Thermodynamics Lab Manual

7 Thermodynamics & Heat Transfer Lab Manual (Kantipur EC) By: Shankar S. Dhami

Experiment No: 1

Temperature Measurement

Objective

The main objective of this experiment is to compare the accuracy and characteristics

response of the different types of thermometers.

Set up requirements

Temperature measurement bench with accessories

Make: Arm field

Model: HT2

Addition:

a) pure water and crushed ice made of pure water

b) stop watch

Equipment Preparation

First of all make sure that the water heater is full with clean water, and place the power

cord to the replaceable in its base. Place the platen on the support bracket above the water

heater. Then crushed the ice into fine particles and fill the vacuum flask with a mixture of

crushed ice and pure water.

Experimental procedure

1) Measure the ambient air temperature by glass thermometer.

2) Insert the bulb of the thermometer into the vacuum flask and stirring carefully to

ensure intimate contact with the water-ice mixture.

3) You will observe that the reading on the thermometer is 0 degree centigrade.

4) Partially unscrew the top portion of the gland fitted to the platen and moisten the

o-ring within the gland. Carefully insert the bulb of thermometer into the water

heater and make sure that the bulb is immersed in the water then tighten the gland

to retain the thermometer.

5) Turn on the rocker switch for water heater and turn the regulator clockwise. After

few minutes water starts to boil and you will observe that the reading on the

thermometer is 100 degree centigrade.

6) Repeat the reading in the mixture of ice and water and boiling water and observe

that the reading is consistently 0 degree centigrade and 100 degree centigrade.

7) Repeat the reading in ice-water mixture and boiling water with different types of

thermometers and record the temperature in the table.


S.N. Type of Thermometers Freezing temperature

of pure water

Boiling temperature of

pure water in degree

centigrade

8) Repeat the above reading in ice-water mixture and boiling water and hot water

and hat air blower with different types of thermometer and record the response

time required in the table:

S.N. Type of

Thermometers

Time

(seconds)

Ice-water

mixture

Boiling water hot air

On the completion of this experiment, turn the regulator fully anti-clockwise and turn the

switch off. Also make sure that the water heater and vacuum flask are empty.


Experiment No: 2

Heat Conduction

Objectives:

To investigate Fourier’s law of linear conduction

To investigate the temperature profile and heat transfer in radial direction of a

cylinder

To investigate the effect of change in cross-sectional area on the temperature

profile

Theory: Heat transfer is defined as the transmission of energy from one region to another as a

result of temperature gradient takes places by the following three modes:

1. Conduction

2. Convection

3. Radiation

Conduction is the transfer of heat from one part of a substance to another part of the same

substance or from one substance to another in physical contact with it, without

appreciable displacement of molecules forming the substance.

Fourier‘s law of heat conduction states that the rate of flow of heat through a simple

homogeneous solid is directly proportional to the area of the section at right angles to the

direction of heat flow, to the change of temperature with respect to the length of the path

of the heat flow.

Mathematically it can be represented by the equation:

Q α A.dt/dx

Where, Q = heat flow through a body per unit time, W

A = surface area of the heat flow (perpendicular to the direction of the flow), m2

dt = temperature difference of the faces of the block of thickness dx through

which heat flow, oC or K

dx = thickness of the body in the direction of flow, m.

Thus,


Q = -k A.dt/dx

Where k = constant of proportionality is known as a thermal conductivity of the body.

Convection is the transfer of heat within a fluid by mixing of one portion of the fluid with

another.

Convection is possible only in a fluid medium and is directly linked with the

transport of medium itself.

Convection constituents the microform of the heat transfer since macroscopic

particles of a fluid moving in space cause the heat exchange.

The effectiveness of the heat transfer by convection d largely depends upon the

mixing motion of the fluid.

The rate equation for the convective heat transfer between a surface and an adjacent fluid

is prescribed by Newton’s law of cooling.

Q = h*A (ts-tf)

Where Q = rate of conductive heat transfer,

A = area exposed to heat transfer,

Ts = surface temperature,

Tf = fluid temperature and

h = co-efficient of conductive heat transfer

Conduction of heat along a simple bar

Observation:

Specimen material: Brass

Thermal conductivity of the specimen from tables:

Diameter of specimen: 25 mm

Length of specimen: 30 mm

Distance between temperature probes: 10 mm

Conduction of heat in radial direction: Observation sheet

Test

no. Wattmet

er watts,

Q

T1

°C

T2

°C

T3

°C

T4

°C

T5

°C

T6

°C

T7

°C

T8

°C

T9

°C

1 5

2 10

3 15


Specimen material: Brass

Thermal conductivity of the specimen from tables:

Outer diameter of specimen: 110 mm

Inner diameter of specimen: 8 mm

Length of specimen: 3 mm

Distance between temperature probes: 10 mm

Test no. Wattmeter

watts, Q

T1 °C T2 °C T3 °C T4 °C T5 °C T6 °C

1 5

2 10

3 15


Experiment No: 3

Air and Water Heat Pump

Set up requirement

Air and water heat pump

Make: P.A. Hilton Ltd.

Model: R831

Equipment Description:

HFC134a vapor generated by absorption of low grade heat in either the air or

water source evaporator is drawn into the compressor. This extraction of heat

from air or water reduces the temperature of the air or water flow leaving the unit.

The work done on the gas by the compressor increases the pressure and

temperature of the refrigerant vapor. This hot high pressure gas flows to a

concentric tube water tube condenser.

In the condenser the gas is desuperheated and then condensed at essentially

constant temperature. Before leaving the condenser the liquid refrigerant is

slightly sub-cooled below the saturation temperature for the condensing pressure

and this liquid then flows to a liquid receiver.

The liquid receiver gives a large volume, into which excess refrigerant can flow

during operating conditions. In addition the receiver ensures that liquid is always

available for changes in demand due to evaporator loading.

The compressor motor has winding resistance losses, internal friction and the

compression process is not isentropic. All of these conditions result in some of the

electrical energy input being covered into heat. The compressor and the motor are

contained within the hermetically sealed steel casing and run in oil which during

normal operation is warmed by circulation around the casing and collects at the

base of the unit. During normal operation some oil will be carried around the

system and under certain conditions may appear in the variable area flow meter as

a discoloration to the flow. This is quite normal and will disappear during normal

running.

As the compressor is designed specifically for heat pump uses a copper heat

transfer coil is located at the base of the compressor with in the oil reservoir. By

passing the cold water from the main supply through this coil before the water is


transferred to the condenser the normally waste heat from the oil can be added to

that given up to the condenser.

Sub-cooled liquid HFC134a at high pressure passes through a panel mounted flow

meter to a thermostatically controlled expansion valve. On passing through the

valve the pressure is reduced to that of the evaporator and the two phase mixture

of the liquid and vapor begins to evaporate within the selected evaporator.

Control of the heat pump is by variation of the condensing temperature by the

source air( or water) temperature and flow rate, and by variation of condensing

temperature by the flow rate of the condenser water.

The range of the source temperature can be extended directing warmed air from a

fan heater at the air intake or by warmed or chilled water to the source water inlet.

Relevant system temperature can be measured by thermocouples and a panel

mounted digital temperature indicator. The thermocouples used are type K

(Nickel-Chrome, Nickel-Aluminum).

Condenser and evaporator pressure are indicated by panel mounted pressure

gauges. Water and refrigerant flow rates are indicated by panel mounted variable

area flow meters.

The electrical input to the compressor motor is indicated by the panel mounted

analog meter.

Purpose;

The purpose of this experiment is

1 To determine the power input, power output as well coefficient of

performance of heat pump.

2 To draw actual vapor compression refrigeration cycle on a P-h diagram

and compare it with the ideal cycle.

1. Experimental procedure:

Turn on the water supply to the unit turn on the main switch.

Select the air evaporator by pressing the evaporator change over switch down.

Set the condenser gauge pressure to between 700 and 1100 kN/m2 by

adjustment of the condenser cooling water flow rate.

Allow the unit time for all system parameters to reach a stable condition and

fill up the observation sheet.

Repeat the above procedure for water evaporator by switching the change over

switch up condition and fill up the observation sheet.

Observation sheet:

For source of low grade heat: Air


S.No. Particulars units

1. Compressor electrical power input (W)………………………………Watts

2. Cooling water inlet temperature (t5)………………………………..……oC

3. Compressor cooling water outlet temperature (t6)…………………….…oC

4. Condenser water outlet temperature (t7)…………………………………oC

5. Condenser water mass flow rate (mc)………..…………………………..g/s

For source of low grade heat: Water

S.No. Particulars units

1. Compressor electrical power input (W) …………………………….Watts

2. Cooling water inlet temperature (t5)…………………………….…….…oC

3. Compressor cooling water outlet temperature (t6)…………………….…oC

4. Condenser water outlet temperature (t7)…………………………………oC

5. Condenser water mass flow rate (mc)……………………………………g/s

Relevant Eqations:

Qcomp = mc Cpw (t6-t5)

Qc = mc Cpw (t7-t6)

COPhp = rate of heat delivered/ compressor electrical power input.

If the heat delivered to the condenser only is considered, then

COPhp = Qc/ W

If the total heat delivered to the water is considered, i.e., including the waste heat from the

compressor cooling oil, then

COPhp = (Qc + Qcomp)/W

Where, Qcomp = heat delivered to cooling water from compressor

Qc = heat delivered to condenser cooling water


COPhp =coefficient of performance of heat pump

Cpw =specific heat of water (4.18kJ/kg oC)

2. Experiment procedure:

1. Turn the water supply to the unit turn on the main switch.

2. Select the water evaporator by pressing the evaporator change over switch up.

3. Set the condenser cooling water flow rate to approximately 50 % of full flow and

evaporator water flow as said by the instructor.

4. Allow the unit time for all of the system parameters to reach a stable condition

and fill up the observation sheet.

Observation sheet:

Atmospheric pressure = 1.05 bar = 105kN/m2

S.No. particulars units

1. HFC134a gauge pressure at compressor suction (p1)…………………….…kN/m2

2. HFC134a absolute pressure at compressor suction (p1)…………………….kN/m2

3. HFC134a gauge pressure at compressor discharge (p2)…………………....kN/m2

4. HFC134a absolute pressure at compressor at discharge (p2)……………….kN/m2

5. HFC134a temperature at compressor suction (t1)…………………….…………oC

6. HFC134a temperature at compressor suction (t2)…………………..…………....oC

7. HFC134a temperature condensed liquid (t3)….....................................................oC

8. HFC134a temperature at expansion valve outlet (t4)………………..….....……..oC

Result and Analysis:

Draw ideal as well as practical vapor compression cycle in the P-h diagram and compare

their energy input, desired output as well as COP.

Documents

Thermodynamics Lab Manual