experiment no 1 determining the state of moist air and calculating the heat balance of air duct

LABORATORY GUIDE FOR THE COURSE “THERMODYNAMICS & HEAT TRANSFER” EXPERIMENT No.1; DETERMINING THE STATE OF MOIST AIR AND CALCULATING THE HEAT BALANCE OF AIR DUCT EXPERIMETNAL OBJECTIVE

VIET NAM NATIONAL UNIVERSITY

HO CHI MINH CITY

HO CHI MINH CITY UNIVERSITY OF

MEMBER

LABORATORY GUIDE FOR THE COURSE

“THERMODYNAMICS & HEAT TRANSFER”

EXPERIMENT No.1; DETERMINING THE STATE OF MOIST AIR

AND CALCULATING THE HEAT BALANCE OF AIR DUCT

EXPERIMETNAL OBJECTIVES AND REQUIREMENTS

1.1.1 Experimental objectives

- Knowing how to measure the temperatures (dry and wet bulb temperature), air flow, pressure and volume;

- Understanding the cooling and dehumidifying process of humid air;

- Understanding the working principle and main components of a basic refrigeration cycle;

- Calculating the heat balance in air duct;

At the outlet of air duct, an anemometer is used to measure the speed and temperature of moist air

Refrigerant in refrigeration system is R22

- Determining the evaporating and condensing temperature of refrigeration system

- From above data, student determines:

Demonstrating the processes of humid air on the t-d diagram (or I-d)

The heat released when humid air passes through the cooling coil

Moisture is removed at cooling coil according to theoretical calculations and experiments

Demonstrating the states of refrigerant on the T-s diagram (corresponding withn theoretical

refrigeration cycle, neglecting the superheat and sub-cooling processes)

1.4 Experimental data

When the system operates at steady state, the condensing water appears on the cooling coil,

student starts doing the experiments with the following requirements:

Student conducts two experiments (Note: after getting the experimental data, student changes

the airflow through the cooling coil)

Experiment 1: Experimental time is 10 minutes, the number of data collection are 3 times

Experiment 2: Experimental time is 10 minutes, the number of data collection are 3 times

Table 2 & 3: The state parameters of moist air

Experiment |

Moist air at inlet of coil Moist air at outlet of coil 1* time 31 27.5 23.92 92.29 17 12.42 50.10 2™! time 31 27.5 23.92 92.29 17.3 12.66 50.93

34 time 31.2 27.8 24.35 93.61 17 12.42 50.52 Average 31.067 27.6 24.063 92.73 17.1 12.5 50.5167

Experiment 2

Moist air at inlet of coil Moist air at outlet of coil 1“ time 31.5 27.7 24.21 93.55 15 14.3 10.35 41.19 2"“time | 31.6 27.9 24.50 94.40 14.6 13 9.56 38.78 3" time 31.3 27.8 24.35 93.71 14.5 13.2 9,68 38.98 Average | 31.467 27.8 24.353 93.8867 14.7 13.5 9,863 39.65

Velocity at outlet of air duct

(m/s) Temperature at outlet of air duct (°C) Water condensed (ml)

Evaporating Evaporating Condensing Condensing

pressure (Gauge) | temperature pressure (Gauge) | temperature

EXPERIMENT 1:

We have:

Amount of water condensed:

Amount of water condensed after 10 minutes:

Error (%):

The heat released when humid air passes through the cooling coil:

EXPERIMENT 2:

We have:

Amount of water condensed:

Amount of water condensed after 10 minutes:

Error (%):

The heat released when humid air passes through the cooling coil:

Demonstrating the processes of humid air on IJ-d diagram: Experiment 1:

At the inlet of air conduct

At the outlet of air conduct:

Experiment 2:

At the inlet of air conduct

At the outlet of air conduct:

EXPERIMENT No.2: DETERMING THE COEFFICIENT OF PERFORMANCE (COP) OF A REFRIGERATION CYCLE USING AIR-COOLED CONDENSER

AND AIR-COOLED EVAPORATOR

2.1 EXPERIMETNAL OBJECTIVES AND REQUIREMENTS

2.1.1 Experimental objectives

- To help students combine theoretical and practical knowledge

- To know the fundamental principle of the air conditioning system incorporating some auxiliary devices

- To help students measure the parameters such as temperature, pressure and calculate the actual heat and COP

2.1.2 Requirements

- Students must understand the refrigeration cycle

- Knowing to apply the mathematic formulas for refrigeration cycle

2.2 EXPERIMENTAL DESCRIPTION

2.2.1 Equipment and supplies

- The model of air conditioning system

- The temperature sensors

2.2.2 Description

To cool the air in the air-conditioning room, the diagram of the experimental model using refrigeration system with refrigerant of R12 is illustrated in figure 1 The compressor (A) compresses the vapor of R12 from the evaporating pressure PO to the condensing pressure Pk Then, this vapor is condensed to liquid at the air-cooled condenser (B) before entering the high-pressure receiver (C) The liquid of R12 at the receiver (C) passes through the expansion valve (I) where the pressure is reduced from Pk

to PO and then this vapor goes to the air-cooled evaporator (J) The heated refrigerant

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vapor at (J) is sucked into the compressor (A) and the principle of operation is repeated again

The refrigeration cycle represented in LogP-I graph

1-2: The process of diabatic compression in the compressor

2-3: The process of isobaric condensation in the condenser

3-4: The process of constant - enthalpy expansion in the throttling valve

4-1: The process of isobaric evaporation in the evaporator

The measurement positions of temperature and pressure in the refrigeration cycle

The manometers P1 and P2 are used to measure the suction and discharge pressures at the throttling valve, respectively and also the discharge pressure of the compressor

The temperatures of the R12 refrigerant entering and leaving the air-cooled condenser (B) are measured by the sensors of Tl and T2

The temperatures of the air entering and leaving the air-cooled condenser (B) are measured by the sensors of T3 and T4, respectively

The temperatures of the R12 refrigerant entering and leaving the air-cooled evaporator (B) are measured by the sensors of TS and T9, respectively

The temperature of the air in the air-conditioning room is measured by the sensors of T6

2.3 EXPERIMENTAL TASKS

In this experiment, the students are required to collect the data on the suction and discharge pressures; the temperatures of the refrigerant entering and leaving the air- cooled condenser, the temperatures of the refrigerant entering and leaving the air-cooled evaporator, the temperatures of the air entering and leaving the air-cooled condenser and the temperatures of the air entering and leaving the air-cooled evaporator Then, combining with the computing results to determine:

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- The state properties of the actual refrigeration cycle

- COP (e) of the theoretical and actual refrigeration cycle

- The heat load of the air-cooled condenser, Qx

- The necessary air flow to receive the heat rejection from the condenser, Gyx

From Table | and the thermodynamic properties of saturated refrigerant R12 and the thermodynamic properties of superheated refrigerant R12, we can fill in Table 3 below:

Table 3: The properties of R12 in refrigeration cycle

State Parameter 1 2 3 4 Pressure 0.9 9.2 9.2 0.9 Temperature -32.56 53.4225 37.4565 -32.56 Enthalpy 273.35 314.787 171.3 171.3 Entropy 2.3663 2.3663 1.906 1.906

b Calculating the heat load of the air-conditioning room

The heat load of the air-conditioning room is the amount of heat from the surrounding environment that passes through the walls due to the difference in the temperature

i Calculating the heat flux that transfers across each wall as follows:

With:

Thickness of layer 1, m

Thermal conductivity of the layer 1, W/mK

The convection heat transfer coefficient outside the air-conditioning room, W/m’K Select

The convection heat transfer coefficient inside the air-conditioning room, W/m’K

Wood 4.32

ii The amount of heat transfer across each wall (W)

F is the area of flat wall, m

Wall Dimension (m x m) Front 0.8x 0.4 Back 0.8x 0.4 Top 0.8 x 0.4 Bottom 0.8 x 0.4 Left 0.4x 0.4 Right 0.4x0.4

Front wall (Mica) :

Back wall (Wood):

Top wall (Wood):

Bottom wall (Wood):

Left wall (Mica+insulation material):

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Right wall (Wood):

ii The heat load of the air-conditioning room (W)

c Determining the flow rate of R12 (kg/s) in refrigeration cycle (Ignoring the heat loss to the surrounding environment)

d Determining the heat load of the condenser Q,(kW)

e Determining the air flow rate passing through the condenser (kg/s)

f Determining the adiabatic compression work of compressor W (kW)

g Determining € (COP)

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EXPERIMENT No 3: CALCULATION OF HEAT EXCHANGERS

3.1 EXPERIMETNAL OBJECTIVES AND REQUIREMENTS

Students carefully read the following contents before conducting the experiments:

- The types of heat transfer: conduction, convection, radiation;

- The formula for calculating the heat rate that water received and rejected;

- The formula for calculating the overall heat transfer coefficient and Reynold number

3.2 EXPERIMENTAL DESCRIPTION

3.2.1 Equipment and supplies

The equipment consists of two heat exchangers (helical-coil and shell and tube heat

exchanger) in which two fluids flow in parallel flow or in counter flow

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Figure 3 - Flowmeters of hot water (FUL) and cold water (FI2)

- There are 4 temperature sensors which are used to measure the temperatures of hot and cold water at inlet and outlet of the heat exchanger The temperatures are shown on the display

screens

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Figure 4 - The working principle of heat exchangers

& Technical specifications:

a The helical - coil heat exchanger:

- The helical-coil heat exchanger has the heat transfer area of 0,1m2 , symbol E2

- The coil made of stainless steel AISI 316 Other parameters include the outside

diameter of 12mm, the thickness of 1mm, the length of 3500mm

- The outside tube made of borosilicate glass with the inside diameter of 100mm

b The shell and tube heat exchanger:

- The shell and tube heat exchanger has the heat transfer area of 0,1m2 , symbol E1

- There are five tubes which made of stainless steel AISI 316 Other parameters include the

outside diameter of 10mm, the thickness of 1mm, the length of 900mm

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- The shell made of borosilicate glass with the inner diameter of 50mm

- There are 12 baffles and baffle cut of 25% shell diameter

3.2.2 Description

& Before starting the experiment:

- Checking the inlet and outlet of water to make sure that they are connected to water pipe

- Checking the power source

- Checking the hot water tank

- Closing the exhaust valves

- Turning on the digital temperature switch

- Turning on the hot and cold water pump

- The hot and cold water flow through the heat exchanger The temperatures are shown on display screens

3.3 EXPERIMENTAL TASKS

& Conducting the following experiments and collecting data:

a Running E1 (Shell and tube heat exchanger) in parallel flow:

Opening valves as V1, V6, V7, V8 and V10

Closing valves as V2, V3, V4, V5, V9 and V11

b Running E1 (Shell and tube heat exchanger) in counter flow:

Opening valves as VI, Võ, V7, V9 and VII

Closing valves as V2, V3, V4, V5, V8 and V10

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c Using E2 (Helical-coil heat exchanger) in parallel flow:

Opening valves as V3, V4, V5, V8 and V10

Closing valves as V1, V2, V6, V7, V9 and V11

d Using E2 (Helical-coil heat exchanger) in counter flow:

Opening valves as V3, V4, V5, V9 and VII

Closing valves as V1, V2, V6, V7, V8 and V10

- Changing the hot and cold water flow rate by adjusting the valves as mentioned above After adjustment, waiting for 2-3 minutes until the temperature sensors are stable, students start getting the experimental data

3.4 EXPERIMENTAL DATA

E1 (Shell and tube heat exchanger) in parallel flow:

Test FH FI2 TH T1 TB TH AT(Hot) |AT(Cold)

Tabulating according to the following form:

a Calculating the heat transfer and overall efficiency at several flow rate:

Where and c, are taken at the average temperature of inlet and outlet water

We calculate the heat transfer for each test:

Similar with cold water:

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Calculating the overall efficiency:

b Calculating the overall heat transfer coefficient:

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Where:

Firstly, we have to calculate :

Then we can calculate k:

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c Determining the Reynolds number:

Cross-section area of steel coil:

We need to calculate first:

Test Fil FR TH TR TB T14 T(cold)

Reynolds number calculating:

E1 (Shell and tube heat exchanger) in counter flow:

a Calculating the heat transfer and overall efficiency at several flow rate:

Where and c, are taken at the average temperature of inlet and outlet water

We calculate the heat transfer for each test:

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Similar with cold water:

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Calculating the overall efficiency:

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b Calculating the overall heat transfer coefficient:

Where:

Firstly, we have to calculate :

Then we can calculate k:

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c Determining the Reynolds number:

Cross-section area of steel coil:

We need to calculate first:

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Reynolds number calculating:

d Comment on results

Comment on overall heat transfer coefficient in two cases:

- In both cases, it seems that the heat transfer coefficient tends to increase when the amount of hot water is set and the amount of water is changed Increasing the amount of hot water also increases the heat transfer coefficient

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- Both parallel and counter-flow heat transfer coefficients are almost the same However, counter-flow seems to be more effective than parallel flow

Comment on Reynolds number in two cases:

- Parallel flow and counterflow are transitional flows Therefore, increasing the amount

of hot water increases the Re number and tends to turbulence

- However, there is no significant difference in the Reynolds numbers for all experiments

E2 (Helical-coil heat exchange) in parallel flow:

Test FH FR Tu TR TB TH | Tthot) | T(cold)