EMS623 Heat Exchange and Waste Minimisation Assignment Sample

Introduction - EMS623 Heat Exchange and Waste Minimisation Assignment

Air conditioning systems experience significant heat transfer energy losses whenever buildup air is expelled out of buildings along with fresh cold air. To minimise energy waste and increase utilization, a heat recovery system is being installed. In this project, a heat exchanger is designed to transfer heat from the exiting air to the incoming air, with water as the circulating medium. This project aims to select and perform a thermodynamic analysis on the heat exchanger which has been transferred 10 kW of heat among the air streams of the air.

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Objectives

• To preheat fresh air, it is desired to transfer 10 kW of heat from the outgoing air.
• To design a heat exchanger using water as the existing liquid.

The methodology used in the analysis entails the determination of the complete coefficient of transfer of heat, the specified coefficient of transfer of heat on the waterside and that of airside, and the chosen dimensions of the heat exchanger (Alaqel et al. 2020). Some methods including the formula for the transfer of heat Q= m X Cp X Δ T and LOG MEAN TEMPERATURE DIFFERENCE (LMTD) method are used to calculate the required geometry for the system. A method of real design involves a calculation of the rate of the flow of water and the increase in temperature of the solution.

Methodology

Assumptions

1. For this design, assume a consistent water flow rate and an inlet temperature of 10°C, representing typical winter tap water conditions. The outlet temperature will be calculated based on the heat transfer rate and mass flow rate of water.
2. The pipes are insulated; ensuring zero heat conduction to the surroundings, so all heat transfer is directly from air to water.
3. We assume an airside heat transfer coefficient of 50 W/m²K for airflow over the finned surface and a waterside heat transfer coefficient of 500 W/m²K, based on turbulent water flow within the tubes (Jamil et al. 2020).

Heat Transfer Analysis

The heat transfer rate for the system is calculated using the basic heat transfer equation:

Q= m X Cp X (Perumal et al. 2022)

From this equation,

Heat transfer rate (Q) = 10KW = 10,000W

Specific heat capacity of water (Cp) = 4.18KJ/Kg°C

Inlet Temperature (Tin) = 10°C

Assumed mass flow rate (m) = 0.12 Kg/s

By using heat transfer equation:

Q= m X Cp X

Where, = Tout – Tin

Tout = Tin + (Q / m X Cp)

Substitute values

Tout = {10 + (10000 / (0.12 X 4180)}

From this calculation find, the value of Tout is 29.33°C.

Design Calculations

Surface area (A) of heat exchanger:

A = Q / (U X ΔTm) (Zheng et al. 2020)

The heat transfer rate is Q=10 kW

The heat transfer coefficient is U=45.45 W/m2K

The value of LOG MEAN TEMPERATURE DIFFERENCE (LMTD)of 15°C, the area of the heat exchange, A is calculated as:

From the above equation calculated the area as, A = 10000 / (45.15 X 15) = 14.67 m^2

The calculated area, A, is 14.67 m².

To reach this area a tube diameter = 0.02 m and length = 2 m, with the heat exchanger consisting of several tubes inside the heat exchanger.

Results

Design of Tube-in-Tube Heat Exchanger

The shell-and-tube heat exchanger design allows one fluid to flow through the inner tube, while the second fluid flows in the surrounding shell. This is because with a counter-flow, arrangement the temperature differential between the two fluids is at its highest and therefore, heat transfer is optimized (Mohammadi et al. 2020). The inner tube in this design contains cold-water circulation while the hot air circulation is through the outer annulus. The selected dimensions for the design are the inner tube diameter is 0.02 m and the length of the design is 2.5 m for the surface area of the heat exchanger. The power for the heat transfer rate is 10 kW, and the length of the tubes is 10 m for the 14.67 m^2 of heat flowing area.

Design of Shell-and-Tube Heat Exchanger

These types of heat exchangers are commonly used in industries due to the large surface area of heat exchange. This design concerns the continuous circulation of cold water through several tubes with hot air being permitted to pass through the tubes placed in a tubular casing. Extra fins provided outside the tubes also enhance the heat exchange rate of the fin and enhance the area. For this project, it is assumed that the shell diameter was 0.1m, with the tube diameter being 0.02m and a total length of 2m. Heating occurs through a sequence of several tubes within the shell having a total heat transfer area of 14.67m^2 (Yang et al. 2020). The fins on the airside surface area are extended to about 30 per cent thus, improving the coefficient of the transfer of the heat. The heat exchanger lie between the two types of fluids is better; second, it is easy to design them for high flow and temperature difference which is very useful in large industrial heat exchange processes such as HVAC systems. Fins also contribute to the enhancement of the heat exchanger making sure it can generate 10 kW of heat transfer as the required power.

Comparison

In heat transfer effectiveness and straightforward addition of new units, the shell and tube exchanger is superior to the tube-in-tube exchanger. While the arrangement of the tubes in parallel with one another, and forming what is known, as a tube-in-tube system is less complex than the concentric tube system, it does not allow for as efficient cooling when encountering large heat loads.

Design and Analysis

The shell and tube exchanger outperforms the tube-in-tube exchanger in heat transfer performance, flexibility and compactness. Even though the tube-in-tube system is easier to construct, it is not feasible when a large amount of heat has to be transferred (Fernandes and Krishanmurthy, 2022). The shell-and-tube exchanger produces better heat transfer characteristics, and the addition of fins, and is most appropriate to large-scale systems.

Figure 1: Heat exchanger

(Source: Design in SolidWorks)

This design shows the design of the Sheel and tube heat exchanger, a device which is used to flow heat between two different liquids without mixing them directly.

Figure 2: Wireframe of the model

(Source: Design in SolidWorks)

This is the wireframe view of the Sheel and tube design which is presented in SolidWorks software.

Figure 3: Sectional View of the model

(Source: Design in SolidWorks)

This image shows that the model is cutting from the top view and can see the other components inside the heat exchanger design.

Figure 4: Inlet and outlet

(Source: Design in SolidWorks)

This diagram is one of the most important components from this component the fluid is passing through.

Figure 5: Tube bundle

(Source: Design in SolidWorks)

This image shows A collection of parallel tubes that run the length of the shell which is designed in SolidWorks (Biçer et al. 2020).

Figure 6: Tube Housing

(Source: Design in SolidWorks)

These are the components of the tube bundle where all the tubes are merged a proper way inside this tube housing.

Conclusions

This project focuses on the heat recovery system, the heat exchanger type of tube-in-tube and shell-and-tube will be discussed. The aim was to take 10 kW of heat from hot air, which is rejected from the building, and transfer this heat to cold water that may initially be at 10°C. Comparing both designs, it was finally determined that the shell and tube heat exchanger was more efficient than the plate, because of the expanded heat transfer area, the fins added on the air side, and the capability of the passage of high flow rates. The shell-and-tube design effectively fulfils the heat transfer demand and generates an almost 14.67 m² heat transfer area with an estimated overall heat transfer coefficient of 45.45 W/m²K. The main advantages of the system which include modularity as well as the improvement in heat transfer make the present system suitable for large systems and the Main HVAC applications of this system.

Reference List

Journals

• Alaqel, S., El-Leathy, A., Al-Ansary, H., Djajadiwinata, E., Saleh, N., Danish, S., Saeed, R., Alswaiyd, A., Al-Suhaibani, Z., Jeter, S. and Al-Balawi, A., 2020. Experimental investigation of the performance of a shell-and-tube particle-to-air heat exchanger. Solar Energy, 204, pp.561-568.
• Almeshaal, M.A. and Choubani, K., 2023. Using the Log Mean Temperature Difference (LMTD) and ε-NTU Methods to Analyze Heat and Mass Transfer in Direct Contact Membrane Distillation. Membranes, 13(6), p.588.
• Biçer, N., Engin, T., Yaşar, H., Büyükkaya, E., Aydın, A. and Topuz, A., 2020. Design optimization of a shell-and-tube heat exchanger with novel three-zonal baffle by using CFD and taguchi method. International Journal of Thermal Sciences, 155, p.106417.
• Fernandes, E.J. and Krishanmurthy, S.H., 2022. Design and analysis of shell and tube heat exchanger. International Journal for Simulation and Multidisciplinary Design Optimization, 13, p.15.
• Jamil, M.A., Goraya, T.S., Shahzad, M.W. and Zubair, S.M., 2020. Exergoeconomic optimization of a shell-and-tube heat exchanger. Energy Conversion and Management, 226, p.113462.
• Mohammadi, M.H., Abbasi, H.R., Yavarinasab, A. and Pourrahmani, H., 2020. Thermal optimization of shell and tube heat exchanger using porous baffles. Applied Thermal Engineering, 170, p.115005.
• Perumal, S., Sundaresan, D., Sivanraju, R., Tesfie, N., Ramalingam, K. and Thanikodi, S., 2022. Heat transfer analysis in counter flow shell and tube heat exchanger using of design of experiments. Thermal science, 26(2 Part A), pp.843-848.
• Prasad, A.K. and Anand, K., 2020. Design Analysis of Shell Tube Type Heat Exchanger. Int. J. Eng. Res. Technol, 9(01).
• Yang, Z., Ma, Y., Zhang, N. and Smith, R., 2020. Design optimization of shell and tube heat exchangers sizing with heat transfer enhancement. Computers & Chemical Engineering, 137, p.106821.
• Zheng, D., Wang, J., Chen, Z., Baleta, J. and Sundén, B., 2020. Performance analysis of a plate heat exchanger using various nanofluids. International Journal of Heat and Mass Transfer, 158, p.119993.
• Zolfalizadeh, M., Zeinali Heris, S., Pourpasha, H., Mohammadpourfard, M. and Meyer, J.P., 2023. Experimental investigation of the effect of graphene/water nanofluid on the heat transfer of a shell‐and‐tube heat exchanger. International Journal of Energy Research, 2023(1), p.3477673.

Author Bio

Alex Taylor   5 Years | PHD

My name is Alex and I have acquired my PhD in Engineering from the University of Cambridge. I received A+ grades in all my semesters and always got appreciated for my assignments. I am also the author of several engineering research papers that have received quite good recognition. I am a expert writer who wants to guide students in writing excellent engineering assignments.