Heat loss / gain

Exothermic, endothermic, or negligible heat loss/gain. 

Hot and cold liquids are mixed at the junction of two pipes. The temperature of the resulting mixture is to be controlled using a control valve on the hot stream. The dynamics of the mixing process, control valve, and temperature sensor/transmitter are negligible and the sensor-transmitter gain is 6 mA/mA. Because the temperature sensor is located well downstream of the junction, an 8 s time delay occurs. There are no heat losses/gains for the downstream pipe. 

For two-phase flow, heat gain/loss is also an important consideration, because this dictates the vapor/liquid fraction of the flow. Apart from changing the overall physical properties, this also changes the flow regime and will have a substantial impact in pressure drop calculation. The heat loss/ gain can be used for compressible fluids for better results however, it is of less importance for multiphase flow, unless the thermodynamic correlations are used to estimate the vapor/liquid fraction of the fluid. 

A separate form has been introduced to calculate the heat transfer resistance. The heat transfer resistance calculation form is presented in Figure 2.19. In the "Input Details" frame of the main form, it is possible to enter the heat loss/gain (gain is -i-ve) value. The design is structured as follows ... 

Enter 0 in the heat loss/gain cell in Figure 2.18 (0 is entered by default). In this situation, the heat loss/gain button can be pressed to calculate the heat transfer resistance alternatively, just do nothing to let the program know that heat loss/gain calculation is not required. 

Add the heat loss/gain value. If this is nonzero, the program will assume the value as calculated externally and use it to estimate the temperature changes in the pipeline. 

Sometimes the heat loss/gain calculation can diverge to an abnormal value, which will be indicated by some abnormal value of outlet... 

It should be noted that this two-phase correlation has not been developed for cross-country pipelines. This program is to be used to design plant battery limit piping. This calculation does not attempt to establish the impact of temperature (heat loss/gain) simply because the impact can only be established once the full fluid dynamics are available. For example, if there is heat loss, some liquid will condense, and vapor and liquid physical properties will change. It is not possible to calculate these without full fluid properties. 

For piping systems operating within at least 150°C above or below ambient temperature, heat loss or gain, respectively, from the piping to the support system should be evaluated, as well as local thermal stresses due to temperature differences between the pipe and its support attachment. Clamp-type supports iasulated from the piping, and extended support connections with the support members covered with iasulation at the support junction and for a distance beyond frequently are used for such systems. 

The kieveisible phenomena represent entropy gain through irrecoverable heat losses as follows, where X is the thermal conductivity and /is the length ... 

Actual system heat loss (or gain) will normally exceed calculated values because of projertions, axial and longitudinal seams, expansion-contraction openings, moisture, workers skill, and physical abuse. 

The second context is the process reac tor. There is a potential for a runaway if the net heat gain of the system exceeds its total heat loss capabihty. A self-heating rate of 3°C/day is not unusual for a monomer storage tank in the early stages of a runaway. This corresponds to 0.00208°C/min, 10 percent of the ARC s detection limit. ARC data for the stored chemical would not show an exotherm until the self-heating rate was 0.02°C/min. Therefore, onset temperature information from ARC testing must be used with considerable caution. 

The continuous current rating of a bus system can be defined by the current at which a steady-state thermal condition can be reached. It is a balance between the enclosure and the conductor s heat gain and heat loss. If this temperature is more than the permissible steady-state thermal limit it must be reduced to the desired level by increasing the size of the conductor or the enclosure or both, or by adopting forced cooling. Otherwise the rating of the bus system will have to be reduced accordingly. 

Heat losses and gains by heat conduction through the building envelope... 

The prevention of unnecessary heat loss or gain, causing poor thermal comfort due to large glazing areas and infiltration, should also he considered. 

Body heat gain or loss The positive or negative change in the heat content of the human body caused by an imbalance between heat production and heat loss. 

Heat balance The thermal balance that occurs in a building when the heat gains equal the heat losses. Also known as balance point or break-even point. 

Thermal discomfort Discomfort experienced due to excessive heat loss or gain from or to the human body due to radiation, convection, conduction, evaporation, or air movement. 

Ventilation heat loss or gain The quantity of sensible and latent heat lost or gained from an enclosure due to natural or mechanical ventilation. 

If a phase change occurs in the process stream for which heat duties are being calculated, it is best to perform a flash calculation and determine the heat loss or gain by the change in enthalpy. For a quick hand approximation it is possible to calculate sensible heat for both the gas and liquid phases of each component. The sum of all the latent and sen -i-ble heats is the approximate total heat duty. 

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