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Procedia Engineering 12 (2011) 141-148

2011 SREE Conference on Engineering Modelling and Simulation

The Modeling and Simulation of Marine Air-condition

Langtao Yana, Jingming Lib, Derong Zhangc,Chunjiang Liud,a*

acd Chongqing Engineering Research Center for Special Ship Digital Design and Manufacturing, Chongqing Jiaotong University,

Chongqing 400074, China bShanghai Maritime University, Shanghai 200135, China

Abstract

To solve the air-condition simulator operational problems in IMO crew training, this paper, taking "Yu Kun" ship as the study object, established the air-condition cooler and compartment temperature dynamic mathematical model. With the Matlab/Simulink real-time simulation tools, reasonable and appropriate algorithm simulation parameters, it achieved the real-time dynamic Simulation on Marine air-condition. This simulation not only provided a powerful guarantee for the ship Air-condition simulator design, but also provided an important basis for the marine air conditioning design.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, Environment and Engineering

Keywords: Marine air-conditioning; Modeling; Simulation

1. Introduction

Marine air-condition provides a suitable working and living environment for the crew and passengers, while offers an important guarantee for the normal operation of ship machinery. So, it's particularly important to hold the real-time dynamic operation of air-condition in time.

IMO, International Maritime Organization, demands the crew air-condition simulator practical operation training pre-service. As an important link of marine air-condition simulator, the modeling and simulation reveals realistic operating conditions, and provides a good simulation platform for the crew to master its running states timely and dynamics, while predict, diagnose the potential and the presence bug. It's not only a teaching tool for training the crew, but also an important basis for the design of marine air-conditions.

*Langtao Yan. Tel.: +086-023-62652621; fax: +086-023-62652495. E-mail address: yanlt023@126.com.

1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.05.023

2. Requirements for marine air -condition technology

Air-condition is mainly used to offer a comfortable working and living environment, meeting the crew and passengers' requirements. It is the comfort air-condition [1], generally used the central air-condition unit and different with the CARA, which some of the production process and the precision instruments used.

Marine Air-condition unit should make the indoor air conditions meet following requirements, under the fixed outdoor design parameters.

(1) Temperature

Air-condition compartment of the ship design criteria is: summer temperature is 24 ~ 28 °C; indoor and outdoor temperature difference does not exceed 6 ~ 10 °C.

(2) Humidity

In summer, desiccant cooling method is used in air-condition, indoor humidity is generally in 40% to 50%.

(3) Fresh degree

If just meet the respiration oxygen needs, the minimum fresh air supply is 2.4 m3 / h • person. However, to make carbon dioxide, smoke and other harmful gases in the air in the allowed level below, the fresh air on the need is achieved 30 ~ 50m3 /h • person.

(4) Air flow rate

The indoor air flow rate to 0.15 ~ 0.2 m/s is appropriate; the maximum does not exceed 0.35 m/s.

3. Mathematical Model

3.1. The mathematical model of air cooler

The air cooler has the following functions: to provide a surface for low-temperature chilled water and air flow heat transfer, to drop the temperature of the air flew through the air cooler. It's the copper tube aluminum fin air cooler. The heat transfer sketch of air cooler is shown in Figure 1.

tio m2 tH

Fig. 1 The heat transfer sketch of air cooler

In figure 1, supposing tli is the inlet temperature of low-temperature chilled water; tlo is the outlet temperature low-temperature chilled water; m2 is the flux of low-temperature chilled water; t hi is the inlet temperature of the air flowing into the cooler; t ho is the outlet temperature of air; m1 is the flux of the air. In the modeling process, in order to simplify it, the paper made the following assumptions according to the actual work of cooler.

(1) Instantly, cold and hot fluid has the same temperature at a cross section perpendicular to the flow direction. In another words, it treats the cooler with the lumped parameters, at the same time excluding the condenser shell heat. If there is a large chilled water flux, the error of this deal is not great.

(2) The inside and outside of the metal tub wall temperature is always similarly to equal. In fact, the condenser wall is thin and the heat capacity of the metal wall is small, while heat transfer coefficient 1 is

large. Therefore, when the temperature range is small, this assumption can meet the precision requirements.

(3) Dirt degree of condenser bundle is the same.

According to the air side heat transfer relationship of air-cooler: accumulation of heat changed per unit time in air side = the heat brought in by air per unit time - the heat transferred to the low temperature chilled water side per unit time. Then, this equation is got [2-4]:

^T = T^KCk (thl- tho) -1 ATm ] (1)

dr W1 R

In the formula, ATm is the average temperature of the cooler; W1 is the heat capacity of air side, W1 = Mhch + MbCb , where, Mk is the air quality of air-cooler; Mb is the quality of the air cooler material; ch is the hot water specific heat; Cb is the material specific heat.

R is the thermal resistance of the air cooler, R = 1/ KA , K is cooler total heat transfer coefficient, A is the cooler cooling area.

Similarly, according to the low-temperature chilled water side heat transfer relationship: accumulation of heat changed per unit time in the low-temperature chilled water side = the heat passed from air to chilled water per unit time - the heat taken away by the low temperature chilled water per unit time. So, this equation is show:

dto 1 .1

= — [- ATm - m2c (to - til)] (2)

dr W2 R

In the formula, W2 is the heat capacity of low temperature waterside, W2 = Mlcl + MbCb , where M { is the quality of the chilled water, c{ is the heat capacity of chilled water.

The average temperature difference ATm takes for logarithmic mean temperature difference:

A T — (th + tfi ) ~ (tho + tio ) (3)

m- t _ t ^V

ln hi io

t ho ~ tli

Type (1) (2) and (3) is the mathematical model of heat transfer for air coolers. W1 W2 in the type can be calculated in the specification of the air coolers.

The prandtl number, motion viscosity, density and thermal conductivity of working medium affect the heat transfer and resistance properties of the heat exchanger. Prandtl number and movement viscosity of water decrease with the increase of water temperature, and thermal conductivity increased with the water temperature becomes larger [2-4]. Thus, with the coolant water temperature, the heat transfer coefficient becomes larger, while the resistance is smaller. Thus, the heat exchanger calculations, in which the working fluid is chilled water, can't ignore the impact of water temperature. Usually, the parameters of water are taken as constant [5].

In the air-cooler, the process of heat transfer from the air flow to the chilled water, its thermal resistance include: the air side convection thermal resistance, the air side fouling resistance, thermal film thermal resistance, low-temperature chilled water side fouling resistance, chilled water side heat transfer resistance. Therefore, the overall heat transfer coefficient formula of the cooler is:

— = — + r + r2 + r3 + — (4)

k hh 123 h KJ

In the formula: K is the overall heat transfer coefficient of Cooler; hh is the heat transfer coefficient of Air-side; rx is the fouling resistance of Air-side; r2 is the thermal resistance of thermal film; r3 is the fouling resistance of low-temperature chilled water side; hl is the heat transfer coefficient of low-temperature chilled water side.

3.2. Mathematical model of compartment temperature

Compartment temperature is an important indicator of air-conditioned comfort. According to the conservation of energy, the energy into the room minuses the energy outflow from the room at per unit time, equals to the indoor storage energy change rate .Then, can get the following equation [6-9]:

Qn + Qex + Qsu - Qo = (VPa ) X Cp X dL (5)

In the formula: Qin is the internal heat source due to thermal cooling load including lighting, body heat and a variety of electrical equipment (such as computers, printers, etc.) cooling. The heat is nothing more than sensible heat and latent heat. The latent heat is calculated as instantaneous cooling load. The sensible heat is composed of the instantaneous and the delay cooling load; Qex is the heat incoming from outdoor to air-conditioned room, therefore, this part of the cooling load is caused by solar radiation and the heat transfer near the cabin or the corridor ;

Qex =E Qm (6)

In the formula: Qexi is the solar radiation heat absorbed by compartment wall and cooling load or cooling load caused by air heat transfer in the cabin area or corridor

Qexi= F xAx (Tw - Tr )n + F xMTy (7)

In the formula: F is the wall area: X is the transfer coefficient of the wall medium; Tw is the temperature close to the compartment or corridor; n is the correction factor for the temperature difference; ATy refers to solar radiation.

In the formula: F is the wall area: X is the transfer coefficient of the wall medium; Tw is the temperature close to the compartment or corridor; n is the correction factor for the temperature difference; ATy refers to solar radiation.

Qsu is the energy which brings by the air through the cooling:

Qsu = K X Vsu X (Tsu - Tr) (8)

In the formula: Vsu is the air supply; Tsu is the supply air temperature; K is the capacity factor of the supply air:

Qo = M X Cp X (Tr - Trt) (9)

In the formula: Tr is the room temperature; Trt is the return air temperature. 4. Simlink Block Diagram

4.1. Air cooler model block diagram

Adjust algebraic equations and differential equations from (1) to (4) so as to get the air conditioner module simulation model, including air cooler simulation model and air heater simulation model. Here is the simulation model of air cooler. The simulation model for air heater and air cooler is similar to each other, so just make the appropriate adjustments to change the corresponding parameters.

Input: t

Coefficient: WK W2, K , A ;

Output: tho ^ tlo .

Air cooler input and output parameters simplified diagram are shown in Figure 2. Simulink simulation model of air cooler module shown as in Figure 3.

Temperature of air inlet .

Air flow

Temperature of chilled water inlet Chilled water flow

„ Temperature of air outlet

^Temperature of chilled water outlet

Fig.2 Air cooler parameters

Fig. 3 Modular model of air-cooler

4.2. Air cooler model block diagram

Adjust cabin temperature all the algebraic equations and differential equations from (5) to (9) to get the simulation model.

Supplying air temperature

Input: Tsu - Vsu;

Coefficient: K Cp pa ; Output: Tr o

Supplying air flow

T ± r _^ Cabin temperature

Fig.4 Cabin Parameters

The input and output parameters Air conditioning compartment simplify the diagram shown as in Figure 4. The input and output parameters Air conditioning compartment simplify the diagram shown as in Figure 5.

Fig. 5 Modular model of Cabin temperature

5. Simulation results analysis

Simulation results as follows based on main parameters of mathematical model, Simlink block diagram and the "Yu Kun" air conditioning system above in Table one.

Tab. 1 Main parameter data for marine air conditioning system

Name of parameter Value Unit Name of parameter Value Unit

Fresh air flow of per person in individual cabin 25 m3/h Fresh air flow of per person in individual cabin 25 m3/h

Fresh air flow of per person in public cabin 15 m3/h Temperature of cooling water inlet 36 °C

Compressor refrigerating capacity 235 kw Temperature of cooling water outlet 41.9 °C

Heat transfer capacity of condenser 320 kw Condensing temperature 45 V

Heat transfer capacity of condenser of evaporator 470 kw Cooling water Consumption 47.2 m3/h

Chilled water flow 67.3 m3/h Flow of Chilled water circulating pump 70 m3/h

Pressure head of Chilled water circulating pump 20 m Design temperature of chilled water inlet 7 V

Design temperature of chilled water outlet 12 °C Heating steam pressure 4 kg

Figure 6 shows the temperature curve of the air-cooler chilled water and air out. Air inlet temperature is 34°C, chilled water inlet temperature is 16°C. The figure formed that air outlet temperature is about 24 °C, and chilled water outlet temperature is about 17 °C, basically consistent with the thermodynamic calculation. There are some fluctuations in the temperature, within the scope of allowable error.

Figure 7 is the temperature curve of cabin, the room selected is the Chief Office cabin. The parameters can get from the appendix, Chief Office compartments Specifications. The initial temperature is 32 °C. Supply air temperature is 23.8 °C. As can be seen from the graph, from 0 to 1500 seconds, temperature

drop is in a faster rate. Nearly after 2000 seconds, the supply air temperature is close to the room temperature, consistent with air-conditioning compartment situation.

In this simulation model, the supply air temperature Tsu is given, but the cabin temperature Tr is obtained from the simulation curve. Figure 7 shows when the supply air temperature is 32 °C, its cabin temperature Tr is 24.5°C from which the temperature difference between the air temperature and indoor temperature can be calculated as the formula AT = Tsu — Tr = 10°C (K) , which meet the technical requirements dT = 10K from the "Dalian Maritime University teaching practice Marian air conditioning,

33 |-,-,-,-,-,-,-,-,-,-

32 -31 \ 3D -1 29 - \

25 - \ 27 - \

26 - S

25 - \

24 - ---•-=

23-1-1-1-1-1-1-1-1-1-

D 5DD 1000 1500 2000 2500 3000 3500 4000 4500 5000

Fig. 6 Temperature curve of chilled water and air out Fig. 7 Temperature curve of cabin

air cooler

6. Conclusion

This paper makes a detailed introduction about the technical requirements and operating principle for the Marine air conditioning and has established mathematical model for cabin cooling in the summer, and then verified this model taking the example of "Yu Kun" Chief Officer compartment, proved that the model is reliable.

The modeling and simulation of Marine air conditioning system concern much ancillary equipments and great variety of knowledge. It not only contains the thermodynamics, kinetics, heat transfer, but also control technique, simulation technology, computer technology and so on. But due to the time constraints and limited knowledge, there still need many improvements for the Marine air conditioning modeling and simulation. As some simulation parameter data is hard to get, all the parameters base on experience, inevitably to be inaccurate. As a result, more precise parameters are in need to make the model work practically

refrigeration technical agreement "[10]

References

[1] Qian Fei, Shixun Lu, Shipping auxiliary, China Dalian, Dalian Maritime University Press, 2001

[2] W.M.Kays,L.London.Compact Heat Exchanges, NewYork:3nd.ed.MacGraco-Hill Book Company,1984.

[3] Shiming Yang, Wenquan Tao, Heat transfer, China BeiJing, Higher education press, 1998.

[4] Stephenson D G,Mitalas G P.Calculation of heat conduction transfer functions for multi-layer slabs.ASHRAE Transactions,1991,77(2):117-126.

[5] Jicheng Wu, The Precision Analysis in the Simplified Thermodynamic Calculation of the Plate-Heat-Exchanger, China Harbin, Journal of Harbin university of C.E & architecture 1999,32(2):50-53

[6] Xihai Wang, Dynamic analysis and Optimization design of shipping Air conditioning, China Dalian, Journal of Dalian Maritime University, 2004.

[7] Weihua Xue, The study of operating performance and energy consumption of frequency conversion control VRV air-conditioning system (Doctoral dissertation), China Shanghai, Tongji University, 2000.

[8] Houjian He, Study on Modeling and Optimizing of Water-system in the Heating Ventilating and Air-conditioning System (Master thesis), China Shenyang, Shenyang University of Technology, 2005.

[9] Guiming Chen, Mingzhao Zhang, Hongyu Qi, Application of the modeling and simulation, China Beijing, Science press,2001

[10] Shanghai ship design institute, Dalian Maritime University teaching practice Marian air conditioning, refrigeration technical agreement, China Shanghai, Shanghai ship design institute, 2005.

Author: Langtao Yan, Male, Han Nationality, born in 1979 at Chongqing, lecturers of the Chongqing Jiaotong University. Research areas: the Marine Automation and Control.

Address: Maritime College ,Chongqing Jiaotong University, Chongqing 400074, China. Email: yanlt023@126.com

Author: Jingming Li, Male, Han Nationality, born in 1951 at Fujian province, lecturers of the Shanghai Maritime University. Research areas: the Marine Automation and Control.

Address: Commercial Ship college , Shanghai Maritime University, Shanghai 200135,China. Email: ljming2007@gmail.com