Download presentation

Published byDakota Bradberry Modified over 2 years ago

1
**ISENTROPIC EFFICIENCY CALCULATIONS POSITIVE-DISPLACEMENT**

for POSITIVE-DISPLACEMENT ROTARY-LOBE BLOWERS Roger E. Blanton, P.E. District Sales Manager Kaeser Compressors, Inc.

2
EFFICIENCY All air and gas compressors are less than 100% efficient

3
**EFFICIENCY P1 V1 T1 Position 1 P2 > P1 V2 < V1 T2 > T1**

4
EFFICIENCY Entropy is a measure of the energy loss

5
**COMPRESSION MODEL Constant entropy (isentropic) process is ideal**

No heat loss and perfectly reversible

6
**ISENTROPIC COMPRESSION**

Follows this relationship, P2 /P1 = (v1/ v2)k » Pvk = a constant where: v = specific volume [ft3/lb] P1, P2 = initial and final pressure [Pabs] k = Cp/Cv = specific heat ratio = 1.4 for air

7
**COMPRESSOR WORK BHF = Big Hairy Formula !!!**

For continuous isentropic compression of a gas obeying the previous relationship, work per unit mass (ft·lb/lb) is Wis = vdP = P1 * v1 * [k / (k-1)] * [(P2 / P1)((k-1) / k) – 1] BHF = Big Hairy Formula !!!

8
POWER hpis = Wis * m / 60 / 550 where m is mass flow rate in lb/min

9
EFFICIENCY Isentropic efficiency of a compressor is the ratio of the ideal isentropic work to the actual work required is = Wis / Wact = hpis / hpact

10
**EXAMPLE CALCULATION Brand K model 42 @ 2000 rpm P1 = 14.7 psia**

P2 = 10 psig (24.7 psia) T1 = 68° F ρ1 (density) = lb/ft3 K = 1.4 (air) BHP = 13.2 (from performance table) CFM = 222 (from performance table) m = 222 * = lb/min

11
**EXAMPLE CALCULATION (cont’d)**

v1 = 1/ ρ1 = 1 / = ft3/lb k / (k-1) = 1.4 / (1.4 – 1) = 1.4 / 0.4 = 3.5 P2 / P1 = 24.7 / 14.7 = 1.68 (k-1) / k) = (1.4 -1) / 1.4 = 0.4 / 1.4 = 0.286 (P2 / P1)((k-1) / k) = = 1.16

12
**EXAMPLE CALCULATION (cont’d)**

Back to the Big Hairy Formula Wis = P1 * v1 * [k / (k-1)] * [(P2 / P1)((k-1) / k) – 1] Wis = 14.7 * * 3.5 * [ ] * 144 = 15,801 ft·lb/lb

13
**EXAMPLE CALCULATION (cont’d)**

hpis = Wis * m / 60 / 550 hpis = * / 60 / 550 = 8 hp

14
**EXAMPLE CALCULATION (cont’d)**

is = hpis / hpact is = 8 / 13.2 = 61% efficient

15
CONCLUSION Repeat this procedure for different blowers at the same pressure

16
CONCLUSION Perform this calculation on blowers bid for a project to evaluate efficiency Look at blower efficiency, not just price when making a decision

17
**CONCLUSION Perform a Life Cycle Cost (LCC) analysis**

Typically a 20 year project horizon is considered Include installation, estimated maintenance, and operating costs Discount the expenses to net present value (NPV) for comparison

18
**CONCLUSION Operating cost greatly outweighs first cost**

Blower efficiency is important for customer satisfaction

Similar presentations

OK

1 The ideal gas EOS can be written in many different ways...

1 The ideal gas EOS can be written in many different ways...

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on pin diode driver Ppt on fair and lovely cream Ppt on object-oriented concepts in java with examples Ppt on hunter commission Ppt on rf remote control robot Ppt on partnership act 1932 Doc convert to ppt online shopping Ppt on pollution of air and water Pdf convert to ppt online Ppt on indian sign language