Feasibility Analysis of a Two Phase
Solar Thermal Water Heater
Solar Thermal Solutions (M15)
Project Supervisor: Dr. Y. Muzychka
April 3rd, 2014
Marcus Davis
Steve Youden
Brain Hurley
Kyle Snow
Agenda
Introduction
 Supporting Theory
 System Overview
 Testing and Analysis
 Feasibility Analysis Results
 Sources of Error and Recommendations
 Budget Overview

Problem Statement

It is unclear if the introduction of two-phase
uniformly segmented plug flow to a flat plate
solar collector is feasible
Objectives
Introduce stable two-phase segmented
flow to a solar thermal water heating
system
 Evaluate effectiveness and economic
feasibility of introducing this flow to a flat
plate solar thermal collector as a retrofit
design

Project Constraints
Time (3.5 months)
 Financial ($450)
 Functionality

◦ Fluids constrained to water and air
◦ Freeze protection not considered
Equipment (i.e. pump, compressor)
 Testing conditions (thermo lab)

BACKGROUND THEORY
Solar Collectors

Special type of heat exchanger
◦ Differs from ‘normal’ heat exchangers that have
fluid to fluid heat exchange
◦ Converts solar radiant energy to thermal energy
Solar Collector Cross Section & Top view (Duffie & Beckman, 2013)
Two-Phase Flow


Segmented fluid flow
Results in increases circulation of liquid
segments, increasing heat transfer
L
=4
d
L
=6
d
L
= 10
d
Optimization Model
Two-phase flow heat transfer/pressure drop model
Liquid Length
=10-20
Air Length
= 3-6
Note: Air bubble lengths < 3 were difficult to create and maintain
SYSTEM DESCRIPTION
Collector Selection

Two options for collectors:
◦ NovaSolaris heat collector
◦ Purchase solar thermal collector
Decision Table

Decision made to move forward using the
readily-available NovaSolaris heat collector
System Description
SYSTEM PREPARATION
FOR TESTING
Goal For Preparation
1.
Create and observe stable, controllable
two-phase segmented flow before
introducing the phenomenon to heat
collector
2.
Integrate heat collector into system
while preserving the segmented flow
quality
Preliminary Flow Testing

Initial observations showed resemblance
of two-phase segmented flow
◦ The air plugs usually segregated
◦ Liquid segments carried significant amount of
residual air bubbles

Suspected that the configuration of the
air injection manifold root of flow issue
Air Injection Manifold Modifications
1.
Inject air through a smaller orifice
◦ Keeps bubble from segregating
2.
Reduce residual air space in manifold
◦ Minimize air in liquid segments
Heat Collector Integration

Found quality of two-phase flow
significantly degraded within collector
◦ Attributed to copper tubing configuration

Need to reduce from 6 to 3 passes to
preserve integrity of experiment
Final Flow Quality
FEASIBILITY ANALYSIS
METHODOLOGY
Feasibility Analysis Methodology
Single-Phase
System
Energy Gained = Ecollector - Epump
Feasibility Analysis Methodology
Two-Phase
System
Energy Gained = Ecollector - Epump - Econtrol - Ecompressor
Feasibility Analysis Methodology
Prove:
Energy Gained
(Single-Phase)
<
Energy Gained
(Two-Phase)
Energy Gained = Energy Outputs – Energy Inputs
TESTING AND RESULTS
DOE Testing
Phase
Intermediate
Testing Phase
Feasibility
Analysis
Testing Phase
DOE Testing
Phase
Intermediate
Testing Phase
Feasibility
Analysis
Testing Phase
Design of Testing Program

DOE (two-factorial experiment) used to
develop testing program
◦
◦
◦
◦
Checks significance of two-factor interaction
Identifies significance/sensitivity of factors
Validates/determines further experiment
Feasibility Analysis based on optimized values
Design of Testing Program

Variables for experiment
◦
◦
◦
◦
Length of Liquid Segment (β)
Length of Gas Segment (δ)
Mass Flow Rate
Angle of Collector
Parameter
Low Value
High Value
β
10
20
δ
3
6
Low
High
0
45
Liquid Flow Rate (l/min)
Angle of Collector (degrees)
Results of DOE Testing

12 tests performed

Conclusions drawn:
◦ Significant model (F-value 5.69 > 4)
◦ No significant 2-Factor interaction
◦ Most significant Factors are:
 Angle of Collector
 Length of air bubbles

Went Forward Using Best Observed
Conditions
DOE Testing
Phase
Feasibility
Analysis
Testing Phase
Intermediate
Testing Phase
Intermediate Testing
3 additional tests performed
 Confirmed that test 4 condition will be used for feasibility
analysis

Air Bubble
Liquid
Test
(δ)
Length (β)
4
13
14
15
6
9
6
6
20
20
26
33
Heat Collected Energy Consumed
Q (W-h)
263.00
215.00
235.00
238.00
Total (W-h)
19.66
21.30
19.39
20.52
Energy
COP
Gained (W-h)
243.34
193.70
215.61
217.48
13.38
10.10
12.12
11.60
Optimization Model Comparison
Experimental results show general trend
of optimization model
Q versus β
300.00
250.00
Q (W)

200.00
150.00
100.00
50.00
0.00
0
5
10
15
20
β
δ=6
δ=9
25
30
35
DOE Testing
Phase
Feasibility
Analysis
Testing Phase
Intermediate
Testing Phase
Feasibility Analysis Testing

Test
Used best two-phase conditions from DOE and
intermediate testing
Test Type
17 Two-Phase
Single Phase Constant Mass
Single Phase 19
Constant
18
Energy Collected
Energy Consumed
Q (W-h)
Total (W-h)
492.77
38.67
454.10
12.74
393.60
38.64
354.96
10.19
1.28
393.40
37.79
355.61
10.41
1.28
Energy Gained
COP
(W-h)
Two Phase Energy
Gained % Increase
Two-Phase versus Single Phase
Q versus Time
1200
1100
Single Phase - Constant Pressure
1000
Single Phase - Constant Mass Flow
Q (W)
900
Two Phase
800
700
600
500
ΔQ ≈
100W
400
300
0
20
40
60
80
Data Points
100
120
140
FEASIBILITY ANALYSIS
RESULTS
Feasibility Results

Additional components required for retrofit
Required Components
Cost
Compressor
Air Injection Manifold
Controller
Total
$50
$150
$20
$220
SunMaxx Solar 4' x 8' Collector
Conditions
365 Sunny Days
200 Sunny Days
Energy/yr
4380 (kWh)
2400 (kWh)
Cost/yr
$479.39
$262.68

Two-Phase Enhancement = 28%

Extra Energy Gained = 0.28 x $262.68 = $72.55

Extra Value Gained = $72.55 - $10 Maintenance = $62.55

Payback Period of Equipment = $220 / $62.55 ≅ 3.5 years
SOURCES OF ERROR
Sources of Error
•
Pump Size (Dultmeier Hypro Shertch 1.5 HP)
Sources of Error
Flow rate measurements (human factors)
 Compressor Gauge Precision
 Data Collection System Accuracy
(Calibration)
 Heat Loss Assumptions

Recommendations
Smaller Pump – 4.2 L/min
 Flow-meter – 0.5 L/min-5L/min
 Run longer tests
 Higher precision
regulator/gauges on compressor
 Complete feasibility analysis on
a commercially available
collector under Newfoundland
conditions

PROJECT
MANAGEMENT
Project Budget
QUESTIONS?
Summary:
Two-Phase Energy Gain versus Single Phase = 28%
Payback period = 3.5 years
Acknowledgements:
Dr. Muzychka, Craig Mitchell, Tom Pike, Glen St.
Croix, Don Taylor
System Description
Divided into 3 different areas
 Heat Collector Subsystem
Heat Collector, Pump, Reservoir, Intermediate Tubing

Air Injection Subsystem
Compressor, Air Injection Manifold, PIC controller

Data Collection Subsystem
Datalogger, Pressure and Temperature Transducers
Performance versus Predicted

Experiments aligned with predicted values
Experimental
Test
Test Type
17 Two-Phase
Single-phase 18 Constant Mass
Single Phase 19 Constant Pressure
Q (W)
492.77
Two-phase
Enhancement
Predicted
Two-Phase
Q (W)
Enhanceme
707.98
Collector
Efficiency
0.70
393.6
1.25
544.6
1.3
0.72
393.4
1.25
544.6
1.3
0.72