A detailed energy analysis of a novel evaporator with latent thermal energy storage ability

Abstract

The direct integration of phase change materials (PCM) into refrigeration and air conditioning systems through compact modules is an identified literature gap. In response to the literature gap, this paper provides a detailed energy analysis of a novel compact thermal energy storage module, that allows its direct integration into a refrigeration system as the evaporator. The study addresses key aspects of thermal energy storage (TES) and heat transfer mechanism that complement the previous analyses of the novel concept. Here the total energy stored in the module (including in all auxiliary parts), the charging/discharging power, and the behaviour of the module when used as a TES module and as a heat exchanger (HEX) are assessed. The results demonstrate the feasibility of the module to work as a TES and as a HEX. When working as a TES, complete charging and discharging was achieved, and 54% of the total energy was stored in the PCM although the PCM only accounts for around 14% of the total mass. Moreover, the highest charging/discharging power was obtained within the temperature range where most of the phase change occurred. When the module works as a HEX, it initially charges/discharges partially until a thermal equilibrium is achieved and the level of charge responds to the variation in the energy supply and demand.

Experimental Assessment of the Influence of the Design on the Performance of Novel Evaporators with Latent Energy Storage Ability

“…where the sub-index i refers to each of the volume elements, n = 9 is the total number of volume elements considered (equal to the number of PCM temperature sensors), m PCM,i is the mass of PCM, m HTF,i is the mass of HTF, and m Al,i is the mass of aluminium in volume element i, a sub-index t refers to the time instant, with t ch being the time taken to complete the charging process. The enthalpy or the specific heat capacity, the measured temperature and the mass of each material were incorporated into the finite element method detailed in [15,28] to obtain the energy level in the module. Thereafter, basic equations of thermodynamics {Equations (3)-( 9)} on heat transfer and energy balance adapted from [29] were used to complete the evaluation.…”

“…To obtain the PCM enthalpy and specific heat capacity over a wider range of temperature, experiments were carried out using DSC 3+ Toledo equipment with 0.1 K precision for temperature and 3 J•s −1 for enthalpy. The results obtained from the DSC measurements were reported in [25] and used to generate the PCM enthalpy curve ℎ (in kJ•kg −1 ) as a function of its temperature 𝑇 (in °C), as shown in Equation (1) [15]. For the comparison of the three modules, experiments were performed for three operating modes, i.e., charging mode, discharging mode, and three-fluids HEX mode.…”

“…The results showed that a homogenous charging of the PCM was achieved at a lower compressor power, whereas charging at a higher compressor power led to a pronounced stratification effect and compressor shutdown for security reasons before the PCM was completely charged. Another study consisted of a detailed energy analysis highlighting the energy contribution in each material and the performance of the whole component in three operating modes and different boundary conditions [15]. The results showed that the highest charging/discharging power was around the PCM phase change temperature and, although the sensible material accounted for 87% of the total weight, more than 54% of the energy was stored in the PCM, due to its high energy density.…”

“…From the aforementioned literature review, the aspects covered in previous studies include the determination of optimal operating conditions for charging and discharging processes [14], the possible operating modes and energy contribution of each material in the module [15], the testing of the module at demo scale in a heat pump that works with a sorption system in a cascade configuration [16], the determination of the optimal size of the novel module [18], the determination of stable operation ranges [20], and the performance analysis of a system coupled with the novel concept in comparison with conventional batteries [17]. One critical aspect not addressed in previous studies is the impact of the design/configuration of the modules on their performance, which is covered in this paper.…”

Standardised methods for the determination of key performance indicators for thermal energy storage heat exchangers

“…In numerical studies reporting internal energy as a function of time is commonly done although most studies report latent stored internal energy (e.g., [71,99,104,130]) or total liquid fraction (e.g., [65, 66, 68, 70, 71, 75, 77, 93, 99, 102, 104, 106, 109, 111, 113, 115, 120-122, 124-128, 130-132, 134, 136]) instead of total stored energy (e.g., [75,111,115,134,137,138]). In experimental studies, the total liquid fraction is sometimes reported (e.g., [67,87,101]) however local temperature measurements are far more commonly reported (e.g., [63,64,69,72,76,83,[87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][105][106][107][108][109][110][111][112][113]…”