Heat Recovery in Air-Conditioning Using Shell-and-Tube Heat Exchanger Assignment Sample

1.0 Introduction

1.1 Overview of the Problem

The challenge for the air-conditioning plant in this office block would be to replace large volumes of stale air while controlling heating costs for incoming fresh air. 90 m³/min would represent loss as well as a sizeable opportunity for heat recovery on discharge. The concept is to employ a run-around heat exchanger system, where the heat extracted from the outgoing air will be transferred to incoming cold air, not only saving energy but also increasing the overall efficiency of the process.

1.2 Importance of Heat Recovery

It states that the sustainable building practices and energy conservation is the heat recovery system that significantly contributes to the lowering of energy consumption with correspondingly reduced green-house gas emissions. Thermal energy that otherwise wastes can be captured and used. A system that improves energy performance through increasing energy efficiency will reduce energy consumption. Installation of a heat exchanger onto your air-conditioning system is generally giving you cost savings right away but at the same time assists long-term sustainability goals. On top of these, regulations also provide for energy-efficient designs that often end in the necessity of heat recovery to be implanted for the proper compliance of modern building practices.

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1.3 Objectives

• To design and analyze a shell-and-tube heat exchanger that can reach a heat transfer rate of 10 kW using a run-around system of heat recovery.
• To model the heat exchanger in order to simulate how it could interact with outgoing and incoming air streams.
• To compare the performance of the heat exchanger designed with respect to other configurations, such as a counter-flow heat exchanger.
• To provide design improvement suggestions based on simulation outputs and identifying parameters that contribute to performance.

2.0 Methodology

In this methodology it provides the design and analysis of a shell-and-tube heat exchanger integrated in an air-conditioning system. In this section it presents the description of the system, assumptions, and approach to modeling in Simulink.

2.1 System Description

2.1.1 Overview of the Air-Conditioning System

In the office building the air-conditioning system is designed to remove the stale air inside and replace it with fresh air and keep the environment cool. In this instance, the system will emit 90 m³/min out of the building while drawing in the same volume of fresh air into the building. The problem is that, it must be able to heat incoming cold air with its cost. This would involve installing a run-around heat recovery system, which has been proposed (Apriandi et al.2023). The latter uses a shell-and-tube heat exchanger, one side of which collects the heat from the outlet air. The other side preheats the inlet air with water flowing through pipes, which are constituted by two finned tube heat exchangers. Total heat transfer between the outlet and inlet air is 10 kW. Heat dissipation into the connecting pipes is minimized with insulation, thus optimizing the efficiency of the system.

2.1.2 Description of the Run-Around Heat Recovery Approach

In the run-around heat recovery technique employs two individual heat exchangers in a loop of water. Stale air leaving the zone passes through the first heat exchanger where it transfers its thermal energy to circulating water. The warmed-up water is transferred to the second heat exchanger, where it warms up the fresh incoming air. The main advantage of this design is the separation of the air streams and the avoidance of cross-contamination, at the same time ensuring that there is smooth transfer of heat (Bassiouny et al.2021). This method also provides an opportunity for continuous operation, because the water can recirculate back and forth between the two exchangers, ensuring effective energy recovery throughout the day. Fins on the air side of the tubes also increase the heat transfer surface area, again improving system performance.

2.2 Assumptions Made

The design and analysis of the heat exchanger, several assumptions were made to simplify calculations and model behavior.

2.2.1 Flow Rates

It is assumed that the inlet airflow rate in the building remains constant at 90 m³/min, identical to the flow rate of the stale air being discharged. It is also presumed that the flow rate of water through the heat exchanger is such that it will achieve the desired heat transfer without any noticeable pressure drop (Münsch et al.2024). Such a value can be estimated to be approximately 1.5 kg/s, generally the typical operational parameter for systems of this nature.

2.2.2 Temperature Rise

It states that to assess the heat exchanger efficiency, a target temperature rise for water is established. Since the water being fed to the heat exchanger would most probably be about 10°C, the temperature rise through the heat exchanger could possibly be as low as around 0°C to 5°C. This could mean that water leaving the heat exchanger would be approximately about 15°C. Air entering is expected to be at about 0°C to 5°C and must be warmed up to a much more feasible temperature.

2.2.3 Heat Transfer Coefficients

The heat transfer coefficients have been considered highly important in determining the effectiveness of the heat exchangers. The values obtained from literature have been used for this work. The overall heat transfer coefficient U was considered to be around 1000 W/m²·K (Marzouk et al.2023). The factor hence considered both air-side and water-side heat transfer coefficients, looking at the fact that there is more than one fin present on the outside surface of the tube, thus enhancing the heat transfer process.

2.3 Designing of the Model

The Simulink model is developed to simulate the heat exchange process and analyze the system's performance.

2.3.1 Overview of the Model

The model consists of many blocks, connected together, which simulate to a limited extent the real physical behavior inside the heat exchanger. The concept design is aimed at simulating the real-world heat transfer between the outgoing air and incoming air by circulating water as closely as possible. The proposed model will be used to visualize the temperature change over time and calculate the total heat transfer received from the system.

2.3.2 Description of Blocks Used

The Simulink model includes several relevant blocks in simulating the heat exchange process. A Constant Block was applied to specify the inflow rate of air being 90 m³/min, where it specifies the first step of the energy transfer process. Subsequently, there's a Gain Block that is actually the computation for the heat transfer with the assistance of the formula Q=U⋅A⋅ΔTlm, as well as having the gain set to 1000 to denote the U as the overall heat transfer coefficient in the process. The Sum Block measures net heat transfer by subtracting losses, using inputs from the Gain Block and any heat loss. A Scope Block plots the temperature rise over time for both the air and water in the system (Patel et al.2023). An Integrator Block plots the temperature rise over time with respect to the heat transfer inputs, showing how the temperature of incoming air increases. Temperature values are also stored in a Data Store Memory block, so it can be used again within the model for complex calculations and comparisons.

2.3.3 Key Equations and Calculations

The main equation used in the model is the heat transfer equation: Q=U⋅A⋅ΔTlm, with Q the rate of heat transfer assumed to be 10 kW. U is the overall heat transfer coefficient assumed to be 1000 W/m²·K, A is the area of the heat exchanger, and ΔTlm is the log mean temperature difference between the outgoing and incoming air and water. With the assumption of constant mass flow rate of water going into the tank being 1.5 kg/s, change in temperature with time is calculated from the equation: ΔT = Q /m.cp with ΔT being the change in water's temperature and cp being the specific heat capacity of water as is approximately 4186 J/kg·K. With these equations implemented within the Simulink model, it is possible to detail the thermal performance of the system: the outcome may further give insight into the effectiveness of the design or approach in accomplishing the desired amount of heat recovery. This approach makes a robust foundation for the sophisticated analysis of the heat exchanger design, significantly contributing to energy efficiency in air-conditioning systems.

3.0 Results

3.1 Simulation Outcomes

The simulation conducted for the fixed-bed catalytic reactor and heat exchanger system yielded several critical outcomes, particularly regarding temperature changes, heat transfer calculations, and performance metrics.

3.1.1 Temperature Changes of Air

Figure 1: Temperature Changes of Air

In this model provides the overall fluctuation in the temperature of the incoming air and the water that is circulated within the heat exchanger. It started with a relatively low temperature, largely dependent upon outdoor conditions at that particular time. As it moved through the heat exchanger, it gained significant temperature as it absorbed heat being transferred from the outgoing warm air. Contrary to the ambient air, the water was gradually increasing its temperature. This gradual increase was directly proportional to the amount of heat exchanged. From the results acquired, it indicated that incoming air temperatures surged from around 15°C to 25°C in a very short period (Abubaker et al.2020). That shows that the heat exchanger does indeed preheat fresh air, before it enters the building.

3.1.2 Heat Transfer Calculations

Figure 2: Heat Transfer Calculations

Heat transfer calculations confirmed that the model is correct and the assumptions made in the overall heat transfer coefficient. Using the formula Q = U⋅A⋅ΔTlmQ = U, the system received the desired amount of heat transfer that was calculated to be 10 kW. The ΔTlm was calculated using the inlet and outlet temperatures of air and water to prove that the design parameters chosen ensured a favorable heat transfer process. Other information were also calculated, which exhibit the requirement for an appropriate area of the heat exchanger. It is estimated to be around 15 m² that is large enough to achieve the required heat transfer amount. In addition, with an overall heat transfer coefficient of 1000 W/m²·K will leave a solid basis for maintaining excellent thermal performance in the system (Qian et al.2021). These calculations validate the design effectiveness concerning the desired heat recovery, which in turn contributes towards the efficiency of the air-conditioning system at the end.

3.2 Design Comparisons

Figure 3: Designing in Simulink Platform

Comparison of various design layouts in reactor configuration regarding the heat exchanger will give a clear insight into performance and efficiency.

3.2.1 Counter Flow vs Shell-and-Tube Heat Exchanger

Figure 4: Air Flow rate and Heat transfer calculation

A comparison was drawn in the design of a counter flow versus a shell-and-tube heat exchanger design. The counter flow heat exchanger typically has a larger temperature difference due to counter streams of flow for hot and cold fluids, which would produce the steepest temperature gradient in the heat exchanger. It is more suited for times when space has to be minimized though high efficiency is required. On the other hand, the shell-and-tube heat exchanger design can be flexible in both detail and operation with allowance for change in velocity and fluid properties. Even though a shell-and-tube design might have slightly lower overall heat transfer coefficients than corresponding counter flow designs, it will often pay back through increased robustness and ease of maintenance (Akindele et al.2021). At the end, the decision among competing designs will be required based on the conditions of an application such as floor space, required effectiveness, and operational flexibility. Thus, the simulation results suggest that the final selection would be between both configurations depending on maintenance capabilities and operational demands.

3.2.2 Discussion of Dimensions and Performance

Figure 5: Discussion of Dimensions and Performance

Dimensions of the heat exchangers were optimized to ensure effectiveness in heat transfer while the manageable pressure drops are established across the system. The calculated area of the heat exchanger with dimensions for the tubes and shell ensured an efficient operation while allowing easy accessibility for easy maintenance. From the performance analysis, the shell-and-tube heat exchanger performed well based on the established operation conditions. The fins on the air side of the tubes also helped to increase the transfer of heat by maximizing exposure area to make it easier to have heat exchange, therefore allowing for better overall efficiency (Zhang et al.2024). Maximum reactor dimensions were concerned with the inhibition of pressure drop in relation to a maximum surface area exposed to catalyst, while flows can cut down on rates if too much pressure drop occurs, therefore wasting energy. The final design was quite holistic and indicated a very good response toward both the thermal and operational requirements.

3.3 Analysis of Less Successful Designs

The optimized design provided positive results, it is essential to consider less successful designs to understand the factors influencing performance.

3.3.1 Factors Influencing Performance

Figure 6: Factors Influencing Performance

In the simulation phase, alternative designs were tested for suboptimal performance mainly due to insufficient surface area in heat exchangers and excessive pressure drops so that energy consumption was gained instead of efficiency. The selected material further added some implications on thermal conductivity, whereas the orientation of the heat exchanger added up to uneven flow patterns and some surplus heat was distributed differently. Such results underpin the importance of appropriate design considerations to ensure improved thermal performance and efficiency (Zhang et al.2024). The results of a simulation validate the chosen design. The results regarding good thermal performance thus create a basis for future refinements in heat exchanger and reactor design in the chemical industry.

4.0 Conclusions

4.1 Summary of Findings

A better thermal performance, with substantial heat recovery and energy consumption, was shown by the design and analysis of the catalytic reactor for oxidation of propylene in a fixed bed. Simulation validation of the chosen configurations confirmed that a shell-and-tube heat exchanger showed significant advantages.

4.2 Suggestions for Design Refinements

The later designs may well incorporate greater surface area in heat exchangers, maximizing heat transfer. Other improvements may be made by exploring other materials with superior thermal properties.

4.3 Implications for Future Work

In this research it provides information that this work confirms the need to consider iterative design for chemical engineering applications. Further work might include further improvements through the use of even more sophisticated modeling techniques and alternative reactor configurations to possibly increase efficiency and minimize by-product formation toward more sustainable industrial processes.

Reference List

Journals

Apriandi, N., Herlambang, Y.D., Alfauzi, A.S. and Lee, S.C., 2023. Shell and Tube Heat Exchanger Design: Utilization of Wasted Energy in Air Conditioning Systems. Eksergi: Jurnal Teknik Energi, 19(2), pp.39-44.

El-Shafie, M., Bassiouny, M.K., Kambara, S., El-Behery, S.M. and Hussien, A.A., 2021. Design of a heat recovery unit using exhaust gases for energy savings in an absorption air conditioning unit. Applied Thermal Engineering, 194, p.117031.

Bari, M.A., Münsch, M., Schöneberger, B., Schlagbauer, B., Tiu, A.A. and Wierschem, A., 2024. Heat recovery optimization of a shell and tube bundle heat exchanger with continuous helical baffles for air ventilation systems. International Journal of Air-Conditioning and Refrigeration, 32(1), p.2.

Marzouk, S.A., Abou Al-Sood, M.M., El-Said, E.M., Younes, M.M. and El-Fakharany, M.K., 2023. A comprehensive review of methods of heat transfer enhancement in shell and tube heat exchangers. Journal of Thermal Analysis and Calorimetry, 148(15), pp.7539-7578.

Patel, A., 2023. Performance analysis of helical tube heat exchanger. TIJER-International Research Journal (www. tijer. org), ISSN, pp.2349-9249.

Abubaker, A.M., Najjar, Y.S. and Ahmad, A.D., 2020. A uniquely finned tube heat exchanger design of a condenser for heavy-duty air conditioning systems. International Journal of Air-Conditioning and Refrigeration, 28(01), p.2050004.

Qian, X., Lee, S.W. and Yang, Y., 2021. Heat transfer coefficient estimation and performance evaluation of shell and tube heat exchanger using flue gas. Processes, 9(6), p.939.

Oni, T.O., Ojo, A.A., Uguru-Okorie, D.C. and Akindele, D.O., 2021. Thermal Analysis of the Effects of Multifaceted Conditions on Performance of Shell-and-Tube Heat Exchanger. European Journal of Engineering and Technology Research, 6(1), pp.69-75.

He, Z., Zhang, Q., Wei, Z., Liao, X., Wu, X., Zhang, J. and Tan, Y., 2024. Modeling Method for Overheated Zone and Two-Phase Zone of Dry Shell-and-Tube Evaporator in Ship Air Conditioning. Processes, 12(2), p.379.

Bianco, N., Fragnito, A., Iasiello, M., Mauro, G.M. and Mongibello, L., 2022. Multi-objective optimization of a phase change material-based shell-and-tube heat exchanger for cold thermal energy storage: Experiments and numerical modeling. Applied Thermal Engineering, 215, p.119047.

Nanditta, R.V., Gowtham, R., Udayakumar, P. and Manikandaraja, G., 2021, October. Experimental investigation of performance of shell and coil heat exchanger in waste heat recovery systems in CI engine. In Journal of Physics: Conference Series (Vol. 2054, No. 1, p. 012060). IOP Publishing.

Lamrani, B., El Marbet, S., Rehman, T.U. and Kousksou, T., 2024. Comprehensive analysis of waste heat recovery and thermal energy storage integration in air conditioning systems. Energy Conversion and Management: X, p.100708.