Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning - Discussion

For the same, refer to Psychrometric Chart & draw the process for sensible heating over it. You should observe various points related to DBT, WBT, Rh, Sp. humidity, enthalpy, sp. volume lines. For the drawn process 1-2, the DBT & WBT increases. As it is a heating process, the number of water particles present in the air will be removed, hence the Rh decreases. Whereas the sp. humidity remains constant. The SP volume increases from 1 to 2. As we are adding heat to the air, its temperature & internal heat increases, which in turn increases the Enthalpy of air.

As sensible heat is done but specific humidity is constant but the air capacity to get vapor increases so air will get more moisture from cotton of wet bulb thermometer and hence cotton will absorbs more heat from mercury and hence the mercury bulb will goes down means cool down means temperature will decrease but if we see by psychometric chart and from left to right as sensible line goes is showing that wet bulb is decreasing.

On Psychometric chart Dry Bulb temp. Increases from left to right. During sensible heating process specific humidity remains constant (i.e. process is showed by horizontal line). So as we move from left to right WBT lines (inclined lines) increases from Bottom left corner to upper right corner. So we can clearly say that WBT increases. Description can easily understood by Psychometric chart.

When the air temp is higher than the liquid so liquid absorbs that heat energy from the air and evaporates it and the liquid-dipped thermometer that records that temperature is called the wet bulb temp.

So when the sensible heat of air is increased it means the wet bulb temp is also increased.

Dry bulb thermometer measures simply the temperature of the air and wet bulb thermometer measures the temperature of saturated air means with 100 percent humidity at that specific temperature if we increase the temperature of air means a number of vapors that an air can store also increases.

If you observe your psychrometric chart, you will observe that the enthalpy and WBT line travel proportionally. In sensible heating the path of process is along the +ve y-axis. Thus you will observe that the three lines of enthalpy, heating and WBT are proportional to each other. Hence.

Wet bulb means thermometer bulb covered with wet cloth. So, the temperature measurement depends on the wet cloth will evaporate or becoming wet. If temp increases the moisture will decrease so the wet bulb become dry (temp increases).

Dry bulb thermometer measures simply the temperature of the air and wet bulb thermometer measures the temperature of saturated air means with 120 percent humidity at that specific temperature.

In latent heating the temperatures remains constant the phases will be changed. But sensible heating the temperature will increased further. So that the wet bulb temperature is increased.

As we know heat flow from higher temperature. To lower temperature so wet bulb will dry means the temperature of wet bulb will increase due to the temperature of air.