Alph is no longer for sale.

I am afraid revenue generated from Alph has not proven to be sufficient to justify its continued sale. I greatly appreciate the support of the folks who have purchased Alph in the past and hope that it will continue to serve you well in the future.

This and related pages will be maintained for archival purposes only.

Craig


Alph One vs Two Stage Refrigeration Example

From your device, you can download the completed example

Goal

This example compares the power required for a single stage propane refrigeration loop, versus that for a two stage system with a flash drum economizer.

Single Stage Refrigeration

Two Stage Refrigeration

Fluids

c3cond
The refrigerant leaving the condenser. This fluid defines the refrigerant composition for both approaches as:

  • C2 = 0.05
  • C3 = 0.90
  • C4 = 0.05

The temperature is set as 40 C to reflect an air cooler outlet. The vapour fraction is 0, for a condensing fluid and thus the pressure is calculated. The flow is retrieved from the calculation of the chillerout fluid.

chillerin
This gets its enthalpy, flow and composition from the condout fluid and its pressure from the calculated chillerout plus a pressure drop specified in the dp variable.

chillerout
This fluid represents the vapour boiling off of the chiller and thus has its vapour fraction set to 1. A chiller temperature of -40 C is assumed and the composition will be the same as the condout fluid.

The flow is calculated by dividing the chiller duty, specified in variable chillerq, by the difference in enthalpy between chillerout and chillerin.

$chillerq / (@.h - @chillerin.h)

condout2
This is the refrigerant leaving the air cooled condenser for the two stage calculation. It uses the same temperature and composition from the single stage condout fluid, has a vapour fraction of 1, but uses the mixed fluid hpin flow rate.

{ sum $p }

chillerin2
This is the feed to the chiller for the two stage calculation. Its pressure comes from the calculated chillerout2 pressure plus dp pressure drop. The composition and enthalpy are taken from the liquid phase of the econ fluid, which represents the economizer flash drum. The flow is retrieved from the chillerout2 calculation.

chillerout2
This is the vapour boiling off of the chiller in the two stage calculation. Like its single stage counterpart, it calculates its flow rate by the total chiller duty divided by the enthalpy difference across the chiller. The composition is that of the liquid leaving the economizer.

econ
This represents the economizer flash drum in the two stage calculation. Its pressure is determined by the specification in the interp variable, while its enthalpy comes from the condout2 fluid as the valve separating them will be isenthalpic. The composition will also be the same as the condout2 liquid, meaning a flash can be done to determine the composition of the low pressure loop.

Since liquid flow will be the same as that calculated for the chillerin2 fluid, the total econ flow is just that divided by the liquid phase fraction.

lpout
This is the fluid from the low pressure compressor (lpcomp) tool and it gets all of its properties from it.

hpin
This is the feed fluid to the high pressure compressor (hpcomp) tool and it gets all of its properties from the mixer tool that combines the economizer vapour with the outlet of the low pressure compressor.

Variables

chillerq

This specified duty for the chiller.

dp

A pressure drop value used in a few places.

interp

The inter stage pressure for the two stage calculation. Obviously this will be somewhere between the higher pressure of condout2 and the low pressure of chillerout2. It can be adjusted back and forth to find the minimum combined compressor power.

totalq

The sum of the low and high pressure compressors and thus the total power required for the two stage solution.

qratio

The single stage compressor power divided by the total two stage compressor power. In this example this works out to about 0.8, showing a significant power saving is possible by implementing the two stage approach.

Tools

comp, lpcomp, hpcomp

The single stage compressor and the low and high pressure compressors for the two stage calculation. All used an adiabatic efficiency of 80%.

mixer

Combines the outlet of the low pressure compressor with the vapour from the economizer.