-nm emission from the thermosphere. The photometer employs a low resolution (10(4)) Fabry-Perot etalon, temperature tuned narrowband (3-A) interference filter, radial chopper, and up/down counting system. The optimum choice of the photometer parameters and a unique method of eliminating the background enabled us to overcome the limitations of the earlier attempts to make measurements on such phenomena as dayglow and has opened up a wide range of uses. However, at present, it is being discussed only in the context of dayglow measurements.

Summary The present study exemplifies the comprehensive thermal analysis to compare and contrast ammonia‐lithium nitrate (NH3‐LiNO3) and ammonia‐sodiumthiocynate (NH3‐NaSCN) absorption systems with and without incorporation of nanoparticles. A well‐mixed solution of copper oxide/water (CuO/H2O) nanofluid is considered inside a flat‐plate collector linked to an absorption chiller to produce 15‐kW refrigeration at −5°C evaporator temperature. Enhancements in heat transfer coefficient, thermal efficiency, and useful heat gain of the collector are evaluated, and the effect of these achievements on the performance of both absorption chillers have been determined for different source temperatures. A maximum 121.7% enhancement is found in the heat transfer coefficient with the application of the nanofluid at 2% nanoparticle concentration. The maximum coefficient of performance observed for the NH3‐NaSCN chiller is 0.12% higher than that for the NH3‐LiNO3 chiller at 0°C evaporator temperature. Contradictory to this, the average system coefficient of performance of the NH3‐LiNO3 absorption system has been found 5.51% higher than that of the NH3‐NaSCN system at the same evaporator temperature. Moreover, the application of the nanofluid enhanced the performance of the NH3‐NaSCN and NH3‐LiNO3 systems by 2.70% and 1.50%, respectively, for lower generator temperature and becomes almost the same at higher temperatures, which altogether recommends the flat‐plate collector–coupled NH3‐LiNO3 absorption system be integrated with a nanofluid.

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We present and discuss a novel mask design that provides multiwavelength measurement capability for the dayglow photometer.