heat loss for bare and lagged pipes

APPARATUS FOR DETERMINING HEAT LOSS FROM BARE AND LAGGED

PIPES

IntroductionHeat transfer 

Discipline of thermal engineering that concerns the transfer of thermal energy from one physical system to another.

Conduction defined as transferring heat or electricity through a conducting medium by way of direct contact

Introduction

Losses by convection -small air gaps exist between the surface wall and insulation

Radiant heat loss -occurs as a result of highly energized molecules transmitting heat by way of waves or particles

IntroductionPipe insulation

-thermal insulation used to prevent heat loss and gain from pipes, to save energy and improve effectiveness of thermal systems.

The benefits include, in addition to reducing costs and environmental impacts of energy consumption.

Reducing or eliminating condensation on cold pipes.Protection from dangerous pipe temperatures.Control of noise.Reduction of unwanted heat gain to air-conditioned

spaces.

Setup:•The test section is consists of four 10 ft lengths of 1-inch standard steel pipe mounted on a framework of welded 2 inch steel angles.

•One of the lengths is bare and the others are air-cell asbestos insulation, 85 % magnesia insulation, silver chrome(aluminum pigment) paint respectively.

1 in standard steel pipe

1 in standard steel pipe

10 ft

10 ft

Bare

Air cell asbestos

85% magnesi

a

Silver chrome paint

head

er

2 inches pipe

Glo

be

valv

e

Drain

•The test pipes are connected to a common header into which steam is introduced either directly from the main or from a line containing a reducing valve.

•Each end of the tested pipe is equipped with a plug-type valve where steam condensate is drained , collected in beakers and measured.

In this apparatus , determining the heat loss from bare and lagged pipe is conducted through :

•Supplying heat from the condensation of steam into the pipe to be tested

•Surface temperatures are measured by means of a portable thermocouple potentiometer.

PROCEDURESteam is first introduced to the common header where in

the flow is regulated through a reducing valve. Make 3 runs with steam pressure at 10psig, 20psig and 30 psig.

After adjusting the system to the desired pressure, crack the drain cock under the header to remove water from the steam line and header.

The four plug-type valves were then opened to blow out any condensate from the pipes, and then closed them until only a small amount of steam escapes along with the condensate.

When the system has reached equilibrium (measured at various points), as determined by surface temperature measurements reading on the thermocouple, collect and measure the condensate from each pipe over a timed interval of 15 ,30 minutes and 1hr, and then during this period, record the following data needed for calculations:

Barometric pressureRoom tempSteam pressure and tempSurface temperatures

The surface-film coefficients and the lagging efficiency are calculated from the temperature of the surfaces and the room.

Heat Loss in insulated pipes:

calculations

PROBLEM…

Assume boiler runs with steam in the pipes at 10 psig, 20 psig, and 30 psig. Determine the theoretical surface temperature at equilibrium and the theoretical condensate in time intervals 15 min, 30 min, and 1 hour

Assumptions… steady stateconstant pressurevelocity = 1ft/sec

Data…length of pipe: 10ftroom temperature: 86°F atmospheric pressure: 14.696psi

thermal conductivities:steel = 26 Btu/hr °F ftasbestos = 0.14 Btu/hr °F ft85% magnesia = 0.034 Btu/hr °F ftSilver Chrome (Al pigment) =

Data: Outside diameter, D’:

Pipe 1 (asbestos) : 2.875’’Pipe 2 (Bare): 1.315’’Pipe 3 (Siver Chrome): 1.315’’Pipe 4 (85%Magnesia): 3.1875’’

PROBLEMSDefective BoilerNo enough description of the boiler. Data’s that are

necessary for calculations like mass flow rate.Its hard to determine which of the pipes has the

described insulationPipes are not properly insulatedDifficulty in determining the surface temp.Condensation of Steam in Parts of the system other

than the test pipes.Condensation in Collecting beakersConvection Current in Air- the convection on air

affects the heat

RecommendationsRehabilitate or Buy a new Boiler Keep track of the boiler’s performanceKeep all records and gather enough data’s of the boiler if

ever buy a new one.Install new insulation for the pipes and keep track of it’s

performanceEach pipe should be tested for leakageLabel the Pipes properly Use thermo coupleThe beaker used should be heated first to avoid errorPut the equipment in a controlled temp. roomPlug type valves at each end of the pipe should be replaced