Uo HTC app for iPhone and iPad

This app for heat transfer engineers allows you to input the information needed to calculate an overall Uo value for a shell and tube heat exchanger (or any heat transfer system using multiple tubes).

The equation programmed is: 1/U = 1/ho + 1/hi*(Do/Di) + Do*ln(Do/Di)/(2*ktube) + Ro + Ri*Do/Di

Where: ho = Heat transfer coefficient of fluid on outside (o) of tubes (BTU / hr f2 F), ho = Heat transfer coefficient of fluid on outside (o) of tubes (BTU / hr f2 F), Do and Di = Diameters of outside (o) and inside (i) of tube (feet), Do and Di = Diameters of outside (o) and inside (i) of tube (feet), ktube = thermal conductivity of tube metal (BTU-ft / hr ft2 F).

Guidance on variables:

For the tubes, the app already has programmed in it preset buttons for standard sizes, as well as the ability to input a manual size. Same goes for the thickness using BWG, or manually entering thickness.

You can also choose Materials of Construction and input an average temperature of the tube and the app automatically adjusts the thermal conductivity based on the material chosen and temperature. There is a limit of temperature ranges to be used for the built-in correlations, and the app will alert you when you are out of range so you know when to override the thermal conductivity manually.

For the individual fluid heat transfer coefficients, you input values for the inside fluid and outside fluid. A table is given on another view (included in the app) for typical ranges of values to use for various fluid types. In the iPad version (only) you can also calculate the hi value rigorously for gasses only (no condensing, just gas phase flow). Guidance for typical air conditions is also provided.

For fouling factors, use standard TEMA tables for references...likely a value of 0 to 0.003 is generally the range, but it is preferred to use 0 unless you are troubleshooting performance of an exchanger quickly.

Once all these values are entered, U is reported. I find the hardest part of doing all the U-calculations is the multiple reciprocals you have to calculate, and especially the log of the ratio of the tube inside and outside diameters. This app just makes it so much easier to execute this calculation quickly and easily.

Look out for my other heat transfer apps in the future.