Q Amount of heat

Heat flow (q) The amount of heat flowing into a system (+) or out of it (—), 

Here Q is the amount of heat contained per unit volume in the substrate, jc is the distance down into the substrate, and t is the time of inadiation. The solutions of this equation depend on the physical conditions of the uradiation. Thus if the surface is subject to a constant energy supply, Qq, the solution is 

A 7 depends on q, the amount of heat transferred. As an example, the transfer of 50 J of heat to an object causes an increase in temperature that is twice as large as the increase caused by 25 J of heat. 

If a body absorbs an amount of heat Q from a reservoir at temperature T, and at the same time does work A, 

AT — In this equation, q is the amount of heat transferred, n is the number of moles of material Involved, 

SQ) = (yp h1),- ( Q)p = (r4l%-Thus, cv, cp are the amounts of heat absorbed per unit increase of temperature at constant volume and at constant pressure respectively. They are the specific heats at constant volume and at constant jwessare respectively. 

Let AU denote the change of intrinsic energy, and let Q be the amount of heat absorbed at the temperature T, in any part of the process. Then, according to the first law  

The thermal condition of the feed is designated as q, and is approximately the amount of heat required to vaporize one mole of feed at the feed tray conditions, divided by the latent heat of vaporization of the feed. One point on the q line is on the 45° line at Xp. 

As a first assumption we take Q independent of temperature, i.e.y we suppose that the same amount of heat is absorbed when a 

Generally, q is small because the outside area is not large in comparison to the amount of heat being transferred, and the energy balance can be simplified. In these conditions it is also convenient to write balances over a differential section of the column. These balances yield the following  

Close to the wall, the fluid velocity is low and a negligible amount of heat is carried along the pipe by the flowing fluid in this region and Q is independent of y. 

We have assumed that the temperatures remain constant during the transference of a finite amount of heat Q, which implies that the heat reservoirs have very large heat capacities. To remove this restriction, we suppose that the amount of heat absorbed is infinitesimal, SQ. Then, for the gain of available energy we have  

Figure 2.10 illustrates how heat pumps can transport heat from a lower to a higher elevation and thereby can cool an already cold temperature substance, such as LH2. The heat pump removes Q, amount of heat from the cold process at the cost of investing W amount of work and delivers Qh quantity of heat to the warm reservoir. In the lower part of Figure 2.10, the idealized temperature entropy cycle is shown for the chiller. The cycle consists of two isothermal and two isentropic (adiabatic) processes  

Energy transfer is directional, and for this reason it is essential to keep track of the signs associated with heat flows. For example, if we drop a heated block of metal into a beaker of cool water, we know that heat will flow from the metal to the water q is negative for metal and positive for the water. The amount of heat flow is the same, however, for both objects. In other words, ijwater = metal more general terms  

A parallel reactor system has an extra degree of freedom compared with a series system. The total volume and flow rate can be arbitrarily divided between the parallel elements. For reactors in series, only the volume can be divided since the two reactors must operate at the same flow rate. Despite this extra variable, there are no performance advantages compared with a single reactor that has the same total V and Q, provided the parallel reactors are at the same temperature. When significant amounts of heat must be transferred to or from the reactants, identical small reactors in parallel may be preferred because the desired operating temperature is easier to achieve. 

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