Laws of heat loss in cylindrical pipes

Laws of heat loss in cylindrical pipes

Heat loss refers to the net heat that is lost during the transfer of heat by an object to its immediate environment.  Therefore, heat loss in cylindrical pipe is the total heat lost during the transfer from the warm pipe areas of the pipe to the cooler environment until equilibrium. At this state of equilibrium no more heat transfer happens since the pipe and its environs are at equal temperature hence no heat loss occurs.

Laws of heat loss in cylindrical pipes

Different physics laws have been used to discuss how heat is lost in cylindrical pipes. Conduction being one of the laws, discusses how pipes lose heat as they conduct heat using conduction. Conduction is the transfer of heat from the warm pipe and its content to the cooler environment through direct contact.  The law of conduction explains how heat is lost when heat is being transferred through direct contact. In addition to this, the law of convection also is used to discuss how heat in cylindrical pipes is lost. According to the law, there are air spaces between the pipe material and the insulation material of the pipe.

The air spaces are very small so as to allow air to flow hence convection occurs.  The law further elaborates that the small air gaps are thermal resistive. The characteristic of the air gaps in the pipes causes heat loss. Radiation is yet another physics law used to discuss how heat is lost in cylindrical pipes. Heat loss according to the law happens due to the presence of molecules with very high energy (Nukiyama, S. 1966). The molecules transmit heat by waving. However, he law emphasizes on the fact that for heat loss to occur through radiation, the pipe and its contents has to be very hot and of very high temperatures than in normal instances such as conduction and convection.

Equation used to calculate heat loss in cylindrical pipes

Heat loss in a pipe is not calculated on the entire area of the pipe given but instead is calculated per linear foot (Bejan, A. 2001). The insulation material increases in thickness from the interior surface to the external surface. The reason behind this is due to the pipe’s shape (Nukiyama, S. 1966). Therefore, this should be considered when calculating the aggregate heat loss in a pipe. As earlier said, since the heat loss in a cylindrical pipe is calculated on linear foot base instead of the whole pipe area, a one foot mean area of the insulated part should be calculated. The heat loss equation is by conduction only is;

Heat loss = [2∏(k) (∆T)] /[(40.944)ln(Do/Di)]

Whereby;

40.944 represent 3.412 conversion factor multiplied by 12”

Do stands for the external insulated diameter

Di is the internal insulated surface

In(Do/Di) =insulation surface area.

An additional 10% convection and radiation heat loss should be added to the equation. Below is a final heat loss in a cylindrical pipe;

Heat loss = [2 π (k)( ΔT)(1.1)] / [(40.944)ln(Do/Di) ]

Factors to consider before installing an in-house pipeline system

When installing a pipeline house system, one should consider what pipe material, pipe size and pipe insulation material is most suitable. Copper is the most suitable material to be used in house pipeline systems. The reason behind this is because copper has suitable flow characteristics. First, copper is durable since it resists corrosion. Copper is malleable and very easy to bend hence self-supporting (Bejan, A. 2001). In addition to this, copper requires just a few fittings and can be recycled hence economical. Mechanical insulation on the other hand is suitable in the house pipeline system.

In the part which is labeled number one, the fluid which is concentrated in this area is exposed to evaporation and therefore absorbs thermal energy. The vapor released during the evaporation process moves through the cylindrical cavity and lowers the temperature at the end of the cylindrical end part two. The vapor upon reaching the area labeled 3 condenses back to fluid form and it finds its way back and releases thermal energy. On the part labeled 4, the fluid from the wick gains higher temperature then flows back and forth.

The reason behind this is because they are made of the desired diameter and thickness. Examples of mechanical insulation materials are fiber glass and polyisocyanature. The materials are made of rigid segmentation.  For house pipeline system the size of s pipe should be considered. The smaller the pipe the suitable it is.  Other factors such as pipe fittings, branch connections, pressure ratings, flange types etc. should also be considered during the installation of a pipeline house system (Nukiyama, S. 1966).  The mostly used combination of pipes in Brampton is; pipes with plastic materials, glass fiber insulation material and big sized pipes.  This is different from other countries since most use vacuum insulation and medium sized pipes. The reason behind this is because, if copper materials were used in Brampton, the pipes would often corrode due to acidity and cause spillage.

Conclusion

Heat in cylindrical pipes is lost during transfer of heat to the surrounding environment. Conduction is the main law explaining how heat is transferred and lost in the process. However, there are other laws that have discussed heat loss although heat lost through these processes is a small amount. The laws are radiation and convection. The three laws as a result give rise to an equation used to calculate heat loss in pipes. Various factors such as the pipe’s material, insulation material and the pipe’s size should be considered before installation of a pipeline system.

Chart showing heat loss in different pipes with different sizes and temperature

References

Bejan, A. (2001). The tree of convective heat streams: its thermal insulation function and the predicted 3/4-power relation between body heat loss and body size. International Journal of Heat and Mass Transfer, 44(4), 699-704.

Nukiyama, S. (1966). The maximum and minimum values of the heat Q transmitted from metal to boiling water under atmospheric pressure. International Journal of Heat and Mass Transfer, 9(12), 1419-1433.

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