During air flow past a wet bulb thermometer in an air-water vapor system, what is the approximate magnitude of h2/ky.Cz____________________?
Show answer Hide answer
Answer: C. 1
Explanation
The psychrometric ratio relates heat transfer coefficient to mass transfer coefficient and humid heat. For an air-water system at ambient temperatures the psychrometric ratio evaluates to approximately one. Unity value arises because the thermal and mass diffusivities of air and water vapor are nearly equal. Lewis number is the ratio of thermal diffusivity to mass diffusivity in fluid mixtures. Wet bulb thermometers measure equilibrium temperatures reached by evaporating moisture into gas streams. Mass transfer coefficients and heat transfer coefficients govern simultaneous heat and mass transfer.
Psychrometric charts used in air conditioning and drying calculations rely on this specific ratio. Engineers apply the Lewis relation to simplify complex simultaneous heat and mass transfer equations. Air-water systems are unique in having a Lewis number close enough to unity for practical simplifications. Zero point sixty is incorrect for air-water systems and applies to different gas-vapor mixtures. Zero point twenty-four represents the specific heat of dry air rather than the psychrometric ratio. Zero point seventy-two is an intermediate value that does not match the air-water psychrometric ratio.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. How is the mass transfer area defined when using a wetted wall column for experimental determinations___________________?
Show answer Hide answer
Answer: C. Known
Wetted wall columns feature a uniform liquid film flowing down the inside of a known vertical tube. The exact geometric dimensions of the vertical tube provide a precisely calculable surface area. Knowing the exact mass...
Q2. How does the reflux ratio of an unlagged distillation column compare under identical process conditions___________________?
Show answer Hide answer
Answer: B. Increases in winter
Unlagged distillation columns lack external thermal insulation exposing the shell to ambient conditions. Winter conditions feature lower ambient temperatures causing increased convective and radiative heat losses. Higher...
Q3. If the liquid rate supplied to an absorber is reduced while keeping the system unchanged, how will the required tower height be affected__________________?
Show answer Hide answer
Answer: A. Increase
Reducing the liquid solvent rate decreases the solute concentration gradient driving force across the tower. Lower driving forces slow down the rate of mass transfer throughout the absorption column height. A smaller mas...
Q4. Continuous drying of granular or crystalline solids is typically carried out using a _______________ dryer?
Show answer Hide answer
Answer: C. Rotary
Rotary dryers provide continuous tumbling action for free-flowing granular or crystalline solids. Continuous rotation ensures excellent contact between the falling solids and the hot drying gas stream. High processing ca...
Q5. What does fractional solvent extraction achieve______________________?
Show answer Hide answer
Answer: B. Employs two solvents
Fractional solvent extraction uses two immiscible or partially miscible solvents to achieve separation. Feed components distribute themselves differently between the two liquid phases based on solubility. Using two disti...
Q6. What type of drier is best suited for handling free-flowing granular solids__________________?
Show answer Hide answer
Answer: A. Rotary
Rotary dryers are specifically designed to tumble and handle free-flowing granular solids efficiently. Internal flights lift and shower the granular solids through the hot drying gas stream continuously. Continuous tumbl...