Overall thermal resistance through flat resistances in series is calculated as the _____________ of individual resistances?
Show answer Hide answer
Answer: D. Sum
Explanation
Thermal resistances in series represent distinct material layers that heat must flow through consecutively. Adding individual thermal resistances linearly yields the total equivalent thermal resistance of the composite wall. This principle is directly analogous to electrical resistors connected in series within an electric circuit. Heat transfer through flat composite walls is modeled using thermal resistance networks in series. Conductive thermal resistance equals layer thickness divided by thermal conductivity and cross-sectional area. Total thermal resistance determines the overall heat transfer rate for a given overall temperature difference.
Insulating industrial buildings and cold storage rooms requires summing insulation layer resistances. Furnace manufacturers use series resistance calculations to select refractory brick and insulation combinations. Energy efficiency audits rely on accurate thermal resistance summation to calculate total heat loss. Averaging individual resistances fails to account for the cumulative thermal barrier presented by multiple layers. Using geometric means violates the fundamental linear addition rules of one-dimensional heat transfer circuits. Multiplying individual resistances would yield dimensionally incorrect thermal circuit calculations.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. 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...
Q2. 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....
Q3. A 0.2 m thick slab has its left face at 80°C and right face exposed to air at 30°C (k = 1.2 W/m.K, convective coefficient = 10 W/m2.K). At steady state, the right face temperature in °C is____________________?
Show answer Hide answer
Answer: D. 48.7
Steady state heat flux through the solid slab must equal the convective heat transfer rate at the right surface. Equating conductive thermal resistance of the slab to the right side convective resistance calculates the i...
Q4. Shell and tube heat exchangers utilize baffles primarily to______________?
Show answer Hide answer
Answer: B. Enhance turbulence
Baffles force shell-side fluid to cross the tube bundle repeatedly instead of bypassing it. This cross-flow pattern significantly enhances fluid turbulence and increases overall heat transfer coefficients. Intensified tu...
Q5. Expansion bellows are incorporated into tubular heat exchanger shells to_____________________?
Show answer Hide answer
Answer: C. Account for the uneven expansion of shell and tube bundles
Expansion bellows absorb the differential thermal expansion occurring between the shell and tubes. Without these flexible joints, severe mechanical stresses would develop during high temperature operations. Absorbing rel...
Q6. The ratio of vapor mass generated per unit mass of steam supplied to an evaporator is termed____________?
Show answer Hide answer
Answer: C. Economy
Steam economy directly measures how efficiently an evaporator utilizes the supplied primary live steam. Dividing the total vapor mass generated by the live steam mass yields this dimensionless ratio. Higher economy value...