Adamson University

College of Engineering

Chemical Engineering Department

UNIT OPERATIONS 1 LABORATORY

EXPERIMENT 10:

BARE AND LAGGED PIPES

SUBMITTED BY:

ANASTACIO, VAN CALVIN O.

CRUZ, NICHOLE M.

LINGAO, NIKKO VINCENT

MARTIN, JEANELL P.

PENALBA, BENJIE T.

SUBMITTED TO:

ENGR. ALBERT D.C EVANGELISTA

I. ABSTRACT

Thermal conductivity is the measure of the ability of a material to allow the flow of heat from its warmer surface through the material to its colder surface; it is determined as the heat energy transferred per unit of time and per unit of surface area divided by the temperature gradient. Temperature gradient is defined as the difference of temperature divided by the distance between the two surfaces usually expressed in watts per Kelvin per meter. The objectives of this experiment are to determine the thermal conductivity and efficiency of the lagging materials. The heat input would be assumed equal to the heat flow rate through the lagged pipe. The material being used in this experiment is the bare and lagged pipes set-up apparatus, boiler, digital thermometers, heat resistant gloves, container and steam condensate collector.

II. INTRODUCTION

Heat transfer is the movement of thermal energy from one thing to another thing of different temperature. These objects could be two solids, a solid and a liquid or gas, or even within a liquid or gas. Heat transfer by conduction involves transfer of energy within a material without any motion of the material as a whole. Energy transfers from more energetic to less energetic molecules when neighbouring molecules collide. Heat flows in direction of decreasing temperatures since higher temperatures are associated with higher molecular energy. The rate of heat transferred naturally depends on the magnitude of the temperature difference, the thermal resistance, and the heat transfer area.

The use of insulation is the most common method of minimizing the heat losses to the surroundings. This increases the resistance therefore lower the rate of heat transfer. The rate of heat lost from a pipe carrying steam can be measured simply by determining the rate of condensation of steam, m, which can be collected at a certain interval of time.

By heat balance, 𝑞𝑙𝑜𝑠𝑡 = 𝑚[𝜆𝑠 + 𝐶𝑝(𝑇𝑠 − 𝑇𝑐)]

Where:

𝑞 = 𝑇𝑜𝑡𝑎𝑙 ℎ𝑒𝑎𝑡 𝑙𝑜𝑠𝑡, 𝐵𝑡𝑢/ℎ𝑟 𝜆𝑠 = 𝐿𝑎𝑡𝑒𝑛𝑡 ℎ𝑒𝑎𝑡 𝑜𝑓 𝑣𝑎𝑝𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛, 𝐵𝑡𝑢/ℎ𝑟 𝑇𝑠 = 𝑆𝑎𝑡𝑢𝑟𝑎𝑡𝑒𝑑 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑠𝑡𝑒𝑎𝑚𝑇𝑐 = 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑐𝑜𝑛𝑑𝑒𝑛𝑠𝑎𝑡𝑒Condensed steam can be collected as saturated liquid under controlled conditions, then we can simplify the above equation to,𝑞 = 𝑚𝜆s

Determining the effectiveness of insulation would therefore be just comparing the heat lost from the pipe with insulation with that of a bare pipe. The rate of condensation would be proportional to the heat lost and the weight of the condensate is directly proportional to its volume. This is assuming that the temperatures and pressures of the condensate are the same. The lagging efficiency could be determined using the equation

𝐿𝑎𝑔𝑔𝑖𝑛𝑔 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = [ 𝑉𝑏 − 𝑉𝑙 𝑉𝑏 ]

Where:𝑉𝑏 = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑐𝑜𝑛𝑑𝑒𝑛𝑠𝑎𝑡𝑒 𝑐𝑜𝑙𝑙𝑒𝑐𝑡𝑒𝑑 (𝑏𝑎𝑟𝑒 𝑝𝑖𝑝𝑒) 𝑉𝑙 = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑐𝑜𝑛𝑑𝑒𝑛𝑠𝑎𝑡𝑒 𝑐𝑜𝑙𝑙𝑒𝑐𝑡𝑒𝑑(𝑙𝑎𝑔𝑔𝑒𝑑 𝑝𝑖𝑝𝑒)

Before heat is transferred to the surroundings, it travels first from the bulk of the steam through the steam film condensate, then through the metal pipe, then through the insulation by conduction until it reaches the surface of the insulation where part of the heat is transferred to the surrounding air by convection and part by radiation to the surrounding walls. That is,𝑞𝑙𝑜𝑠𝑡 = 𝑞𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑜𝑛 = 𝑞𝑐𝑜𝑛𝑣𝑒𝑐𝑡𝑖𝑜𝑛 + 𝑞𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 𝑞𝑙𝑜𝑠𝑡 = ℎ𝑐𝐴𝑜((𝑇𝑠 − 𝑇𝑎 ) + ℎ𝑟𝐴𝑜(𝑇𝑠 − 𝑇𝑤)

Where:

hc = Heat transfer coefficient by convection

hr = Heat transfer coefficient by radiation

Ts = Surface temperature of insulation

Ao = Outside area of insulation

For practical purposes, Ta =Tw , therefore becomes,

𝑞𝑙𝑜𝑠𝑡 = (ℎ𝑐 + ℎ𝑟)𝐴𝑜(𝑇𝑠 − 𝑇𝑎)

III. Materials/ Equipments Needed:

1. Bare and Lagged Pipe Apparatus Set- Up

2. Boiler

3. Digital Thermometers

4. Heat Resistant Gloves

5. Container

6. Steam Condensate Collector

IV. PROCEDURE

The bare and lagged pipe apparatus set- up was preheated for five (5) minutes by allowing the steam through the tubes until the temperature reading becomes stable. The valves were then opened at the end of each tube. Then, a constant pressure of the incoming team was set by adjusting the valve that controls the steam inflow. This was done by closing the valves at the end of the tubes and measuring the pressure when it becomes constant. The corresponding temperature was also measured. The valves at the end of the tubes were opened and the steam was allowed to run through for five (5) minutes. The condensates at the end of the tubes were collected using a metal basin.

After five (5) minutes, the temperature at the inlet and outlet of the tubes were recorded using thermometers. The temperature and the volume of the condensate were measured. The temperature of the condensate was immediately recorded as it drops into the metal basin so that the minimal heat is lost upon measurement

V. RESULTS AND DISCUSSION

At the Boiler:

Pressure: 41 PSI

Temperature (Steam): 149oC

Pipe Type Inlet Temperature (oC) Outlet Temperature (oC)Pipe 1: Perlite 34.3 39Pipe 2: Normal 73 73.6

Pipe 3: Three (3) Times Coated 74 78

Pipe 4: Insulated 41.1 44Table 1: Inlet and Outlet Temperature Readings per type of Pipe

Pipe Type Time (s) Temperature (oC) Volume of the Condensate (mL)

Pipe 1: Perlite 30 58.1 1050Pipe 2: Normal 30 86 1250

Pipe 3: Three (3) Times Coated 30 85.9 1350

Pipe 4: Insulated 30 61 450Table 2: Volume of the Condensate Readings

Pipe Type Heat Lost (J/s)Pipe 1: Perlite 2637.18Pipe 2: Normal 2522.95

Pipe 3: Three (3) Times Coated 2523.37Pipe 4: Insulated 2602.45

Table 3: Experimental Heat Lost per Pipe

Pipe Type Efficiency (%)Pipe 1: Perlite 16

Pipe 3: Three (3) Times Coated 8Pipe 4: Insulated 64

Table 4: Lagging Efficiency

VI. CONCLUSION

It can be concluded that the determined experimental and theoretical heat losses for each pipe shows reasonably same results through the use of the heat transfer coefficient for convection and radiation in computing for heat losses. Pipe 4, the Insulated Pipe, gave the highest lagging efficiency among all the pipes.