Peak heat transfer coefficients using steam heating are achieved when the steam is_________________?
Show answer Hide answer
Answer: B. Saturated
Explanation
Saturated steam condenses at a constant temperature releasing its full latent heat of vaporization efficiently. Superheated steam must first be cooled to saturation temperature which involves lower single phase heat transfer coefficients. Wet steam contains liquid droplets that can accumulate and thicken the condensate film resistance on surfaces. Steam is widely used as a heating medium in industrial reboilers and evaporators due to high latent heat. Saturated steam exists at the exact boiling point corresponding to its operating pressure. Latent heat represents the massive amount of energy released during the phase change from vapor to liquid.
Chemical processing plants utilize saturated steam headers to maintain precise and uniform heating temperatures. Avoiding superheated steam prevents unnecessary thermal stresses and maintains maximum heat transfer rates. Proper steam trap maintenance ensures that condensate is removed without letting wet steam degrade efficiency. Supersaturated steam conditions are unstable and do not provide optimal phase change heat transfer coefficients. Wet steam introduces liquid droplets that hinder heat transfer and reduce overall condensation efficiency. Stating none of these is incorrect because saturated steam achieves the highest possible condensing coefficients.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. Non-condensable gases degrade vapor film coefficients; how do superheated vapor film coefficients compare to saturated vapor ones___________________?
Show answer Hide answer
Answer: C. Some
Superheated vapor film coefficients depend on competing physical effects during condensation and convective cooling processes. Initial forced convection of superheated vapor can yield lower heat transfer coefficients tha...
Q2. Local surface conductance for vertical laminar film condensation is expressed as (with t = film thickness) _________________?
Show answer Hide answer
Answer: B. ∝ 1/t
Local surface conductance represents the local heat transfer coefficient across the condensate film. Nusselt's laminar film condensation theory proves that surface conductance is inversely proportional to film thickness....
Q3. The Graetz number is associated with___________________
Show answer Hide answer
Answer: D. Heat transfer in laminar flow
The Graetz number is a dimensionless group that characterizes laminar heat transfer in internal pipe and conduit flows. It is defined mathematically as the mass flow rate multiplied by specific heat capacity divided by t...
Q4. Fully developed thermal and hydrodynamic laminar pipe flow under constant wall heat flux exhibits a Nusselt number of__________________?
Show answer Hide answer
Answer: B. 4.36
Analytical solution of the energy equation for fully developed laminar pipe flow under constant heat flux yields a constant Nusselt number. The mathematical derivation for circular tubes with uniform wall heat flux resul...
Q5. Industrial practices cap heat exchanger cooling water outlet temperatures below 50°C primarily to prevent_________________?
Show answer Hide answer
Answer: B. Excessive corrosion
Corrosion rates of carbon steel and copper alloy heat exchanger tubes accelerate significantly at elevated temperatures. Keeping cooling water outlet temperatures below fifty degrees Celsius helps control material degrad...
Q6. Reducing radiation heat loss from a mild steel surface by lowering its emissivity is best accomplished via__________________?
Show answer Hide answer
Answer: B. Painting the surface white (with aluminium paint)
Radiation heat loss is directly proportional to the surface emissivity of the material emitting the thermal energy. Giving a metal surface a smooth polished mirror finish minimizes its ability to emit thermal radiation....