- Steam Theory
- 1. Basics of Steam
- 2. Steam Control
- 3. Steam Heating
- 4. Basics of Steam Traps
- 5. Steam Trap Selection
- Steam Trap Selection: How Application Affects Selection
- Steam Trap Selection: Understanding Specifications
- Steam Trap Selection: Safety Factor and Life Cycle Cost
- Traps and Orifices Part 1
- Traps and Orifices Part 2
- Casting vs. Forging
- Applications of Different Types of Steam Traps
- Don't Get Steamed : Selecting Steam Trap Design
- Understanding Steam Traps
- Compare Two Fixed Orifice Venturi Products to a Variable Orifice Free Float Steam Trap
- 6. Steam Trap Problems
- 7. Steam Trap Management
- 8. Water Hammer
- Water Hammer: What is it?
- Water Hammer: The Mechanism
- Water Hammer: Cause and Location
- Water Hammer: In Steam Distribution Lines
- Water Hammer: In Equipment
- Water Hammer: In Condensate Transport Piping
- Identifying Water Hammer Using a Thermal Camera
- Mitigation of Water Hammer in Vertical Flashing Condensate Transport Piping
- Stop Knocking Your Condensate Return
- Steam Trap Management: Do Something; Anything. Please!
- 9. Risk Mitigation
- 10. Steam Quality
- 11. Steam Distribution
- 12. Condensate Recovery
- Introduction to Condensate Recovery
- Returning Condensate and When to Use Condensate Pumps
- Condensate Recovery: Vented vs. Pressurized Systems
- Condensate Recovery Piping
- What is Stall?
- Methods of Preventing Stall
- Cavitation in Condensate Pumps
- Steam Heat Exchangers are Underworked and Over-Surfaced
- Allocate New Plant Focus to Steam System Design—Part 2
- Optimize Reboiler Performance via Effective Condensate Drainage
- Vent Away Condensate Pump Frustrations in a Flash
- 13. Energy Efficiency
- Tips to improve steam plant efficiency
- Advice on Winter Preparation for Steam Systems
- Insulating Traps
- Steam Compressors
- Why Save Energy?
- Management Strategies for Conserving Energy
- Recovering Steam Clouds and Waste Heat
- Waste Heat Recovery
- Boiler Energy Saving Tips
- Steam Line Energy Saving Tips
- Steam-Using Equipment Energy Saving Tips
- Preventing Steam Leaks
- Handle Steam More Intelligently
- Optimize the Entire Steam System
- Use Available Data to Lower System Cost
- 14. Compressed Air / Gas
- 15. Other Valves
Comparing Steam and Hot Water Heating
Differences between Steam and Hot Water Heating
Both steam and hot water are commonly used as heating media in industrial applications. They may look different, but both are, in fact, water. So, how should you use these two heat sources differently?
At atmospheric pressure, water boils at 100°C [212°F]. To use liquid water at temperatures above 100°C, you must continuously apply pressure above the saturation level to the system.
Conversely, since the saturation temperature of steam at atmospheric pressure is 100°C, it is not possible to create saturated steam below 100°C simply by reducing its pressure with a pressure reducing valve. A vacuum pump is necessary to precisely control steam at below 100°C.
Because of this, in the majority of cases, hot water is used to heat at less than 100°C and steam is used for heating at over 100°C.
How Saturated Steam and Hot Water Transfer Heat
Herein, we will refer to saturated steam simply as steam. As a heating medium, steam offers the following advantages:
- It transfers heat through condensation. When it condenses, it releases a large amount of latent heat.
- It condenses at a constant temperature (the saturation temperature).
For these two reasons, steam heats faster and more evenly compared to hot water.
Vacuum steam heating systems have been developed so that the advantages of saturated steam can be utilized for heating below 100°C. In contrast, hot water transfers sensible heat through convection. In this process, the hot water transfers its heat to the product and its own temperature drops.
Hot water heating is therefore less uniform and transfers heat slower compared to steam heating.
Applications Where Hot Water Excels
With the advent of vacuum steam heating systems, steam heating has become possible even below 100°C. Is there still any merit in hot water heating, which is inferior to steam heating in terms of uniformity and heat transfer rate?
We argue that there is. Hot water heating has different features from steam heating. There are some heating processes in which the product itself generates heat (for example through an exothermic reaction) and becomes hotter than the heating medium. If this additional heat is not removed properly, the overall temperature may rise too high and the product may be ruined.
To prevent this, the excess heat needs to be removed and the product must be properly cooled. Hot water is a powerful tool in such a case. Hot water can be used as a medium for cooling products. In cooling processes, hot water absorbs the heat of the product again through convection. It collects this heat with the same heat transfer efficiency as when imparting it in heating processes.
Such processes employ forced convection, a heat transfer method in which hot water is constantly passed across the heat transfer surface. Through forced convection, the water absorbs the heat of the product making it possible to cool the system by transferring heat to the outside.
Applications Best Suited to Each Medium
What if steam were used in a cooling application? Like with hot water, when steam is cooler than the product, it absorbs some of the product's heat as it moves across the heat transfer surface.
When steam is used in a heating process, it condenses after it loses its heat, allowing new steam to enter the chamber. However, when steam itself is heated, it does not condense, and so new steam cannot flow into the chamber. Furthermore, since a steam trap should be preventing it from flowing out of the equipment, the steam cannot take enough heat away from the product to cool it.
Another reason why steam is not suited to indirect cooling processes is that its heat capacity is smaller than that of hot water.
For example, for adult humans, who typically have a body temperature of around 36.5°C [97.7°F], standing outside on a 30°C [86°F] day feels hot, but sitting in a 30°C bath water can give you a chill. Even at the same temperature, air (a gas like steam) will absorb less heat from the human body than water due to its lower heat transfer efficiency.
- Steam heating: Quick and uniform heat transfer, useful in heating processes
- Hot water heating: Capable of both heating and cooling, advantageous in heating processes that involve cooling
Keep these differences in mind when choosing whether to heat with steam or hot water.
When it comes to cooling processes, however, there is another method that should be considered as an alternative to hot water: vacuum steam cooling. We discuss vacuum steam cooling in more detail in an upcoming article.
|Steam Pressure Control||Heating with Steam|