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Welcome to my presentation : 

Welcome to my presentation 1 Presented by: K. M. Taufiqul Arif ID: MS-100705

Title: Psychrometric Chart : 

Title: Psychrometric Chart Course No: BGE-5103 Course Name: Food Processing Technology 2

Introduction : 

Introduction Definition Psychrometrics : The field of engineering concerned with the determination of physical and thermodynamic properties of gas-vapor mixtures. The term derives from the Greek ”psuchron” meaning "cold"  and ”metron” meaning "means of measurement". A psychrometric chart presents physical and thermal properties of moist air in a “graphical “form.  The psychrometric chart graphically represents the interrelation of air temperature and moisture content. (ref: wikipedia/psychometric chart) 3

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Standard Psychrometric Chart 4

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6 Dry-bulb temperature is the commonly measured temperature from a thermometer. It is called “dry-bulb” since the sensing tip of the thermometer is dry. Dry-bulb temperature is located on the horizontal, or x-axis, of the psychrometric chart and lines of constant temperature are represented by vertical chart lines.

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7 Wet-bulb temperature is determined when air is circulated past a wetted sensor tip. It represents the temperature at which water evaporates and brings the air to saturation.  measured by a hygrometer or a sling psychrometer and is shown as sloping lines on the psychrometric chart.

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8 Relative humidity is a measure of the amount of water that air can hold at a certain temperature. It is “relative” to the amount of water that air, at that same temperature, can hold at 100 percent humidity, or saturation. Exp: Air at 60 percent relative humidity contains 60 percent of the water it could possibly hold (at that temperature). It could pick up 40 percent more water to reach saturation. Lines of constant relative humidity are represented by the curved lines running from the bottom left and sweeping up through to the top right of the chart.

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9 The humidity ratio of moist air is the weight of the water contained in the air per unit of dry air. Humidity ratio is found on the vertical, y axis with lines of constant humidity ratio running horizontally across the chart.

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10 Dewpoint temperature indicates the temperature at which water will begin to condense out of moist air. Dewpoint temperature is determined by moving from a state point horizontally to the left along lines of constant humidity ratio until the upper, curved, saturation temperature boundary is reached.

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11 Enthalpy (H) is the heat content of unit mass of the atmosphere, in kJ/kg, relative to the heat content of 0C dry air. It is indicated on the psychrometric chart by a third set of sloping lines, near to, but not quite the same as the web-bulb lines.

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12 Specific volume indicates the space occupied by air. It is the inverse of density and is expressed as a volume per unit weight. Lines of constant specific volume are almost vertical lines with scale values written below the dry-bulb temperature scale and above the upper boundary’s saturation temperature scale.

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Process 0-1: Sensible heating Process 0-2: Sensible cooling Process 0-3: Humidifying Process 0-4: Dehumidifying Process 0-5: Heating and humidifying Process 0-6: Cooling and dehumidifying Process 0-7: Cooling and humidifying Process 0-8: Heating and dehumidifying 13 Basic psychrometric processes Static point

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14 Psychrometric processes, i.e. any changes in the condition of the atmosphere, can be represented by the movement of the state point on the psychrometric chart. Common processes include: Sensible cooling / sensible heating Cooling and dehumidification /heating and humidification Humidification / dehumidification Evaporative cooling / chemical dehydration

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A psychrometric process that involves The increase or decrease in the temperature of air without changing its humidity ratio. Example: passing moist air over a room space heater and of kiln air over the heating coils. 16 Sensible Heating or Cooling

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17 A psychrometric process that involves the simultaneous increase in both the dry bulb temperature and humidity ratio of the air Heating and Humidification

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18 A psychrometric process that involves the removal of water from the air as the air temperature falls below the dewpoint temperature. Cooling and Dehumidification

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19 A psychrometric process that involves the cooling of air without heat loss or gain. Sensible heat lost by the air is converted to latent heat in the added water vapor. Adiabatic or Evaporative Cooling

Applications : 

Applications To measure moisture in cold storage To assess air temperature To identify appropriate cooling temperature by comparing the moisture content To know the dew point to preserve perishable commodities. Help to affirm a steady point in the chart To set an appropriate condition for preserving food materials 20

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21 THANK YOU . . .

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