Question

A specific advantage of using steam as a heating medium in exchangers is its

• A. Inexpensiveness
• B. High value of latent heat
• C. High film coefficient
• D. Non-corrosive condensate

Hint:

Think about why steam is so widely used in power plants and industrial heating processes. The large amount of energy stored in its latent heat is a key reason for its effectiveness as a heat transfer fluid.

Answer 1

The Correct Option is B

Step 1: Understand the process of heat transfer with condensing steam.
When steam is used as a heating medium in a heat exchanger, it typically condenses on the heat transfer surface, releasing its latent heat of condensation at a relatively constant temperature (the saturation temperature corresponding to the steam pressure). This phase change allows for a large amount of heat to be transferred with a small temperature difference. 
Step 2: Analyze each of the given options as a potential advantage.
(1) Inexpensiveness: While steam can be relatively inexpensive to generate in many industrial settings, its cost depends heavily on the fuel source and the efficiency of the boiler. Therefore, inexpensiveness is not a universally specific advantage compared to other heating media in all situations. (2) High value of latent heat: Water has a significantly high latent heat of vaporization (and condensation) compared to many other common fluids. This means that a relatively small amount of steam can transfer a large quantity of heat as it condenses, making it a very efficient heating medium. This high energy density associated with the phase change is a distinct advantage. (3) High film coefficient: The heat transfer coefficient on the condensing steam side (film coefficient) is generally high compared to single-phase heat transfer of liquids or gases. This high heat transfer coefficient leads to a better overall heat transfer rate in the exchanger for a given temperature difference and surface area. So, this is also an advantage. However, the question asks for a specific advantage, and the high latent heat is a more fundamental and universally recognized benefit of using steam for heating. (4) Non-corrosive condensate: While steam condensate can be relatively clean and may be reused in the boiler, it is not necessarily non-corrosive. Dissolved gases like oxygen and carbon dioxide in the condensate can lead to corrosion of metallic surfaces. Proper treatment of boiler feedwater and condensate is often required to minimize corrosion. Therefore, this is not a specific and guaranteed advantage of using steam. 
Step 3: Determine the most specific and significant advantage.
Considering the options, the high latent heat of condensation is a uniquely significant advantage of using steam as a heating medium. It allows for efficient heat transfer at a relatively constant temperature. While a high film coefficient is also beneficial, it is a consequence of the condensation process, which is driven by the release of latent heat. The inexpensiveness and non-corrosiveness are not guaranteed or specific to all situations involving steam. Therefore, the high value of latent heat is the most specific and prominent advantage of using steam as a heating medium in heat exchangers.