brott wrote:Once again I am faced with converting from lb/sec to gal/hr.

The product is water that is injected in with #2 Diesel Fuel for a combustion turbine. The water is measured in lb/sec and I report in Gallons. I am looking to convert water lb/sec to water gal/hr.

Jody,

With a conversion problem such as you have here, unit analysis is the best way to do your conversion.

You have pounds per second. In order to get to gallons per hour you need to make two different conversion; pounds of water to gallons, and seconds to hours.

Lay out your problem by making a set of "Railroad tracks," and place the initial quantity in the first block:

- Code: Select all
`lbs |`

----|

sec |

We know that water weighs 8.34 pounds per gallon. That means that 0.12 gallons weighs one pound.

- Code: Select all
` lb | 0.12 gal |`

-----|----------|

sec | lb |

There are sixty seconds per minute, lets add that:

- Code: Select all
` lb | 0.12 gal | 60 sec |`

-----|----------|--------|

sec | lb | min |

There are 60 minutes per hour, so:

- Code: Select all
` lb | 0.12 gal | 60 sec | 60 min |`

-----|----------|--------|--------|

sec | lb | min | hr |

Now we're converting pounds to gallons, seconds to minutes, and minutes to seconds. What we do next is cancel like terms on the top and bottom of the railroad tracks:

lb | 0.12 gal | 60

sec | 60

min |

-----|------------|----------|----------|

sec |

lb |

min | hr |

lbs cancels out, seconds cancel out, and minutes cancel out, leaving use with gallons per hour. Now multiply the terms out: 0.12 x 60 x 60 = 432.

This means that 1 lb/sec is equal to 432 gal/hr.

You can use this technique to convert any values that you have a conversion for, no matter how complex. Simply place a conversion factor onto the railroad tracks for each value you have, cancel the like terms, and multiply and divide the remaining values.

William J. Knight

Health Physicist

Los Alamos National Labs