Analysis of Novel Compression Concepts for Heat … · Analysis of Novel Compression Concepts for...

Slide 1

© Eckhard A. Groll October 3, 2016

Analysis of Novel Compression Concepts for Heat Pumping, Air Conditioning and

Refrigeration Applications

Oklahoma State University Seminar Presentation

Dr.-Ing. Eckhard A. Groll

Reilly Professor of Mechanical Engineering

Director of the Office of Professional Practice

Purdue University

Ray W. Herrick Laboratories

West Lafayette, Indiana 47907, USA

Phone: 765-494-7429; Fax: 765-494-7427

E-mail: [email protected]

Slide 2


Contents

Introduction

Modeling of Compressors

Rotating Spool Compressor

S-RAM Compressor

Bowtie Compressor

Z-Compressor

Linear Compressor

Slide 3


Introduction Overview of Refrigeration Compressors

Compressor Types

Positive Displacement Compressors Dynamic Compressors

Axial Flow Machines

Radial Flow Machines

Orbital Compressors

Rotary (Rotational Piston) Compressors

Reciprocating Compressors

Rotary (Sliding) Vane Compressor

Rolling Piston Compressor

Screw Compressor

Scroll Compressor

Trochoidal Compressor

Single Shaft: Single-Screw Compressor

Double Shaft: Twin-Screw Compressor

…

…

…

…

Slide 4


Introduction Range of Applications of Compressors

Domestic Refrigerators & Freezers

Automotive Air Cond’g

Room Air Conditioners

Unitary Air Conditioners

& Heat Pumps

Commercial Air Cond’g & Refrigeration

Large Air Conditioning

Cooling Capacity

Fractional 200 kW (50 tons)

Reciprocating

Fractional 10 kW (3 tons)

Rotary

5 kW (1.5 tons) 70 kW (20 tons)

Scroll

150 kW (40 tons) 1500 kW (400 tons)

Screw

350 kW (100 tons) and up

Centrifugal

Slide 5


Political and economic concerns

» Global warming

» Ozone depletion

» Increased competition

Technological advances

» New working fluids

» New design and manufacturing capabilities

» New applications

Introduction Motivation for New Compression Concepts

Slide 6


Introduction Overview of Refrigeration Compressors

Compressor Types

Positive Displacement Compressors Dynamic Compressors

Axial Flow Machines

Radial Flow Machines

Orbital Compressors

Rotary (Rotational Piston) Compressors

Reciprocating Compressors

Rotary (Sliding) Vane Compressor

Rolling Piston Compressor

Screw Compressor

Scroll Compressor

Trochoidal Compressor

Single Shaft: Single-Screw Compressor

Double Shaft: Twin-Screw Compressor

…

…

Slide 7


Contents

Introduction



S-RAM Compressor

Bowtie Compressor

Z-Compressor

Linear Compressor

Slide 8


Modeling of Compressors: Underlying Principles

Compressor modeling relies on many engineering

disciplines:

» Thermodynamics

– e.g.: Changes in refrigerant properties

» Fluid mechanics

– e.g.: Flow of refrigerant in chambers and flow passages

» Solid mechanics

– e.g.: Forces acting on valves and the resulting deformations

» Electrical engineering

– e.g.: Conversion of electrical energy to mechanical energy in a motor

» Chemical engineering

– e.g.: Unwanted decomposition of refrigerant and oil

Slide 9


Modeling of Compressors: Process Dynamics

Compressor modeling relies on understanding of

various time scales inside the compressor

Refrigerant pressure

Valve movement

Load on shaft

Motor angular velocity

Motor current and voltage

Temperature of suction gas

Ambient temperature

Component temperature

sns ms s ks

Time scale

Valve opening & closing

Slide 10


Modeling of Compressors: Model Flow Chart

Slide 11


(properties) (geometry) (leakage) (heat transfer)

Conservation of Mass and Energy

» Combined mass and energy balance can be solved in

series for dρ/dθ and dT/dθ:

1

in in out out

dV uh uV V Q m h m h

ddT

udV

T

1 1

in out

d dVm m

d V d

Modeling of Compressors: Compression Process Equations

Slide 12


Schematic of energy flows inside a hermetic compressor

: friction modelmech

: motor mapmotor

RPM

Given values

ambT

gasT

shellT

wallT

motor lossQ

wall,gasQ

gas,shellQ

shell,ambQ

suc

evap super

T

T T

elecW

shaftW

compWfriction lossQ

gas cyl,inT TdisT

dis,gasQ

oilT

oil,gasQ

oil,shellQ

cyl,outT

rad,wall,shellQ

rad,shell,ambQ

rad,dis,shellQ

Modeling of Compressors: Modeling Approach

Slide 13


Contents

Introduction



S-RAM Compressor

Bowtie Compressor

Z-Compressor

Linear Compressor

Slide 14


• Introduced by Kemp et al. (2008, 2010)

• Performance data presented by Orosz et al. (2012)

• Model(s) presented by Bradshaw et al. (2013) and Bradshaw, C.R. (2013)

Motivation: Achieve competitive compressor performance at

significantly reduced manufacturing costs

Rotating Spool Compressor: Design

Slide 15


Rotating Spool Compressor: Design

Slide 16


Rotating Spool Compressor: Features

Four major components

with simple geometry for

reduced manufacturing

cost

Spool face motion nearly

eliminates frictional and

leakage losses between

the vane and face

Active sealing elements

allow for creative solutions

to minimize leakage and

friction

Leakage Paths

Slide 17


Rotating Spool Compressor: Geometry

Slide 18


Rotating Spool Compressor: Model Validation

Power Consumption Volumetric Efficiency

Slide 19


Rotating Spool Compressor: Design Optimization

Discharge Temperature Volumetric Efficiency

Slide 20


Rotating Spool Compressor: Performance of 6th Gen. Prototype

Overall Isentropic Efficiency Volumetric Efficiency

Data of Latest Prototype Spool Compressor, 141 kW (40 ton)

Orosz, J., Bradshaw, C.R., Kemp, G., and Groll, E.A., “Updated Performance and Operating Characteristics of a Novel Rotating Spool Compressor,” Proc. 23rd Int’l Compr. Eng. Conf. at Purdue, Paper 1377, Purdue Univ., W. Lafayette, IN, July 11-14, 2016

Slide 21


Rotating Spool Compressor: Summary

Latest generation prototype achieves competitive

volumetric and energy efficiencies

Manufacturing cost much lower than scroll

compressors

Size range comparable to reciprocating compressors

Commercialization interaction with multiple

compressor manufacturers

Concept shows good performance as an expander in

ORC applications

Slide 22


Contents

Introduction



S-RAM Compressor

Bowtie Compressor

Z-Compressor

Linear Compressor

Slide 23


S-RAM Compressor: Overview

• High-efficiency mechanism to convert rotary shaft

motion into piston reciprocating motion

• Can mechanically change displacement independent of

speed … No VFD

• 35+ patents issued since the first patent in 2000 (www.s-ram.com)

Slide 24


S-RAM Compressor: CO2 Compressor Specifications

• Characteristics

» Suction Volume: 345 cm3

» Nominal Flow Rate: ~30 m3/hr at 1500 rpm

» Nominal Capacity: 100 kW (CO2 at 0oC)

• Advantages

» Oil free

» Less frictional power loss

» Variable capacity control (25% to 100%) (constant clearance volume above the piston top!)

Slide 25


S-RAM Compressor: Kinematics Model

Piston Displacement/Velocity/Acceleration

Slide 26


S-RAM Compressor: In-Cylinder Process Model

Effect of discharge pressure

P-V diagram In-cylinder refrigerant temperature

Slide 27



Valve Models

Slide 28



Effect of stroke-to-bore ratio

Instantaneous refrigerant leakage through clearance

between piston assembly and cylinder wall

Instantaneous heat transfer between

in-cylinder refrigerant and cylinder wall

Slide 29


S-RAM Compressor: Predicted Efficiencies

Effect of stroke-to-bore ratio

Volumetric Efficiency:

0

vol

suc

m

V Nn

Compressor

displacement

volume

Compressor

speed

Number of

cylinders

Yang, B., Kurtulus, O., and Groll, E.A., “An Integrated Model for an Oil Free Carbon Dioxide Compressor Using Sanderson-Rocker Arm Motion (S-RAM) Mechanism,” Proc. 23rd Int’l Compr. Eng. Conf. at Purdue, Paper 1336, Purdue Univ., W. Lafayette, IN, July 11-14, 2016

Slide 30


S-RAM Compressor: Summary

Oil-free compression provides large application range

Variable capacity control while keeping clearance

volume constant gives high performance at different

operating conditions

Competitive compressor performance at different

pressure ratios

Future Work:

» Frictional power loss analysis

» Global energy balance analysis

» Validation of model predictions

Slide 31


Contents

Introduction



S-RAM Compressor

Bowtie Compressor

Z-Compressor

Linear Compressor

Slide 32


Bowtie Compressor: Overview

Motivation: Provide mechanical capacity control without

changing clearance volume

» Avoid re-expansion losses associated with the increased clearance

volumes in many capacity control solutions

» Based on Beard-Pennock variable-stroke compressor

» Blade reciprocates axially instead of linearly

» Cylinder can move in direction of springs

Slide 33


Bowtie Compressor: Basic Geometry

Slide 34


Bowtie Compressor: Prototype Design

Leakage passages:

» Through the radial

clearance

» Over the vane

» Between the side vane

and the journal shaft

» Between the journal

bearing and the journal

shaft

» Between the top vane

and the journal shaft

,011 leakm

,022 leakm ,044 leakm

,033 leakm

,055 leakm

Slide 35


Bowtie Compressor: Model Validation

-24 -22 -20 -18 -16 -14 -1210

12

14

16

18

20

22

Ma

ss F

low

Ra

te (

lbm

/hr)

Evaporating Temperature (oC)

Tcond

=43.3oC,Map

Tcond

=43.3oC,Model

Tcond

=48.9oC,Map

Tcond

=48.9oC,Model

Tcond

=54.4oC,Map

Tcond

=54.4oC,Model

-24 -22 -20 -18 -16 -14 -12

160

170

180

190

200

210

220

230

Po

we

r In

pu

t (W

)

Evaporating Temperature (oC)

Tcond

=43.4oC,Map

Tcond

=43.4oC,Model

Tcond

=48.9oC,Map

Tcond

=48.9oC,Model

Tcond

=54.4oC,Map

Tcond

=54.4oC,Model

Power Consumption Mass Flow Rate

Slide 36


0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

50

52

54

56

58

60

62

Ove

rall

Ise

ntr

op

ic C

om

pre

sso

r E

ffic

ien

cy (

%)

Clearance (m)

Use model to optimize clearance dimensions and ratio of vane radius

to height

Friction

losses

dominate

0.2

5

0.5

0

0.7

5

1.0

0

1.2

5

1.5

0

1.7

5

2.0

0

2.2

5

2.5

0

2.7

5

1.470

1.475

1.480

1.485

1.490

1.495

1.500

1.505

1.510

1.515

1.520

Mass Flow Rate, Swept Angle = 25.05o

Mass Flow Rate, Swept Angle = 31.89o

o.s.c

, Swept Angle = 25.05o

o.s.c

, Swept Angle = 31.89o

Ratio of Vane Radius and Height

Co

mp

resso

r M

ass F

low

Ra

te (

g/s

ec)

59.0

59.2

59.4

59.6

59.8

60.0

60.2

60.4

60.6

60.8

61.0

Ove

rall Is

en

trop

ic C

om

pre

sso

r Effic

ien

cy (%

)

Leakage

losses

dominate

Maximum

performance

Bowtie Compressor: Design Optimization

Slide 37


Bowtie Compressor: Performance Results

Modeled results for compressor at 54.4ºC condensing,

-23.3ºC evaporating and 32.2ºC suction temperature:

0 50 100 150 200 250 300 350 4000

10

20

30

40

50

60

70

80

90

Mo

tor

Eff

icie

ncy (

%)

Shaft Power (W)

Tecumseh Recipro. Compressor Model (TP1390)Compressor Motor Map

3.0 3.5 4.0 4.5 5.00.6

0.8

1.0

1.2

1.4

1.6

Mass Flow Rate

o.s.c

Swept Volume (cm3)

Ma

ss F

low

Ra

te (

g/s

ec)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

-52.0%

-42.8%

-31.4%

-17.5%

-20.6%

-14.8%-9.2%

Overa

ll Isentro

pic

Com

pre

ssor E

fficie

ncy(%

)

-4.3%

Slide 38


Bowtie Compressor: Summary

Overall isentropic efficiency only drops from

60 to 50% when suction volume is reduced from

4.70 cm3 to 3.04 cm3 (almost 50% decrease)

Change in overall isentropic efficiency could be

significantly less if appropriate electric motor is used

Feasible, “lower-cost” alternative to electronic variable

speed compressor for domestic refrigerator/freezer

Current interest by German Company in electronic

cabinet cooling using reversed Brayton cycle.

Slide 39


Contents

Introduction



S-RAM Compressor

Bowtie Compressor

Z-Compressor

Linear Compressor

Slide 40


Z-Compressor: Motivation

Motivation: Reduce noise and vibration by developing a rotary

compressor without an eccentric

» Simultaneously compresses

two pockets of gas separated

by a Z-blade

» Z-blade provides

continuous variation

in chamber volume

without eccentric

» Cylindrical vane

separates suction

and compression

chambers on each

level

Lower suction

chamber

Upper suction

chamber

Upper compression

chamber

Lower

compression

chamber Vane

Blade

Slide 41


Z-Compressor: Basic Geometry

Modeling Assumption:

» Upper and lower chambers identical, but separated by

180º rotation

» Frictional and electric losses rejected to high pressure

gas in shell

» Shell exchanges heat with ambient

» Constant pressure suction

Slide 42


Z-Compressor: Model Validation

Mass flow rate

35

40

45

50

55

60

65

70

75

35 45 55 65 75

m experimental [kg/h]

m m

od

el

[kg

/h]

+7 %

-7 %

Power input

500

700

900

1100

1300

500 700 900 1100 1300

W experimental [W]W

mo

del

[W]

+7 %

-7 %

Slide 43


Leakage losses

0

1

2

3

4

5

6

0.20 0.30 0.40 0.50 0.60

(h/D)

mL [

kg

/h]

Paths L6-L9 Paths L4-L5

Z-Compressor: Performance Results

Lower volumetric efficiency than currently available rolling

piston compressors due to increased leakage paths

» Between suction and compression chambers on same level

» Between levels

» Between chambers and shell

Slide 44


Z-Compressor: Design Optimization

Improve volumetric efficiency by reducing mass flow

through the most significant leakage path, which is

between the Z-blade and cylinder wall

» Reduce clearance between z-blade and cylinder

– Frictional losses increase

» Reduce diameter of

Z-blade

– If cylinder height

is increased to

maintain same

chamber volume,

leakage around

vane increases Comparison of friction losses at various contacts

Average frictional losses

0

5

10

15

20

25

30

35

Thrust bearing Journal bearing Blade-cylinder Flat region of the

blade

Contact

Wlo

ss [

W]

Average frictional losses

0

5

10

15

20

25

30

35

Thrust bearing Journal bearing Blade-cylinder Flat region of the

blade

Contact

Wlo

ss [

W]

Slide 45


Z-Compressor: Design Optimization, cont’d

Volumetric efficiency

Reference

Piston ring

0.800

0.825

0.850

0.875

0.900

0.925

0.950

15.0 17.5 20.0 22.5 25.0 27.5 30.0

Blade-cylinder clearance [m]

v

Overall isentropic efficiency

Reference

Piston ring

0.550

0.575

0.600

0.625

0.650

15.0 17.5 20.0 22.5 25.0 27.5 30.0

Blade-cylinder clearance [m]

s

Impact of blade-cylinder clearance change on compressor efficiencies

Slide 46


Z-Compressor: Summary

Compared to current rotary compressors:

» Lower noise and vibration

» But also, lower volumetric efficiency

Dimensions can be optimized to balance leakage and

friction losses for maximum isentropic efficiency

Feasible alternative to rolling piston compressor

for room and small unitary air conditioners,

but “higher” manufacturing costs

Current interest by Canadian company for small-scale

air compression application

Slide 47


Contents

Introduction



S-RAM Compressor

Bowtie Compressor

Z-Compressor

Linear Compressor

Slide 48


Linear Compressor: Control Volumes

Slide 49


Linear Compressor: FBD of Piston with EOM

p gasx k

p effx c

( )mech pk x

,p CGM J

x

driveF

Note: both forces act

through centroid

(Coupling)

(Stiffness)

(Damping)

(Inertial)

2

( )p p eff p gas mech p mech drive

CG mech mech p

M x c x k k x k F

J k k x

Slide 50


Linear Compressor: Stroke Control/Friction Factor

Impact of dead volume and dry friction factor on efficiencies

Volumetric Efficiency Overall Isentropic Efficiency

Slide 51


Linear Compressor: Capacity Control

Variable stroke can be

utilized to generate

variable capacity

By assuming 10 °C

subcooling at the

condenser outlet, a

cycle can be simulated

A linear compressor

provides high

performance over wide

capacity ranges

System COP and 2nd Law Effectiveness

Slide 52


All else constant, vary net

dead volume by increasing

xdead

Simulates a variable stroke

compressor

As dead volume increases the

recoverable energy increases

The mechanical springs act as

capacitance, allowing energy

to be recaptured that would

otherwise be lost

Overall Isentropic Efficiency

Linear Compressor: Comparison to Reciprocating Compr.

Slide 53


kmech f g Vd fres x/D vol o,is

N/m - m cm cm3 Hz - - -

30600 0.2 4 0.5 2 60 0.4 0.96 0.86

Key Compressor Dimensions and Predicted Performance

• 200 W cooling capacity

• Replaced compression

springs with planar

springs

• Moved location of

mechanical springs

• New linear bearing

selection

Linear Compressor: Final Design

Slide 54


Linear Compressor: Summary

Linear compressors are the highest performing

compressors on the market

Only two commercial products available

» Embraco and LG

» Both are for refrigerator-freezer application

Research interest focuses on scaling to larger

capacities

Slide 55


Thank you!

Date post:	19-Aug-2018
Category:	Documents
Upload:	vuongkien
View:	223 times
Download:	0 times

Analysis of Novel Compression Concepts for Heat … · Analysis of Novel Compression Concepts for...

Documents