Heat Transfer Analysis in Double Pipe Heat Exchanger
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Questions and Answers

What effect does an increase in Reynolds number have on heat transfer in a double pipe heat exchanger?

  • It increases turbulence and improves convective heat transfer. (correct)
  • It reduces turbulence, leading to worse heat transfer.
  • It decreases the overall heat transfer coefficient.
  • It has no significant effect on heat transfer.

    • What is the purpose of the orifice meters used in the experimental setup?

  • To control fluid flow rates.
  • To calculate thermal conductivity.
  • To measure temperature differences.
  • To measure pressure differences. (correct)

    • Which symbol represents the heat transfer rate in the nomenclature?

  • 𝑈
  • 𝑚
  • ∆𝑇#$
  • 𝑄 (correct)

    • What unit is used to measure thermal conductivity according to the nomenclature?

    <p>W/m.K</p> Signup and view all the answers

    What was the role of the eight thermocouples in the experimental setup?

    <p>To monitor temperature changes at various points.</p> Signup and view all the answers

    What kind of heat exchanger was primarily studied in this experiment?

    <p>Double pipe heat exchanger</p> Signup and view all the answers

    What is the relationship between Reynolds number and heat transfer coefficient as found in the study?

    <p>They are directly proportional.</p> Signup and view all the answers

    What is represented by the symbol 𝑈 in the nomenclature?

    <p>Overall heat transfer coefficient</p> Signup and view all the answers

    What was the primary purpose of the experiment discussed?

    <p>To investigate the effect of the Reynolds number on heat transfer</p> Signup and view all the answers

    Which valves were designated for co-current flow in the experiment?

    <p>Valves 1-4</p> Signup and view all the answers

    What indicates errors in the steam generator during the experiment?

    <p>Unsteady flow rate and conditions</p> Signup and view all the answers

    What is the expected relationship between Reynolds number and heat transfer coefficient?

    <p>Heat transfer coefficient increases with increasing Reynolds number</p> Signup and view all the answers

    Which method was used to calculate mass flow rates in the experiment?

    <p>Pressure difference measurements</p> Signup and view all the answers

    What was a major reason for discrepancies between theoretical and experimental results?

    <p>Heat loss due to lack of insulation</p> Signup and view all the answers

    What type of flow was found to be more efficient under specific conditions in the experiment?

    <p>Counter-current flow was more efficient in run 1 and run 4</p> Signup and view all the answers

    What additional calculations were performed alongside mass flow rates in the experiment?

    <p>Prandtl number and Reynolds number calculations</p> Signup and view all the answers

    What is one reason the co-current approach value is expected to be higher?

    <p>The exit temperature of one stream approaches that of the other.</p> Signup and view all the answers

    How is the Reynolds number related to the mass flow rate?

    <p>It is directly proportional.</p> Signup and view all the answers

    What primarily causes the deviation in the Reynolds number for cold streams across different runs?

    <p>Fluctuations in the viscosity of the cold stream.</p> Signup and view all the answers

    What is the expected relationship between the Nusselt number and the Reynolds number?

    <p>Nusselt number increases with an increase in Reynolds number.</p> Signup and view all the answers

    Why is counter-current flow considered more efficient than co-current flow?

    <p>The logarithmic temperature difference is higher.</p> Signup and view all the answers

    What anomaly was observed in Runs 2 and 3 regarding Q values?

    <p>Co-current flow values were higher than expected.</p> Signup and view all the answers

    What influences the individual heat transfer coefficients for hot flow?

    <p>Viscosity values which change with temperature.</p> Signup and view all the answers

    What observation can be made regarding the Q values in theoretical Runs 1 and 4 compared to co-current?

    <p>Counter-current Q values exceeded co-current Q values.</p> Signup and view all the answers

    What is primarily observed in the experiment regarding the Reynolds number?

    <p>Its effect on the heat transfer coefficient.</p> Signup and view all the answers

    How is the volumetric flow rate of the cold stream outlet measured?

    <p>By measuring time for a certain volume of fluid.</p> Signup and view all the answers

    What does the range value in heat exchangers represent?

    <p>The difference between the outlet and inlet temperature of the same stream.</p> Signup and view all the answers

    Why does the co-current flow mode have a smaller range than the counter-current flow?

    <p>Because temperatures of streams converge as they flow in the same direction.</p> Signup and view all the answers

    What is the steady state condition defined by in this experiment?

    <p>When temperature data from a thermocouple remains the same three times in a row.</p> Signup and view all the answers

    What is altered in the experiment to observe the effect on the cold stream?

    <p>The flow direction and flow rate based on pressure difference.</p> Signup and view all the answers

    Which statement accurately describes the approach of co-current heat exchangers?

    <p>It is generally smaller than counter-current approaches.</p> Signup and view all the answers

    What factor is NOT directly measured in this heat transfer experiment?

    <p>Pressure differences in the cold stream.</p> Signup and view all the answers

    What is the formula for calculating the mass flow rate in kg/s?

    <p>$m = 1.223 \times (\Delta P)^{0.5}$</p> Signup and view all the answers

    Which formula is used to calculate the Reynolds number?

    <p>$Re = \frac{\rho V D}{\mu}$</p> Signup and view all the answers

    What is the correct expression for the Prandtl number?

    <p>$Pr = \frac{\mu C_p}{k}$</p> Signup and view all the answers

    For heating, how is the Nusselt number calculated according to the correlation provided?

    <p>$Nu = 0.023 Re^{0.5} Pr^{0.5}$</p> Signup and view all the answers

    What is the formula used to calculate the overall heat transfer coefficient?

    <p>$U + A = \frac{1}{r} ln(r_1/r_2)$</p> Signup and view all the answers

    How is the hydraulic diameter ($D_h$) calculated?

    <p>$D_h = D_{outer} - D_{inner}$</p> Signup and view all the answers

    Which parameter is NOT a requirement for choosing a correlation for Nusselt number?

    <p>Temperature range of $0 \leq T \leq 100$</p> Signup and view all the answers

    What are the units used for thermal conductivity ($k$) in the context provided?

    <p>W/m·K</p> Signup and view all the answers

    What is the correct formula for calculating the theoretical heat transfer rate?

    <p>𝑄 = 𝑈𝐴(∆𝑇#$)</p> Signup and view all the answers

    How is the volumetric flow rate calculated?

    <p>Volume divided by time</p> Signup and view all the answers

    What is the density of water at 290°C used in the calculations?

    <p>0.7319 kg/m³</p> Signup and view all the answers

    What does the symbol U represent in the heat transfer equation?

    <p>Overall heat transfer coefficient</p> Signup and view all the answers

    Which of the following is NOT a formula related to calculating heat transfer?

    <p>𝑄 = 𝑚𝐶𝑉(∆𝑇)</p> Signup and view all the answers

    What is the purpose of using the Prandtl number in heat transfer calculations?

    <p>To relate momentum diffusivity to thermal diffusivity</p> Signup and view all the answers

    Which formula is used to calculate the mass flow rate from volumetric flow rate?

    <p>$mass = volume \cdot 𝜌$</p> Signup and view all the answers

    Study Notes

    Heat Transfer Characteristics of a Double Pipe Heat Exchanger (DP)

    • The study analyzed the thermal dynamics of co-current and counter-current flow double pipe heat exchangers
    • The effect of Reynolds number on heat transfer coefficients was investigated
    • Experimental setup included eight thermocouples and two orifice meters for pressure measurement
    • The setup allowed for precise data collection under various operational conditions
    • Higher Reynolds numbers increased turbulence and improved convective heat transfer
    • A strong relationship was found between Reynolds number and heat transfer coefficient
    • Counter-current flow provided more efficient heat transfer with a constant temperature gradient
    • Co-current flow had decreasing temperature differences throughout the system, resulting in lower thermal efficiency
    • Experimental setup limitations and equipment errors possibly led to unexpected results
    • Maintaining steady-state conditions during experiments was a challenge for accurate heat transfer rate evaluations
    • The research yielded practical findings to validate the theoretical relationship between mass flow rate and pressure drop

    Nomenclature

    • ρ: Density (kg/m³)
    • Cp: Heat Capacity (J/kg⋅K)
    • Q: Heat transfer rates (W)
    • h: Individual heat transfer coefficient (W/m²⋅K)
    • ATlm: Log mean temperature difference (K)
    • m: Mass flow rate (kg/s)
    • NuD: Nusselt number (dimensionless)
    • U: Overall heat transfer coefficient (W/K)
    • Pr: Prandtl number (dimensionless)
    • ΔP: Pressure difference (bar)
    • Re: Reynolds number (dimensionless)
    • k: Thermal conductivity (W/m⋅K)
    • μ: Viscosity (Ns/m²)

    Abstract

    • This study analysed the thermal dynamics of co-current and counter-current flow double pipe heat exchangers, investigating the effect of Reynolds number on heat transfer coefficients.
    • Experiments varied hot and cold fluid velocities to obtain different Reynolds numbers.
    • An expected stronger relationship between Reynolds number and heat transfer coefficient was found with experimental results being affected by experimental setup limitations.
    • Counter current flow had a greater thermal efficiency compared with co-current flow.
    • The study yielded practical findings to validate the theoretical relationship between mass flow rate and pressure drop.

    Experimental Procedure

    • The system used a double pipe heat exchanger to observe the effects of various flows
    • Eight thermocouples measured the temperature of hot and cold fluid flows
    • Ten valves were used to control and arrange flow direction and achieve co/counter current flows
    • Pressure difference was monitored with an orifice meter
    • Steady-state conditions were ensured by monitoring and controlling temperatures and pressure differences.

    Results

    • Data collected on mass flow rates for hot/cold fluids, are presented in a table
    • Temperature changes across the heat exchanger were plotted graphs for both co-current flow and counter-current flow
    • Tables include temperature data for both co-current and counter-current flows for various runs
    • Plots of temperature vs. length for co-current runs are included
    • Plots of temperature vs. length for counter-current runs are included
    • Reynolds numbers were calculated for each fluid stream

    Discussion

    • The primary objective was to study the effect of Reynolds number and temperature differences on heat transfer
    • Experimental observations showed that higher Reynolds number led to increased turbulence and improved convective heat transfer, in line with expectations.
    • Co-current flow had notably lower temperature differences compared to counter-current flow.
    • Differences were observed in experimental results compared to theoretical results, possibly due to limitations in the experimental setup's size, insulation, and unsteady flow rate or instrumentation errors
    • The unsteady flow rate of steam led to varying pressure drop differences in the experiment.

    Conclusion

    • The experiment investigated Reynolds number effects on heat transfer coefficients in co/counter flow heat exchangers
    • It examined the impact of directional flow (co/counter) on heat transfer efficiency within experimental constraints.
    • Findings validated or showed discrepancy with theoretical models.

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    DP Report PDF - Heat Transfer Characteristics

    Description

    This quiz explores fundamental concepts related to heat transfer in double pipe heat exchangers. It covers topics such as the impact of Reynolds number on heat exchange efficiency, the use of orifice meters, nomenclature symbols, and the role of thermocouples in experimental setups. Test your knowledge and understanding of these critical engineering principles.

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