Air conditioning systems cool homes and businesses by directly lowering the air temperature and pulling humidity out. They also heat homes by transferring energy to water.
If the air coming out of your vents is warm rather than cold, a clogged air flow issue may be the cause. It can also be caused by rodents chewing on ductwork.
The radiant section of a fired heater is the portion that picks up heat by radiation from flame and hot flue gas/refractory. This section contains bank of tubes that may be either cylindrical or cabin type, with the coil configuration helical or serpentine. These tubes stand or hang vertically in a circle around the floor mounted burners. These heaters can be designed with or without a convection section. An all radiant design is less expensive but a convection section allows higher power capacity for the same duty.
Just below the radiant section is a shield (shock tube) section that contains rows of tubes that shield the convection section from direct radiation. Several important measurements are normally made here like bridgewall or breakwall temperature, flue gas oxygen and ppm combustibles and draft measurement.
Because of the radiant section heat transfer, it is very important that the gas temperature at the refractory surface be as low as possible to avoid harmful emissions like NOx. To achieve this target modern combustion technologies like flameless combustion and HiTAC are used. This is normally combined with internal flue gas recirculation technology to dilute the combustion zone with fresh air to reduce the NOx levels.
As the name suggests, convection is heat transfer through the movement of fluids. This can be air or any other liquid or gas. This is the mode of heat transfer that happens in a mechanically ventilated building. Specifically, as the sun warms the building interior, the warmer air has a lower density than cooler air and rises up in the building, where it is replaced with more cooler outside air by convection.
In the HVAC in Chesapeake VA and Refrigeration field, convection is commonly modeled using heat exchangers such as cooling coils. A heat balance is conducted on the exchanger to show that the system has a net loss of heat from the hot gas (such as air) to the cold fluid (such as water).
Explicitly modeling convection requires an accurate temperature distribution, which can be computationally expensive. COMSOL Multiphysics allows you to simplify this process by modeling free convection within the Heat Transfer interface using the Equivalent Conductivity for Convection feature. This increases the thermal conductivity of the air based on correlations that depend on the dimensions of the cavity and the temperature variations across it.
Flue Gas Stack
A flue gas stack is a tall structure through which combustion product gases are exhausted into the atmosphere. Sometimes called a chimney stack, these structures can be up to 1,300 feet (396 meters) high. They are designed to increase the stack effect and improve the dispersion of pollutant emissions.
Draft loss from the system is controlled by a combination of factors including wind fluctuations, chimney height and layout, burner firing rate, air heaters, stack economizers and dampers, and barometric conditions. The system also has a natural draft based on the thermodynamic relationship between internal and external pressures.
In the United States and in many other countries, atmospheric dispersion modeling regulations limit the maximum stack height to what is known as the GEP (Good Engineering Practice) stack height. Any stack that exceeds this limit must be inspected by the appropriate environmental protection agency. GEP stacks require a special inspection and maintenance program to prevent acid condensation and corrosion on the inside of the stack.
In a normal pregnancy, your baby will move into the head-first position before delivery. But sometimes your baby doesn’t reposition and is still born with their butt downwards into the birth canal (breech presentation). This is not considered normal and is generally considered to be a pregnancy complication.
Around 5% of full-term pregnancies have a breech baby. It is possible for a breech baby to be delivered vaginally but it is generally safest for you and your baby to have a caesarean section.
Your healthcare professional may try to turn your breech baby using a procedure called external cephalic version (ECV) around 37 weeks gestation. This is only about 65% effective and it also carries some risks. For this reason, most healthcare providers will only recommend this option if it is thought that you and your baby are suitable for a vaginal breech delivery. This patient information is based on the RCOG Green-top Clinical Guidelines No 20a External cephalic version and Reducing Incidence of Term Breech Presentation and No 20b Management of Breech Presentation, which you can find here and here.