An overview of the significant innovations in photocatalysts for H2 development, photocatalyst selection criteria, and photocatalytic modifications to improve the photocatalytic activity was examined in this Review, as well as mechanisms and thermodynamics. A variety of semiconductors have been examined in a structured fashion, such as TiO2-, g-C3N4-, graphene-, sulfide-, oxide-, nitride-, oxysulfide-, oxynitrides, and cocatalyst-based photocatalysts. The techniques for enhancing the compatibility of metals and nonmetals is discussed in order to boost photoactivity within visible light irradiation. In particular, further deliberation has been carried out on the development of heterojunctions, such as type I, type II, and type III, along with Z-systems, and S-scheme systems. It is important to thoroughly investigate these issues in the sense of visible light irradiations to enhance the efficacy of photocatalytic action. In fact, another advancement in this area may include hiring mediators including grapheme oxide and metals to establish indirect Z-scheme montages with a correct band adjustment. The potential consideration of reaction chemology, mass transfer, kinetics of reactions, restriction of light diffusion, and the process and selection of suitable light and photoreactor also will optimize sustainable hydrogen output efficiency and selectivity.

The present article is focused to improve the thermal performance of solar air heater using Liquid crystal thermography (LCT) approach, an improved type solar air heater comprises of winglet type rib roughened surface. In the present case, an experimental analysis and its effects on heat transfer and collector efficiency are examined using non-dimensional roughness parameters taken as relative roughness pitch (P/e) ranges between 5–12, attack angle (α) values of 30 degree-75 degree and relative roughness width (W/w) ranges between 3–7.These experimental results when compared with the smooth channel was improved by 17 % to 46 % under the given conditions.

The additive manufacturing technology is best suited for the use of nanocomposite materials. They have the remarkable capacity to adapt to changing conditions by altering their physical, chemical, and biological characteristics. Additive manufacturing (AM) creates three-dimensional objects by layering materials together. Nanocomposite materials have a greater surface to volume ratio in the reinforced phase, making them suitable for AM. Polymer nanocomposites, nylon-12, nylon-6, graphene nanoplates, polyamide 12 are some materials for AM enhancing the product quality. TiC/Ti nanocomposite, Ceramic-based nanocomposite, Polymer/carbon nano tube nanocomposites, PA6/Hectorite clay nanocomposites are being discussed in briefly. SLA, 3DP, SLS, EP, FDM, etc. are the techniques of for manufacturing of products in additive manufacturing. Fundamentals of seven AM processes, its mechanical properties are discussed in this chapter. This chapter also goes through a few of the flaws. The use of nanomaterials in the area of AM has a lot of promise, and there is a growing interest among academics and industry to look for new advancements. New creative nanomaterials and AM techniques are still being researched, and the collaborative energy between these two fascinating areas will shape the future of AM and nanocomposites.

The solar air heater’s thermal efficiency is relatively poor owing to the flat collector surface. This article’s primary objective is to increase the collectors’ thermal efficiency of rectangular ducts of solar air heater by adopting a novel V-shaped twisted rib element with staggering orientation. Experimentations are performed for various flow Reynolds numbers ranging from 3 k to 21 k, roughness pitch-to-rib height ratio ranging from 7 to 11, and staggering distance-to-rib height ratio between 2 and 6. Dispersion of Nusselt number over the collector surface is achieved through the liquid crystal thermography technique. Among the varied rib and flow constraints, it is observed that a maximum thermal performance enhancement index of 2.69 is observed, with the optimum value of the roughness parameter at a rib pitch-to-height ratio of 9 and a staggering distance-to-height ratio of 4. Mathematical correlation has also been developed using a regression model to estimate the Nusselt number in terms of non-dimensional roughness parameters. The percentage deviation between the Nusselt number attained from established relationships and the investigational results is found to be giving very satisfactory outcomes. The thermal efficiency of the smooth surface is recognized at 41.64% which increases for the roughened surface of twisted V-ribs to 73.63%. Hence employing twisted V-ribs as an artificial roughness element no doubt increases the Nusselt number, thermohydraulic performance enhancement index, and thermal efficiency, but it also exerts less frictional power of solar air heater.

This paper deals with the study of heat transfer in solar air heater consisting of winglet-shaped roughness on the absorber plate using liquid crystal thermography technique. The winglet-type roughness element was placed on the absorber surface of a rectangular channel solar air heater having an aspect ratio of 4. The absorber surface was heated uniformly by a constant heat flux of 800 W/m². The non-dimensional roughness parameter considered was relative roughness pitch, i.e., P/e, and its values range between 5 and 12 with Reynolds number (Re) ranges between 6500 and 22,000. The value of angle of attack, i.e., alpha and relative roughness width (W/w) was kept constant, and the relative roughness pitch was varied to measure the heat transfer coefficient. The enhancement in heat transfer has been compared, and it is observed that at P/e of 8 for angle of attack (α) of 60 degrees resulting its optimum value. The enhancement of heat transfer with the increase in Reynolds number is also noted.