Surreal image of glowing onions in green light, representing exergy analysis.

Unlocking Onion's Potential: How Exergy Analysis Can Revolutionize Food Drying

Beau Callahan monogram
Beau Callahan in Climate & Environment November 2026 • 4 min read.

"Discover how exergy analysis optimizes onion drying, slashing energy waste and boosting sustainability for a greener, more efficient food industry."


In an era where energy efficiency and sustainable practices are paramount, industries are constantly seeking innovative methods to optimize their processes. The food processing sector, a significant consumer of energy, is no exception. Drying, a crucial step in preserving various food products, is notoriously energy-intensive. However, a groundbreaking approach known as exergy analysis offers a pathway to revolutionize drying processes, making them more efficient and environmentally friendly.

Exergy analysis, unlike traditional energy analysis, delves deeper into the quality of energy and its potential for conversion. It identifies where energy is lost or degraded, providing valuable insights for improvement. This method is particularly beneficial in complex systems like food dryers, where energy transformations occur at multiple stages.

This article explores the application of exergy analysis to onion drying, a common practice in the food industry. By understanding how this advanced analytical tool can minimize energy waste, enhance product quality, and promote sustainability, manufacturers and consumers can make more informed decisions, paving the way for a greener and more efficient food industry.

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Measuring Onion-Drying Performance

Exergy analysis has been applied to onion drying in cabinet, continuous-convection, and MSSICB dryers. Researchers have examined exergy loss, exergetic improvement potential, and the exergetic sustainability index under different temperatures, drying periods, air velocities, product thicknesses, and belt speeds. In the MSSICB study, exergy utilization, exergy utilization ratio, and improvement potential increased with air-drying temperature and velocity and decreased with belt linear speed, while exergy efficiency and specific energy consumption decreased as temperature and velocity increased.

The Shift to Exergy Analysis

A 2018 study examined continuous-convection onion drying by analyzing how dryer temperature and air velocity affected exergy performance. This work represents an important step beyond simply tracking energy use, because it focused on the quality and potential of energy transfers within the drying process. The article’s stated purpose was to clarify exergy behavior under changing dryer parameters and support more informed development of onion-drying systems.

What is Exergy Analysis and Why Does it Matter for Onion Drying?

Surreal image of glowing onions in green light, representing exergy analysis.

Exergy analysis is a thermodynamic analysis technique that evaluates the quality and potential of energy resources. Unlike traditional energy analysis, which only considers the quantity of energy, exergy analysis assesses the usefulness or potential of energy to perform work. It identifies inefficiencies by pinpointing locations where energy is degraded or lost, providing a more accurate picture of the true energy consumption and waste within a system.

For onion drying, exergy analysis offers several critical advantages:

  • Pinpointing Inefficiencies: It helps identify specific stages in the drying process where the most significant energy losses occur.
  • Optimizing Energy Use: By understanding the exergy flows, engineers can optimize the drying parameters (temperature, airflow, etc.) to minimize waste.
  • Enhancing Sustainability: Reducing energy consumption directly translates to a smaller carbon footprint, promoting more sustainable practices.
  • Improving Product Quality: Efficient drying processes also help maintain the nutritional value, color, and texture of the dried onions.
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New Directions in Onion Drying

A 2025 study investigated intermittent solar-electric onion drying using solar-electric drying, intermittent solar-electric drying, and intermittent solar-electric drying with storage. Average specific energy consumption was reported as 0.76 kWh/kg for ISED and 0.66 kWh/kg for ISEDS. The study also reported sustainability-index values of 1.99, 1.45, and 1.51 and waste-exergy ratios of 0.49, 0.63, and 0.61 for SED, ISED, and ISEDS, respectively.

Why Energy Analysis Alone Falls Short

The cited engineering research argues that energy analysis alone cannot accurately and reliably describe the thermodynamic behavior of sophisticated machines and systems. For onion drying, this limitation motivates separate examination of exergy rather than relying only on total energy balances. A related review reported that future work should develop suitable dryers for different drying conditions, products, capacities, and drying times, indicating that no single design automatically resolves all performance challenges.

Convective Exergy Efficiency

In a convective onion-drying study at 60 °C, exergy efficiency was reported as 50.6% at an air velocity of 0.5 m/s, 54.9% at 1 m/s, and 73.0% at 2 m/s. These results show higher exergy efficiency at the tested higher air velocity. Nevertheless, the study characterized convective drying as moderately poor in exergy-efficiency terms, leaving substantial room for improvement.

In essence, exergy analysis transforms the approach to onion drying from a basic energy balance exercise to a strategic optimization endeavor. This leads to better resource management, cost savings, and a more environmentally responsible operation.

The Future of Food Drying: Embracing Exergy Analysis

As industries worldwide strive for greater efficiency and sustainability, exergy analysis emerges as a vital tool for optimizing food drying processes. By understanding the quality and potential of energy, manufacturers can minimize waste, reduce environmental impact, and enhance product quality. Embracing exergy analysis is not just a technological upgrade; it’s a step toward a more sustainable and responsible future for the food industry.

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A Sustainability Metric for Drying

A sustainability analysis of drying technologies proposes specific exergy consumption as a measure of how efficiently non-renewable resources are used. Expressing this metric in kilojoules per kilogram of extracted water links thermodynamic performance to the amount of moisture removed. The source identifies minimization of specific exergy consumption and related energy metrics as an objective for future drying-technology research.

What comparison and testing conditions show

  • 13The lowest energy consumption and exergy losses in the reported comparison occurred with a 13 mm diameter, 3 m/s airflow, and a temperature of 313 K.[1]

What drying measurements say about performance

The minimums reported for energy use and exergy loss occurred together under specified conditions, but that result does not by itself establish that those conditions are optimal for onion drying or other products.[1]

Texture responses differed with drying technique and operating intensity: harder, chewier slices were associated with higher convective temperatures or microwave power, and microwave-treated slices had higher values than convectively dried ones.[2]

How exergy fits into food-drying comparisons

Exergy indicators and Grassmann diagrams are presented as tools for assessing efficiency across industrial food chains, extending the approach beyond a single dryer or product.[3]

A review considers which exergy indicators suit food-industry applications and discusses the challenges posed by industrial food chains and food-process characteristics.[3]

What remains uncertain for onion dryers

  • How well do results from a laboratory-scale dryer with controlled air temperature and velocity carry over to industrial food chains with their distinct process conditions?[1] [3]
  • How should dryer temperature be balanced against overheating and overly rapid drying when using a cabinet dryer?[4]
  • When the food type or dryer changes, how do air temperature, airflow, humidity, food moisture, and piece size combine to determine drying time?[4]

Sources

  1. Exergy Analyses of Onion Drying by Convection: Influence of Dryer Parameters on Performance (pmc.ncbi.nlm.nih.gov)
  2. Open Access CAAS Agricultural Journals: Convective and microwave drying of onion slices regarding texture attributes (www.agriculturejournals.cz)
  3. The use of exergetic indicators in the food industry - A review. (www.tandfonline.com)
  4. untitled (www.fao.org)

About this Article -

Written with AI assistance from published research, and reviewed by the Mystum team. See our About page for more information.

Everything You Need To Know

1

What is exergy analysis, and why is it important in the context of drying onions?

Exergy analysis is a method used to assess the quality and potential of energy within a system, going beyond just measuring the quantity of energy. It focuses on how useful the energy is for doing work and identifies where energy is wasted or degraded. In the context of onion drying, exergy analysis is important because it helps to pinpoint exactly where energy is being lost, allowing for optimization of the drying process to reduce waste, enhance sustainability by lowering the carbon footprint, and improve the quality of the dried onions.

2

How does exergy analysis differ from traditional energy analysis, and why is this difference significant?

Traditional energy analysis only considers the quantity of energy being used in a process, while exergy analysis looks at the quality and potential of that energy to perform work. The key difference is that exergy analysis identifies where energy is degraded or lost, providing a more detailed understanding of inefficiencies. This is crucial because simply knowing the total energy input (as in traditional analysis) doesn't reveal how much of that energy is actually used effectively. Without understanding this, you can't optimize the process to reduce waste and improve efficiency as effectively.

3

How can manufacturers use exergy analysis to improve the onion drying process, and what are the implications of these improvements?

By using exergy analysis in onion drying, manufacturers can identify specific areas where energy is being wasted, such as heat loss in the drying equipment or inefficiencies in airflow. This understanding enables them to adjust parameters like temperature and airflow to minimize these losses. The implications include reduced energy consumption, lower operational costs, a smaller environmental footprint, and potentially higher quality dried onion products due to more controlled drying conditions.

4

In what ways does exergy analysis contribute to sustainability in food processing?

Sustainability is enhanced through exergy analysis because it promotes the efficient use of energy resources. By minimizing energy waste in processes like onion drying, exergy analysis directly contributes to a smaller carbon footprint and reduces the environmental impact of food production. This aligns with the growing global emphasis on sustainable practices and responsible resource management, making it a valuable tool for industries aiming to reduce their ecological footprint.

5

Is exergy analysis limited to onion drying, or can it be applied to other areas of food processing or industries?

While the text focuses on onion drying, exergy analysis can be applied to a wide range of food drying processes and other energy-intensive industrial applications. Its principles of identifying and minimizing energy waste are universally applicable. For example, it could be used to optimize the drying of fruits, vegetables, grains, or even in processes beyond food production, such as chemical manufacturing or power generation, to improve efficiency and sustainability across various sectors.

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