Coupling of solid oxide fuel cell exhaust with vapour absorption refrigeration system for refrigerated truck application: Modelling and experimental investigation.

Amakiri, Eridei Lucky (2021). Coupling of solid oxide fuel cell exhaust with vapour absorption refrigeration system for refrigerated truck application: Modelling and experimental investigation. University of Birmingham. Ph.D.

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Abstract

Refrigerated trucks for both chilled and frozen products; pharmaceutical and perishable foods, are conventionally fitted with a vapour compression refrigeration system that is powered by either the vehicle main engine or an auxiliary diesel engine on board. This process increases the fuel consumption rate, greenhouse gas emissions especially during idling, reduced engine performance and efficiency, and increased noise pollutions among others. Hence, attentions have shifted to using available waste heat to drive heat driven refrigeration systems.

Vapour absorption refrigeration system (VARS) is one heat driven technology that has been in existence for decades. It has been mainly used in commercial building and recently has been looked at for automotive applications. Researches have been conducted to couple the vehicle engine exhaust heat with VARS for refrigerated trucks or car air-conditioning purposes. This process has its demerits of the unavailability of enough heat during idling times, noise and increased emissions. This thesis looked at the feasibility of using environmental friendly high temperature fuel cell (solid oxide fuel cell) auxiliary power system that generates electricity and heat. The electricity can be used for auxiliary load or on board appliances while the heat generated is harnessed to drive the VARS.

There is temperature mismatch between the SOFC exhaust heat (600-900oC) and that required at the desorber of the VARS (120-240oC). Therefore, an internally finned tube-in-shell heat exchanger and heat transfer fluid (thermal oil) were employed to couple these two different units (fuel cell exhaust heat and VARS).
A detailed component and system level modelling of the VARS is carried out and the influence of design and the various operating conditions was investigated. A brassboard was used to experimentally investigate the feasibility of the technology. Experimental results from the test bench are used to validate the modelling results and prove the practical feasibility of the technology. Results showed that 1.84 kW of heat was recovered from a simulated SOFC stack of 5 kWe, at cathode exhaust flow rate of 0.03019 kg/s. The recovered amount of heat is able to cater to a 1 kW refrigeration load for a small refrigerated truck. It was also shown that a 1.84 kW of heat would still be recovered to meet the same 1 kW refrigeration load employing a 1 kWe SOFC at lower exhaust flow rates. Employing a 1 kW SOFC will increase the heat exchanger effectiveness and overall heat transfer coefficient by between 81.1 to 85 %, and 39.22 to 59.5 % respectively.

It was also shown that an evaporator temperature of 4oC was achieved when the recovered simulated SOFC exhaust heat was integrated experimentally with the VARS. This was due to loss of heat at the desorber of the VARS where only a maximum of 0.5 kW (out of 1.84 kW) of heat was transferred from the coupling fluid (thermal oil) to the ammonia-water solution. This results in less ammonia desorption from the solution thereby causing reduced cooling at the evaporator.
There has been no study reported in the public domain as regards experimental work of a small VARS refrigerated truck, hence the work reported here is a novelty in this regard. Another scientific contribution/novelty of this research is the experimental integration of fuel cell exhaust heat as energy source to drive VARS for refrigerated transport application which has never been done.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):