PhD Lay-out
1. Introduction
a. Energy crisis
b. Organic Rankine cycle
i. Advantages
ii. Components
iii. Applications
2. The transcritical Rankine cycle
a. Literature study and introduction about transcritical ORCs
b. Modelling in EES
i. Terminology
ii. Energy equations
iii. Performance indicators
c. Classification of working fluids
d. Selection of working fluid via parametric analysis
e. Parametric study for transcritical cycle (and subcritical)
i. Parameter range
ii. Choose best working fluids for the parameter range
iii. Comparison with subcritical Rankine cycle
f. Heat exchanger design for ORCs using supercritical fluids
i. Heat exchange equations
ii. Convection coefficient
3. Heat transfer to supercritical fluids
a. Literature study: Research (nuclear reactors …)
4. Thermophysical properties
a. Investigation of the behaviour of the thermophysical properties in the critical and
pseudo-critical region: Use Xprop of coolprop
b. Similarity (dimensionless parameters) between water, CO2 and several refrigerants
c. Specifics of the behaviour of thermophysical properties of coolants in the singlephase near-critical region  subdivision in pseudoliquid, pseudophase transition and
pseudogas regime
5. Test setup for local heat transfer measurements
a. Sizing: via temperature program, mass flow rate and type of waste heat
i. Pump, length and diameter test section, relief valve, condenser
b. Compatibility of the test setup: vertical, horizontal, inclined
c. Choosing working conditions – combinations
i. Variables SCP fluid: mass flow rate, pressure, inlet enthalpy (temperature)
ii. Variables heating source: heat flux
6. Flow-sounding studies
a. Laser designation techniques
7. Turbulent heat transfer in round tubes under heating conditions in round tubes
a. Heat transfer phenomena at supercritical fluids
i. Normal heat transfer
8.
9.
10.
11.
ii. Heat transfer enhancement
iii. Heat transfer deterioration
b. Nature of heat transfer deterioration
i. Subdivision according to Kurganov in 6 groups
c. Correlations
i. Normal heat transfer - Heat transfer enhancement
ii. Heat transfer deterioration
Hydraulic studies
a. Pressure drop at supercritical pressure
b. Correlation
Case studies for complete heat exchangers
a. Tube in tube (R125-water and R245fa-thermal oil)
b. Plate heat exchanger (Queensland, R125 and R245fa)
c. Thermohydraulic design of a supercritical heat exchanger for organic Rankine cycles
(thesis proposal)
Discussion about the use of the correlation for complete HXs
Future works
a. Mixtures
b. Different angles
c. Kenics static mixtures for improved heat transfer
d. 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
o Transcritical ORCs
o Supercritical forced convective heat transfer
 Cycle architecture of transcritical ORCs with EES
o Part 1: Simulation for sizing test setup
 Thermophysical properties
o Part 1: Investigation of the behaviour of the thermophysical properties
o Part 2: Understand the meaning of the several thermophysical properties
o 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)
o Part 2: Measurements on a heat exchanger
01/10/2013  31/03/2014
 Designing a test setup
 Experiments for supercritical heat transfer
o Part 1: Measurements on a single heated tube
01/04/2014  30/09/2014
 Experiments for supercritical heat transfer
o Part 1: Measurements on a single heated tube
 Data reduction
o Part 1: General characteristics
o Part 2: Detailed characteristics
o Part 3: Data reduction using neural networks
01/10/2014  31/03/2015
 Experiments for supercritical heat transfer
o Part 1: Measurements on a single heated tube
 Experiments for supercritical heat transfer
o Part 2: Measurements on a heat exchanger
 Data reduction
o Part 1: General characteristics
o Part 2: Detailed characteristics
o Part 3: Data reduction using neural networks
01/04/2015  30/09/2015
 Cycle architecture of transcritical ORCs with EES
o Part 2: Simulation with the new correlation from the experiments
 Cycle architecture of transcritical ORCs with EES
o 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
Inlet cooling water inlet temperature = 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:
o Working fluid:
 Pressure
 inlet temperature
 mass flow
o 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:
o All parts needed
o
Ask price and order
Start building
Software Labview
Experiments for supercritical heat transfer
Part 1: Measurements on a single heated tube




What to measure
o Mass flow
o Fluid inlet temperature
o Fluid outlet temperature
o Electrical uniform wall heat flux via measurement of voltage and current.
o Outside wall temperature of the pipe in intervals along and around the pipe.
o Pressures (pressure drop)
Stability of the system
o Check stability temperatures and pressure for cte mass flow and heat flux
Configuration
o Several diameters
o Several inclinations  vertical, horizontal and inclined
o Smooth tubes!
o 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
o Plate heat exchangers
o Horizontal shell and tube
o
o
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.
o Develop a steady state correlation for the overall HTC of the SC fluid
o Compare the dynamics between experiments and simulation
o Step disturbances in process variables
Use of static mixers for improved heat transfer
o E.g. Kenics Static Mixer
Data reduction
Part 1: General characteristics





Vertical upward flow
o Heat transfer is enhanced for:
 Higher mass flux
 Lower heat flux
Vertical downward flow
o Heat transfer is enhanced for:
 Higher mass flux
 Lower heat flux
Horizontal
o Heat transfer is enhanced for:
 Higher mass flux
 Lower heat flux
Inclined downward flow
o Heat transfer is enhanced for:
 ???
 Effect on plate heat exchangers
Use of static mixers for improved heat transfer in 1 tube
o 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