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Given the dry-bulb temperature, T_db andrelative humidity, Φ, the wet-bulb, T_wbtemperature may be calculated from the psychrometric equation(Jones, 1994):

P_vsΦ – P_ss =P_atmA (T_wb-T_db )                                             (1)

Use your input from the Table below.

The input T_wb and T_db are in ^oC(used in Eqs. (2) and (3) in Kelvin).   

P_ss = saturated vapor pressure atT_wb (kPa)

P_vs = saturated vapor pressure atT_db (kPa)   

P_ss = 10^[30.59051- 8.2 log₁₀T_wb + 0.0024804 T_wb – 3142.31/T_wb] ..........(2)

and

P_vs = 10^[30.59051- 8.2 log₁₀T_db + 0.0024804 T_db – 3142.31/T_db]     ........(3)

In the above two equations T is inKelvin and P in kPa (you have to convertthe temperatures from the input in ^oC to Kelvin).

P_atm= atmospheric pressure (kPa)(P_atm =101.325 kPa)

T_db = dry-bulb temperature(^oC)

T_wb = wet-bulb temperature(^oC)

A    = 6.66x10^-4C^-1 (constant for sling psychrometer)

Φ = relative humidity (%) used in the calculations as (%/100).For example, for 80% relative humidity, input 0.8.

Solve Equation (1) for the wet-bulb temperature usingNewton-Raphson method. The input is as follows:T_db= in ^oC and Φ= in % (to beconverted in the program to fraction, i.e., Φ=50% means Φ=0.5). Setthe tolerance to 10^-4 . In other words, the absolutedifference between the results of two successive iterations shouldnot be more than 10^-4. Check your answer usingPsychrometric chart/Thermo Textbook. Also, to check if your resultsare correct, use f=100% and you should getT_wb=T_db. S is yourlisting number.

S (for future use)	Tdb (C)	Relative Humidity (%)
1	25	45