A bibliometric analysis of publications in Drying Technology in selected drying areas

Even a cursory look at the tables of contents of most issues of Drying Technology clearly shows a preponderance of papers devoted to various aspects of spray drying as well as microwave drying. The former is not unexpected as spray drying finds truly extensive applications in numerous industrial sectors ranging from chemicals, ceramics, biotechnology products, dairy products, foods, pharmaceuticals to polymers. On the other hand, microwave drying has consistently attracted a lot of attention despite somewhat limited large-scale industrial applications at this time. Some of the other areas of industrial interest such as heat pump drying, superheated steam drying, rotary drying, have not been highly research-intensive in recent decades. The objective of this editorial is to carry out a simple bibliometric analysis to identify areas and postulate possible reasons for the observed trends in selected areas. No pretender is made that the conclusions of this limited study are all inclusive since it is only confined to publications in Drying Technology. Scores of journals in sciences, engineering, and technology do publish archival papers on drying and dewatering. Some areas such as freeze-drying, drying of coatings, drying of wood have major specialized publication outlets other than this journal. Readers should note that this analysis is limited to papers that have appeared in this journal since its inception in 1982 through August 2020 using data available in the journal’s database.

Figures 1–4 display the number of papers devoted to microwave drying, spray drying, superheated steam drying and heat pump-assisted drying published annually (since 1982) in Drying Technology. Microwave-assisted drying has attracted more attention from a large number of researchers, academics, and industry over a long period due to its unique volumetric heating capability, scalability, and ease of application in different areas. Over 1110 articles have been published on microwave-assisted drying of various products during 1982–2020, with 4.23% and 4.68% of the articles emphasizing modeling and literature review, respectively. The publishing trend of articles on microwave-assisted drying is depicted in Figure 1; it is clearly observed that the application of microwaves for drying/heating of a wide range of products from food, pharmaceutical, leather, wood, waste sludge, ceramics, coal is continuously rising. A greater number of articles have been published on microwave-assisted drying/heating of food products, while exploring more insights on the interaction of microwave and various food products with the complex structure of heterogeneous compounds without substantial loss of nutrients, which directly affect human health. Besides, the inherent nonuniformity of microwave heating resulting in the generation of hotspots, optimization of microwave parameters for a wide range of food products and development of cost-effective processes and equipment appear to be reasons for a large number of publications on microwave drying of food products.

Figure 1. Total publications on microwave drying.

Figure 2. Total publications on spray drying.

Figure 3. Total publications on superheated steam drying.

Figure 4. Total publications on heat pump drying.

Spray drying is noted to be another area of research with a large number of publications in Drying Technology since 1982. The publication trend of articles on spray drying is graphically shown in Figure 2; this shows that articles published rose monotonically during 1982 and 2012, followed by a decreasing trend during 2012 to 2018. However, the percent increase in the number of articles after 2018 has been found to rise, due probably to upsurge in applications of spray drying techniques in various areas such as the drying of pharmaceuticals, dairy, and food products along with microencapsulation of various compounds. Over 500 articles were published from 1982 through 2020, with 5.91% and 2.16% of the articles on modeling and literature review, respectively. The number of articles on spray drying may be somewhat restricted due to its applicability to only liquid products, whereas microwave drying has relevance in both solid as well as liquid products. The powder formation, stability of bioactive compounds, hygienic design requirement of spray dryer, encapsulation of various compounds, energy consumption, CFD modeling and product quality interactions are found to be main themes of spray drying research. It should be noted that spray drying literature also appears prominently in journals devoted to foods and pharmaceuticals.

Superheated steam (SHD) drying is another area of research for many researchers and academics. The trend of publications on superheated steam drying is depicted in Figure 3; the number of publications is fewer but has gradually increased from 1982 to 2015. However, a decreasing trend of publications can be noted during the last five years (2015–2020). A total of 153 articles were published during 1982–2020, with 3.26% and 1.96% of the articles emphasizing modeling and literature review, respectively. Simulation of superheated steam drying, microbial inactivation, effect on quality characteristics of various products and drying of coal are the theme areas of superheated steam drying.

The trend of publications on heat pump drying during 1982–2020 is shown in Figure 4. During the initial period (1982–1990) of the inception of the journal no articles have been reported; however, an increasing trend of publications is observed from 1991 to 2020. The quality of dried products and drying characteristics of food products, exergoeconomic analysis, energetic and exergetic performance are the main themes. During 1982–2020, 86 articles on heat pump drying were published, with 5.81% and 10.46% of the articles focusing on modeling and literature review, respectively.

A simple bibliometric analysis of the major themes of publications in this journal since its inception has uncovered recent trends in drying R&D. It should be noted that the conclusions are limited to this journal. A comprehensive study is warranted of the patent literature as well as publications in a large number of disciplinary, multi-disciplinary as well as trade literature covering a wider range of thematic areas. It is obvious that the technical and scientific literature on drying is continuing to grow unabated although the cost of energy continues to stabilize at a lower level.

Shivanand S. Shirkole
Assistant Editor, Drying Technology
Institute Chemical Technology Mumbai, ICT-IOC Odisha Campus, Bhubaneswar, India
[email protected]