Ratio, sensible/ total heat

A further complication arises with the application to temperate conditions of room air-conditioners which have heen designed primarily for tropical markets. These units typically work with a sensible/total heat ratio of 0.7. Plotting this process line on the psychrometric chart (see Figure 35.3) shows that the ADP will he about 9°C. 

The term e/(e — 1), which appears in equations 1 and 2, was first developed to account for the sensible heat transferred by the diffusing vapor (1). The quantity S represents the group ratio of total transported energy to convective heat transfer. Thus it may be thought of as the fractional... 

Zh Ratio of sensible heat removed from vapor to total heat transferred Dimensionless Dimensionless... 

Total heat Sensible heat Latent heat Sensible heat ratio... 

Where the pan is in the air stream the condition downstream of the pan has increased moisture content (kg/kg) found from the airflow and moisture input. On a psychrometric chart, this will lie on a line of sensible-to-total heat ratio of 0.3. Thus, the psychrometric plot shows a steep rise in moisture content with a small rise in dry bulb temperature. The latter is a disadvantage when cooling is... 

Z Ratio of change in sensible heat of gas stream to change in total heat of ... 

When the unknown intcrfacial temperature 2J is eliminated and the ratio Z of sensible and total heat transfers... 

The term e/(ee — 1), which appears in equations 1 and 2, was first developed to account for the sensible heat transferred by the diffusing vapor (1). The quantity 8 represents the group M4-C 4 / hg, the ratio of total transported energy to convective heat transfer. Thus it may be thought of as the fractional influence of mass transfer on the heat-transfer process. The last term of equation 3 is the latent heat contributed to the gas phase by the fog formation. The vapor loss from the gas phase through both surface and gas-phase condensation can be related to the partial pressure of the condensing vapor by using Dalton s law and a differential material balance. 

The above swii can be eliminated by controlling the preheater heat duty or, better still, the preheater heat duty per unit feed flow (362), instead of the preheater outlet temperature. For steam (or condensing vapor) preheaters, the duly per unit feed flow equals the ratio of the measured steam (or vapor) flow to the measured feed flow times a constant, the constant being the steam latent heat. For a sensible-heated preheater, the above ratio is multiplied by the measured hot-side temperature difference, and the constant is the average hot-fluid heat capacity. For two or more feed preheaters, it is best to compute their total heat duty on-line and ratio it to the feed (68, 259). The computation can be readily performed using conventional analog instrumentation. Similar techniques cured the above-cited swing problems (239,259). 

SENSIBLE HEAT FACTOR - The ratio of sensible heat to total heat. 

Sensible Heat Factor. The ratio of the change in sensible (constant moisture content) cooling enthalpy to the change in total cooling enthalpy. 

AHs/AHt) = the ratio of the change in sensible heat to the total enthalpy change, (dr/dHt) = slope of the temperature-enthalpy curve, x = vapour quality, mass fraction of vapour,... 

In assessing the ability of an HVAC system to maintain acceptable humidity levels in the building, the more important performance parameter is the sensible heat ratio (SHR) of the equipment. The SHR is defined as the ratio of the sensible cooling load to the total cooling load. Improved latent performance is characterized by a lower SHR. Defining the relationships between SHR and other dehumidification indices is also convenient. In particular, the latent heat ratio (LHR) can be defined as the latent cooling load fraction, and the latent to sensible ratio (LSR) can be defined as the ratio of latent load to sensible load. These ratios appear as... 

The relationships among the psychrometric states, loads, and sensible heat ratio are shown graphically in Fig. 3. For a given pair of entering and leaving air states, sensible, latent, and total loads are proportional to the differences in temperature, humidity ratio, and enthalpy, respectively, as shown in the figure. The SHR is defined by the slope of the line connecting the two points. 

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