Moist air at 35 C and 55 relative humidity is heated using a

Moist air at 35 C and 55% relative humidity is heated using a common furnace to 70 C. From the psychrometric chart, determine how much heat is added per m³ initial moist air and what the final dew-point temperature is.

Solution

Note: For solution of this numerical use psychrometric chart.

Given Temperature is 35 ^oC and relative humidity is 55 %

so find point with combination of this 2 which gives initial entalpy (h₁) as 84 KJ/kg dry air and

specific volume as 0.9 m³ /kg of dry air

This air is heated to 70 ^oC so draw straight line on chart and find final enthalpy (h₂) as 123 KJ/kg dry air

So heat required is (h₂ - h₁) = 123 -84 = 39 KJ/kg dry air

But answer required is heat required per m³ of initial moist air = 39/0.9 = 43.33 KJ/m³

For dew point temperature go on the straight line towards 100 % RH and go straight down on DBT which gives DPT of air and which is 25 ^oC