Flow and Heat Transfer Simulations for the Design of the Helsinki Vuosaari Harbour Ice Control System

Cold Regions Science and Technology 55 (2009) 304–310

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Cold Regions Science and Technology

journal homepage: www.elsevier.com/locate/coldregions

Flow and heat transfer simulations for the design of the Helsinki Vuosaari harbour ice control system

Huachen Pan a,⁎, Esa Eranti b,1 a Institute of Mechatronic Engineering, Hangzhou Dianzi University, 310013 China b Eranti Engineering Oy, Harjuviita 6 A, FIN-02110 Espoo Finland article info abstract

Article history: The accelerated growth of brash ice is a problem that the port operator has to deal with in busy cold region Received 22 May 2008 harbour basins. Flow and heat transfer simulations have to be used to investigate the ice control design options Accepted 2 September 2008 for the new Helsinki Vuosaari harbour. For that purpose, a flow and heat transfer solver has been modified to combine 3 types of empirical ice-melting models, i.e. the smooth ice model, the slightly rough ice model and Keywords: the rough ice model, as the heat transfer boundary conditions. A simple bubbler model has also been developed Ice control into the flow solver to simulate the complicated bubble-driven water flow in the harbour basin. Bubbler Port The ice control problem for the Vuosaari harbour has two parts. One is the supply of warm water across a CFD narrow basin. A suction pump arrangement has been studied as an alternative to crossing the basin with a pipe. The thermal energy balance and the ice melting in the basin have been estimated numerically. The numerical investigations show that the heat-supply efficiency can be of the order of 95% if the suction is 5 m3/s while the warm water supply flow is 4 m3/s. The principal problem is how to combine the warm water supply and bubbler devices to melt ice effectively in the main harbour basin. Five design options with different warm water supply locations and bubbler arrangements have been studied using numerical simulations. A solution that provides fairly even ice-melting patterns for the berths has been found. More than 70% of the thermal input gets used for ice melting in the basin according to the simulation. The paper illustrates, how flow and heat transfer simulations can be used for the design of ice control systems. It shows that the use of bubbler lines may greatly improve the efficiency of warm water input in ice control. © 2008 Elsevier B.V. All rights reserved.

1. Introduction 3) Costs to ship operators from icebreaking tug assistance in the harbour area; The Port of Helsinki is currently constructing a new harbour to 4) Repair costs to ship owners and to the port when excessive force is Vuosaari (see Fig. 1), a location in the Eastern suburb of Helsinki. used in harbour manoeuvres; Accelerated growth of brash ice is a problem that the port operator has to 5) Costs to the port in icebreaking and overtime; deal with especially in the busy main harbour basin (see Fig. 2). The traffic 6) Costs of extreme measures like lifting of ice from the harbour basin pushes brash ice to the back of the harbour basin. Large accumulations of with cranes or breaking the ice collar attached to the pier wall with brash ice and the consolidated ice collar that tends to attach to the pier pneumatic tools in harsh winter conditions. wall makes access to the berth difficult and time consuming even with the help of a harbour icebreaker (Eranti and Lee, 1986). Many Finnish harbours take advantage of thermal effluents in The economical consequences of heavy harbour ice conditions dealing with ice problems. In some cases thermal energy is con- accumulate mainly during severe winters. They come from several centrated to the berth side or turning area by the help of surface sources like: current developers or air bubbling (see Fig. 3). While the amount of waste heat is typically large, of the order of 100 MW, the efficiency 1) Costs to the industry when freights and deliveries are delayed; ratio (amount of thermal power consumed for ice melting at the 2) Costs to ship operators in fuel costs, overtime and other expenses when target area as a fraction of thermal input) is usually low. Most of the schedules are kept with special measures and berthing windows are thermal energy available for melting ice in the harbour basin drifts not missed; away. In this case only 11–16 MW of external thermal energy is ⁎ Corresponding author. Tel.: +86 571 8152 6519; fax: +86 571 8687 8604. available for ice melting. This energy comes from a local power plant E-mail addresses: [email protected] (H. Pan), [email protected].fi (E. Eranti). in the form of water slightly above freezing point. No realistic way of 1 Tel.: +358 9 455 7500; fax: +358 9 455 7500. attracting sufficient amounts of thermal energy into the main

Fig. 1. Aerial view of the Vuosaari harbour with the main harbour basin in the middle. harbour basin from the surrounding sea area has been found as difference between mean air temperature of the day and 0 °C, either the water temperature even near bottom is just marginally above positive or negative) between the highest point in the autumn and freezing point. the lowest point next spring on the cumulative degree–day time Thus the study focused on 1) how to get the external thermal curve for one freezing season. energy to the harbour basin and 2) how to deliver and focus it for ice The available external thermal energy is not sufficient to keep melting in the most cost efficient manner in the harbour basin. The the harbour basin open through cold winter periods. However, it first task studied the option of using a suction pump to get the thermal has the potential to keep the brash ice layer thin and loose espe- effluents from the discharge point across a channel to a pipe crossing cially at the berth line. No significant difficulties in harbour opera- the harbour field. The alternative to this option was to construct a tions are expected in such conditions even in the harshest winter gravity flow arrangement at the discharge point and to cross the conditions. channel with a pipe. The second task studied efficiency of warm water Several alternatives existed in ice-melting solutions for the new inflow options to the main harbour basin and alternative bubbler line Vuosaari harbour in Helsinki. Those alternatives were involved with arrangements. locations and flow rates of the warm water piping and bubblers. As part Historically the average freezing index in Vuosaari is about 600 of the pre-construction engineering investigation, CFD method and (°C× days). The extreme value (once in 50 years) is about 1500 empirical ice-melting heat transfer models have been used to simulate (°C×days). Freezing index is the number of degree–days (the the flow and heat transfer of the water in and around the harbour.

Fig. 2. Brash ice accumulation at the Helsinki Southern harbour basin in 2003. 306 H. Pan, E. Eranti / Cold Regions Science and Technology 55 (2009) 304–310

Fig. 3. Thermal efﬂuents directed along the berth line with a surface current generator at the Tornio Röyttä harbour.

The objective is to ﬁnd the effective ice-melting solution with low where x, y and z are Cartesian co-ordinates; ρ is density; u, v and w construction cost. are velocity components. p is pressure; τ is shear stress; and g is

CFD is a relatively mature technology nowadays for most ordinary gravity acceleration; cp is the specific heat, T temperature, μt the flow and heat transfer problems. However for ice-melting problems turbulent viscosity and q̇the heat energy generation per unit volume. and bubbler flow in the water, extra models must be built in the Ф is the viscous dissipation function. Γ is expressed as computer program. C ¼ k=c þ μ =Pr In this study, we implement empirical ice-water heat transfer models p t into CFD code and use a practical approach to simulate the bubbler where, k is heat conductivity and Pr is the turbulent Prandtl number. flows. With these measures, we are able to simulate the ice-melting The above mentioned partial different equations can be solved by problems with warm water supply into the harbour basin and with a SIMPLE scheme originally proposed by Patankar (1980),with bubbler system. momentum interpolations for co-located grid by Rhie and Chow (1983) and improved for complicated geometries using multi-block, 2. CFD method body-fitted grid by Pan (2000). To obtain turbulent viscosity, a k–ε turbulence model is used for The flow solver is basically a Navier–Stokes solver (Pan, 2000) core flow regions. An algebraic turbulence model is used for near wall suitable for most flow and heat transfer applications. Modifications region. When the first-layer grid is coarse, the wall function method is have been added to make it suitable for ice-melting problems. used to treat the near wall turbulence. Here we have continuity equation 3. Heat transfer models @ @ @ ðÞþρ ðÞþρ ðÞ¼ρ ð1Þ @ u @ v @ w 0 x y z The processes and rate of brash ice formation resulting of repeated ice breaking and brash ice melting caused by warm water current have momentum equations been studied extensively over the years in the Saimaa Channel (Nyman and Eranti, 2005). @ @ @ @p @ @ ÀÁ ðÞþρuu ðÞþρvu ðÞ¼ρwu − þ ðÞþτxx τyx Heat loss and the corresponding ice formation from repeatedly @x @y @z @x @x @y fi @ broken brash ice layer are mainly a combination of 1) freezing of the ne þ ðÞþτ ρg ð2Þ crushed ice, slush and water mixture, 2) freezing of glazed ice block @z zx x surfaces, 3) cooling of the turned ice block and freezing at the block @ @ @ @p @ ÀÁ @ ÀÁ surface as it turns again and 4) freezing of wetted snow. The following ðÞþρuv ðÞþρvv ðÞ¼ρwv − þ τ þ τ @x @y @z @y @x xy @y yy approximation (Nyman and Eranti, 2005) has been developed for ÀÁ @ estimating heat loss q (W/m2) in Saimaa Channel with a brash ice layer þ τzy þ ρgy ð3Þ @z thickness of 1–2 m and average winter wind velocity of 3–4m/s: @ @ @ @p @ @ ÀÁ : : ðÞρuw þ ðÞρvw þ ðÞρww ¼ − þ ðÞτxz þ τyz ¼ 0 9 0 3 ð6Þ @x @y @z @z @x @y q 12Ta n @ þ ðÞþτzz ρgz ð4Þ @z where Ta is the average air temperature below 0 °C and n is the breaking frequency (times/day). and heat transfer equation The formation of new ice comes readily from the heat loss and breaking width. It can be seen that heat loss in a frequently broken (i.e. @ @ @ Q ðÞþρuT ðÞþρvT ðÞρwT ð5Þ several times a day) brash ice layer approaches that from open water @x @y @z at freezing point. The rate of brash ice formation decreases moderately @ @ @ @ @ @ ÀÁ ¼ C T þ C T þ C T þ μ Φ þ = as a function of brash ice layer thickness. It is larger than previously t q cp @x @x @y @y @z @z thought (Eranti and Lee, 1986). H. Pan, E. Eranti / Cold Regions Science and Technology 55 (2009) 304–310 307

Table 1 Summary of the simulation cases in task 1

Cases Sea current, Inflow rate, Outflow Outflow Heat supply m/s m3/s rate, m3/s temperature, °C efficiency, % 1 0 4 5 0.7653 95.66 2 0.05 4 5 0.7577 94.71 3 0 4 4 0.8615 86.15 4 0 4 6 0.6471 97.06

3.3. Rough ice model

¼ 1:5 ð9Þ q2 k1ATwVw

where coefﬁcients

k1 ¼ 4

A ¼ 4800:

The ice melting equation (Eq. (9)) is a simplification of the Saimaa Channel brash ice-melting model (Nyman and Eranti, 2005). One should note that melting rate for brash ice is significantly larger than for level ice. The cap of 200 W/m2 corresponds to heat loss from an fl Fig. 4. Narrow basin (located at left side in Fig. 1) and ow conditions for task 1. open water surface at −10 °C.

3.4. Bubbler flow model The melting of the brash ice layer under the influence of a warm current depends on current velocity, water temperature and rough- The bubblers are mechanical devices under the sea to produce air ness of the underside of the brash ice layer. The following ice-melting bubbles. When the air bubbles move up, they induce the water model has been used: moving up together, thus forming an upward flow washing and 2 Assuming that heat flux with the cap value of 200 W/m is melting the ice above. The bubbler flow is difficult to calculate due to sufficient to melt the ice away and remains almost constant for water– the two-phase nature. air interface in a typical winter in Finland, the heat flux in unit surface A full investigation into the two-phase flow phenomenon is out of area to melt ice or prevent ice formation can be expressed as question in this engineering simulation project. To have a simple model to closely model the flow driven by bubbles, we simply create a ¼ ðÞþ ; ð7Þ q min q1 q2 200 slightly lower density region just between bubblers and water surfaces to produce a buoyant force. By adjusting the density level we are able to where q1 is the heat flux due to heat conductivity

kT q ¼ w 1 d where Tw is the temperature in Celsius at a distance d below the ice surface. In this model the water heat conductivity is set as k ¼ 0:5 q2 is the convective heat ﬂux which are modelled differently according to the ice roughness levels. Here we classify the ice roughness into 3 levels: smooth, slightly rough and rough.

3.1. Smooth ice model

¼ 0:8 ð8Þ q2 cwiTwVw where cwi ¼ 1000 is the ice convective heat transfer coefﬁcient, Vw is water speed at distance d below the ice respectively.

3.2. Slightly rough ice model

Everything is the same as in the smooth ice model (Eq. (8)) except Fig. 5. Velocity vectors (m/s) of water ﬂow from a warm water channel into the narrow ¼ cw 2000 basin. 308 H. Pan, E. Eranti / Cold Regions Science and Technology 55 (2009) 304–310

smallnarrowbasinontheleft.Ontheleftsideofthenarrowbasin, there is a power plant warm water exit. To supply the warm water into the harbour main basin without building an underwater pipeline across the narrow basin, and without losing too much heat energy is the ﬁrst engineering problem to be solved. We call this as task 1. The warm water will be pumped away from an inlet on the right side of the narrow basin and supplied to the main harbour basin through a pipeline. Task 2 is to choose the location of the warm water exit in the main harbour basin and how to arrange the bubbler system so that the optimal ice-melting solution can be achieved.

4.1. Task 1

The first task is to study a narrow harbour basin shown in Fig. 4. The width of the basin is about 45 m in the narrow part and about 75 m in the wider part. The depth is 7 m. As indicated in the figure, a warm water flow with 1 °C is discharged into the basin. The water is pumped away from the basin through a round exit hole on the opposite pier wall. The diameter of the exit hole is 2 m and the centre of the exit hole is 3 m below the surface. In task 1 the smooth ice model is used. In the model the distance d is the distance of the first computational cell centre below the surface. fl 2 Fig. 6. Water surface heat ux (W/m ) in the basin. Blue colour indicates the area where Its value is 0.22 m. the ice is melted. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) The computational grid has 32 cells across the basin, 136 cells along the basin and sea and 16 cells in vertical direction. For flow solver a 0.05-meter surface roughness is given in all surfaces. All solid surfaces are assumed to be thermally insulated, except the ice create buoyant jet flows with velocity profiles close to data given in surface. The temperature at the sea boundaries is set to 0°. literatures (Carey, 1983; Ashton, 1978 and Tuthill and Stockstill, 2005). There are four simulation cases in task 1, which are shown in Table 1. Fig. 5 shows velocity vectors of the flow at about 2 m below 4. Description of the simulation tasks the water surface for case 2. Warm water of 1 °C flows into the channel with flow rate of 4 m3/s. Water is pumped out from the channel at flow There are two engineering problems to be solved for the harbour rate of 5 m3/s. Sea current of 5 cm/s is imposed outside of the channel designers. to study the current effect on the heat transfer inside the channel. If we look at the birds-eye view of the Vuosaari harbour in Fig. 1, Fig. 6 shows the heat energy loss (W/m2) from water to ice or to air we can see that there are a main harbour basin on the right and a (dark blue region) at air temperature of −10 °C. Total heat loss is about

Fig. 7. Main harbour basin (located at the right side of Fig. 1) and the inﬂow options for task 2. H. Pan, E. Eranti / Cold Regions Science and Technology 55 (2009) 304–310 309

Table 2 Summary of the conditions and results for task 2

Cases North–South bubbler Inflow option (Fig. 7) Discharge flow rate, Discharge temperature, Sea outflow temperature, Sea outflow rate, length, m m3/s °C °C m3/s 1. End discharge 400 1 5 0.8 0.002463 505 Rough ice model 2. 90-degree discharge 400 2 4 1 0.002621 504 Rough ice model 3. Long bubblers 750 2 4 1 0.001577 504 Rough ice model 4. 45-degree discharge 400 3 4 1 0.002400 504 Rough ice model 5. 45-degree discharge 400 3 4 1 0.003462 504 Slightly rough ice model

5% in which 2% is lost in the area shown in Fig. 5. The rest is lost to ice the hole is 1.3 m from the surface and 10 m from North pier wall. The melting in other areas or transported away by sea current. Besides, the discharge hole of options 2 and 3 has a diameter of 2 m and the centre small warm water exit channel itself contributes also about 1% of heat of the hole is located 1.5 m below the surface and 400 m from North energy loss. When pump-out flow is reduced to 4 m3/s, the total heat pier wall. loss is increased threefold. That is caused by heavy heat loss to the In task 2 the rough ice model and the slightly rough ice model are open sea with no net inflow from the sea. However when pump-out used. In the model the distance d is about 1 m below the ice for both flow is increased to 6 m3/s, the total heat loss is reduced only smooth and rough ice models. marginally. The computational grid has 48 cells across the harbour basin (East– West), 80 cells along the harbour basin (North–South) and 24 cells in 4.2. Task 2 vertical direction. For the flow solver a 0.05-meter surface roughness is given for sea bottom and ice surfaces. The roughness at the harbour The main harbour basin is shown in Fig. 7. The length of the basin is pier wall is 0.005 m. All solid surfaces are assumed to be thermally 750 m and the width is 250 m. All bubblers are 0.5 m away from the insulated, except the ice surface. pier wall. On the North pier wall the 249-meter bubbler system has a There are five simulation cases in task 2. Table 2 summarizes the 5 stronger nominal air flow rate of 0.37 m3/s m. The East/West pier walls cases and their key features. Case 3 has long bubblers but without are equipped bubbler systems with weaker nominal air flow rate of warm water discharge. Due to the limited space it is difficult to show 0.26 m3/s m. The basin depth is 12.5 m. The bubbler system is all results in figure. The results of case 4 are given because it gives submerged at 11 m deep, or 1.5 m above the bottom. As indicated in balanced ice melting with an efficiency ratio of 70%. The dark blue area the figure, a sea current of 0.04 m/s is assumed. The sea inflow in Fig. 8 indicates that ice melting is most efficient at the end of the temperature is 0 °C. harbour basin and along the berths. The flow lines shown in Fig. 9 Three options of warm water discharge are indicated in Fig. 7. The shows the complicated flow pattern caused mainly by the bubblers. discharge hole for option 1 has a diameter of 1.4 m and the centre of Warm water is circulated many times in the harbour basin before it flows out to the sea.

Fig. 8. Heat energy loss (W/m2) in the main harbour basin, when warm flow is charged at flow rate of 4 m3/s and at temperature of 1 °C, at location 400 m away from the North Fig. 9. Flow lines (colour scale in m/s) of water particles that go through the bubbler pier wall, 45-degree discharge angle (case 4). (For interpretation of the references to system for case 4. (For interpretation of the references to colour in this figure legend, the colour in this figure legend, the reader is referred to the web version of this article.) reader is referred to the web version of this article.) 310 H. Pan, E. Eranti / Cold Regions Science and Technology 55 (2009) 304–310

5. Conclusions There is currently a lot of interest for ice control in harbours located in the high arctic with freezing indexes up to 6000 (C×days). Arctic sea The flow and heat transfer simulations have been applied for the water has a high salinity and a typical winter temperature of the order Helsinki Vuosaari harbour project. Classical computational fluid of −2 °C, while the melting temperature of sea ice ranges closer to 0 °C. dynamics and heat transfer method are combined with the empirical There are often also strong currents. The thermodynamics of warm ice-water heat transfer models as well as bubbler system model. water circulation and ice-melting change significantly in such Based on practical experience from harbours of Kotka Mussalo and conditions. Compared to the Vuosaari arrangement there is generally Oulu with similar ice control arrangements, the simulations give a need for more thermal energy and for optional methods of focusing realistic description on the ice-melting heat transfer process. The total the energy for ice melting in the berth area. thermal energy balance across the computational domain is found to be realistic. Acknowledgements The Port of Helsinki chose to construct a gravity flow arrangement to the power plant discharge point and to cross the channel with a The authors wish to thank the Port of Helsinki for permission to pipe. The cost of a suction pump facility and its operation proved to be publish this paper. heavier than this arrangement. The warm water is discharged from the centre of the harbour basin References towards its end at a 45-degree angle. The North–South bubbler lines – have a length of 580 m. This is case 4 with longer bubbler lines. The Ashton, G.D.,1978. Numerical simulation of air bubbler systems. Can. J. Civ. Eng. 5, 231 238. Carey, K.L., 1983. Melting ice with air bubbles. Cold Regions Tech. Digest 83 (1). arrangement provides a calculated efficiency of more than 70%. Eranti, E., Lee, G.C., 1986. Cold Region Structural Engineering. McGraw-Hill. Approximately 400 000 m3 of brash ice would be melted in the main Nyman, T. and Eranti, E. 2005. Simulation of ice development in the Saimaa Channel. harbour basin in an extreme winter. The operational ice conditions are VTT Research Report TUO34-055444 (in Finnish). Pan, H., 2000. Flow simulations for turbomachineries. Proc. of 4th Asian Computational expected to remain non-problematic even throughout extreme Fluid Dynamics Conference, pp. 290–295. Mianyang China. winters. The theoretical payback for this system has been estimated Patankar, S.V., 1980. Numerical Heat Transfer and Fluid Flow. Hemisphere. to be 3 years. Rhie, C.M., Chow, W.L., 1983. Numerical study of the turbulent flow past an airfoil with trailing edge separation. AIAA J. 21, 1525–1532. This study shows that CFD technology, combined with empirical Tuthill, A.M., Stockstill, R.L., 2005. Field and laboratory validation of high-flow air knowledge on ice melting, can be a useful tool in harbour design to bubbler mechanics. ASCE J. Cold Reg. Eng. 19, 85–99. find out the most effective and economical means of ice control.