Sensible heat measure

The amount of heat absorbed or lo.st by a substance that causes a change in the temperature of the substance is sensible heat, ft is called sensible heat because it can be measured by the change in temperature it causes. For example, as heat is added to a piece of steel the temperature of that steel increases and can be measured. The general equation for calculating sensible heat is ... 

In a typical example (33) a fresh feed of 8% polybutadiene rubber in styrene is added with antioxidant, mineral oil, and recycled monomer to the first reactor at 145 lbs./hr. The reactor is a 100-gallon kettle at approximately 50% tillage with the anchor rotating at 65 rpm. The contents are held at 124°C and about 18% conversion. Cooling is effected via the sensible heat of the feed stream and heat transfer to the reactor jacket. In this reactor the rubber phase particles are formed, their average size determined and much of their morphology established. Particle size is controlled to a large measure by the anchor rpm. 

Many of the conservation measures require detailed process analysis plus optimization. For example, the efficient firing of fuel (category 1) is extremely important in all applications. For any rate of fuel combustion, a theoretical quantity of air (for complete combustion to carbon dioxide and water vapor) exists under which the most efficient combustion occurs. Reduction of the amount of air available leads to incomplete combustion and a rapid decrease in efficiency. In addition, carbon particles may be formed that can lead to accelerated fouling of heater tube surfaces. To allow for small variations in fuel composition and flow rate and in the air flow rates that inevitably occur in industrial practice, it is usually desirable to aim for operation with a small amount of excess air, say 5 to 10 percent, above the theoretical amount for complete combustion. Too much excess air, however, leads to increased sensible heat losses through the stack gas. 

There are considerable problems in measuring heat transfer coefficients where only sensible heat is transferred because of the difficulties in measuring particle surface temperatures in a fluidized bed (Vazquez... 

When we increase the reflux rate, the tower-top temperature drops— let s say from 300 to 240°F. Actually, the temperature of the vapor leaving all the trays in the tower will decrease. The effect is bigger on the top tray, and gradually gets smaller, as the extra reflux flows down the tower. If the top-tray temperature has dropped by 60°F, then the vapor temperature leaving tray 9 might drop by only 5°F. Let s assume that the extra reflux causes the temperature of the vapor from tray 4 to decrease by 40°F. We can say that the sensible-heat content of the vapor has decreased. Sensible heat is a measure of the heat content of a vapor, due to its temperature. If the specific heat of the vapor is 0.5 Btu/[(lb)(°F)], then the decrease in the sensible-heat content of the vapor, when it cools by 40°F, is 20 Btu/lb. 

The sensible heat of the air is measured with a dry-bulb thermometer, whereas the latent heat of the water vapor can be calculated from the air s relative humidity. 

This effect is especially important in the semi-batch reactor. If the temperature difference between reactor and feed is important and/or the feed rate is high, this term may play a dominant role, the sensible heat significantly contributing to reactor cooling. In such cases, when the feed is stopped, it may result in an abrupt increase of the reactor temperature. This term is also important in calorimetric measurements, where the appropriate correction must be performed. 

Within the framework of the AsiaFlux program, Saigusa et al. (2005) measured the C02 fluxes since 1993 in the forest ecosystem of Takayama using an aerodynamic method to estimate the vertical gradient of C02 concentration and a vortex divergence method to calculate the coefficient of diffusion over the forest canopy. Also, measurements were made of vortex fluxes of sensible heat, water vapor, and C02. 

When (2.25) is integrated from the initial condition t = 0 and Ca = Cao to t —> oo and Ca -> 0 in the case of adiabatic reactor (US = 0), the adiabatic temperature rise A rad = 7 id - To is obtained, which represents a useful measure of practical utility of the system reactivity in terms of the maximum temperature obtainable when chemical energy is entirely transformed into sensible heat. 

The Jakob number is basically a measure of the importance of subcooling expressing, as it does, the change in the sensible heat per unit mass of condensed liquid in the film relative to the enthalpy associated with the phase change. The Jakob number is small for many problems, i.e the sensible heat change across the liquid film is small compared to the latent heat release. For example, for cases involving the condensation of steam, Ja, is typically of the order of 0.01. 

A typical heat balance for Run LSF 34 on No. 6 oil is given in Table V. The calculated efficiencies are also given in the table. Heat input terms consist of the input heat from the fuel, the fuel sensible heat, and the makeup water sensible heat. The heat available from combustion of the fuel is calculated from the measured volumetric flow rate, the measured fuel heating value, and the measured fuel density at the nozzle temperature. The fuel sensible heat contains the fuel mass flow rate, the measured temperature at the nozzle, a reference temperature, and an estimated specific heat for the oil of 0.480 Btu/lb°F. The specific heat was taken from graphical information in the ASME Power Test Code. Similarly, the water sensible heat calculation contains a tabular value... 

All of the important heat effects are illustrated by this relatively simple chemical manufacturing process. In contrast to sensible heat effects, which are characterized by temperature changes, the heat effects of chemical reaction, phase transition, and the formation and separation of solutions are determined from experimental measurements made at constant temperature. In this chapter we apply thermodynamics to the evaluation of most of the heat effects that accompany... 

The CEN/TC 295 draft standard prEN 13240 [1] is based on measurements of efficiency and flue gas emissions at a nominal burning rate. The emission factors are based on concentration measurements of the pollutants in the due gas. The efficiency is calculated indirectly by the flue loss method taking into account the thermal due gas losses (sensible heat) and the chemical losses (combustible gases, here as carbon monoxide, CO). 

Liquid temperatures in the tubes of an LTV evaporator are far from uniform and are difficult to predict. At the lower end, the liquid is usually not boiling, and the liquor picks up heat as sensible heat. Since entering liquid velocities are usually very low, true heat-transfer coefficients are low in this nonboiling zone. At some point up the tube, the liquid starts to boil, and from that point on the liquid temperature decreases because of the reduction in static, friction, and acceleration heads until the vapor-liquid mixture reaches the top of the tubes at substantially vapor-head temperature. Thus the true temperature difference in the boiling zone is always less than the total temperature difference as measured from steam and vapor-head temperatures. 

Also simultaneously measure sensible heat flux (or evaporation). ... 

Figure 9. Fluxes of methanol measured with a fast response PTR-MS instrument during hay harvesting at a field site in western Austria. The data shown are for methanol fluxes on the second day after hay cutting, and for periods when the prevailing wind was suitable. Methanol fluxes largely correlated with air temperature, declined sharply in the afternoon, and approached zero as the hay harvest began after 15 45. Also plotted are sensible heat flux (i.e. transfer of heat due to conduction and convection) and latent heat flux (i.e. heat loss due to evaporation of liquid water). Data redrawn from Ref. [45].

WET-BULB TEMPERATURE. The wet-bulb temperature is the steady-state, non-equilibrium temperature reached by a small mass of liquid immersed under adiabatic conditions in a continuous stream of gas. The mass of the liquid is so small in comparison with the gas phase that there is only a negligible change in the properties of the gas, and the effect of the process is confined to the liquid. The method of measuring the wet-bulb temperature is shown in Fig. 23.4. A thermometer, or an equivalent temperature-measuring device such as a thermocouple, is covered by a wick, which is saturated with pure liquid and immersed in a stream of gas having a definite temperature T and humidity ff. Assume that initially the temperature of the liquid is about that of the gas. Since the gas is not saturated, liquid evaporates, and because the process is adiabatic, the latent heat is supplied at first by cooling the liquid. As the temperature of the liquid decreases below that of the gas, sensible heat is transferred to the liquid. Ultimately a steady... 

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