PhD Lay-out

  1. Introduction
  2. Energy crisis
  3. Organic Rankine cycle
  4. Advantages
  5. Components
  6. Applications
  7. The transcritical Rankine cycle
  8. Literature study and introduction about transcritical ORCs
  9. Modelling in EES
  10. Terminology
  11. Energy equations
  12. Performance indicators
  13. Classification of working fluids
  14. Selection of working fluid via parametric analysis
  15. Parametric study for transcritical cycle (and subcritical)
  16. Parameter range
  17. Choose best working fluids for the parameter range
  18. Comparison with subcritical Rankine cycle
  19. Heat exchanger design for ORCs using supercritical fluids
  20. Heat exchange equations
  21. Convection coefficient
  22. Heat transfer to supercritical fluids
  23. Literature study: Research (nuclear reactors …)
  24. Thermophysical properties
  25. Investigation of the behaviour of the thermophysical properties in the critical and pseudo-critical region: Use Xprop of coolprop
  26. Similarity (dimensionless parameters) between water, CO2 and several refrigerants
  27. Specifics of the behaviour of thermophysical properties of coolants in the single-phase near-critical region subdivision in pseudoliquid, pseudophase transition and pseudogas regime
  28. Test setup for local heat transfer measurements
  29. Sizing: via temperature program, mass flow rate and type of waste heat
  30. Pump, length and diameter test section, relief valve, condenser
  31. Compatibility of the test setup: vertical, horizontal, inclined
  32. Choosing working conditions – combinations
  33. Variables SCP fluid: mass flow rate, pressure, inlet enthalpy (temperature)
  34. Variables heating source: heat flux
  35. Flow-sounding studies
  36. Laser designation techniques
  37. Turbulent heat transfer in round tubes under heating conditions in round tubes
  38. Heat transfer phenomena at supercritical fluids
  39. Normal heat transfer
  40. Heat transfer enhancement
  41. Heat transfer deterioration
  42. Nature of heat transfer deterioration
  43. Subdivision according to Kurganov in 6 groups
  44. Correlations
  45. Normal heat transfer - Heat transfer enhancement
  46. Heat transfer deterioration
  47. Hydraulic studies
  48. Pressure drop at supercritical pressure
  49. Correlation
  50. Case studies for complete heat exchangers
  51. Tube in tube (R125-water and R245fa-thermal oil)
  52. Plate heat exchanger (Queensland, R125 and R245fa)
  53. Thermohydraulic design of a supercritical heat exchanger for organic Rankine cycles (thesis proposal)
  54. Discussion about the use of the correlation for complete HXs
  55. Future works
  56. Mixtures
  57. Different angles
  58. Kenics static mixtures for improved heat transfer
  59. CFD for HTD  turbulent transfer and heat transfer reduction due to reduction in shear stresses due to buoyancy and thermal acceleration.

My research

Goals and deadlines

01/10/2012  31/03/2013
  • Literature study
  • Transcritical ORCs
  • Supercritical forced convective heat transfer
  • Cycle architecture of transcritical ORCs with EES
  • Part 1: Simulation for sizing test setup
  • Thermophysical properties
  • Part 1: Investigation of the behaviour of the thermophysical properties
  • Part 2: Understand the meaning of the several thermophysical properties
  • Part 3: Investigate similarity between several fluids
  • Designing a test setup
01/04/2013  30/09/2013
  • Designing a test setup
  • Experiments for supercritical heat transfer (QU, AU)
  • Part 2: Measurements on a heat exchanger
01/10/2013  31/03/2014
  • Designing a test setup
  • Experiments for supercritical heat transfer
  • Part 1: Measurements on a single heated tube
01/04/2014  30/09/2014
  • Experiments for supercritical heat transfer
  • Part 1: Measurements on a single heated tube
  • Data reduction
  • Part 1: General characteristics
  • Part 2: Detailed characteristics
  • Part 3: Data reduction using neural networks
01/10/2014  31/03/2015
  • Experiments for supercritical heat transfer
  • Part 1: Measurements on a single heated tube
  • Experiments for supercritical heat transfer
  • Part 2: Measurements on a heat exchanger
  • Data reduction
  • Part 1: General characteristics
  • Part 2: Detailed characteristics
  • Part 3: Data reduction using neural networks
01/04/2015  30/09/2015
  • Cycle architecture of transcritical ORCs with EES
  • Part 2: Simulation with the new correlation from the experiments
  • Cycle architecture of transcritical ORCs with EES
  • Part 3: Simulation of complete transcritical ORC
01/10/2015  31/03/2016
  • Writing of PhD manuscript

Cycle architecture of transcritical ORCs with EES

Part 1: Simulation for sizing test setup

Make a simulation program of a transcritical Rankine cycle for a fixed:

  • Heat source inlet temperature = 150°C
  • Supercritical pressure = 1.01 – 1.2 pcrit
  • Inletcooling water inlettemperature = 15°C
  • Condensing temperature = 26°C
  • Pinch point in the HXs = 2°C
  • Simple tube-in-tube HX for the vapour generator (check for typical diameter in S&T HXs)
  • Typical HX for the condenser (check with existing condensers)
  • Use existing correlations of supercritical forced convection heat exchange

In the first step to have an idea of the needed HX surface, mass flow rates for working fluid and condenser for the test setup.

Part 2: Simulation with the new correlation from the experiments

After performing experiments with a tube-in-tube HX (water or thermal oil as heat source), use the new correlation and compare the prediction of the outlet temperature with the measurements.

  • Take 2 or 3 working fluids
  • Range of conditions:
  • Working fluid:
  • Pressure
  • inlet temperature
  • mass flow
  • Heat source:
  • mass flow
  • inlet temperature
  • Compare also the results with existing correlations

Part 3: Simulation of complete transcritical ORC

Using the new correlation (also compare with existing correlations), check the following performance indicators:

  • Power output
  • (Exergy efficiency)
  • Size HX
  • Power output/Size HX
  • Power output/Cost HX (or Power output/Cost system)

Thermophysical properties

Part 1: Investigation of the behaviour of the thermophysical properties

Choose several refrigerants.

  • Make a table and plot via Refprop, EES or Coolprop to show the variation of cp, , Pr,  and  with the temperature and pressure (from subcritical to supercritical 1.5 pcrit and from T<Tcrit to T> Tcrit).
  • Compare the steepness and magnitude of these variations.
  • Determine for each pressure the pseudo-critical temperature and put this in a graph and table.
  • Example

Part 2: Understand the meaning of the several thermophysical properties

  • Specific heat cp
  • Density 
  • Prandtl number Pr
  • Dynamic and kinematic viscosity and 
  • Thermal conductivity 

Part 3: Investigate similarity between several fluids

  • What is similarity?
  • Make a plot for water, CO2 and several refrigerants like the one below to state similarity

Designing a test setup

  • Determine parameter range
  • Sizing of the test setup:
  • All parts needed
  • Ask price and order
  • Start building
  • Software Labview

Experiments for supercritical heat transfer

Part 1: Measurements on a single heated tube

  • What to measure
  • Mass flow
  • Fluid inlet temperature
  • Fluid outlet temperature
  • Electrical uniform wall heat flux via measurement of voltage and current.
  • Outside wall temperature of the pipe in intervals along and around the pipe.
  • Pressures (pressure drop)
  • Stability of the system
  • Check stability temperatures and pressure for cte mass flow and heat flux
  • Configuration
  • Several diameters
  • Several inclinations  vertical, horizontal and inclined
  • Smooth tubes!
  • L/d~100 or more
  • Determine the hydraulic resistance preliminarily under adiabatic conditions  to recognize the considerable influence of wall roughness on hydraulic resistance in the same rang of Re numbers, within which the abnormal HT data will be than later obtained (paper Kurganov).

Part 2: Measurements on a heat exchanger

Queensland, Australia (work on plate heat exchangers)

  • Mass flow
  • Working fluid inlet temperature
  • Working fluid outlet temperature
  • Heat source inlet temperature
  • Heat source outlet temperature
  • Pressure after pump
  • Check stability temperatures and pressure for constant mass flow and heat flux  for error analysis
  • Configuration
  • Plate heat exchangers
  • Horizontal shell and tube
  • Vertical shell and tube
  • Tube in tube

Results of this have to be correlated with the model and test setup single tube.

  • Develop dynamic models for the complete HXs (plate, tube-in-tube, S&T) as function of Re and Pr. The models should predict the outlet temperatures of the SC fluid in a certain range of the experimental values and predict the dynamic response to step disturbances in the process variables.
  • Develop a steady state correlation for the overall HTC of the SC fluid
  • Compare the dynamics between experiments and simulation
  • Step disturbances in process variables
  • Use of static mixers for improved heat transfer
  • E.g. Kenics Static Mixer

Data reduction

Part 1: General characteristics

  • Vertical upward flow
  • Heat transfer is enhanced for:
  • Higher mass flux
  • Lower heat flux
  • Vertical downward flow
  • Heat transfer is enhanced for:
  • Higher mass flux
  • Lower heat flux
  • Horizontal
  • Heat transfer is enhanced for:
  • Higher mass flux
  • Lower heat flux
  • Inclined downward flow
  • Heat transfer is enhanced for:
  • ???
  • Effect on plate heat exchangers
  • Use of static mixers for improved heat transfer in 1 tube
  • E.g. Kenics Static Mixer

Part 2: Detailed characteristics

  • Plot wall temperature as function of x or x/d: for each several conditions of mass flow and heat flux, pressure and inlet temperature.
  • Plot bulk temperature as function of x or x/d: for each several conditions of mass flow and heat flux, pressure and inlet temperature.
  • Plot bulk and wall temperature on one plot as function of x or x/d.
  • Plot HTC as function of bulk temperature
  • Plot HTC as function of wall temperature
  • To investigate the influence of the heat flux, this must be varied and check the influence on the wall temperature and thus HTC.

Part 3: Data reduction using neural networks